Polymeric particulate systems for immunotherapy of cancer

Abstract

Immunotherapy has been established as a groundbreaking approach to treat cancer. It involves modulation of the host’s immune response to fight cancer. This is achieved by either enhancing tumor-specific T cell responses or inhibition of the tumor-induced immune suppression. Immunotherapy, however faces several challenges such as local immunosuppression in the tumor area leading to immunological tolerance. To overcome these challenges, particulate formulations such as nano- and microparticles containing immunotherapeutics have been developed to increase therapeutic efficacy and reduce toxicity of immunotherapy. This thesis investigates two strategies towards using particulate systems based on a biodegradable polymer, poly(lactic-co-hydroxymethylglycolic acid) (pLHMGA) in immunotherapy of cancer: therapeutic cancer vaccines and local delivery of immunomodulatory antibodies. Additionally this research aims to evaluate the feasibility of polymeric particulate systems as alternative for commonly-used water-in-oil (W/O) emulsions such as incomplete Freund’s adjuvant (IFA) in cancer immunotherapy. W/O emulsions are pharmaceutically not well-defined their administration is associated with severe local side effects such as inflammation, granuloma, pain and swelling.

Cancer vaccines usually comprise of tumor-specific antigens and adjuvants and intend to induce a strong and durable tumor-specific CD8+ T cell immune response. In this thesis, ovalbumin-loaded pLHMGA nanoparticles (NPs) were initially evaluated as model vaccines in vitro and in vivo with promising results. Encouraged by these results, a therapeutic cancer vaccine was designed based on human papillomavirus oncoprotein (HPV16 E7) which has shown promise in clinical trial. An HPV SLP antigen derived from HPV16 E7, and poly IC (TLR3 ligand-adjuvant) were encapsulated in pLHMGA NPs and the therapeutic efficacy of the vaccine was evaluated in mice. Encapsulation of HPV SLP antigen in NPs substantially enhanced the population of HPV-specific CD8+ T cells when combined with poly IC either co-encapsulated with the antigen or in its soluble form. The therapeutic efficacy of NPs containing poly IC in tumor eradication was equivalent to that of the IFA formulation. Importantly, administration of pLHMGA nanoparticles was not associated with adverse effects.Immunomodulatory antibodies enhance the anti-tumor immune response by altering the stimulatory or inhibitory signals on DCs and T cells. The systemic administration of these antibodies in their soluble form has however been associated with severe toxicity and autoimmune reactions. In this thesis, pLHMGA MPs were loaded with antiCD40 (an immunostimulatory antibody) and antiCTLA4 (an immune check point blocker) and studied in vivo The antibody-loaded microparticles showed comparable therapeutic efficacy to the IFA formulation with no local adverse effects in MC38 tumor-bearing mice. Moreover the microparticles exhibited lower antibody serum levels in comparison with IFA formulations which lowers the probability of systemic adverse effects.

In summary, this thesis discusses various applications of nano- and microparticulate carrier systems based on a hydrophilic aliphatic polyester, pLHMGA, in immunotherapy. Antigens, adjuvants and antibodies were encapsulated in pLHMGA nano- and microparticles. These particles have shown in vitro cytocompatibility and are well tolerated in vivo. Furthermore, the therapeutic efficacy of formulations based on pLHMGA polymers were comparable to commonly used W/O IFA emulsions in tumor-bearing mice and therefore pLHMGA delivery systems are excellent alternatives for IFA.