ATM Loss Confers Greater Sensitivity to ATR Inhibition than PARP Inhibition in Prostate Cancer

Alterations in DNA damage response (DDR) genes are common in advanced prostate tumors and are associated with unique genomic and clinical features. ATM is a DDR kinase that has a central role in coordinating DNA repair and cell-cycle response following DNA damage, and alterations are present in approximately 5% of advanced prostate tumors. Recently, inhibitors of PARP have demonstrated activity in advanced prostate tumors harboring DDR gene alterations, particularly in tumors with alterations. However, the role of alterations in DDR genes beyond in mediating PARP inhibitor sensitivity is poorly understood. To define the role of loss in prostate tumor DDR function and sensitivity to DDR-directed agents, we created a series of -deficient preclinical prostate cancer models and tested the impact of loss on DNA repair function and therapeutic sensitivities. loss altered DDR signaling, but did not directly impact homologous recombination function. Furthermore, loss did not significantly impact sensitivity to PARP inhibition but robustly sensitized to inhibitors of the related DDR kinase ATR. These results have important implications for planned and ongoing prostate cancer clinical trials and suggest that patients with tumor alterations may be more likely to benefit from ATR inhibitor than PARP inhibitor therapy. SIGNIFICANCE: ATM loss occurs in a subset of prostate tumors. This study shows that deleting ATM in prostate cancer models does not significantly increase sensitivity to PARP inhibition but does sensitize to ATR inhibition.