Formulation Effects on Immune Response to Nanocarriers Encapsulating TLR 7 Agonist

Abstract

Abstract Recent decades have witnessed remarkable progress in cancer immunotherapy as an approach to enhancing host immune response against cancer. Particularly, a cancer vaccine comprised of antigen, vaccine adjuvant, and delivery system has gained widespread attention, which can elicit immune response by activating dendritic cells (DCs), the critical antigen-presenting cells (APCs) 1. In the past decades, nanoformulations have gained extensive attention as drug carriers for improved cancer immunotherapy. Imidazoquinoline-based toll-like receptor (TLR) 7 agonist, imiquimod (IMQ), a cytokine inducer, could elicit DC activation. TLR7 activation stimulates myeloid differentiation primary-response gene 88 (MyD88) signaling pathways, elicit DCs to upregulate costimulatory molecules, secrete type I interferons and pro-inflammatory cytokines, and stimulate T cell- mediated immune response 2. The development of a variety of nanoformulations as drug carriers, such as polymeric poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) and liposomes, has broadened the application of TLR7 agonist in cancer immunotherapy. However, an improved understanding of how formulation factors could influence the immune response to nanocarriers encapsulating TLR 7 agonist can drive the discovery of more efficient platforms to deliver TLR 7 agonist to immune system for enhanced cancer immunotherapy. In this thesis, we encapsulated IMQ in PLGA NPs that were either naturally anionic or modified with didodecyldimethylammonium bromide (DMAB) to generate cationic surface charge. In addition, 18:0 PC 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoyl-3-trimethylammonium-propane (chloride salt) (DOTAP) were employed to formulate IMQ-loaded anionic DSPC liposomes and cationic DOTAP liposomes. These formulations were evaluated for in vitro DC activation and antigen presentation with a model antigen, ovalbumin (OVA), using bone marrow-derived dendritic cells (BMDCs) and DC 2.4 cell line. Cell viability assay showed that PLGA NPs and DSPC liposomes showed negligible cytotoxicity on BMDCs and DC 2.4 at low concentrations, whereas DMAB-PLGA NPs and DOTAP liposomes exhibited obvious cytotoxicity at relatively low concentrations. Also, anionic PLGA NPs were superior to other nanoformulations in eliciting costimulatory molecule expression by DCs, whereas cationic DOTAP liposomes were superior in inducing antigen presentation by DCs compared with other nanoformulations. Overall, our studies demonstrated that IMQ loaded PLGA NPs showed both better biocompatibility and stronger DC activation efficacy compared with other formulations. However, further studies are needed to understand the mechanism of formulation effects on immune response to nanocarriers encapsulating TLR 7 agonist. Definitely, the development of more efficient drug delivery systems encapsulating TLR agonists could contribute to vaccine-based cancer immunotherapy.