MEK inhibition leads to BRCA2 downregulation and sensitization to DNA damaging agents in pancreas and ovarian cancer models

Abstract

// Francesca Vena 1, * , Ruochen Jia 1, * , Arman Esfandiari 1 , Juan J. Garcia-Gomez 1 , Manuel Rodriguez-Justo 2 , Jianguo Ma 3 , Sakeena Syed 3 , Lindsey Crowley 3 , Brian Elenbaas 3 , Samantha Goodstal 3 , John A. Hartley 1 and Daniel Hochhauser 1 1 Cancer Research UK Drug-DNA Interactions Research Group, UCL Cancer Institute, Paul O’Gorman Building, University College London, London WC1E 6DD, UK 2 Department of Research Pathology, UCL Cancer Institute, London EC1M6BQ, UK 3 EMD Serono Research and Development Institute, Billerica 01821, MA, USA * These authors have contributed equally to this work Correspondence to: Daniel Hochhauser, email: d.hochhauser@ucl.ac.uk Keywords: DNA damage; pancreatic cancer; ovarian cancer; targeted therapy; MEK inhibitors Received: January 08, 2018      Accepted: January 15, 2018      Published: January 22, 2018 ABSTRACT Targeting the DNA damage response (DDR) in tumors with defective DNA repair is a clinically successful strategy. The RAS/RAF/MEK/ERK signalling pathway is frequently deregulated in human cancers. In this study, we explored the effects of MEK inhibition on the homologous recombination pathway and explored the potential for combination therapy of MEK inhibitors with DDR inhibitors and a hypoxia-activated prodrug. We studied effects of combining pimasertib, a selective allosteric inhibitor of MEK1/2, with olaparib, a small molecule inhibitor of poly (adenosine diphosphate [ADP]-ribose) polymerases (PARP), and with the hypoxia-activated prodrug evofosfamide in ovarian and pancreatic cancer cell lines. Apoptosis was assessed by Caspase 3/7 assay and protein expression was detected by immunoblotting. DNA damage response was monitored with γH2AX and RAD51 immunofluorescence staining. In vivo antitumor activity of pimasertib with evofosfamide were assessed in pancreatic cancer xenografts. We found that BRCA2 protein expression was downregulated following pimasertib treatment under hypoxic conditions. This translated into reduced homologous recombination repair demonstrated by levels of RAD51 foci. MEK inhibition was sufficient to induce formation of γH2AX foci, suggesting that inhibition of this pathway would impair DNA repair. When combined with olaparib or evofosfamide, pimasertib treatment enhanced DNA damage and increased apoptosis. The combination of pimasertib with evofosfamide demonstrated increased anti-tumor activity in BRCA wild-type Mia-PaCa-2 xenograft model, but not in the BRCA mutated BxPC3 model. Our data suggest that targeted MEK inhibition leads to impaired homologous recombination DNA damage repair and increased PARP inhibition sensitivity in BRCA-2 proficient cancers.