Bladder cancer is the 9th most common and 13th most lethal cancer globally, as reported by the Globocan 2022 WHO report. It is classified into non-muscle-invasive bladder cancer (NMIBC) and muscle-invasive bladder cancer (MIBC), with doxorubicin being a standard chemotherapy drug for MIBC. However, its cardiotoxicity limits its use. This study explores the combination of doxorubicin with vorinostat, an HDAC inhibitor, to enhance therapeutic efficacy and mitigate side effects.

Human urothelial bladder cancer cell lines (5637 and BFTC 905) were cultured and treated with doxorubicin and vorinostat. Cell viability was assessed using the MTT assay, and the effects of drug combinations were analyzed using Combination Index (CI) values calculated via Compusyn software. Western blot analysis was utilized to evaluate apoptotic markers and to confirm the mechanisms of cell death induced by the drug combinations. Additionally, in vivo studies were conducted using NOD SCID mice to assess tumor growth inhibition.

The combined treatment of doxorubicin and vorinostat demonstrated synergistic cytotoxicity in both bladder cancer cell lines, with CI values indicating moderate to strong synergistic effects. The combination significantly induced apoptosis, evidenced by the cleavage of PARP, caspases, and γ-H2AX, suggesting DNA damage. In tumor sphere assays, only the combined treatment notably inhibited sphere growth. In vivo, the combination treatment significantly reduced tumor growth compared to single treatments, although some toxicity was observed with doxorubicin.

The synergistic effects of doxorubicin and vorinostat highlight the potential of this combination in bladder cancer therapy, as it may reduce doxorubicin dosage and associated cardiotoxicity. Further clinical validation is necessary to confirm these findings and optimize treatment protocols for bladder cancer patients.