Abstract P5-05-06: Proteomics studies reveal important pathway and phosphoprotein changes contributing to cancer stem cell properties and drug resistance of triple negative breast cancer cells cultured in attached and suspension conditions

Abstract

Abstract Breast tumors without ER, PR and HER2 expression are referred to as triple-negative breast cancer (TNBC) and have been associated with a higher rate of recurrence and distant metastasis compared to other types of breast cancers. Because they lack a clear therapeutic target, chemotherapy is the only systemic treatment option for TNBC patients. Previous works suggested that the chemotherapy-resistant residual tumor cells may contribute to the high rate of recurrence and metastasis of TNBC. Recently cancer stem cells and circulating tumor cells have been reported to have a close relationship with cancer metastasis. Culturing tumor cells in suspension conditions was also reported to be an efficacious way to enrich cancer stem cells and to mimic the living conditions for circulating tumor cells. In the current study, four TNBC cell lines HCC1937, HCC1187, MDA-MB-468 and MDA-MB-231 were cultured in both attached and non-attached suspension conditions. HCC1937 and MDA-MB-231 cells formed tumorspheres in suspension condition and became more resistant to docetaxel comparing to those in the attached condition. Although MDA-MB-468 cells were unable to form tumorspheres in suspension conditions they formed clusters of aggregated cells that were also more resistant to docetaxel in suspension. HCC1187 cells could not form either tumorspheres or clusters in suspension conditions and were found to be more sensitive to docetaxel. Toward uncovering the signaling changes in these cell lines in different conditions, we performed a proteomics study to compare the phosphoproteomes of these cells in both culturing conditions. Totally 2,027 phosphorylated protein groups with no decoy, 5,474 unique phosphopeptides and 5,711 unique phosphosites were identified by a LTQ-Orbitrap LC-MS/MS system. Pathway analysis showed that MAPK signaling pathway, Focal adhesion pathway, p53 signaling pathway and MicroRNA pathways were dramatically changed in HCC1937, MDA-MB-231 and MDA-MB-468 cells, suggesting that these pathways may contribute to the stem cell properties and drug resistance of these cells. To further find out why HCC1187 behaved differently from the three other cell lines, we analyzed the phosphoprotein changes between the two groups in both culturing conditions. Interestingly, in the suspension condition, 17 phosphoproteins down-regulated in the three cell lines were found to be up-regulated in HCC1187 and one phosphoprotein up-regulated in the three cell lines was found to be down-regulated in HCC1187. More detailed studies of these functional changes to the phosphoproteome may further elucidate the roles of cancer stem cells and circulating tumor cells in drug resistance and relapse in TNBC. Citation Format: Xinyu Deng, Joe Capri, Huan Ming Hsu, Morris Kohanfars, William Luo, Puneet Souda, Julian P Whitelegge, Helena R Chang. Proteomics studies reveal important pathway and phosphoprotein changes contributing to cancer stem cell properties and drug resistance of triple negative breast cancer cells cultured in attached and suspension conditions [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-05-06.