Antigen-independent tumor targeting by CBX-12 (alphalex™–exatecan) induces long-term antitumor immunity

Aims: To determine whether antigen-independent targeting of the TOP1 inhibitor exatecan to tumor with a pH-sensitive peptide (CBX-12) produces superior synergy with immunotherapy compared with unconjugated exatecan. Materials & methods:In vitro and ex vivo functional assays were performed via FACS and ELISA assays. In vivo efficacy was evaluated in the syngeneic CT26 model. Results: CBX-12 combined with anti-PD-1 or anti-CTLA4 results in delayed tumor growth and complete response, with cured animals displaying long-term antitumor immunity. CBX-12 stimulates expression of MHC 1 and PD-L1 and is an inducer of immunogenic cell death, producing long-term immune recognition of tumor cells and resultant antitumor immunity. Conclusion: The authors' data provide the rationale for exploring immunotherapy combinations with CBX-12 in clinical trials.Although combinations of chemotherapy and immunotherapy have shown great promise for cancer treatment, they have also demonstrated significant safety concerns that require dose reductions. Targeting chemotherapy to the tumor can avoid these safety issues, thereby enhancing efficacy of combination therapies. CBX-12 is a novel peptide-drug agent targeting the TOP1-inhibiting drug exatecan to tumor via pH-sensitive peptide. Unlike tumor targeting via antibody, CBX-12 universally targets all solid tumors. CBX-12 avoids the immune cell toxicity of nontumor-targeted exatecan and safely synergizes with immunotherapies. CBX-12 treatment causes tumor cells to express and secrete molecules that result in activation of immune components to recognize and eliminate tumor cells. These data support the upcoming clinical trials of CBX-12 in combination with immunotherapy.