RNA G‑Quadruplexes in Kirsten Ras (<i>KRAS</i>) Oncogene as Targets for Small Molecules Inhibiting Translation

The human KRAS transcript contains a G-rich 5′-UTR sequence (77% GC) harboring several G4 motifs capable to form stable RNA G-quadruplex (RG4) structures that can serve as targets for small molecules. A biotin–streptavidin pull-down assay showed that 4,11-bis­(2-aminoethylamino)­anthra­[2,3-b]­furan-5,10-dione (2a) binds to RG4s in the KRAS transcript under low-abundance cellular conditions. Dual-luciferase assays demonstrated that 2a and its analogue 4,11-bis­(2-aminoethylamino)­anthra­[2,3-b]­thiophene-5,10-dione (2b) repress translation in a dose-dependent manner. The effect of the G4-ligands on Panc-1 cancer cells has also been examined. Both 2a and 2b efficiently penetrate the cells, suppressing protein p21KRAS to <10% of the control. The KRAS down-regulation induces apoptosis together with a dramatic reduction of cell growth and colony formation. In summary, we report a strategy to suppress the KRAS oncogene in pancreatic cancer cells by means of small molecules binding to RG4s in the 5′-UTR of mRNA.