We have recently developed an enzyme-directed immunostimulant (EDI) prodrug motif, which is metabolized to active immunostimulant by cancer cells and, following drug efflux, activates nearby immune cells, resulting in immunogenicity. In this study, we synthesized several EDI prodrugs featuring an imidazoquinoline immunostimulant resiquimod (a Toll-like receptor 7/8 agonist) covalently modified with glycosidase enzyme-directing groups selected from substrates of β-glucuronidase, α-mannosidase, or β-galactosidase. We compared the glycosidase-dependent immunogenicity elicited by each EDI in RAW-Blue macrophages following conversion to active immunostimulant by complementary glycosidase. At a cellular level, we examined EDI metabolism across three cancer cell lines (B16 melanoma, TC2 prostate, and 4T1 breast cancer). Comparing the relative immunogenicity elicited by each EDI/cancer cell combination, we found that B16 cells produced the highest EDI prodrug immunogenicity, achieving >95% of that elicited by unmodified resiquimod, followed by TC2 and 4T1 cells (40% and 30%, respectively). Immunogenicity elicited was comparable for a given cell type and independent of the glycosidase substrate in the EDIs or differences in functional glycosidase activity between cell lines. Measuring drug efflux of the immunostimulant payload and efflux protein expression revealed that EDI/cancer cell-mediated immunogenicity was governed by efflux potential of the cancer cells. We determined that, following EDI conversion, immunostimulant efflux occurred through both P-glycoprotein-dependent and P-glycoprotein-independent transport mechanisms. Overall, this study highlights the broad ability of EDIs to couple immunogenicity to the metabolism of many cancers that exhibit drug efflux and suggests that designing future generations of EDIs with immunostimulant payloads that are optimized for drug efflux could be particularly beneficial.

Multidrug-Resistant (MDR) cancers attenuate chemotherapeutic efficacy through drug efflux, a process that transports drugs from within a cell to the extracellular space via ABC (ATP-Binding Cassette) transporters, including P-glycoprotein 1 (P-gp or ABCB1/MDR1). Conversely, Toll-Like Receptor (TLR) agonist immunotherapies modulate activity of tumor-infiltrating immune cells in local proximity to cancer cells and could, therefore, benefit from the enhanced drug efflux in MDR cancers. However, the effect of acquired drug resistance on TLR agonist efflux is largely unknown. We begin to address this by investigating P-gp mediated efflux of TLR 7/8 agonists. First, we used functionalized liposomes to determine that imidazoquinoline TLR agonists Imiquimod, Resiquimod, and Gardiquimod are substrates for P-gp. Interestingly, the least potent imidazoquinoline (Imiquimod) was the best P-gp substrate. Next, we compared imidazoquinoline efflux in MDR cancer cell lines with enhanced P-gp expression relative to parent cancer cell lines. Using P-gp competitive substrates and inhibitors, we observed that imidazoquinoline efflux occurs through P-gp and, for Imiquimod, is enhanced as a consequence of acquired drug resistance. This suggests that enhancing efflux susceptibility could be an important consideration in the rational design of next generation immunotherapies that modulate activity of tumor-infiltrating immune cells.

Herein, this work reports the first synthetic vaccine adjuvants that attenuate potency in response to small, 1-2 °C changes in temperature about their lower critical solution temperature (LCST). Adjuvant additives significantly increase vaccine efficacy. However, adjuvants also cause inflammatory side effects, such as pyrexia, which currently limits their use. To address this, a thermophobic vaccine adjuvant engineered to attenuate potency at temperatures correlating to pyrexia is created. Thermophobic adjuvants are synthesized by combining a rationally designed trehalose glycolipid vaccine adjuvant with thermoresponsive poly-N-isoporpylacrylamide (NIPAM) via reversible addition fragmentation chain transfer (RAFT) polymerization. The resulting thermophobic adjuvants exhibit LCSTs near 37 °C, and self-assembled into nanoparticles with temperature-dependent sizes (90-270 nm). Thermophobic adjuvants activate HEK-mMINCLE and other innate immune cell lines as well as primary mouse bone marrow derived dendritic cells (BMDCs) and bone marrow derived macrophages (BMDMs). Inflammatory cytokine production is attenuated under conditions mimicking pyrexia (above the LCST) relative to homeostasis (37 °C) or below the LCST. This thermophobic behavior correlated with decreased adjuvant R g is observed by DLS, as well as glycolipid-NIPAM shielding interactions are observed by NOESY-NMR. In vivo, thermophobic adjuvants enhance efficacy of a whole inactivated influenza A/California/04/2009 virus vaccine, by increasing neutralizing antibody titers and CD4 + /44 + /62L + lung and lymph node central memory T cells, as well as providing better protection from morbidity after viral challenge relative to unadjuvanted control vaccine. Together, these results demonstrate the first adjuvants with potency regulated by temperature. This work envisions that with further investigation, this approach can enhance vaccine efficacy while maintaining safety.

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