Pancreatic ductal
adenocarcinoma (PDAC) is an aggressive
malignancy with a poor prognosis.
Gemcitabine, as a single agent or in combination
therapy, remains the frontline
chemotherapy despite its limited efficacy due to de novo or acquired chemoresistance. There is an acute need to decipher mechanisms underlying chemoresistance and identify new targets to improve patient outcomes. Here, we report a novel role for the ST6Gal-I
sialyltransferase in
gemcitabine resistance. Utilizing MiaPaCa-2 and BxPC-3 PDAC cells, we found that knockdown (KD) of ST6Gal-I expression, as well as removal of surface α2-6
sialic acids by
neuraminidase, enhances
gemcitabine-mediated cell death assessed via clonogenic assays and cleaved
caspase 3 expression. Additionally, KD of ST6Gal-I potentiates
gemcitabine-induced DNA damage as measured by comet assays and quantification of γH2AX foci. ST6Gal-I KD also alters
mRNA expression of key
gemcitabine metabolic genes, RRM1, RRM2, hENT1, and DCK, leading to an increased
gemcitabine sensitivity ratio, an
indicator of
gemcitabine toxicity.
Gemcitabine-resistant MiaPaCa-2 cells display higher ST6Gal-I levels than treatment-naïve cells along with a reduced
gemcitabine sensitivity ratio, suggesting that chronic
chemotherapy selects for clonal variants with more abundant ST6Gal-I. Finally, we examined Suit2 PDAC cells and Suit2 derivatives with enhanced metastatic potential. Intriguingly, three metastatic and chemoresistant subclones, S2-CP9, S2-LM7AA, and S2-013, exhibit up-regulated ST6Gal-I relative to parental Suit2 cells. ST6Gal-I KD in S2-013 cells increases
gemcitabine-mediated DNA damage, indicating that suppressing ST6Gal-I activity sensitizes inherently resistant cells to
gemcitabine. Together, these findings place ST6Gal-I as a critical player in imparting
gemcitabine resistance and as a potential target to restore PDAC chemoresponse.