Association of ABCB1 genetic polymorphisms with susceptibility to colorectal cancer and therapeutic prognosis

Correlation between ABCB1 and OLIG2 polymorphisms and the severity and prognosis of patients with cerebral infarction

This study investigated the relationship between ATP-binding cassette sub-family B member 1 (ABCB1) and OLIG2 single nucleotide polymorphism (SNP) and neurological injury severity and outcome in cerebral infarction (CI). The neurological injury severity of 298 CI patients was evaluated by the National Institutes of Health Stroke Scale. The prognosis of CI patients at 30 days after admission was evaluated by the modified Rankin Scale. And 322 healthy people were selected as the control group. The SNPs of the ABCB1 gene (rs1045642) and OLIG2 gene (rs1059004 and rs9653711) were detected by TaqMan probe PCR, and the distribution of SNPs genotype was analyzed. SNP rs9653711 was correlated with CI. Recessive models of rs1045642 and rs9653711 were correlated with CI. The genotypes of rs1045642 and rs9653711 and genetic models were associated with CI severity. rs1045642 had no correlation with CI prognosis, while rs9653711 had less correlation. The genotype distribution and recessive model were associated with CI prognosis. SNP rs1059004 was not associated with CI severity and prognosis. Alcohol consumption, hypertension, diabetes, hyperlipidemia, and high levels of homocysteine (HCY) were independent risk factors for CI, while hypertension, hyperlipidemia, and HCY were associated with poor prognosis of CI. ABCB1 rs1045642 and OLOG2 rs9653711 are associated with CI severity.

The Interaction between Four Polymorphisms and Haplotype of ABCB1, the Risk of Non-Small Cell Lung Cancer, and the Disease Phenotype

P-glycoprotein, product of the ABCB1 (ATP binding cassette subfamily B member 1) gene, has been reported to play an important role in multiple drug resistance during cancer therapy. However, its influence on non-small cell lung cancer (NSCLC) risk has not been clearly defined. The aim of the present study was to examine the association between clinicopathological factors and SNPs T-129C, C1236T, G2677T/A, and C3435T, as well as its haplotype, and to investigate the role of ABCB1 polymorphisms in NSCLC development. The study included 80 patients who suffered from NSCLC and underwent surgery to remove the tumour and 96 healthy controls. The tissues were genotyped by PCR-RFLP and sequencing methods, and the haplotype frequencies in both groups were estimated. The SNP C3435T was identified as a NSCLC risk factor. The presence of mutated allelic variant T (p=0.0103) or homozygote TT (p=0.0099) was observed significantly more often in cancer patients than in healthy controls. The two groups also demonstrated a highly significant difference in common haplotype frequency (p=0.01). The T_-129-T₁₂₃₆-T₂₆₇₇-T₃₄₃₅ haplotype was found to be most closely associated with NSCLC risk. Although the investigated polymorphisms were not related to demographic features, clinicopathological lung tumour characteristics, or blood morphology indices, marginally significant correlations were found with some variables: C1236T with age of disease onset (p=0.0410); C3435T with smoking status (p=0.0561). As the findings indicate, lung cancer and control groups demonstrate significantly different patterns of -129/1236/2677/3435 haplotype distribution; T-T-T-T haplotype contributes to NSCLC susceptibility, and this effect is probably mainly dependent on C3435T. So far, similar studies were published in other populations.

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.

ABC transporter superfamily. An updated overview, relevance in cancer multidrug resistance and perspectives with personalized medicine

The ATP binding-cassette superfamily corresponds the mostly transmembrane transporters family found in humans. These proteins actively transport endogenous and exogenous substrates through biological membranes in body tissues, so they have an important role in the regulation of many physiological functions necessary for human homeostasis, as well as in response regulation to several pharmacological substrates. The development of multidrug resistance has become one of the main troubles in conventional chemotherapy in different illnesses including cancer, being the increased efflux of antineoplastic drugs the main reason for this multidrug resistance, with a key role of the ABC superfamily. Likely, the interindividual variability in the pharmacological response among patients is well known, and may be due to intrinsically factors of the disease, genetic and environmental ones. Thus, the understanding of this variability, especially the genetic variability associated with the efficacy and toxicity of drugs, can provide a safer and more effective pharmacological treatment, so ABC genes are considered as important regulators due to their relationship with the reduction in pharmacological response. In this review, updated information about transporters belonging to this superfamily was collected, the possible role of these transporters in cancer, the role of genetic variability in their genes, as well as some therapeutic tools that have been tried to raise against main transporters associated with chemoresistance in cancer.

Effect of ABC transporter expression and mutational status on survival rates of cancer patients

ATP-binding cassette (ABC) transporters mediate multidrug resistance in cancer. In contrast to DNA single nucleotide polymorphisms in normal tissues, the role of mutations in tumors is unknown. Furthermore, the significance of their expression for prediction of chemoresistance and survival prognosis is still under debate. We investigated 18 tumors by RNA-sequencing. The mutation rate varied from 27,507 to 300885. In ABCB1, three hotspots with novel mutations were in transmembrane domains 3, 8, and 9. We also mined the cBioPortal database with 11,814 patients from 23 different tumor entities. We performed Kaplan-Meier survival analyses to investigate the effect of ABC transporter expression on survival rates of cancer patients. Novel mutations were also found in ABCA2, ABCA3, ABCB2, ABCB5, ABCC1-6, and ABCG2. Mining the cBioPortal database with 11,814 patients from 23 different tumor entities validated our results. Missense and in-frame mutations led to altered binding of anticancer drugs in molecular docking approaches. The ABCB1 nonsense mutation Q856* led to a truncated P-glycoprotein, which may sensitize tumors to anticancer drugs. The search for ABC transporter nonsense mutations represents a novel approach for precision medicine.. Low ABCB1 mRNA expression correlated with significantly longer survival in ovarian or kidney cancer and thymoma. In cancers of breast, kidney or lung, ABC transporter expression correlated with different tumor stages and human populations as further parameters to refine strategies for more individualized chemotherapy.

Pharmacogenomics to Predict Tumor Therapy Response: A Focus on ATP-Binding Cassette Transporters and Cytochromes P450

Pharmacogenomics is an evolving tool of precision medicine. Recently, due to the introduction of next-generation sequencing and projects generating "Big Data", a plethora of new genetic variants in pharmacogenes have been discovered. Cancer resistance is a major complication often preventing successful anticancer treatments. Pharmacogenomics of both somatic mutations in tumor cells and germline variants may help optimize targeted treatments and improve the response to conventional oncological therapy. In addition, integrative approaches combining copy number variations and long noncoding RNA profiling with germline and somatic variations seem to be a promising approach as well. In pharmacology, expression and enzyme activity are traditionally the more studied aspects of ATP-binding cassette transporters and cytochromes P450. In this review, we briefly introduce the field of pharmacogenomics and the advancements driven by next-generation sequencing and outline the possible roles of genetic variation in the two large pharmacogene superfamilies. Although the evidence needs further substantiation, somatic and copy number variants as well as rare variants and common polymorphisms in these genes could all affect response to cancer therapy. Regulation by long noncoding RNAs has also been shown to play a role. However, in all these areas, more comprehensive studies on larger sets of patients are needed.

Association between MDR1 polymorphisms and XELIRI and XELOX chemoresistance in Saudi patients with colorectal cancer

Multidrug resistance member 1 (MDR1) is located on chromosome 7 and encodes P-glycoprotein, which is universally accepted as a drug resistance biomarker. MDR1 polymorphisms can alter protein expression or function, which has been previously reported to associate with various types of malignancies, such as colorectal cancer (CRC). Therefore, the present study aimed to determine the effects of MDR1 polymorphisms on drug responses of Saudi patients with CRC. DNA samples were obtained from 62 patients with CRC and 100 healthy controls. Genotypes and allele frequencies of MDR1 single nucleotide polymorphisms (SNPs) G2677T and T1236C were determined using the PCR-restriction fragment length polymorphism procedure. The results showed no significant differences in the genotype distribution and allele frequency of T1236C between patients with CRC and controls. However, G2677T was found to serve a highly significant role in protecting against the progression of CRC. In addition, none of the genotypes in SNPs T1236C and G2677T was found to affect chemoresistance to XELIRI and XELOX. In conclusion, although T1236C in the MDR1 gene is not associated with CRC risk, G2677T protects against the development of CRC. Neither of the MDR1 SNPs tested were associated with the risk of chemoresistance. Therefore, these two SNPs cannot be used as molecular markers for predicting drug response in patients with CRC.

Brazilian cohort and genes encoding for drug-metabolizing enzymes and drug transporters

Background & aim: Genetic variability in drug absorption, distribution, metabolism and excretion (ADME) genes contributes to the high heterogeneity of drug responses. The present study investigated polymorphisms of ADME genes frequencies and compared the findings with populations from other continents, available in the 1000 Genome Project (1 KGP) and the Exome Aggregation Consortium (ExAC) databases. Methodology & results: We conducted a study of 100 patients in Brazil and a total of 2003 SNPs were evaluated by targeted next-generation sequencing in 148 genes, including Phase I enzymes (n = 50), Phase II enzymes (n = 38) and drug transporters (n = 60). Overall, the distribution of minor allele frequency (MAF) suggests that the distribution of 2003 SNPs is similar between Brazilian cohort, 1 KGP and ExAC; however, we found moderate SNP allele-frequency divergence between Brazilian cohort and both 1000 KGP and ExAC. These differences were observed in several relevant genes including CYP3A4, NAT2 and SLCO1B1. Conclusion: We concluded that the Brazilian population needs clinical assessment of drug treatment based on individual genotype rather than ethnicity.

Association between ABCB1 (3435C>T) polymorphism and susceptibility of colorectal cancer: A meta-analysis

Studies on the relationship between ABCB1 3435C>T polymorphism (rs1045642) and colorectal cancer (CRC)susceptibility have yielded inconclusive results. To clarify this issue, we undertook a meta-analysis to investigate the relationship between rs1045642 and CRC risk.Three electronic scientific publication databases (Cochrane Library, Pubmed, Embase) were screened using specific search terms. Relevant literature was identified using literature traceability methods. Selected publications were evaluated according to the inclusion and exclusion criteria. Effect size information (odds ratio and the corresponding 95% confidence interval [CI]) was obtained following quality assessment and data extraction from the included publications, and a meta-analysis conducted. Statistical analysis was performed with the Stata sofz (Version 13.0) software.Overall, 17 case-control studies involving 7129 CRC patients and 7710 healthy control subjects satisfied the criteria for inclusion in the meta-analysis. There was no significant association between ABCB1 3435C>T polymorphism and CRC risk in any of the genetic models. In the CC versus CT model (I = 20.9%, Pheterogeneity = .276), CC versus CT + TT model (I = 45.6%, Pheterogeneity = .102) and CT versus CC + TT model (I = 17.8%, Pheterogeneity = .298) analyses, between-study heterogeneities were detected as significant in Asian populations. In the CT versus TT model (I = 24%, Pheterogeneity = .254) and CC + CT versus TT model (I = 0, Pheterogeneity = .55), between-study heterogeneities were found to be significant in groups of different populations.The meta-analysis described here suggests that the ABCB1 3435C>T polymorphism is not related to CRC susceptibility.

ABCB1 variants C3435T and T129C are not associated with colorectal cancer risk

Background

Colorectal cancer (CRC) is one of the most prevalent cancers in Saudi Arabia that is highly characterized with poor survival rate and advanced metastasis. Many studies contribute this poor outcome to the expression of ABC transporters on the surface of cancer cells.

Objectives

In this study, two ABCB1 variants, C3435T and T129C, were examined to evaluate their contribution to CRC risk.

Methods

125 subjects (62 CRC patients and 63 healthy controls) were involved. The DNA was isolated and analyzed with PCR-RFLP to determine the different genotypes. The hardy-Weinberg equilibrium was performed to determine genotype distribution and allele frequencies. Fisher's exact test (two-tailed) was used to compare allele frequencies between patients and control subjects.

Results

The study showed that for SNP C3435T, the population of both CRC patients and controls were out of Hardy-Weinberg equilibrium. Genotype distribution for CRC patients was (Goodness of fit χ2 = 20, df= 1, P≤0.05), whereas, for the controls the genotype distribution was (Goodness of fit χ2 = 21, df =1, P ≤0.05). For SNP T129C, all subjects showed normal (TT) genotype.

Conclusion

There was no significant association between ABCB1 3435C>T and 129T>C polymorphisms with CRC risk.

Midostaurin Reverses ABCB1-Mediated Multidrug Resistance, an in vitro Study

Overexpression of ABC transporters in cancer cells is an underlying mechanism of multidrug resistance (MDR), leading to insensitive response to chemotherapeutic strategies. Thus, MDR is often results in treatment failure in the clinic. In this study, we found midostaurin, a Food and Drug Administration (FDA)-approved anti-leukemia drug, can antagonize ATP-binding cassette subfamily B member 1 (ABCB1)-mediated MDR. Our results indicated that midostaurin has the capacity to antagonize ABCB1-mediated MDR, while no significant reversal effect was found on ATP-binding cassette subfamily G member 2 (ABCG2)-mediated MDR. Our subsequent resistance mechanism studies showed that midostaurin directly inhibited the efflux function of the ABCB1 transporter without alteration of the expression level or the subcellular localization of ABCB1 transporter. In addition, midostaurin inhibited the ATPase activity of ABCB1 transporter in a dose-dependent manner. Moreover, our in silico docking study predicted that midostaurin could interact with the substrate-binding sites of ABCB1 transporter. This novel finding could provide a promising treatment strategy that co-administrating midostaurin with anticancer drugs in the clinic could overcome MDR and improve the efficiency of cancer treatment.

Polymorphisms in DNA repair pathway genes and ABCG2 gene in advanced colorectal cancer: correlation with tumor characteristics and clinical outcome in oxaliplatin-based chemotherapy

Objective

Multiple factors are involved in oxaliplatin-resistant process in colorectal cancer (CRC) patients including decreased drug accumulation and enhanced capacity to repair and tolerate DNA damage. In the present study, we aimed to assess the impact of six single-nucleotide polymorphisms (SNPs) in DNA repair genes and ABCG2 gene on prognosis in advanced CRC patients treated with oxaliplatin-based chemotherapy.

Methods

In this study, 580 advanced CRC patients were recruited. Six SNPs of DNA repair genes (XPA rs10817938, XPA rs2808668, XPC rs2607775, and WRN rs1346044) and ABCG2 gene (rs2231142 and rs2622621) were genotyped by using the TaqMan assay.

Results

Regarding interaction with environmental factors, ABCG2 rs2231142 and the first-degree family history of cancer and XPC rs2607775 or ABCG2 rs2622621 and lymph node metastases status demonstrated significant interactions. Of these six SNPs, XPA rs10817938 CT/ TT genotypes retained its significant association with longer overall survival (OS) (P=0.008) in CRC patients receiving oxaliplatin-based chemotherapy (n=580). Furthermore, a significantly better impact on the disease-free survival (DFS) (P=0.001) and OS (P<0.0001) was found in ABCG2 rs2231142CA/AA carriers. Furthermore, ABCG2 rs2622621 CG/GG genotype was verified to be an independent poor prognostic factor in DFS (P=0.010) and OS (P=0.030). In the stratification analysis, XPA rs10817938 CT/CC, rs2231142 CA/AA, and rs2622621 CC genotypes of ABCG2 were predictive of significantly better prognosis in the patients with tumor differentiation grade 3 (n=523), clinical stage IV (n=73), or lymph node-positive status (n=557). Additionally, multivariate logistic regression and multiple dimension reduction analysis consistently revealed that the combination of selected SNPs and five known risk factors showed a better prediction prognosis and represented the best model to predict CRC prognosis.

Conclusion

The current data indicated that the XPA gene and ABCG2 gene had significant interaction with environmental factors and prognosis, which could provide a comprehensive understanding of the implications of those SNPs in the prediction of prognosis in advanced CRC patients receiving oxaliplatin-based chemotherapy.

Selonsertib (GS-4997), an ASK1 inhibitor, antagonizes multidrug resistance in ABCB1- and ABCG2-overexpressing cancer cells

Overexpression of ATP-binding cassette (ABC) transporters is one of the most important mechanisms responsible for the development of multidrug resistance (MDR). Selonsertib, a serine/threonine kinase inhibitor, targets apoptosis signal-regulating kinase 1 (ASK1) and is now in phase III clinical trial for the treatment of non-alcoholic steatohepatitis (NASH). In this study, we investigated whether selonsertib could reverse MDR-mediated by ABC transporters, including ABCB1, ABCG2, ABCC1 and ABCC10. The results showed that selonsertib significantly reversed ABCB1- and ABCG2-mediated MDR, but not MDR-mediated by ABCC1 or ABCC10. Mechanism studies indicated that the reversal effect of selonsertib was related to the attenuation of the efflux activity of ABCB1 and ABCG2 transporters, without the protein level decrease or change in the subcellular localization of ABCB1 or ABCG2. Selonsertib stimulated the ATPase activity of ABCB1 and ABCG2 in a concentration-dependent manner, and in silico docking study showed selonsertib could interact with the substrate-binding sites of both ABCB1 and ABCG2. This study provides a clue into a novel treatment strategy, which includes a combination of selonsertib with antineoplastic drugs to attenuate MDR-mediated by ABCB1 or ABCG2 in cancer cells overexpressing these transporters.

Population Pharmacokinetics and Adverse Events of Erlotinib in Japanese Patients with Non-small-cell Lung Cancer: Impact of Genetic Polymorphisms in Metabolizing Enzymes and Transporters

Determinants of interindividual variability in erlotinib pharmacokinetics (PK) and adverse events remain to be elucidated. This study with 50 Japanese non-small-cell lung cancer patients treated with oral erlotinib at a standard dose of 150 mg aimed to investigate whether genetic polymorphisms affect erlotinib PK and adverse events. Single nucleotide polymorphisms (SNPs) in genes encoding metabolizing enzymes (CYP1A1, CYP1A2, CYP2D6, CYP3A4, CYP3A5, UGT1A1, UGT2B7, GSTM1, and GSTT1) or efflux transporters (ABCB1, and ABCG2) were analyzed as covariates in a population PK model. The ABCB1 1236C>T (rs1128503) polymorphism, not ABCB1*2 haplotype (1236TT-2677TT-3455TT, rs1128503 TT-rs2032582 TT-rs1045642 TT), was a significant covariate for the apparent clearance (CL/F), with the TT genotype showing a 29.4% decrease in CL/F as compared with the CC and the CT genotypes. A marginally higher incidence of adverse events (mainly skin rash) was observed in the TT genotype group; however, patients with high plasma erlotinib exposure did not always experience skin rash. None of the other SNPs affected PK or adverse events. The ABCB1 genotype is a potential predictor for erlotinib adverse events. Erlotinib might be used with careful monitoring of adverse events in patients with ABCB1 polymorphic variants.

Haplotypes of ABCB1 1236C >T (rs1128503), 2677G >T/A (rs2032582), and 3435C >T (rs1045642) in patients with bullous pemphigoid

Bullous pemphigoid (BP) constitutes the most prevalent disease in the group of bullous dermatoses with the autoimmune background. Some authors suggest that certain cytokines (IL-2, IFN-γ) may be transported by P-glycoprotein (P-gp), the product of the ABCB1 gene. ABCB1 polymorphism might affect not only the effectiveness of treatment with drugs that are P-gp substrates but also contribute to the development of diseases, including BP. In the present work, we resolved to conduct a haplotype analysis of ABCB1 in patients with BP and to answer the question of whether any of the haplotypes are able to affect the incidence of this entity. The study involved 71 patients with BP and 100 healthy volunteers. Determination of polymorphisms 1236C > T and 3435C > T in ABCB1 was carried out with the PCR-RFLP (Polymerase Chain Reaction-Restriction Fragment Length Polymorphism) method. The 2677G > T/A ABCB1 polymorphism was analyzed with the allele-specific PCR method. It was observed that the 1236T-2677G-3435T haplotype occurred with a statistically significantly lower frequency in patients with BP than in controls (1.4 vs. 10.0%). Carriers of this haplotype were also shown to have had a low relative risk for BP (OR = 0.13, p = 0.003). Haplotype analysis of ABCB1 conducted in patients with BP demonstrated that the 1236T-2677G-3435T haplotype may protect against development of this entity.

Associations between genetic polymorphisms of membrane transporter genes and prognosis after chemotherapy: meta-analysis and finding from Seoul Breast Cancer Study (SEBCS)

Membrane transporters can be major determinants of the pharmacokinetic profiles of anticancer drugs. The associations between genetic variations of ATP-binding cassette (ABC) and solute carrier (SLC) genes and cancer survival were investigated through a meta-analysis and an association study in the Seoul Breast Cancer Study (SEBCS). Including the SEBCS, the meta-analysis was conducted among 38 studies of genetic variations of transporters on various cancer survivors. The population of SEBCS consisted of 1338 breast cancer patients who had been treated with adjuvant chemotherapy. A total of 7750 SNPs were selected from 453 ABC and/or SLC genes typed by an Affymetrix 6.0 chip. ABCB1 rs1045642 was associated with poor progression-free survival in a meta-analysis (HR = 1.33, 95% CI: 1.07-1.64). ABCB1, SLC8A1, and SLC12A8 were associated with breast cancer survival in SEBCS (P_gene < 0.05). ABCB1 rs1202172 was differentially associated with survival depending on the chemotherapy (P_interaction = 0.035). Our finding provides suggestive associations of membrane transporters on cancer survival.

Association between MDR1 C3435T polymorphism and colorectal cancer risk: A meta-analysis

BACKGROUND

The multidrug resistance gene 1(MDR1) C3435T polymorphism has been reported to be associated with colorectal cancer (CRC) risk in Asians, however the results were inconsistent. Thus, we performed a meta-analysis to generate large-scale evidence on the association between C3435T polymorphism and CRC risk in Asian populations.

METHODS

The PubMed, Web of Science, Embase, CNKI, and Chinese Biomedicine databases were searched up to January 15, 2017. The odd ratios (ORs) and 95% confidence intervals (95% CIs) were calculated by a fixed-effects or random-effects model. Sensitivity and cumulative meta-analysis were also performed.

RESULTS

A total of 7 studies involving 4818 individuals were included in this pooled-analysis. The results suggested that persons carrying a T allele at the C3435T polymorphism had a significantly decreased risk of CRC in Asian population (T vs C: OR = 0.897, 95%CI = 0.826-0.975, P = .01), and the significant association was also observed in another 2 genetic models (TT vs CC: OR = 0.721, 95%CI = 0.605-0.861, P < .001; TT vs TC+CC: OR = 0.679, 95%CI = 0.579-0.795, P < .001). Moreover, the results of sensitivity and cumulative meta-analysis indicated the stable of our results. Finally, funnel plot and Egger's test showed no evidence of publication bias.

CONCLUSIONS

In summary, this meta-analysis provided evidence that MDR1 C3435T polymorphism is associated with a decreased risk of CRC in Asian population.

Clinically relevant genetic variants of drug-metabolizing enzyme and transporter genes detected in Thai children and adolescents with autism spectrum disorder

Single-nucleotide polymorphisms (SNPs) among drug-metabolizing enzymes and transporters (DMETs) influence the pharmacokinetic profile of drugs and exhibit intra- and interethnic variations in drug response in terms of efficacy and safety profile. The main objective of this study was to assess the frequency of allelic variants of drug absorption, distribution, metabolism, and elimination-related genes in Thai children and adolescents with autism spectrum disorder. Blood samples were drawn from 119 patients, and DNA was extracted. Genotyping was performed using the DMET Plus microarray platform. The allele frequencies of the DMET markers were generated using the DMET Console software. Thereafter, the genetic variations of significant DMET genes were assessed. The frequencies of SNPs across the genes coding for DMETs were determined. After filtering the SNPs, 489 of the 1,931 SNPs passed quality control. Many clinically relevant SNPs, including CYP2C19*2, CYP2D6*10, CYP3A5*3, and SLCO1B1*5, were found to have frequencies similar to those in the Chinese population. These data are important for further research to investigate the interpatient variability in pharmacokinetics and pharmacodynamics of drugs in clinical practice.

Role of ABC transporters in fluoropyrimidine-based chemotherapy response

Since over 50 years, 5-fluorouracil (5-FU) is in use as backbone of chemotherapy treatment regimens for a wide range of cancers including colon, breast, and head and neck carcinomas. However, drug resistance and severe toxicities such as mucositis, diarrhea, neutropenia, and vomiting in up to 40% of treated patients often lead to dose limitation or treatment discontinuation. Because the oral bioavailability of 5-FU is unpredictable and highly variable, 5-FU is commonly administered intravenously. To overcome medical complications and inconvenience associated with intravenous administration, the oral prodrugs capecitabine and tegafur have been developed. Both fluoropyrimidines are metabolically converted intracellularly to 5-FU, which then needs metabolic activation to exert its damaging activity on RNA and DNA. The low response rates of 10-15% of 5-FU monotherapy can be improved by combination regimens of infusional 5-FU and leucovorin together with oxaliplatin (FOLFOX) or irinotecan (FOLFIRI), thereby increasing response rates to 30-40%. The impact of metabolizing enzymes in the development of fluoropyrimidine toxicity and resistance has been studied in great detail. In addition, membrane drug transporters, which are critical determinants of intracellular drug concentrations, may play a role in occurrence of toxicity and development of resistance against fluoropyrimidine-based therapy as well. This review therefore summarizes current knowledge on the role of drug transporters with particular focus on ATP-binding cassette transporters in fluoropyrimidine-based chemotherapy response.

A systematic review and meta-analysis of somatic and germline DNA sequence biomarkers of esophageal cancer survival, therapy response and stage

Recent advances in next generation sequencing reinforce the potential for DNA sequence markers to guide esophageal cancer management. We report the first systematic review and meta-analysis, identifying 94 markers of outcome and 41 of stage. Overall, evidence was poor. Meta-analyses demonstrated outcome associations for 6 tumor and 9 germline variants: priorities for prospective evaluation.

Introduction

There is an urgent need for biomarkers to help predict prognosis and guide management of esophageal cancer. This review identifies, evaluates and meta-analyses the evidence for reported somatic and germline DNA sequence biomarkers of outcome and stage.

Methods

A systematic review was carried out of the PubMed, EMBASE and Cochrane databases (20 August 2014), in conjunction with the ASCO Level of Evidence scale for biomarker research. Meta-analyses were carried out for all reported markers associated with outcome measures by more than one study.

Results

Four thousand and four articles were identified, 762 retrieved and 182 studies included. There were 65 reported markers of survival or recurrence 12 (18.5%) were excluded due to multiple comparisons. Following meta-analysis, significant associations were seen for six tumor variants (mutant TP53 and PIK3CA, copy number gain of ERBB2/HER2, CCND1 and FGF3, and chromosomal instability/ploidy) and seven germline polymorphisms: ERCC1 rs3212986, ERCC2 rs1799793, TP53 rs1042522, MDM2 rs2279744, TYMS rs34743033, ABCB1 rs1045642 and MTHFR rs1801133. Twelve germline markers of treatment complications were reported; 10 were excluded. Two tumor and 15 germline markers (11 excluded) of chemo (radio)therapy response were reported. Following meta-analysis, associations were demonstrated for mutant TP53, ERCC1 rs11615 and XRCC1 rs25487. There were 41 tumor/germline reported markers of stage; 27 (65.9%) were excluded.

Conclusions

Numerous DNA markers of outcome and stage have been reported, yet few are backed by high-quality evidence. Despite this, a small number of variants appear reliable. These merit evaluation in prospective trials, within the context of high-throughput sequencing and gene expression.

FOLFOX/FOLFIRI pharmacogenetics: The call for a personalized approach in colorectal cancer therapy

While 5-fluorouracil used as single agent in patients with metastatic colorectal cancer has an objective response rate around 20%, the administration of combinations of irinotecan with 5-fluorouracil/folinic acid or oxaliplatin with 5-fluorouracil/folinic acid results in significantly increased response rates and improved survival. However, the side effects of systemic therapy such as myelotoxicity, neurotoxicity or gastrointestinal toxicity may lead to life-threatening complications and have a major impact on the quality of life of the patients. Therefore, biomarkers that would be instrumental in the choice of optimal type, combination and dose of drugs for an individual patient are urgently needed. The efficacy and toxicity of anticancer drugs in tumor cells is determined by the effective concentration in tumor cells, healthy tissues and by the presence and quantity of the drug targets. Enzymes active in drug metabolism and transport represent important determinants of the therapeutic outcome. The aim of this review was to summarize published data on associations of gene and protein expression, and genetic variability of putative biomarkers with response to therapy of colorectal cancer to 5-fluorouracil/leucovorin/oxaliplatin and 5-fluorouracil/leukovorin/irinotecan regimens. Gaps in the knowledge identified by this review may aid the design of future research and clinical trials.

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.

Clinical importance of recently discovered gene variants in colon cancer recurrence and prognosis

SUMMARY 

Colorectal cancer survival has increased over the past few years, mainly due to the advances in the metastatic setting. Nonetheless, in the adjuvant scenario, minor improvements have been made, as the tumor's anatomopathological features remain to be most important factors for predicting the risk of recurrence and the prognosis. A deeper understanding of the molecular mechanisms involved in colorectal carcinogenesis, progression, invasion and metastasis development, have laid the groundwork for the search of genetic biomarkers that can help identify patients at a higher risk of recurrence. Common germline variants in genes within molecular pathways responsible for cancer development and progression have proven to influence the probability of relapse and the patient's prognosis. Here, we systematically review the relevance of genetic variants as prognostic biomarkers in colorectal carcinoma.