TITLE OF THESIS: Development & Application Of Biomaterials For Drug Delivery

ABSTRACT

The fields of biomedicine and nanotechnology have mutually benefited from the development of efficient drug delivery system (DDS). DDS are biomaterials with biodegradable, biocompatible, environmentally responsive and targeting properties, which have significantly impacted the modern day health care system.

Since the first FDA approval of a drug delivery carrier, namely PLGA/leuprolide acetate in 1989, more than 10 biodegradable materials are now commercially available for the treatment of cancer, hormonal deficiency, edema, bipolar disorder, and for alcohol & opioid dependence. A range of inorganic (gold, silver, iron, and silica) and organic (polymers, dendrimers, micelles, and hydrogels) biomaterials have also been investigated and are being used as drug delivery carriers in clinical trials.

Biomaterials such as silica microparticles, hydrogels, organic and inorganic nanoparticles have been intensely studied for the delivery of small molecule therapeutics such as chemotherapeutics in research. Recently, proteins and peptide based therapeutics are increasingly recognized as novel drugs with applications ranging from immunological diseases to cancer. The stability and refolding of protein is one major problem in successful delivery of proteins in the human body. Proteins are biological molecules which easily denature by chemical physical and biological stresses. Hence the field of biomaterials provides an excellent platform for successful delivery of protein based drugs in vitro and in vivo. Furthermore, thermally responsive hydrogels are being reported as unique macromolecular chaperones, which maintain weak non-covalent interactions with misfolded proteins and refold them into native form as a function of thermal flexibility of hydrogels.

The first chapter in this thesis will briefly review on the history & development of different biomaterials over the past few decades and their application as a drug delivery carrier. The second chapter will describe the research on the development and functionalization of diatomaceous earth embedded core shell materials, which are capable of encapsulating two chemotherapeutic drugs (doxorubicin and paclitaxel) at constant molar ratios, in different compartments of a single drug delivery carrier and show synergistic anticancer response in different cancer cell lines. Physiologically stable and stimuli-responsive β-Cyclodextrin capped diatomaceous earth microparticles are developed by the concept of host-guest chemistry. β-Cyclodextrin capped diatomaceous earth microparticles are prepared by covalent conjugation of adamantane (guest) molecules on silica scaffold, followed by their interactions with β-Cyclodextrin molecules via host guest complexation. Doxorubicin and paclitaxel were then encapsulated at different concentrations and locations within the self- assembled microparticles (shell of β-Cyclodextrin verses core of diatoms) via adsorption. The encapsulation of each drug in different compartments of delivery carrier (core of diatoms versus shell of Cyclodextrin) was then used as a method to control the release rate of both drugs in situ, and to maintain the optimal molar ratios of two drugs required for their synergistic outcomes in vitro. The results suggest that encapsulation of paclitaxel in diatomaceous earth microparticles core and of doxorubicin in β-Cyclodextrin:Adamantane corona, produces synergistic activities at all studied concentrations in cancer cell lines. Paclitaxel encapsulated in diatomaceous earth microparticles core is expected to facilitate slow release of hydrophobic drug in cell culture media as, only 7% of encapsulated hydrophobic drug is released over a period of 24 h, while release of doxorubicin from β- Cyclodextrin:Adamantane shell is complete (100%) within few hours of encapsulation. This difference in release profile of two drugs maintained molar ratio of doxorubicin/paclitaxel of 30 or higher in cell culture conditions, resulting in combinatorial index value of less than one and yielded synergistic response. In contrast, cells treated with doxorubicin loaded diatomaceous earth microparticles core and paclitaxel loaded shell resulted in the combinatorial index value of more than one and showed strong antagonistic activities for all studied concentrations of the drugs in cancer cell lines. The third chapter of this thesis describes the development of thermoresponsive hydrogels and explores the structural changes in hydrogels matrix. Poly (vitamin B5 analogous methacrylamide) P(B5AMA) hydrogels of different net charges, hydrophobicity and cross-linking densities were synthesized by a free radical polymerization method. The role of P(B5AMA) hydrogel for the restoration of enzymatic activity of thermally denatured enzymes (lysozyme and carbonic anhydrase), as a function of temperature and time and for the presence of residual water in the hydrogel architecture were then evaluated. The data reveals that water release efficacies of P(B5AMA)hydrogel at 37 °C are directly related to the enzymatic efficacies of proteins. The refolding efficacies of lysozyme and carbonic anhydrase in the presence of collapsed P(B5AMA) hydrogel (after the removal of free residual water) were 17.58 ± 0.6 and 36.5 ± 1.8, respectively and were comparable to the refolding efficacies of proteins in saline solution. The hydrated P(B5AMA) hydrogels, in contrast showed protein refolding efficacies of 65.4 ± 6.58 for lysozyme and 78.65 ± 1.97 for carbonic anhydrase. The fourth chapter of this thesis provides a brief conclusion and future directions to further explore the field of drug delivery. The facile synthesis and self-assembly of diatoms, β-Cyclodextrin and adamantane provides a great platform to encapsulate different drugs at constant feed ratios and optimize their response as a function of release rate of two drugs from the delivery carriers. The proven biocompatible nature of FDA approved materials utilized during the study suggests their accelerated evaluation and translation into clinical studies. On the other hand, hydrogel with promising protein renaturation efficacies were further evaluated for their interactions with denatured proteins, and the role of thermal flexibility of the hydrogel matrix in protein refolding capabilities was elucidated. Further studies are being conducted to evaluate the role of hydrogels in the restoration of the native structure of amyloid plaques for the treatment of Alzheimer’s disease.

Anyone who wishes to attend the public presentation should contact the grad studies coordinator at gsc@upei.ca to receive the link to the meeting.