LAUSR

BReast CAncer 1 and 2 (BRCA1/2) tumor suppressor genes are frequently mutated in familial breast and ovarian cancers. Recent clinical trials in breast cancers with BRCA1/2 mutations indicate that 50-75% of patients may not have response to poly (ADP-ribose) polymerase inhibitors (PARP) inhibitors. Thus, identification of novel molecular targets and therapeutic interventions are needed to improve poor clical outcome and patient survival. Here we report that Eukaryotic Elongation Factor-2 Kinase (EF2K), an atypical kinase, is highly upregulated in BRCA1+ mutated cell lines and involved in colony formation, migration/ invasion and enhances the effect of PARP inhibitors. Furthermore, in vivo therapeutic targeting of EF2K by once a week systemic injections with magnetic nanoparticles (MNPs) incorporating EF2K siRNA significantly inhibits growth of BRCA1+ tumors in orthotopic xenograft models in mice by inhibition of tumor cell proliferation, angiogenesis and induction of robust apoptosis, which were associated with in vivo inhibition of clinically relevant molecular pathways including, proliferation, survival/drug resistance (PI3K/Akt, c-Myc), cell cycle (Cyclin D1), motility/invasion (Src/FAK/Paxillin), translation (4E-BP1), angiogenesis (VEGF) and stem-cell markers. No toxicity was detected during the study and by postmortem analysis of major organs, indicating that targeting EF2K is safe. The combination of PARP inhibitor (AZD2281, Oleparib) with MNP-EF2K siRNA enhanced significantly growth inhibition in MDA-MB-436 cells indicting EF2K siRNA sensitize BRCA1 + mutation breast cancer cells to PARP inhibitors. Collectively, our results suggest, for the first time, that EF2K is involved in tumorigenesis and progression and may serve as a potential therapeutic target in BRCA1+ mutated breast cancers. Citation Format: Elif Asik, Nermin Kahraman, Tulin Guray, Murvet Volkan, Gabriel Lopez-Berestein, Bulent Ozpolat. Eukaryotic Elongation Factor 2 Kinase (eEF-2K) is a novel therapeutic target in BRCA1+ mutated breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1125. doi:10.1158/1538-7445.AM2017-1125