Design, synthesis, bio-evaluation, and mechanism of action of novel allosecurinine derivatives as STAT3-based antitumor agents in vitro and in vivo.

As cancer is the second leading cause of human death, novel antitumor agents need to be developed urgently. Our previous studies revealed that the derivatization of allosecurinine at the C-12 position is viable for discovering STAT3 pathway inhibitors as antitumor agents. In this study, we derivatized the allosecurinine at the C-15 position, screened the antitumor activity, and elucidated the mechanism of action. A Heck reaction was performed to obtain a series of allosecurinine derivatives AH-1∼AH-29. We performed MTT and CCK8 assays to screen the antitumor potency. The structure-activity relationship was also discussed. Scratch assay, flow cytometry, and laser confocal microscopy were performed to study the phenotypic changes. Western blotting (WB) analysis and cell thermal shift assay (CETSA) were performed to determine the mechanism of action of the representative compound AH-26. We also recorded the pharmacokinetic (PK) parameters of AH-26 in rats. Finally, we performed subcutaneous tumor xenografting in nude mice to evaluate the in vivo antitumor activity. The results revealed that most of the C-15 derivatives showed high antitumor activity. The most active compound (AH-26) showed satisfactory activity and selectivity between cancer cells and normal cells. AH-26 induced mitochondria-mediated apoptosis and differentiation of leukemia cells, inhibited the migration of SKOV3 and HGC-27 cells, and blocked the cell cycle at the G1 phase. Further studies on the mechanism revealed that AH-26 can stabilize STAT3 and then inhibit its phosphorylation, which is important for its antitumor activities. Additionally, AH-26 showed antitumor activity and no toxicity. These results revealed that AH-26 is a novel and safe STAT3-based antitumor agent. This study provided the foundation for discovering STAT3 inhibitors and antitumor agents.