An autophagy-dependent cell death of MDA-MB-231 cells triggered by a novel Rhein derivative 4F.

Triple negative breast cancer (TNBC) has very poor prognosis and no efficacious therapeutic options due to the absence of a validated molecular target. Therefore, novel therapeutic strategies against TNBC are urgently needed. Our team synthesized and screened a series of compounds derived from Rhein, of which 4F was selected for further analysis based on its ability to produce the vacuolated appearance of cells. Using Cell counting kit-8 assay, colony-formation assay, cell apoptosis and cell cycle assay, we compared the antitumor effects of 4F, Rhein and Cisplatin on a TNBC cell line MDA-MB-231 in vitro. The vacuoles in MDA-MB-231 cells were observed and analyzed by hematoxylin-eosin staining and transmission electron microscopy. Autophagy and apoptosis-related proteins including p62, Microtubule Light Chain 3 (LC3), Beclin-1 and Caspase-3 were determined by western blot. The tandem mRFP-GFP-LC3 Lentivirus was used for monitoring the maturation step of autophagosomes. Our data revealed that 4F had lower cytotoxicity to normal breast cell line MCF-10A as compared with positive drug Doxorubicin. Although 4F had better cytotoxicity than Rhein, it had no influence on cells apoptosis in 4F-treated cells. Accumulation of autolysosomes and autophagosomes was observed in 4F-treated MDA-MB-231 cells, accompanied by increased level of Beclin-1 protein. Enhanced autophagic flux was verified by higher ratio of LC3-II/LC3-I, the degradation of p62 protein and alteration in red and green fluorescence puncta. These findings suggested that the process of MDA-MB-231 cell death induced by 4F seemed rely mainly on autophagy rather than apoptosis. 4F may be an alternative drug candidate against TNBC and merits more exploration.