Sulfasalazine attenuates evading anticancer response of CD133-positive hepatocellular carcinoma cells.

CD133-positive cells in hepatocellular carcinoma (HCC) exhibit cancer stem cell (CSC)-like properties as well as resistance to chemotherapeutic agents and ionizing radiation; however, their function remains unknown. In this paper, we identified a hitherto unknown mechanism to overcome CD133-induced resistance to anticancer therapy. We applied an alternative approach to enrich the CD133-positive HCC population by manipulating 3D culture conditions. Defense mechanisms against reactive oxygen species (ROS) in CSC spheroids were evaluated by fluorescence image-based phenotypic screening system. Further, we studied the effect of sulfasalazine on ROS defense system and synergistic therapeutic efficacy of anticancer therapies both in culture and in vivo HCC xenograft mouse model. Here, we found that oxidative stress increase CD133 expression in HCC and increased CD133 expression enhanced the capacity of the defense system against ROS, and thereby play a central role in resistance to liver cancer therapy. Moreover, ablation of CD133 attenuated not only the capacity for defense against ROS, but also chemoresistance, in HCC through decreasing glutathione (GSH) levels in vitro. Sulfasalazine, a potent xCT inhibitor that plays an important role in maintaining GSH levels, impaired the ROS defense system and increased the therapeutic efficacy of anticancer therapies in CD133-positive HCC but not CD133-negative HCC in vivo and in vitro. These results strongly indicate functional roles for CD133 in ROS defense and in evading anticancer therapies in HCC, and suggest that sulfasalazine, administered in combination with conventional chemotherapy, might be an effective strategy against CD133-positive HCC cells.