Association of isocitrate dehydorgenase-1 (IDH-1) mutations with elevated oncometabolite 2-hydroxyglutarate (2HG) in advanced colorectal cancer.

627 Background: IDH-1 mutations are common in AML, gliomas, and intrahepatic cholangiocarcinoma. The enzyme product of the IDH-1 R132 variant preferentially catalyzes the NADPH-dependent reduction of alpha-ketoglutarate to the oncometabolite R-2-Hydroxyglutarate (R-2HG), resulting in accumulation of R-2HG, relative to its enantiomer, S-2HG. Elevated plasma levels of 2HG and/or higher ratios of R/S have been observed in AML and intrahepatic cholangiocarinoma, but not in gliomas. Only a few cases of IDH-1/2 mutations have been reported in advanced colorectal cancers (CRC). We investigated plasma levels of 2HG and relative ratios of R/S in CRC patients harboring IDH-1/2mutations. Methods: Between 2012 and 2015, 428 patients with advanced CRC were molecularly profiled through the COMPACT and IMPACT programs at the Princess Margaret Cancer Centre. Tumor DNAs were isolated from FFPE archived samples and genotyped using a customized Sequenom panel or Illumina MiSeq TruSeq Amplicon Cancer Panel in a CLIA-certified laboratory. Plasma samples from patients harboring IDH-1/2mutations and 4 gender/age matched control patients were analyzed for 2HG, R-2HG and S-2HG using HPLC tandem mass spectrometry coupled with a CHIROBIOTIC R column. Results: Of 428 patients with advanced CRC, 4 (0.9%) patients were identified to harbor IDH-1 mutation. No IDH-2 mutations were detected. The variants identified were R132C (2 patients), R132S, and R132H. 3 of 4 patients also harbored KRAS mutations. Patients with IDH-1 mutations had higher levels of 2HG (319 ± 102 ng/ml vs 195 ± 43 ng/ml, p = 0.043). The ratio of R/S were 0.44, 0.75, 1.59, and 2.60 in 4 patients with IDH-1 mutations and 1.3, 0.90, 0.41 and 0.67 in 3 patients without IDH-1mutations. Conclusions: IDH-1 mutations are rare in advanced CRC. 3 of 4 patients in our study had concurrent KRAS mutations. Patients with IDH-1 mutations had higher levels of oncometabolite 2HG compared with controls with no difference in R/S ratio.