An Association between OXPHOS-Related Gene Expression and Malignant Hyperthermia Susceptibility in Human Skeletal Muscle Biopsies.

Malignant hyperthermia (MH) is a pharmacogenetic condition of skeletal muscle that manifests in hypermetabolic responses upon exposure to volatile anaesthetics. This condition is caused primarily by pathogenic variants in the calcium-release channel RYR1, which disrupts calcium signalling in skeletal muscle. However, our understanding of MH genetics is incomplete, with no variant identified in a significant number of cases and considerable phenotype diversity. In this study, we applied a transcriptomic approach to investigate the genome-wide gene expression in MH-susceptible cases using muscle biopsies taken for diagnostic testing. Baseline comparisons between muscle from MH-susceptible individuals (MHS, n = 8) and non-susceptible controls (MHN, n = 4) identified 822 differentially expressed genes (203 upregulated and 619 downregulated) with significant enrichment in genes associated with oxidative phosphorylation (OXPHOS) and fatty acid metabolism. Investigations of 10 OXPHOS target genes in a larger cohort (MHN: n = 36; MHS: n = 36) validated the reduced expression of ATP5MD and COQ6 in MHS samples, but the remaining 8 selected were not statistically significant. Further analysis also identified evidence of a sex-linked effect in SDHB and UQCC3 expression, and a difference in ATP5MD expression across individuals with MH sub-phenotypes (trigger from in vitro halothane exposure only, MHSh (n = 4); trigger to both in vitro halothane and caffeine exposure, MHShc (n = 4)). Our data support a link between MH-susceptibility and dysregulated gene expression associated with mitochondrial bioenergetics, which we speculate plays a role in the phenotypic variability observed within MH.

KRAS and BRAF mutations in advanced colorectal cancer are associated with poor prognosis but do not preclude benefit from oxaliplatin or irinotecan: results from the MRC FOCUS trial.

PURPOSE: Activating mutation of the KRAS oncogene is an established predictive biomarker for resistance to anti-epidermal growth factor receptor (anti-EGFR) therapies in advanced colorectal cancer (aCRC). We wanted to determine whether KRAS and/or BRAF mutation is also a predictive biomarker for other aCRC therapies. PATIENTS AND METHODS: The Medical Research Council Fluorouracil, Oxaliplatin and Irinotecan: Use and Sequencing (MRC FOCUS) trial compared treatment sequences including first-line fluorouracil (FU), FU/irinotecan or FU/oxaliplatin in aCRC. Tumor blocks were obtained from 711 consenting patients. DNA was extracted and KRAS codons 12, 13, and 61 and BRAF codon 600 were assessed by pyrosequencing. Mutation (mut) status was assessed first as a prognostic factor and then as a predictive biomarker for the benefit of adding irinotecan or oxaliplatin to FU. The association of BRAF-mut with loss of MLH1 was assessed by immunohistochemistry. RESULTS: Three hundred eight (43.3%) of 711 patients had KRAS-mut and 56 (7.9%) of 711 had BRAF-mut. Mutation of KRAS, BRAF, or both was present in 360 (50.6%) of 711 patients. Mutation in either KRAS or BRAF was a poor prognostic factor for overall survival (OS; hazard ratio [HR], 1.40; 95% CI, 1.20 to 1.65; P < .0001) but had minimal impact on progression-free survival (PFS; HR, 1.16; 95% CI, 1.00 to 1.36; P = .05). Mutation status did not affect the impact of irinotecan or oxaliplatin on PFS or OS. BRAF-mut was weakly associated with loss of MLH1 staining (P = .012). CONCLUSION: KRAS/BRAF mutation is associated with poor prognosis but is not a predictive biomarker for irinotecan or oxaliplatin. There is no evidence that patients with KRAS/BRAF mutated tumors are less likely to benefit from these standard chemotherapy agents.

Association of molecular markers with toxicity outcomes in a randomized trial of chemotherapy for advanced colorectal cancer: the FOCUS trial.

PURPOSE: Predicting efficacy and toxicity could potentially allow individualization of cancer therapy. We investigated putative pharmacogenetic markers of chemotherapy toxicity in a large randomized trial. PATIENTS, MATERIALS, AND METHODS: Patients were randomly assigned to different sequences of chemotherapy for advanced colorectal cancer. First-line therapy was fluorouracil (FU), irinotecan/FU (IrFU) or oxaliplatin/FU (OxFU). Patients allocated first-line FU had planned second-line irinotecan alone, IrFU, or OxFU. The primary toxicity outcome measure was toxicity-induced delay or dose reduction; the secondary outcome was Common Terminology Criteria of Adverse Events grade >or= 3 toxicity. DNA was analyzed in 1,188 patients; 1,036 were assessable for the primary outcome, including 688 treated with FU, 270 with IrFU (first or second line), 280 with OxFU (first or second line), 184 with irinotecan alone, and 454 with any irinotecan-containing regimen. Ten polymorphisms were assessed: thymidylate synthase-enhancer region (TYMS-ER), thymidylate synthase 1494 (TYMS-1494), dihydropyrimidine dehydrogenase (DPYD), methylenetetrahydrofolate reductase (MTHFR), mutL homolog 1 (MLH1), UDP glucuronyltransferase (UGT1A1), ATP-binding cassette group B gene 1 (ABCB1), x-ray cross-complementing group 1 (XRCC1), glutathione-S-transferase P1 (GSTP1), and excision repair cross-complementing gene 2 (ERCC2). Results Using the primary outcome measure, no polymorphism was significantly associated (P < .01) with the toxicity of any regimen or with the difference in toxicity of IrFU or OxFU versus FU alone. Trends (of doubtful significance) were seen for associations of XRCC1, ERCC2, and GSTP1 with toxicity during irinotecan regimens: XRCC1, primary end point, any irinotecan-containing regimen (P = .045); ERCC2, secondary end point, irinotecan alone (P = .003); GSTP1, secondary end point; IrFU (P = .039); and irinotecan alone (P = .05). There was no evidence of association of UGT1A1*28 with irinotecan toxicity. CONCLUSION: These results do not support the routine clinical use of the evaluated polymorphisms, including UGT1A1*28. Further investigation of XRCC1, ERCC2, and GSTP1 as potential predictors of irinotecan toxicity is warranted.