134 Epigenetic immunomodulation by SGI-110 combined with immune checkpoint blockade for new therapeutic strategies

Abstract

Background: SGI-110 is a dinucleotide of decitabine (DAC) and deoxyguanosine formulated as a low volume SQ injection that extends DAC exposure compared to DAC IV. Our in vitro and in vivo evidences identified a strong immunomodulatory activity of SGI-110 on human cancer cells of different histotype and on human melanoma xenografts, and showed a remarkable anti-tumor effect once combined with anti-CTLA-4 mAb in a syngeneic mouse model. In this study we evaluated the contribution of anti-tumor immune responses in the reduction of tumor growth achieved by this therapeutic combination. Materials and Methods: The mammary carcinoma cells TS/A (2×105) were implanted SQ in Balb/c mice. Animals bearing palpable tumors were treated with 3mg/kg of SGI-110 (days 1−5), alone or combined with 100 mg of anti-murine CTLA-4 mAb (days 8, 11 and 14). The immunomodulatory effects of treatment were studied on tumor and normal tissues by RTPCR and by quantitative RT-PCR analysis of murine CTA expression. Immunohistochemical evaluation of tumor infiltrating immune cells was also performed. P1A-promoter methylation was tested by quantitative Methylation-Specific PCR (qMSP) on genomic DNA from tumor tissues. Results: The expression of P1A and Mage-a family members was induced in tumor tissues from animals treated with SGI-110, either alone or in combination with anti-CTLA-4 mAb, but not from mice treated with antiCTLA-4 mAb alone. Levels of P1A-specific mRNA were similar in tumors from mice treated with SGI-110 alone (3.18×10−04 P1A/b-actin molecules) or combined with anti-CTLA-4 mAb (1.18×10−04 P1A/b-actin molecules). The DNA hypomethylating effect of SGI-110 was sustained by the reduction of P1A promoter methylation in cancer tissues from SGI-110(16%) and combination(7%) treated mice vs control. Epigenetic remodelling was restricted to tumor tissue leaving almost unaltered normal ones. The contribution of immune cells in the therapeutic effectiveness of treatment was supported by the increased frequency of tumor infiltrating CD3+ cells in the combination arm (11±1.9) vs control (3.7±1.4) or single agent, antiCTLA-4 mAb (3±1.1) and SGI-110 (4.1±1.7), treated mice. Conclusion: These data highlight the involvement of the immune system in the anti-tumor effect of SGI-110 combined with CTLA-4 blockade. Based on these experimental evidences, an exploratory phase I trial to evaluate safety and immunobiologic activities of the combination is being activated in advanced melanoma patients.