AZD7648: A potent and selective inhibitor of DNA-PK with pharmacodynamic and monotherapy anti-tumor activity

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) and is a critical component of the DNA Damage Response (DDR). DSB can be induced by a range of agents, including chemotherapy, radiation or Poly ADP Ribose Polymerase (PARP) inhibitors such as olaparib, and thus a DNA-PK inhibitor is likely to sensitize to these agents. DNA-PK inhibitors may also be effective as monotherapy in tumors with high endogenous levels of DNA damage resulting from defects in other DNA repair pathways. We have developed a highly potent and selective inhibitor of DNA-PK, AZD7648 (pDNA-PK IC50 in A549 cells = 92 nM). AZD7648 shows broad growth inhibitory activity across a panel of 244 cancer cell lines (GI50 1.3 - 30 µM). Consistent with known synthetic lethal interactions with DNA-PK, AZD7648 shows a 10-13-fold greater growth inhibitory effect in FaDu head and neck and A549 non-small cell lung cancer cell lines with ATM knocked out (KO) by zinc finger nuclease or CRISPR respectively compared to their isogenic wild-type counterparts (WT). This growth inhibition is associated with increased levels of DNA damage as measured by micronuclei formation detected using high-content immunofluorescence (2-fold increase vs DMSO at 2 µM AZD7648). Moreover, a 6-fold increase in chromosomal breaks are detected in the ATM KO cells using metaphase spread analysis (mean breaks/cell: FaDu ATM KO = 1.7, ATM WT = 0.28) In vivo, monotherapy treatment with AZD7648 (75-100 mg/kg bid) inhibited tumor growth in a panel of 14 PDX and 2 xenograft models, derived from breast, lung, ovarian and head and neck cancers. This included models with and without loss of ATM. Treatment with AZD7648 resulted in dose-dependent inhibition of the phosphorylation of DNA-PK (S2056), RPA32 (S4/8) and nuclear γH2AX in FaDu ATM KO xenografts, where AZD7648 75mg/kg inhibited γH2AX and phosphorylation of DNA-PK (S2056) and RPA32 (S4/8) by 71, 98 and 95% respectively at 2 h after dosing. These data confirm that DNAPK inhibition using AZD7648 has potent pharmacodynamic and monotherapy anti-tumor activity in a range of pre-clinical models. This includes, but is not restricted to, models with engineered and endogenous loss of ATM. Citation Format: Elaine B. Cadogan, Jacqueline H. Fok, Antonio Ramos-Montoya, Neil James, Valeria Follia, Mercedes Vazquez-Chantada, Paul Winjhoven, Lenka Oplustil O’Connor, Ankur Karmokar, Anna Staniszewska, Emma Dean, Simon J. Hollingsworth, Barry Davies. AZD7648: A potent and selective inhibitor of DNA-PK with pharmacodynamic and monotherapy anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3505.