Retinoic acid increases the anticancer effect of paclitaxel by inducing differentiation of cancer stem cells in melanoma

Malignant melanoma is a highly lethal disease, and advanced stages of melanoma have proven to be resistant to many chemotherapeutic drugs including temozolomide and paclitaxel. Cancer stem cells (CSCs) have been identified and isolated in different cancers including melanoma, and have been proven playing important role in the drug resistance. Retinoic acid (RA) is a promising anticancer agent, which can induce differentiation of CSCs. The main purpose of the present study was to evaluate the possible RA-induced differentiation of melanoma CSCs and sensitization of melanoma CSCs to paclitaxel. Our results show that CSCs of human melanoma A375 cells was more tolerant to paclitaxel than other non-CSCs melanoma cells. On the contrary, RA had stronger inhibitory effect on melanoma CSCs than on non-CSCs. At the same time, RA could arrest the cell cycle of CSCs and reduce the expression of Sox-2, Oct-4 in CSCs of melanoma, thereby induced the differentiation of CSCs and increased its sensitivity to paclitaxel. With this study we concluded that RA increases the anticancer effect of paclitaxel by inducing differentiation of cancer stem cells in melanoma, and the combined application of RA and paclitaxel may be more effective in the treatment of melanoma.