Abstract 6162: RRM1 inhibition enhances anti-tumor immunity by ubiquitination degradation DNMT1 through PI3K/AKT pathway

Abstract Patients with driver-gene-negative non-small cell lung cancer still need to rely on chemotherapy combined with immunotherapy. Some studies have suggested that chemotherapy drugs can promote the innate immune system, but the mechanism of that is still unclear. Ribonucleotide reductase large subunit (RRM1) is the main target of the commonly used chemotherapy drug gemcitabine, which exerts anti-tumor effects by inhibiting DNA replication and repair. We constructed human A549, Calu-1 cell lines and mouse KP (KRASG12D/P53KO) cell lines with stable knockdown of RRM1 and found that knockdown of RRM1 can significantly inhibit the growth of tumor cells in vivo and in vitro. RNA-sequencing was used to detect the changes in the transcriptome after RRM1 knockdown. Through GO analysis and KEGG analysis, we found that the DNA damage caused by RRM1 inhibition can cause the non-classical NF-κB signaling pathway to be upregulated, thereby causing an inflammatory response dominated by IL-6. However, at the same time, we found that the RNA recognition innate immune response pathway, which mainly recognizes dsRNA, was also activated. Therefore, we speculate that RRM1 inhibition affects the epigenetic changes of tumor cells. We found that the expression level of DNMT1 protein was downregulated after RRM1 knockdown, and its mRNA level remained unchanged, indicating that post-transcriptional modification of DNMT1 protein occurred. The reduction in DNMT1 protein expression reduced the overall DNA methylation level of the cell, thereby causing the activation of the type I interferon innate immune response pathway dominated by RIG-I/MAVS/TBK1/IRF3. Further mechanistic studies found that RRM1 inhibition mainly reduces the phosphorylation level of AKT protein by inhibiting the intracellular PI3K-AKT signaling pathway, thereby reducing the phosphorylation level of DNMT1 protein, and ultimately promoting the ubiquitination degradation pathway of DNMT1 protein. Therefore, by combining RRM1 inhibitors with DNMT1 inhibitors, the epigenetic drug decitabine (DAC) can further inhibit the expression of DNMT1, thereby promoting the type I interferon innate immune response pathway caused by chemotherapy drugs rather than the inflammatory response dominated by IL6, and exerting a synergistic anti-tumor effect on tumor growth in vivo. In summary, our research shows that inhibiting RRM1 can promote DNMT1 ubiquitination degradation through the PI3K/AKT signaling pathway, thereby activating the RNA recognition-induced type I interferon innate immune response pathway to exert anti-tumor effects. Combining with the epigenetic drug DAC can enhance the effect of this pathway, thereby better combining with immunotherapy to exert better anti-tumor effects. This provides a new idea for the treatment of chemotherapy combined with immunotherapy. Citation Format: Nan Jiang, Jianya Zhou. RRM1 inhibition enhances anti-tumor immunity by ubiquitination degradation DNMT1 through PI3K/AKT pathway [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 6162.