Molecular factors of 5-fluorouracil metabolism in colorectal cancer: analysis of primary tumor and lymph node metastasis

Pharmacologic resistance in colorectal cancer: a review

Colorectal cancer (CRC) persists as one of the most prevalent and deadly tumor types in both men and women worldwide. This is in spite of widespread, effective measures of preventive screening, and also major advances in treatment options. Despite advances in cytotoxic and targeted therapy, resistance to chemotherapy remains one of the greatest challenges in long-term management of incurable metastatic disease and eventually contributes to death as tumors accumulate means of evading treatment. We performed a comprehensive literature search on the data available through PubMed, Medline, Scopus, and the ASCO Annual Symposium abstracts through June 2015 for the purpose of this review. We discuss the current state of knowledge of clinically relevant mechanisms of resistance to cytotoxic and targeted therapies now in use for the treatment of CRC.

TS gene polymorphisms are not good markers of response to 5-FU therapy in stage III colon cancer patients

AIM

Although the predictive and prognostic value of thymidylate synthase (TS) expression and gene polymorphism in colon cancer has been widely studied, the results are inconclusive probably because of methodological differences. With this study, we aimed to elucidate the role of TS gene polymorphisms genotyping in therapy response in stage III colon carcinoma patients treated with 5-FU adjuvant chemotherapy.

PATIENTS AND METHODS

251 patients diagnosed with stage III colon carcinoma treated with surgery followed by 5-FU based adjuvant therapy were selected. The variable number of tandem repeats (VNTR) and the single nucleotide polymorphism (SNP) in the 5'untranslated region of the TS gene were genotyped.

RESULTS

There was a positive association between tumor T stage and the VNTR genotypes (p = 0.05). In both univariate and multivariate survival analysis no effects of the studied polymorphisms on survival were found. However, there was an association between both polymorphisms and age. Among patients younger than 60 years, the patients homozygous for 2R seemed to have a better overall survival, whereas among the patients older than 67 this longer survival was seen by the carriers of other genotypes.

CONCLUSION

We conclude that the TS VNTR and SNP do not predict response to 5-FU therapy in patients with stage III colon carcinoma. However, age appears to modify the effects of TS polymorphisms on survival.

Predictive diagnostics in colorectal cancer: impact of genetic polymorphisms on individual outcomes and treatment with fluoropyrimidine-based chemotherapy

The 5-fluorouracil (5-FU)-based chemotherapy is a standard treatment for patients with colorectal cancer. However, a relevant number of patients suffer from severe toxic side effects, such as haemotoxicity, while lacking clinical response to adjuvant therapy. The inter-individual variations of drug toxicity and efficacy of the pyrimidine antagonist observed in clinical practice are mainly determined by genetic polymorphisms. The screening of genotypes, such as thymidylate synthase, dihydropyrimidine dehydrogenase, methylene tetrahydrofolate reductase, orotate phosphoribosyltransferase or glutathione S-transferase, could help identifying those patients with colorectal carcinoma who can actually benefit from a 5-FU-based therapy. The current chapter elucidates the roles of the polymorphisms in the enzymes involved in the 5-FU metabolic pathway as prognostic and predictive markers. It reports on the relationship between various genotypes in patients with colorectal carcinoma and their responsiveness to a 5-FU-based chemotherapy, and concludes with an outlook on possible future directions in treatment of colorectal cancer.

Regulation of genes of the circadian clock in human colon cancer: reduced period-1 and dihydropyrimidine dehydrogenase transcription correlates in high-grade tumors

Expression of dihydropyrimidine dehydrogenase (DPD) displays a regular daily oscillation in nonmalignant cells. In colorectal cancer cells, the expression of this 5-fluorouracil-metabolizing enzyme is decreased, but the reason remains unclear. In this study, we analyzed by real-time reverse transcription-PCR (RT-PCR) the expression of DPD and of members of the cellular oscillation machinery, period 1 (Per1), period 2 (Per2), and CLOCK, in primary colorectal tumors and normal colon mucosa derived from the same patients. Analysis of tumors according to differentiation grade revealed a 0.46-fold (P = 0.005) decrease for DPD mRNA and a 0.49-fold (P = 0.004) decrease for Per1 mRNA in undifferentiated (G3) tumors compared with paired normal mucosa. In this tumor cohort, the correlation between DPD and Per1 levels was r = 0.64, P < 0.01. In moderately differentiated (G2) colon carcinomas, reduction of DPD and Per1 mRNA levels did not reach significance, but a significant correlation between the respective mRNA levels was detectable (r = 0.54; P < 0.05). The decrease and correlation of DPD and Per1 mRNA levels were even more pronounced in female (G3) patients (DPD: female, 0.35-fold, P < 0.001 versus male, 0.58-fold, P < 0.05; and Per1: female, 0.47-fold, P < 0.01 versus male, 0.52-fold, P < 0.01). The highly significant correlation of DPD mRNA with Per1 mRNA expression suggests control of DPD transcription by the endogenous cellular clock, which is more pronounced in women. Our results also revealed a disturbed transcription of Per1 during tumor progression, which might be the cause for disrupted daily oscillation of DPD in undifferentiated colon carcinoma cells.