The Discovery And Mechanism Study Of NRAS Plasma Membrane Translocation Inhibitor

The RAS family includes three RAS genes,which encode four highly homologous proteins: H-,N-,and KRAS4 A and 4B,differing mainly at the carboxyl terminus.RAS oncogenic mutations,mostly KRAS and NRAS,are common in human cancers.Since the enzymatic activity of RAS is used to turn itself off and its GTP binding affinity is very high,RAS proteins have been difficult to target.Identification of alternative means to block the RAS oncogenic signaling is critical for developing therapies against RAS-driven cancer.We took a chemical biology approach to discover novel therapeutic strategies for RAS-related cancer.Since the biological activity of RAS proteins relies upon lipid modifications and RAS regulates lipid metabolisms in cancer cells,we used a RAS specific cell viability assay to screen a bioactive lipid library for potential therapeutics against RAS-related cancer.We found that endocannabinoid/endovanilloid Narachidonoyl dopamine(NADA)could effectively kill RAS-transformed cells.The structure-activity analysis showed that its anti-RAS activity requires both the dopamine and arachidonoyl moieties in the same molecule,but in a manner independent of its ability to engage cannabinoid or vanilloid receptors.Further analysis showed that NADA was more active in killing cells transformed by palmitoylated oncogenic NRAS or KRAS4 A than that of KRAS4 B that is non-palmitoylated.Consistently,NADA was more active in inhibiting the phosphorylation of ERK in NRAS-transformed cells than that in KRAS4 Btransformed cells.Interestingly,NADA blocked the plasma membrane translocation of NRAS and KRAS4 A,but not that of KRAS4 B.Significant effect of NADA on palmitoylated NRAS levels was not detected,suggesting that NADA inhibits NRAS plasma membrane translocation through a novel mechanism.These results demonstrate that NADA engages a novel mechanism of inhibiting the plasma membrane translocation and neoplastic transforming activity of NRAS.We also screened a structurally novel kinease inhibitor library and identified compound 999# possessing anti-proliferation ability.Since RAS mutations play critical roles in hematological malignancies as well as in solid tumors,the new findings would help to develop novel therapies for a broad range of human cancers.