Abstract 3098: Nanotherapeutics for combination drug and gene therapy in treating glioblastoma multiforme

Gliomas represent approximately 80% of all malignant brain tumors, and glioblastoma multiforme (GBM), the most aggressive type, accounts for nearly half of all gliomas. Despite treatment strategies including surgery, radiation, and chemotherapy, the 5-year survival rate for brain cancer is only 35%. New therapeutic strategies are necessary to improve the outcomes of this disease. Chemotherapy with DNA alkylating agents is commonly used in treatment for GBM. Research has shown that better therapeutic response of GBM tumors to alkylating agents and increased survival rate is indicative in patients with epigenetic silencing of O6-methylguanine-DNA methyltransferase (MGMT), a gene responsible for DNA repair. Therefore, we propose a treatment strategy combining drug and gene therapy to target and silence MGMT to sensitize cells to treatment with temozolomide (TMZ) or lomustine (CCNU), both DNA alkylating agents. We previously developed cationic, amphiphilic copolymer poly(lactide-co-glycolide)-g-polyethylenimine (PgP) and demonstrated its utility for nucleic acid delivery. Here, we examine the ability of PgP as a drug and siRNA delivery carrier to overcome drug resistance and improve anticancer activity through combination drug and gene therapy for GBM treatment. PgP micelles were designed and synthesized for delivery of hydrophobic drugs in the PLGA core and negatively charged nucleic acids in the positively charged PEI shell through electrostatic interactions. RNA binding and polyplex stability assays were performed using agarose gel electrophoresis. Cytotoxicity of TMZ, CCNU, and/or PgP/siMGMT polyplexes was determined by MTT assay. Silencing of MGMT on the protein and mRNA level was determined using western blotting and qPCR, respectively. Our results demonstrated that PgP effectively forms stable complexes with siRNA and protects siRNAs from serum- and ribonuclease-mediated degradation, confirming the potential of the polyplex for in vivo delivery. We demonstrated that PgP/siMGMT polyplexes mediate knockdown of MGMT protein as well as a significant ~56% and ~68% knockdown of MGMT mRNA in T98G GBM cells compared to cells treated with PgP complexed with non-targeting siRNA (siNT) at a 60:1 and 80:1 nitrogen:phosphate (N:P) ratio, respectively. Further, co-treatment of PgP/siMGMT polyplexes with TMZ or CCNU enhanced anticancer activity in T98G GBM cells compared to treatment with the PgP/siMGMT polyplex, TMZ, or CCNU alone. Future studies will determine efficacy of drug-loaded and siRNA-complexed PgP for combination therapy in vitro as well as using a xenograft GBM model for local delivery. Successful combinatorial drug and gene therapy using PgP may overcome drug resistance and improve therapeutic outcomes for patients with glioblastoma. Citation Format: Angela A. Alexander-Bryant, Breanne Hourigan, Michael Lynn, Jeoung Soo Lee. Nanotherapeutics for combination drug and gene therapy in treating glioblastoma multiforme [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3098. doi:10.1158/1538-7445.AM2017-3098