N. Villafane1,2, Y. Tsang2, K. Scott2 1Baylor College Of Medicine,Michael E. DeBakey Department Of Surgery,Houston, TX, USA 2Baylor College Of Medicine,Department Of Molecular And Human Genetics,Houston, TX, USA
Introduction: Pancreatic ductal adenocarcinoma (PDAC) is not one of the most prevalent cancers but is by far one of the deadliest given its 5-year survival rate of <5%. The majority of PDAC tumors harbor activating mutations in the KRAS oncogene, a therapeutically undruggable and initiating “driver” event found in >90% of early-stage lesions. Following activation of KRAS, PDAC acquires other driver mutations that include inactivating events in tumor suppressor genes and numerous low frequency gene mutations, amplifications, and deletions likely required for KRAS-mediated tumor progression. Our objective is to determine which of these events are functional drivers or “driver effectors” required for KRAS biology, as targeting these events or their activated pathways offers hope of improving patient outcomes.
Methods: We used a highly-vetted list of 250 amplified gene candidates (copy number > 5; GISTIC q-value < 0.075) that was previously defined at our lab by analyzing The Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium (ICGC) PDAC datasets (derived from 218 tumors). We engineered pooled gene libraries consisting of DNA-barcoded open reading frame (ORF) clones encoding the amplified driver candidates. We used a lentiviral vector to deliver these ORFs to human pancreatic ductal epithelial (HPDE) cells engineered with a doxycycline-inducible KRASG12D allele in order to identify ORFs that drive tumor growth and metastasis in mice maintained on or off doxycycline diet to control for KRASG12D activation.
Results: Our screens identified SEMA6A, a transmembrane protein member of the axon guidance pathway, as a high priority PDAC target. Our data indicate that SEMA6A expression is increased through KRASG12D– mediated down-regulation of miR145. This suggests that the SEMA6A/plexinA2/A4 signaling pathway may be hyper-activated in the presence of oncogenic KRAS, resulting in cell cycle progression and tumor growth.
Conclusion: Screening of candidate driver pools in our laboratory has revealed potent drivers of PDAC, such as SEMA6A. High priority PDAC drivers resulting from these functional screens will lead to the discovery of detection biomarkers and potential targets for drug development efforts needed for patients suffering from this disease.