KRAS Mutation And Protein Levels In-gastric Signet Ringcell Carcinoma Cancer Patients And Response To MEK Inhibitor

Objectives:Gastric cancer(GC)is a corrunon malignancy in our country,accounting for more than 50 percent of stomach cancer seach year in the total number of new cancer cases throughout the world.Gastric signet ring cell carcinoma(SRCC)is a special kind of gastric cancer and accounts for 19%.Advanced SRCC has long been thought to have worse prognosis than other forms of GC due to high possibility of peritoneal metastasis.There are few researches and studies about the gene function of gastric signet ring cell carcinoma currently.The RASgene is located in the center of the intracellular signaling pathway and recent studies have suggested that KRAS plays an important role in gastric cancer.The aim of this study is to confirm the clinical and pathological relationship with the expression of KRAS in GC patients,to assess the prognostic effect of KRAS mutation and expression levels in gastric cancer patients and to explore the its potential role in targeted therapy.Method:We examined KRAS protein levels in 132 stage Ⅰ-Ⅳ gastric cancer using immunochemistry(IHC).KRAS mutation was detected by next generation exome sequencing.Mutation levels of Kras were examined in five human gastric cell lines(AGS,SNU601,SNU668,KATO-Ⅲ and NUGC-4)by Sanger sequencing.Cytosensitivity of MEK inhibitors(AZD6244)and mTOR inhibitors(AZD2014)in the five cell lines was examined by MTT.Results:① The median age of the total number of 132 gastric cancer patients was 58 years(range:30-82).There were 75 gastric cancer samples with the pathology of signet-ring cell carcinoma(SRCC),while another 57 samples with adenocarcinoma.80%of gastric SRCC samples have high expression of KRAS protein compared with 38.6%of gastric adenocarcinomas(P<0.001).②Among 75 gastric SRCC cancer patients,KRAS mutations in codon 12 and 151 were detected in 8(10.67%)patients,including 7 mutations of G12V and one mutation of G151A.The median overall survival(OS)was 12.5 months(95%CI=9.57 to 15.43 months)for patients with KRAS mutation,and 15.8months(95%CI=11.76 to 19.84 months)for patients without KRA5 mutation(P=0.031).③Kras G12D mutation was detected in GC cell line AGS and SRCC a cell line SNU601.Kras Q61K mutation was detected in SRCC cell line SNU668.NUGC-4 and KATO-Ⅲ are KRAS wide type.The IC50 values of AZD6244 for SNU601,SNU668,AGS,NUGC-4 and KATO-Ⅲ were 663.5nM,538.7nM,3345 nM,15270 nM and 20726 nM,which showed SNU601 and SNU668 were hypersensitive to the MEK inhibitorConclusion:①The expression of KRAS protein is related with pathologic types of GC.KRAS is highly expressed in SRCC.②SRCC patients with KRAS mutation have shorter OS compared to SRCC patients without KRAS mutation.③Gastric SRCC cell lines with KRAS mutation is sensitive to MEK inhibitor(AZD6244).The results provide insights into the important role of mutant KRAS in the prognosis and response to MEK inhibitor of gastric SRCC patients.Gastric SRCC with such oncogenic KRAS mutations might be suitable for targeted therapy with MEK inhibitors.