Abstract 4236: Effects of a DNMT1-selective inhibitor on T-cell activity and tumor cells intrinsic pro-inflammatory response

Abstract Previous studies indicate that while combinations of DNA methyltransferase inhibitors, such as decitabine or 5-azacytadine, with immunotherapies has shown potential in activating anti-tumor activity, their limited clinical success could be attributed to the systemic delivery and toxic effects on the immune cells in the microenvironment, which may explain the lack of activity in clinical trials. To explore the potential of combining an epigenetic inhibitor with an immunomodulatory agent, the effects of a DNMT1 inhibitor on T-cell activity and intrinsic pro-inflammatory responses in tumor cells were examined. Human and mouse cancer cell lines or isolated T-cells were treated with DNMT1-selective inhibitors and assessed for gene expression, global DNA methylation, mass cytometry, fluorescent cytometry, and chemokine ELISA. DNMT1-selective inhibitors triggered a pro-inflammatory transcriptional response in human cancer cell lines similar to decitabine. In human T-cells, DNMT1 inhibition reduced proliferation and increased markers of both anti-inflammatory and pro-inflammatory phenotypes, with these changes being reversible upon compound removal. Mouse T-cells similarly exhibited temporary loss of proliferation and increased anti-inflammatory and pro-inflammatory phenotypes. Additionally, DNMT1 inhibition elevated the expression of anti-inflammatory cytokines IL-10 and IL-4 in both human and mouse T-cells. Notably, DNMT1 inhibition resulted in a lasting pro-inflammatory transcriptional response in malignant cancer cell lines, whereas the effect on normal cells was reversible. In summary, DNMT1-selective inhibitors may boost the efficacy of immuno-oncology therapies by inducing a pro-inflammatory response in cancer cell lines while minimizing impact on T-cells through alternative dosing schedules. Further research is required to compare DNMT1-selective inhibitors with traditional HMAs and to study the interaction between immune and cancer cells in vivo. Identifying biomarkers for patient stratification could help optimize treatment strategies. This study highlights the importance of evaluating the impact of small molecule inhibitors on both tumor characteristics and immune responses to optimize conditions for effective anti-tumor responses. Citation Format: Shane W. O'Brien, Satyajit Rajapurkar, Anthony Della Pietra, Helen Sun, Andrew Fedoriw, Michael McCabe, Melissa Pappalardi. Effects of a DNMT1-selective inhibitor on T-cell activity and tumor cells intrinsic pro-inflammatory response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4236.