Members of the RAS family of GTPases (which comprises KRAS, NRAS, and HRAS) are major oncogenes. Especially, mutations in the RAS genes are major oncogenes with a high occurrence rate in human cancers. RAS-RAF-MEK-ERK and RAS-PI3K-PDK1-AKT pathways are essential to cell survival and proliferation. SOS1 is also the guanine nucleotide exchange factor (GEF) and activator of RAS. In particular, SOS1 inhibitors effectively down-regulate active RAS in tumor cells. Complete inhibition of the RAS-RAF-MEK-ERK pathway in cells with wild-type KRAS. In a mutant KRAS cell line, SOS1 inhibition results in a reduction of phospho-ERK activity by 50%. In this study, Roman C. Hillig, et al describe the identification of potent and cell-active inhibitor BAY-293.

BAY-293 efficiently disrupts the interaction between KRAS and its exchange factor SOS1. Remarkably, BAY-293 selectively inhibits the KRAS–SOS1 interaction with an IC50 of 21 nM. Moreover, BAY-293 inhibits the activation of RAS in HeLa cells, with IC50 values in the submicromolar range. Besides, BAY-293 shows efficient antiproliferative activity against wild-type KRAS cell lines (K-562, MOLM-13) and cell lines with KRASG12C mutation (NCI-H358, Calu-1) with IC50s of 1,090 nM, 995 nM, 3,480 nM, and 3,190 nM, respectively. Furthermore, BAY-293 efficiently inhibits pERK levels in K-562 cells after incubation for 60 min without affecting total protein levels of ERK. SOS1 inhibition has synergistic antiproliferative potential when combined with direct covalent KRASG12C inhibitors.

Researchers therefore present BAY-293 as a tool for the further investigation of RAS–SOS1 biology in vitro. Taken together, inhibition of GEFs may represent a viable approach for targeting RAS-driven tumors.

Hillig RC, et al. Discovery of potent SOS1 inhibitors that block RAS activation via disruption of the RAS-SOS1 interaction. Proc Natl Acad Sci U S A. 2019 Feb 12;116(7):2551-2560.