Abstract 2114: Glycosyltransferase ST6Gal-I protects against chemotherapy induced DNA damage and subsequent apoptosis in pancreatic adenocarcinoma cells

ST6Gal-I is a sialyltransferase that adds α2-6 linked sialic acids to cell surface proteins as they pass through the trans-Golgi. Sialic acids, being negatively charged, are able to alter the function of selected cell surface receptors, which leads to dysregulation of various downstream cellular pathways. Overexpression of ST6Gal-I has been observed in various cancers including ovarian and pancreatic cancer. We have previously shown that knockdown of ST6Gal-I expression increases ovarian cancer cell susceptibility to the chemotherapeutic drug cisplatin. In the present study we further investigate whether resistance to additional drugs such as gemcitabine, the front line treatment for pancreatic cancer, is affected by ST6Gal-I activity. MiaPaCa-2 and BxPC3 pancreatic cancer cell lines, having high ST6Gal-I expression, were employed for our studies. To elucidate the mechanistic role of ST6Gal-I in gemcitabine resistance we created stable ST6Gal-I knockdown lines of MiaPaCa-2 and BxPC3 cells. Gemcitabine induced cell death was more pronounced in the knockdown cell lines, indicated by heightened activation of caspase-3. Gemcitabine is metabolized to a nucleoside analogue, gemcitabine triphosphate, which induces apoptosis by promoting DNA damage. Increased single stand DNA damage in the knockdown cells was confirmed using alkaline comet assay. Gemcitabine treatment led to greater activation of DNA damage markers and response elements (γH2AX, phospho CHK1, phospho CHK2), along with increased levels of cleaved caspase-3 in the knockdown cells as compared to empty vector control cells. We next developed a stable gemcitabine resistant MiaPaCa-2 cell line by growing parental cells in gemcitabine. We selected for the population of cells that survived and were able to replicate in gemcitabine containing media. ST6Gal-I levels were found to be increased in the stable gemcitabine resistant lines relative to parental cell lines, suggesting that cells with high ST6Gal-I expression selectively survive gemcitabine treatment. By measuring the levels of genes involved in activation over those responsible for inactivation of gemcitabine, we were able to obtain a gemcitabine sensitivity predictive ratio for MiaPaCa-2 and BxPC3 ST6Gal-I knockdown, empty vector, parental and stable gemcitabine resistant cell lines. This ratio has been described previously in literature as a metric for gauging gemcitabine resistance. According to the ratios obtained, ST6Gal-I knockdown enhanced drug sensitivity whereas high expression of ST6Gal-I offered protection against gemcitabine induced apoptosis. Collectively these data indicate that upregulation of ST6Gal-I imparts tumor cell survival through prevention of gemcitabine induced DNA damage. Citation Format: Asmi Chakraborty, Matthew Schultz, Hoa Q. Trummell, James A. Bonner, Susan Bellis. Glycosyltransferase ST6Gal-I protects against chemotherapy induced DNA damage and subsequent apoptosis in pancreatic adenocarcinoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2114.