Abstract 4956: Proteomics-based characterization of pathways involved in tamoxifen resistance in breast cancer cells

Background: Although the introduction of tamoxifen (tam) has contributed to the improved survival of breast cancer patients there are those that relapse despite treatment due to de novo or acquired resistance to the drug. Since the mechanisms involved in tam resistance likely involve various pathways, techniques like mass spectrometry allowing simultaneous analyses of multiple proteins are of great value. Our aim is to identify pathways involved in tam resistance by using a mass spectrometry. Material and methods: Mass spectrometry based proteomics was used to investigate the proteomic changes associated with tam exposure using a tam-responsive and resistant cell line, MCF7 and MCF7/LCC2, respectively. Cytosolic and nuclear fractions were subjected to a shotgun proteomics approach. This included immobilised pH gradient-isoelectric focusing (IPG-IEF) of trypsinized peptides followed by Maldi-TOF/TOF mass spectrometry. Advanced biostatistics was applied to narrow identified targets to those which were significantly deregulated. Results: Preliminary results indicate a clear distinction between the nuclear and cytosolic fractions in regards to proteins. Various proteins were differentially deregulated in MCF7 compared to the resistant cell line both at the basal level and following tam treatment. At basal level, glucose-6-phosphate dehydrogenase, fatty acid synthase and keratin 18 were significantly upregulated in resistant cells as compared to parental MCF7 cells. Interestingly, tam treatment in MCF7 cells induced a significant increase in expression of several proteins involved in the p53 pathway and related to Huntingtin (HTT) while downregulating other proteins related to Retinoic Acid Receptor alpha (RARA). In contrast, resistant cells showed upregulation of proteins involved with RARA without exhibiting any specific deregulated proteins related to HTT or p53. Conclusions: Basal differences in protein expression were observed between the tam-sensitive and resistant cell line. Our results indicate that there are potentially deregulated proteins in the tam-sensitive cell line involved in p53, RARA, and HTT pathways in a manner that differs from the resistant one. The expression of the identified proteins will be further characterized. Understanding of the mechanisms involved in tam resistance can potentially aid in the development of new drugs and serve as prognostic biomarkers. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4956.