Relevance of methylenetetrahydrofolate reductase gene variants C677T and A1298C with response to fluoropyrimidine-based chemotherapy in colorectal cancer: a systematic review and meta-analysis

Pharmacogenomic-guided dosing of fluoropyrimidines beyond DPYD: time for a polygenic algorithm?

Fluoropyrimidines are chemotherapeutic agents widely used for the treatment of various solid tumors. Commonly prescribed FPs include 5-fluorouracil (5-FU) and its oral prodrugs capecitabine (CAP) and tegafur. Bioconversion of 5-FU prodrugs to 5-FU and subsequent metabolic activation of 5-FU are required for the formation of fluorodeoxyuridine triphosphate (FdUTP) and fluorouridine triphosphate, the active nucleotides through which 5-FU exerts its antimetabolite actions. A significant proportion of FP-treated patients develop severe or life-threatening, even fatal, toxicity. It is well known that FP-induced toxicity is governed by genetic factors, with dihydropyrimidine dehydrogenase (DPYD), the rate limiting enzyme in 5-FU catabolism, being currently the cornerstone of FP pharmacogenomics. DPYD-based dosing guidelines exist to guide FP chemotherapy suggesting significant dose reductions in DPYD defective patients. Accumulated evidence shows that additional variations in other genes implicated in FP pharmacokinetics and pharmacodynamics increase risk for FP toxicity, therefore taking into account more gene variations in FP dosing guidelines holds promise to improve FP pharmacotherapy. In this review we describe the current knowledge on pharmacogenomics of FP-related genes, beyond DPYD, focusing on FP toxicity risk and genetic effects on FP dose reductions. We propose that in the future, FP dosing guidelines may be expanded to include a broader ethnicity-based genetic panel as well as gene*gene and gender*gene interactions towards safer FP prescription.

Effects of polymorphisms in the MTHFR gene on 5-FU hematological toxicity and efficacy in Thai colorectal cancer patients

Background

The two common methylenetetrahydrofolate reductase (MTHFR) polymorphisms 677G>A and 1298A>C may have been affecting 5-FU toxicity in cancer patients for decades. Drug efficacy has also been shown by previous studies to be affected. In this study, we investigated the effects of these polymorphisms on 5-FU hematological toxicity and treatment efficacy, to provide enhanced pharmacological treatment for cancer patients.

Methods

This is a retrospective study involving 52 Thai colorectal cancer patients who were treated with 5-FU based therapy, using TaqMAN real-time PCR to genotype the MTHFR polymorphisms (677G>A and 1298A>C). The toxicity and response rate were assessed using standardized measures.

Results

Neutropenia was significantly more likely to be experienced (P=0.049, OR=7.286, 95% CI=0.697-76.181) by patients with the MTHFR 677G>A polymorphism, in the same way as leukopenia (P =0.036, OR=3.333, 95%CI=2.183-5.090) and thrombocytopenia (P<0.001, OR=3.917, 95%CI=2.404-6.382). The MTHFR 1298A>C polymorphism had no statistical association with hematological toxicity in 5-FU treatment. The response rate to 5-FU was not significantly affected by these two polymorphisms.

Conclusion

The MTHFR polymorphism 677G>A is a significant risk factor for developing leukopenia, neutropenia and thrombocytopenia as toxic effects of 5-FU therapy in cancer patients. Therefore, patients receiving 5-FU-based therapy should be aware of their polymorphisms as one risk factor for experiencing severe toxicity.

Predicting drug response and toxicity in metastatic colorectal cancer: the role of germline markers

INTRODUCTION

Despite the introduction of targeted agents leading to therapeutic advances, clinical management of patients with metastatic colorectal cancer (mCRC) is still challenged by significant interindividual variability in treatment outcomes, both in terms of toxicity and therapy efficacy. The study of germline genetic variants could help to personalize and optimize therapeutic approaches in mCRC.

AREAS COVERED

A systematic review of pharmacogenetic studies in mCRC patients published on PubMed between 2011 and 2021, evaluating the role of germline variants as predictive markers of toxicity and efficacy of drugs currently approved for treatment of mCRC, was perfomed.

EXPERT OPINION

Despite the large amount of pharmacogenetic data published to date, only a few genetic markers (i.e., DPYD and UGT1A1 variants) reached the clinical practice, mainly to prevent the toxic effects of chemotherapy. The large heterogeneity of available studies represents the major limitation in comparing results and identifying potential markers for clinical use, the role of which remains exploratory in most cases. However, the available published findings are an important starting point for future investigations. They highlighted new promising pharmacogenetic markers within the network of inflammatory and immune response signaling. In addition, the emerging role of previously overlooked rare variants has been pointed out.

Pharmacogenomic Profile of Amazonian Amerindians

Given the role of pharmacogenomics in the large variability observed in drug efficacy/safety, an assessment about the pharmacogenomic profile of patients prior to drug prescription or dose adjustment is paramount to improve adherence to treatment and prevent adverse drug reaction events. A population commonly underrepresented in pharmacogenomic studies is the Native American populations, which have a unique genetic profile due to a long process of geographic isolation and other genetic and evolutionary processes. Here, we describe the pharmacogenetic variability of Native American populations regarding 160 pharmacogenes involved in absorption, distribution, metabolism, and excretion processes and biological pathways of different therapies. Data were obtained through complete exome sequencing of individuals from 12 different Amerindian groups of the Brazilian Amazon. The study reports a total of 3311 variants; of this, 167 are exclusive to Amerindian populations, and 1183 are located in coding regions. Among these new variants, we found non-synonymous coding variants in the DPYD and the IFNL4 genes and variants with high allelic frequencies in intronic regions of the MTHFR, TYMS, GSTT1, and CYP2D6 genes. Additionally, 332 variants with either high or moderate (disruptive or non-disruptive impact in protein effectiveness, respectively) significance were found with a minimum of 1% frequency in the Amazonian Amerindian population. The data reported here serve as scientific basis for future design of specific treatment protocols for Amazonian Amerindian populations as well as for populations admixed with them, such as the Northern Brazilian population.

MTHFR c.665C>T guided fluoropyrimidine therapy in cancer: gender-dependent effect on dose requirements

OBJECTIVES

The fluoropyrimidine derivatives 5-Fluorouracil and Capecitabine are widely used for the treatment of solid tumors. Fluoropyrimidine metabolism involves a cascade of different enzymes, including MTHFR enzyme. MTHFR c.665C>T polymorphism, leading to decreased MTHFR activity, is a potential pharmacogenomic marker for fluoropyrimidine drug response. The aim of the present study was to analyze the association of MTHFR c.665C>T polymorphism with fluoropyrimidine response in terms of therapy induced adverse events (AEs), requirement of dose reduction and delayed drug administration or therapy discontinuation.

METHODS

The study group consisted of 313 fluoropyrimidine-treated cancer patients. PCR-RFLP was used to analyze MTHFR c.665C>T polymorphism.

RESULTS

In female patients, MTHFR c.665 CT and TT genotypes were associated with dose reduction (p=0.029). In gender stratification, regression analysis adjusted for age of disease onset, body surface area and AE incidence, showed that MTHFR CT and TT genotypes increased both need for fluoropyrimidine dose reduction (OR 5.050, 95% CI 1.346-18.948, p=0.016) and percentage of dose reduction (β=3.318, 95% C.I. 1.056-5.580, p=0.004) in female patients. Such differences were not present in male patients. No other associations were found.

CONCLUSIONS

MTHFR c.665C>T polymorphism was associated with fluoropyrimidine dose reduction in female cancer patients. This gender*MTHFR interaction merits further investigation.

TYMS 3'-UTR Polymorphism: A Novel Association with FOLFIRINOX-Induced Neurotoxicity in Pancreatic Cancer Patients

Pancreatic ductal adenocarcinoma (PDAC) is a highly fatal malignancy that has the worst 5-year survival rate of all of the common malignant tumors. Surgery, chemotherapy, and/or chemoradiation remain the main tactics for PDAC treatment. The efficacy of chemotherapy is often compromised because of the substantial risk of severe toxicities. In our study, we focused on identification of polymorphisms in the genes involved in drug metabolism, DNA repair and replication that are associated with inter-individual differences in drug-induced toxicities. Using the microarray, we genotyped 12 polymorphisms in the DPYD, XPC, GSTP1, MTHFR, ERCC1, UGT1A1, and TYMS genes in 78 PDAC patients treated with FOLFIRINOX. It was found that the TYMS rs11280056 polymorphism (6 bp-deletion in TYMS 3'-UTR) predicted grade 1-2 neurotoxicity (p = 0.0072 and p = 0.0019, according to co-dominant (CDM) and recessive model (RM), respectively). It is the first report on the association between TYMS rs11280056 and peripheral neuropathy. We also found that PDAC patients carrying the GSTP1 rs1695 GG genotype had a decreased risk for grade 3-4 hematological toxicity as compared to those with the AA or AG genotypes (p = 0.032 and p = 0.014, CDM and RM, respectively). Due to relatively high p-values, we consider that the impact of GSTP1 rs1695 requires further investigation in a larger sample size.

Influence of FPGS, ABCC4, SLC29A1, and MTHFR genes on the pharmacogenomics of fluoropyrimidines in patients with gastrointestinal cancer from the Brazilian Amazon

PURPOSE

Fluoropyrimidines are one of the most used drug class to treat cancer patients, although they show high levels of associated toxicity. This study analyzed 33 polymorphisms in 17 pharmacogenes involved with the pharmacogenomics of fluoropyrimidines, in gastrointestinal cancer patients undergoing fluoropyrimidine-based treatment in the Brazilian Amazon.

METHODS

The study population was composed of 216 patients, 92 of whom have an anatomopathological diagnosis of gastric cancer and 124 of colorectal cancer. The single nucleotide polymorphisms (SNP) were genotyped by allelic discrimination using the TaqMan OpenArray Genotyping technology, with a panel of 32 customized assays, run in a QuantStudio ™ 12K Flex Real-Time PCR System (Applied Biosystems, Life Technologies, Carlsbad USA). Ancestry analysis was performed using 61 autosomal ancestry informative markers (AIMs).

RESULTS

The study population show mean values of 48.1% European, 31.1% Amerindian, and 20.8% African ancestries. A significant risk association for general and severe toxicity was found in the rs4451422 of FPGS (p = 0.001; OR 3.40; CI 95% 1.65-7.00 and p = 0.006; OR 4.63; CI 95% 1.56-13.72, respectively) and the rs9524885 of ABCC4 (p = 0.023; OR 2.74; CI 95% 1.14-6.65 and p = 0.024; OR 5.36; IC 95% 1.24-23.11, respectively) genes. The rs760370 in the SLC29A1 gene (p = 0.009; OR 6.71; CI 95% 1.16-8.21) and the rs1801133 in the MTHFR toxicity (p = 0.023; OR 3.09; CI 95% 1.16-8.21) gene also demonstrated to be significant, although only for severe toxicity. The results found in this study did not have statistics analysis correction.

CONCLUSION

Four polymorphisms of the ABCC4, FPGS, SLC29A1, and MTHFR genes are likely to be potential predictive biomarkers for precision medicine in fluoropyrimidine-based treatments in the population of the Brazilian Amazon, which is constituted by a unique genetic background.

A Genotyping/Phenotyping Approach with Careful Clinical Monitoring to Manage the Fluoropyrimidines-Based Therapy: Clinical Cases and Systematic Review of the Literature

Fluoropyrimidines (FP) are mainly metabolised by dihydropyrimidine dehydrogenase (DPD), encoded by the DPYD gene. FP pharmacogenetics, including four DPYD polymorphisms (DPYD-PGx), is recommended to tailor the FP-based chemotherapy. These polymorphisms increase the risk of severe toxicity; thus, the DPYD-PGx should be performed prior to starting FP. Other factors influence FP safety, therefore phenotyping methods, such as the measurement of 5-fluorouracil (5-FU) clearance and DPD activity, could complement the DPYD-PGx. We describe a case series of patients in whom we performed DPYD-PGx (by real-time PCR), 5-FU clearance and a dihydrouracil/uracil ratio (as the phenotyping analysis) and a continuous clinical monitoring. Patients who had already experienced severe toxicity were then identified as carriers of DPYD variants. The plasmatic dihydrouracil/uracil ratio (by high-performance liquid chromatography (HPLC)) ranged between 1.77 and 7.38. 5-FU clearance (by ultra-HPLC with tandem mass spectrometry) was measured in 3/11 patients. In one of them, it reduced after the 5-FU dosage was halved; in the other case, it remained high despite a drastic dosage reduction. Moreover, we performed a systematic review on genotyping/phenotyping combinations used as predictive factors of FP safety. Measuring the plasmatic 5-FU clearance and/or dihydrouracil/uracil (UH2/U) ratio could improve the predictive potential of DPYD-PGx. The upfront DPYD-PGx combined with clinical monitoring and feasible phenotyping method is essential to optimising FP-based chemotherapy.