Chalcones bearing a 3,4,5-trimethoxyphenyl motif are capable of selectively inhibiting oncogenic K-Ras signaling.

Ras proteins are small GTPases which regulate cellular proliferation, differentiation, and apoptosis. Constitutively active mutant Ras are expressed in ~15-20% human cancers, and K-Ras mutations account for ~85% of all Ras mutations. Despite the significance of Ras proteins in refractory cancers, there is no anti-Ras drug available in clinic. Since K-Ras must interact with the plasma membrane (PM) for biological activity, inhibition of the K-Ras/PM interaction is a tractable approach to block oncogenic K-Ras activity. Here, we discovered chalcones 1 and 8 exhibit anti-K-Ras activity, and show that the compounds mislocalize K-Ras from the PM and block oncogenic K-Ras signal output. Also, 1 inhibits the growth of K-Ras-driven human cancer cells. Our data suggest that 1 could be a promising starting point for developing anti-K-Ras cancer drug.

Sphingomyelin Metabolism Is a Regulator of K-Ras Function.

K-Ras must localize to the plasma membrane (PM) for biological activity. We show here that multiple acid sphingomyelinase (ASM) inhibitors, including tricyclic antidepressants, mislocalized phosphatidylserine (PtdSer) and K-RasG12V from the PM, resulting in abrogation of K-RasG12V signaling and potent, selective growth inhibition of mutant K-Ras-transformed cancer cells. Concordantly, in nude mice, the ASM inhibitor fendiline decreased the rate of growth of oncogenic K-Ras-expressing MiaPaCa-2 tumors but had no effect on the growth of the wild-type K-Ras-expressing BxPC-3 tumors. ASM inhibitors also inhibited activated LET-60 (a K-Ras ortholog) signaling in Caenorhabditis elegans, as evidenced by suppression of the induced multivulva phenotype. Using RNA interference against C. elegans genes encoding other enzymes in the sphingomyelin (SM) biosynthetic pathway, we identified 14 enzymes whose knockdown strongly or moderately suppressed the LET-60 multivulva phenotype. In mammalian cells, pharmacological agents that target these enzymes all depleted PtdSer from the PM and caused K-RasG12V mislocalization. These effects correlated with changes in SM levels or subcellular distribution. Selected compounds, including sphingosine kinase inhibitors, potently inhibited the proliferation of oncogenic K-Ras-expressing pancreatic cancer cells. In conclusion, these results show that normal SM metabolism is critical for K-Ras function, which may present therapeutic options for the treatment of K-Ras-driven cancers.