ABSTRACT
Aim To investigate the anti-tumor effect of celastrol(CEL)on colorectal cancer and the possible targets/mechanisms. Methods The cytotoxic activities of CEL were evaluated against A549, HCT-116, HepG2 by CCK-8 method. Western blotting was used to detect the expression level of STAT3 and its upstream and downstream proteins(JAK2, Survivin, MCL-1)in HCT-116 cells before and after CEL treatment Flow cytometry was applied to assess CEL's apoptosis and cell-cycle arrest effect in HCT-116 cells. SPR detection and molecular docking analysis were performed to further assess the binding ability between CEL and STAT3 protein. Lastly, human colorectal cancer organoid culture was constructed to verify the anti-tumor effect of CEL. Results CEL showed significant cytotoxicity to A549(IC50 = 2.37±0.02 μmol·L-1), HCT-116(IC50 = 1.40±0.21 μmol·L-1)and HepG2(IC50 = 2.52±0.02 μmol·L-1). Additionally, CEL could effectively decrease the level of p-STAT3 and the downstream gene expression of STAT3(Survivin and MCL-1)in a concentration-dependent manner; however, CEL did not affect the total level of STAT3 and upstream kinases JAK2. Moreover, CEL could induce apoptosis of HCT-116 cells concentration-dependently and arrest the cell cycle. According to the SPR analysis, CEL showed a strong binding affinity with the KD value(the equilibrium dissociation constant)of 60.38 μmol·L-1. Molecular docking analysis also suggested that CEL bound to the SH2 domain of STAT3. Lastly, CEL showed much better activity than the positive drug oxaliplatin(L-OHP)on all the colorectal cancer organoids. Conclusions CEL shows a significant anti-colorectal cancer effect, potentially caused by a direct target inhibiting STAT3, inducing apoptosis, and blocking the cell cycle.