Methylene tetrahydrofolate reductase (MTHFR) gene rs1801133 C>T polymorphisms and response to 5-FU based chemotherapy in patients with colorectal cancer: a meta-analysis

Abstract Background: Methylene tetrahydrofolate reductase (MTHFR) catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine. Single nucleotide polymorphisms (SNP) of MTHF rs1801133 C>T can influence susceptibility to colorectal cancer. However, an association between MTHFR rs1801133 C>T polymorphisms and response to 5-Fluorouracil (5-FU) based chemotherapy in patients with colorectal cancer was not clear. Methods: Studies relevant to MTHFR rs1801133 C>T polymorphisms and response to 5-FU based chemotherapy in patients with colorectal cancer were systematic searched in the electronic databases of PubMed, Web of Science, Embase, and China National Knowledge Infrastructure (CNKI). The genotypes of CC, CT, and TT were extracted from each included publication. The genotypes CC, CT, and TT distribution in 5-FU based chemotherapy response and resistance groups were calculated and pooled through random or fixed effect model by the effect size of odds ratio (OR) and 95% confidence interval (95% CI). The publication bias was evaluated through Begg’s funnel plot and Egger’s line regression test. Results: After searching the electronic databases, 16 studies related to MTHFR gene rs1801133 C>T polymorphisms and a response to 5-FU based chemotherapy in patients with colorectal cancer were included in the present meta-analysis. The pooled data showed no statistical difference in tumor response rate between CT+TT and CC groups in the dominant genetic model CT+CC vs CC (OR=1.21, 95% CI: 0.93~1.59, p>0.05) and recessive model TT vs CT+CC (OR=1.37, 95% CI: 0.91~2.06, p>0.05). The grade 3-4 adverse reaction rate between CT+TT and CC groups also had no statistical difference in the dominant genetic model CT+CC vs CC (OR=0.90, 95% CI: 0.76~1.07, p>0.05) and recessive model TT vs CT+CC (OR=1.12, 95% CI: 0.84~1.50, p>0.05). The Begg’s funnel plot and Egger’s line regression test demonstrated no publication bias. Conclusion: The response and adverse reaction of 5-FU based chemotherapy in colorectal patients were not different in terms of MTHFR rs1801133 C>T polymorphisms.


Introduction
Methylene tetrahydrofolate reductase (MTHFR) is a key enzyme in folate metabolism and methionine metabolism. The rs1801133 C>T polymorphism of the MTHFR gene lead to a decrease in enzyme activity, inhibit the folic acid metabolism cycle, affect the synthesis of pyrimidine or purine, and lead to the damage of DNA synthesis or repair, as well as the defect or canceration of cell growth [1]. In recent years, with the development of pharmacogenomics, researchers began to explore the relationship between MTHFR gene SNPs and the sensitivity to chemotherapy regimens. 5-FU based chemotherapy regimen is extensive and used long-term clinically for esophageal-gastric cancer [2] and colorectal carcinoma [3,4]. However, most of the studies relevant MTHFR rs1801133 C>T polymorphisms and response to 5-FU based chemotherapy in patients with colorectal cancer were retrospective studies with small sample size. Therefore, we performed this meta-analysis by pooling the open published studies of the relationship between MTHFR rs1801133 C>T polymorphisms and 5-FU based chemotherapy response in order to provide a more reliable evidence for the rational use of 5-FU chemotherapy regimen in clinical practice.

Publications searching and inclusion
The electronic databases of PubMed, Web of Science, Embase, and CNKI were systematic searched to identify relevant studies related to MTHFR gene rs1801133 C>T polymorphisms and a response to 5-FU based chemotherapy in patients with colorectal cancer (Figure 1). The searching text words were methylene tetrahydrofolate reductase/MTHFR, colorectal cancer/colon cancer/rectal cancer/colorectal carcinoma/ colon carcinoma/ rectal carcinoma/ OR CRC, and chemotherapy. The publication screening procedure was last performed in October 10, 2018. The study inclusion criteria was (1) the patients were diagnosed of colorectal cancer by pathology, (2) the chemotherapy regimen was 5-FU based,(3) genotype of CC, CT, and TT can be extracted from original publications, and (4) tumor response rate and adverse reaction can be calculated from original studies of different genotype.
Ethical approval: The conducted research is not related to either human or animals use.

Data extraction from original publication
After reviewing the included full text paper, the general information and useful data was extracted by two reviewers independently and checked by a third reviewer as described according to the Cochrane Handbook for systematic reviews. The general information included the name of the authors, the manuscript publication year, region, chemotherapy regimen, and chemotherapy adverse reaction and response. The useful data of sample size, distribution of CC, CT, TT genotype in tumor response and resistance groups were carefully extracted from the original publications.

Statistical methods
STATA/SE 11.0 StataCorp LP, http://www.stata.com software were used for the data analysis. The odds of CC, CT and TT genotypes in chemotherapy sensitivity groups versus chemotherapy resistance groups, or grade 3-4 adverse reaction groups versus non-grade 3-4 adverse reaction groups were expressed by odds ratio (OR) and 95% confidence intervals (95% CI). The statistical heterogeneity across the included 16 publications in each effect size was assessed by I 2 test [5]. The OR was pooled by random or fixed effect models according to statistical heterogeneity. The publication bias was assessed by Begg's funnel plot and Egger's line regression tests [6].

Tumor response rate in recessive mutation model [TT vs (CT+CC) ]
For recessive genetic model [TT vs (CT+CC) ], the pooled OR for tumor response rate between TT and CT+CC groups was (OR=1.37, 95% CI: 0.91~2.06, p>0.05) in a fixed effect model without statistical difference, Figure 3.

Grade 3-4 adverse reaction in dominant mutation model[(CT+TT) vs CC]
For

Publication bias analysis
The publication bias of the included 16 studies was assessed by Begg's funnel plot (Figure 6)

Discussion
Colorectal cancer (CRC) is one of the most diagnosed malignant tumor of the digestive system [23]. It was the fourth most diagnosed cancer in the United States with an estimated 143,460 new cases in the year 2012 [24]. The general prognosis of the early stage CRC was good in patients who received surgery. However, the 5-year survival rate was low even under the treatment of chemoradiotherapy for advanced stages of the disease. The most used chemotherapy regimen was fluorouracil (5-FU) based chemotherapy regimen for colorectal cancer patients [4,25]. Folic acid is involved in the synthesis and transformation of nucleotides. Methylene tetrahydrofolate reductase (MTHFR), a key enzyme in folate metabolism, catalyzes the irreversible conversion of 5,10-methylene tetrahydrofolate (5,10-MTHF) to 5-methyltetrahydrofolate, which converts homocysteine to methionine and then to S-adenosylmethionine (SAM). The most common SNP site of MTHFR gene is rs1801133 C>T, where cytosine C mutates to thymine T (677C > T), resulting in alanine being replaced by valine, which reduces the activity of MTHFR [26][27][28][29]. 5-FU is transformed into fluorouracil deoxynucleotide (FdUMP) in cells with thymidylate synthase (TS) and 5,10-MTHF, inhibiting the function of thymidylate synthase, preventing the conversion of deoxyuridine (dUMP) to deoxythymidine (dTMP), affecting DNA synthesis [30,31]. Therefore, MTHFR gene rs1801133 C>T polymorphisms can affect 5-FU base chemotherapy in patients with colorectal cancer.  Recently, several studies [16,18,20] have discussed the correlation between MTHFR gene rs1801133 C>T polymorphisms and response to 5-FU based chemotherapy in patients with CRC. However, because of small sample size and weak statistical power, clinical evidence was weak. Therefore, we performed this metaanalysis in order to further evaluate the relationship between MTHFR rs1801133 C>T polymorphism and 5-FU based chemotherapy response in order to provide a more reliable evidence for the rational use of 5-FU chemotherapy regimens in clinic. We found the response and adverse reaction of 5-FU based chemotherapy in colorectal patients was not different in terms of MTHFR rs1801133 C>T polymorphisms.
Although we did not find any correlation between MTHFR rs1801133 C>T polymorphism and 5-FU based chemotherapy response or adverse reactions, the results demonstrated a trend that patients with TT/CT genotype were more prone to response to 5-FU based chemotherapy response and had less grade 3-4 adverse reactions.

Conclusion
Base on the present evidence, the response and adverse reactions of 5-FU based chemotherapy in colorectal patients were not different in terms of MTHFR rs1801133 C>T polymorphisms. However, only 16 publications were included with a relative small sample size. More studies are needed to further discuss this correlation.