DNA-dependent kinase (DNA-PK) is a nuclear serine/threonine protein kinase complex that is a key component of the non-homologous end joining (NHEJ) process. DNA-PK plays an important role in the cellular response to DNA damage through the detection and repair of DNA double strand breaks (DSB). AZD7648 is a potent inhibitor of DNA-PK (0.6 nM in biochemical assay, 89 nM in A549 cells). AZD7648 inhibits ionising radiation (IR)-induced DNA-PK S2056 auto phosphoryalation with an IC50 of 92 nM in A549 non-small cell lung cancer (NSCLC) cells. In A549 cells, AZD7648 (≥1 µM) in combination with 2Gy IR for 48 hours led to a significant accumulation of cells arrested in the G2/M of the cell cycle, a 4-fold increase in micronuclei formation, and 3-fold induction of γH2AX, pATM S1981 and 53BP1 foci formation compared with IR alone. In vivo the combination of AZD7648 with IR (5x 2Gy) induced tumour regression in H1299 and A549 NSCLC xenografts in a dose-dependent manner (84 and 11% regression respectively). Similarly, liposomal doxorubicin (2.5 mg/kg weekly) in combination with AZD7648 (37.5 mg/kg bid) induced tumour regressions in the BT474c ER+ breast cancer xenograft model and in a TNBC PDX model (63% and 33% regression respectively).
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