Plasma central carbon metabolite changes associated with KRAS mutation and circulating tumor DNA (ctDNA) status in colorectal cancer (CRC).

Abstract

181 Background: KRAS mutations have been widely characterized as markers of poor prognosis in CRC. In stage IV CRC, KRAS mutations are predictive of benefit to anti-EGFR therapy. ctDNA has increasingly been recognized as a prognostic biomarker in CRC as well. We evaluated the association between plasma metabolites and KRAS mutation or ctDNA status in a longitudinal, observational cohort of patients with stage I-IV CRC. Methods: This was a retrospective analysis of prospectively collected blood samples from a single-institute cohort of patients with stage I-IV CRC. All blood samples were collected at pre-chemotherapy baseline. A modified Epi proColon 2.0 CE (Epigenomics AG) assay was used for plasma ctDNA testing on the methylated SEPTIN9 gene (mSEPT9). ctDNA positivity was defined as a mSEPT9 percentage of methylation reference (PMR) value greater than zero. Up to 150 metabolites of central carbon metabolism were analyzed by mass spectrometry and high-performance liquid chromatography. Analytes were compared by relative area under the curve (AUC) and differences evaluated by ANOVA. The mean AUC was used in patients with metabolites measured from > 1 timepoint of collection. Patients were stratified by ctDNA status (positive or negative) and KRAS mutant (MT) or wildtype (WT) status. Results: A total of 32 patients were included with median age 65 years (range 20-90). The majority were female (53%) and had stage IV disease (78%). Of 25 patients with stage IV CRC, 88% had pre-chemotherapy blood samples collected in the first-line setting. Most patients were KRAS MT (44%) compared to KRAS WT (37%) or unknown KRAS status (19%). The most common KRAS MT subtypes were G12D (29%), G12V (29%), G13D (21%), and G12C (14%). The mean overall survival in this cohort was 27.4 months while the mean mSEPT9 PMR value was 2553.6. When stratified by ctDNA status, ctDNA positivity was associated with decreased levels of essential amino acids (lysine, methionine, threonine) and the non-essential amino acid arginine (all p < 0.05). Compared to KRAS WT tumors, KRAS MT tumors were associated with increased levels of proline, phenylalanine, and intermediates of glycolysis (lactate), MTA cycle (SAM, 5-Methioadenosine), and O-GlcNAcylation (GlcNac, all p < 0.05). Conclusions: We are the first to demonstrate the feasibility of associating central carbon metabolites with ctDNA and KRAS mutation status. As ctDNA positivity and KRAS MT status have evolving prognostic potential in CRC, associated metabolic signatures may identify metabolic pathways for novel biomarker development. Our findings also show that KRAS MT CRC appears to be enriched in intermediates of glycolytic, methyl donor, and O-GlcNAcylation pathways.