Enhancing anti-tumor immunity through intratumoral combination therapy with amphiphilic conjugates of oxaliplatin and imidazoquinoline TLR7/8 agonist

The efficacy of conventional chemotherapy does not only rely on the cytotoxic action of the drug compound itself. Indeed, proper drug-induced immunogenic cell death (ICD) can stimulate immunosurveillance and mount a systemic anti-tumor response. We aimed to further amplify the therapeutic activity of oxaliplatin (OxPt) chemotherapy-induced ICD by combining this with an imidazoquinoline (IMDQ) TLR7/8 agonist. We hypothesized that innate immune activation by TLR7/8 activation primes the immune system against tumor neoantigens, thereby mounting tumor-specific T cell responses that contribute to killing primary tumor cells and distal metastases. To this end, we initially synthesized a covalent conjugate of OxPt, an imidazoquinoline TLR7/8 agonist (<i>i.e.</i>, IMDQ), and an alkyl lipid. We hypothesized that such a lipidated conjugate would, upon intratumoral injection, increase the residence time in the tumor and reduce systemic dissemination and, hence, off-target toxicity. Whereas combination therapy with OxPt and IMDQ in native form improved, relative to single treatment, the anti-tumor efficacy against the primary treated tumor and a secondary distal tumor, this was not the case for OxPt-IMDQ-lipid conjugate therapy. We then altered the molecular design of the combination therapy and synthesized amphiphilic OxPt and IMDQ conjugates, comprising a cholesteryl motif and a hydrophilic poly(ethylene glycol) (PEG) chain. Intratumoral combination therapy with OxPt-PEG-cholesteryl and IMDQ-PEG-cholesteryl reduced, compared to native drug compounds, systemic innate inflammatory responses, and more efficiently eradicated primary and distal tumors. Furthermore, we found that combination therapy with OxPt-PEG-cholesteryl and IMDQ-PEG-cholesteryl induced antigen-specific anti-tumor responses and high infiltration levels of CD8+ T cells into the tumor.