Antibodies In Cancer Therapy: New Targets, Applications And Combination Strategies

Abstract

Over the last decade, antibodies have become an important component in the arsenal of cancer therapeutics. Their high-specificity, low-off target effects, desirable pharmacokinetics and high success rate are a few of the many attributes that make them amenable for development as drugs. The work presented here explores the targeting, mechanisms and use of antibody-based cancer therapy. In the first chapter, we used a phage display-based cell panning procedure to develop two fully humanized antibodies, Tw1S4_6 and Tw1S4_AM6, that bind specifically to HSPG2/perlecan, a protein found to be overexpressed on tumor cells. Immunohistochemistry studies revealed high HSPG2 expression across various tumor sub-types including melanoma, bladder cancer, glioblastoma and ovarian cancer. There was significant correlation between high HSPG2 expression and poor survival in triple negative breast cancer, bladder and ovarian cancers. The data presented here points towards the relevance of HSPG2 as a novel target for not only triple negative breast cancer but other malignancies as well. Based on its over-expression in different solid tumors, we evaluated HSPG2 as a therapeutic target in the second chapter. We observed significant tumor growth inhibition with Tw1S4_AM6 in the triple negative MDA-MB-231-LM2 breast cancer xenograft model. This efficacy was reduced in NSG mice, suggesting NK cell-mediated antibody dependent cellular cytotoxicity (ADCC) as a potential mechanism of action. In vitro studies using human PBMCs confirmed induction of ADCC with anti-HSPG2 antibodies. In addition, conjugation of Tw1S4_AM6 on the surface of polymeric nanoparticles enabled increased tumor cell uptake of nanoparticles, suggesting Tw1S4_AM6 could be valuable as a targeting ligand for drug delivery systems. There is a significant interest in designing therapeutic agents that can enhance ADCC and thereby improve clinical responses with approved antibodies. We have developed a suite of highly substituted imidazoquinolines, which activate TLR 7 and/or 8 and induce significantly higher levels of cytokines compared to the FDA-approved TLR7 agonist, imiquimod. In the third chapter, we evaluated our series of TLR7/8 agonists for their ability to improve ADCC. Our studies show that the second generation TLR 7/8 agonists induce robust pro-inflammatory cytokine secretion and activate NK cells. These agonists also enhanced ADCC in vitro. Finally, we found that these agonists significantly improved the anticancer efficacy of two monoclonal antibodies in vivo. Thus, the work presented here encompasses the three critical aspects of antibody therapeutics: identifying the target, understanding their mechanisms, and leveraging these mechanisms to improve their efficacy.