A small molecule inhibitor of ARF GTPase protein 1 limits liver and colon cancer cell growth and metastasis.

ARF GTPase protein 1 (GIT1) is a scaffold protein that is overexpressed in hepatocellular carcinoma (HCC) and colorectal cancer (CRC). GIT1 forms a complex with methionine adenosyltransferase 2B (MAT2B) that activates RAS-RAF-MEK-ERK signaling in HCC and CRC to enhance tumorigenicity. Here, we investigated in a proof-of-concept study whether a small molecule that disrupts GIT1-MAT2B interaction can be effective in HCC and CRC treatment. Since the GIT1 crystal structure is unavailable, we developed a molecular model and used computer-based drug discovery approach to screen for small molecules targeting the GIT1 ankyrin repeat domain, the region closest to where MAT2B interacts that is accessible. Of nine compounds tested, compound 3 (C3) selectively interacts with GIT1 and shows an anti-cancer effect in a GIT1-dependent manner. C3 is antiproliferative, induced apoptosis and G2/M cell cycle arrest while inhibiting colony formation and migration in liver and colon cancer cells. C3 lowered interaction between GIT1 and MAT2B, and with downstream effectors cRAF, MEK and ERK, lowering MEK activity and cyclin D1 expression. Unexpectedly, C3 stabilized GIT1 interaction with cyclin B1 while weakening cyclin B1's interaction with components of the anaphase promoting complex, concomitant with sustained cyclin B1 expression and mitosis arrest. In mice, C3 administration was well tolerated and inhibited murine CRC growth and liver metastasis in immune competent mice and human CRC growth in the livers of nude mice. In conclusion, a small molecule inhibitor that disrupts GIT1's normal interactome is a promising new approach to treating liver and colon cancers.