The chemotherapeutic agent pacilitaxel (TaxolTM) plays an important role in the treatment of breast and ovarian carcinoma. Unfortunately acquired resistance to paclitaxel limits the clinical efficacy of this agent in both malignancies. The molecular mechanisms of acquired paclitaxel resistance are due in part to over expression of the multi -drug-resistance- 1 (MDR-1)-mediated drug export pump. Several laboratory and clinical studies support the hypothesis that there are additional mechanisms of acquired paclitaxel resistance in clinical cancers. Work in my laboratory has focused on identifying genes important in producing the paclitaxel resistance phenotype. Initial studies using the differential display technique and cDNA array technology identified several genes not previously associated with the paclitaxel resistance the functional role of these genes in directly inducing the paclitaxel resistant phenotype remained unclear. To increase the likelihood of identifying functionally important genes in the paclitaxel phenotype we have designed a functional cloning strategy to identify Taxol-Resistance-Inducing Genes or TRIGs. Specifically, cDNA from paclitaxel-resistant breast and ovarian cancer cell lines have been cloned into plasmids to form expression libraries designed to identify genes that are directly involved in the paclitaxel resistant phenotype. Care has been taken to select paclitaxel resistant lines that do not over express MDR-1. Preliminary functional cloning experiments have already identified one gene, TRIC-1, than when retransfected into a paclitaxel sensitive line generate not only a paclitaxel resistance, but also a multi-drug resistant phenotype that is independent of MDR-1 over expression. In addition, the principal investigator has accessed to a large ample set of both women with advance breast cancer and Taxol resistant ovarian cancer. The specific aims of this grant proposal will include: 1) the further characterization of genes identified through this functional cloning technique; 2) the further characterization of the TRIG-1 gene; 3) correlation of TRIC and MDR-1 expression with clinical, this will include correlation of response to neoadjuvant paclitaxel with TRIC/MDR-1 expression in locally advanced breast cancer and response to paclitaxel (with or without vx-710 (an MDR-1 inhibitor)) in women with recurrent ovarian cancer. When completed this analysis should both expand the list of molecules directly involved in the paclitaxel resistance phenotype and, most importantly, focus attention on those molecules directly involved in paclitaxel resistance in the clinical setting.