Potential of dihydropyrimidine dehydrogenase genotypes in personalizing 5-fluorouracil therapy among colorectal cancer patients

Effect of DPYD, MTHFR, ABCB1, XRCC1, ERCC1 and GSTP1 on chemotherapy related toxicity in colorectal carcinoma

ABCB1, DPYD, MHTFR, XRCC1, ERCC1, GSTP1 and UGT1A1 genetic variants affect proteins related to CRC chemotherapy toxicity. A retrospective cohort study was conducted in 194 CRC patients. In first line treatment, DPYD rs17376848 AG genotype was associated with hematological toxicity (OR = 4.85; p = 0.03); GSTP1 G-allele (OR = 3.01; p = 0.005) and MTHFR rs1801133 T allele (OR = 2.51; p = 0.03) with respiratory toxicity; GSTP1 G-allele with cardiovascular toxicity (OR = 4.05; p = 0.01); ERCC1 rs11615 GG genotype with neurological toxicity (OR = 3.98; p = 0.01) and with asthenia (OR = 2.91; p = 0.08); XRCC1 rs1799782 T allele (OR = 0.31; p = 0.03) and GSTP1 G-allele (OR = 1.81; p = 0.01) with cutaneous toxicity. In second line treatment, XRCC1 rs1799782 T-allele was associated with asthenia (OR = 0.17; p = 0.03) and XRCC1 rs25487 T-allele with gastrointestinal toxicity (OR = 3.03; p = 0.005). After stratifying by treatment, in the 5-Fluorouracil group, the DPYD rs17376848 AG genotype was associated with hematological toxicity (OR = 2.76; p = 0.003), ABCB1 rs1045642 T-allele with the need of treatment adjustment due to toxicity (OR = 3.06; p = 0.01), and rs1045642 CC genotype with gastrointestinal toxicity (OR = 5.80; p = 0.03). In the capecitabine group, the MTHFR rs1801131 CC genotype was associated with asthenia (OR = 3.48; p = 0.009). In the oxaliplatin group, rs1045642 TT genotype was associated with the need to adjust treatment (OR = 0.32; p = 0.02), ERCC1 rs11615 GG genotype with asthenia (OR = 3.01; p = 0.01) and rs1615 GSTP1 GG genotype with respiratory toxicity (OR = 5.07; p = 0.009). ABCB1 rs1045642 T-allele reduces the need for treatment modification with both 5FU and oxaliplatin. Although several biomarkers predicted different toxic effects, they cannot be considered as risk factors for severe toxicity.

Evaluation of adverse effects of chemotherapy regimens of 5-fluoropyrimidines derivatives and their association with DPYD polymorphisms in colorectal cancer patients

BACKGROUND

5-Fluorouracil (5-FU) and capecitabine are fluoropyrimidine derivatives that mainly metabolized with dihydropyrimidine dehydrogenase enzyme (DPD). The genetic polymorphism in the genes encoding this enzyme may result in a decrease or loss of enzyme activity which may lead to the accumulation of medicines, their metabolites and potential toxicity.

METHOD

This cross-sectional study was conducted on 88 participants with colorectal cancer (CRC). After DNA extraction, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was used to determine the DPD gene (DPYD) polymorphisms including IVS 14 + 1 G > A, 2846 A > T and 2194 G > A. Chemotherapy-induced side effects were evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE Version 5.0).

RESULT

Data were collected from 227 chemotherapy cycles of 88 patients with CRC. In a comparison of FOLFOX and FOLFIRI regimens, there was no significant difference in the occurrence of chemotherapy-induced diarrhea, nausea, vomiting and oral mucositis. However, the peripheral neuropathy was more frequent in patients who were treated with FOLFOX (P <  0.001) and hair loss was more common in patients who received FOLFIRI regimen (P = 0.048). Incidence of the DPD IVS14 + 1 G > A polymorphism was observed in four patients (5.5%). There was no association between IVS14 + 1 G > A polymorphism and the occurrence of adverse reactions.

CONCLUSION

FOLFOX and FOLFIRI were the most common regimens in CRC patients and their toxicity profile was different in some adverse reactions. Prevalence of IVS14 + 1G > A variant was relatively higher than other similar studies.

TRIAL REGISTRATION

Approval code; IR.MAZUMS.REC.95.2480.

Clinical evaluation of germline polymorphisms associated with capecitabine toxicity in breast cancer: TBCRC-015

PURPOSE

Capecitabine is important in breast cancer treatment but causes diarrhea and hand-foot syndrome (HFS), affecting adherence and quality of life. We sought to identify pharmacogenomic predictors of capecitabine toxicity using a novel monitoring tool.

METHODS

Patients with metastatic breast cancer were prospectively treated with capecitabine (2000 mg/m²/day, 14 days on/7 off). Patients completed in-person toxicity questionnaires (day 1/cycle) and automated phone-in assessments (days 8, 15). Correlation of genotypes with early and overall toxicity was the primary endpoint.

RESULTS

Two hundred and fifty-nine patients were enrolled (14 institutions). Diarrhea and HFS occurred in 52% (17% grade 3) and 69% (9% grade 3), respectively. Only 29% of patients completed four cycles without dose reduction/interruption. In 39%, the highest toxicity grade was captured via phone. Three single nucleotide polymorphisms (SNPs) associated with diarrhea-DPYD*5 (odds ratio [OR] 4.9; P = 0.0005), a MTHFR missense SNP (OR 3.3; P = 0.02), and a SNP upstream of MTRR (OR 3.0; P = 0.03). GWAS elucidated a novel HFS SNP (OR 3.0; P = 0.0007) near TNFSF4 (OX40L), a gene implicated in autoimmunity including autoimmune skin diseases never before implicated in HFS. Genotype-gene expression analyses of skin tissues identified rs11158568 (associated with HFS via GWAS) with expression of CHURC1, a transcriptional activator controlling fibroblast growth factor (beta = - 0.74; P = 1.46 × 10^-23), representing a previously unidentified mechanism for HFS.

CONCLUSIONS

This is the first cancer pharmacogenomic study to use phone-in self-reporting, permitting augmented toxicity characterization. Three germline toxicity SNPs were replicated, and several novel SNPs/genes having strong functional relevance were discovered. If further validated, these markers could permit personalized capecitabine dosing.

Analysis of very important pharmacogene variants in the Tibetan population from China

Personalized medicine, the treatment best suited for an individual, is a hot field of clinical research in the world. Many recent studies have shown that genetic variations have a great influence on the treatment. This study aimed to identify the distribution differences of very important pharmacogene (VIP) variants between the Tibetan population and the other 26 populations from the 1000 Genomes project. Based on the PharmGKB database, we successfully genotyped 50 VIP variants located in 27 genes in the Tibetan population. We also compared the genotype frequencies of VIP variants between Tibetan population and the other 26 populations. Without adjustment, the Chi-square test showed that the only significant variant between Tibetans and every other group was rs1801159 in dihydropyrimidine dehydrogenase (DPYD), followed by rs1800566 in NAD(P)H quinone dehydrogenase 1 (NQO1) and rs1051296 in solute carrier family 19 member 1 (SLC19A1). After Bonferroni's multiple adjustments, the genotype frequencies distribution of DPYD rs1801159 was found to be different in Tibetans compared to the other 26 groups, apart from ACB and ASW. Moreover, genetic structure/F-statistics (Fst) analysis and the phylogenetic tree illustrated that Tibetans had a closer affinity with CDX, CHB, CHS, JPT and KHV. Our data will complement pharmacogenomics information of the Tibetan population and provide theoretical support for the realization of individualized medical treatment for Tibetans in the future.

The germline genetic component of drug sensitivity in cancer cell lines

Patients with seemingly the same tumour can respond very differently to treatment. There are strong, well-established effects of somatic mutations on drug efficacy, but there is at-most anecdotal evidence of a germline component to drug response. Here, we report a systematic survey of how inherited germline variants affect drug susceptibility in cancer cell lines. We develop a joint analysis approach that leverages both germline and somatic variants, before applying it to screening data from 993 cell lines and 265 drugs. Surprisingly, we find that the germline contribution to variation in drug susceptibility can be as large or larger than effects due to somatic mutations. Several of the associations identified have a direct relationship to the drug target. Finally, using 17-AAG response as an example, we show how germline effects in combination with transcriptomic data can be leveraged for improved patient stratification and to identify new markers for drug sensitivity.

Little is known about the contribution of germline genetic variants to cancer drug sensitivity. Here, the authors devise an approach for joint analysis of germline variants and somatic mutations, identifying substantial germline contributions to variation in drug sensitivity.

Pharmacogenetics of toxicity of 5-fluorouracil, doxorubicin and cyclophosphamide chemotherapy in breast cancer patients

The differences in patients' response to the same medication, toxicity included, are one of the major problems in breast cancer treatment. Chemotherapy toxicity makes a significant clinical problem due to decreased quality of life, prolongation of treatment and reinforcement of negative emotions associated with therapy. In this study we evaluated the genetic and clinical risk factors of FAC chemotherapy-related toxicities in the group of 324 breast cancer patients. Selected genes and their polymorphisms were involved in FAC drugs transport (ABCB1, ABCC2, ABCG2,SLC22A16), metabolism (ALDH3A1, CBR1, CYP1B1, CYP2C19, DPYD, GSTM1, GSTP1, GSTT1, MTHFR,TYMS), DNA damage recognition, repair and cell cycle control (ATM, ERCC1, ERCC2, TP53, XRCC1). The multifactorial risk models that combine genetic risk modifiers and clinical characteristics were constructed for 12 toxic symptoms. The majority of toxicities was dependent on the modifications in components of more than one pathway of FAC drugs, while the impact level of clinical factors was comparable to the genetic ones. For the carriers of multiple high risk factors the chance of developing given symptom was significantly elevated which proved the factor-dosage effect. We found the strongest associations between concurrent presence of clinical factors - overall and recurrent anemia, nephrotoxicity and early nausea and genetic polymorphisms in genes responsible for DNA repair, drugs metabolism and transport pathways. These results indicate the possibility of selection of the patients with expected high tolerance to FAC treatment and consequently with high chance of chemotherapy completion without the dose reduction, treatment delays and decline in the quality of life.

Role of Preemptive Genotyping in Preventing Serious Adverse Drug Events in South Korean Patients

INTRODUCTION

Preemptive and multi-variant genotyping is suggested to improve the safety of patient drug therapy. The number of South Koreans who would benefit from this approach is unknown.

OBJECTIVE

We aimed to quantify the number of patients who may experience serious adverse drug events (ADEs) due to high-risk pharmacogenetic variants and who may benefit from preemptive genotyping.

METHODS

The health claims dataset of the Korean Health Insurance Review and Assessment service for 3 % of the South Korean population for year 2011 was used to calculate the number of patients exposed to 84 drugs covered by National Health Insurance with pharmacogenomic biomarkers. The product of ADE risk-conferring genotype prevalence, ADE prevalence rates, and genotype effect sizes in South Koreans or East Asians derived from published literature and the 1000 Genomes Project, and the drug exposure data were solved to estimate the number of South Koreans in whom preemptive genotyping may prevent serious ADEs.

RESULTS

Among 1,341,077 patients in the dataset with prescriptions, 47.4 % were prescribed a drug whose response was affected by genetic variants and 31.9 % were prescribed at least one drug with serious ADEs modulated by these variants. Without genetic testing, the number of South Korean patients predicted to experience serious ADEs due to their higher ADE risk genotypes was estimated at 729. Extrapolating this to the total South Korean population indicated that approximately 24,300 patients in 2011 might have benefitted from preemptive genotyping.

CONCLUSIONS

This study quantified the number of South Korean patients predicted to have serious ADEs and demonstrated the need for preemptive genotyping to assist safer drug therapy in South Korea.

Dihydropyrimidine dehydrogenase pharmacogenetics for predicting fluoropyrimidine-related toxicity in the randomised, phase III adjuvant TOSCA trial in high-risk colon cancer patients

Background:

Dihydropyrimidine dehydrogenase (DPD) catabolises ∼85% of the administered dose of fluoropyrimidines. Functional DPYD gene variants cause reduced/abrogated DPD activity. DPYD variants analysis may help for defining individual patients’ risk of fluoropyrimidine-related severe toxicity.

Methods:

The TOSCA Italian randomised trial enrolled colon cancer patients for 3 or 6 months of either FOLFOX-4 or XELOX adjuvant chemotherapy. In an ancillary pharmacogenetic study, 10 DPYD variants (*2A rs3918290 G>A, *13 rs55886062 T>G, rs67376798 A>T, *4 rs1801158 G>A, *5 rs1801159 A>G, *6 rs1801160 G>A, *9A rs1801265 T>C, rs2297595 A>G, rs17376848 T>C, and rs75017182 C>G), were retrospectively tested for associations with ⩾grade 3 fluoropyrimidine-related adverse events (FAEs). An association analysis and a time-to-toxicity (TTT) analysis were planned. To adjust for multiple testing, the Benjamini and Hochberg’s False Discovery Rate (FDR) procedure was used.

Results:

FAEs occurred in 194 out of 508 assessable patients (38.2%). In the association analysis, FAEs occurred more frequently in *6 rs1801160 A allele carriers (FDR=0.0083). At multivariate TTT analysis, significant associations were found for *6 rs1801160 A allele carriers (FDR<0.0001), *2A rs3918290 A allele carriers (FDR<0.0001), and rs2297595 GG genotype carriers (FDR=0.0014). Neutropenia was the most common FAEs (28.5%). *6 rs1801160 (FDR<0.0001), and *2A rs3918290 (FDR=0.0004) variant alleles were significantly associated with time to neutropenia.

Conclusions:

This study adds evidence on the role of DPYD pharmacogenetics for safety of patients undergoing fluoropyrimidine-based chemotherapy.

Examination of multiple UGT1A and DPYD polymorphisms has limited ability to predict the toxicity and efficacy of metastatic colorectal cancer treated with irinotecan-based chemotherapy: a retrospective analysis

Background

To evaluate a new UGT1A and DPYD polymorphism panel to better predict irinotecan-induced toxicity and the clinical response in Chinese patients with metastatic colorectal cancer (mCRC).

Methods

The genotypes of UGT1A (UGT1A1*6, UGT1A1*27, UGT1A1*28, UGT1A7*2, UGT1A7*3, UGT1A7*4 and UGT1A9*22) and DPYD (DPYD*5, DPYD c.1896 T > C, and DPYD*2A) were examined by direct sequencing in 661 mCRC patients receiving irinotecan-based chemotherapy. The influences of UGT1A and DPYD polymorphisms on severe irinotecan-induced toxicities and clinical outcomes were assessed.

Results

In the cohort studied here, the incidence of UGT1A1*6, UGT1A1*28, UGT1A7*2, UGT1A7*3, UGT1A9*22, DPYD*5, and DPYD c.1896 T > C variants were 34.8%, 24.2%, 34.3%, 39.4%, 81.8%, 48.4% and 20.4%, respectively. UGT1A1*27 and DPYD*2A had low frequencies and UGT1A7*4 was not found. A total of 59 patients (8.9%) suffered severe diarrhea and 136 patients (20.6%) suffered severe neutropenia. UGT1A1*28 heterozygotes (OR = 2.263, 95%CI 1.395–3.670), UGT1A1*28 homozygotes (OR = 5.910, 95%CI 1.138–30.672) and UGT1A1*6 homozygotes (OR = 4.737, 95%CI 1.946–11.533) were independent risk factors for severe neutropenia. UGT1A polymorphisms were not found to relate to severe diarrhea. DPYD*5 was determined to be an independent risk factor for severe diarrhea (OR = 2.143, 95%CI 1.136–4.041). Neither DPYD*5 nor DPYD c.1896 T > C was found to relate to severe neutropenia. In the first-line irinotecan-based treatment, UGT1A1*28 and DPYD*5 contributed to higher response rates (P = 0.043 and P = 0.019, respectively), while DPYD*5 was found to associate with better progression-free survival (P = 0.015). UGT1A1*27 contributed to worse overall survival (P < 0.001).

Conclusion

Results still showed UGT1A1*6 and UGT1A1*28 to be partially associated with irinotecan-induced toxicity and clinical response. An examination of more UGT1A loci, except for UGT1A1*6 and UGT1A1*28, was not helpful to improve the predictive value of irinotecan-based toxicity and efficacy. An examination of DPYD*5 assisted in the prediction of severe diarrhea.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3406-2) contains supplementary material, which is available to authorized users.

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.

Network pharmacology of cancer: From understanding of complex interactomes to the design of multi-target specific therapeutics from nature

Despite massive investments in drug research and development, the significant decline in the number of new drugs approved or translated to clinical use raises the question, whether single targeted drug discovery is the right approach. To combat complex systemic diseases that harbour robust biological networks such as cancer, single target intervention is proved to be ineffective. In such cases, network pharmacology approaches are highly useful, because they differ from conventional drug discovery by addressing the ability of drugs to target numerous proteins or networks involved in a disease. Pleiotropic natural products are one of the promising strategies due to their multi-targeting and due to lower side effects. In this review, we discuss the application of network pharmacology for cancer drug discovery. We provide an overview of the current state of knowledge on network pharmacology, focus on different technical approaches and implications for cancer therapy (e.g. polypharmacology and synthetic lethality), and illustrate the therapeutic potential with selected examples green tea polyphenolics, Eleutherococcus senticosus, Rhodiola rosea, and Schisandra chinensis). Finally, we present future perspectives on their plausible applications for diagnosis and therapy of cancer.

Predictive and prognostic markers in the treatment of metastatic colorectal cancer (mCRC): personalized medicine at work

This article clarifies prognostic and predictive markers in the treatment of colorectal cancer. Multiple chemotherapeutic drugs are approved for metastatic colorectal cancer (mCRC), but available guidelines are often not helpful in directing drug selections. It would be desirable to define patient populations before chemotherapy by biomarkers that predict outcome and toxicities. RAS mutational evaluation remains the only established biomarker analysis in the treatment of mCRC. BRAF mutant tumors are associated with poor outcome. Chemotherapeutic combination therapies still remain the most active treatments in the armamentarium, and future trials should address the need to prospectively investigate and validate biomarkers.

Clinical validity of a DPYD-based pharmacogenetic test to predict severe toxicity to fluoropyrimidines

Pre-therapeutic DPYD pharmacogenetic test to prevent fluoropyrimidines (FL)-related toxicities is not yet common practice in medical oncology. We aimed at investigating the clinical validity of DPYD genetic analysis in a large series of oncological patients. Six hundred three cancer patients, treated with FL, have been retrospectively tested for eight DPYD polymorphisms (DPYD-rs3918290, DPYD-rs55886062, DPYD-rs67376798, DPYD-rs2297595, DPYD-rs1801160, DPYD-rs1801158, DPYD-rs1801159, DPYD-rs17376848) for association with Grade ≥3 toxicity, developed within the first three cycles of therapy. DPYD-rs3918290 and DPYD-rs67376798 were associated to Grade ≥3 toxicity after bootstrap validation and Bonferroni correction (p = 0.003, p = 0.048). DPYD-rs55886062 was not significant likely due to its low allelic frequency, nonetheless one out of two heterozygous patients (compound heterozygous with DPYD-rs3918290) died from toxicity after one cycle. Test specificity for the analysis of DPYD-rs3918290, DPYD-rs55886062 and DPYD-rs67376798 was assessed to 99%. Among the seven patients carrying one variant DPYD-rs3918290, DPYD-rs55886062 or DPYD-rs67376798 allele, not developing Grade ≥3 toxicity, 57% needed a FL dose or schedule modification for moderate chronic toxicity. No other DPYD polymorphism was associated with Grade ≥3 toxicity. Our data demonstrate the clinical validity and specificity of the DPYD-rs3918290, DPYD-rs55886062, DPYD-rs67376798 genotyping test to prevent FL-related Grade ≥3 toxicity and to preserve treatment compliance, and support its introduction in the clinical practice.

DPD and UGT1A1 deficiency in colorectal cancer patients receiving triplet chemotherapy with fluoropyrimidines, oxaliplatin and irinotecan

AIMS

Triplet chemotherapy with fluoropyrimidines, oxaliplatin and irinotecan is a standard therapy for metastatic colorectal cancer (CRC). Single nucleotide polymorphisms (SNPs) in DPYD and UGT1A1 influence fluoropyrimdines and irinotecan adverse events (AEs). Low frequency DPYD variants (c.1905 + 1G > A, c.1679 T > G, c.2846A > T) are validated but more frequent ones (c.496A > G, c.1129-5923C > G and c.1896 T > C) are not. rs895819 T > C polymorphism in hsa-mir-27a is associated with reduced DPD activity. In this study, we evaluated the clinical usefulness of a pharmacogenetic panel for patients receiving triplet combinations.

METHODS

Germline DNA was available from 64 CRC patients enrolled between 2008 and 2013 in two phase II trials of capecitabine, oxaliplatin and irinotecan plus bevacizumab or cetuximab. SNPs were determined by Real-Time PCR. We evaluated the functional variants in DPYD (rare: c.1905 + 1G > A, c.1679 T > G, c.2846A > T; most common: c.496A > G, c.1129-5923C > G, c.1896 T > C), hsa-mir-27a (rs895819) and UGT1A1 (*28) genes to assess their association with grade 3-4 AEs.

RESULTS

None of the patients carried rare DPYD variants. We found DPYD c.496A > G, c.1129-5923C > G, c.1896 T > C in heterozygosity in 19%, 5% and 8%, respectively, homozygous rs895819 in hsa-mir-27a in 9% and homozygous UGT1A1*28 in 8%. Grade 3-4 AEs were observed in 36% patients and were associated with DPYD c.496A > G (odds ratio (OR) 4.93, 95% CI 1.29, 18.87; P = 0.021) and homozygous rs895819 in hsa-mir-27a (OR 11.11, 95% CI 1.21, 102.09; P = 0.020). Carriers of DPYD c.1896 T > C and homozygous UGT1A1*28 showed an OR of 8.42 (95% CI 0.88, 80.56; P = 0.052). Multivariate analysis confirmed an independent value for DPYD c.496A > G and c.1896 T > C.

CONCLUSIONS

Concomitant assessment of DPYD variants and the UGT1A1*28 allele is a promising strategy needing further validation for dose personalization.

Undetected toxicity risk in pharmacogenetic testing for dihydropyrimidine dehydrogenase

Fluoropyrimidines, the mainstay agents for the treatment of colorectal cancer, alone or as a part of combination therapies, cause severe adverse reactions in about 10%–30% of patients. Dihydropyrimidine dehydrogenase (DPD), a key enzyme in the catabolism of 5-fluorouracil, has been intensively investigated in relation to fluoropyrimidine toxicity, and several DPD gene (DPYD) polymorphisms are associated with decreased enzyme activity and increased risk of fluoropyrimidine-related toxicity. In patients carrying non-functional DPYD variants (c.1905+1G>A, c.1679T>G, c.2846A>T), fluoropyrimidines should be avoided or reduced according to the patients’ homozygous or heterozygous status, respectively. For other common DPYD variants (c.496A>G, c.1129-5923C>G, c.1896T>C), conflicting data are reported and their use in clinical practice still needs to be validated. The high frequency of DPYD polymorphism and the lack of large prospective trials may explain differences in studies’ results. The epigenetic regulation of DPD expression has been recently investigated to explain the variable activity of the enzyme. DPYD promoter methylation and its regulation by microRNAs may affect the toxicity risk of fluoropyrimidines. The studies we reviewed indicate that pharmacogenetic testing is promising to direct personalised dosing of fluoropyrimidines, although further investigations are needed to establish the role of DPD in severe toxicity in patients treated for colorectal cancer.

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.

Influence of DPYD Genetic Polymorphisms on 5-Fluorouracil Toxicities in Patients with Colorectal Cancer: A Meta-Analysis

Our meta-analysis aggregated existing results from relevant studies to comprehensively investigate the correlations between genetic polymorphisms in dihydropyrimidine dehydrogenase (DPYD) gene and 5-fluorouracil (5-FU) toxicities in patients with colorectal cancer (CRC). The MEDLINE (1966∼2013), the Cochrane Library Database (Issue 12, 2013), EMBASE (1980∼2013), CINAHL (1982∼2013), Web of Science (1945∼2013), and the Chinese Biomedical Database (CBM) (1982∼2013) were searched without language restrictions. Meta-analyses were conducted with the use of STATA software (Version 12.0, Stata Corporation, College Station, TX, USA). Seven clinical cohort studies with a total of 946 CRC patients met our inclusion criteria, and NOS scores of each of the included studies were ≥5. Our findings showed that DPYD genetic polymorphisms were significantly correlated with high incidences of 5-FU-related toxicity in CRC patients. SNP-stratified analysis indicated that there were remarkable connections of IVS14+1G>A, 464T>A, and 2194G>A polymorphisms with the incidence of marrow suppression in CRC patients receiving 5-FU chemotherapy. Furthermore, we found that IVS14+1G>A, 496A>G, and 2194G>A polymorphisms were correlated with the incidence of gastrointestinal reaction. Ethnicity-stratified analysis also revealed that DPYD genetic polymorphisms might contribute to the development of marrow suppression and gastrointestinal reaction among Asians, but not among Caucasians. The present meta-analysis suggests that DPYD genetic polymorphisms may be correlated with the incidence of 5-FU-related toxicity in CRC patients.

Pharmacogenetics of cancer drugs

The variability in treatment outcomes among patients receiving the same therapy for seemingly similar tumors can be attributed in part to genetics. The tumor's (somatic) genome largely dictates the effectiveness of the therapy, and the patient's (germline) genome influences drug exposure and the patient's sensitivity to toxicity. Many potentially clinically useful associations have been discovered between common germline genetic polymorphisms and outcomes of cancer treatment. This review highlights the germline pharmacogenetic associations that are currently being used to guide cancer treatment decisions, those that are most likely to someday be clinically useful, and associations that are well known but their roles in clinical management are not yet certain. In the future, germline genetic information will likely be available from tumor genetic analyses, creating an efficient opportunity to integrate the two genomes to optimize treatment outcomes for each individual cancer patient.