Design of Intratumoral Immunostimulant Formulations

Abstract

Cancer immunotherapy involves stimulation of the body’s own immune system to fight cancer. Tumors possess myriad suppressive mechanisms that facilitate evasion of the immune system. Immunotherapy aims to stimulate immune cells to recognize and attack tumor tissue. While immunostimulatory agents have achieved some success in treating cancer, systemic toxicity remains a major concern. In particular, systemic exposure to immunostimulants can activate immune cells outside of target tissues, which can potentially induce side effects or autoimmune reactions. In the treatment of solid tumors, intratumoral (IT) therapy offers unique benefits as an anti-cancer strategy, especially in the ability to bypass obstacles of trafficking, tumor penetration, and severe adverse events associated with systemic delivery. IT administration of immunostimulants, for example, can work synergistically with checkpoint inhibitors making a nonresponsive ‘cold’ tumor ‘hot’ by recruiting and activating tumor infiltrating lymphocytes. Unfortunately IT administration does not necessarily preclude the manifestation of systemic adverse events; therapy transport out of the tumor and back into systemic circulation can lead to similar adverse events as seen with systemic exposure. While many researchers have worked to optimize the efficacy of immunostimulants, few have approached delivery design with the consideration of drug retention after IT administration. This dissertation sought to explore delivery strategies for two negatively charged immunostimulants, polyI:C and CpG, which are potent toll-like receptor 3 (TLR3) and TLR9 agonists, respectively. Both compounds exhibit strong induction of interferons, leading to a proinflammatory environment after binding to TLRs, thus generating memory and tumor-specific T cells. Both TLR3 and TLR9 are located intracellularly; thus negatively-charged polyI:C and CpG macromolecules must be internalized by immune cells in order to be efficacious. To achieve both goals of increased retention and intracellular delivery, polycations were selected as a delivery tool. Polycations have historically been employed for intracellular delivery of nucleic acid material. This dissertation suggests that electrostatics can aid in injection site retention through interactions with highly negatively charged extracellular matrix. In chapter 2, polylysine, at a range of molecular weights, was evaluated for its ability to complex with immunostimulants and subsequently activate TLR(s). Chapter 3 presented a novel idea utilizing Glatiramer Acetate (GA), better known as Copaxone® as a delivery tool for immunostimulants. GA is a highly positively-charged polypeptide and is currently an FDA-approved therapy for multiple sclerosis. In this work, we generated small nanoparticles known as polyplexes, which form when mixing positively-charged GA and negatively-charged immunostimulant(s) (polyI:C or CpG). Together from chapters 2 and 3, we found that the relationship between complexation and TLR activation depends on the strength of the interaction in the polyplex. In a tumor model of head and neck squamous cell carcinoma, GA polyplexes were able to decrease tumor burden as compared to the vehicle controls. Therefore, this dissertation demonstrates that using polycations to complex with immunostimulant(s) is a promising approach to effectively deliver therapies and stimulate a local immune response.