Variant isoforms of CD44 involves acquisition of chemoresistance to cisplatin and has potential as a novel indicator for identifying a cisplatin-resistant population in urothelial cancer

BACKGROUND: Cisplatin is the most commonly used chemotherapeutic agent in the treatment of patients with metastatic and/or recurrent urothelial cancer. However, the effectiveness of these treatments is severely limited due to the development of cisplatin resistance. Cancer stem cells have been documented as one of the key hypotheses involved in chemoresistance. CD44v8–10 has been identified as one of the new cancer stem cells markers and was recently shown to enhance the antioxidant system by interaction with xCT, a subunit of the cystine transporter modulating intracellular glutathione synthesis. The aim of the present study was to investigate the clinical role of CD44v8–10 and the molecular mechanism underlying the acquisition of cisplatin resistance through CD44v8–10 in urothelial cancer. METHODS: We analyzed the clinical significance of the immunohistochemical CD44v9 expression, which detects the immunogen of human CD44v8–10, in 77 urothelial cancer patients treated with cisplatin-based systemic chemotherapy for recurrence and/or metastasis. We then evaluated the biological role of CD44v8–10 in the acquisition of cisplatin resistance using the urothelial cancer cell lines, T24 and T24PR, which were generated to acquire resistance to cisplatin. RESULTS: The 5-year cancer-specific survival rate was significantly lower in the CD44v9-positive group than in the CD44v9-negative group (P = 0.008). Multivariate analyses revealed that CD44v9 positivity was an independent risk factor of cancer-specific survival (P = 0.024, hazard ratio = 5.16) in urothelial cancer patients who had recurrence and/or metastasis and received cisplatin-based chemotherapy. The expression of CD44v8–10 and xCT was stronger in T24PR cells than in T24 cells. The amount of intracellular glutathione was significantly higher in T24PR cells than in T24 cells (p < 0.001), and intracellular reactive oxygen species production by cisplatin was lower in T24PR cells than in T24 cells. Furthermore, the knockdown of CD44v8–10 by siRNA led to the recovery of cisplatin sensitivity in T24PR cells. CONCLUSIONS: CD44v9 in tumor specimens has potential as a novel indicator for identifying a cisplatin-chemoresistant population among urothelial cancer patients. CD44v8–10 contributes to reactive oxygen species defenses, which are involved in chemoresistance, by promoting the function of xCT, which adjusts the synthesis of glutathione.