A small-sized imidazole-derived ligand binds to the KRAS promoter G-quadruplex and inhibits cancer growth with enhanced immunomodulation.

KRAS overactivation is commonly present in a diversity of solid tumors. Recently, small-molecule inhibitors of the KRAS G12C mutation have been approved for clinical use, marking the end of the long era of KRAS as an "undruggable" target. However, new approaches to suppress a wide spectrum of KRAS abnormalities are still needed to be developed. G-quadruplex (G4) is located in the nuclease hypersensitive element (NHE) region of the promoter and controls KRAS expression. To date, only a few KRAS G4 ligands with coplanar aromatic scaffolds have been discovered. These compounds fall outside the "drug-like" chemical space and lack satisfactory selectivity between KRAS G4 and other DNAs. In this study, a series of drug-like, indolium-based analogs binding toward KRAS G4 were engineered, and BN1, derived from imidazole, was selected as the most potent ligand. BN1 effectively suppressed KRAS expression, thereby downregulating the MEK-ERK pathway and PD-L1 expression in tumor cells. In vivo experiments demonstrated that BN1 effectively reduced tumor burden while exhibiting immunostimulatory effects, including the increase of CD8 IFNγ cells, the decrease of CD4 Foxp3 cells, and the regulation of cytokines. Collectively, it is the first time, to our knowledge, to report a KRAS G4-directed small-molecule ligand with antitumor efficacy related to enhanced immunomodulation.