A New Small Molecule Suppresses KRAS-mutant Cancers

The RAS proteins are GTP binding proteins that function as molecular switches for regulating cell differentiation,proliferation and survival.There are three main members of the RAS family:HRAS,NRAS and KRAS,all of which have been found to drive cancer formation and progression.Mutations in RAS are found in approximately a third of human cancers.KRAS is the most frequently mutated RAS isoform,having been shown to be mutated in 90%of pancreatic adenocarcinomas,45%of colorectal cancers,and 35%of lung adenocarcinomaas.KRAS-mutant cancers are among the most aggressive and malignant cancer type.The patient with mutant KRAS showns poor prognosis.To date,no effective stratery targeting mutated KRAS has been introduced into clinical practice.Hence,KRAS is an attractive therapeutic target for the treatment of cancers.Recent studies have shown that mutant KRAS promotes the metabolic shifting in cancer cells.In another word,the KRAS-mutant tumor cells much rely on metabolic reprogramming changes.Hence,it is probabaly a new therapeutic approach for the treatment of KRAS-muant tumors by targeting metabolic reprogramming.To test this hypothesis,we examined metabolism reprogramming in KRAS isogenic cells using metabonomics analysis.Comparing to those KRAS wild-type counterparts,the levels of metabolites in the glutathione(GSH)metabolism pathway are significantly higher in KRAS-mutant cells.Previous studies have shown that cysteine which comes from cystine is a crucial time-limiting amino acid during intracellular GSH synthesis.Therefore,we assumed that the KRAS-mutant cells bear high intracellular glutathione mainly due to eleveated absorbability rate of cystine.Next,we tested the uptake of cystine in KRAS isogenic cell lines,and our results showed that the uptake of cystine was remarkably increased in KRAS-mutant cells.The uptake of cysteine in cells is mainly mediated by System xc-,a counter-transport of glutamate and cysteine,and SLC7A11 is the specific and functional light chain subunit of System xc-.We further test the expression of SLC7A11 in KRAS isogenic cells,and the result showed that the expression of SLC7A11 was notably increased in the KRAS-mutant cells.These results probably indicate that the growth of KRAS-mutant cells may dependent on SLC7A11 expression.We further showed that knockdown of SLC7A11 with siRNA selectively killed KRAS-mutant cancer cells.Sulfasalazine(SAS),an specific inhibitor of System xc-,potently inhibited the growth of KRAS mutant cancer cells in vitro and in vivo.All of these results suggest that System xc-is required for the survival of KRAS-mutant cells.The System xc-may be a new therapeutic targets for KRAS-muant tumors.To develop more potent System xc-inhibitor,we screened a chmical libraly and optimize the lead hit,we finally identified a small molecule,named HG106,as a selective System xc-inhibitor.As expected,HG106 selectively and significantly killed the KRAS-mutant cancer cells through increasing oxidant stress and ER stress,and reducing the membrane potential of mitochondria.On the basis of System xc-inhibition,HG106 supressed the tumor growth in the patient-derived xenograft mouse model and the Lox-STOP-Lox-KrasG12D mouse model.In summary,our study shows that glutathione metabolism is reprogrammed in KRAS-mutant cells,and SLC7A11 is a novel synthetic lethal gene of mutant KRAS.HG106,a potent System xc-inhibitor,selectively inhibited the growth of KRAS-mutant cancer cells in vitro and in vivo.These findings may provide therapeutic opportunities for KRAS-mutant tumors.