Dual ENPP1/ATM depletion blunts DNA damage repair boosting radioimmune efficacy to abrogate triple-negative breast cancer.

The ATP-hydrolytic ectoenzyme ENPP1 has been implicated in the metastasis and recurrence in triple-negative breast cancer (TNBC), primarily by contributing to tumor cell survival and treatment resistance. However, the precise mechanisms remain unclear. In a model of local recurrence (LR), circulating tumor cells (CTC) engrafting in the post-resection tumor bed developed a radioresistant phenotype linked to an ENPP1-gene signature which was also identified in TNBC patients, suggesting ENPP1´s role in genome integrity. Blockade of ENPP1 using a permeable ENPP1 inhibitor (AVA-NP-695) reduced radioresistance, mechanistically attributed to decreased homologous recombination (HR) resulting in persistent DNA damage, as evidenced by enhanced tail moment and sustained γH2AX formation. This impaired DNA damage repair (DDR) sensitized tumor cells to ionizing radiation (IR). Notably, several DDR inhibitors (i) (including PARPi and ATMi) showed the highest synergy score in a targeted pharmacological screening. In vivo, dual ENPP1/ATM inhibition heightened radiosensitivity, compromised tumor cell survival and enhanced STING-TBK1 signaling by preventing ENPP1-mediated cGAMP hydrolysis. This resulted in robust innate and long-lasting adaptive antitumor immune memory responses, leading to significant tumor regression. Remarkably, combined treatment post-IR reduced spontaneous metastasis and local recurrence, and induced abscopal effects that impacted distant tumor spread in orthotopic tumor models. Thus, these findings position ENPP1 as a critical link between genome integrity and immunosuppression, offering promising translational opportunities for treating local or distant dissemination in TNBC.