Targeted delivery aids in minimizing most of the drug-originated systemic toxic effects as well as improving the pharmacokinetic properties of anticancer therapeutics. Tumor targeting using hyaluronic acid (HA) as the targeting ligand has attracted a great deal of interest among a host of strategies developed to target the overexpressed tumor specific receptors. HA is an endogenous molecule that possesses a lot of biological functions in the human body. The role of HA synthases, HA degrading enzymes and the interaction of HA with its primary receptor CD44 in tumor metastasis and angiogenesis is really complex and controversial to date. However, overexpression of CD44receptors on tumor surface has been well studied, which have been utilized to direct tumor targeted drugs. Most of the HA based targeting systems were HA drug conjugates and surface modified colloidal carriers which required covalent modification. The lack of accurate structural characterization of these systems resulted in modification of HA binding sites that could affect the efficient cellular uptake. LbL technique is a simple and facile method to incorporate several materials into polyelectrolyte assemblies for drug delivery applications. HA being a negatively charged polysaccharide can be easily incorporated into such systems without any covalent modification. Although HA based polyelectrolyte multilayer films and microcapsules have been reported in combination with polycations like PAH, PLL and chitosan, their application as targeted drug delivery systems have not yet been explored. Herein, two LbL architectures with HA as the terminal layer have been investigated as targeted drug carriers, which can recognize overexpressed CD44 receptors in metastatic breast cancer cells. In the first part of the thesis, a novel polyelectrolyte nanocapsule system composed of biopolymers HA and protamine sulphate (PR) as the wall components was prepared and characterized. These pH and enzyme responsive nanocapsules were then utilized for efficient loading and release of anticancer drug doxorubicin (dox). Higher drug release was observed in simulated intracellular conditions like acidic pH and presence of hyaluronidase enzyme as compared to physiological pH. In the second part of the thesis, dox incorporated bovine serum albumin (BSA) nanoparticles modified with HA-Poly(l-Lysine) multilayers were developed and characterized. The drug release pattern of the dox loaded BSA nanoparticles was found to depend on the presence of a protease enzyme trypsin than pH variations. Both of these drug delivery systems were then evaluated for their cell targeting efficiency and cytotoxicity in CD44+ positive metastatic breast cancer cell line MDA MB 231. The final layer HA facilitated targeted delivery of these drug carriers via CD44 receptor mediated endocytosis. The enhanced cellular uptake followed by sustained delivery of dox by virtue of slow intracellular enzymatic degradation of the drug carriers resulted in their improved cytotoxicity as compared to free dox. Further in vitro biodistribution and tumor suppression efficiency of both the systems were studied in breast cancer xenograft models using BALB/c nude mice. Enhance accumulation of dox in the tumor tissue and significant tumor reduction were observed when treated with encapsulated dox using the HA based nanocarriers as opposed to free dox.

The past few years have witnessed significant work being directed towards drug delivery systems with layer-by layer (LbL) technique prominently featured as one of the most sought after approach. However, majority of the studies were focused on the fabrication of microcapsules which produced numerous drawbacks resulting in reduced applicability. This has spurred research into nanocapsules which has proved to overcome most of the drawbacks that plagued microcapsules by being able to evade the reticulo-endothelial system, exhibit enhanced permeability and retention in tumours etc. The capsules fabricated by the LbL technique requires a suitable combination of cationic and anionic polyelectrolytes which ensures that it is able to effectively protect the cargo it encapsulates as well as enhance its bio-applications. With numerous advantages such as biocompatibility and biodegradability to name a few, chitosan has proved to be an ideal cationic polyelectrolyte. Thus, this thesis focuses on the various therapeutic applications of LbL fabricated chitosan based nanocapsules. The first work focuses on the targeted delivery of the somatostatin analogue, Octreotide conjugated nanocapsules to over expressed somatostatin receptors. These LbL fabricated nanocapsules composed of chitosan and dextran sulfate (CD) encapsulate the anti cancer drug, doxorubicin and are found to attain site specificity as well as enhanced anti-proliferative activity. The results indicated that the nanocapsules were biocompatible and when conjugated with octreotide was found to have an enhanced internalization into SSTR expressing cells, thereby making it a viable strategy for the treatment of tumors that has an over expression of somatostatin receptors such as pancreatic carcinoma, breast carcinoma etc. The objective of the second work was to develop an efficient drug delivery system such as CD nanocapsules for encapsulation of Ciprofloxacin in order to combat infection by Salmonella, an intracellular and intra-phagosomal pathogen. In vitro and in vivo experiments showed that this delivery system can be used effectively to clear Salmonella infection. The increased retention of ciprofloxacin in tissues delivered by CD nanocapsules as compared to the conventional delivery proved that the same therapeutic effect was obtained with reduced dosage and frequency of Ciprofloxacin administration. The third work deals with the probiotic, Saccharomyces boulardii which is found to be effective against several gastrointestinal diseases but had limited clinical application due to its sensitivity to acidic environment. However, encapsulation of S. boulardii with chitosan and dextran sulfate ensured enhanced viability and selective permeability on exposure to acidic and alkaline conditions experienced during gastro intestinal transit. The final work involves the fabrication of novel pH responsive nanocapsules composed of chitosan-heparin which facilitate the intracellular delivery of a model anti-cancer drug, doxorubicin.