POLYMERIC NANO-CARRIERS FOR TARGETED DELIVERY OF HYDROPHOBIC DRUGS

Abstract

The synthesis of nanoparticles with improved properties and superior performance is a constant area of research which includes interdisciplinary fields of material science, chemistry and biology. Polymer based nanoparticulate delivery systems are particularly feasible over metal nanoparticles due to structural versatility which provides controlled drug release profiles, biocompatibility, and biodegradability. They also have the properties of enhanced permeability and retention (EPR) effect that permits preferential accumulation in the tumor tissue. Despite extensive efforts to combat cancer, it remains one of the principal causes of morbidity and mortality, making it imperative to develop effective treatment methods. However, conventional chemotherapeutics are mainly hydrophobic drugs having low bioavailability and non-selective distribution throughout the body, leading to damage of healthy cells and tissues with toxic sideeffects. Consequently, it is of utmost importance to develop novel delivery systems which can enhance the therapeutic efficacy of anti-cancer drugs and selectively target cancer cells, resulting in low toxicity. Consequently, hybrid nanoparticles made up of synthetic and natural polymers have attracted much interest due to their intriguing properties which can be tuned as desired. Wherein, natural polymers bestow biocompatibility, and synthetic polymers contribute to mechanical properties. Approaches that have been investigated to achieve these multicomponent polymer systems resulting from the mixing of two or more polymers include nanocomposites, blends, graft copolymers, block copolymers, and interpenetrating polymer networks (IPNs). Among the available polymers, chitosan, poly (lactic-co-glycolic acid) (PLGA), poly (2-hydroxyethyl methacrylate) (PHEMA), and stearic acid-soya lecithin based solid lipid nanoparticles offer numerous advantages such as ability to entrap hydrophobic drugs, reduced toxicity, tumor selectivity by EPR effect, and distinct molecular architecture which lends itself to modification for active targeting of cancer cells. With this perspective, the present work was undertaken with a view to study the effect of these polymeric nanomaterials on the cellular uptake and the cytotoxic effect of the entrapped hydrophobic drug. Active targeting was realized by conjugation of folate (FA) and Biotin (B) ii to the surface of the nanoparticles since Folate receptors (FR) and Biotin receptors (BR) are significantly overexpressed on the surface of a variety of cancer cells. In brief, Chapter 1 and 2 presents the introduction and a detailed literature review of the therapeutic nanocarriers, properties of the selected polymers and their applications in drug delivery. A brief review of the targeting moieties with particular focus on application of Folate in cancer targeting is also provided. Chapter 3 details the Materials and Methods of the entire thesis. The procedure for the physicochemical characterization of the prepared nanoparticles and cell culture assays are listed here. Chapter 4 details the synthesis of chitosan nanoparticles (CSNPs) to encapsulate the hydrophobic drug curcumin (cur). Chitosan is a cationic natural polymer with extensive biomedical applications. Surface modification of the CSNPs by conjugation with folic acid (FACSNPs) and biotin (B-CSNPs) ligands was carried out to formulate targeted nanoparticles. The formation of curcumin loaded nanocomposites (CSNPs@cur, FA-CSNPs@cur and BCSNPs@ cur) was established by various characterization approaches. The cellular uptake of these NPs was determined in Folate receptor (FR) and Biotin receptor (BR) positive MCF-7 (breast cancer cells) and in non-cancerous FR and BR negative HEK293 (human embryonic kidney) cells at low doses. The antiproliferative and apoptotic effect of the targeted and nontargeted NPs was investigated by cell-based assays. The cytotoxic effect of FA-CSNPs@cur was more pronounced in MCF-7 cells, when compared to B-CSNPs@cur and nominal cell mortality was observed in HEK293 cells as compared to cancer cell lines. In Chapter 5, the influence of encapsulating the drug in negatively charged nanoparticles on cellular toxicity was studied. Poly (lactic-co-glycolic acid) (PLGA) is an extensively used FDA approved biodegradable, synthetic polymer in formulation of nanomedicines. All the characterizations and cell line-based studies were performed similar to that in chapter 4. When compared between the performance of chitosan NPs and PLGA NPs, FA-CSNPs exhibited enhanced cytotoxicity, therefore, chitosan and folate were selected for surface modification to formulate multi-polymer nanocarriers as described in chapter 6 and 7. In Chapter 6, the impact of encapsulating the hydrophobic curcumin in a negatively charged lipophilic polymer-lipid NPs on drug delivery was studied. Solid lipid nanoparticles (SLNs) iii made up of stearic acid and soya lecithin and chitosan were formulated to form core-shell SLNs, which were conjugated with FA to create targeted CS-SLNs. Finally, Chapter 7 the synthesis of interpenetrating polymeric nanoparticles with chitosan and hydrogel forming HEMA polymer. These synthetic FA-conjugated hydrophilic NPs with surface negative charge were tested in vitro for cell cytotoxicity and targeting efficiency in MCF-7 and HEK293 cells. In a nutshell, different polymer-based nanomaterials are presented as nanomedicines to efficaciously deliver hydrophobic curcumin and enhance its antiproliferative efficacy in cancer cells. Therefore, this present thesis is an endeavor to develop multicomponent polymeric nanomaterials as delivery systems for hydrophobic drugs.