Chemotherapy (CT) resistance in ovarian cancer is related to multiple factors, and assessment of these factors is necessary for the development of new drugs and therapeutic regimens. In an effort to identify such determinants, we evaluated the expression of approximately 21,000 genes using DNA microarray screening in paired tumor samples taken prior to and after CT treatment from 6 patients with predominantly advanced stage, high-grade epithelial ovarian cancer. A subset of differentially expressed genes was selected from all microarray data by initial filtering on confidence at p=0.05, followed by filtering on expression level (≥2-fold). Using these selection criteria, we found 121 genes to be commonly up-regulated and 54 genes to be down-regulated in the post-CT tumors, compared to primary tumors. Up-regulated genes in post-CT tumors included substantial number of genes with previously known implication in mechanisms of chemoresistance (TOP2A, ETV4, ABCF2, PRDX2, COX2, COX7B, MUC1, MT3, MT2A), and tumorigenesis (SCGB2A2, S100A9, YWHAE, SFN, ATP6AP1, MGC5528, ASS, TACC3, ARHGAP4, SRA1; MGC35136, PSAP, SPTAN1, LGALS3BP, TUBA4, AMY2B, PPIA, COX1, GRB2, CTSL). Down-regulated genes in post-CT samples mostly included genes implicated in chemosensitivity (GRP, TRA1, ADPRTL1, TRF4-2), cell proliferation and cell cycle control (NGFRAP1, TPD52L1, TAX1BP1) and tumor suppression and apoptosis (SMOC2, TIMP3, AXIN1, CASP4, P53SCV). Additionally, gene clustering analysis revealed the existence of two distinct expression signatures of chemoresistant tumors, which was further confirmed by assessment of some genetic (p53 gene mutation status) and clinical parameters (CT regimens). Our data suggest that intrinsic and acquired chemoresistant phenotypes of post-CT tumors may be attributed to the combined action of different factors implicated in mechanisms of chemoresistance, tumor invasion/progression and control of cell proliferation. This type of molecular profiling could have important clinical implications in resolving chemoresistance and the development of novel treatment strategies designed to prevent its emergence.

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