Design, Synthesis, and Evaluation of Novel <i>p</i>‑(Methylthio)styryl Substituted Quindoline Derivatives as Neuroblastoma RAS (NRAS) Repressors via Specific Stabilizing the RNA G‑Quadruplex

The human proto-oncogene neuroblastoma RAS (NRAS) contains a guanine-rich sequence in the 5′-untranslated regions (5′-UTR) of the mRNA that could form an RNA G-quadruplex structure. This structure acts as a repressor for NRAS translation and could be a potential target for anticancer drugs. Our previous studies found an effective scaffold, the quindoline scaffold, for binding and stabilizing the DNA G-quadruplex structures. Here, on the basis of the previous studies and reported RNA-specific probes, a series of novel p-(methylthio)­styryl substituted quindoline (MSQ) derivatives were designed, synthesized, and evaluated as NRAS RNA G-quadruplex ligands. Panels of experiments turned out that the introduction of p-(methylthio)­styryl side chain could enhance the specific binding to the NRAS RNA G-quadruplex. One of the hits, 4a-10, showed strong stabilizing activity on the G-quadruplex and subsequently repressed NRAS’s translation and inhibited tumor cells proliferation. Our finding provided a novel strategy to discover novel NRAS repressors by specifically binding to the RNA G-quadruplex in the 5′-UTR of mRNA.