Thymidylate Synthase (TYMS) and Dihydropyrimidine Dehydrogenase (DPYD) Polymorphisms in the Korean Population for Prediction of 5-Fluorouracil-Associated Toxicity

DPYD Genotyping Recommendations: A Joint Consensus Recommendation of the Association for Molecular Pathology, American College of Medical Genetics and Genomics, Clinical Pharmacogenetics Implementation Consortium, College of American Pathologists, Dutch Pharmacogenetics Working Group of the Royal Dutch Pharmacists Association, European Society for Pharmacogenomics and Personalized Therapy, Pharmacogenomics Knowledgebase, and Pharmacogene Variation Consortium

The goals of the Association for Molecular Pathology Clinical Practice Committee's Pharmacogenomics (PGx) Working Group are to define the key attributes of pharmacogenetic alleles recommended for clinical testing and a minimum set of variants that should be included in clinical PGx genotyping assays. This document series provides recommendations for a minimum set of variant alleles (tier 1) and an extended list of variant alleles (tier 2) that will aid clinical laboratories when designing assays for PGx testing. The Association for Molecular Pathology PGx Working Group considered the functional impact of the variant alleles, allele frequencies in multiethnic populations, the availability of reference materials, and other technical considerations for PGx testing when developing these recommendations. The goal of this Working Group is to promote standardization of PGx testing across clinical laboratories. This document will focus on clinical DPYD PGx testing that may be applied to all dihydropyrimidine dehydrogenase-related medications. These recommendations are not to be interpreted as prescriptive but to provide a reference guide.

DPYD genetic polymorphisms in non-European patients with severe fluoropyrimidine-related toxicity: a systematic review

BACKGROUND

Pre-treatment DPYD screening is mandated in the UK and EU to reduce the risk of severe and potentially fatal fluoropyrimidine-related toxicity. Four DPYD gene variants which are more prominently found in Europeans are tested.

METHODS

Our systematic review in patients of non-European ancestry followed PRISMA guidelines to identify relevant articles up to April 2023. Published in silico functional predictions and in vitro functional data were also extracted. We also undertook in silico prediction for all DPYD variants identified.

RESULTS

In 32 studies, published between 1998 and 2022, 53 DPYD variants were evaluated in patients from 12 countries encompassing 5 ethnic groups: African American, East Asian, Latin American, Middle Eastern, and South Asian. One of the 4 common European DPYD variants, c.1905+1G>A, is also present in South Asian, East Asian and Middle Eastern patients with severe fluoropyrimidine-related toxicity. There seems to be relatively strong evidence for the c.557A>G variant, which is found in individuals of African ancestry, but is not currently included in the UK genotyping panel.

CONCLUSION

Extending UK pre-treatment DPYD screening to include variants that are present in some non-European ancestry groups will improve patient safety and reduce race and health inequalities in ethnically diverse societies.

Adverse drug events associated with fluorouracil use in patients with metastatic colorectal cancer: a real-world pharmacovigilance study based on the FDA adverse event reporting system

BACKGROUND

Fluorouracil (5-FU) is widely used to treat metastatic colorectal cancer (mCRC), but real-world safety data is limited. Our study aimed to evaluate 5-FU's safety profile in a large mCRC population using the FAERS database.

RESEARCH DESIGN AND METHODS

We conducted disproportionality analyses to identify adverse drug events associated with 5-FU use in mCRC patients from 2004 to 2023. Subgroup analyses, gender difference analyses, and logistic regression were also performed.

RESULTS

We identified 1,458 reports with 5-FU as the primary suspected drug, with males accounting for 48.8% of reports. Gastrointestinal disorders were the most common adverse event (864 cases), while pregnancy-related conditions showed the strongest signal intensity (ROR = 2.97). We found 19 preferred terms with positive signals, including ischemic hepatitis (ROR = 59.32), blood iron increased (ROR = 59.32), and stress cardiomyopathy (ROR = 51.94). Males were more susceptible to weight loss and skin toxicity. Most adverse events occurred within the first month of 5-FU administration.

CONCLUSION

Our study provides a comprehensive analysis of 5-FU's safety profile in mCRC patients, helping healthcare professionals mitigate risks in clinical practice.

Pan-Asian adapted ESMO Clinical Practice Guidelines for the diagnosis, treatment and follow-up of patients with metastatic colorectal cancer

The European Society for Medical Oncology (ESMO) Clinical Practice Guidelines for the diagnosis, treatment and follow-up of patients with metastatic colorectal cancer (mCRC), published in late 2022, were adapted in December 2022, according to previously established standard methodology, to produce the Pan-Asian adapted (PAGA) ESMO consensus guidelines for the management of Asian patients with mCRC. The adapted guidelines presented in this manuscript represent the consensus opinions reached by a panel of Asian experts in the treatment of patients with mCRC representing the oncological societies of China (CSCO), Indonesia (ISHMO), India (ISMPO), Japan (JSMO), Korea (KSMO), Malaysia (MOS), the Philippines (PSMO), Singapore (SSO), Taiwan (TOS) and Thailand (TSCO), co-ordinated by ESMO and the Japanese Society of Medical Oncology (JSMO). The voting was based on scientific evidence and was independent of the current treatment practices, drug access restrictions and reimbursement decisions in the different Asian countries. The latter are discussed separately in the manuscript. The aim is to provide guidance for the optimisation and harmonisation of the management of patients with mCRC across the different countries of Asia, drawing on the evidence provided by both Western and Asian trials, whilst respecting the differences in screening practices, molecular profiling and age and stage at presentation, coupled with a disparity in the drug approvals and reimbursement strategies, between the different countries.

Pan-Asian adapted ESMO Clinical Practice Guidelines for the diagnosis treatment and follow-up of patients with localised colon cancer

The most recent version of the European Society for Medical Oncology (ESMO) Clinical Practice Guidelines for the diagnosis, treatment and follow-up of localised colon cancer was published in 2020. It was decided by both the ESMO and the Japanese Society of Medical Oncology (JSMO) to convene a special virtual guidelines meeting in March 2021 to adapt the ESMO 2020 guidelines to take into account the ethnic differences associated with the treatment of localised colon cancer in Asian patients. These guidelines represent the consensus opinions reached by experts in the treatment of patients with localised colon cancer representing the oncological societies of Japan (JSMO), China (CSCO), India (ISMPO), Korea (KSMO), Malaysia (MOS), Singapore (SSO) and Taiwan (TOS). The voting was based on scientific evidence and was independent of the current treatment practices and drug availability and reimbursement situations in the different Asian countries.

Potential role of CMPK1, SLC29A1, and TLE4 polymorphisms in gemcitabine-based chemotherapy in HER2-negative metastatic breast cancer patients: pharmacogenetic study results from the prospective randomized phase II study of eribulin plus gemcitabine versus paclitaxel plus gemcitabine (KCSG-BR-13-11)

Background

In this study, we evaluated the association between genetic polymorphisms of 23 genes associated with gemcitabine metabolism and the clinical efficacy of gemcitabine in breast cancer patients.

Patients and methods

This prospective, pharmacogenetic study was conducted in cooperation with a phase II clinical trial. A total of 103 genetic polymorphisms of the 23 genes involved in gemcitabine transport and metabolism were selected for genotyping. The associations of genetic polymorphisms with overall survival, progression-free survival (PFS), and 6-month PFS were analyzed.

Results

A total of 91 breast cancer patients were enrolled in this study. In terms of 6-month PFS, rs1044457 in CMPK1 was the most significant genetic polymorphism [55.9% for CT and TT and 78.9% for CC, P < 0.001, hazard ratio (HR): 4.444, 95% confidence interval (CI): 1.905-10.363]. For the rs693955 in SLC29A1, the median duration of PFS was 5.4 months for AA and 10.5 months for CA and CC (P = 0.002, HR: 3.704, 95% CI: 1.615-8.497). For the rs2807312 in TLE4, the median duration of PFS was 5.7 months for TT and 10.4 months for CT and CC (P = 0.005, HR: 4.948, 95% CI: 1.612-15.190). In survival analysis with a multi-gene model, the TT genotype of rs2807312 had the worst PFS regardless of other genetic polymorphisms, whereas the CA genotype of rs693955 or the CT genotype of rs2807312 without the AA genotype of rs693955 had the best PFS compared with those of other genetic groups (P < 0.001).

Conclusions

Genetic polymorphisms of rs1044457 in CMPK1, rs693955 in SLC29A1, and rs2807312 in TLE4 were significantly associated with the 6-month PFS rate and/or the duration of PFS. Further studies with a larger sample size and expression study would be helpful to validate the association of genetic polymorphisms and clinical efficacy of gemcitabine.

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This is the largest pharmacogenetic study of gemcitabine-based breast cancer treatment in a prospective clinical trial.

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Several genetic polymorphisms in CMPK1, SLC29A1, and TLE4 were associated with 6-month PFS rate and the duration of PFS.

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The result of this study may contribute to the personalized treatment of breast cancer.

DPYD c.1905 + 1G>A Promotes Fluoropyrimidine-Induced Anemia, a Prognostic Factor in Disease-Free Survival, in Colorectal Cancer

Background and Aim: In 10-30% of colorectal cancer (CRC) patients, toxic reactions occur after fluoropyrimidine-based chemotherapy. A dihydropyridine dehydrogenase (DPYD) gene variant, c.1905 + 1G>A, leads to intolerance to fluoropyrimidines. Due to the low frequency of this variant in many populations, the prevalence of fluoropyrimidine-induced hematologic side effects in CRC patients with the c.1905 + 1G>A variant is unclear. In this study, we investigated the prevalence of the DPYD c.1905 + 1 variants in a Turkish CRC cohort and the potential effects of these variants on fluoropyrimidine-induced hematologic side effects. Materials and Methods: The DPYD c.1905 + 1 variant was genotyped using polymerase chain reaction-restriction fragment length polymorphism analysis and confirmed by Sanger sequencing in peripheral blood samples of 100 CRC patients who received fluoropyrimidine-based chemotherapy and 60 healthy volunteers. The association of c.1905 + 1 variants with susceptibility to hematologic side effects was evaluated. Results: The DPYD c.1905 + 1G>A variant was more common in the CRC group than in the healthy control group (p = 0.001). The presence of the c.1905 + 1G>A variant was associated with thrombocytopenia (p = 0.039) and anemia (p = 0.035). CRC patients with fluoropyrimidine-induced anemia had shorter disease-free survival than CRC patients without fluoropyrimidine-induced anemia (p = 0.0009). Conclusions: Before administering fluoropyrimidine-based chemotherapy, genetic screening for the DPYD c.1905 + 1G>A variant should be performed with the aim of preventing anemia and anemia-induced complications in CRC patients.

Gender-dependent association of TYMS-TSER polymorphism with 5-fluorouracil or capecitabine-based chemotherapy toxicity

Aim: TYMS gene encodes for TS enzyme involved in 5-fluorouracil (5-FU) and capecitabine (CAP) metabolism. This study assessed the association of TYMS-TSER and 3RG>C polymorphisms with 5-FU/CAP adverse event (AE) incidence. Materials & methods: TYMS-TSER and 3RG>C polymorphisms were analyzed by use of PCR/PCR-RFLP in 313 5-FU/CAP-treated cancer patients. Results: Female TYMS-TSER 2R carriers were at increased risk for 5-FU/CAP AEs (odds ratio: 2.195; p = 0.032). 2R/2R genotype was the only factor that increased risk for delayed drug administration or therapy discontinuation (odds ratio: 5.049; p = 0.016). No other associations were found. Conclusion: TYMS-TSER 3R/2R polymorphism was associated with incidence of AEs in female cancer patients. This gender-driven association potentially implicates the ER that, in female patients, potentially regulates TS expression.

Mucosal Injury during Anti-Cancer Treatment: From Pathobiology to Bedside

Mucositis is one of the most common debilitating side effects related to chemotherapy (CT), radiation therapy (RT), targeted agents and immunotherapy. It is a complex process potentially involving any portion of the gastrointestinal tract and injuring the mucosa, leading to inflammatory or ulcerative lesions. Mechanisms and clinical presentation can differ according both to the anatomic site involved (oral or gastrointestinal) and the treatment received. Understanding the pathophysiology and management of mucosal injury as a secondary effect of anti-cancer treatment is an important area of clinical research. Prophylaxis, early diagnosis, and adequate management of complications are essential to increase therapeutic success and, thus, improve the survival outcomes of cancer patients. This review focuses on the pathobiology and management guidelines for mucositis, a secondary effect of old and new anti-cancer treatments, highlighting recent advances in prevention and discussing future research options.

Low Incidence of the DPD IVS14+1G>A Polymorphism in Jordanian Breast and Colorectal Cancer patients

Background:

Dihydropyrimidine dehydrogenase (DPD) is a crucial enzyme in the catabolism of 5-fluorouracil (5-FU), a drug that is frequently used in cancer therapy. Patients with deficient DPD activity are at risk of developing severe 5-FU–associated toxicity. One possible cause of deficiency is genetic polymorphisms in the DPD gene, such as IVS14+1G>A.

Aim:

The present study was conducted to screen for the IVS14+1G>A polymorphism in cancer patients receiving 5-FU and a control group.

Methods:

A total of 40 cancer patients (30 colorectal cancer (CRC) and 10 breast cancer patients) were enrolled in this study. One hundred healthy controls were also tested using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). DNA sequence analysis was carried out to confirm the presence of the IVSI14+1G>A polymorphism.

Results:

Only one CRC patient showed heterozygous IVS14+1G>A polymorphism in the DPD gene.

Conclusion:

The results of this study demonstrated a very low frequency of the IVS14+1G>A polymorphism among Jordanian patients with colorectal and breast cancer.

New Frontiers in the Pathobiology and Treatment of Cancer Regimen-Related Mucosal Injury

Mucositis is a common complication of chemotherapy, radiotherapy and targeted agents. It often affects compliance to anticancer therapies as it frequently causes schedule delays, interruptions or discontinuations of treatment. Moreover, the economic impact related to the management of mucositis is topical and several estimations of additional hospital costs due to this clinical condition have been recently reported. The ability to determine risk factors for mucositis, to early detect its onset, to assess correctly the degree of this toxicity and to plan its multidisciplinary management are all key elements to guarantee the quality of life of patients and to avoid useless dose reduction or interruption of treatment. The pathogenesis of mucositis is multifactorial and it is classily subdivided into oral and gastrointestinal mucositis according to its anatomic presentation. Treatment and patients’ related factors might help in predicting the frequency and the potential degree of symptoms onset. Here we discuss about clinical presentation and pathogenesis of mucositis in relation to different kinds of treatments. Moreover, we focus on therapeutic and prevention strategies, describing past and present management according to international guidelines and the most promising new data about agents potentially able to further improve the treatment of mucositis in the next future.

Association and prediction of severe 5-fluorouracil toxicity with dihydropyrimidine dehydrogenase gene polymorphisms: A meta-analysis

The aim of the present study was to evaluate the association and prediction of dihydropyrimidine dehydrogenase gene (DPYD) polymorphisms and the risk of 5-fluorouracil (5-FU) severe toxicity in cancer patients. A meta-analysis of the published literature was conducted to summarize evidence for DPYD gene polymorphisms associated with an increased risk of severe 5-FU toxicity in patients with cancer from an Asian population. Relevant literature was identified using the PubMed and Cochrane databases on April 11, 2014. Combined risk ratios and 95% confidence intervals (CIs) were calculated in a fixed-effects model. A total of 5 clinical studies were retrieved in the meta-analysis, including 764 cancer patients with DPYD gene polymorphisms who received 5-FU-based chemotherapy. Overall, DPYD gene polymorphisms were associated with the increased risk of 5-FU severe toxicity [risk ratio=2.54 (2.15-3.00); 95% CI, 19.46-84.57; P=0.0001]. In conclusion, the present meta-analysis suggested that polymorphisms of several DPYD gene polymorphisms are associated with an increased risk of severe toxic response to 5-FU.

A unique case of a patient with rectal cancer who developed benign esophageal stenosis after localized rectal radiation and systemic chemotherapy

Acute esophagitis and esophageal strictures typically occur after local radiation therapy to the thoracic field. Toxicity is usually limited to the field of radiation and potentially augmented by concomitant use of chemotherapy, however esophageal stricturing due to chemotherapy alone is exceedingly rare. Gastrointestinal toxicity has been previously reported in the setting of 5-fluorouracil (5-FU)-based chemotherapy with abnormal thymidylate synthase or dihydropyrimidine dehydrogenase activities. We present a unique case of isolated chemotherapy-induced esophageal stricture in the setting of stage IIIa rectal adenocarcinoma which presented shortly after initiation of treatment with 5-FU-based chemotherapy in a patient with normal thymidylate synthase and dihydropyrimidine dehydrogenase assays. These findings prompt further investigation of pathways and potential risk factors leading to esophageal toxicity in patients treated with 5-FU-based chemotherapy.

Thymidylate synthase genetic polymorphisms and colorectal cancer risk: a meta-analysis

AIM

The effects of thymidylate synthase (TS) polymorphisms on susceptibility to colorectal cancer (CRC) have been investigated in many studies, but the results remain conflicting rather than conclusive. To resolve these conflicts, we performed a quantitative synthesis of the evidence on the association between these two polymorphisms and CRC risk.

METHODS

All eligible case-control studies published up to September 2013 were identified by searching PubMed, Web of Science and CNKI. Effect sizes of odds ratio (OR) and 95% confidence interval (95% CI) were calculated by using a fixed- or random-effect model.

RESULTS

A total of 11 case-control studies were included, including 10 studies (3324 cases and 4622 controls) for TSER polymorphism and 9 studies (3223 cases and 3886 controls) for TS1494del6 polymorphism. Overall, no significant association between the TS polymorphisms and CRC risk was found. In the subgroup analysis by ethnicity, a significantly association were found among Caucasian populations for TSER polymorphism; but for TS1494del6 polymorphism, no significantly association was observed in both Asian and Caucasian populations. When stratifying by source of controls, we found there was a statistically significant association between TSER polymorphism and risk of CRC in the population-based population; however, we detected no association in both population-based and hospital-based populations for TS1494del6 polymorphism.

CONCLUSIONS

This meta-analysis suggests that the TSER polymorphism in TS gene but not TS1494del6 polymorphism might be a protective factor for CRC among Caucasian populations.

ABCC11/MRP8 polymorphisms affect 5-fluorouracil-induced severe toxicity and hepatic expression

AIM

Because 5-fluorodeoxyuridine monophosphate (5-FdUMP), an anabolic active metabolite of 5-fluorouracil (5-FU), is a substrate of MRP8 (encoded by ABCC11), we investigated whether ABCC11 polymorphisms play a role in severe toxicity of 5-FU.

PATIENTS & METHODS

Genomic DNA from 672 cancer patients treated with 5-FU monotherapy and with documented toxicity according to WHO criteria was genotyped for 12 ABCC11 tag SNPs. Functional impact of polymorphisms was assessed in a Caucasian human liver cohort (n = 150) and by recombinant expression of MRP8 protein variants.

RESULTS

Univariate and multivariate analysis identified rs17822471 (G>A, T546M) as risk factor of severe leukopenia (p = 0.021, odds ratio [95%CI]: 3.31 [1.26-8.66]) but not of other toxicity types. MRP8 protein expression in human liver was 1.7-fold lower in carriers compared with wild-type (p = 0.02). Recombinant expression confirmed the effect of T546M on protein expression.

CONCLUSION

Since MRP8 is expressed in bone marrow blasts and leukocytes, lower expression may lead to intracellular accumulation of 5-FdUMP and increased risk of leukopenia.

Gene expression profile of 5-fluorouracil metabolic enzymes in laryngeal cancer cell line: predictive parameters for response to 5-fluorouracil-based chemotherapy

BACKGROUND

5-fluorouracil (5-FU) is an antifolate chemotherapeutic that has become established in many therapeutic regimes, but sensitivity variations and development of resistance are common problems that limit the efficiency of the treatments. Inter-individual variations to 5-FU outcome have been attributed to different expression profiles of genes related to folate metabolism.

METHODS

To elucidate the mechanisms of variations to 5-FU outcome, the authors investigated MTHFR, DHFR, TYMS and SLC19A1 folate genes expression for 5-FU response in laryngeal cancer cell line (Hep-2). Concentrations of 10, 50, and 100 ng/mL of 5-FU chemotherapeutic were added separately in Hep-2 cell line for 24 hours at 37 °C. Cell sensibility was evaluated with fluorescein isothiocyanate (FITC) label Bcl-2 by flow cytometry. The real-time quantitative PCR (qPCR) technique was performed for quantification of gene expression using TaqMan(®) Gene Expression Assay. ANOVA and Bonferroni's post hoc tests were utilized to statistical analysis.

RESULTS

The numbers of viable Hep-2 cells with 10, 50, and 100 ng/mL concentrations of 5-FU chemotherapy were 15.87, 28.3 and 68.9%, respectively. Statistical analysis showed significant association between control group and increased expression for TYMS gene in cells treated with 100 ng/mL/5-FU chemotherapy (P<0.05).

CONCLUSIONS

The authors found association between the highest 5-FU dose chemotherapy and increased expression levels for TYMS folate gene in laryngeal cancer cell line. Although these experiments were performed in vitro, the results suggest that genetic factors are thought to play an important role in drug metabolism and may be useful for predicting treatment outcomes.

Comparative functional analysis of DPYD variants of potential clinical relevance to dihydropyrimidine dehydrogenase activity

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme of the uracil catabolic pathway, being critically important for inactivation of the commonly prescribed anti-cancer drug 5-fluorouracil (5-FU). DPD impairment leads to increased exposure to 5-FU and, in turn, increased anabolism of 5-FU to cytotoxic nucleotides, resulting in more severe clinical adverse effects. Numerous variants within the gene coding for DPD, DPYD, have been described, although only a few have been demonstrated to reduce DPD enzyme activity. To identify DPYD variants that alter enzyme function, we expressed 80 protein-coding variants in an isogenic mammalian system and measured their capacities to convert 5-FU to dihydro-fluorouracil, the product of DPD catabolism. The M166V, E828K, K861R, and P1023T variants exhibited significantly higher enzyme activity than wild-type DPD (120%, P = 0.025; 116%, P = 0.049; 130%, P = 0.0077; 138%, P = 0.048, respectively). Consistent with clinical association studies of 5-FU toxicity, the D949V substitution reduced enzyme activity by 41% (P = 0.0031). Enzyme activity was also significantly reduced for 30 additional variants, 19 of which had <25% activity. None of those 30 variants have been previously reported to associate with 5-FU toxicity in clinical association studies, which have been conducted primarily in populations of European ancestry. Using publicly available genotype databases, we confirmed the rarity of these variants in European populations but showed that they are detected at appreciable frequencies in other populations. These data strongly suggest that testing for the reported deficient DPYD variations could dramatically improve predictive genetic tests for 5-FU sensitivity, especially in individuals of non-European descent.

DPYD IVS14+1G>A and 2846A>T genotyping for the prediction of severe fluoropyrimidine-related toxicity: a meta-analysis

AIM

In the present study we conducted a systematic review and meta-analysis of published data to quantify the impact of the DPYD IVS14+1G>A and 2846A>T variants on the risk of fluoropyrimidine-related toxicities and to determine sensitivity and specificity testing for DPYD variants.

METHODS

Relevant studies were identified through PubMed and Web of Knowledge databases, studies included were those published up until to May 2012. Study quality was assessed according to the HuGENET guidelines and Strengthening the Reporting of Genetic Association (STREGA) recommendations.

RESULTS

Random-effects meta-analysis provided evidence that carriers of DPYD IVS14+1G>A are at higher risk of ≥3 degrees of overall grade toxicity, hematological toxicity, mucositis and diarrhea. In addition, a strong association was also found between carriers of the DPYD 2846T allele and overall grade ≥3 toxicity or grade ≥3 diarrhea. An inverse linear relationship was found in prospective studies between the odds ratio of DPYD IVS14+1G>A and the incidence of overall grade ≥3 toxicity, indicating an higher impact in cohorts in which the incidence of severe toxicity was lower.

CONCLUSION

The results of this meta-analysis confirm clinical validity of DPYD IVS14+1G>A and 2846A>T as risk factors for the development of severe toxicities following fluoropyrimidine treatment. Furthermore, the sensitivity and specificity estimates obtained could be useful in establishing the cost-effectiveness of testing for DPYD variants.

MicroRNA-433 negatively regulates the expression of thymidylate synthase (TYMS) responsible for 5-fluorouracil sensitivity in HeLa cells

BACKGROUND

Thymidylate synthase (TYMS) is an important folate-dependent enzyme in DNA synthesis and an important target for cancer chemotherapy. High TYMS expression levels in tumors are generally associated with resistance to 5-fluorouracil (5-FU). The cause of the variability in TYMS expression is still not fully understood, however, only a small proportion of the TYMS expression can be explained by TYMS genetic polymorphisms. The purpose of this study is to identify novel microRNAs (miRNAs) which regulate the expression of TYMS and to determine whether miRNAs binding to the 3'-untranslated region (UTR) of TYMS mRNA affect the proliferation of HeLa cells treated with 5-FU.

METHODS

An in silico search was performed to find potential binding sites of miRNAs in TYMS mRNA. The efficacy of predicted miRNAs at the 3'-UTR of TYMS mRNA was evaluated using a dual-luciferase reporter assay. TYMS mRNA and protein expression in HeLa cells was quantified with real-time RT-PCR and Western blotting, respectively. The effects of miR-433 on cell proliferative activity were determined by WST-8 assay.

RESULTS

The overexpression of miR-433 was associated with significantly decreased reporter activity in the plasmid containing the 3'-UTR of TYMS mRNA (P < 0.01). The levels of TYMS mRNA and protein in HeLa cells were significantly decreased by the overexpression of miR-433 (P < 0.05). Furthermore, miR-433 increased inhibition of cell proliferation in HeLa cells treated with 5-FU at over 2.0 μM.

CONCLUSION

The results indicate that miR-433 post-transcriptionally regulates the expression of TYMS mRNA and protein, and increases sensitivity to 5-FU in HeLa cells. This is the first report showing that a miRNA regulating TYMS expression has a significant impact on sensitivity to 5-FU treatment.

Screening of dihydropyrimidine dehydrogenase genetic variants by direct sequencing in different ethnic groups

Dihydropyrimidine dehydrogenase (DPYD) is an enzyme that regulates the rate-limiting step in pyrimidine metabolism, especially catabolism of fluorouracil, a chemotherapeutic agent for cancer. In order to determine the genetic distribution of DPYD, we directly sequenced 288 subjects from five ethnic groups (96 Koreans, 48 Japanese, 48 Han Chinese, 48 African Americans, and 48 European Americans). As a result, 56 polymorphisms were observed, including 6 core polymorphisms and 18 novel polymorphisms. Allele frequencies were nearly the same across the Asian populations, Korean, Han Chinese and Japanese, whereas several SNPs showed different genetic distributions between Asians and other ethnic populations (African American and European American). Additional in silico analysis was performed to predict the function of novel SNPs. One nonsynonymous SNP (+199381A > G, Asn151Asp) was predicted to change its polarity of amino acid (Asn, neutral to Asp, negative). These findings would be valuable for further research, including pharmacogenetic and drug responses studies.

Functional polymorphisms of folate metabolism and response to chemotherapy for colorectal cancer, a systematic review and meta-analysis

OBJECTIVES

Many primary studies have considered the association of polymorphisms of folate metabolism and response to 5-fluorouracil (5-FU) and capecitabine in patients with colorectal cancer. The conclusions from these studies have been conflicting and few have considered large cohorts of patients. Therefore, we have completed a systematic review and meta-analyses to summarize some of the findings to date. We conducted searches for any studies that had addressed the prognostic value of genotype analysis of thymidylate synthetase (TYMS), Methylenetetrahydrofolate reductase (MTHFR) and dihydrofolate reductase (DHFR).

METHODS

We collected data on the study designs, and completed meta-analyses to pool congruent data about treatment effect. A narrative summary is presented for 39 studies that describe three TYMS genotypes and two MTHFR genotypes associated with response to 5-FU-based chemotherapy.

RESULTS

Data were synthesized from up to 2402 patients for the most commonly studied markers TYMS 5' UTR repeat polymorphism (rs45445694) and MTHFR 677 C>T (rs1801133). We found that the TYMS genotype associated with the lowest protein expression (2R/2R) was significantly associated with improved clinical benefit; the pooled risk ratio was relative risk=1.36 [1.11, 1.65]; P=0.003. Moreover, the same trend was observed for adverse effects; the pooled risk ratio was 2.04 [1.42, 2.95]; P=0.0001.

CONCLUSION

There is a small but statistically significant association between treatment effect (both intended effects and adverse events) and a TYMS genotype associated with low protein expression; however, the effect size is small and therefore indicates limited clinical utility.

Dihydropyrimidine dehydrogenase gene as a major predictor of severe 5-fluorouracil toxicity

The importance of polymorphisms in the dihydropyrimidine dehydrogenase (DPD) gene (DPYD) for the prediction of severe toxicity in 5-fluorouracil (5-FU) based chemotherapy has been controversially debated. As a key enzyme in the catabolism of 5-FU, DPD is the top candidate for pharmacogenetic studies on 5-FU toxicity, since a reduced DPD activity is thought to result in an increased half-life of the drug, and thus, an increased risk of toxicity. Here, we review the current knowledge on well-known and frequently studied DPYD variants such as the c.1905+1G>A splice site variant, as well as the recent discoveries of important functional variation in the noncoding regions of DPYD. We also outline future directions that are needed to further improve the risk assessment of 5-FU toxicity, in particular with respect to metabolic profiling and in the context of different combination therapeutic regimens, in which 5-FU is used today.

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.

Pharmacogenetic tests in cancer chemotherapy: what physicians should know for clinical application

Significant efforts to develop pharmacogenomic predictors have been made to guide more effective and safer chemotherapy. Although a considerable amount of data has been generated from numerous experimental or clinical studies, there is a large gap between pharmacogenomic knowledge and clinical application. This review will focus on eight pharmacogenetic tests including TYMS, DPYD, UGT1A1, CYP2D6, EGFR, KRAS, FCGR3A, and BRCA1/2 to predict toxicity or response to commonly used chemotherapeutic agents. We will discuss the current level of evidence, if the current pharmacogenetic tests are appropriate for clinical application, and how to integrate the pharmacogenomic information into routine clinical practice.

Intragenic deletions and a deep intronic mutation affecting pre-mRNA splicing in the dihydropyrimidine dehydrogenase gene as novel mechanisms causing 5-fluorouracil toxicity

Dihydropyrimidine dehydrogenase (DPD) is the initial enzyme acting in the catabolism of the widely used antineoplastic agent 5-fluorouracil (5FU). DPD deficiency is known to cause a potentially lethal toxicity following administration of 5FU. Here, we report novel genetic mechanisms underlying DPD deficiency in patients presenting with grade III/IV 5FU-associated toxicity. In one patient a genomic DPYD deletion of exons 21–23 was observed. In five patients a deep intronic mutation c.1129–5923C>G was identified creating a cryptic splice donor site. As a consequence, a 44 bp fragment corresponding to nucleotides c.1129–5967 to c.1129–5924 of intron 10 was inserted in the mature DPD mRNA. The deleterious c.1129–5923C>G mutation proved to be in cis with three intronic polymorphisms (c.483 + 18G>A, c.959–51T>G, c.680 + 139G>A) and the synonymous mutation c.1236G>A of a previously identified haplotype. Retrospective analysis of 203 cancer patients showed that the c.1129–5923C>G mutation was significantly enriched in patients with severe 5FU-associated toxicity (9.1%) compared to patients without toxicity (2.2%). In addition, a high prevalence was observed for the c.1129–5923C>G mutation in the normal Dutch (2.6%) and German (3.3%) population. Our study demonstrates that a genomic deletion affecting DPYD and a deep intronic mutation affecting pre-mRNA splicing can cause severe 5FU-associated toxicity. We conclude that screening for DPD deficiency should include a search for genomic rearrangements and aberrant splicing.

Population-based differences in treatment outcome following anticancer drug therapies

Population-based differences in toxicity and clinical outcome following treatment with anticancer drugs have an important effect on oncology practice and drug development. These differences arise from complex interactions between biological and environmental factors, which include genetic diversity affecting drug metabolism and the expression of drug targets, variations in tumour biology and host physiology, socioeconomic disparities, and regional preferences in treatment standards. Some well-known examples include the high prevalence of activating epidermal growth factor receptor (EGFR) mutations in pulmonary adenocarcinoma among northeast (China, Japan, Korea) and parts of southeast Asia (excluding India) non-smokers, which predict sensitivity to EGFR kinase inhibitors, and the sharp contrast between Japan and the west in the management and survival outcome of gastric cancer. This review is a critical overview of population-based differences in the four most prevalent cancers in the world: lung, breast, colorectal, and stomach cancer. Particular attention is given to the clinical relevance of such knowledge in terms of the individualisation of drug therapy and in the design of clinical trials.

Toxicity and efficacy of 5-fluorouracil and capecitabine in a patient with TYMS gene polymorphism: A challenge or a dilemma?

5-Fluorouracil (5-FU) is an antimetabolite that acts during the S phase of the cell cycle. The active metabolite, 5-fluorodeoxyuridine monophosphate inhibits thymidylate synthase (TS), thus preventing DNA synthesis, which leads to imbalanced cell growth and ultimately cell death. 5-FU and its oral prodrug capecitabine are used in the treatment of a number of solid tumors, including colorectal, breast, gastric, pancreatic, prostate, and bladder cancers. Common side effects include leukopenia, diarrhea, stomatitis, nausea, vomiting, and alopecia. Hand-foot syndrome (HFS) is a relatively common side effect of cytotoxic chemotherapy. It is more frequently associated with 5-FU, capecitabine, and cytarabine. This article reports on the case of a 55-year-old black man with metastatic colorectal carcinoma that was refractory to recommended treatment measures who developed grade 3 HFS after treatment with modified FOLFOX6 (leucovorin [LV]/5-FU/oxaliplatin) and bFOL (bolus 5-FU/LV/oxaliplatin) regimens. Treatment was discontinued despite excellent response to chemotherapy. The patient had progression of disease on IROX (irinotecan/oxaliplatin) and irinotecan/cetuximab regimens. He was started on gemcitabine/capecitabine and developed HFS again, which was controlled with aggressive skin care and vitamin B6 treatment. Full sequencing of the dihydropyrimidine dehydrogenase (DPYD) gene and analysis of the human TS gene (TYMS) promoter region was performed. Pharmacogenetic testing revealed 2R/2R genotype of TYMS gene, which is associated with up to a 2.5-fold risk of toxicity to 5-FU therapy. Hand-foot syndrome has proven to be a dose-limiting toxicity of 5-FU, especially of capecitabine, leading to significant morbidity. Hand-foot syndrome seems to be dose dependent, and both peak drug concentration and total cumulative dose determine its occurrence. Genetic variations such as polymorphic abnormality of TYMS are potential causative factors for a significant portion of serious adverse reactions to 5-FU-based therapy.

Mutational spectrum of dihydropyrimidine dehydrogenase gene (DPYD) in the Tunisian population

Dihydropyrimidine dehydrogenase enzyme (DPD) deficiency is a pharmacogenetic syndrome leading to severe side-effects in patients receiving therapies containing the anticancer drug 5-fluorouracil (5-FU). The aim of this population study is to evaluate gene variations in the coding region of the dihydropyrimidine dehydrogenase gene (DPYD) in the Tunisian population. One hundred and six unrelated healthy Tunisian volunteers were genotyped by denaturing HPLC (DHPLC). Twelve variants in the coding region of the DPYD were detected. Allele frequencies of DPYD*5 (A1627G), DPYD*6 (G2194A), DPYD*9A (T85C), A496G, and G1218A were 12.7%, 7.1%, 13.7%, 5.7%, and 0.5%, respectively. The DPYD alleles DPYD*2A (IVS 14+1g>1), DPYD*3 (1897 del C) and DPYD*4 (G1601A) associated with DPD deficiency were absent from the examined subjects. We describe for the first time a new intronic polymorphism IVS 6-29 g>t, found in an allelic frequency of 4.7% in the Tunisian population. Comparing our data with that obtained in Caucasian, Egyptian, Japanese and African-American populations, we found that the Tunisian population resembles Egyptian and Caucasian populations with regard to their allelic frequencies of DPYD polymorphisms. This study describes for the first time the spectrum of DPYD sequence variations in the Tunisian population.

Genetic variations and haplotype structures of the DPYD gene encoding dihydropyrimidine dehydrogenase in Japanese and their ethnic differences

Dihydropyrimidine dehydrogenase (DPD) is an inactivating and rate-limiting enzyme for 5-fluorouracil (5-FU), and its deficiency is associated with a risk for developing a severe or fatal toxicity to 5-FU. In this study, to search for genetic variations of DPYD encoding DPD in Japanese, the putative promoter region, all exons, and flanking introns of DPYD were sequenced from 341 subjects including cancer patients treated with 5-FU. Fifty-five genetic variations, including 38 novel ones, were found and consisted of 4 in the 5'-flanking region, 21 (5 synonymous and 16 nonsynonymous) in the coding exons, and 30 in the introns. Nine novel nonsynonymous SNPs, 29C>A (Ala10Glu), 325T>A (Tyr109Asn), 451A>G (Asn151Asp), 733A>T (Ile245Phe), 793G>A (Glu265Lys), 1543G>A (Val515Ile), 1572T>G (Phe524Leu), 1666A>C (Ser556Arg), and 2678A>G (Asn893Ser), were found at allele frequencies between 0.15 and 0.88%. Two known nonsynonymous variations reported only in Japanese, 1003G>T (*11, Val335Leu) and 2303C>A (Thr768Lys), were found at allele frequencies of 0.15 and 2.8%, respectively. SNP and haplotype distributions in Japanese were quite different from those reported previously in Caucasians. This study provides fundamental information for pharmacogenetic studies for evaluating the efficacy and toxicity of 5-FU in Japanese and probably East Asians.