Ellagic acid resensitizes gemcitabine-resistant bladder cancer cells by inhibiting epithelial-mesenchymal transition and gemcitabine transporters

Abstract

Gemcitabine (GCB) resistance is a major issue in bladder cancer chemoresistance, but its underlying mechanism has not been determined. Epithelial-mesenchymal transition (EMT) has been shown to be comprehensively involved in GCB resistance in several other cancer types, but the direct connection between EMT and GCB remains unclear. This study was designed to elucidate the mechanism of EMT-related GCB resistance in bladder cancer and identify a potential phytochemical to modulate drug sensitivity. The biological effects of ellagic acid (EA) or its combined effects with GCB were compared in GCB-resistant cells and the GCB-sensitive line in terms of cell viability, apoptosis, motility, and in vivo tumorigenicity. The molecular regulation of EMT-related GCB resistance was evaluated at both the mRNA and protein expression levels. Our results indicated that TGF-β/Smad induced the overactivation of EMT in GCB-resistant cells and reduced the expression of GCB influx transporters (hCNT1 and hENT1). Moreover, ellagic acid (EA) inhibited the TGF-β signaling pathway both in vitro and in vivo by reducing Smad2, Smad3, and Smad4 expression and thereby resensitized GCB sensitivity. In conclusion, our results demonstrate that TGF-β/Smad-induced EMT contributes to GCB resistance in bladder cancer by reducing GCB influx and also elucidate the novel mechanisms of EA-mediated inhibition of TGF-β/Smad-induced EMT to overcome GCB resistance. Our study warrants further investigation of EA as an effective therapeutic adjuvant agent for overcoming GCB resistance in bladder cancer.