Influence of polymorphisms of ABCB1 and ABCC2 on mRNA and protein expression in normal and cancerous kidney cortex

Pharmacogenetic insights into ABCB1, ABCC2, CYP1A2, and CYP2B6 variants with epilepsy susceptibility among Egyptian Children: A retrospective case-control study

BACKGROUND

Pediatric epilepsy is a complicated neuropsychiatric disorder that is characterized by recurrent seizures and unusual synchronized electrical activities within brain tissues. It has a substantial effect on the quality of life of children, thus understanding of the hereditary considerations influencing epilepsy susceptibility and the response to antiepileptic medications is crucial. This study focuses on assessing the correlation of the ABCB1, ABCC2, CYP1A2, and CYP2B6 genetic polymorphisms with the susceptibility to epileptic seizures and their contributions to antiepileptic medication throughout the course of the disease.

METHODS

This study included 134 Egyptian epileptic children, comprising 67 drug-responsive and 67 drug-resistant patients, along with 124 healthy controls matching for age, gender, and geographical district. Genotyping of the rs2032582, rs717620, rs2273697, rs762551, and rs3745274 variants was performed using the PCR technique. Statistical analyses, including haplotype, multivariate, logistic regression, and bioinformatics approaches, were conducted to evaluate the associations within the disease.

RESULTS

The ABCC2*rs717620 (T allele) revealed an increased risk of epilepsy compared to healthy controls (OR = 2.12, p-value < 0.001), with the rs717620 (C/T + T/T genotypes) showing significant differences between drug-responsive and drug-resistant patients (p-value < 0.05). Moreover, the ABCC2*rs2273697 (A allele) indicated a decreased risk of epileptic seizures compared to healthy controls (OR = 0.51, p-value = 0.033), with the rs2273697 (G/A + A/A genotypes) indicating a significant association with drug-resistant patients (OR = 0.21, p-value = 0.002). The rs717620*T/rs2273697*G haplotype was significantly correlated with an elevated risk of epileptic seizures within drug-responsive patients (OR = 2.26, p-value = 0.019). Additionally, the CYP1A2*rs762551 (A allele) represented a protective effect against epilepsy susceptibility (OR = 0.50, p-value < 0.001), with the rs762551 (G/A + A/A genotypes) disclosing a substantial association with a decreased risk of epileptic seizures among drug-resistant patients compared to drug-responsive patients (OR = 0.07, p-value < 0.001). Conversely, the ABCB1*rs2032582 (G allele) and the CYP2B6*rs3745274 (T allele) did not attain a significant difference with the epilepsy risk compared to healthy controls (p-value > 0.05).

CONCLUSIONS

The findings of our study emphasize the importance of pharmacogenetic screening in epilepsy research, particularly regarding to drug-resistant patients. The ABCC2*rs717620 variant conferred a significant correlation with elevated risk of epileptic seizures, while the ABCC2*rs2273697 and CYP1A2*rs762551 variants confirmed their contributions as protective markers against epilepsy development. Conversely, the ABCB1*rs2032582 and CYP2B6*rs3745274 alleles were not considered as independent risk factors with the course of epilepsy disease.

ABCB1 Is Frequently Methylated in Higher-Grade Gliomas and May Serve as a Diagnostic Biomarker of More Aggressive Tumors

ABCB1 belongs to a superfamily of membrane transporters that use ATP hydrolysis to efflux various endogenous compounds and drugs outside the cell. Cancer cells upregulate ABCB1 expression as an adaptive response to evade chemotherapy-mediated cell death. On the other hand, several reports highlight the role of the epigenetic regulation of ABCB1 expression. In fact, the promoter methylation of ABCB1 was found to be methylated in several tumor types, including gliomas, but its role as a biomarker is not fully established yet. Thus, the aim of this study was to analyze the methylation of the ABCB1 promoter in tumor tissues from 50 glioma patients to verify its incidence and to semi-quantitively detect ABCB1 methylation levels in order to establish its utility as a potential biomarker. The results of this study show a high interindividual variability in the ABCB1 methylation level of the samples derived from gliomas of different grades. Additionally, a positive correlation between ABCB1 methylation, the WHO tumor grade, and an IDH1 wild-type status has been observed. Thus, ABCB1 methylation can be regarded as a potential diagnostic or prognostic biomarker for glioma patients, indicating more aggressive tumors.

Association of UGT1A1*6, UGT1A1*28, or ABCC2 c.3972C>T genetic polymorphisms with irinotecan-induced toxicity in Asian cancer patients: Meta-analysis

Effects of UGT1A1*6 and UGT1A1*28 genetic polymorphisms on irinotecan-induced severe toxicities in Asian cancer patients are inconclusive. Also, ABCC2 c.3972C>T may affect toxicity of irinotecan. The aim was to assess the aggregated risk of neutropenia or diarrhea in Asian cancer patients taking irinotecan and inherited UGT1A1*6, UGT1A1*28, or ABCC2 c.3972C>T genetic variants. A PubMed literature search for eligible studies was conducted. Odds ratios (ORs) were measured using RevMan software where p values <0.05 were statistically significant. Patients that inherited both UGT1A1*6 and UGT1A1*28 genetic variants (heterozygous: UGT1A1*1/*6 + *1/*28 and homozygous: UGT1A1*6/*6 + *28/*28) were significantly associated with increased risk of neutropenia and diarrhea compared to patients with UGT1A1*1/*1 (neutropenia: OR 2.89; 95% CI 1.97-4.23; p < 0.00001; diarrhea: OR 2.26; 95% CI 1.71-2.99; p < 0.00001). Patients carrying homozygous variants had much stronger effects in developing toxicities (neutropenia: OR 6.23; 95% CI 3.11-12.47; p < 0.00001; diarrhea: OR 3.21; 95% CI 2.13-4.85; p < 0.00001) than those with heterozygous variants. However, patients carrying the ABCC2 c.3972C>T genetic variant were not significantly associated with neutropenia (OR 1.67; 95% CI 0.98-2.84; p = 0.06) and were significantly associated with a reduction in irinotecan-induced diarrhea (OR 0.31; 95% CI 0.11-0.81; p = 0.02). Asian cancer patients should undergo screening for both UGT1A1*6 and UGT1A1*28 genetic variants to reduce substantially irinotecan-induced severe toxicities.

Pharmacokinetics of free and total mycophenolic acid in paediatric and adult renal transplant recipients: Exploratory analysis of the effects of clinical factors and gene variants

Clinical and genetic influencing factors on free fraction of mycophenolic acid (MPA) have rarely been discussed. The present study investigated whether the clinical and genetic factors could explain the variability in the pharmacokinetics of free MPA (fMPA) and total MPA (tMPA) in Chinese paediatric and adult renal transplant recipients. Twenty-eight paediatric and 31 adult patients were enrolled, and the concentrations of tMPA and fMPA were determined at 0 h (predose) and 0.5, 1, 1.5, 2, 4, 5, 8, 9, 10 and 12 h after mycophenolate mofetil administration. Genetic polymorphisms of UGTs (rs671448, rs1042597, rs2741049, rs62298861, rs7439366, rs12233719) and ABCC2 (rs717620) were simultaneously determined. The clinical and genetic data were analysed and reported. tMPA and fMPA concentrations adjusted for dose per body weight were consistently higher in adults than in paediatric patients. In the paediatric group, only albumin and time after transplantation correlated significantly with the MPA-free fraction variation, which could explain 32.4% of the variability. Besides, ABCC2 polymorphism, albumin and time after transplantation correlated significantly with the MPA-free fraction variation in adults, which could explain 56.9% of the variability. The influencing factors in the paediatric group are different from those in adults, which may be due to age-related transporter expression.

Pharmacogenetic Profiling in High-Risk Soft Tissue Sarcomas Treated with Neoadjuvant Chemotherapy

Neoadjuvant chemotherapy based on anthracyclines and ifosfamide for high-risk soft tissue sarcomas (STS) of the extremities and trunk is a controversial treatment option. There are substantial interindividual differences in clinical outcomes in patients treated with neoadjuvant chemotherapy. The aim of this study was to evaluate, as biomarkers, polymorphisms in genes encoding drug-metabolizing enzymes, drug transporters, or drug targets and their association with toxicity and survival in STS patients treated with neoadjuvant chemotherapy. We analysed variants in genes involved in anthracycline metabolism (ABCB1, ABCC2, NQO1, CBR3, and SLC22A16) and in ifosfamide catabolism (ALDH1A1) in 79 treated patients. Two genes showed significant association after adjusted multivariate analysis: ABCC2 and ALDH1A1. In patients treated with anthracyclines, ABCC2 rs3740066 was associated with risk of febrile neutropenia (p = 0.031), and with decreased overall survival (OS) (p = 0.024). ABCC2 rs2273697 was associated with recurrence-free survival (RFS) (p = 0.024). In patients treated with ifosfamide, ALDH1A1 rs3764435 was associated with RFS (p = 0.046). Our pharmacogenetic study shows for the first time that variants in genes regulating the metabolism of neoadjuvant chemotherapy may be helpful to predict toxicity and survival benefit in high-risk STS treated with neoadjuvant chemotherapy. Further validation studies are needed to establish their clinical utility.

Associations Between Genetic Polymorphisms Within Transporter Genes and Clinical Response to Methotrexate in Chinese Rheumatoid Arthritis Patients: A Pilot Study

Purpose

To investigate the associations between genetic polymorphisms within transporter genes and clinical response to methotrexate (MTX) in Chinese rheumatoid arthritis (RA) patients.

Patients and Methods

A total of 100 RA patients receiving MTX were prospectively followed up for approximately 3 months to determine the clinical response based on several criteria, including European League Against Rheumatism (EULAR) good and moderate response, disease activity score in 28 joint counts – erythrocyte sedimentation rate (DAS28-ESR) low disease activity (LDA), change in DAS28-ESR (ΔDAS28-ESR) and ΔDAS28-ESR >0.6. Fifty-four single nucleotide polymorphisms (SNPs) within seven transporter genes, including SLC19A1, ABCB1, ABCC1~4 and ABCG2, were genotyped.

Results

Multivariable analysis revealed that SLC19A1 rs12659 and rs3788200, ABCC2 rs3740066, rs4148396 and rs717620 were significantly associated with EULAR good and moderate response, and ABCC2 rs3740066 and rs717620 were significantly associated with DAS28-ESR LDA, and ABCB1 rs1128503, rs4148737 and ABCC3 rs2277624, rs4148416 were significantly associated with ΔDAS28-ESR. Moreover, 12 genetic polymorphisms were found to be significantly associated with ΔDAS28-ESR >0.6. With adjustment for corresponding confounders, SLC19A1 TGAA haplotype consisting of rs1051266, rs1131596, rs12659 and rs3788200 was significantly associated with EULAR good and moderate response and ΔDAS28-ESR >0.6 compared with the most common haplotype CAGG. The ABCC2 haplotype TTT composed of rs717620, rs4148396 and rs3740066 was significantly associated with EULAR good and moderate response and ΔDAS28-ESR >0.6 compared with the most common haplotype CCC.

Conclusion

Our results highlight the potential of genetic polymorphisms within transporter genes, particularly SLC19A1 and ABCC2, as predictors of clinical response to MTX in Chinese RA patients.

CRISPR System-Linked Self-Assembling Nanoplatforms for Inspection and Screening of Gastric Cancer Stem Cells

Cancer stem cells (CSCs) possess a high degree of plasticity, constituting a formidable challenge to identify and screen CSCs in situ with outstanding specificity and sensitivity. To overcome this limitation, a self-assembled heterodimer consisting of clustered regularly interspaced short palindromic repeats/Cas12a (named A-CCA) linkage is designed for in situ identification and screening of gastric CSCs (GCSCs) from gastric cancer cells (GCCs). In this system, the editable character of crRNA performs recognition of dual-targets in GCSCs, effectively boosting the specificity of identification, while the enzymatic reaction of Cas12a contributes meaningfully to the sensitivity of sensing, enabling in situ examination and screening of GCSCs. Specifically, the A-CCA nanoplatforms hybridized with ABCG 2 and ABCB 1 overexpress in GCSCs, which can generate heterodimers and simultaneously restore the function of trans-cleavage. At this time, the asymmetry of the heterodimer causes a circular dichroism signal, which together with the recovered fluorescence signal form a dual-signals output system that can further ensure the precision of screening GCSC. Therefore, fluorescence-enhanced GCSCs can be sorted out from GCCs by flow cytometry. Furthermore, GCSCs screened by this assay possess extremely aggressive tumorigenic efficiency, providing a fundamental research object for further developing CSC targeted drugs in vivo.

Diagnostic and prognostic value of ABC transporter family member ABCG1 gene in clear cell renal cell carcinoma

As the most common histologic subtype of renal cancer, clear cell renal cell carcinoma (ccRCC) poses a serious threat to public health. However, there are no specific molecular-targeted drugs for ccRCC at present. Human ATP-binding cassette (ABC) transporter family plays an important role in homeostasis maintenance. This study aimed to evaluate the potential diagnostic value of ABC genes in ccRCC. A total of 952 samples of ccRCC patients (707) and controls (245) from three different datasets were included for analysis. Receiver operating characteristic analysis and t-test were used to analyze the differential expression of ABC genes in ccRCC patients and control samples at mRNA level during screening and validations. The Cancer Genome Atlas (TCGA-ccRCC) dataset was utilized to investigate the correlation between ABC genes expression and prognostic value in ccRCC. We then investigated the interactions between ABCG1 and proteins in the Comparative Toxicogenomics Database (CTD). Finally, we found that ATP-binding cassette transporter G member 1 (ABCG1) was over-expressed in ccRCC patients compared with healthy samples at mRNA level. Cox regression analysis and Kaplan-Meier analysis showed that ccRCC patients with high ABCG1 expression had better overall survival (OS) than those patients with low expression (hazard ratio (HR) = 0.662, p = 0.007). This study demonstrated that ABCG1 is a potential diagnostic and prognostic biomarker in ccRCC and discussed the molecular mechanisms underlying the relationship between ccRCC and ABCG1, which might provide guidance for better management and treatment of ccRCC in the future.

ABCG2 polymorphism, age and leukocyte count may contribute to oral mucositis in oncopediatric patients

The study investigated the relationship between genetic polymorphisms and the development of oral mucositis in pediatric patients undergoing chemotherapy involving methotrexate. A longitudinal study was conducted with 64 patients, and oral mucositis was evaluated by the modified Oral Assessment Guide, which aims to diagnose and classify oral mucositis. Epithelial cells were obtained by mouthwash and DNA was extracted. The polymorphisms MTHFR (rs1801133), DNMT3B (rs2424913), ABCC2 (rs717620), ABCG2 (rs2231137) and ABCG2 (rs2231142) were analyzed by PCR-RFLP method. Demographic, hematological and biochemical data were collected from medical records. Statistical analysis was performed using the SPSS software adopting a p-value of 0.05. Male sex predominated (56.2%), and the mean age was 10.8 years (± 4.9). Oral mucositis affected 65.6% of the patients, of which 61.9% developed the severe form of the disease. For the ABCG2 gene (rs2231142), the rare A allele and CA genotype were more frequent in individuals with mucositis (p= 0.02; RR = 0.60; CI = 0.387 - 0.813). The severity of the disease was mainly observed in younger patients (median = 9 years; p=0.02). Patients with severe oral mucositis presented lower leukocytes count (median = 2.150 mm3) compared to patients with the mild/moderate form (median = 4.200 mm3; p=0.03). Female patients and each 10,000-platelet increase were protective factors against the onset of oral mucositis (p=0.02). It is concluded that rs2231142 polymorphism increases the likelihood of oral mucositis and younger patients and patients with low leukocytes counts are more likely to develop severe form.

Polymorphism in Gene for ABCC2 Transporter Predicts Methotrexate Drug Survival in Patients with Psoriasis

Background and Objectives: Methotrexate is widely prescribed for the treatment of moderate-to-severe psoriasis. As drug survival encompasses efficacy, safety, and treatment satisfaction, such studies provide insights into successful drug treatments in the real-life scenario. The objective was to define methotrexate drug survival and reasons for discontinuation, along with factors associated with drug survival, in a cohort of adult patients with moderate-to-severe plaque psoriasis. Materials and Methods: Data on methotrexate treatment were extracted from our institutional registry. Drug survival was estimated by Kaplan–Meier analysis, and predictors of drug survival were analyzed by Cox proportional hazards regression. Results: We included 133 patients treated with methotrexate. Due to significant effects of the year of treatment initiation, drug survival analysis was performed for 117 patients who started methotrexate in 2010 or later. Median methotrexate drug survival was 11.0 months. Overall, 89% of patients discontinued treatment, with over half of these (51%) due to lack of efficacy. Significantly longer drug survival was seen for patients who discontinued treatment due to lack of efficacy versus drug safety (p = 0.049); when stratified by sex, this remained significant only for women (p = 0.002). The patient ABCC2 rs717620 genotype was significantly associated with drug survival in both univariate log-rank and multivariate Cox regression analyses, with variant T allele associated with longer drug survival (hazard ratio, 0.606; 95% confidence interval, 0.380–0.967; p = 0.036). Conclusions: We have identified the novel association of patient ABCC2 rs717620 genotype with methotrexate drug survival. This pharmacogenetic marker might thus help in the management of psoriasis patients in daily practice.

Drug-drug-gene interactions as mediators of adverse drug reactions to diclofenac and statins: a case report and literature review

Concomitant treatment with drugs that inhibit drug metabolising enzymes and/or transporters, such as commonly prescribed statins and nonsteroidal anti-inflammatory drugs (NSAIDs), has been associated with prolonged drug exposure and increased risk of adverse drug reactions (ADRs) due to drug-drug interactions. The risk is further increased in patients with chronic diseases/comorbidities who are more susceptible because of their genetic setup or external factors. In that light, we present a case of a 46-year-old woman who had been experiencing acute renal and hepatic injury and myalgia over two years of concomitant treatment with diclofenac, atorvastatin, simvastatin/fenofibrate, and several other drugs, including pantoprazole and furosemide. Our pharmacogenomic findings supported the suspicion that ADRs, most notably the multi-organ toxicity experienced by our patient, may be owed to drug-drug-gene interactions and increased bioavailability of the prescribed drugs due to slower detoxification capacity and decreased hepatic and renal elimination. We also discuss the importance of CYP polymorphisms in the biotransformation of endogenous substrates such as arachidonic acid and their modulating role in pathophysiological processes. Yet even though the risks of ADRs related to the above mentioned drugs are substantially evidenced in literature, pre-emptive pharmacogenetic analysis has not yet found its way into common clinical practice.

ABCB1, ABCG2, ABCC1, ABCC2, and ABCC3 drug transporter polymorphisms and their impact on drug bioavailability: what is our current understanding?

INTRODUCTION

Interindividual differences in drug response are a frequent clinical challenge partly due to variation in pharmacokinetics. ATP-binding cassette (ABC) transporters are crucial determinants of drug disposition. They are subject of gene regulation and drug-interaction; however, it is still under debate to which extend genetic variants in these transporters contribute to interindividual variability of a wide range of drugs.

AREAS COVERED

This review discusses the current literature on the impact of genetic variants in ABCB1, ABCG2 as well as ABCC1, ABCC2, and ABCC3 on pharmacokinetics and drug response. The aim was to evaluate if results from recent studies would increase the evidence for potential clinically relevant pharmacogenetic effects.

EXPERT OPINION

Although enormous efforts have been made to investigate effects of ABC transporter genotypes on drug pharmacokinetics and response, the majority of studies showed only weak if any associations. Despite few unique results, studies mostly failed to confirm earlier findings or still remained inconsistent. The impact of genetic variants on drug bioavailability is only minor and other factors regulating the transporter expression and function seem to be more critical. In our opinion, the findings on the so far investigated genetic variants in ABC efflux transporters are not suitable as predictive biomarkers.

Aberrant DNA Methylation of ABC Transporters in Cancer

ATP-binding cassette (ABC) transporters play a crucial role in multidrug resistance (MDR) of cancers. They function as efflux pumps, resulting in limited effectiveness or even failure of therapy. Increasing evidence suggests that ABC transporters are also involved in tumor initiation, progression, and metastasis. Tumors frequently show multiple genetic and epigenetic abnormalities, including changes in histone modification and DNA methylation. Alterations in the DNA methylation status of ABC transporters have been reported for a variety of cancer types. In this review, we outline the current knowledge of DNA methylation of ABC transporters in cancer. We give a brief introduction to structure, function, and gene regulation of ABC transporters that have already been investigated for their DNA methylation status in cancer. After giving an overview of the applied methodologies and the CpGs analyzed, we summarize and discuss the findings on aberrant DNA methylation of ABC transporters by cancer types. We conclude our review with the discussion of the potential to target aberrant DNA methylation of ABC transporters for cancer therapy.

Genetic Polymorphisms and the Efficacy of Platinum-Based Chemotherapy: Review

Previous studies have indicated that genetic variations in individuals may result in changes in gene expression and amino acids. The effect of these changes may lead to different responses to platinum-based chemotherapy. A vast response rate interval and a short survival rate indicate that the efficacy and efficiency of the selection of chemotherapy have not been optimized. This article aims to illustrate the potential relationship of various genetic polymorphisms in response to platinum-based chemotherapy for several types of cancer. This review was conducted using articles from the last three- and five-year periods (2014-2019) that use gene polymorphism and its relationship to the efficacy of platinum-based chemotherapy as their theme. A total of 26 out of 488 relevant articles were included based on specific criteria. Through various mechanisms, genes, including ERCC1, ERCC2/XPD, XPC, XPA, XRCC1, APE-1, PARP1, OGG1, ABCC2, MRP, GSTP1, GSTM1, GSTT1, MATE1, and OCT2, have been associated with patient response to platinum-based chemotherapy. We conclude that genetic polymorphism analysis is recommended for the management of cancer so that each patient can be administered therapy based on his or her genetic profile to achieve an effective and efficient outcome.

ABCB1 Genetic Variants as Predictors of Irinotecan-Induced Severe Gastrointestinal Toxicity in Metastatic Colorectal Cancer Patients

Irinotecan is widely used in the treatment of metastatic colorectal cancer (mCRC) despite its severe toxicities. Toxicity is often associated with the UGT1A1*28/*28 genotype. An explanation for idiopathic toxicity beyond the UGT1A1 biomarker, however, remains a major concern for clinicians. One of the main irinotecan transporters is P-glycoprotein (P-gp), which is a hepatic efflux pump encoded by ABCB1. P-gp is involved in the biliary excretion of irinotecan and its active metabolite SN-38. We aimed to assess whether functional variants in ABCB1 also contribute to identifying patients at risk of toxicity. A cohort of 308 mCRC patients treated with irinotecan-based regimens were genotyped for polymorphisms in ABCB1 (rs1128503, rs2032582, and rs1045642). The effect of these variants and their haplotypes on irinotecan-induced severe toxicity (diarrhea, neutropenia, asthenia, nausea, and mucositis) was assessed. After adjusting for the relevant clinical and pathological parameters in the multivariate analysis, we found rs1128503 was significantly associated with severe diarrhea and mucositis (P=0.014 and P=0.002, respectively). Additionally, rs2032582 was associated with severe mucositis (P<0.001). Our results show that rs1128503 genotyping could help to predict severe gastrointestinal toxicity induced by irinotecan.

Genetic variability of the ABCC2 gene and clinical outcomes in pancreatic cancer patients

Pancreatic ductal adenocarcinoma (PDAC) has an extremely poor prognosis, caused by various factors, such as the aggressiveness of the disease, the limited therapeutic options and the lack of early detection and risk markers. The ATP binding cassette subfamily C member 2 (ABCC2) protein plays a critical role in response to various drugs and is differentially expressed in gemcitabine sensitive and resistant cells. Moreover, single nucleotide polymorphisms (SNPs) in the gene have been associated with differential outcomes and prognosis in several tumour types. The aim of this study was to investigate the possible association between SNPs in the ABCC2 gene and overall survival (OS) in PDAC patients. We analysed 12 polymorphisms, including tagging-SNPs covering all the genetic variability of the ABCC2 gene and genotyped them in 1415 PDAC patients collected within the Pancreatic Disease ReseArch (PANDoRA) consortium. We tested the association between ABCC2 SNPs and PDAC OS using Cox proportional hazard models. We analysed PDAC patients dividing them by stage and observed that the minor alleles of three SNPs showed an association with worse OS [rs3740067: hazard ratio (HR) = 3.29, 95% confidence interval (CI) = 1.56-6.97, P = 0.002; rs3740073: HR = 3.11, 95% CI = 1.52-6.38, P = 0.002 and rs717620: HR = 2.90, 95% CI = 1.41-5.95, P = 0.004, respectively] in stage I patients. In patients with more advanced PDAC, we did not observe any statistically significant association. Our results suggest that rs3740067, rs3740073 and rs717620 could be promising prognostic markers in stage I PDAC patients.

Association between ABCB1, ABCG2 carrier protein and COX-2 enzyme gene polymorphisms and breast cancer risk in a Turkish population

Aim

Breast cancer is the most common cancer and the second leading cause of cancer-related deaths among women. Several genetic and environmental factors are known to be involved in breast cancer pathogenesis, but the exact etiology of this disease is complicated and not completely understood. We aimed to investigate whether the gene polymorphisms of ABCB1 and ABCG2 carrier proteins and COX-2 enzyme affect breast cancer risk.

Method

ABCG2 C421A (rs2231142), ABCB1 C3435T (rs1045642), COX-2 T8473C (rs5275) and COX-2 G306C (rs5277) were genotyped 104 breast cancer patients and 90 healthy controls using a real-time PCR for breast cancer susceptibility.

Results

Patients carrying ABCG2 C421A, the CC genotype, had a higher risk of disease compared with patients carrying any A allele (OR = 3.06; 95% CI = 1.49–6.25, p = 0.0019). The other variants showed no association with breast cancer (p > 0.05). Comparing the pathological parameters with the variants, only, the frequency of C allele of ABCB1 C3435T was significantly lower in the estrogen receptor-α (ERα) (OR = 2.25; 95% CI: 0.75–6.76; p = 0.041) and progesterone receptor (PgR) (OR = 3.67; 95% CI: 1.34–10.03; p = 0.008) positive breast cancer patients.

Conclusion

ABCB1 C3435T and ABCG2 C421A might represent a potential risk factor for breast cancer for Turkish women.

Roles of Hepatic Drug Transporters in Drug Disposition and Liver Toxicity

Hepatic drug transporters are mainly distributed in parenchymal liver cells (hepatocytes), contributing to drug's liver disposition and elimination. According to their functions, hepatic transporters can be roughly divided into influx and efflux transporters, translocating specific molecules from blood into hepatic cytosol and mediating the excretion of drugs and metabolites from hepatic cytosol to blood or bile, respectively. The function of hepatic transport systems can be affected by interspecies differences and inter-individual variability (polymorphism). In addition, some drugs and disease can redistribute transporters from the cell surface to the intracellular compartments, leading to the changes in the expression and function of transporters. Hepatic drug transporters have been associated with the hepatic toxicity of drugs. Gene polymorphism of transporters and altered transporter expressions and functions due to diseases are found to be susceptible factors for drug-induced liver injury (DILI). In this chapter, the localization of hepatic drug transporters, their regulatory factors, physiological roles, and their roles in drug's liver disposition and DILI are reviewed.

Effects of ABCC2 and SLCO1B1 Polymorphisms on Treatment Responses in Thai Metastatic Colorectal Cancer Patients Treated with Irinotecan-Based Chemotherapy

Purpose:

Irinotecan is an anticancer medicine which is used mostly in metastatic colorectal cancer (mCRC) treatment as second or third line chemotherapy. Several factors affect its efficacy and toxicity, including pharmacogenomics. This study aimed to investigate the impacts of ABCC2 and SLCO1B1 polymorphisms on treatment responses in irinotecan-based chemotherapy in 49 Thai mCRC patients.

Materials and Methods:

Forty-nine participants with mCRC enrolled in this study received irinotecan-based chemotherapy from January to June 2017. Genotypic analyses of ABCC2 (C>T, rs717620) and SLCO1B1 (A>G, rs2306283) were performed. Treatment responses were evaluated after at least three cycles of chemotherapy were given.

Results:

Allele frequencies of ABCC2 (C>T) and SLCO1B1 (A>G) were found at 18.37% and 78.57%, respectively. Neither was associated with treatment responses. However, combined genotypes of ABCC2 and SLCO1B1 tended to be associated with clinical benefits in terms of partial responses (PR) and stable disease (SD). All patients (100%) with at least one variant allele of SLCO1B1 and ABCC2 were in a PR or SD group, while patients with other genotypes had progressive disease (PD) at 45.5% to 70%, (p = 0.059).

Conclusion:

The combined effect of ABCC2 and SLCO1B1 polymorphisms tended to be associated with treatment responses in irinotecan-based treated mCRC patients. Therefore, such polymorphisms could be factors impacting inter-individual variation of irinotecan efficacy in Thai mCRC patients.

Pharmacogenetic variants and response to neoadjuvant single-agent doxorubicin or docetaxel: a study in locally advanced breast cancer patients participating in the NCT00123929 phase 2 randomized trial

OBJECTIVES

Taxanes and anthracyclines are widely used in the treatment of breast cancer, although the benefit is limited to a proportion of patients and predictive biomarkers for clinical outcome remain elusive.

PATIENTS AND METHODS

We carried out a pharmacogenetic study in 181 patients with locally advanced breast cancer enrolled in a phase 2 randomized clinical trial (NCT00123929), where patients were randomly assigned to receive neoadjuvant single-agent docetaxel 100 mg/m(2) (n=84) or doxorubicin 75 mg/m(2) (n=97). We studied the association of 226 single nucleotide polymorphisms (SNPs) in 15 key drug biotransformation genes with neoadjuvant pathological tumor response residual cancer burden index to docetaxel and to doxorubicin.

RESULTS

We identified a significant association for rs162561, an intronic SNP located in the cytochrome P450 family 1 subfamily B member 1 (CYP1B1) gene, with tumor response in patients treated with single-agent docetaxel (dominant model: β=1.02, 95% confidence interval=0.49-1.55; P=1.77×10(-4)), and for rs717620, an SNP located in the promoter of the ATP-binding cassette subfamily C member 2 (ABCC2) gene, in patients treated with neoadjuvant doxorubicin (recessive model: β=1.67; 95% confidence interval=0.26-3.11; P=0.02).

CONCLUSION

We identified two polymorphisms in CYP1B1 and ABCC2 associated with tumor pathological response following docetaxel or doxorubicin neoadjuvant monotherapy, respectively. Although further validation is required, these variants could be potential predictive genetic markers for treatment outcome in breast cancer patients.

Association of ABCC2 polymorphism and gender with high-density lipoprotein cholesterol response to simvastatin

Aim: The clinical benefits of lipid-lowering therapy with statins are widely recognized. However, the lipid-lowering efficacy of statins shows significant differences between individuals. ABCC2 has been demonstrated to contribute to the transmembrane transport of the substrate compounds. The ABCC2 SNPs may be important factors that affect individual differences in clinical drug response. The aim of this study was to evaluate the association of rs717620 of ABCC2 with treatment response to simvastatin in a Chinese Han population. Methods: A total of 318 subjects were medicated with simvastatin 20 mg/day for 12 weeks after enrollment. Venous blood was obtained before and after simvastatin treatment for measurement of blood lipid profile. Subjects were classified into high-response and low-response groups depending on whether their lipid profile change was higher or lower than median change values. The ABCC2 SNP rs717620 was genotyped from blood samples with a snapshot assay. Results: A total of 12 weeks of treatment with simvastatin significantly decreased low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), triglycerides (TGs) and significantly increased high-density lipoprotein cholesterol (HDL-C; p < 0.05). In multivariate analysis, there were no significant genetic effects of SNP rs717620 on the incidence of high- or low-response patients among TC, TG and LDL-C groups. However, rs717620 A-allele and female gender are significantly associated with the risk of low-response of HDL-C elevation after simvastatin treatment. Conclusion: ABCC2 rs717620 and female gender may be related to the low-effect of simvastatin treatment on the HDL-C level in the Chinese Han population. Female Chinese patients with hyperlipidemia carrying rs717620 GA/AA genotypes might have reduced benefit from simvastatin treatment.

Association of Allelic Interaction of Single Nucleotide Polymorphisms of Influx and Efflux Transporters Genes With Nonhematologic Adverse Events of Docetaxel in Breast Cancer Patients

PURPOSE

Nonhematologic adverse events (AEs) of docetaxel constitute an extra burden in the treatment of cancer patients and necessitate either a dose reduction or an outright switch of docetaxel for other regimens. These AEs are frequently associated with genetic polymorphisms of genes encoding for proteins involved docetaxel disposition. Therefore, we investigated that association in Malaysian breast cancer patients.

MATERIALS AND METHODS

A total of 110 Malaysian breast cancer patients were enrolled in the present study, and their blood samples were investigated for different single nucleotide polymorphisms using polymerase chain reaction restriction fragment length polymorphism. AEs were evaluated using the Common Terminology Criteria for Adverse Events, version 4.0.

RESULTS

Fatigue, nausea, oral mucositis, and vomiting were the most common nonhematologic AEs. Rash was associated with heterozygous and mutant genotypes of ABCB1 3435C>T (P < .05). Moreover, patients carrying the GG genotype of ABCB1 2677G>A/T reported more fatigue than those carrying the heterozygous genotype GA (P < .05). The presence of ABCB1 3435-T, ABCC2 3972-C, ABCC2 1249-G, and ABCB1 2677-G alleles was significantly associated with nausea and oral mucositis. The coexistence of ABCB1 3435-C, ABCC2 3972-C, ABCC2 1249-G, and ABCB1 2677-A was significantly associated with vomiting (P < .05).

CONCLUSION

The prevalence of nonhematologic AEs in breast cancer patients treated with docetaxel has been relatively high. The variant allele of ABCB1 3435C>T polymorphism could be a potential predictive biomarker of docetaxel-induced rash, and homozygous wild-type ABCB1 2677G>A/T might predict for a greater risk of fatigue. In addition, the concurrent presence of specific alleles could be predictive of vomiting, nausea, and oral mucositis.

The Pharmacogenetics of Immune-Modulating Therapy

Immunosuppressive drugs are a prerequisite in organ transplantation to prevent rejection and are also widely used in inflammatory diseases such as inflammatory bowel disease (IBD) or also in some hematologic malignancies-depending on the mode of action. For thiopurine analogs the polymorphic thiopurine S-methyltransferase (TPMT) was early detected to be associated with thiopurine-induced leukopenia; recent studies identified also NUDT15 to be related to this severe side effect. For drugs like methotrexate and mycophenolate mofetil a number of ADME genes like UDP-glucuronosyltransferases (UGTs) and ABC efflux transporters were investigated, however, with partly contradicting results. For calcineurin inhibitors like cyclosporine and in particular tacrolimus however, cytochrome P450 3A4 and 3A5 variants were found to significantly affect the pharmacokinetics. Genetic variants in genes encoding relevant pharmacodynamic proteins, however, lacked compelling evidence to affect the clinical outcome. This chapter reviews the current evidence on the association of pharmacogenetic traits to dose finding and clinical outcome of small-molecule immunosuppressants. Moreover this chapter critically summarizes suitability to apply pharmacogenetics in clinical practice in order to optimize immunosuppressant therapy.

ABCC2-24C > T polymorphism is associated with the response to platinum/5-Fu-based neoadjuvant chemotherapy and better clinical outcomes in advanced gastric cancer patients

Several studies have evaluated the efficacy of neoadjuvant treatment using oxaliplatin and fluoropyrimidines in advanced gastric cancer (GC). However, preoperative biomarkers predictive of clinical outcome remain lacking. We examined polymorphisms in the MTHFR, DPYD, UMPS, ABCB1, ABCC2, GSTP1, ERCC1, and XRCC1 genes to evaluate their usefulness as pharmacogenetic markers in a cohort of 103 GC patients treated with preoperative chemotherapy. DNA was extracted from peripheral blood cells, and the genotypes were analyzed using a SNaPShot^TM assay, polymerase chain reaction amplification, and sequencing. The ABCC2-24C > T (rs717620) genotype was associated with pathologic response to neoadjuvant chemotherapy. Patients with the TT and TC genotypes responded to neoadjuvant chemotherapy 3.80 times more often than those with the CC genotype (95% CI: 1.27–11.32). Patients with the CC genotype also had poorer outcomes than those with other genotypes. Thus, ABCC2-24C > T polymorphism may help to predict the response to preoperative chemotherapy in GC patients.

Gender-Specific Association Between ABCC2 -24C>T SNP and Reduction in Triglycerides in Chilean Patients Treated With Atorvastatin

Statins are the first-line therapy prescribed to lower plasma cholesterol levels. Although being safe and showing several beneficial cholesterol-independent pleiotropic effects, a significant variability regarding statin's therapeutic goals has been abundantly documented, but less understood. We aimed to investigate the influence of the ABCC2 -24C>T single nucleotide polymorphism on Chilean hypercholesterolaemic individuals treated for 4 weeks with 10 mg/day atorvastatin. A total of 127 individuals medicated with atorvastatin 10 mg/day/4 weeks were included. Lipid profiles were determined before and after drug administration by conventional assays. Genotyping of the ABCC2 rs717620 SNP (-24C>T) was performed with TaqMan^® Drug Metabolism Genotyping Assays. As expected, atorvastatin reduced TC, LDL-C and TG concentrations (p < 0.05). Also, HDL-C levels were increased (p < 0.05). Minor allele frequency for the rs717620 was 0.232. Overall, atorvastatin response was not associated with the ABCC2 rs717620 SNP (p > 0.05). Nonetheless, in male individuals carrying the -24T allele, we observed an attenuated reduction in both TG values and the TG/HDL-C ratio after 10 mg/day atorvastatin. This study indicates that TG levels and the TG/HDL-C ratio are affected by the rs717620 SNP in Chilean males but not female individuals after atorvastatin treatment.

The predictive value of ABCB1, ABCG2, CYP3A4/5 and CYP2D6 polymorphisms for risperidone and aripiprazole plasma concentrations and the occurrence of adverse drug reactions

We investigated in ninety Caucasian pediatric patients the impact of the main polymorphisms occurring in CYP3A, CYP2D6, ABCB1 and ABCG2 genes on second-generation antipsychotics plasma concentrations, and their association with the occurrence of adverse drug reactions. Patients with the CA/AA ABCG2 genotype had a statistically significant lower risperidone plasma concentration/dose ratio (Ct/ds) (P-value: 0.007) and an higher estimated marginal probability of developing metabolism and nutrition disorders as compared to the ABCG2 c.421 non-CA/AA genotypes (P-value: 0.008). Multivariate analysis revealed that the ABCG2 c.421 CA/AA genotype was found associated to a higher hazard (P-value: 0.004) of developing adverse drug reactions classified as metabolism and nutrition disorders. The ABCB1 2677TT/3435TT genotype had a statistically significant lower aripiprazole Ct/ds if compared with patients with others ABCB1 genotypes (P-value: 0.026). Information obtained on ABCB1 and ABCG2 gene variants may result useful to tailor treatments with these drugs in Caucasian pediatric patients.

Steady-state pharmacokinetics of mycophenolic acid in renal transplant patients: exploratory analysis of the effects of cyclosporine, recipients' and donors' ABCC2 gene variants, and their interactions

PURPOSE

The study aims to evaluate the impact of recipients' and donors' polymorphisms in multidrug resistance-associated protein 2 (MRP2) gene ABCC2 -24C>T and 1249G>A on disposition of mycophenolic acid (MPA) and their interaction with cyclosporine (CsA) (compared to tacrolimus, TAC) in stable de novo adult renal transplant patients of Croatian origin.

METHODS

A total of 68 recipient-donor pairs were genotyped. Steady-state pharmacokinetics of MPA was assessed by the model-independent method.

RESULTS

Adjusted for MPA formulation, renal function, type of calcineurin inhibitor and recipients' and donors' genotypes at the two loci, donors' A-allele at 1249G>A was associated with a reduced peak (29%) and early (AUC_0-2, 33%) exposure and increased MPA clearance (26%). Donors' A-allele combined with CsA was associated with 78% higher MPA clearance, 49% lower early and 48% lower total exposure as compared to wild type homozygosity + TAC. Recipients' SNPs per se did not reflect on MPA disposition. However, A-allele at 1249G>A + CsA (compared to wild type + TAC) was associated with a numerically greater increase in MPA clearance (59 vs. 41%), reduction in total exposure (36 vs. 27%) and increase in absorption rate (C _max/AUC) (56 vs. 37%) than observed for the main effect of CsA. Less pronounced effects were observed for the combination of variant allele at -24C>T and CsA.

CONCLUSION

Considering MPA disposition, data indicate: donors' ABCC2 1249G>A polymorphism increases clearance and reduces exposure; CsA increases clearance and reduces exposure by inhibiting MRP2 in the gut, the liver, and the kidney; donors' ABCC2 1249G>A polymorphism enhances the renal CsA effect, while recipients' polymorphism seems to enhance the liver and the gut CsA effects.

Relationship between ABCB1 3435TT genotype and antiepileptic drugs resistance in Epilepsy: updated systematic review and meta-analysis

Background

Antiepileptic drugs (AEDs) are effective medications available for epilepsy. However, many patients do not respond to this treatment and become resistant. Genetic polymorphisms may be involved in the variation of AEDs response. Therefore, we conducted an updated systematic review and a meta-analysis to investigate the contribution of the genetic profile on epilepsy drug resistance.

Methods

We proceeded to the selection of eligible studies related to the associations of polymorphisms with resistance to AEDs therapy in epilepsy, published from January 1980 until November 2016, using Pubmed and Cochrane Library databases. The association analysis was based on pooled odds ratios (ORs) and 95% confidence intervals (CIs).

Results

From 640 articles, we retained 13 articles to evaluate the relationship between ATP-binding cassette sub-family C member 1 (ABCB1) C3435T polymorphism and AEDs responsiveness in a total of 454 epileptic AEDs-resistant cases and 282 AEDs-responsive cases. We found a significant association with an OR of 1.877, 95% CI 1.213–2.905. Subanalysis by genotype model showed a more significant association between the recessive model of ABCB1 C3435T polymorphism (TT vs. CC) and the risk of AEDs resistance with an OR of 2.375, 95% CI 1.775–3.178 than in the dominant one (CC vs. TT) with an OR of 1.686, 95% CI 0.877–3.242.

Conclusion

Our results indicate that ABCB1 C3435T polymorphism, especially TT genotype, plays an important role in refractory epilepsy. As genetic screening of this genotype may be useful to predict AEDs response before starting the treatment, further investigations should validate the association.

Are Polymorphisms in Genes Relevant to Drug Disposition Predictors of Susceptibility to Drug-Induced Liver Injury?

Despite considerable progress in identifying specific HLA alleles as genetic risk factors for some forms of drug-induced liver injury, progress in understanding whether genetic polymorphisms relevant to drug disposition also contribute to risk for developing this serious toxicity has been more limited. Evidence from both candidate-gene case control studies and genome-wide association studies is now discussed. In the case of genes relevant to drug metabolism, polymorphisms in cytochromes P450, UDP-glucuronosyltransferases, N-acetyltransferases and glutathione S-transferases as risk factors for DILI are assessed. The relevance of ABC transporters to drug-induced liver injury is also considered, together with data showing associations of particular ABCB11, ABCB1 and ABCC2 polymorphisms with some forms of drug-induced liver injury. Very few of the associations with genes relevant to drug disposition that have been reported have been well replicated. Even apparently well-studied associations such as that between isoniazid liver injury and N-acetyltransferase 2 slow acetylators remain problematic, though it seems likely that polymorphisms in drug metabolism genes do contribute to risk for some specific drugs. A better understanding of genetic risk factors for drug-induced liver injury will require further genome-wide association studies with larger numbers of cases, especially for forms of drug-induced liver injury where HLA genotype does not appear to be a risk factor.

Polymorphisms of Genes Encoding Multidrug Resistance Proteins as a Predictive Factor for Second-Line Docetaxel Therapy in Advanced Non-small Cell Lung Cancer

Multidrug resistance (MDR) remains a substantial problem in chemotherapy. The purpose of the study was to investigate potential factors, including MDR genes polymorphisms, that could be used in qualification for second-line docetaxel therapy in non-small cell lung cancer (NSCLC) patients after failure of platinum based chemotherapy. Study group comprised of 58 Caucasian subjects. Evaluation of Single Nucleotide Polymorphisms (SNPs) of ABCC2/MRP2 and ABCB1/MDR1 genes was performed using the High Resolution Melting (HRM) technique. TUBB3 gene expression was evaluated on RNA isolated from tumor tissue. Results with p value of <0.05 were considered significant. Factors associated with reduced risk of disease progression included good performance status (PS), long period between diagnosis and docetaxel treatment, and smoking for <10 pack-years. Disease control occurred more often in patients with G/G genotype of the ABCC2/MRP2 gene. Median overall survival was 4.25 months. Factors such as: good PS, disease control after docetaxel, long period from diagnosis to docetaxel, lack of significant weight loss, and third-line treatment were associated with prolongation of patients survival. Overall survival probability was significantly lower in patients with significant weight loss, poor PS, lack of disease control after docetaxel, and without third-line treatment. Factors that characterized the highest risk of survival shortening were: inability to apply third-line treatment, lack of best response to first-line therapy, poor PS, and C/G or G/G genotypes of ABCC2/MRP2 gene. We concluded that assessed factors had mainly prognostic and not predictive value. Finding reliable molecular predictors for second line docetaxel therapy requires further clinical trials.

Polymorphisms associated with renal adverse effects of antiretroviral therapy in a Southern Brazilian HIV cohort

OBJECTIVE

This study evaluated the impact of seven single nucleotide polymorphisms in five candidate genes (ABCB1, ABCC2, ABCC4, SLC22A6, and SLC22A11) in relation to nephrotoxicity associated with highly active antiretroviral therapy (HAART) in HIV-infected individuals.

METHODS

The following single nucleotide polymorphisms were genotyped by real-time PCR: ABCB1 rs1045642, ABCC2 rs717620 and rs2273697, ABCC4 rs1751034 and rs3742106, SLC22A6 rs11568626, and SLC22A11 rs11231809 in 507 HIV-infected patients from the city of Porto Alegre, Southern Brazil, receiving HAART for, at least, 1 year.

RESULTS

From the 507 HIV-infected patients recruited, 19.1% presented a reduction in estimated glomerular filtration rate (eGFR). A total of 16 (3.2%) patients fulfilled the criteria for chronic kidney disease (defined as eGFR<60 ml/min/1.73 m). Individuals carrying at least one T allele of ABCC2 -24 C>T (rs717620) presented lower eGFR than C/C homozygotes (104 ± 22 vs. 108 ± 22 ml/min/1.73 m, independent-samples t-test, P=0.040). In multivariate analysis, the predictors associated with decreased eGFR were time of treatment, tenofovir use, atazanavir/ritonavir use, and carrying one T allele of ABCC2 -24 C>T.

CONCLUSION

Our data support the importance of genetic factors in the etiology of nephrotoxicity in patients treated with HAART. Studies to verify treatment implications of genotyping before HAART initiation may be advisable to guide the selection of an appropriate antiretroviral therapy regimen.

Efflux transporter variants as predictors of drug toxicity in lung cancer patients: systematic review and meta-analysis

Chemotherapeutic drugs are underutilized in lung cancer management due in part to serious adverse drug reactions (ADRs).

AIM

With studies revealing an association between interindividual patient ADR variation and efflux transporter variants, we carried out a meta-analysis and systemic review, in order to highlight current knowledge regarding the strength of association between efflux transporter SNPs variants and chemotherapeutic-drug induced ADRs.

MATERIALS & METHODS

Papers were sourced from MEDLINE, Cochrane Library, CINHL, EMBASE, Web of Knowledge, Scopus. The Cochrane Collaboration Risk of Bias Tool v13 was used to evaluate six types of bias domains for each of the publications reviewed.

RESULTS

Twenty-five publications comprising three randomised control trials, two retrospective case-controls and 20 clinical observation studies, totalling 3578 patients, were deemed eligible for review. Of the known efflux drug transporters, we report findings on the ABC members ABCB1, ABCC1, ABCC2, ABCG2, ABCA1, ABCC4 and ABCC5. Meta-analysis showed an decreased risk of irinotecan-induced neutropenia in patients expressing ABCB1 2677G>T/G (odds ratio [OR]: 0.24; 95% CI: 0.1-0.59; p = 0.002) but increased risk for ABCC2 3972T>T (OR: 1.67; 95% CI: 1.01-2.74; p = 0.04). ABCG2 34G>A was associated with a threefold increased risk of irinotecan-induced diarrhea (95% CI: 1.00-6.24; p = 0.05).

CONCLUSION

The majority of studies have identified a role for variants in effluxdrug transporters in contributing to lung cancer treatment-associated ADRs. However, for implementation of use of these transporter genetic variants as prognostic markers for ADR risk, future studies must incorporate larger patient numbers.

Genetic risk factors for clozapine-induced neutropenia and agranulocytosis in a Dutch psychiatric population

Prescription of clozapine is complicated by the occurrence of clozapine-induced reduction of neutrophils. The aim of this study was to identify genetic risk factors in a population of 310 Dutch patients treated with clozapine, including 38 patients developing neutropenia and 31 patients developing agranulocytosis. NQO2 1541AA (NRH quinone oxidoreductase 2; protects cells against oxidative metabolites) was present at a higher frequency in agranulocytosis patients compared with control (23% versus 7%, P=0.03), as was ABCB1 (ABC-transporter-B1; drug efflux transporter) 3435TT (32% versus 20%, P=0.05). In patients developing neutropenia, ABCB1 3435TT and homozygosity for GSTT1^null (glutathione-S-transferase; conjugates reactive clozapine metabolites into glutathione) were more frequent compared with control (34% versus 20%, P=0.05 and 31% versus 14%, P=0.03), whereas GSTM1^null was less frequent in these patients (31% versus 52%, P=0.03). To investigate whether combinations of the identified genetic risk factors have a higher predictive value, should be confirmed in a larger case-control study.

ABCB1 and ABCC2 and the risk of distant metastasis in Thai breast cancer patients treated with tamoxifen

BACKGROUND

Genetic polymorphisms of drug-metabolizing enzymes and transporters have been extensively studied with regard to tamoxifen treatment outcomes. However, the results are inconclusive. Analysis of organ-specific metastasis may reveal the association of these pharmacogenetic factors. The aim of this study is to investigate the impact of CYP3A5, CYP2D6, ABCB1, and ABCC2 polymorphisms on the risk of all distant and organ-specific metastases in Thai patients who received tamoxifen adjuvant therapy.

METHODS

Genomic DNA was extracted from blood samples of 73 patients with breast cancer who received tamoxifen adjuvant therapy. CYP3A5 (6986A>G), CYP2D6 (100C>T), ABCB1 (3435C>T), and ABCC2 (-24C>T) were genotyped using allelic discrimination real-time polymerase chain reaction assays. The impacts of prognostic clinical factors and genetic variants on disease-free survival were analyzed using the Kaplan-Meier method and Cox regression analysis.

RESULTS

In the univariate analysis, primary tumor size >5 cm was significantly associated with increased risk of distant metastasis (P=0.004; hazard ratio [HR] =3.05; 95% confidence interval [CI], 1.44-6.47). In the multivariate analysis, tumor size >5 cm remained predictive of distant metastasis (P<0.001; HR=5.49; 95% CI, 2.30-13.10). ABCC2 -24CC were shown to be associated with increased risk of distant metastasis (P=0.040; adjusted HR=2.34; 95% CI, 1.04-5.27). The combined genotype of ABCC2 -24CC - ABCB1 3435 CT+TT was associated with increased risk of distant and bone metastasis (P=0.020; adjusted HR=2.46; 95% CI, 1.15-5.26 and P=0.040; adjusted HR=3.70; 95% CI, 1.06-12.89, respectively).

CONCLUSION

This study indicates that polymorphisms of ABCC2 and ABCB1 are independently associated with bone metastasis. Further prospective studies with larger sample sizes are needed to verify this finding.

ABCC2 polymorphisms and survival in the Princess Margaret cohort study and the NCIC clinical trials group BR.24 trial of platinum-treated advanced stage non-small cell lung cancer patients

BACKGROUND

The drug transporter ABCC2 is upregulated in non-small cell lung cancer (NSCLC) and implicated in platinum resistance. We evaluated the association between germline polymorphisms in the ABCC2 gene and survival outcomes of platinum-treated advanced NSCLC patients.

MATERIAL AND METHODS

Ten candidate and tagging germline polymorphisms in the ABCC2 gene were genotyped in a discovery cohort of 170 platinum-treated stage IV NSCLC patients from the Princess Margaret Cancer Centre. Associations with overall survival were assessed using multivariate Cox proportional hazard models adjusted for prognostic variables. To validate our results, we analyzed the association of the two top polymorphisms in the ABCC2 gene on survival outcomes of 219 stage IIIB-IV NSCLC patients enrolled on the NCIC Clinical Trials Group BR.24 clinical trial.

RESULTS

Only one polymorphism was validated across both cohorts for an association with overall survival: the A allele of the ABCC2 polymorphism, rs8187710 (4544G>A), was associated with adverse overall survival (adjusted hazard ratio [aHR] 2.22; 95% CI: 1.2-4.0; p=0.009) among our stage IV NSCLC patients. A significant association with overall survival (aHR 1.73; 95% CI: 1.0-2.9; p=0.036) was observed for the same ABCC2 polymorphism in the BR.24 validation cohort. No other ABCC2 polymorphisms were associated with outcome.

CONCLUSION

The ABCC2 polymorphism, rs8187710 (4544G>A), is associated with overall survival in platinum-treated advanced NSCLC patients. Additional studies are needed to evaluate the predictive versus prognostic nature of this relationship, and to explore the functional effect of this polymorphism on the pharmacokinetics of platinum drugs.

Clinical validity of new genetic biomarkers of irinotecan neutropenia: an independent replication study

The overall goal of this study was to provide evidence for the clinical validity of nine genetic variants in five genes previously associated with irinotecan neutropenia and pharmacokinetics. Variants associated with absolute neutrophil count (ANC) nadir and/or irinotecan pharmacokinetics in a discovery cohort of cancer patients were genotyped in an independent replication cohort of 108 cancer patients. Patients received single-agent irinotecan every 3 weeks. For ANC nadir, we replicated UGT1A1*28, UGT1A1*93 and SLCO1B1*1b in univariate analyses. For irinotecan area under the concentration-time curve (AUC0-24), we replicated ABCC2 -24C>T; however, ABCC2 -24C>T only predicted a small fraction of the variance. For SN-38 AUC0-24 and the glucuronidation ratio, we replicated UGT1A1*28 and UGT1A1*93. In addition to UGT1A1*28, this study independently validated UGT1A1*93 and SLCO1B1*1b as new predictors of irinotecan neutropenia. Further demonstration of their clinical utility will optimize irinotecan therapy in cancer patients.

The recessive model of MRP2 G1249A polymorphism decrease the risk of drug-resistant in Asian Epilepsy: a systematic review and meta-analysis

ABCC2 gene polymorphisms have been shown to be associated with drug-resistant epilepsy. However, the published results were controversial. To comprehensively re-evaluate the association between ABCC2 gene polymorphisms and drug-resistant epilepsy in Asian, we carried out this meta-analysis, which included eight related studies. Studies were selected using PUBMED, Web of science, the Cochrane database of system reviews and Embase. Pooled odds ratio (OR) with 95% confidence interval (CI) was used to assess the association. Studies with 1302 drug-resistant cases and 1563 drug-sensitive controls were included. No significant association was detected by combined analyses for C-24T, G-1774delG, C3972T and G2934A. However, significant association was found in recessive model for G1249A polymorphism (GG vs. GA+AA: OR=0.72, 95%CI=0.53-0.96, P=0.03), indicating the recessive model of G1249A in MRP2/ABCC2 might decrease the risk of drug resistance in Asian epilepsy.

Report of new haplotype for ABCC2 gene: rs17222723 and rs8187718 in cis

The ATP-binding cassette, subfamily C [CFTR/MRP], member 2 (ABCC2) gene is a member of the ATP-binding cassette transporters and is involved in the transport of molecules across cellular membranes. Substrates transported by ABCC2 include antiepileptics, statins, tenofovir, cisplatin, irinotecan, and carbamazepine. Because of the pharmacogenomics implications, we developed a clinical laboratory-developed assay to test for seven variants in the ABCC2 gene: c.3563T>A (p.V1188E, rs17222723), c.1249G>A (p.V417I, rs2273697), c.3972C>T (p.I1324I, rs3740066), c.2302C>T (p.R768W, rs56199535), c.2366C>T (p.S789F, rs56220353), c.-24C>T (5'UTR, rs717620), and c.4544G>A (p.C1515Y, rs8187710). During the validation process, we noted several DNA samples, obtained from the Coriell Cell Repository, that contained both c.3563T>A, c.4544G>A, and a third variant, suggesting that c.3563T>A and c.4544G>A are in cis on the chromosome in some individuals. We obtained DNA samples from a trio (father, mother, and child), tested their ABCC2 variants, and confirmed that c.3563T>A and c.4544G>A were in cis on the same chromosome. Here, we report a new haplotype in ABCC2.

New insights in the biology of ABC transporters ABCC2 and ABCC3: impact on drug disposition

INTRODUCTION

For the elimination of environmental chemicals and metabolic waste products, the body is equipped with a range of broad specificity transporters that are present in excretory organs as well as in several epithelial blood-tissue barriers.

AREAS COVERED

ABCC2 and ABCC3 (also known as MRP2 and MRP3) mediate the transport of various conjugated organic anions, including many drugs, toxicants and endogenous compounds. This review focuses on the physiology of these transporters, their roles in drug disposition and how they affect drug sensitivity and toxicity. It also examines how ABCC2 and ABCC3 are coordinately regulated at the transcriptional level by members of the nuclear receptor (NR) family of ligand-modulated transcription factors and how this can be therapeutically exploited.

EXPERT OPINION

Mutations in both ABCC2 and ABCC3 have been associated with changes in drug disposition, sensitivity and toxicity. A defect in ABCC2 is associated with Dubin-Johnson syndrome, a recessively inherited disorder characterized by conjugated hyperbilirubinemia. Pharmacological manipulation of the activity of these transporters can potentially improve the pharmacokinetics and thus therapeutic activity of substrate drugs but also affect the physiological function of these transporters and consequently ameliorate associated disease states.

Polymorphisms of the drug transporters ABCB1, ABCG2, ABCC2 and ABCC3 and their impact on drug bioavailability and clinical relevance

INTRODUCTION

Human ATP-binding cassette (ABC) transporters act as translocators of numerous substrates across extracellular and intracellular membranes, thereby contributing to bioavailability and consequently therapy response. Genetic polymorphisms are considered as critical determinants of expression level or activity and subsequently response to selected drugs.

AREAS COVERED

Here the influence of polymorphisms of the prominent ABC transporters P-glycoprotein (MDR1, ABCB1), breast cancer resistance protein (BCRP, ABCG2) and the multidrug resistance-associated protein (MRP) 2 (ABCC2) as well as MRP3 (ABCC3) on the pharmacokinetic of drugs and associated consequences on therapy response and clinical outcome is discussed.

EXPERT OPINION

ABC transporter genetic variants were assumed to affect interindividual differences in pharmacokinetics and subsequently clinical response. However, decades of medical research have not yielded in distinct and unconfined reproducible outcomes. Despite some unique results, the majority were inconsistent and dependent on the analyzed cohort or study design. Therefore, variability of bioavailability and drug response may be attributed only by a small amount to polymorphisms in transporter genes, whereas transcriptional regulation or post-transcriptional modification seems to be more critical. In our opinion, currently identified genetic variants of ABC efflux transporters can give some hints on the role of transporters at interfaces but are less suitable as biomarkers to predict therapeutic outcome.

Clinical impact of ABCC1 and ABCC2 genotypes and haplotypes in mediating imatinib resistance among chronic myeloid leukaemia patients

WHAT IS KNOWN AND OBJECTIVE

The introduction and success of imatinib mesylate (IM) has brought about a paradigm shift in chronic myeloid leukaemia (CML) treatment. However, despite the high efficacy of IM, clinical resistance develops due to a heterogeneous array of mechanisms. Pharmacogenetic variability as a result of genetic polymorphisms could be one of the most important factors influencing resistance to IM. The aim of this study was to investigate the association between genetic variations in drug efflux transporter ABCC1 (MRP1) and ABCC2 (MRP2) genes and response to IM in patients with CML.

METHODS

We genotyped 215 Malaysian patients with CML (comprising of two groups with 108 IM resistant and 107 IM responsive) for polymorphisms of ABCC1 (2012G>T and 2168G>A) and ABCC2 (-24C>T, 1249G>A and 3972C>T) genes. Genotype, allele and haplotype frequencies were compared between two groups of patients. Patients with CML were further stratified according to their clinical response to IM into those having cytogenetics and molecular responses, and the associations with genotypes were evaluated.

RESULTS AND DISCUSSION

We observed no significant differences in the distribution of any of the tested genotypes between the investigated groups. However, on evaluating the risk association, ABCC2 T₋₂₄ G₁₂₄₉ T₃₉₇₂ haplotype was found to be associated with IM resistance (P = 0·046). These results suggest that haplotype variants -24T and 3972T might be associated with lower expression of ABCC2 protein and reduced transport activity and hence might be contributing to development of IM resistance.

WHAT IS NEW AND CONCLUSION

Our results suggest the ABCC2 T₋₂₄ G₁₂₄₉ T₃₉₇₂ haplotype was associated with imatinib resistance. However, the evidence is as yet insufficient to establish this haplotype as a predictive biomarker for response to the drug.

Pharmacogenetic considerations for acute lymphoblastic leukemia therapies

INTRODUCTION

Advances in our understanding of the pathobiology of childhood acute lymphoblastic leukemia (ALL) have led to risk-targeted treatment regimens and remarkable improvement in survival rates. Still, up to 20% of patients experience treatment failure due to drug resistance. Treatment-related toxicities are often life-threatening and are the primary cause of treatment interruption, while ALL survivors may develop complications due to exposure to chemotherapy and/or irradiation during a vulnerable period of development. Different factors may contribute to variable treatment outcomes including patient genetics that has been shown to play important role.

AREAS COVERED

This review summarizes candidate gene and genome-wide association studies that identified common polymorphisms underlying variability in treatment responses including a few studies addressing late effects of the treatment. Genetic variants influencing antileukemic drug effects or leukemic cell biology have been identified, including for example variants in folate-dependent enzymes, influx and efflux transporters, metabolizing enzymes, drug receptor or apoptotic proteins.

EXPERT OPINION

Many pharmacogenetic studies have been conducted in ALL and a variety of potential markers have been identified. Yet more comprehensive insight into genome variations influencing drug responses is needed. Whole exome/genome sequencing, careful study design, mechanistic explanation of association found and collaborative studies will ultimately lead to personalized treatment and improved therapeutic and health outcomes.

Association of -24CT, 1249GA, and 3972CT ABCC2 gene polymorphisms with methotrexate serum levels and toxic side effects in children with acute lymphoblastic leukemia

Acute lymphoblastic leukemia patients after being treated with methotrexate, have differences in methotrexate serum levels and toxic side effects. One of the main determinants of these toxic side effects is the host pharmacogenetics. The aim of this study was to evaluate the association of -24CT, 1249GA, and 3972CT ABCC2 gene polymorphisms with serum levels, and toxic side effects of methotrexate in childhood acute lymphoblastic leukemia. Applying polymerase chain reaction and restriction fragment length polymorphism techniques, the prevalence of -24CT, 1249GA, and 3972CT ABCC2 gene polymorphisms was evaluated in 65 acute lymphoblastic leukemia patients. The relationship between polymorphisms and methotrexate serum levels and toxicities was studied. A reverse significant relationship was detected between 3972T allele carriers and hepatotoxicity (P = 0.01, OR = 0.25, 95% CI = 0.09-0.72). Also, 1249A allele carriers had increased rate of gastrointestinal toxicity (P = 0.05, OR = 3.47, 95% CI = 1.04-11.57). No significant relationship was detected between -24CT polymorphism and methotrexate toxic side effects. There was no significant relationship between these three polymorphisms and methotrexate serum levels. Genotyping for 3972CT and 1249GA ABCC2 gene variants maybe useful in acute lymphoblastic leukemia to optimize methotrexate therapy and reducing the associated toxicity.

The effects of ABCC2 G1249A polymorphism on the risk of resistance to antiepileptic drugs: a meta-analysis of the literature

AIMS

The G1249A variant of the multidrug resistance-associated protein 2 (ABCC2) gene may be associated with the development of antiepileptic drug (AED) resistance. Although numerous studies have investigated the association between the G1249A variant and the risk of drug resistance in epilepsy, the results of these studies have been inconclusive. To assess the role of G1249A polymorphism in drug resistance in epilepsy, a meta-analysis was performed.

MATERIALS AND METHODS

We systematically reviewed relevant studies retrieved by the PubMed and Embase. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated based on the date extracted from the studies to evaluate the strength of association. We also analyzed the heterogeneity and sensitivity of each report and the publication bias of the studies.

RESULTS

A total of 6 published studies, involving 2213 patients (1100 patients with drug-resistant epilepsy and 1113 controls with drug-responsive epilepsy) were reviewed in the present meta-analysis. The overall results indicated that the variant genotypes were associated with a significantly decreased risk of AED resistance (AA vs. GG: OR=0.372, 95% CI=0.182-0.762; recessive model: OR=0.399, 95% CI=0.200-0.795) (fixed-effects model). A stratified analysis by ethnicity showed similar findings for Caucasians in an additive model (A vs. G: OR=0.700, 95% CI=0.494-0.992).

CONCLUSIONS

The meta-analysis suggests that the ABCC2 G1249A polymorphism is significantly associated with a decreased risk of AED resistance. However, further functional investigations are warranted to validate the association.