High grade serous ovarian cancer is typified by p53 mutation, high degrees of genomic instability and the development of chemo-resistance. Genomic translocations result from incorrectly repaired DNA double strand breaks (DSBs). DNA-PKcs is a central catalytic component of the error prone non-homologous end joining (NHEJ) DSB repair mechanism. We report here that DNA-PKcs is frequently amplified in copy number in HGSC and that amplification correlates with higher DNA-PKcs gene expression and poorer patient outcome (PFS/OS) using both in-house and publicly available datasets (TCGA). Targeting DNA-PKcs, pharmacologically or by RNAi, enhances apoptosis in response to platinum treatment in platinum resistant cell lines and primary models. Furthermore we report that inhibition of DNA-PK restores response to cisplatin in chemoresistant ovarian cancer cells in vivo. SKOV-3 tumor xenografts were implanted subcutaneously into Balb/c Nu/Nu mice and treated with DNA-PKcs inhibitor NU7441 for 2 weeks alone or in combination with cisplatin. DNA-PK inhibition or cisplatin treatment alone were ineffective however in combination they decreased tumor growth at 14 days by 90%, relative to platinum only treatment. On investigating the mechanism of DNA-PKcs mediated chemoresistance we revealed that, in response to DNA damage, DNA-PKcs phosphorylates AKT on serine residue 473 in the nucleus of platinum resistant ovarian tumor cells, but not sensitive cells from the same patient. Phosphorylation at AKT threonine 308 is unaffected and DNA-PK inhibition does not interfere with insulin-mediated phosphorylation of AKT S473. DNA-PK mediated AKT activation in chemoresistant cells results in inhibitory phosphorylation of the pro-apoptotic protein BAD and stabilisation of the anti-apoptotic Bcl-2 protein resulting in the observed attenuation of apoptotic response to platinum treatment. DNA-PK inhibition is an attractive therapeutic strategy for resensitising resistant tumors to platinum based therapy, directly linking the DNA damage caused by platinum to the pro-survival AKT pathway, without interfering with normal physiological roles of AKT.

Citation Format: Curry E, Cheraghchi-Bashi-Astaneh A, Chen M, Cunnea P, De Sousa C, Maginn E, Dai Y, Liu E, Wasan H, Mills G, Bowtell D, Gabra H & Stronach EA. DNA-PKcs is amplified in high grade serous ovarian cancer (HGSC), correlates with poor outcome and drives resistance to platinum therapy via the AKT signaling pathway [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr AS20.