ARTICLE ABSTRACT
DNA-dependent protein kinase (DNA-PK), a driver of the non-homologous end-joining (NHEJ) DNA damage response (DDR) pathway, plays an instrumental role in repairing double-strand breaks (DSBs) induced by DNA-damaging poisons. We evaluate ZL-2201, an orally bioavailable, highly potent, and selective pharmacological inhibitor of DNA-PK activity, for the treatment of human cancerous malignancies. ZL-2201 demonstrated greater selectivity for DNA-PK and effectively inhibited DNA-PK autophosphorylation in a concentration- and time-dependent manner. Initial data suggested a potential correlation between ATM deficiency and ZL-2201 sensitivity. Moreso, ZL-2201 showed strong synergy with topoisomerase II inhibitors independent of ATM status in vitro. In vivo oral administration of ZL-2201 demonstrated dose-dependent antitumor activity in the NCI-H1703 xenograft model and significantly enhanced the activity of approved DNA-damaging agents in A549 and FaDu models. From a phospho-proteomic mass spectrometry screen, we identified and validated that ZL-2201 and PRKDC siRNA decreased Ser108 phosphorylation of MCM2, a key DNA replication factor. Collectively, we have characterized a potent and selective DNA-PK inhibitor with promising monotherapy and combinatory therapeutic potential with approved DNA-damaging agents. More importantly we identified phospho-MCM2 (Ser108) as a potential proximal biomarker of DNA-PK inhibition that warrants further preclinical and clinical evaluation.
