Abstract 4038: A functional genomics approach to the identification of genes involved in resistance to Oxaliplatin in colorectal cancer

• Published in: Cancer research (Chicago, Ill.) Ill.), 2018-07, Vol.78 (13_Supplement), p.4038-4038
• Main Authors: Invrea, Federica, Cavicchioli, Francesca, Petti, Consalvo, Russo, Rosalia, Isella, Claudio, Medico, Enzo
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2018-4038

Currently, the first line therapy for metastatic colorectal cancer (CRC) is the FOLFOX regimen, which includes Oxaliplatin in combination with Fluorouracil and Leucovorin. Responses to FOLFOX range from overt regressions (35%) to full resistance (25%), and eventually all patients become resistant. Indeed, the molecular mechanisms of Oxaliplatin resistance remain mostly to be understood. To identify genes involved in sensitivity/resistance to Oxaliplatin, we designed an integrated approach including forward genetic screens and computational analyses. The pipeline includes: (i) stable transduction of CRC cells with pooled shRNA libraries; (ii) Oxaliplatin treatment for six weeks to select a drug-resistant subpopulation; (iii) identification of shRNA constructs enriched in the Oxaliplatin-resistant subpopulation by next-generation sequencing analysis. We focused the shRNA libraries targeting phosphatases and ubiquitin conjugation pathway genes. The first are involved in several biological processes, reversing the biochemical activity of kinases and typically acting as feedback loop regulators. The second direct proteins to degradation by the proteasome regulating homeostasis, cell cycle, and DNA repair pathways. HCT116 CRC cells, markedly sensitive to Oxaliplatin, were transduced in duplicate with both shRNA libraries. After Oxaliplatin treatment for six weeks, resistant populations emerged from the library-transduced cells, but not from control-transduced cells. To reveal shRNA constructs responsible of such phenotype, we extracted genomic DNA from transduced cells and, upon amplification of shRNA constructs by targeted PCR and next-generation sequencing, we compared the repertoire of shRNA sequences in HCT116 cells selected with Oxaliplatin with that of cells grown in standard medium. Screening hits were then prioritized for functional characterization, resulting in a phosphatase (CDC25C) and an ubiquitin ligase candidate (DCAF17). In conclusion, we successfully setup a functional genomic screening for acquired resistance to Oxaliplatin in CRC. Specific shRNA constructs from both the phosphatase and ubiquitin ligase libraries were enriched after Oxaliplatin treatment, highlighting candidate genes whose loss of function could potentially drive resistances to Oxaliplatin. Citation Format: Federica Invrea, Francesca Cavicchioli, Consalvo Petti, Rosalia Russo, Claudio Isella, Enzo Medico. A functional genomics approach to the identification of genes involved in