Trichostatin A, a histone deacetylase inhibitor, induces synergistic cytotoxicity with chemotherapy via suppression of Raf/MEK/ERK pathway in urothelial carcinoma

In this study, we aimed to investigate the antitumor effects of trichostatin A (TSA), an antifungal antibiotic that inhibits histone deacetylase (HDAC) family of enzymes, alone or in combination with anyone of the three chemotherapeutic agents (cisplatin, gemcitabine, and doxorubicin) for the treatment of human urothelial carcinoma (UC). Two high-grade human UC cell lines (T24 and NTUB1) were used. Cytotoxicity and apoptosis were assessed by MTT assay and flow cytometry, respectively. The expression of phospho-c-Raf, phospho-MEK1/2, and phospho-ERK1/2 was measured by western blotting. ERK siRNA knockdown and the specific MEK inhibitor U0126 were used to examine the role of Raf/MEK/ERK signaling pathway in combined cytotoxicity of TSA and chemotherapy. TSA co-treatment with any one of the three chemotherapeutic agents induced synergistic cytotoxicity (combination index < 1) and concomitantly suppressed chemotherapeutic drug-induced activation of Raf-MEK-ERK pathway. Combination of ERK siRNA knockdown and treatment with the specific MEK inhibitor (U0126) enhanced the cytotoxic effects of the chemotherapy on UC cells. These observations were confirmed in a xenograft nude mouse model. Moreover, activated Raf/MEK/ERK pathway was observed in human bladder UC specimens from patients with chemoresistant status. In conclusion, TSA elicits a synergistic cytotoxic response in combination with chemotherapy via targeting the Raf/MEK/ERK pathway. TSA elicits synergistic cytotoxic response in combination with three DNA-damaging drugs (cisplatin, gemcitabine, and doxorubicin). Activated Raf/MEK/ERK pathway is involved in chemoresistant mechanism of UC. Combining chemotherapeutic agents with HDAC inhibitor (TSA) or with targeting Raf/MEK/ERK pathway is promising to circumvent chemoresistance in UCs.