Synergy between oxaliplatin and adenovirus initiates immunogenic cell death in human colorectal carcinoma cells

Externalization of Calreticulin (CALR) is the critical first step in the initiation of Immunogenic Cell Death. Since Oxaliplatin (OX) cooperates with an oncolytic chimeric human adenovirus Ad5/3-NP2.ADP (ADP) to induce adaptive immunity as well as regression of established cancer, we sought to determine whether the cooperation was additive or synergistic. Methods include immunohistochemistry (IHC) for Calreticulin expression in mice 11 days after intratumoral injection of the OX-ADP mixture. In vitro assays with limiting dilutions of OX and ADP on human Clone A colorectal carcinoma cell monolayers were cultured for 3 days and cytotoxicity, viral infectivity by GFP, and the expression of externalized CALR (ectoCALR) on Clone A cells measured by static cytometry. Synergy was measured using SynergyFinder 3.0 (Ianevski et al., PMC9252834) that creates 2-D interactive surfaces to measure synergy and antagonism. Areas of synergy have mean scores > 10. IHC revealed strong CALR expression in OX-ADP treated tumors, weak expression in tumors injected with OX or ADP alone and minimal in PBS treated controls. Mean Viral Infectivity synergy score was 27.2 for the area of (Ox μM, ADP MOI): (0.12μM, 4 MOI) to (12.5μM, 100 MOI) while mean synergy score for ectoCALR expression was 29.2 for OX/ADP (0.01μM, 0.16) to (0.12μM, 20 MOI). The role of oxidative and endoplasmic reticulum stress as the basis of synergy is under study. Oxaliplatin and adenovirus are synergistic in their ability to initiate ICD which is important for vaccine development.