Ephrins/eph as novel synthetic lethal targets in Kras-mutant colorectal cancer.

Abstract

e13578 Background: Mutations in the Kras proto-oncogene are found in 40%-45% of colorectal cancer (CRC) patients and occur mainly in codon 12 and 13. Kras mutant (MT) CRC tumours are resistant to EGFR mAb therapies. Clear understanding of the biology of KrasMT CRC is important, and identification of druggable targets uniquely required by KrasMT CRC tumours has the potential to fill a gap in the therapeutic armamentarium of advanced CRC. The aim of this study was to identify novel targets whose knock-down is synthetically lethal with Kras mutation in CRC models. Methods: Transcriptional profiling (Almac Diagnostics CRC DSA) of primary KrasMT and WT CRC tissues and paired KrasMT and WT CRC xenografts models was performed and Metacore pathway analysis was used to identify individual genes from novel Kras-dependent pathways for incorporation into a primary RNAi screen. Results: Using clinical and in vivo KrasMT/WT CRC samples and public available Kras signatures, we identified 30 signalling pathways and 160 genes associated with KrasMT CRC cancer. The primary Kras siRNA screen identified a number of novel Kras synthetic lethal target genes with a critical role in EMT and cell adhesion/migration. In particular, down-regulation of members of the EpH/Ephrin family was found to be lethal in KrasMT but not KrasWT cells. These results were confirmed in secondary and tertiary siRNA screens using a panel of KrasMT/WT CRC cell lines and multiple siRNA sequences. In addition, EpHA1, EpHA2 and EpHA4 silencing resulted in strong increase in apoptosis in KrasMT cells and this was further synergistically enhanced in the presence of chemotherapy (5-FU, CPT-11) treatment. Interestingly, EpHA1, EpHA2 and EpHA4 silencing also inhibited migration of KrasMT cells. Conclusions: This study demonstrates the utility of microarray expression data, Metacore and siRNA screens to identify novel Kras synthetic lethal targets and pathways. In addition, we found that EpHA1, EpHA2 and EpHA4 are important novel targets for KrasMT CRC tumours.