Whole gene expression profiling shows a differential transcriptional response to CISPLATINUM in BRCA-1 defective versus BRCA1-reconstituted breast cancer cells

BRCA1-defective breast tumors are characterized by basal-like molecular phenotype.HCC1937 is a BRCA1-defective breast cancer cell line which discloses higher sensitivityto cisplatinum (CDDP) as compared to the BRCA1 full length cDNA transfected cloneHCC1937/wtBRCA1. To study the molecular bases of BRCA1-related differentialsensitivity to the drug, we analyzed the whole gene expression profile of HCC1937 andHCC1937/wtBRCA1 cells following in vivo and in vitro exposure of tumor cells toCDDP. Differential in vivo sensitivity was evaluated in xenografted tumors in SCIDmice after 4 weeks of treatment with CDDP (5 mg/kg) or vehicle. Tumors wereretrieved from animals 4 hours after the last dose of the drug or vehicle. In vitro datawere obtained exposing HCC1937 and HCC1937/wtBRCA1 cell lines to CDDP at IC50doses of 30 and 70mM, or at 60 and 140hM respectively, for 3 and 12 hours. Geneexpression profiling was performed by Affymetrix technology using GeneArray 1.0ST.Array data were analyzed using Gene Expression Console, GeneSpring software andIngenuity Pathway Analysis (IPA). The search for canonical pathways by IPA identifiedan upregulation of G2/M DNA damage checkpoint pathway, in a dose- and timedependentmanner, as well as the down regulation of Notch signaling pathway inHCC1937 cells, after treatment with CDDP in vitro. Both pathways were not affected inBRCA1-reconstituted cells. The in vivo data analysis identified, in HCC1937/wtBRCA1tumors, following CDDP exposure, modulation of pathways involving AKT3 andPRKAR2B, also known as RII-BETA, a cAMP-dependent protein kinase. Our datacorrelate with previous evidence of AKT as factor of resistance to CDDP. In conclusionfunctional status of BRCA1 differentially modulates response to CDDP in vitro and in vivo. Signaling pathways involving Notch, AKT and RII-BETA are involved in theseevents. These findings might be of interest to design novel therapeutic approaches inBRCA1-defective tumors.