Gambogic Acid Improves Cisplatin Resistance of Bladder Cancer Cells through the Epithelial-Mesenchymal Transition Pathway Mediated by the miR-205-5p/ZEB1 Axis

Objective:<bold> </bold>Bladder cancer (BC) is primarily treated with cisplatin-based chemotherapy, but the development of cisplatin resistance often leads to BC recurrence. This study is focused on assessing the potential of gambogic acid (GA) in mitigating BC cells' cisplatin resistance, along with an analysis of the underlying mechanism involved. Methods:<bold> </bold>Cisplatin was administered to human bladder transitional cell carcinoma cells (T24) at various concentration gradients to induce cisplatin-resistant (T24-DDP) cells. Several experimental groups were set: T24 group, T24-DDP group, T24-DDP+DDP group, T24-DDP+GA group, T24-DDP+DDP+GA group, T24-DDP+DDP+GA+miR-NC group, and T24-DDP+DDP+GA+miR-205-5p inhibitor group. The cell counting kit-8 (CCK-8) assay, Transwell migration assay, and scratch assay were respectively carried out for assessment of cell proliferation, invasion, and migration. Western blot analysis was conducted for detection of the protein expression of E-cadherin, ZEB1, Vimentin, N-cadherin, LRP, MRP, and P-gp in the cells, while the relative expression level of miR-205-5p was determined by qRT-PCR. Results:<bold> </bold>In comparison with the T24-DDP group, cells in the T24-DDP+GA group showed enhanced sensitivity to cisplatin. Furthermore, as indicated by CCK-8 assay, GA improved T24-DDP cells' sensitivity to cisplatin, potentiated the effects of cisplatin, and exerted an inhibitory effect on the invasion, proliferation, as well as migration of T24-DDP cells. Through Western blot analysis, GA was revealed to significantly inhibit the expression of N-cadherin, E-cadherin, and Vimentin, as well as that of cisplatin-resistant proteins MRP, P-gp, and LRP in BC cells. In addition, shown by further experiments, GA promoted miR-205-5p expression and simultaneously inhibited ZEB1 expression within the cells. Conclusion:<bold> </bold>GA alleviates BC cells' cisplatin resistance through the epithelial-mesenchymal transition pathway mediated by the miR-205-5p/ZEB1 axis.