Antitumor Effects of Tryptanthrin on Colorectal Cancer by Regulating the Mitogen-Activated Protein Kinase Signaling Pathway and Targeting Topo I and IDO1

Tryptanthrin (TRYP) is an indole quinazoline alkaloid with a range of pharmaceutical activities, but the specific mechanism of TRYP against colorectal cancer (CRC) remains obscure. The purpose of this study was to evaluate the antitumor effects of TRYP on CRC models both <i>in vitro</i> and <i>in vivo</i> and further analyze its concrete mechanisms. The results of the <i>in vitro</i> experiment show that TRYP effectively inhibited the proliferation and migration of SW620 cells, arrested the cell cycle at the S phase, and induced cell apoptosis. Deeply, TRYP dramatically increased the expression of Bax and cleaved caspase 3 while decreasing the expression of Bcl-2. The results of transcriptome sequencing implied that the inhibitory effects of TRYP were closely related to the mitogen-activated protein kinase (MAPK) signaling pathway, and the results of western blotting verified that TRYP could decrease the expression of p-Erk and increase the expression of p-p38 and p-Jnk. Besides, our results identified that topoisomerase I (Topo I) and indole amine 2,3-dioxygenase 1 (IDO1) were the targets of TRYP. <i>In vivo</i>, the results showed that different TRYP doses significantly inhibited tumor growth in mice, induced different degrees of necrosis in tumor tissues, decreased the expression level of Ki67 protein, and increased the apoptotic signal in tumor tissues. The findings demonstrated the inhibitory effects of TRYP on CRC, and the mechanisms were tightly connected to inhibiting the activity of Topo I and IDO1 and regulating the expression of the MAPK signaling pathway. Especially, it was first identified that TRYP could directly inhibit Topo I to arrest SW620 at the S phase. Therefore, this work established a scientific basis for the development of TRYP.