Thesis (Ph. D.)--University of Rochester. Department of Chemical Engineering, 2015.
Small molecule anticancer agents present many challenges for systemic drug delivery including rapid blood clearance, nonspecific extravasation and accumulation, and inability to overcome multidrug resistant cell mechanisms. Nanoparticle (NP) drug carriers have shown promise in prolonging circulation and reducing off-target accumulation/toxicity of drugs, and allow cell/tissue-specific targeting and enhanced intracellular delivery of therapeutic agents. Due to these advantages, many drug-loaded NPs have been investigated clinically as anticancer therapies, with some success in achieving clinical approval. Currently, induction therapies for acute myeloid leukemia (AML) focus on elimination of rapidly dividing cells, but fail to eliminate a small, but important, subset of AML cells that are characteristically quiescent. These cells are called leukemia stem cells (LSCs) because they are self-renewing, multipotent, and capable of recapitulating the leukemic disease even after remission is achieved. The small molecule drug, parthenolide (PTL), is cytotoxic towards LSCs, but is plagued by
poor aqueous solubility, which leads to rapid blood clearance and ultimately inefficacy in vivo. To enhance the aqueous solubility of PTL, a polymer micelle drug delivery system was developed. Additionally, PTL-loaded micelles were functionalized with cell-specific targeting molecules to enhance the specificity of therapeutic delivery. Using reversible addition-fragmentation chain transfer (RAFT) polymerizations, a variety of poly(styrenealt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) and poly(styrene-alt-maleic anhydride)-b-poly(butyl acrylate) (PSMA-b-PBA) amphiphilic diblock copolymers were synthesized and subsequently self-assembled into core-shell micelle NPs. Micelles with the largest hydrophobic cores were the most stable in aqueous solutions, exhibited the highest hydrophobic drug loading, and most prolonged drug release. Additionally, PS exhibited superior loading of PTL versus PBA cores, likely due to increased pi-bonding between drug and core. Thus, predominantly hydrophobic PSMA-b-PS micelles (e.g., PSMA₁₀₀-b-PS₂₅₈) were studied for their ability to deliver therapeutic doses of PTL to MV4-11 human AML cells in vitro. Similar to free PTL, PTL-loaded micelles exhibited a dose-dependent cytotoxicity towards AML cells in vitro, and unloaded micelles were nontoxic even at the highest requisite dose. Further, PTL-loaded micelles were internalized by MV4-11 cells via clathrin-mediated endocytosis. Uptake of micelles and subsequent release of PTL delayed cytotoxicity compared to free PTL doses, but resulted in a decreased dependence on exofacial binding to AML cell surface thiols. To increase the specificity of PTL-loaded micelles to AML cells, micelles were functionalized with
antibody and peptide targeting molecules. Antibody and peptide functionalization drastically enhanced micelle binding to AML cells in vitro, as measured by flow
cytometry. Thus, a functionalized micelle delivery system for PTL was developed that efficiently loaded PTL and enhanced localization of therapeutic NPs to AML cells. Future studies include investigation of efficacy and specificity of targeted therapies in mixed primary cell cultures as well as in diseased mice.
