Abstract 3506: AZD7648, a potent and selective inhibitor of DNA-PK, potentiates activity of the PARP inhibitor olaparib resulting in sustained anti-tumour activity in xenograft and PDX models

DNA-dependent kinase (DNA-PK) is a nuclear serine/threonine protein kinase complex and 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 double strand breaks (DSB). DSB can be induced by a range of agents, including chemotherapy and radiation. The PARP inhibitor olaparib has also been shown to induce DSB as a consequence of trapping PARP proteins at sites of damaged DNA. Therefore, we hypothesised that DNA-PK inhibitors may combine therapeutically with PARP inhibitors. AZD7648 is a highly potent and selective inhibitor of DNA-PK (pDNA-PK cell IC50 = 92 nM) The combination treatment of AZD7648 with olaparib for 10 - 12 days in vitro leads to at least 20% greater cell growth inhibition compared with either agents as monotherapies in a panel of cell lines with deficiencies in the ATM pathway (e.g. cells lacking ATM protein or where ATM substrates are not phosphorylated after exposure to DSB inducing agents). This effect is also seen in isogenic ATM knock-out (KO) FaDu head and neck and A549 non-small cell lung cancer cell lines. At concentrations of AZD7648 (0.6 - 2 µM) and olaparib (1 µM) that have monotherapy activity in the ATM KO cells but not in their wild-type counterparts (WT), the combination treatment enhanced the G2/M cell cycle arrest caused by olaparib and led to greater levels of micronuclei formation as detected using high-content immunofluorescece assays (mean per cell: FaDu WT = 0.1, FaDu ATM KO = 0.4). This was associated with a larger quantity of chromosomal aberrations in the ATM KO versus WT cells following combination treatment detected by metaphase spread analysis (mean per cell: FaDu ATM KO = 5.5, FaDu WT = 1.2). The same phenotype was observed in A549 ATM KO versus WT cell lines. In vivo, continuous dosing of AZD7648 (75 mg/kg bid) in combination with olaparib (100 mg/kg qd) inhibited the growth of FaDu WT tumours by ~60%. However, in the FaDu ATM KO tumours complete regressions were seen after 70 days of dosing and no re-growth was detected up to 220 days later. Additionally, in PDX models of breast, lung, ovarian and head and neck cancer this combination showed tumour growth inhibition (50-100%) in 13 models and regression in 5 models, only one of these five models being ATM pathway deficient. These data confirm that DNA-PK inhibition using AZD7648 enhances the efficacy of olaparib in vitro and in vivo, providing