CNS Drug Delivery Systems: Novel Approaches

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CNS Drug Delivery Systems: Novel Approaches Shadab A. Pathan1, Zeenat Iqbal1, Syed M. A. Zaidi3, Sushma Talegaonkar1, Divya Vohra2, Gaurav K. Jain1, Adnan Azeem1, Nitin Jain1, Jigar R. Lalani4, Roop K. Khar1 and Farhan J. Ahmad1,3* 1

Department of Pharmaceutics, Faculty of Pharmacy, 2Department of Pharmacology, Faculty of Pharmacy, 3Faculty of Interdisciplinary Studies, Hamdard University, New Delhi-110062, India, 4Department of Pharmacy, Faculty of Technology & Engineering, The M.S. University of Baroda, Vadodara-390001, Gujarat, India Received: May 16, 2008; Accepted: November 22, 2008; Revised: November 28, 2008

Abstract: The brain is a delicate organ, and nature has very efficiently protected it. The brain is shielded against potentially toxic substances by the presence of two barrier systems: the blood brain barrier (BBB) and the blood cerebrospinal fluid barrier (BCSFB). Unfortunately, the same mechanisms that protect it against intrusive chemicals can also frustrate therapeutic interventions. Despite aggressive research, patients suffering from fatal and/or debilitating central nervous system (CNS) diseases, such as brain tumours, HIV encephalopathy, epilepsy, cerebrovascular diseases and neurodegenerative disorders, far outnumber those dying of all types of systemic cancers or heart diseases. The abysmally low number of potential therapeutics reaching commercial success is primarily due to the complexity of the CNS drug development. The clinical failure of many probable candidates is often, ascribable to poor delivery methods which do not pervade the unyielding BBB. It restricts the passive diffusion of many drugs into the brain and constitutes a significant obstacle in the pharmacological treatment of central nervous system (CNS) disorders. General methods that can enhance drug delivery to the brain are, therefore, of great pharmaceutical interest. Various strategies like non-invasive methods, including drug manipulation encompassing transformation into lipophilic analogues, prodrugs, chemical drug delivery, carrier-mediated drug delivery, receptor/vector mediated drug delivery and intranasal drug delivery, which exploits the olfactory and trigeminal neuronal pathways to deliver drugs to the brain, are widely used. On the other hand the invasive methods which primarily rely on disruption of the BBB integrity by osmotic or biochemical means, or direct intracranial drug delivery by intracerebroventricular, intracerebral or intrathecal administration after creating reversible openings in the head, are recognised. Extensive review pertaining specifically, to the patents relating to drug delivery across the CNS is currently available. However, many patents e.g. US63722506, US2002183683 etc., have been mentioned in a few articles. It is the objective of this article to expansively review drug delivery systems for CNS by discussing the recent patents available.

Keywords: Patents, drug targeting, CNS, BBB, nanoparticles, liposomes, polymers. 1. INTRODUCTION In 1998, the global market for CNS drugs was US $33 billion, which was roughly, half that of the global market for cardiovascular drugs. This was when the global burden of CNS affictions had risen remarkably and an expected US $1.5 billion people around the world were likely to suffer from one or the other brain diseases. The recent advances in understanding the causes as well as treatment approaches to CNS disorders have governed the pharmaceutical interest in this field, which is evident from the rapid growth in the global CNS drugs. Market which reached a US $55.5 billion in 2005, and is further forecasted to expand to US $63.9 billion in 2010 [1]. In spite of an impressive increase in CNS drug discovery leading to numerous molecules indicated in neurological disorders the biggest impediment remains the effective delivery of these agents across the BBB. Despite aggressive research, patients suffering from fatal or debilitating CNS diseases, such as brain tumours, HIV encephalopathy, epilepsy, cerebrovascular diseases and neurodegenerative disorders, far outnumber those dying of *Address Correspondence to this author at the Department of Pharmaceutics, Faculty of Pharmacy, Jamia Hamdard (Hamdard University), New Delhi-110062, India; Tel: +91-09810720387; Fax: +91-11-26059663; E-mail: [email protected]

1872-2113/09 $100.00+.00

all types of systemic cancers or heart diseases [2]. The blood brain barrier (BBB) represents an insurmountable barrier for the majority of drugs including anticancer agents, antibiotics, peptides and other oligo- and macromolecular drugs [3-6]. The presence of BBB often turns out to be the sole reason for the clinical failure of even a highly potent neurotherapeutic agent. 2. BLOOD BRAIN BARRIER (BBB) The brain is shielded against potentially toxic substances by the presence of two barrier systems: the blood brain barrier (BBB) and the blood cerebrospinal fluid barrier (BCSFB) [7]. The term “blood brain barrier” was first coined in 1900 by Lewandowsky, while studying the limited penetration of potassium ferrocyanate into the brain [8]. The structure of the BBB is subdivided into two components: the endothelial or capillary barrier and the ependymal barrier. The BBB is considered to be the major route for the uptake of serum ligands since its surface area is approximately 5000-fold greater than that of BCSFB. The BBB is formed by a complex cellular system of endothelial cells, astroglia, pericytes, perivascular macrophages, and a basal lamina. Compared to other tissues, brain endothelia have the most intimate cell-to-cell connections: endothelial cells adhere strongly to each other, forming structures specific to the CNS called "tight junctions" or zonula occludens. © 2009 Bentham Science Publishers Ltd.

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They involve two opposing plasma membranes which form a membrane fusion with cytoplasmic layer on either side. These tight junctions prevent cell migration or cell movement across endothelial cells. A continuous uniform basement membrane surrounds the brain capillaries [9]. This basal lamina encloses contractile cells called pericytes, which form an intermittent layer and probably play some role in phagocytosis and defence if the BBB is breached. Astrocytic end feet, which cover the brain capillaries, build a continuous sleeve and maintain the integrity of the BBB by the synthesis and secretion of soluble growth factors (e. g.) gamma-glutamyl transpeptidase) essential for the endothelial cells to develop their BBB characteristics. The brain capillary network has an average spacing of just 40 microns in between the capillaries and is so dense that each brain cell essentially has its own vessel for nutrient supply [10]. The BBB, which consists of the endothelium of the brain vessels, the basal membrane and neuroglial cells, acts to limit the transport of substances into the brain [11]. Owing to its stringent permeability, it allows only restricted entry of promising drugs to the target brain tissues and is presumed to be the key hurdle in developing CNS drugs. On the contrary, this limitation is constructively used by the drug developers to mitigate or remove CNS side-effects of drugs targeting peripheral receptors which may also populate the CNS. Many polar therapeutic agents are unable to reach the CNS because of the absence of paracellular pathways in the BBB. The presence of few endocytic vesicles in the CNS capillaries further removes a transcellular route for free diffusion of substances into the interstitium [12, 13]. Further,

Fig. (1). CNS drug delivery approaches.

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a large number of more lipophilic drugs are also subject to the activity of efflux transporters (P-glycoproteins and MRP, the multi-drug resistance-related proteins). As a result of this difficulty of delivering drugs across the BBB, a significant number of CNS diseases have poorly met therapy [14,15]. The parameters considered optimum for a compound to transport across the BBB are: •

Compound should be unionised.

•

Its log P value should be near to 2.

•

Its molecular weight should be less than 400 Da.

•

Cumulative number of hydrogen bonds should not go beyond 8 to10 [16].

The factors which need profound understanding while designing a delivery system for neurotherapeutic agents are given in Table 1. 3. APPROACHES TO CNS DRUG DELIVERY To overcome the multitude of barriers restricting CNS drug delivery of potential therapeutic agents, numerous drug delivery strategies have been developed. These strategies generally fall into one or more of the following categories: invasive, non-invasive or miscellaneous techniques [17-19]. The CNS drug delivery tree encompassing the various possible strategies is given below in the Fig. (1). 3.1. Non-Invasive Approaches A variety of non-invasive brain drug delivery methods have been investigated, that make use of the brain blood

CNS Drug Delivery

Table 1.

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Factors Affecting Drug Transport Across BBB [17-19] Factors Affecting Drug Transport Across BBB

•

Concentration gradient of drug/polymer

•

Molecular charge

•

Molecular weight of the drug

•

Affinity for receptors or carriers

•

Lipophilicity of the drug

•

Cerebral blood flow

•

Sequestration by other cells

•

Systemic enzymatic stability

•

Affinity for efflux proteins (e.g. Pgp

•

Metabolism by other tissues

•

Pathological status

•

Clearance rate of drug/polymer

•

Flexibility, conformation of drug/polymer

•

Cellular enzymatic stability

vessel network to gain widespread drug distribution. Noninvasive techniques of delivery may be of a chemical or biological nature. Such methods usually rely upon drug manipulations which may include alterations as prodrugs, lipophilic analogues, chemical drug delivery, carrier-mediated drug delivery, receptor/vector mediated drug delivery etc. Intranasal drug delivery which primarily exploits the olfactory and trigeminal neuronal pathways has also gained a recent reappraisal as a potential non-invasive approach [20]. 3.1.1. Chemical Methods The main premise for the chemical methods remains the use of prodrugs. An extension of the concept uses the chemical transformation of drugs by changing the various functionalities. The chemical change is usually designed to improve some deficient physicochemical property such as membrane permeability or solubility. For example, esterification or amidation of hydroxy-, amino-, or carboxylic acidcontaining drugs may greatly enhance the lipid solubility and hence, entry into the brain. Generally, conversion to the active form is realized via an enzymatic cleavage. Going to the extremes of the lipophilic precursor scale, a possible choice for CNS prodrugs is to link the drug to a lipid moiety, such as a fatty acid, a glyceride or a phospholipid. Such prodrug approaches were explored for a variety of acidcontaining drugs, like levodopa [21]. Problems associated with prodrugs are: the poor selectivity and poor tissue retention of some of these molecules. Besides, the lipidization strategy involves the addition of lipid-like molecules through modification of the hydrophilic moieties in the drug structure. Lipid-soluble molecules are believed to be transported through the BBB by passive diffusion but the lipidization of molecules generally increases the volume of distribution, particularly due to to plasma protein-binding which affects all other pharmacokinetic parameters. Furthermore, increasing lipophilicity tends to increase the rate of oxidative metabolism by cytochrome P-450 and other enzymes. While increased lipophilicity may improve diffusion across the BBB, it also tends to increase uptake into other tissues, causing an increased tissue burden [22, 23]. Chemical approaches disclosed for delivering drugs to the brain include lipophilic addition and modification of hydrophilic drugs, (e.g., N-methylpyridinium-2-carbaldoxime chloride; 2-PA by Bodor et al. [24, 25]. Linkage of prodrugs to biologically active compounds is yet another strategy, e.g., phenylethylamine coupled to nicotinic acid has been modified to form N-methylnicotinic acid esters and

amides by Bodor [26]. Derivatization of compounds to centrally acting amines, e.g., dihydropyridinium quaternary amine derivatives; has also been suggested by Bodor [27]. Caging compounds within glycosyl-, maltosyl-, diglucosyland dimaltosyl-derivatives of cyclodextrin is reported by Bodor in US Patent 5017566 [28]. Loftsson in 1994 disclosed usage of cyclodextrin complexes [29]. Yaksh et al. disclosed a patent enclosing compounds in cyclodextrin caged complexes [30]. Robert Katz et al. described sitespecific biomolecular complexes comprising of a therapeutic, prophylactic and diagnostic agent. The complexes are further covalently bonded with cationic carriers and permeabilizer peptides for delivery across the BBB and with targeting moieties for uptake by target brain cells. Invented complexes are particularly useful for delivery of a biologically active agent to the glial tissue of the brain as well as to the cortical, cholinergic and adrenergic neurons. The mentioned therapeutic complexes or conjugates comprise of an omega-3 fatty acid such as alpha-linolenic acid, eicosapentaenoic acid or docosahexaenoic acid and derivatives thereof [31]. Christian and Samuel T. in US20060189547A1 disclosed hydrophilic N-linked pharmaceutical compositions, methods of their preparation and use in neuraxial drug delivery comprising of a glycosyl- CNS acting prodrug compound covalently N-linked with a saccharide through an amide or amine bond and a formulary consisting of an additive, stabilizer, carrier, binder, buffer, an excipient, an emollient, disintegrant, lubricating agent, an antimicrobial agent , with the provision that the saccharide moiety is not a cyclodextrin or a glucuronide. Compounds produced according to the methods of invention find a variety of uses in therapeutic methods for treating symptoms of various neurologic dysfunctions [32]. Atlas; Daphne et al. in U.S. patent application 20060211628A1, disclosed a method of treating multiple sclerosis, using effective amount of a compound having: (a) A combination of molecular weight and membrane miscibility properties for permitting the compound to cross the BBB of the organism; (b) A readily oxidizable chemical group for exerting antioxidant properties; and (c) A chemical make-up for permitting the compound or its intracellular derivative to accumulate within the cytoplasm of cells [33]. Chung et al. invented inositol derivatives in accordance with the invention. The derivatives are effective in significantly enhancing the transportation of various therapeutic molecules across a biological membrane, [34]. In US patent application 20070203080A1 Lipshutz; Bruce H., described the synthesis of new ubiquinol

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analogues as well as methods of using these compounds to deliver drug moieties to the CNS [35]. 3.1.2. Biological Methods Biological approaches of CNS drug delivery primarily emanate from the understanding of the physiological and anatomical nuances of the BBB transportation. Of the many available approaches, conjugation of a drug with antibodies is an important mechanism. Other biological methods for targeting exploit ligands in the form of sugar or lectins, which can be directed to specific receptors found on cell surfaces [36, 37]. The antibody-drug conjugate is directed towards an antigen residing on or within the target tissues. For example, the OX26 antibody, the 8D3 MAb or the R17217 MAb which are all antibodies to transferrin receptor (TfR), were able to undergo receptor-mediated transcytosis across the mouse BBB via the endogenous TfR. Unfortunately, it is difficult to find target tissues bearing specific antigens that will provide a unique targeting effect. Demeule Michel invented a non-invasive and flexible method, and a carrier for transporting paclitaxel. The formula for the invented compounds or conjugates is R-L-M, wherein R is aprotinin or a fragment, L is a linker or a bond and M is the drug. This invention is based on the discovery, that aprotinin binds to and crosses the brain capillary endothelial wall in a very effective manner. Aprotinin is known in the art to be a basic polypeptide, that effectively inhibits a variety of serine proteases, including trypsin, chymotrypsin, kallikrein and pepsin. The transendothelial transport of aprotinin is approximately 10-50 times higher than that of other proteins, including transferrin or ceruloplasmin [38]. Antibodies are particularly well suited for targeting BBB receptor-mediated transcytosis systems given their high affinity and specificity for their ligands [39]. As examples, appropriately-targeted antibodies that recognize extracellular epitopes of the insulin and transferrin receptors can act as artificial transporter substrates that are effectively transported across the BBB and deposited into the brain interstitium via the transendothelial route [40]. Shusta et al. in WO2007143711 disclosed non-invasive transport of small molecules such as methotrexate using anti-transferrin receptor antibodies. Proteins such as nerve growth factor, brain derived neurotrophic factor and basic fibroblast growth factor were delivered to the brain after intravenous administration by using an anti-transferrin receptor antibody. This invention provides antibodies that bind to endothelial cell receptors resulting in endocytosis of the receptor and bound ligands. The invention comprises of an isolated antibody fragment having the amino acid sequence linked to a pharmaceutically active compound [41]. Megalin ligands are carriers or vectors for the delivery of active agents via transcytosis to brain and are patented by Starr et al. who disclosed RAP (receptor-associated protein), which serves to increase the transport of the therapeutic agent. In some embodiments, the megalin ligand or megalin-binding fragment of such a ligand may be modified as desired to enhance its stability or pharmacokinetic properties (e. g. PEGylation of the RAP (receptor-associated protein) moiety of the conjugate, mutagenesis of the RAP moiety of the conjugate) [42]. In another patent Neuwelt. disclosed monoclonal antibody conjugated for the delivery of the drugs

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across the BBB [43]. Pardridge, disclosed the delivery of radiopharmaceuticals across BBB with a monoclonal antibody. [125I]-A
1-40 was mono-bionylated and conjugated to a BBB drug delivery system that comprised of a complex of the 83-14 monoclonal antibody to the human insulin receptor, which was tagged with Streptavidin. The effect to produce a marked increase in Rhesus monkey brain uptake of the [125I]-A
1-40 at 3 hrs following the i.v. injection [44]. In patent number WO2007036022 Abulrob et al. disclosed subunits and multimers of subunits suitable for use in inducing the transport of one or more cargo substances into a cell and in some instances across a cell. The subunits may have a targeting domain, such as an antibody or antibody fragment; a multimerization domain, such as a verotoxin Bsubunit mutant scaffold, and a cargo molecule such as a drug or imaging agent, which may be directly linked to the subunit or may be packaged in a liposome, nanoparticle, or the like. In some instances, the targeting domain may have affinity for a blood brain barrier antigen and may be capable of inducing cell-mediated transcytosis to facilitate the delivery of cargo molecule across the blood brain barrier. In some instances, the targeting region may have affinity for a cancer antigen and may be capable of inducing cell-mediated endocytosis [45]. Tchistiakova et al. invented a polypeptide comprising of at least one peptide following motif of sequence identity number : Yl-Y2-X-Y3-X-Y4-X-Ys, where Y1 is a positively charged amino acid; such as Arg or Lys; Y2 is Val, Leu, Ile or Met; Y3 is negatively charged amino acid such as Glu or Asp; Y4 is negatively charged amino acid such as of Glu or Asp; Ys is Thr; X is any amino acid, an analogue, or a derivative comprising of one or more ligands in association with a carrier. The association of the ligand and the carrier can be achieved by chemical, genetic or physical linking of the ligand and the carrier, by mixing the above components or by their co-administration [46]. Beliveau et al. in 2002 invented polypeptides derived from aprotinin and aprotinin analogues as well as conjugates and pharmaceutical compositions comprising of these polypeptides for treating a patient of a neurological disease. The invention also related to the use of these polypeptides for transporting a compound or drug across the blood brain barrier [47]. Further, US patent application 20060182684A1 Beliveau; Richard [48] and US patent application 20060189515A1 Beliveau et al. related to a non-invasive and flexible method and carrier for transporting a compound or drug across the blood brain barrier of an individual. This comprised of the step of administering to the patient a compound comprising of the agent attached to aprotinin, a pharmaceutically acceptable salt of aprotinin, a fragment of aprotinin or a pharma-ceutically acceptable salt of a fragment of aprotinin [49]. Receptor-recognizing molecular fragment(s) in the form of proteins like apolipoproteins bonded to the particle surface for the delivery of drug to specific tissue or CNS was described by Mueller et al. [50]. The use of molecular Trojan horses to ferry drugs or genes across the BBB is described in U.S. Patent Nos. 4801575 and 6372250 [51, 52]. The linking of drugs to MAb transport vectors is facilitated with the use of avidinbiotin technology. In this approach, the drug or protein therapeutic

CNS Drug Delivery

is monobiotinylated and bound to a conjugate of the antibody vector and avidin or streptavidin. The use of avidin-biotin technology to facilitate linking of drugs to antibody-based transport vectors is described in US patent number 6287792 [53]. Fusion proteins have also been used, where a drug is genetically fused with the MAb transport vector. More particularly, the present invention involves the development of "humanized" monoclonal antibodies MAb that may be attached to pharmaceutical agents to form compounds that are able to readily bind to the human insulin receptor (HIR). The compounds are able to cross the human BBB by way of insulin receptor-mediated endocytosis, the receptors being located on the brain capillary endothelium. Composition that is capable of delivering a large enzyme across the BBB comprising: a large enzyme; and a blood brain barrier targeting agent linked via an avidin-biotin linkage [54]. In the field of peptide discovery for carrying drugs through the blood brain barrier, Forni et al. invented a peptide comprising of the sequence: H2N-Gly-Phe-D-ThrGly-Phe-Leu~Ser-CONH23, wherein the serine residue may be functionalised with sugar residues; other amino acids can replace the first two amino acids of the N-terminal portion, The order of which can be reversed, and their number may be different from two. The invention also relates to a conjugate of said peptides with a pharmaceutically acceptable polyester or polyamide polymer, nanoparticle systems comprising said conjugates, and pharmaceutical compositions comprising said nanoparticle systems to prepare medicinal products designed to cross the blood brain barrier. Wherein, the said medicinal products take the form of nanoparticle systems [55]. Hochman Shawn in patent application WO2005094497 provides methods for delivering a neuroactive fusion molecule across the blood-brain or blood-nerve barriers comprising: (a) administering by nonintramuscular means, a neuroactive fusion molecule comprising a therapeutic polypeptide and a delivery polypeptide to a subject, such that the bloodstream of the said subject is capable of transporting said administered neuroactive fusion molecule to a fenestrated capillary of the said subject; and (b) wherein, said administered fusion molecule is delivered across said fenestrated capillary and into a neurone. The neurone can be, for example, a central nervous system neurone, a peripheral neurone, an enteric nervous system neurone, or an autonomic nervous system neurone [56]. Ferguson Ian A. in US2003083299 patented methods for delivering polypeptides into central nervous system (CNS) tissue in humans. It also relates to methods for targeting the delivery of polypeptides to specific populations or types of neurons that reside entirely within the brain or spinal cord tissue. For that a genetic vector is used to transfect one or more neurons which "straddle" the BBB, such as sensory neurons, nocioceptive neurons, or lower motor neurons. This is done by administering the vector in a manner that causes it to contact neuronal projections that extend outside the BBB. Once inside a peripheral projection that belongs to a BBB-straddling neuron, the vectors will be transported into the main cell body of the neuron through a process called retrograde transport. Inside the main cell

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body, at least one gene carried by the genetic vector will be expressed to form polypeptides. Some of these polypeptides (which can include leader sequences that will promote anterograde transport and secretion by BBB-straddling neurons) will be transported by the neurons to secretion sites inside the BBB. The polypeptides will be secreted by transfected neurons at locations inside the BBB, and will then contact and exert their effects upon secondary "target" neurons located entirely within the BBB. By using this system, polypeptides that stimulate nerve growth or activity can be used to treat neurodegenerative diseases, impaired limbs in stroke victims, etc., and polypeptides that suppress neuronal activity can be used to treat unwanted excessive neuronal activity, such as neuropathic pain. This approach also provides new methods for delivering endocrine and paracrine polypeptides into the CNS, thereby allowing improved medical and reproductive treatments in humans, and improved ability to modulate growth, maturation, reproduction or other endocrine-related functions among livestock, endangered species, and other animals [57]. An invention that pertains to compositions for increasing the permeability of the bloodbrain barrier in an animal is patented by Kozarich et al. These compositions are permeabilizers of the blood-brain barrier which are peptides having a core sequence of amino acids or amino acid analogues. In the core peptide, the sequence is arginineproline-hydroxyproline-glycine-thienylalanine-serineproline-4-Me-tyrosine-(CH2NH)-arginine [58]. In 2007, Daneman et al. discovered that the NgRHl cell surface receptor, an antigen preferentially expressed in endothelial cells, is involved in regulating blood-brain barrier (BBB) permeability. Invention provides a method of modulating BBB permeability comprising of the step of administering an agent to a subject, wherein the said agent targets a human NgRHl cell surface receptor that is present in the brain. Non- limiting examples of the agents useful for modulating BBB permeability via NgRHl include inorganic molecules, peptides, peptide-mimetics, antibodies, liposomes, small interfering RNAs, antisense protiens, aptamers and external guide sequences [59]. In US patent number 4801575 Pardridge, describes the preparation of chimeric peptides by coupling or conjugating the pharmaceutical agent to a transportable peptide. The chimeric peptide purportedly passes across the barrier via receptors for the transportable peptide. Trans-portable peptides, or vectors, mentioned as suitable for coupling to the pharmaceutical agent include insulin, transferrin, insulinlike growth factors I and II, basic albumin and prolactin [60]. U.S. patent number 4902505 to Pardridge et al. describes the use of chimeric peptides for neuropeptide delivery through the blood-brain barrier. A receptor-specific peptide is used to carry a neuroactive hydrophilic peptide through the BBB. The disclosed carrier proteins, which are capable of crossing the BBB by receptor-mediated trans-cytosis, include histone, insulin, transferrin, insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), basic albumin and prolactin [61]. U.S. patent number 5442043 to Fukuta et al. disclosed using an insulin fragment as a carrier in a chimeric peptide for transporting a neuro-peptide across the bloodbrain barrier [62]. Bentley et al. in 2003 provided a method

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for delivering a peptide into the brain of a human or other animal through the blood-brain barrier. The peptide to be delivered is bonded to a water soluble, non-peptidic polymer to form a conjugate. The conjugate is then administered into the blood circulation of an animal so that the conjugate passes across the blood-brain barrier and into the brain. The water-soluble non-peptidic polymer can be selected from the group consisting of polyethylene glycol and copolymers of polyethylene glycol and polypropylene glycol activated for conjugation by covalent attachment to the peptide [63]. US Patent number 5833988 to Friden described a method for delivering a neuropharmaceutical or diagnostic agent across the blood-brain barrier employing an antibody against the transferrin receptor. A nerve growth factor or a neurotrophic factor is conjugated to a transferrin receptorspecific antibody. The resulting conjugate is administered to an animal and is capable of crossing the BBB [64]. Another method for delivering hydrophilic compounds into the brain by receptor-mediated transcytosis is described by Pardridge et al. A monoclonal antibody to the transferrin receptor (OX26 MAb) modified with streptavidin is used to transport the cationic protein, brain-derived neurotrophic factor (BDNF) through the BBB. BDNF is first modified with PEG.sup.2000-biotin to form BDNF-PEG.sup.2000-biotin, which is then bound to the streptavidin-modified antibody OX26 MAb. The resulting conjugate was shown to be able to cross the BBB into the brain [65]. Temsamani et al. patented use of taxoid for brain cancers, a compound consisting of at least one taxol derivative bound to at least one vector peptide capable of increasing the solubility of the said derivative and advantageously of allowing it to be transported across the blood brain barrier. The invention also relates to the preparation of these compounds and to the pharmaceutical compositions containing them, useful for the treatment of cancers, most particularly of brain cancers [66]. Temsamani et al. also patented a compound consisting of at least an antibody or an antibody fragment bound to at least a vector peptide capable of transporting it across the BBB [67]. In US patent application 20070264351 Nelson et al. invented a highly efficient artificial low-density lipoprotein (LDL) carrier system for the targeted delivery of therapeutic agents across the blood-brain barrier (BBB). In particular, this invention relates to artificial LDL particles comprised of three lipid elements: phosphatidyl choline, fatty-acylcholesterol esters and at least one apolipoprotein. The present invention further relates to compositions, methods and kits comprising of artificial LDL particles for targeting drugs to and across the BBB for the prevention and treatment of brain diseases [68]. 3.1.3. CNS Drug Delivery Through Novel Carriers 3.1.3.1. Colloidal Drug Carriers In general, colloidal drug carriers include micelles, emulsions, liposomes and nanoparticles (nanospheres and nanocapsules).It is noteworthy that only liposomes and nanoparticles have been largely exploited for brain drug delivery because the methods of preparation are generally simple and easy to scale-up [69]. The aim of using colloidal carriers is generally, to increase the specificity towards cells

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or tissues, to improve the bioavailability of drugs by increasing their diffusion through biological membranes and/or to protect them against enzyme inactivation. Moreover, the colloidal systems allow access of non-transportable drugs across the BBB by masking their physicochemical characteristics through their encapsulation in these systems. The fate of colloidal particles after intravenous administration is determined by a combination of biological and physicochemical events that need to be considered in the design of efficient drug carrier systems. After intravenous administration, all colloidal immunoglobulins, albumin, the elements of the complement, fibronectin, etc may undergo a process known as “opsonization” thus, colloidal particles that present hydrophobic surface properties are efficiently coated with plasma components (opsonins) and rapidly removed from the circulation, since the macrophages of the liver and the spleen own their specific receptors for these opsonins. However, colloidal particles that are small and hydrophilic enough can escape, at least partially, from the opsonization process and consequently, remain in the circulation for a relatively longer period of time. Additionally, the concept of “steric hindrance” has been applied to avoid the deposition of plasma proteins either by adsorbing some surfactant molecules (such as copolymers of polyoxyethylene and polyoxypropylene) at the surface of the colloids or by providing a sterical stability by the direct chemical link of polyethyleneglycol (PEG) at the surface of the particles. In addition, active targeting can be achieved by the attachment of a specific ligand (such as a monoclonal antibody) onto the surface of the colloidal particle, preferentially at the end of the PEG molecules, since the targeted colloidal particles will be much more efficient if they are also sterically stabilized [70-72]. The fate of various colloidal carriers after administration is illustrated in Fig. (2) given below. Polymeric Micelles and Microemulsions Polymeric micelles as drug delivery systems are formed by amphiphilic copolymers having an A-B diblock structure with A, the hydrophilic (shell) and B, the hydrophobic (core) polymers. The polymeric micelles are thermodynamically and kinetically stable in aqueous media. They have a size range of several tens of nanometers with a considerably narrow distribution. This narrow size range is similar to that of viruses and lipoproteins. Several reviews have analyzed in great detail, the properties of the different copolymers used in the preparation of the polymeric micelles, as well as the physical chemistry of these systems, which may influence their properties such as their size distribution, stability, drugloading capacity, drug release kinetics, blood circulation time and biodistribution [73-75]. Earlier studies have shown that poloxamer (PluronicTM) micelles conjugated with antibodies may improve brain distribution of haloperidol, a neuroleptic agent. This approach has resulted in a dramatic improvement of drug efficacy. This result indicates that PluronicTM micelles provide an effective transport of solubilized neuroleptic agents across the BBB [76]. However, recent investigations made by the same group demonstrated that only PluronicTM unimers allowed cell penetration in bovine BMEC monolayers of molecules such as rhodamine-123, digoxin or

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Fig. (2). Fate of various colloidal carriers after oral administration.

doxorubicin by inhibition of the P-gp-mediated drug-efflux system. Other studies have shown an increased analgesic effect when enkephalin, biphalin or morphine were administered as a cocktail with Pluronic P-85 at a concentration of 0.01%. It is noteworthy that the analgesia was lower with a higher concentration of Pluronic P-85 (0.1%) due to micellar trapping, which reduces the free drug concentration available for transcellular flux [77-80]. Ringe et al. invented a method of producing a delivery vehicle by the miniemulsion method, comprising of nanoparticles made by the said method, optionally also having a surface-modifying agent and a pharmaceutical agent to cross one or more physio-logical barriers, in particular the blood-brain-barrier. This subsequently showed modified-release characteristics such as sustained-release or prolonged-release of a pharmaceutical agent in the target tissue [81]. Polymeric Nanoparticles Therapeutic strategies to probe the CNS are limited by the restrictive tight junctions at the endothelial cells of the BBB. To overcome the impositions of the BBB, polymeric biocompatible drug carriers, e.g., nanoparticles, liposomes

have been applied to the CNS for many applications such as cancers. Nanoparticles mostly consist of polymers and are about 10 to 200 nm in size. Some researchers managed to produce efficient nanoparticles that ensure rapid transport of drug-charged particles across the BBB. Nanoparticles from polybutyl cyanoacrylate are able to transport drugs by encapsulating or binding them to the surface of the nanoparticles [82]. However, these nanoparticles cannot be transported directly across the BBB only by coating them with Polysorbate-80. Nanoparticles consisting of polycyanoacrylate that were coated with polyethylene glycol could only overcome the BBB if, due to an infection of the brain, the BBB is defective and has become more permeable [83]. Wang et al. found a cationic polymer (polyethylenimine) with which the drug can bypass the BBB and which uses an intramuscular injection in the tongue to introduce drugs into the brain using retrograde axonal transport. Rousselle et al. transported doxorubicin across the BBB using a peptide vector. The drug to be transported is covalently bound to D-penetrantin, a peptide, and synB1, which facilitate transport across the BBB without

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causing efflux by the P-glycoprotein. Other ways include transporting nanoparticles via the transferrin receptor by binding them to ligands. This system however has the setback that the particles can be charged with a small quantity of the substance to be transported only [84]. Compared with other colloidal carriers, polymeric nanoparticles present a higher stability when in contact with the biological fluids. Also, their polymeric nature permits the attainment of the desired properties such as controlled- and sustained-drug release. Ideal properties of nanoparticles to cross the CNS are mentioned in Table 2. A number of possibilities which can explain the mechanism of the delivery of drugs by nanoparticles across the blood-brain barrier are as follows: 1.

An increased retention of the nanoparticles in the brain blood capillaries combined with an adsorption to the capillary walls could create a higher concentration gradient that would enhance the transport of drug across the endothelial cell layer and as a result its delivery to the brain.

2.

A general surfactant effect characterized by the solubilization of endothelial cell membrane lipids that would lead to membrane fluidisation and enhanced drug permeability through the BBB.

3.

The nanoparticles could lead to an opening of the tight junctions between the endothelial cells. The drug could then permeate through the tight junctions either in free form or together with the nanoparticles in bound form.

4.

The nanoparticles may be endocytosed by the endothelial cells followed by the release of the drug within these cells and its delivery to the brain.

5.

The nanoparticles with bound drugs could be transcytosed through the endothelial cell layer.

6.

The Polysorbate-80 used as the coating agent could inhibit the efflux system, especially P-glycoprotein (Pgp) [85].

Heppe et al. in US2006051423 patented a chitosan-based transport system for overcoming the BBB. The transport system contains at least one substance selected from the group consisting of chitin, chitosan, chitosan oligosaccharides, glucosamine and derivatives thereof (molecular weights ranging from 179 Da to 400 kDa), and optionally one or more active agents and/or one or more markers and/or one or more ligands [87]. Chen patent number CN1850032 Table 2.

Ahmad et al.

disclosed a nano prepa-ration of antimycotic amphotericin B (AmB) using n-butyl polycyanoacrylate as carrier material [88]. WO2004017945 discloses the use of nanoparticles for the transfection of DNA into eukaryotic cells. It further discloses the DNA administration to a target organ in the human or animal body, for example, the brain in the case of brain tumours. It also discloses the use of substances (stabilizers) which act as enhancers of the bond between the DNA and the nano-particles. Among others, Diethylaminoethyl-(DEAE)-dextran and dextran 70,000 are listed as stabilizers [89].Kreuter et al. WO2007110152 invented a system for targeted-active substance delivery for administering a pharma-cologically active substance to the CNS of a mammal across the BBB, where the system for targeted-drug delivery comprises of nanoparticles of Poly(DL-lactide) and/or Poly(DL-lactide-co-glycolide and at least one pharmacologically active substance which is absorbed into the nanoparticles, adsorbed thereon or is incorporated therein, and includes a coating of the surfaceactive substance Pluronic(TM) 188, which is deposited on the nanoparticles loaded with active substance, and to methods for producing the system for targeted active substance delivery and the use of the system for targeted active substance delivery for the treatment of a disease or an impairment of the CNS [90]. Kreuter Jorg et al. US6117454 disclosed a novel method of delivering drugs and diagnostics across the BBB. Drugs or diagnostic agents are incorporated into nanoparticles which have been fabricated in conventional ways. These nanoparticles are then coated with additional surfactant and adminisrered to animals or humans. This invention is based on the surprising finding that treatment of nanoparticles having a drug absorbed, adsorbed or incorporated therein with a sufficient coating of an appropriate surfactant allows the adsorbed drug to traverse the BBB. The basic drug targeting system is made by the following process: a.

Formation of a suspension of nanoparticles by polymerization or dispersion,

b.

Sorption of an active ingredient to the nanoparticle, and

c.

Coating such nanoparticles with one or more layers of an appropriate surfactant [91].

U.S. patent no. US6419949 invented by Gasco Maria Rosa disclosed pharmaceutical compositions in the form of nanoparticles suitable for passage through the intestinal mucosa, the BBB and the BCFB. Said nanoparticles have a size ranging from 40 to 150 nm, and are formed by one or

Ideal Properties of Nanoparticles For Crossing CNS [86] Ideal Properties of Nanoparticles for Brain Drug Delivery

•

Nontoxic, biodegradable, and biocompatible

•

Scalable and cost-effective manufacturing process

•

Particle diameter between 10- 100 nm

•

•

Physical stability in vivo and in vitro

Amenable to small molecules, peptides, proteinsor nucleic acids

•

Avoidance from RES (Reticulo-endothelial system) leads to prolonged blood circulation time

•

•

CNS targeted delivery via receptor-mediated transcytosis across brain capillary endothelial cells

Formulation stability, minimal nanoparticle excipient-induced drug alteration (chemical degradation/ alteration, protein denaturation)

•

Controlled-drug release profiles

CNS Drug Delivery

more lipids optionally in combination with a steric stabilizer and by a drug. They are prepared dispersion in an aqueous medium at 2-4°C, a hot prepared oil/water or water/oil/water microemulsion comprising one or more lipids, a surfactant agent, a cosurfactant and optionally a steric stabilizer [92]. Dennis et al. in US 7195780 invented a nanotube comprising: a hollow tubular body comprising a first end and a second end, wherein the first end is open; and a first end cap positioned over the first open end, wherein the end cap is attached to the hollow tubular body by a covalent bond and the particle has a maximum dimension of less than 100
m. Alternatively, the nanocap can be held in place by electrostatic forces, hydrogen bonding or other non-covalent interactions. The present invention provides a method for the in vivo delivery of a bioactive agent comprising of administering the bioactive agent contained within a nanotube to target the CNS [93]. Sabel in US patent application 20020034474A1 disclosed a composition and method of fabrication in which nanoparticles may be used as a tool to deliver drugs to a specific target within or on a mammalian body, specifically, by using stabilizers other than Dextran 70,000 during the polymerization process. In the present invention, a drug is either incorporated into or adsorbed onto the stabilized nanoparticles. This drug/nano-particle complex is then administered to the organism through any route such as by oral administration, injection or inhalation, whereupon the drug exerts its effects at the desired site of pharmacological action. The present invention also discussed a method of preparation of non-coated nanoparticles as drug carriers for a wide range of drugs in order to allow the targeting of drug to a specific site in the mammalian body, specifically in order to enhance the penetration of drugs or diagnostic agents across the BBB. The said method does not require a coating procedure during the fabrication of nanoparticles. Nanoparticles could be prepared by polymerization, in a per se known manner, one or more monomeric and/or oligomeric precursor(s) of said polymeric material in the presence of said stabilizer(s); loading one or more physiologically effective substance(s) to be delivered [94]. Few patents also disclosed nanosizing of neurotherapeutic agents to improve their efficacy as by Gustow et al. who envisaged a nanosized fromulation of the topiramate, an antiepileptic agent, to improve its efficacy and reduce its dose [95]. Solid lipid nanoparticles (SLN) were developed at the beginning of the 1990s as an alternative carrier system to emulsions, liposomes, and polymeric nanoparticles. SLN can provide advantages including stabilization of incorporated compounds, controlled release, and occluviseness. The solid lipid nanoparticles by virtue of surface functionalization, neutral lipid character and nanoscale particle sizecan effectively transport a delivery package such as biologically active agents, pharmaceutically active agents, magnetically active agents, and/or imaging agents across the BBB and into the brain tissue [96-98]. Shastri et al. in WO2006044660 discloses an invention which relates to methods of delivering at least one biologically, pharmaceutically or magnetically active agent, or imaging agent across the BBB, cellular lipid bilayer and into a cell, and to a subcellular structure with functionalized solid lipid nanoparticles comprising a neutral lipid and

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functionalized polymer comprising of at least one ionic or ionizable moiety. The patent also discloses method of SLN preparation, as lipids and pharmaceutically active agents for preparing the solid lipid nanoparticles of the invention compositions can be dissolved in a binary solvent system comprising, for example, of dimethylformamide and acetone. An aqueous solution of comprising functionalized polymer, for example poly (acrylic acid), can then be added to the binary solvent system. A system comprising a solid lipid nanoparticle, a surface functionalized layer surrounding the solid lipid nanoparticle and a pharmaceutically active agent is then formed. The solvents can be removed, thereby yielding a system for the delivery of a pharmaceutically active agent across the blood brain barrier [99]. Liposomes for CNS Drug Delivery It has also been suggested that liposomes can enhance drug delivery to the brain across the BBB. Liposomes are small vesicles (usually submicron-sized) comprising of one or more concentric bilayers of phospholipids separated by aqueous compartments. Although liposomes have been reported to enhance the uptake of certain drugs into the brain after intravenous injection [100]. US patent application 20020025313A1 Micklus et al. disclosed immunoliposomes and pharmaceutical compositions capable of targeting pharmacological compounds to the brain. Liposomes are coupled to an antibody binding fragment such as Fab, F(ab').sub.2, Fab'or or a single chain polypeptide antibody which binds to a receptor molecule present on the vascular endothelial cells of the mammalian BBB. Typically the antibody binding fragment is prepared from a monoclonal antibody. The receptor is preferably of the brain peptide transport system, such as the transferrin receptor, or insulin receptor, IGF-I or IGF-2 receptor. The antibody binding fragment is preferably coupled by a covalent bond to the liposome [101]. CN1833633 Chen Ya Li patented a liposome able to pass through blood brain barrier contains the blood brain barrier anchor site (5-15 mol %), the phosphatide with high phase-change temp, cholesterol and fusion aid. A composite medicine using said liposome as a carrier for passing through the blood brain barrier for treating the diseases of the central nerve system and its preparing process are also disclosed [102]. Pardrige disclosed a non-invasive gene targeting to brain by liposomes. Liposomes containing therapeutic genes are conjugated to multiple brain barrier and brain cell membrane targeting agents to provide transport of the encapsulated gene across the BBB. After crossing the BBB, the encapsulated gene expresses the encoded therapeutic agent within the brain to provide therapeutic effect and diagnosis of neurological disorders [103]. Pardrige and Huwyler disclosed liposomes for transporting the therapeutic agents across the CNS. Invention discusses brain specific targeting vehicle for transporting neuropharmacological agents across the BBB. Liposomes are sterically stabilized by attaching ligands to the surface of the liposomes [104]. As several patents disclosed the use of liposomes as a potential delivery system for brain targeting, many research papers also supported the use of liposomes for CNS drug delivery as given in Table 3 below [105-111]:

80 Recent Patents on Drug Delivery & Formulation, 2009, Vol. 3, No. 1

3.2. Invasive Methods Although, the ease and compliance of non-invasive delivery methods is often not associated with direct or invasive delivery of drugs to the brain, it often shows up as the sole alternative wherein the drugs elicit right physicochemical properties. Generally, only low molecular weight, lipid-soluble molecules and a few peptides and nutrients can cross this barrier to any significant extent, either by passive diffusion or using specific transport mechanisms [112]. So, for most drugs it is not possible to achieve therapeutic levels within the brain tissue following intravenous or oral administration. In addition, highly potent drugs (e.g., anticancer drugs and neurotrophic factors) that may be necessary to be delivered to the CNS, often cause serious toxic side effects when administered systemically. The drug can be administered directly into the brain tissue [113]. Many ways are explored for direct intracranial drug delivery by intracerebroventricular, intracerebral or intrathecal administration after creating holes in head or Disrupting the BBB integrity by osmotic blood brain barrier disruption or biochemical BBB disruption and also by employing controlled release biodegradable drug delivery systems which are able to control the release rate of an incorporated drug in a pre-determined manner over periods of days to months [114-120]. 3.2.1. Disruption of the BBB One of the earliest techniques to circumvent the BBB for therapeutic purpose and the first to be used in humans was developed by Neuwelt (1989). The idea behind this approach was to break down the barrier temporarily by injecting a sugar solution (mannitol) into arteries in the neck. The resulting high sugar concentration in brain capillaries sucks water out of the endothelial cells, shrinking them thus opening the tight junctions [121]. In current practice, the effect lasts for 20-30 min, during which the drugs that would not normally cross the BBB diffuse freely. This method Table 3.

Ahmad et al.

allows the delivery of chemotherapeutic agents in patients with malignant glioma, cerebral lymphoma and disseminated CNS germ cell tumours, with a subsequent decrease in morbidity and mortality compared with patients receiving systemic chemotherapy alone. However, this approach also causes several undesirable side effects in humans, including physiological stress, transient increase in intracranial pressure, and unwanted delivery of anticancer agents to normal brain tissue. In addition, this technique requires considerable expertise for administration. However, disrupting the BBB even for brief periods leaves the brain vulnerable to infection and damage from toxins. Even substances that circulate harmlessly through the peripheral bloodstream, such as albumin, can have deleterious effects if they enter the brain [122]. Intrathecal injection allows administration of agents directly into the brain ventricles and spinal fluid by puncturing the membranes surrounding the brain. Sustained-delivery of agents directly into the spinal fluid can be attained by the use of infusion pumps that are implanted surgically. These spinal fluid delivery techniques are used to treat brain cancers, infections, inflammation and pain. However, they do not penetrate deeply into the brain. Clinicians prefer to avoid intrathecal injections because they frequently are ineffective and can be dangerous. Substances injected intrathecally are distributed unevenly, slowly and incompletely in the brain. Since the volume of the spinal fluid is small, increase in intracerebral pressure may occur with repeated injections. Furthermore, improper needle or catheter placement can result in seizure, bleeding, encephalitis and a variety of other severe side effects [123]. In WO9807367 Jolesz discloses image guide methods and apparatus for ultrasound delivery of compounds through the blood brain barrier to selected locations in the brain, target a selected location in the brain of a patient, and apply ultrasound to affect the tissues and/or fluids, at that location, a change detectable by imaging. At least a portion of the brain in the vicinity of the selected location is imaged, e.g.,

Liposomes for Brain Targeting

Candidate Drug Amphotericin B

Type of Liposome

Target CNS Disease

Route of Administration

Reference

Liposomes (commercial

Infection

Intravenously

[105]

Autoimmune

Intravenously

[106]

Brain Tumour

Intravenously

[107-108]

formulation Ambisone®, Fujisawa, USA) [3H]-Prednisolone

Pegylated liposomes

Encephalitis Doxorubicin

Pegylated liposomes (commercial formulation Caelyx®)

IFN-
gene plasmid

Cationic liposomes

Brain Tumour

Intratumoural

[109]

Antisense epidermal growth factor

Cationic liposomes

Brain Tumour

Intratumoural

[110]

Doxorubicin

Polymeric nanoparticles

Glioblastoma

Intravenous

[3]

Quinoline derivatives

Polymeric nanoparticles

Alzheimer’s Disease

Intravenous

[111]

CNS Drug Delivery

via magnetic resonance imaging to confirm the location of that change. A compound, e.g., a neuro-pharmaceutical in the patient's bloodstream, is delivered to the confirmed location by applying ultrasound to effect opening of the blood brain barrier at that location, and thereby to induce uptake of the compound there [124]. An another PCT application entitled “ Parenteral delivery system” disclosed hypertonic solution of sugar by different means of administration to open the BBB to permit the entry into the CNS of a co-administered chemical compound such as nutrient or a therapeutic or a diagnostic agent [125]. 3.2.2. Direct Drug Delivery One strategy to overcome the BBB that has been used extensively in clinical trials is the direct administration of drugs by intraventricular and intracerebral routes. The drugs can be infused intraventricularly using a plastic reservoir (Ommaya reservoir) implanted subcutaneously in the scalp and connected to the ventricles within the brain via an outlet catheter.Unfortunately, there are several problems, apart from the surgical intervention required. Firstly, in the human brain the diffusion distances from cerebrospinal fluid (CSF) to a drug target site may only be several centimeters, and for drugs relying only on diffusion for penetration, insufficient concentration of drug may reach the target site Secondly, the microvessels of the brain secrete interstitial fluid at a low but finite rate, generating a flow towards the CSF spaces, which also works against diffusive drug penetration. Finally, the high turnover rate of the CSF (total renewal every 5-6 hrs in humans) means that injected drug is being continuously cleared back into the blood. In practice, drug injection into the CSF is a suitable strategy only for sites close to the ventricles. For drugs that need to be at elevated levels for long periods for an effective action, continuous or pulsatile infusion may be necessary [126,127]. WO2004043334 disclosed an apparatus for delivering a non steroidal anti -inflammatory drug (NSAID) supplied to the body of a subject for delivery to at least a portion of a CNS of the subject via the systemic blood circulation, including a stimulator adapted to stimulate at least one site of the subject, during at least a portion of the time when the NSAID is present in the blood. The apparatus uses electrical, chemical, mechanical and/or odorant stimulation [128]. Shalev and Gross invented an apparatus for modifying a property of the brain of a patient, including electrodes applied to the sphenopalatine ganglion (SPG) or a neural tract originating in or leading to the SPG. A control unit drives the electrodes to apply a current capable of inducing (a) an increase in permeability of a BBB of the patient, (b) a change in cerebral blood flow of the patient, and/or (c) an inhibition of the parasympathetic activity of the SPG [129]. US Patent 5752 515 to Jolesz et al. describes an apparatus for image-guided ultrasound delivery of compounds through the BBB. At least a portion of the brain in the vicinity of the selected location is imaged, e. g., via magnetic resonance imaging, to confirm the location of that change. A compound, e.g., a nerotherapeutic, in the patient's bloodstream is delivered to the confirmed location by applying ultrasound to effect opening of the BBB at that location and, thereby, to induce uptake of the compound there [130]. US Patent 6405079 describes a method for the suppression or

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prevention of various medical conditions, including pain, movement disorders, autonomic disorders and neuropsychiatric disorders. The method includes positioning an electrode adjacent to or around a sinus, orfalx cerebri and activating the electrode to apply an electrical signal to the site. In a further embodiment for treating the same conditions, the electrode dispenses a medication solution or analgesic to the site. The patent also describes surgical techniques for implanting the electrode [131]. Miller Landon et al. provided a direct central nervous system catheter which can be directly inserted into the ventricle space or spinal canal to provide access which enables the sampling of the CSF and/or monitoring of intracranial pressure while at the same time facilitating the aseptic delivery of therapeutic agents and/or drugs directly into the cerebrospinal fluid and the management of CSF temperature. The direct CNS catheter includes a catheter body defining at least one lumen and having a drug delivery branch, a monitoring/sensing branch, and optional branches if desired, each branch being connected in fluid communication with the lumen [132]. US2006009450 Tobinick provides specific methods of using and administering etanercept to improve cognitive function in a human, for both the treatment and prevention of cognitive impairment or, alternatively, to enhance cognitive function. The methods of the present invention include not only the perispinal administration of etanercept (which itself can be accomplished in various ways, including transcutaneous, interspinous injection or catheter delivery into the epidural or interspinous space) but also other novel methods of localized administration, specifically including intranasal adminis-tration. Perispinal administration involves anatomically localized delivery performed so as to place the therapeutic molecule directly in the vicinity of the spine, and, for the purposes of this patent, administration which is outside of the intrathecal space [133]. In US patent application 20070055214A1 Gilbert entitled “Method for delivering drugs to tissue under microjet propulsion” disclosed a new and useful device and method for the needle-free delivery of drugs with minimal trauma to tissue and that are suitable for delivering drugs in sensitive areas of the body such as the eye, nasal passageways, brain, mouth and other areas of the body [134]. US5720720 Laske et al. disclosed a method of high-flow microinfusion which provides convection-enhanced delivery of agents into the brain and other solid tissue structures. The method involves positioning the tip of an infusion catheter within a tissue structure and supplying an agent through the catheter while maintaining a pressure gradient from the tip of the catheter during infusion. Agent delivery rates of 0.5 to 15.0
l/min have been used experimentally with infusion distances greater than 1 cm from the delivery source. The method can be used to deliver various drugs, protein toxins, antibodies for treatment or imaging, proteins in enzyme replacement therapy, growth factors in the treatment of various neurodegenerative disorders, viruses and in gene therapy. An infusion catheter developed for the high-flow microinfusion includes a plurality of elongated slits adjacent to a tapered portion of the catheter which are parallel to the axis of the catheter and spaced symmetrically about the circumference thereof. The infusion catheter is used in a convention-enhanced delivery system in which, after the

82 Recent Patents on Drug Delivery & Formulation, 2009, Vol. 3, No. 1

infusion catheter is positioned in a tissue situs, it is connected to a pump which delivers a desired agent and maintains a desired pressure gradient throughout delivery of the agent [135]. Targeted-drug delivery into the brain desires precise anatomically localized delivery of the drug to the desired tissue and benefits from the differentiation or localization of normal and abnormal tissues. Present systems of imageguided placement of intracranial probes, such as drug delivery catheters, include framed and frameless technologies, which typically use images acquired preoperatively to create a three-dimensional space on which the surgical navigation is based. Framed systems use externally applied frames to establish the fiducials for navigation, whereas frameless systems use optical, electromagnetic or ultrasound sensors and mechanical arms to track the position of surgical tools and instruments during surgical procedures. US6537232 Kucharczyk et al. disclosed a device and method for monitoring intracranial pressure during magnetic resonance (MR) image-guided neurosurgical procedures, such as intracranial drug delivery procedures, wherein an MR-compatible microsensor pressure transducer coupled to a pressure sensing diaphragm located a) at the tip, b) on a lateral side, and/or c) in multiple locations of an MRcompatible catheter is inserted into a lateral cerebral ventricle, cerebral cistern, subarachnoid space, subdural or extradural spaces, venous sinuses or intraparenchymal tissue locations under MR imaging guidance, and is used to record intracranial pressures over hours to days in patients undergoing diagnostic or therapeutic neurologic interventions [136]. US 7241283 Putz disclosed a method of treating a tissue region in the brain of a patient comprising: inserting into the brain an outer catheter having a passageway extending between a proximal end and at least one port, the outer catheter guiding the inner catheter to the tissue region; and transferring fluids between the tissue region and the proximal end through the passageway [137]. 3.2.3. Intracerebral Implants Over the past few years, research in galenic pharmacy has allowed the development of implantable polymer systems which protect active substances against degradation while at the same time allowing their controlled local release decreasing the systemic side effects. The advantages of these implantable polymer systems have recently prompted several teams to study their use in central nervous system pathologies. Different CNS diseases principally brain tumours and neurodegenerative disorders such as Parkinson’s and Huntington’s diseases can be treated with intracranially administered controlled drug delivery systems [138-140]. The efficiency of various devices has been investigated in animal models and some systems have also been subjected to clinical trials [141,142]. The first (and so far only) pharmaceutical product that is available on the market based on the principle of intracranial controlled drug delivery is Gliadel®. It comprises of a disc-shaped wafer, consisting of BCNU (1,3-bis(2- chloroethyl)-1-nitrosourea; carmustine) as the drug (loading: 3.85%) and poly[bis(p-carboxyphenoxy)] propane-sebacic acid (PCPP:SA) as the biodegradable polymer. Gliadel® was developed in the early to mid 1990’s by the group of Henry Brem and obtained Food and Drug

Ahmad et al.

Administration (FDA) approval in 1996 for the treatment of recurrent glioblastoma multiforme [143-145]. A multiparticulate drug delivery system for the same type of treatment has been proposed by the groups of Benoit and Menei 5fluorouracil (5-FU)-loaded poly (lactic-co-glycolic acid) (PLGA)-based microparticles. These micro-particles have the advantage that they can be administered by stereotaxic means using standard syringes. Thus, both operable and inoperable tumours can be treated [146]. The most widely known device is the ALZETTM minipump, a reservoir-type system which can continuously deliver a solution containing a drug, for example, dopamine or a dopamine agonist, for up to four weeks. The delivery is through a cannula which is chronically implanted into the CNS. Drug delivery directly to the brain interstitium using polymeric devices releases unprecedented levels of drug directly to an intracranial target in a sustained fashion for extended periods of time. The fate of a drug delivered to the brain interstitium from the biodegradable polymer was based on: (1) Rates of drug transport via diffusion and fluid convection, (2) Rates of elimination from the brain via degradation, metabolism and permeation through capillary networks, and (3) Rates of local binding and internalization [147]. Controlled-release polymers used to deliver drugs to the CNS were first demonstrated in U.S. 4883666 [148]. A method whereby a small controlled-delivery device implanted into the CNS was used to deliver vasopressin to the cerebrospinal fluid with zero-order kinetics was described by Boer et al. [149], but zero-order release was not obtained for a period beyond one week. In summary, only in US 4883666 has a method been disclosed whereby substances can be delivered to the CNS which is clinically practicable and safe, and which is characterized by long-term controlled release kinetics. The device is a matrix-system. The term "matrix" as used herein is defined as a polymeric carrier matrix that is biocompatible and sufficiently resistant to chemical and/or physical destruction by the environment of use such that the matrix remains essentially intact throughout the release period. This type of release is particularly desirable as a treatment for a variety of CNS disorders since it allows targeting of drugs to the brain without adverse effects arising from variations in delivery. Nathalie et al. US Patent No. 6803052 describes invention related to the use of biodegradable microspheres that release a radiosensitizing anticancer agent for treating glioblastoma. The use of said biodegradable microspheres according to the invention results in a patient survival time of least 90 weeks, a therapeutically effective concentration being maintained in the parenchymatous area throughout this time. The microspheres used preferably contain 5-fluorouracil put in to the tumour by intratissular injection. The radiotherapy targeting the tumorous mass is dosed at 60 Gy over approximately 6 weeks. The invention also relates to a method for producing the biodegradable microspheres by emulsion-extraction, and to a suspension containing the biodegradable microspheres obtained using this method [150]. Sabel et al. disclosed a polymeric drug delivery system for the delivery of any substance to the central

CNS Drug Delivery

nervous system. The delivery system is preferably implanted in the central nervous system for delivery of the drug directly to the central nervous system. These implantable devices can be used, for example, to achieve continuous delivery of dopamine, which cannot pass the blood brain barrier, directly into the brain for an extended time period. The implantable devices display controlled, "zero-order" release kinetics, a life time of a minimum of several weeks or months even when the devices contain water soluble, low molecular weight compounds, biocom-patibility, and relative noninvasiveness. The polymeric devices are applicable in the treatment of a variety of central nervous system disorders [151]. Brem et al. invented a method and devices for localized delivery of a chemo-therapeutic agent to solid tumours. The devices consist of reservoirs which release drug over an extended time period while at the same time preserving the bioactivity and bioavailability of the agent. In the most preferred embodiment, the device consists of biodegradable polymeric matrixes, although reservoirs can also be formulated from non-biodegradable polymers or reservoirs connected to implanted infusion pumps. The devices are implanted within or immediately adjacent to the tumours to be treated or the site where they have been surgically removed. The examples demonstrate the efficacy of paclitaxel and camptothecin delivered in polymeric implants prepared by compression molding of biodegradable and non-biodegradable polymers, respectively. The results are highly statistically significant. These methods can be used to make micro-implants (micro-particles, microspheres and microcapsules encapsulating drug to be released), slabs or sheets, films, tubes, and other structures. A preferred form for infusion or injection is micro-implants [152]. 3.3. Alternative Route of Administration An alternative route to CNS drug delivery is the intranasal administration. Intranasal drug administration offers rapid absorption to the systemic blood avoiding firstpass metabolism in the gut wall and the liver. This route of administration has been shown to present a safe and acceptable alternative to parenteral administration of various drugs. Delivery of drugs into the brain by administering the drug in the olfactory area and also a small number of patents has been issued that describe the use of the olfactory pathways to the brain as possible alternative drug delivery methods. For example, US Patent No. 5624898 issued by Frey [153]; WO033813A1 issued by Frey [154]; WO09901229A1 issued by Gizurarson [155] and WO044350A1 issued by Cevc [156]. US Patent 5756071 to Mattern et al. describes a method for nasally administering aerosols of therapeutic agents to enhance penetration of the blood brain barrier. The patent describes a metering spray designed for pernasal application, the spray containing at least one sex hormone or at least one metabolic precursor of a sex hormone or at least one derivative of a sex hormone or combinations of these, excepting the precursors of testosterone, or at least one biogenic amine, with the exception of catecholamines [157]. CA2560798 Parnell Francis W. provided the non-invasive transnasal and transocular drug delivery to the central nervous system using eriodictyon fluid extract technology. By administration through the olfactory nerve or the optical nerve, the delivery of a biologically active substance of interest into the CNS

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83

and CSF can be enhanced through bypassing the BBB. The invention involves the use of eriodictyon fluid extract as an excipient in compositions and systems for administering drugs to the olfactory or optical nerve. An apparatus to enhance the delivery of at least one delivery substance into the central nervous system of a mammal, utilizing the olfactory pathway(s) as a direct delivery route for the substance from an exogenous source via the mammal's olfactory area to a target site of the mammal's central nervous system, bypassing the mammal's blood brain barrier comprising: (a) a drug; (b) an excipient composition comprising eriodictyon fluid extract; and (c) a pressurized delivery device, configured to deliver the drug and excipient to the olfactory nerve administered through nasal route [158]. In CN1579407 Wu et al. discloses a nasal cavity administration preparation which can resist the brain infection of AIDS. It belongs to medicine preparation technology field for anti-AIDS virus, and uses hydroxyl inosine as pharmacologic active ingredient, adds in pH value regulator, penetration advancing agent, thickener, equalpenetration regulator, antiseptic and produces them into a preparation suitable for nose cavity, solves the problem that the current medicine with oral, muscle injection or other modes. The medicine can penetrate the vein blood brain barrier to the brain, the release and absorption of the preparation in the invention are quick, the medicine can gather in the brain, the medicine density in brain is upgraded prominently, at the same time, the invention has character that the nasal cavity mucous coat and cilium toxin are small [159]. Summary of various patents pertaining to intranasal brain drug delivery is given in the Table 4 mentioned below [160-199]. As nasal route of administration is found to be a validated route of drug delivery to brain many scientists have revealed that ocular route can be the next alternative for CNS drug targeting. In this regard U.S. 7241283 Abdulrazik, Muhammad entitled “Method for central nervous system targeting through the ocular route of drug delivery”. Surprisingly, the inventor of the present invention has found that a conventional pharmaceutical agent, when administered by ocular route of drug delivery, provides good CNS targeting. In the present invention, pharmaceutical composition is a N-methyl-D-aspartate receptor antagonist. Preferably, the N-methyl-D-aspartate receptor antagonist is memantine, brimonidine. A study was conducted to examine for the first time the neuro-ocular tissue distribution of brimonidine following one single 50
l instillation of 3H-Alphagan aqueous solution (0.2%) into the albino rabbit eye. Both the eyes and the brain were dissected. Both side specimens of aqueous humor, cornea, iris, lens, vitreous humor, conjunctiva, sclera, ciliary body, choroid, retina, optic nerve, optic tract, olfactory bulb, as well as corpus callosum and blood samples were collected. The corpus callosum was chosen as an indicator of general availability of the drug in the brain. The olfactory bulbs were included to rule out ocular-brain drug delivery through the nasal cavity [200]. In US20070265203A1 Eriksson et al. disclosed a method and compositions for modulating blood-neural barrier (BNB) for the treatment of CNS conditions such as oedema, and for increased drug delivery efficacy across the BNB. The present invention further relates to improved tPA

84 Recent Patents on Drug Delivery & Formulation, 2009, Vol. 3, No. 1

Table 4.

Ahmad et al.

Patents Pertaining To Intranasal Brain Drug Delivery Drug

Application

Delivery

Related Patent

Ref.

Frey II W H. US5624898 (1997)

[160]

Frey II, W H. W000033813 (2000)

[161]

System Neurotrophic Agents

Brain Disorders

-

Frey II, W H. WO07947A1 (1991)

[162]

Frey II, WH. US20016180603 (2001)

[163-169]

Frey II, W. H. EP0504263B1 (1997) Frey II, W. H. US20030215398A1 (2003) Frey II, W. H. US20020072498A1 (2002) Frey II, W. H. US20016313093 (2001) Frey II, W. H. US20026342478 (2002) Frey II, W. H. US20026407061 (2002) Melanocortin-4 Receptor Agonist

Obesity,

-

Type II Diabetes

Xiao et al. US20030229025A1 (2003)

[170-172]

Xiao et al. US20070004743A1 (2007) Xiao et al.WO03072056A2 (2003)

Nicotinic Antagonist

Nicotine Withdrawal

-

Houdi, A.A. US20006121289 (2000)

[173]

Folic Acid, Cholinesterase

Alzheimer's Disease

-

Hussain et al.US20026369058 (2002)

[174]

Liquid, Gel, Powder

Quay, S.C. US20060003989A1 (2006)

[175]

Heller et al. US20060141029A1 (2006)

[176-178]

Galantamine Catecholic Butane (NDGA Compounds)

Obesity, Diabetes, Hypertension

-

Heller et al. US20060141047A1 (2006) Huang et al. US20060141025A1 (2006)

NMDA Receptor Antagonist, MAO Inhibitor

Parkinson's Disease, Multiple Sclerosis, Alzheimer's Disease

Extended Release Dosage Form

Meyerson et al. US20050245617A1 (2005)

[179]

Went et al. US20060252788A1 (2006)

[180-182]

Meyerson et al. US20060240043A1 (2006) Levin, B. H.: US20050281751A1 (2005)

Delta-9-THC

-

-

Hussain et al. US20036380175 (2003)

[183]

Clotrimazole

Huntington's Disease

-

Cummings et al. US20070037800A1 (2007)

[184]

Huperzine-A

Senile Dementia

-

Tao et al. CN1621039 (2005)

[185]

Neurotrophic Agents

Brain Disorders

Liposomes, Sustained Release Matrix, Lipid Based Micelles

Frey et al. WO000033814 (2000)

[186-189]

Frey II, W. H.: WO00033813A1 (2000) Frey II, W. H.: US20030072793(2003) Frey II, W. H.: EP1137401B1 (2005)

Proteosomes Glatiramer

Neurodegenerative Disorders

Nanoemulsion

Frenkel et al. US20060229233A1 (2006)

[190]

Diazepam

Epilepsy

Microemulsions

Choi et al. US20050002987A1 (2005)

[191,192]

Choi et al. WO04110403A1 (2004) Benzodiazepines Valproic Acid Carbamazepines

Epilepsy

Nasoadhesive Microemulsions

Ambikanandan et al. 1061/MUM (2005)

[193]

Sedatives

Insomnia

Nasoadhesive Microemulsions

Ambikanandan et al.1124/MUM/ (2005)

[194]

Triptans, Caffeine

Migraine

Nasoadhesive Microemulsions

Ambikanandan et al.1125/MUM/ (2005)

[195]

CNS Drug Delivery

Recent Patents on Drug Delivery & Formulation, 2009, Vol. 3, No. 1

85

(Table 4) Contd…. Drug

Application

Delivery

Related Patent

Ref.

System Maps

Immunomodulator

Dendrimer

Solomon, B.: US20060034855A1 (2006)

[196]

Lorazepam

Epilepsy

Spray

Wermeling, D.P. :US20016610271 (2001)

[197,198]

Wermeling, D.P. :US20010055571A1 (2001) Zolpidem

Insomnia

Cyclodextrin / Chitosan Sols

treatment of ischemic cerebrovascular and related diseases in combination with antagonism of the PDGF signalling pathway. The inventive method and composition is particularly suitable for conjunctive therapy of ischemic stroke using tPA and an anti-PDGF-C antagonist or an anti-PDGFR-alpha antagonist [201]. 3.4. Novel Methods The challenging domain of effective brain delivery has led to a keen scientific pursuit and as a result many novel methods have been invented and patented. In these series, researchers have revealed the use of iontophoresis as an adjuvant for CNS drug delivery. Iontophoresis has been defined as the active introduction of ionised molecules into tissues by means of an electric current. The parent US patent application of this CIP, Ser. No. 09/197,133 relates to a noninvasive method and device for delivery of a biologically active agent that is transported by means of iontophoresis and/or phonophoresis directly to the CNS using the olfactory pathway to the brain and thereby circum-venting the BBB and is known as transnasal iontophoretic delivery. Besides the non-invasive methods, the present invention also describes the invasive methods and devices for enhanced and controlled delivery of a biologically active agent to the CNS that also circumvents the BBB. US Patent application 20020183683A1 Lerner disclosed invasive and non-invasive CNS drug delivery methods and devices for use in these methods that essentially circumvent the BBB utilizing iontophoresis as delivery technique that allows for enhanced delivery of a biologically active agent into the CNS of a mammal as well as for (pre)-programm-able and controlled transport [202]. In US application 20030191426A1, Lerner et al. invented a device to enhance the delivery of a drug or other substance of interest into a selected organ or tissue, comprising of special electrodes, one of the electrodes carrying a container with the selected drug or other substance of interest, said electrodes being capable of being positioned at preselected locations of said organ or tissue, wherein the electrodes are all connected with a selected energy source which generates and maintains an energy field before and during the enhanced delivery of said substance, under the influence of which delivery is accomplished in a direction from the active to the passive electrode and into said organ or tissue . The energy source may be selected from suitable sources providing an electric field, a magnetic field, ultrasonic waves, high energy waves like laser beams, or a combination thereof. Further a method for the enhanced delivery of said drug or other substance of interest to an

Castile. US20070140981A1 (2007)

[199]

internal organ or target tissue of an organism, for example the brain, bypassing the BBB, is disclosed [203]. LeBowitz US Patent application 20060121018A1 disclosed methods and compositions for targeting therapeutic proteins to the brain. Methods and compositions of the invention involve associating an IGF moiety with a therapeutic protein in order to target the therapeutic protein to the brain. Soluble fusion proteins that include an IGF targeting moiety are transported to neural tissue in the brain from blood. Methods and compositions of the invention include therapeutic applications for treating lysosomal storage diseases. The invention also provides nucleic acids and cells for expressing IGF fusion proteins [204]. Lamensdorf et al. US Patent application 20060142227A1; “Amphiphilic peptide-PNA conjugates for the delivery of PNA through the blood brain barrier” The invention provides molecules comprising of a nucleic acid, a hydrophobic moiety and a positively charged moiety, useful in the delivery of a nucleic acid sequence across a cellular membrane. The invention further relates to the use of these molecules for the delivery of a nucleic acid sequence to the brain across the blood brain barrier for diagnostic and therapeutic applications [205]. 4. CURRENT & FUTURE DEVELOPMENTS A number of concrete examples where successful delivery and sustained activity have been achieved were provided. They clearly prove that, with adequate design, the approach can provide substantially increased and prolonged brain exposure of the drugs. From the discussion it was found that many delivery systems like polymeric Nanoparticles and liposomes are the promising carriers to deliver drugs beyond the BBB for the scrutiny of the central nervous system. This is even more evident in light of the fact that most of the potentially available drugs for CNS therapies are large hydrophilic molecules, e.g., peptides, proteins and oligonucleotides that do not cross the BBB. Among the several strategies attempted in order to overcome this problem, properly tailored NPs may have a great potential. The large amount of evidence regarding brain drug delivery by means of P80-coated NPs cannot be ignored or considered as single evidence even though its action mechanism is not completely understood. Lipid NPs, e.g. SLN, NLC, LDC NPs, may represent, in fact, promising carriers since their prevalence over other formulations in terms of toxicity, production feasibility and scalability is widely documented in the literature. The ability of engineered liposomes to enter into brain tumours makes

86 Recent Patents on Drug Delivery & Formulation, 2009, Vol. 3, No. 1

Table 5.

Ahmad et al.

Patent Status of Therapeutics Used to Treat Various Brain Disorders

Brain Disorder

Molecules Patented Or Under Investigation* Drugs

Peptides

Cerebral ischemia/ Stroke

Deferoxamine, Trientine, Ebselen, Heregulin, Cobalt, Tetrathiomolybdate, Remacemide, Nicergoline, Hydergine, Lubeluzole

Growth factors, Brain-derived neurotrophic factor, Interleukin1, Tumour necrosis factor-, Vasoactive intestinal peptide, Leuenkephalin, pyruvate, N-acetyl cysteine amide, lactate

Brain Tumours

Procarbazine, Lomustine, Vincristine, Temozolomide, Dexamethasone

Epidermal growth factor receptor antisense, RNA interference

Pain

Morphine, Frovatriptan, Cannabinoids, Oxycodone, Levallorphan, Fentanyl, Alfentanil

Interleukin-1, Enkephalins, Botulinum toxin, Dynorphin, Endorphin

Alzheimer’s disease

Ambenonium, Edrophonium, Neostigmine, Tacrine, Rivastigmine, Pyridostigmine, Galantamine

Peptide T, Interleukin-1

Parkinsonism

Selegiline, Rimantadine, Amantadine, Levodopa, Taolcapone, Entacapone, Pramipexole, Ropinirole

Glial-derived neurotrophic factor, Interleukin-1, Tyrosine hydroxylase

Obesity

Diltiazem, Phentermine, Sibutramine, Rimonabant, Melanocortin4 receptor agonist

Leptin, -Melanocyte stimulating hormone

Migraine

Frovatriptan, Ergotamine, Sumatriptan, Rizatriptan, Zolmitriptan, Tumor necrosis factor antagonists

Botulinum toxin, Interleukin-1

AIDS

Zidovudine, Efavirenz, Tenofovir, Saquinavir

Human Immuno Virus coat protein, Interferon-, T-20 peptides

Epilepsy

Phenytoin, Ethosuximide, Topiramate, Gabapentin, Carbamazepine, Lamotrigine

----

Anxiety

Flurazepam, Alprazolam, Diazepam, Lorazepam, Clonazepam, Propranolol, Buspirone

----

Insomnia

Temazepam, Lorazepam, Flurazepam, Nitrazepam, Midazolam, Diphenhydramine

----

Schizophrenia

Chlorpromazine, Clozapine, Risperidone, Olanzapine

----

Depression

Imipramine, Fluoxetine, Sertraline, Moclobemide, Phenelzine, Bupropion

----

Narcotic Addiction

Dihydro--erythroidine,Mecamylamine, Pempidine, Succinylcholine, Trimethaphean, Chlorisondamine, Hexamethonium, Pentolinium, Methadone

----

* No brain targeted delivery system available

them potential delivery systems for brain targeting. Biodegradable polymers are also making their place in the area of matrix type sustained-release of neurotherapeutics. Every delivery system has some potential advantages over each other along with some limitations but it’s a need of the hour to design a developmental programme in such a way that the delivery of the drugs across the BBB should be looked simultaneously along with the discovery programmes. Patient compliance and risk-benefit ratio suggest the use of non-invasive methods of drug delivery over invasive methods. A technology of chimeric peptides which are potential BBB transport vectors and have been applied to several peptide pharmaceuticals, nucleic acid therapeutics, and small molecules to make them CNS transportable. The concept of Trozen Horses is looking promising for brain targeting which will be amenable to all kinds of molecules, genes, peptides etc. But the path of CNS drug development and delivery is full of hurdles. There are challenges ahead of

us to resolve the question of delivery of the drugs to CNS. More research is in progress to address such challenging problems. It is clear that this failure is ascribable to a wrong design in the drug discovery and development programs that overlook the fundamental contribution of a well sustained drug delivery program. A long way of optimization and evaluation is still, however, needed before potential clinical application. In the absence of an effective BBB technology, the pharmaceutical industry cannot provide therapeutics for the majority of patients with brain disorders. It is estimated that the global CNS pharmaceutical market would have to grow by more than 500% just to equal the cardiovascular market. If BBB delivery solutions were in place for either small or large molecules, then almost any pharmaceutical could enter clinical drug development programs and therapies could be developed for most CNS disorders. A sound review of the patents dealing with CNS drug delivery approaches has shown that scientific interest in the field has

CNS Drug Delivery

risen but a lot needs to be done. The poor status of potent molecules available in customized formats produces a dismal picture for a vast population waiting to be treated. Table 5 presented below summarizes the drugs available for brain disorders along with their routes of administration. ACKNOWLEDGEMENT The authors are thankful to the Central Council for Research in Unani Medicine (CCRUM) under the Ministry of AYUSH, Government of India for providing generous funding and support to the Department of Pharmaceutics, Jamia Hamdard. REFERENCES [1] [2]

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