Cancer immunotherapy emerged as a novel therapeutic approach to destroy tumor cells, and it has grown towards clinical transition following successful fundamental research and clinical trials. Immunotherapy by efficacious adjuvants is critical for increasing protective immune responses against infectious disease and cancer. STING and TLR9 agonists are interesting candidates for novel immunotherapies for the treatment of cancer. In this study, the antitumoral effects of ADU-S100 as a potent STING agonist and CpG ODN1826 as TLR9 agonist in single and combined forms in CT-26 colon adenocarcinoma model was evaluated. This model was induced in female BALB/c mice which were divided into five groups treated with PBS, ADU-S100 (20 and 40 µg), CpG ODN (40 µg) and ADU-S100 (20 µg) + CpG ODN (20 µg). The tumor volumes and weights of mice were measured every other day. On the 30th day, tumor, spleen and liver tissues of mice were isolated for histopathological analysis. Hematological analysis was performed on heart blood. Intratumoral injection of agonists induced significant tumor suppression in all treatment groups with profound effect in combination group that received half concentration of single form. Also, histopathological analysis of tumor tissues showed the presence of apoptotic and inflammatory cells and increased number of lymphocytes in the blood samples of the treatment groups indicating the effective role of these agonists in clearing the tumor. Thus, such synergy of adjuvant may have an effective role in cancer immunotherapy and offer new perspectives on combination of agonists that trigger innate immune sensors during malignancy.

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