Ellagic Acid Resensitizes Gemcitabine-Resistant Bladder Cancer Cells by Inhibiting Epithelial-Mesenchymal Transition and Gemcitabine Transporters.

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-ß/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-ß 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-ß/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-ß/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.

Decreased drug resistance of bladder cancer using phytochemicals treatment.

The aim of the study is to investigate the ability of phytochemicals to overcome the multiple drug resistance (MDR) of bladder cancer. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to evaluate the cytotoxic sensitivity of T24-GCB cells, a GCB resistant cell line, to different phytochemicals, including capsaicin, quercetin, curcumin, and resveratrol, and their combination with gemcitabine. Western blot analysis was used to detect the expression of membranous ABCC2 and metabolic proteins, DCK, TK1, and TK2 in tumor cells. Animal models were used to confirm the treatment efficacy of phytochemicals in combination with gemcitabine to bladder cancer. The observed/expected ratio of cytotoxicity analysis revealed that capsaicin has synergistic effect with gemcitabine to T24-GCB cells in a dose-dependent pattern. Quercetin, curcumin, and resveratrol have additive effect with gemcitabine to T24-GCB cells. Capsaicin and quercetin alone and combination with gemcitabine decreased the expression of ABCC2 and DCK and TKs, in T24-GCB cells. On the contrary, resveratrol and curcumin alone and combination with gemcitabine increased the expression of ABCC2 but decreased cytoplasmic kinases simultaneously. In xenografted subcutaneous tumor model on nude mice, combination treatment of capsaicin and gemcitabine demonstrated the highest tumor suppression effect when compared to capsaicin or gemcitabine treatment alone. The MDR of bladder cancer is closely related to membranous ABCC2, cytoplasmic DCK, and TKs expression. Capsaicin owns the strongest synergistic cytotoxic effect of gemcitabine to T24-GCB cells. This combination regimen may provide as an adjunctive treatment for overcoming MDR in bladder cancer.

The modulation study of multiple drug resistance in bladder cancer by curcumin and resveratrol.

Gemcitabine (GCB), which functions via the inhibition of DNA synthesis, is commonly used in the treatment of bladder cancer; however, its response rate is not satisfactory due to the development of drug resistance. The potential for phytochemicals to reverse drug resistance in bladder cancer tumor cells was evaluated. A human bladder cancer cell line, T24, was cultured, and GCB-resistant cells (T24-GCB) were also established. The acquired resistance of T24-GCB to GCB was measured using an MTT assay. The gene expression of ATP-binding cassette (ABC) transporter protein family members was analyzed using reverse transcription-quantitative PCR analysis, and western blotting was performed to verify ABC family protein, cytoplasmic thymidine kinase (TK) and poly (ADP-ribose) polymerase (PARP) expression on whole cell lysates. Subsequently, resveratrol and curcumin were used to evaluate their modulation potential in decreasing the drug resistance of T24-GCB cells to GCB using MTT and migration assays. T24-GCB cells have increased drug resistance ability, with an 18.75-fold higher ID50 value compared with native T24 cells (105 vs. 5.6 nM). T24-GCB cells also exhibit increased cross resistance to mitomycin C and paclitaxel. The mRNA expression of ABCC2 in T24-GCB cells increased compared with that in native T24 cells. Via western blot analysis, it was determined that the expression of ABCC2 protein was also increased in T24-GCB cells. Conversely, the expression of ABCB1, ABCG2, deoxycytidine kinase (DCK), TK1 and TK2 decreased. Following curcumin and resveratrol treatment alone or combined with GCB, additive cytotoxic enhancement was observed, and the migratory abilities of T24-GCB cells were significantly decreased. Western blot analysis revealed that ABCC2 protein expression increased, and DCK, TK1 and TK2 expression decreased following co-treatment of T24-GCB cells with GCB + curcumin or resveratrol compared with GCB alone. Of note, there was a marked increase in cleaved-PARP expression in T24-GCB cells treated with a combination of GCB + curcumin or resveratrol. Both curcumin and resveratrol could reverse the drug resistance of T24-GCB cells in an additive pattern though PARP enhancement without changes in ABCC2 and DCK, TK1 and TK2 expression.