CB-5083 and luteolin synergistically induce the apoptosis of bladder cancer cells via multiple mechanisms.

PURPOSE: Bladder cancer (BC) is a common urological malignancy for which effective treatments are lacking. In recent years, valosin-containing protein (VCP) has emerged as a potential target for the treatment of cancers. CB-5083 is a VCP inhibitor that has been evaluated in phase I clinical trials. However, drug resistance and severe side effects hamper the application of CB-5083. Mounting evidence suggests that combined treatment is a useful strategy to improve anticancer efficiency with lower toxicity. The aim of this study was to evaluate the combined effects of CB-5083 and luteolin (Lut), a natural flavonoid, on BC cells.

METHODS

Cellular viability was measured via MTT assays. The cell cycle distribution, degree of cell death and mitochondrial membrane potential were assayed via flow cytometry. mRNA levels were assayed via qRT-PCR. Protein levels were measured via western blotting. RNA interference was applied to knockdown genes. Xenograft experiments were conducted to evaluate the toxicity in vivo.

RESULTS

Cotreatment with CB-5083 and luteolin synergistically reduced the viability of BC cells. In addition, cotreatment with CB-5083 and Lut synergistically induced cell cycle arrest at the G1 phase and apoptosis in BC cells. Mechanistically, CB-5083/Lut cooperatively reduced the expression of Bcl-xl and Mcl-1 in BC cells. Moreover, CB-5083 and Lut synergistically induced endoplasmic reticulum (ER) stress in BC cells. The genetic or pharmacological inhibition of ER stress markedly reduced the degree of apoptosis induced by CB-5083, Lut or their combination in BC cells. In addition, combined treatment with CB-5083 and Lut synergistically repressed the growth of BC cells in vivo.

CONCLUSION

Our data suggest that combined treatment with CB-5083 and Lut might be applied to treat BC.