Effect of cystathionine beta-synthase variant 844ins68bp and methylenetetrahydrofolate reductase A1298C polymorphisms in xenografts on 5-FU efficacy and doubling time

MTHFR polymorphisms and capecitabine-induced toxicity in patients with metastatic colorectal cancer

OBJECTIVE

The availability of current chemotherapeutic options for metastatic colorectal cancer (mCRC) has increased survival, but it is also accompanied by considerable morbidity. Fluoropyrimidines are the mainstay of systemic therapy. Germline pharmacogenetic markers involved in 5-fluorouracil pharmacodynamics could provide individualized pretreatment tools for predicting toxicity. Research on methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms and fluoropyrimidine treatment outcome has focused on intravenous 5-fluorouracil and has yielded inconclusive results. The literature on pharmacogenetics in capecitabine-based chemotherapy is scarce. Therefore, we analysed the association of MTHFR gene polymorphisms and the occurrence of serious toxicity of first-line capecitabine monotherapy and combination therapy.

METHODS

One hundred and twenty-seven patients treated with first-line monotherapy capecitabine and 141 patients on capecitabine-irinotecan combination therapy were recruited from the CAIRO trial, an open-label phase III randomized trial, comparing sequential versus combination chemotherapy with capecitabine, irinotecan and oxaliplatin in mCRC. All patients were genotyped for MTHFR 1298A>C and 677C>T polymorphisms and analysed in both cohorts separately for the association between the MTHFR genotype and incidence of grade 3-4 overall toxicity and specific adverse events, as well as efficacy parameters.

RESULTS

MTHFR 1298A>C and 677C>T genotypes were not associated with grade 3-4 overall toxicity, febrile neutropenia or hand-foot syndrome. MTHFR 1298CC homozygotes showed a borderline significantly higher incidence of grade 3-4 diarrhoea compared with MTHFR 1298AC or AA individuals (25 vs. 5%, P=0.041) in the monotherapy cohort. No significant association was found between the MTHFR genotypes and efficacy parameters in either treatment cohort.

CONCLUSION

MTHFR polymorphisms are not associated with toxicity or efficacy in mCRC patients treated with capecitabine-based chemotherapy.

Genetic variation in the cysteine biosynthesis pathway causes sensitivity to pharmacological compounds

Complex traits are the product of multiple genes with effects that depend on both the genetic and environmental background. Although this complexity makes a comprehensive genetic analysis difficult, identification of even a single gene provides insight into the biochemical and/or signaling pathway underlying a trait. However, it is unknown whether multiple pathways, and consequently multiple genes, must be identified to adequately understand a trait's molecular basis. Using crosses between three natural isolates of Saccharomyces cerevisiae, we mapped sensitivity to a number of pharmacologically active compounds to a single nonsynonymous polymorphism in cystathione-beta-synthase (CYS4), which is required for the first committed step in the cysteine biosynthesis pathway. Drug sensitivity is mediated by a deficiency in cysteine and consequently glutathione production, because drug sensitivity is abrogated by cysteine or glutathione supplementation. Within a diverse panel of 60 natural yeast isolates, the drug-sensitive CYS4 allele is rare, and glutathione supplementation failed to alleviate drug-dependent growth defects in two other drug-sensitive strains. These results implicate the cysteine/glutathione biosynthesis pathway as a significant, but not the sole contributor to pharmacological variation in yeast.