Abstract
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.