Associations of various gene polymorphisms with toxicity in colorectal cancer patients receiving oral uracil and tegafur plus leucovorin: a prospective study

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.

The Road so Far in Colorectal Cancer Pharmacogenomics: Are We Closer to Individualised Treatment?

In recent decades, survival rates in colorectal cancer have improved greatly due to pharmacological treatment. However, many patients end up developing adverse drug reactions that can be severe or even life threatening, and that affect their quality of life. These remain a limitation, as they may force dose reduction or treatment discontinuation, diminishing treatment efficacy. From candidate gene approaches to genome-wide analysis, pharmacogenomic knowledge has advanced greatly, yet there is still huge and unexploited potential in the use of novel technologies such as next-generation sequencing strategies. This review summarises the road of colorectal cancer pharmacogenomics so far, presents considerations and directions to be taken for further works and discusses the path towards implementation into clinical practice.

The Identification of Admixture Patterns Could Refine Pharmacogenetic Counseling: Analysis of a Population-Based Sample in Mexico

Pharmacogenetic analysis has generated translational data that could be applied to guide treatments according to individual genetic variations. However, pharmacogenetic counseling in some mestizo (admixed) populations may require tailoring to different patterns of admixture. The identification and clustering of individuals with related admixture patterns in such populations could help to refine the practice of pharmacogenetic counseling. This study identifies related groups in a highly admixed population-based sample from Mexico, and analyzes the differential distribution of actionable pharmacogenetic variants. A subsample of 1728 individuals from the Mexican Genomic Database for Addiction Research (MxGDAR/Encodat) was analyzed. Genotyping was performed with the commercial PsychArray BeadChip, genome-wide ancestry was estimated using EIGENSOFT, and model-based clustering was applied to defined admixture groups. Actionable pharmacogenetic variants were identified with a query to the Pharmacogenomics Knowledge Base (PharmGKB) database, and functional prediction using the Variant Effect Predictor (VEP). Allele frequencies were compared with chi-square tests and differentiation was estimated by F_ST. Seven admixture groups were identified in Mexico. Some, like Group 1, Group 4, and Group 5, were found exclusively in certain geographic areas. More than 90% of the individuals, in some groups (Group 1, Group 4 and Group 5) were found in the Central-East and Southeast region of the country. MTRR p.I49M, ABCG2 p.Q141K, CHRNA5 p.D398N, SLCO2B1 rs2851069 show a low degree of differentiation between admixture groups. ANKK1 p.G318R and p.H90R, had the lowest allele frequency of Group 1. The reduction in these alleles reduces the risk of toxicity from anticancer and antihypercholesterolemic drugs. Our analysis identified different admixture patterns and described how they could be used to refine the practice of pharmacogenetic counseling for this admixed population.

Colorectal cancer: pharmacogenetics support for the correct drug prescription

Pharmacogenetics (PGx) in clinical practice is a tool that the clinician can use to guide, in a personalized way, the most suitable treatment that will be administered to the patient. The objective of this review is to summarize in a practical and accessible rational way, the advances that currently exist for the application of PGx in colorectal cancer chemotherapy management through the study of the patients' germline polymorphisms. To define the polymorphisms that can be applied, we rely on three fundamental cornerstones: the recommendations of drug regulatory agencies; the implementation guidelines prepared by expert consortia in PGx and information from clinical annotations (the drug/polymorphism relation) according to the scientific level of evidence assigned by PharmGKB experts.

The use of pharmacogenetics to increase the safety of colorectal cancer patients treated with fluoropyrimidines

Fluoropyrimidines (FP) are given in the combination treatment of the advanced disease or as monotherapy in the neo-adjuvant and adjuvant treatment of colorectal cancerand other solid tumors including breast, head and neck and gastric cancer. FP present a narrow therapeutic index with 10 to 26% of patients experiencing acute severe or life-threatening toxicity. With the high number of patients receiving FP-based therapies, and the significant effects of toxicities on their quality of life, the prevention of FP-related adverse events is of major clinical interest. Host genetic variants in the rate limiting enzyme dihydropyrimidine dehydrogenase (DPYD) gene are related to the occurrence of extremely severe, early onset toxicity in FP treated patients. The pre-treatment diagnostic test of 4 DPYD genetic polymorphisms is suggested by the currently available pharmacogenetic guidelines. Several prospective implementation projects are ongoing to support the introduction of up-front genotyping of the patients in clinical practice. Multiple pharmacogenetic studies tried to assess the predictive role of other polymorphisms in genes involved in the FP pharmacokinetics/pharmacodynamic pathways, TYMS and MTHFR, but no additional clinically validated genetic markers of toxicity are available to date. The development of next-generation sequencing platforms opens new possibilities to highlight previously unreported genetic markers. Moreover, the investigation of the genetic variation in the patients immunological system, a pivotal target in cancer treatment, could bring notable advances in the field. This review will describe the most recent literature on the use of pharmacogenetics to increase the safety of a treatment based on FP administration in colorectal cancer patients.

Host genetic profiling to increase drug safety in colorectal cancer from discovery to implementation

Adverse events affect the pharmacological treatment of approximately 90% of colorectal cancer (CRC) patients at any stage of the disease. Chemotherapy including fluoropyrimidines, irinotecan, and oxaliplatin is the cornerstone of the pharmacological treatment of CRC. The introduction of novel targeted agents, as anti-EGFR (i.e. cetuximab, panitumumab) and antiangiogenic (i.e. bevacizumab, ziv-aflibercept, regorafenib, and ramucirumab) molecules, into the oncologist's toolbox has led to significant improvements in the life expectancy of advanced CRC patients, but with a substantial increase in toxicity burden. In this respect, pharmacogenomics has largely been applied to the personalization of CRC chemotherapy, focusing mainly on the study of inhered polymorphisms in genes encoding phase I and II enzymes, ATP-binding cassette (ABC)/solute carrier (SLC) membrane transporters, proteins involved in DNA repair, folate pathway and immune response. These research efforts have led to the identification of some validated genetic markers of chemotherapy toxicity, for fluoropyrimidines and irinotecan. No validated genetic determinants of oxaliplatin-specific toxicity, as peripheral neuropathy, has thus far been established. The contribution of host genetic markers in predicting the toxicity associated with novel targeted agents' administration is still controversial due to the heterogeneity of published data. Pharmacogenomics guidelines have been published by some international scientific consortia such as the Clinical Pharmacogenomics Implementation Consortium (CPIC) and the Dutch Pharmacogenetics Working Group (DPWG) strongly suggesting a pre-treatment dose adjustment of irinotecan based on UGT1A1*28 genotype and of fluoropyrimidines based on some DPYD genetic variants, to increase treatment safety. However, these recommendations are still poorly applied at the patient's bedside. Several ongoing projects in the U.S. and Europe are currently evaluating how pharmacogenomics can be implemented successfully in daily clinical practice. The majority of drug-related adverse events are still unexplained, and a great deal of ongoing research is aimed at improving knowledge of the role of pharmacogenomics in increasing treatment safety. In this review, the issue of pre-treatment identification of CRC patients at risk of toxicity via the analysis of patients' genetic profiles is addressed. Available pharmacogenomics guidelines with ongoing efforts to implement them in clinical practice and new exploratory markers for clinical validation are described.

Pre-treatment evaluation of 5-fluorouracil degradation rate: association of poor and ultra-rapid metabolism with severe toxicity in a colorectal cancer patients cohort

Despite the wide use of 5-fluorouracil-based chemotherapy, development of severe toxicity that follow the treatment is not a rare event. The efforts to establish pretreatment tools for toxicity prediction, led to the development of various pharmacogenetic and biochemical assays, mainly targeted to assess the activity level of dihydropyrimidine dehydrogenase (DPD), the main metabolizing enzyme for 5-fluorouracil. Using peripheral blood mononuclear cells, we developed a biochemical assay, that is not limited to the evaluation of DPD activity, but determines the net result of all the enzymatic transformation of 5FU, in terms of the amount of drug consumed by the cells in a time unit. This parameter, named 5-fluorauracil degradation rate, presents a normal distribution inside the population and highlight the presence of an ultra-rapid metabolizers class of subjects, besides the expected poor metabolizers class. Here we will show that, in a colorectal cancer patient cohort, both poor and ultra-rapid metabolizers have significantly increased the risk of developing severe toxicity (grade3–4). Patient stratification depending on the individual 5-fluorouracil degradation rate allows to identify a 10% of the overall population at high risk of developing severe toxicity, compared to the 1.3% (as assessed in the Italian population) identified by the most commonly employed pharmacogenetic test, including the DPD polymorphism IVS14+1G>A.

Pre-treatment assay of 5-fluorouracil degradation rate (5-FUDR) to improve prediction of 5-fluorouracil toxicity in gastro-esophageal cancer

Background

5-fluorouracil (5-FU) based chemotherapy is the most common first line regimen used in gastric and gastroesophageal junction cancer, but development of severe toxicity is a main concern in the treatment. The present study is aimed to evaluate a novel pre-treatment assay, known as the 5-FU degradation rate (5-FUDR), as a predictive factor for 5-FU toxicity.

Methods

Pre-treatment 5-FUDR and gene polymorphisms related to 5-FU metabolism (DPYDIVS14+1G>A, MTHFRA1298T or C677T, TMYS TSER) were characterized in gastro-esophageal cancer patients. Association with toxicities was retrospectively evaluated, using multivariate logistic regression analysis.

Results

107 gastro-esophageal cancer patients were retrospectively analyzed. No relation between gene polymorphisms and toxicity were detected, while low (< 5^th centile) and high (> 95^th centile) 5-FUDRs were associated with development of grade 3-4 toxicity (OR 11.14, 95% CI 1.09-113.77 and OR 9.63, 95% CI 1.70-54.55, p = 0.002).

Conclusions

Compared to currently used genetic tests, the pre-treatment 5-FUDR seems useful in identifying patients at risk of developing toxicity.

Degradation Rate of 5-Fluorouracil in Metastatic Colorectal Cancer: A New Predictive Outcome Biomarker?

Background

5-FU based chemotherapy is the most common first line regimen used for metastatic colorectal cancer (mCRC). Identification of predictive markers of response to chemotherapy is a challenging approach for drug selection. The present study analyzes the predictive role of 5-FU degradation rate (5-FUDR) and genetic polymorphisms (MTHFR, TSER, DPYD) on survival.

Materials and Methods

Genetic polymorphisms of MTHFR, TSER and DPYD, and the 5-FUDR of homogenous patients with mCRC were retrospectively studied. Genetic markers and the 5-FUDR were correlated with clinical outcome.

Results

133 patients affected by mCRC, treated with fluoropyrimidine-based chemotherapy from 2009 to 2014, were evaluated. Patients were classified into three metabolic classes, according to normal distribution of 5-FUDR in more than 1000 patients, as previously published: poor-metabolizer (PM) with 5-FU-DR ≤ 0,85 ng/ml/10⁶ cells/min (8 pts); normal metabolizer with 0,85 < 5-FU-DR < 2,2 ng/ml/10⁶ cells/min (119 pts); ultra-rapid metabolizer (UM) with 5-FU-DR ≥ 2,2 ng/ml/10⁶ cells/min (6 pts). PM and UM groups showed a longer PFS respect to normal metabolizer group (14.5 and 11 months respectively vs 8 months; p = 0.029). A higher G3-4 toxicity rate was observed in PM and UM, respect to normal metabolizer (50% in both PM and UM vs 18%; p = 0.019). No significant associations between genes polymorphisms and outcomes or toxicities were observed.

Conclusion

5-FUDR seems to be significantly involved in predicting survival of patients who underwent 5-FU based CHT for mCRC. Although our findings require confirmation in large prospective studies, they reinforce the concept that individual genetic variation may allow personalized selection of chemotherapy to optimize clinical outcomes.

Variants in CDA and ABCB1 are predictors of capecitabine-related adverse reactions in colorectal cancer

Adverse reactions to capecitabine-based chemotherapy limit full administration of cytotoxic agents. Likewise, genetic variations associated with capecitabine-related adverse reactions are associated with controversial results and a low predictive value. Thus, more evidence on the role of these variations is needed. We evaluated the association between nine polymorphisms in MTHFR, CDA, TYMS, ABCB1, and ENOSF1 and adverse reactions, dose reductions, treatment delays, and overall toxicity in 239 colorectal cancer patients treated with capecitabine-based regimens. The ABCB1*1 haplotype was associated with a high risk of delay in administration or reduction in the dose of capecitabine, diarrhea, and overall toxicity. CDA rs2072671 A was associated with a high risk of overall toxicity. TYMS rs45445694 was associated with a high risk of delay in administration or reduction in the dose of capecitabine, HFS >1 and HFS >2. Finally, ENOSF1 rs2612091 was associated with HFS >1, but was a poorer predictor than TYMS rs45445694. A score based on ABCB1-CDA polymorphisms efficiently predicts patients at high risk of severe overall toxicity (PPV, 54%; sensitivity, 43%) in colorectal cancer patients treated with regimens containing capecitabine. Polymorphisms in ABCB1, CDA, ENOSF1,and TYMS could help to predict specific and overall severe adverse reactions to capecitabine.

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.

Pharmacogenomics of fluorouracil -based chemotherapy toxicity

INTRODUCTION

5- fluorouracil (5-FU), alone or in combination, is the most prevalent and effective chemotherapeutic agent for the treatment of cancers of the head and neck, breast, pancreas and gastrointestinal tract.

AREAS COVERED

Three rare DPYD mutations, a splice mutation in intron 14 (c.1905+1G>A) and two nonsynonymous coding variants (c.1679T>G, c.2846A>T), have consistently been associated with severe 5-FU toxicity. A relatively common haplotype, hapB3, containing three intronic polymorphisms (c.483+18G>A; c.680+139G>A; c.959-51T>C) and a synonymous mutation c.1236G>A linked to c.1129-5923C>G, is a major contributor to early onset severe toxicity. TYMS VNTR 2R and TYMS-3'-UTR 6-bp ins-del variants were associated with global toxicity in capecitabine-treated patients. A candidate gene study of capecitabine-related toxicity reported that the s12132152 were strongly associated with hand-foot syndrome (HFS), whereas rs7548189 was associated with diarrhea. The rs2612091 and rs2741171, which are downstream of TYMS and intronic for ENOSF1, were associated with increased global toxicity and HFS.

EXPERT OPINION

Sex-dependent differences, ethnicity, cancer types and 5-FU-based chemotherapy regimens might affect the heterogeneity of genetic variants for predictive 5-FU-related toxicity. Future approaches using genome-wide association analyses may help in identifying additional candidate genes causally involved in the path mechanisms of 5-FU-related toxicity.

Germline oncopharmacogenetics, a promising field in cancer therapy

Pharmacogenetics (PGx) is the study of the relationship between inter-individual genetic variation and drug responses. Germline variants of genes involved in drug metabolism, drug transport, and drug targets can affect individual response to medications. Cancer therapies are characterized by an intrinsically high toxicity; therefore, the application of pharmacogenetics to cancer patients is a particularly promising method for avoiding the use of inefficacious drugs and preventing the associated adverse effects. However, despite continuing efforts in this field, very few labels include information about germline genetic variants associated with drug responses. DPYD, TPMT, UGT1A1, G6PD, CYP2D6, and HLA are the sole loci for which the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) report specific information. This review highlights the germline PGx variants that have been approved to date for anticancer treatments, and also provides some insights about other germline variants with potential clinical applications. The continuous and rapid evolution of next-generation sequencing applications, together with the development of computational methods, should help to refine the implementation of personalized medicine. One day, clinicians may be able to prescribe the best treatment and the correct drug dosage based on each patient's genotype. This approach would improve treatment efficacy, reduce toxicity, and predict non-responders, thereby decreasing chemotherapy-associated morbidity and improving health benefits.

Pharmacogenetics research on chemotherapy resistance in colorectal cancer over the last 20 years

During the past two decades the first sequencing of the human genome was performed showing its high degree of inter-individual differentiation, as a result of large international research projects (Human Genome Project, the 1000 Genomes Project International HapMap Project, and Programs for Genomic Applications NHLBI-PGA). This period was also a time of intensive development of molecular biology techniques and enormous knowledge growth in the biology of cancer. For clinical use in the treatment of patients with colorectal cancer (CRC), in addition to fluoropyrimidines, another two new cytostatic drugs were allowed: irinotecan and oxaliplatin. Intensive research into new treatment regimens and a new generation of drugs used in targeted therapy has also been conducted. The last 20 years was a time of numerous in vitro and in vivo studies on the molecular basis of drug resistance. One of the most important factors limiting the effectiveness of chemotherapy is the primary and secondary resistance of cancer cells. Understanding the genetic factors and mechanisms that contribute to the lack of or low sensitivity of tumour tissue to cytostatics is a key element in the currently developing trend of personalized medicine. Scientists hope to increase the percentage of positive treatment response in CRC patients due to practical applications of pharmacogenetics/pharmacogenomics. Over the past 20 years the clinical usability of different predictive markers has been tested among which only a few have been confirmed to have high application potential. This review is a synthetic presentation of drug resistance in the context of CRC patient chemotherapy. The multifactorial nature and volume of the issues involved do not allow the author to present a comprehensive study on this subject in one review.

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.

Pharmacogenetic markers of toxicity for chemotherapy in colorectal cancer patients

Chemotherapeutic agents used in colorectal cancer are frequently associated with severe adverse reactions that compromise the efficacy of treatment. Predicting toxicity could enable therapy to be tailored. Genetic variations have been associated with toxicity in patients treated with fluoropyrimidines (5-fluorouracil, capecitabine and tegafur), oxaliplatin, irinotecan and cetuximab. Complexity of treatment and variability in toxicity classifications make it difficult to compare studies. This article analyzes the association between toxicity and polymorphisms in DPYD, TYMS, MTHFR, ABCB1, UGT1A1, ERCC1, ERCC2, XRCC1, GSTT1 and GSTM1. In addition, the state-of-the-art and future perspectives are discussed.

Multifactorial pharmacogenetic analysis in colorectal cancer patients receiving 5-fluorouracil-based therapy together with cetuximab-irinotecan

AIM

To examine the predictive value of gene polymorphisms potentially linked to toxicity, clinical response, time to progression and overall survival, following cetuximab-tegafur-uracil (UFT)-irinotecan therapy.

METHODS

Fifty-two patients with advanced colorectal cancer were enrolled in an ancillary pharmacogenetic study of the phase II CETUFTIRI trial. Treatment consisted of 21 day cycles of cetuximab (day 1-day 8-day 15, 250 mg m(-2) week(-1) following a 400 mg m(-2) initial dose) together with irinotecan (day 1, 250 mg m(-2)) and UFT-folinic acid (days 1-14, 250 mg m(-2) day(-1) UFT, 90 mg day(-1) folinic acid). Analysed gene polymorphisms (blood DNA) were as follows: EGFR (CA repeats in intron 1, -216G>T, -191C>A), EGF (61A>G), FCGR2A (131Arg>His), FCGR3A (158Phe>Val), UDP-glycosyltransferase1-polypeptide A1 (TA repeats), TYMS (28 bp repeats, including the G>C mutation on the 3R allele, 6 bp deletion in 3' UTR) and MTHFR (677C>T, 1298A>C).

RESULTS

Maximum toxicity grade was linked to EGFR-191C>A polymorphism, with 71.1% grade 3-4 toxicity in CC patients vs. 28.6% in other patients (P= 0.010). A tendency to a better response was observed in patients bearing the TYMS 3RG allele (P= 0.029) and those bearing the FCGR3A 158Val genotype (P= 0.020). The greater the score of favourable TYMS and FCGR3A genotypes, the better the response rate (P= 0.009) and the longer the overall survival (P= 0.007). In multivariate analysis, the score of favourable genotypes was a stronger survival predictor than the performance status.

CONCLUSIONS

Present data suggest the importance of FCGR3A 158Phe>Val and TYMS 5' UTR polymorphisms in responsiveness and survival of patients receiving cetuximab-fluoropyrimidine-based therapy.

Association between CASP8 and CASP10 polymorphisms and toxicity outcomes with platinum-based chemotherapy in Chinese patients with non-small cell lung cancer

Caspase-8 and caspase-10 play crucial roles in both cancer development and chemotherapy efficacy. In this study, we aimed to comprehensively assess single nucleotide polymorphisms (SNPs) of the caspase-8 (CASP8) and caspase-10 (CASP10) genes in relation to toxicity outcomes with first-line platinum-based chemotherapy in patients with advanced non-small cell lung cancer (NSCLC). We genotyped 13 tag SNPs of CASP8 and CASP10 in 663 patients with advanced NSCLC treated with platinum-based chemotherapy regimens. Associations between SNPs and chemotherapy toxicity outcomes were identified in a discovery set of 279 patients and then validated in an independent set of 384 patients. In both the discovery and validation sets, variant homozygotes of CASP8 rs12990906 and heterozygotes of CASP8 rs3769827 and CASP10 rs11674246 and rs3731714 had a significantly lower risk for severe toxicity overall. However, only the association with the rs12990906 variant was replicated in the validation set for hematological toxicity risk. In a stratified analysis, we found that some other SNPs, including rs3769821, rs3769825, rs7608692, and rs12613347, were significantly associated with severe toxicity risk in some subgroups, such as in nonsmoking patients, patients with adenocarcinoma, and patients treated with cisplatin combinations. Consistent results were also found in haplotype analyses. Our results provide novel evidence that polymorphisms in CASP8 and CASP10 may modulate toxicity outcomes in patients with advanced NSCLC treated with platinum-based chemotherapy. If validated, the findings will facilitate the genotype-based selection of platinum-based chemotherapy regimens.

S-1 as a core anticancer fluoropyrimidine agent

INTRODUCTION

5-FU is a core anticancer agent for GI and other malignancies, and infusional 5-FU regimens have been widely utilized. Orally administrable fluoropyrimidine prodrugs have been developed to enhance the anticancer efficacy of 5-FU and to reduce its adverse reactions.

AREAS COVERED

S-1 is an FT-based oral 5-FU prodrug in combination with a DPD inhibitor (CDHP) and an OPRT inhibitor (Oxo), which exerts the following effects: i) maintaining normal gut immunity, Oxo can decrease GI toxicities of 5-FU; ii) sustaining high plasma 5-FU concentrations, Cmax of FBAL after S-1 administration is extremely low, which dramatically decreases adverse reactions such as HFS, neurotoxicities and cardiotoxicities; iii) plasma 5-FU concentrations vary less extensively after S-1 administration and iv) S-1 can be safely administered to patients with DPD deficiency. Furthermore, the alternate-day S-1 administration can reduce the GI toxicities and myelotoxicities of 5-FU without reducing its anticancer efficacy, enabling patients to continue the oral administration for 6 - 12 months.

EXPERT OPINION

Replacement of regimens with infusional 5-FU and other fluoropyrimidines by the alternate-day S-1 administration may be recommended because the latter procedure is efficient for patients while sustaining the enhanced anticancer efficacy of 5-FU and without reducing its dose intensity.

Frequency of uridine monophosphate synthase Gly(213)Ala polymorphism in Caucasian gastrointestinal cancer patients and healthy subjects, investigated by means of new, rapid genotyping assays

AIMS

Uridine monophosphate synthase (UMPS) is a fundamental enzyme in pyrimidine synthesis. A single-nucleotide polymorphism, a G-C transversion at the 638th nucleotide, was demonstrated to increase UMPS activity and suggested to have clinical effects. The aims of this study were to set up simple genotyping methods and investigate the UMPS 638G>C polymorphism in the Caucasian population.

RESULTS

Two hundred forty-one patients with gastrointestinal cancers and 189 healthy subjects were enrolled. Genomic DNA was extracted from peripheral blood. A polymerase chain reaction-restriction fragment length polymorphism (RFLP) method was implemented using a forward primer incorporating a mismatched base to produce an artificial restriction site and BsrI restriction enzyme digestion; a denaturing high performance liquid chromatography (DHPLC) method was developed to further speed up UMPS genotyping. A 153 bp UMPS gene fragment was successfully amplified and analyzed in all samples. RFLP and DHPLC results showed a 100% match and where confirmed by direct sequencing. UMPS genotype distribution was similar in patients with cancer and control subjects.

CONCLUSIONS

Although no association was detected between UMPS variants and gastrointestinal cancer risk in Caucasians, polymerase chain reaction-RFLP with BsrI digestion and DHPLC set up at 59°C are reliable and cost-effective methods to genotype UMPS.

Combinations of polymorphisms in genes involved in the 5-Fluorouracil metabolism pathway are associated with gastrointestinal toxicity in chemotherapy-treated colorectal cancer patients

PURPOSE

The purpose of this study was to investigate whether specific combinations of polymorphisms in genes encoding proteins involved in 5-fluorouracil (5-FU) pharmacokinetics and pharmacodynamics are associated with increased risk of treatment-induced toxicity.

EXPERIMENTAL DESIGN

We analyzed two cohorts of 161 and 340 patients, the exploration and validation cohort, respectively. All patients were treated similarly with 5-FU-based adjuvant chemotherapy. We analyzed 13 functional polymorphisms and applied a four-fold analysis strategy using individual polymorphisms, haplotypes, and phenotypic enzyme activity or expression classifications based on combinations of functional polymorphisms in specific genes. Furthermore, multifactor dimensionality reduction analysis was used to identify a genetic interaction profile indicating an increased risk of toxicity.

RESULTS

Alleles associated with low activity of methylene tetrahydrofolate reductase (MTHFR) were associated with decreased risk of toxicity [OR(Exploration) 0.39 (95% CI: 0.21-0.71, P = 0.003), OR(Validation) 0.63 (95% CI: 0.41-0.95, P = 0.03)]. A specific combination of the MTHFR 1298A>C and thymidylate synthase (TYMS) 3'-UTR (untranslated region) ins/del polymorphisms was significantly associated with increased toxicity in both cohorts [OR(Exploration) 2.40 (95% CI: 1.33-4.29, P = 0.003), OR(Validation) 1.81 (95% CI: 1.18-2.79, P = 0.007)]. The specific combination was also associated with increased cumulative incidence and earlier occurrence of severe toxicity during treatment.

CONCLUSIONS

Our results indicate that MTHFR activity and a specific combination of the MTHFR 1298A>C and TYMS 3'-UTR ins/del polymorphisms are possible predictors of 5-FU treatment-related toxicity.