P5-01-07: Identification of SORBS2 as a Candidate Marker To Predict Metastatic Relapse in Breast Cancer.

Abstract Background Elucidation of promising cancer biomarkers from gene expression data can provide important insight into the relationship between signaling networks and cancer. SORBS2, sorbin and SH3 domain containing 2, is a multi-adapter protein involved in signal transduction associated to the cytoskeleton and was reported to be strongly repressed in pancreatic and cervical cancers. Methods: With the purpose of identifying genes involved in metastatic process, we compared gene expression profiling of 19 invasive ovarian cancers and 24 borderline tumors. Prognostic value of the selected genes was then tested in a gene expression array database that includes 1659 patients with early breast cancer (Gyorffy B et al. 2010). Upon isolation of SORBS2 as a predictor, its involvement in cell migration and tumor progression was investigated in vitro. Small interfering RNA targeting SORBS2 was used to downregulate its expression in T47D and Hela, two cell lines overexpressing SORBS2. Functional effect of siRNA-induced knockdown of SORBS2 on cell viability was determined by WST-1 assay and Trypan Blue exclusion test. Effect on cell migration was evaluated by wound-healing and transwell assays. Western blot analyses were also performed to examine the expressions of proteins involved in cell survival, death and migration. Results: High-throughput analyses of genes that are differentially expressed between borderline ovarian tumors and invasive carcinoma demonstrated that SORBS2 is significantly downregulated in invasive carcinoma (FDR<10e-10). Moreover, SORBS2 loss was a strong predictor of relapse in a gene expression array dataset of 1659 patients presenting an early breast cancer (HR=0.62, 0.52−0.72, p=6.4e-10). In vitro studies showed that SORBS2 specific downregulation stimulated cell proliferation, by an average of 40%, in T47D and Hela cell lines. SORBS2 knockdown had no effect on either cell migration rate or protein expressions of p-FAK and p-Paxillin, two focal adhesion proteins which are critical to cell adhesion and migration. No significant variations in protein expressions of Akt/mTOR pro-survival or caspases activation pathways were observed. Gene expression profiling before and after SORBS2 dowregulation is ongoing in the two cell lines. Conclusion: This study is the first to provide evidence for an antiproliferative activity of SORBS2 with no effect on cell migration in breast cancer cells. Our clinical and in vitro data suggest that SORBS2 is a candidate marker to predict relapse in patients with early breast cancer. Molecular mechanisms mediating the antiproliferative effect of SORBS2 are currently being investigated. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-01-07.