Design of multifunctional nanomaterials to improve cancer gene therapy
Gene therapy shows promise for individualized cancer therapies. Compared to conventional treatments, this approach offers a variety of advantages, including a multiplicity of gene targets that define tumor clinical behavior, high specificity, low off target toxicity, and suppression of drug resistance. However, the lack of efficient delivery strategies for gene-specific agents and preclinical models for evaluation of the efficacy of gene-based therapeutics has impeded its clinical application. Nanoparticles provide a flexible platform for fabricating novel delivery vehicles capable of transporting gene-specific therapeutic agents to target tumors. Among the various types of nano-carriers for cancer therapy, superparamagnetic iron oxide nanoparticles have emerged as a leading candidate as they have a host of advantages compared to other formulations. The iron oxide core facilitates the condensation of other molecules to it that confer biological properties that promote stability during transport through the circulation, penetration of physiological barriers such as the blood brain barrier, and targeted uptake by tumor cells by pinocytosis and endocytosis. Nanoparticles are formulated to minimize off target toxicity by using materials that are inherently biocompatible and facilitate rapid clearance from the circulation. Most importantly, these properties are maintained when the nanoparticles are derivatized to transport biologically active nucleic acids to affect tumor gene expression. This dissertation documents the development of multifunctional drug delivery nanoparticles to improve cancer gene therapy. We first developed and characterized the functionality of an iron oxide-based nanoparticle containing a copolymer that binds a biologically active gene that activates an inherent tumor cell death pathway. This nanoparticle was also derivatized with a targeting peptide to improve tumor-specific gene delivery. The nanoparticle displayed little intrinsic toxicity and mediated excellent uptake of biologically active gene as evidenced by elevated glioblastoma (GBM) cell killing in vitro and suppression of GBM xenograft growth in vivo. We next modified the nanoparticle to deliver RNA interference (RNAi)-based gene therapy. In collaboration with faculties in the Department of General Surgery, we demonstrated that nanoparticle-mediated small interfering RNA (siRNA) delivery can effectively suppress expression of target genes in cancer cells without notable cytotoxicity in vitro. Importantly, we have shown that recognition of a tumor cell surface epitope by an antibody-derivatized nanoparticle improves binding to target cells and greatly enhances inhibition of target gene expression in an orthotopic liver cancer mouse model in vivo. After evaluating the efficacy of targeted delivery of siRNA, we determined the effect of siRNA-mediated suppression of biochemical pathways associated with malignancy and of another with drug resistance in GBM cells in vitro. siRNA-mediated gene suppression reduced GBM cell motility, a hallmark of aggressive behavior, increased endogenously-induced apoptosis and increased sensitivity to temozolomide, the standard drug for GBM, by reducing the level a of key DNA repair enzyme, O6-methylguanine-DNA methyltransferase (MGMT). Systemic delivery of tumor targeting-nanoparticles carrying anti-MGMT-siRNAs reduced MGMT expression in an orthotopic xenograft model of a human GBM. Of clinical significance, reduction of tumor xenograft MGMT activity was accompanied by statistically significantly longer survival compared to control-treated animals. Our findings are the first substantive demonstration of a potential anti-resistance therapy that may enhance the efficacy of current GBM treatments and prolong survival. Finally, we have developed a three-dimensional (3D) tissue culture model to better mimic of tumor microenvironment for the evaluation of nanoparticle-mediated gene delivery. Significantly, we found that targeted gene delivery was only observed in cells cultured in scaffolds whereas cells cultured on two-dimensional (2D) plates showed no difference in gene delivery between targeted and non-target control nanoparticles. In vivo evaluation of gene delivery in a xenograft tumor mouse model further demonstrated that 3D culture system can correctly modeled nanoparticle-mediated targeted delivery in vivo.