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DNA-damaging poisons and replicative stress commonly result in increased double-strand breaks (DSBs) in tumor cells. Non-homologous end joining (NHEJ), driven by the enzymatic function of DNA-PK, is one of the critical pathways employed to repair such DSBs. Inhibition of DNA-PK kinase activity impairs NHEJ, potentiates the activity of DNA-damaging agents, and inhibits survival of tumor cells incapable of repairing DSBs via other means, including homologous recombination (HR). We have developed an orally bioavailable, highly potent, and selective pharmacological inhibitor of DNA-PK activity, ZL-2201, for the treatment of cancer. ZL-2201 demonstrates enzymatic inhibition of DNA-PK in the single-digit nM range, with nearly 500-fold or greater selectivity against other phosphatidylinositol 3-kinase-related kinases (PIKKs). In addition, ZL-2201 showed high selectivity for DNA-PK kinase activity in a kinase panel screening study and a clean off-target profile with no appreciable inhibition against a panel of diverse, safety-relevant targets. We demonstrate that ZL-2201 effectively inhibits DNA-PK autophosphorylation and its downstream target phospho-RPA in multiple cell lines in a concentration- and time-dependent manner. DNA-PK has been shown previously to have synthetically lethal interactions with ATM. Therefore, we profiled the impact of ATM expression on the antiproliferative effects of ZL-2201. Cancer cell lines possessing defects in ATM displayed greater sensitivity to ZL-2201 compared to ATM-WT cancer cell lines. These observations were recapitulated in two ATM knockout isogenic cell lines. Moreover, ZL-2201 displayed minimal effects in a DNA-PK deficient model or in normal human and canine colon and kidney cell lines. Independent of ATM status, ZL-2201 showed strong synergy in vitro with topoisomerase II inhibitors. Following oral administration of ZL-2201 in vivo, ZL-2201 demonstrated dose-dependent and exposure-dependent antitumor activity against multiple models, with the greatest activity against ATM deficient human cancer xenografts. Antitumor activity correlated with duration of ZL-2201 exposure and level of target engagement. In addition, ZL-2201 significantly enhanced the activity of DNA-damaging agents in vivo, even in human cancer xenograft models with limited monotherapy antitumor activity for ZL-2201. The projected human PK properties, based on the ADME properties across species and PK properties in preclinical species of ZL-2201, suggest that ZL-2201 is suitable for oral administration. In conclusion, ZL-2201 demonstrates potent and selective inhibition of DNA-PK enzymatic activity, strong synergy with DNA damaging agents in vitro and in vivo, antitumor activity against multiple human xenograft models, and a favorable projected human PK profile. ZL-2201 is expected to enter clinical development in 2022. Citation Format: Shruti Lal, Bee-Chun Sun, Yuping Chen, Tom Huang, Neil Bhola, Vivian Morton, Kevin Chen, Shanghua Xia, Haoyu Zhang, Qiuping Ye, Petter Veiby, David I. Bellovin, Yuhua Ji. Discovery and characterization of ZL-2201, a potent, highly-selective, and orally bioavailable small-molecule DNA-PK inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2594. |
