MDR1 Single Nucleotide Polymorphisms Research Articles

P.107: Pattern of CYP3A5 and MDR-1 single nucleotide polymorphism and its impact on tacrolimus levels and clinical outcomes in living renal allograft recipient.

P.107: Pattern of CYP3A5 and MDR-1 single nucleotide polymorphism and its impact on tacrolimus levels and clinical outcomes in living renal allograft recipient.

Pattern of CYP3A5 and MDR-1 single nucleotide polymorphism and its impact on Tacrolimus levels and clinical outcomes in living renal allograft recipient

Abstract Introduction Renal transplant is best form of renal replacement therapy. Most favored immunosuppression includes Tacrolimus, mycophenolate mofetil and steroids. Tacrolimus has narrow therapeutic index and requires therapeutic drug monitoring (TDM). However, there is wide variation in tacrolimus level with weight based fixed dosage regimens. This variability is due to polymorphism of major pathways of metabolism ie CYP3A5 and MDR1 genes. Fast metabolizer require higher dosage and slow metabolizer require lower dosage. Genotype based dosing strategy may be useful to achieve early therapeutic level and reduce infections and rejections. Methodology 160 transplant patients at tertiary care hospital in India were included in this study from 2016 to 2018. Genetic polymorphism analysis in CYP3A5 and MDR1 gene was carried out at time of transplant. All patients were given a fixed weight-based dosage of Tacrolimus. Data was analyzed in relation to genotype polymorphism. Results and discussion 69.2% of Wild variants of CYP 3A5 (Fast metabolizers) have low initial tacrolimus levels. 51.5% of Homo variants (Slow metabolizers) have high initial tac levels. However, all variants achieve optimum tacrolimus levels at same time (mean 12.4 days). There were higher number of infections among slow metabolizers. Conclusion A fixed dosing regimen with TDM result in high and low initial tacrolimus levels in slow and fast metabolizers respectively and more infections in slow metabolizers. However, graft rejections being fewer in number, were not different. A larger sample with genotype based dosing is required to test such a strategy.

Association of Single-Nucleotide Polymorphisms of MDR1 and OPN Genes with Reproductive Traits in Different Breeds of Sows

Association of Single-Nucleotide Polymorphisms of MDR1 and OPN Genes with Reproductive Traits in Different Breeds of Sows

A population approach of rifampicin pharmacogenetics and pharmacokinetics in Mexican patients with tuberculosis

The aim of this study was to develop a population pharmacokinetic model of rifampicin (RMP) in Mexican patients with tuberculosis (TB) to evaluate the influence of anthropometric and clinical covariates, as well as genotypic variants associated with MDR1 and OATP1B1 transporters.A prospective study approved by Research Ethics Committee was performed at Hospital Central in San Luis Potosí, Mexico. TB patients under DOTS scheme and who signed informed consent were consecutively included. Anthropometric and clinical information was retrieved from medical records. Single nucleotide polymorphisms in MDR1 (C3435T) and SLCO1B1 (A388G and T521C) genes were evaluated. RMP plasma concentrations and time data were assessed with NONMEM software.A total of 71 Mexican TB patients from 18 to 72 years old were included for RMP quantification from 0.3 to 12 h after dose; 329 and 97 plasma concentrations were available for model development and validation, respectively. Sequential process includes a typical lag time of 0.25 h prior to absorption start with a Ka of 1.24 h−1 and a zero-order absorption of 0.62 h to characterize the gradual increase in RMP plasma concentrations. Final model includes total body weight in volume of distribution (0.7 L/kg, CV = 26.8%) and a total clearance of 5.96 L/h (CV = 38.5%). Bioavailability was modified according to time under treatment and generic formulation administration.In conclusion, a population pharmacokinetic model was developed to describe the variability in RMP plasma concentrations in Mexican TB patients. Genetic variants evaluated did not showed significant influence on pharmacokinetic parameters. Final model will allow therapeutic drug monitoring at early stages.

Effect of CYP3A5 and ABCB1 Gene Polymorphisms on Tacrolimus Blood Concentration in Renal Transplant Recipients.

Tacrolimus (Tac) is a calcineurin inhibitor (CNI). Its therapeutic range is narrow and pharmacokinetic properties vary among patients. CYP3A5 and MDR1 single-nucleotide polymorphisms (SNPs) are the most effective polymorphisms that play an significant role in the pharmacokinetics of Tac. We investigated the influence of CYP3A5 (A6986G) and MDR1 (C3435T) gene polymorphisms on Tac trough concentration (C0), dose requirements (mg/kg), and dose-adjusted concentrations (ng/mL per mg/kg/d). CYP3A5 [*1/*1 (expresser), *1/*3 (expresser); *3/*3 (non-expresser)] and MDR1 (CC, CT, TT) gene polymorphisms were determined by allele-specific polymerase chain reaction in 67 adult Turkish renal transplant patients. The Tac dose (mg/kg/d) and C0 of each patient was acquired from the patient's file and dose-adjusted concentrations (ng/mL per mg/kg/d) were calculated at the 1st, 3rd, 6th, and 12th months after transplantation. The correlated serum hematocrit, platelet, urea, creatinine, and albumin were also determined. The CYP3A5*1/*3 and CYP3A5*3/*3 allelic frequencies were 5.97% and 94.03%, respectively. There were no patients with the CYP3A5*1/*1 genotype. Tac dose was significantly lower in *3/*3 genotype than in *1/*1 genotype (3rd and 6th months: p ≤ 0.001; 12th month: p ≤ 0.05). Dose-adjusted Tac concentration was statistically higher in the *3/*3 genotype than in *1/*1 genotype at the 3rd and 6th months (p ≤ 0.05). The allelic frequencies of MDR1 CC, CT, and TT were 26.87%, 49.25%, and 23.88%, respectively. No statistically significant differences were detected between MDR1 genotypes and in all analyzed laboratory parameters. CYP3A5 but not MDR1 genetic polymorphisms affected the Tac pharmacokinetics and dose requirements in renal transplant recipients. Pharmacogenetic methods can be used for selecting the initial dose to individualize immunosuppressive therapy.

Selected Genetic Polymorphisms Associated with Hypoxia and Multidrug Resistance in Monoclonal Gammopathies Patients.

Adaptive response to hypoxia is regulated by several mechanisms and transcription factors, including hypoxia-inducible factors (HIFs). Activation of HIF-1α is associated with increased expression of P-glycoprotein and multidrug resistance in cancer cells. In this retrospective study, we analyzed candidate single-nucleotide polymorphisms (SNPs) in HIF-1α and HIF-1β associated with risk of monoclonal gammopathy of undetermined significance (MGUS) or multiple myeloma (MM). Genotypes of SNPs associated with hypoxia were determined in an independent cohort of monoclonal gammopathies (MG) (275 MM and 228 MGUS patients) and in 219 cancer-free controls by real time polymerase chain reaction allelic discrimination. When MM patients were compared to controls, protective role of CG genotype compared to CC in HIF-1β (rs2228099) for MM development was observed (OR = 0.65; CI 0.45-0.95; p = 0.026). Even after adjustment for patients' age and body mass index (BMI), there were significantly lower odds (OR = 0.55; p = 0.045) of developing MM patients of CG genotype in comparison to CC genotype. Log-rank test confirmed association of GT haplotype (rs11549467, rs2057482) in HIF-1α with better overall survival (median 41.8 months; (CI 35.1-48.5)) for "none GT" and median 93.8 months (CI 31.3-156.4) for "at least one GT" haplotype (p = 0.0500). Further, significant associations between SNPs in MDR1 and outcome of MM were found in 110 MM patients that underwent bortezomib-based treatment. Our study showed a genetic predisposition for risk of MG development and/or outcome of MM patients; nevertheless, further studies are needed to confirm our initial analysis.

Association of C3435T, C1236T and C4125A Polymorphisms of the MDR-1 Gene in Egyptian Children with Acute Lymphoblastic Leukaemia

Background:P-glycoprotein (P-gp), a membrane transporter encoded by the multidrug resistance-1 (MDR1) gene, influences pharmacokinetics and metabolism of anticancer drugs and contributes to multidrug resistance phenotype in acute lymphoblastic leukemia (ALL). Genetic variation ofMDR1 in ALL patients is increasingly recognized as a factor influencing response to treatment.Aim:To investigate the possible role of MDR-1 gene polymorphisms (C3435T, C1236T and C4125A) as risk factors for the development and clinical outcome of ALL in Egyptian children.Materials and Methods:Genotyping of MDR-1 C3435T, C1236T and C4125A single nucleotide polymorphisms (SNPs) was accomplished using a polymerase chain reaction–restriction fragment length polymorphism (RFLP-PCR) assay with 120 childhood ALL patients and 100 healthy controls.Results:Homozygous T with the C3435T SNP showed a protective effect as compared to homozygous C (OR=0.748) while heterozygous CT correlated with a poor outcome (high risk, drug unresponsiveness, relapse and high percentage of death). Additionally, the T allele of the C1236T SNP showed a significant relation with ALL risk (OR=1.6). However, there were no significant differences in the genotype and allele frequencies of MDR-1 SNPs between patients and controls. Only one genotype (CC) and one allele of MDR-1 (C4125A) were seen. Neither CA/AA genotypes nor A alleles were present in ALL patients and normal controls. TC was the predominant haplotype in both groups, while CT proved to be minor. The cumulative incidence of relapse was higher with the CC genotype of C1236T as compared with TT.Conclusion:From our preliminary data, the CT genotype of C3435T is associated with a poor ALL outcome while the CC genotype of C1236T is related with an increased incidence of relapse. Although our results provide assistance for oncologist choice of individual therapeutic strategy taking the patient genetic repertoire into consideration, further investigations with larger sample size should be conducted to validate our results.

Association between MDR1 gene polymorphisms and the risk of Crohn's disease in a cohort of Algerian pediatric patients.

The multi-drug resistance gene (MDR1) has raised increasing interest as a susceptibility gene for Crohn's disease (CD). The role of MDR1 single-nucleotide polymorphisms (SNPs) in the predisposition and behavior of CD in the pediatric population is still elusive. Here, we investigated whether SNPs in MDR1 are associated with CD in Algerian pediatric patients. A case-control study was conducted enrolling 47 pediatric CD patients and 100 controls. All subjects were genotyped for the most common MDR1 SNPs (C3434T, C1236T, and G2677A/T) using PCR-RFLP method. We also explored the association between polymorphisms and clinical sub-phenotypes. We have detected no significant association of C3435T SNP and pediatric CD. However, we observed a significantly higher frequency of the risk alleles, 1236T and 2677T/A among the CD patients compared to controls. Moreover, the risk allele 1236T was associated to a higher risk for resective surgery. Our data suggest that the C1236T and G2677A/T SNPs in the MDR1 gene are associated with CD and the C1236T risk allele with a more severe course of disease in Algerian pediatric patients. Further analysis using larger patients group and functional studies would be interesting to elucidate the role of MDR1 gene in pediatric CD.Pediatric Research (2016); doi:10.1038/pr.2016.163.

Molecular and cytogenetic changes in multi-drug resistant cancer cells and their influence on new compounds testing

Multi-drug resistance (MDR) is a major obstacle to successful cancer treatment. Therefore, in vitro models are necessary for the investigation of the phenotypic changes provoked by cytotoxic agents and more importantly for preclinical testing of new anticancer drugs. We analyzed chromosomal, numerical, and structural changes after development of MDR, alterations in p53 and PTEN, single nucleotide polymorphisms (SNPs) in the mdr1 gene and corresponding protein expression of P-glycoprotein (P-gp) in three human MDR cancer cell lines: non-small cell lung carcinoma NCI-H460/R, colorectal carcinoma DLD1-TxR, and glioma U87-TxR. In addition, we explored how these molecular and phenotypic alterations influence the anticancer effect of new drugs. Cytogenetic analysis showed polyploidy reduction after development of MDR in U87-TxR. Losses of 6q in all resistant cancer cell lines and inactivation of p53 in U87-TxR and PTEN in DLD1-TxR were also revealed. Overexpression of P-gp was observed in all MDR cancer cell lines. We evaluated the anticancer activities and MDR reversal potential of Akt inhibitor GSK690693, Ras inhibitor Tipifarnib, and two P-gp inhibitors (jatrophane diterpenoids). Their effects vary due to the cell-type differences, existence of MDR phenotype, presence of mdr1 SNP, and tumor suppressors' alterations. Tipifarnib and jatrophane diterpenoids significantly sensitized MDR cancer cells to paclitaxel. In conclusion, investigated MDR cancer cells obtained new molecular and cytogenetic characteristics that may serve as potential clinical prognostic markers. In addition, these MDR cancer cell lines present a valuable model for preclinical evaluation of new anticancer agents.

Polymorphisms of MDR1, CYP2C19 and P2Y12 genes in Indian population: Effects on clopidogrel response

Influence of genetic variations on the response of clopidogrel, an antiplatelet drug is implicated. In the present study, the prevalence of single nucleotide polymorphisms of MDR1 (C3435T), CYP2C19 [CYP2C19*2 CYP2C19*3, CYP2C19*17] and P2Y12 (i-T744C) in Indian population and their effects on clopidogrel response was analyzed. To analyze the prevalence of polymorphisms, 102 healthy individuals were recruited. Clopidogrel response was assessed by ADP induced platelet aggregation in clopidogrel naïve acute myocardial infarction (AMI) patients (n = 26) screened from 100 AMI cases, before loading dose of 300 mg, at 24 h before next dose and 6 days after on 75 mg per day and platelet aggregation inhibition (PAI) was calculated between these time intervals. Genotyping was carried out by PCR-based restriction enzyme digestion method for C3435T of MDR1 and i-T744C of P2Y12, by multiplex PCR for CYP2C19*2 (G681A) and CYP2C19*3 (G636A) and by nested PCR for CYP2C19*17 (C806T). The effect of the above mentioned genetic variations on PAI was analyzed. Variant allele of CYP2C19*3 was not observed while the prevalence of 3435T of MDR1 (0.524), CYP2C19*2 (681A, 0.352); i-744C of P2Y12 (0.088), as well as wild type allele CYP2C19*17 (C806, 0.897) associated with decrease clopidogrel response were observed. Trend toward poor response to clopidogrel was observed at 24 h with the variant genotypes of CYP2C19*2 and i-T744C of P2Y12 as compared to wild type. The present study did show a trend toward impaired response of clopidogrel to inhibit platelet aggregation with variant genotypes of CYP2C19*2 and iT744C of P2Y12 compared to respective wild type genotype at 24 h.

Frequency of MDR1 single nucleotide polymorphisms in a Jordanian population, including a novel variant

The multidrug resistance gene (MDR1 or ABCB1) codes for P-glycoprotein, which plays an important role in regulating absorption, distribution, and elimination of drugs. We examined MDR1 gene variants in 100 unrelated subjects from various regions of Jordan. The MDR1 gene was scanned using direct sequencing. Six rare variants in MDR1 were detected, including a new variant, T3075A. This variant did not affect the protein sequence (synonym for threonine). Among the common SNPs, the frequencies of rs1128503 (C1236T) genotypes were: 0.23 (CC), 0.41 (CT) and 0.36 (TT). For the rs2032582 (G2677T) SNP, genotype frequencies were 0.38 for GG, 0.45 for GT, 0.13 for TT, 0.03 for GA, and 0.01 for TA, whereas for rs1045642 (C3435T), genotype frequencies were 0.17 for CC, 0.5 for CT and 0.33 for TT. The observed distribution of the common variants in the Jordanian population was within the range detected in other populations. These data on MDR1 gene variants in the Jordanian population will be useful for investigations on response to P-glycoprotein substrate drugs.

Polymorphisms in the Human Organic Cation Transporter (hOCT1) (Solute Carrier Family 22, SLC22A1) and the Multidrug Resistance Gene (MDR1, ABCB1): Correlation with Imatinib Levels and Clinical Course in Chronic Myeloid Leukemia Patients

AbstractAbstract 1340▪▪This icon denotes a clinically relevant abstract Background:Drug metabolism/disposition genes have substantial impact on drug pharmacology. Single nucleotide polymorphisms (SNPs) may affect gene activity. For CML, the human organic cation transporter (hOCT1) transports imatinib mesylate (IM) into cells. The multidrug resistance gene MDR1 effluxes IM. MDR1 SNPs are correlated with response to IM (Dulucq et al, 2008). We studied hOCT1 and MDR1 SNPs and correlated them with plasma levels and clinical response to IM. We studied an exon 2 hOCT1 SNP (480C>G, Phe160Leu) for which homozygosity (GG) is associated with IM failure (Kim, 2009), and an exon 7 SNP (1222A>G, Met408Val) which correlated with major molecular remission (MMR) (Takahashi, 2010). Both are prevalent in Caucasians (exon 2 SNP: 22%, exon 7 SNP: 60%) (Kerb, 2006). Methods:We studied 84 chronic phase CML patients (pts) aged 17–89 years, followed from 16 months (mos) to 20 yrs from diagnosis (mean 94 mos). 19% were diagnosed during or prior to 2000. Time to initiating IM ranged from <1 to 108 mos (median <1 mo). IM therapy duration ranged 12–142 mos (mean 75). 61 pts took 400 mg/day, 14 pts took >400 mg (mean 621 mg), and 9 pts took <400 mg (mean 283 mg). Trough IM levels were performed on 81 pts by Novartis Pharmaceuticals. Treatment response was defined as per European Leukemia Net criteria. Until 2004, MMR was defined as PCR negativity using RT-PCR, and thereafter, using real time PCR (BCR/Abl<0.1% on an international scale). Results:The overall mean IM trough level was 1,168 ng/ml (+/–477), and varied by dose. Pts on 400 mg had a mean level of 1145 (+/– 468), pts on >400 mg had 1392 (+/– 472), and pts on <400 mg had 909 (+/– 425).Table 1 shows genotype frequencies.Table 1Genotype frequencieshOCT1MDR1Ex. 2% (n)Ex. 7% (n)2677% (n)3435% (n)CC60 (50)GG40 (33)GG76 (62)CC32 (27)CG32 (27)AG48 (40)GT16 (13)CT37 (31)GG8 (7)AA12 (10)TT8 (7)TT31 (26)hOCT1 exon 2 GG homozygotes had higher IM levels than CG/CC genotypes (1231 +/− 644 versus 1162 +/−463). hOCT1 GG patients were on slightly higher doses (mean 457 +/− 162 mg compared to 422 +/− 96 mg for CC/CG pts). hOCT1 exon 7 AA homozygotes had the same IM levels as did GG/AG pts (1178 +/− 477 for AA, 1177 +/− 476 for GG/AG). This is despite the fact that the AA homozygotes were on higher doses (500 +/− 134 mg for AA, 413 +/− 93 mg for GG/AG). Notably, 20% (2/10) AA patients failed IM compared to 11% (8/73) GG/AG pts.MDR1 2677 TT had lower than average IM levels (964 +/− 557) on a mean dose of 414 +/− 90 mg. Pts with genotypes 2677GG/GT had IM levels of 1195+/−473 on a slightly higher dose of 428 +/− 104 mg.MDR1 3435 TT homozygotes had similar IM levels to CC/CT pts (TT: 1127 +/− 434; CC/CT: 1188 +/− 434). TT patients were on slightly lower doses (404 +/− 77 compared to 434 +/− 111 mg).82/84 of the pts are still alive and 82% are still on IM. 15 pts discontinued IM (10 treatment failures, 5 due to intolerance). Only two pts developed accelerated phase or blast crisis.Time to MMoR is seen in Table 2, as related to genotype.Table 2Time to MMR (mos)hOCT1MDR1Ex. 2mosEx. 7mosG2677TmosC3435 TmosCC15.4GG16.3GG12.1CC13CG14.2AG12.3GT14.6CT11.6GG8AA17.6TT20.2TT20.120 pts lost molecular remission (LMR) at some point. Some of these had received IM as second line therapy (average 17.7 mos from diagnosis to starting IM). Half of the LMR events occurred when no second like TKIs were available so IM dose was increased. Half the pts with LMR switched to a newer TKI. Of treatment failures, there was a tendency to more A alleles in hOCT1 Exon 7 (AG or AA) and more T alleles in both MDR1 SNPs (GT/TT for 2677 and CT/TT for 3435). Conclusions:1. IM levels are associated with clinical response in CML. Treatment failures may be caused by suboptimal IM dosing. Alternate TKIs may overcome this problem. 2. Failures were more likely in pts for whom IM was not front line therapy. 3. Genotypes seem to correlate with IM levels and with treatment response for both SNPs. The hOCT1 AA genotype was associated with a higher dose requirement and more treatment failures. TT genotype for both MDR1 SNPs correlated with longer time to MMR (Table 2). Disclosures:Rund:Novartis Corporation: Honoraria, Research Funding.

MDR1 polymorphisms (G2677T and C3435T) in B-chronic lymphocytic leukemia

The human multidrug resistance (MDR1) gene encodes P-glycoprotein, which affects the pharmacokinetics of many drugs. We investigated whether common MDR1 single-nucleotide polymorphisms (C3435T and G2677T) affect predisposition to B-chronic lymphocytic leukemia (B-CLL). Genotyping was performed in 65 patients with CLL and in 70 controls using polymerase chain reaction—restriction fragment length polymorphism. We observed a higher frequency of carriers of 3435CT gene among B-CLL patients as compared to normal individuals (58.5 vs. 22.9 %, p = <0.001). The genotype 3435CT was associated with B-CLL [odds ratio = 4.8, 95 % confidence interval = 2.3–10.0]. Moreover, patient and control groups did not differ significantly regarding the MDR1 genotype (G2677T). Furthermore, no correlation was shown between the MDR1 (3435 or 2677) genotypes and clinical and laboratory data of patient group. These data indicate that MDR1 C3435T single-nucleotide polymorphism may carry an increased risk of developing B-CLL.

MDR1 single nucleotide polymorphism C3435T in Turkish patients with non-small-cell lung cancer

We assessed whether single nucleotide polymorphisms (SNPs) in MDR1 gene C3435T predicted the outcome of platinum-based chemotherapies and survival in our non small cell lung cancer (NSCLC) patients. A total of 79 non-small cell lung cancer patients were enrolled to study. We determined the MDR1 C3435T single nucleotide gene polymorphisms. Median age was 60years: 91.7% male, 8.9% female. We found that CC, CT, TT genotype and T, C allele frequencies in lung cancer patients as 24.1%, 62%, 13.9% and 44.3%, 55.7%, respectively. Patients with CT genotype had a higher response rate (11.4%) than the other genotypes. However, this difference is not statistically significant (p=0.743). Cox regression analysis for overall survival showed that ECOG PS status 0 (HR PS 1 vs. 0, 5.68 p=0.002; HR of PS 2 vs. 0 is 21.579, p=0.001; HR of PS 3 vs. 0 is 35.35, p=0.001), stage ≤II (HR of stage III vs. I+II is 17.77; p=0.016, HR of stage IV vs. I+II is 26.97, p=0.006), and albumin level ≥3g/dl (HR of albumin <3g/dl vs. ≥3g/dl is 2.46, p=0.044) were the most important prognostic factors (also, time to progression was related to these factors). There was no significant association between the genotypes and clinicopathologic parameters; however, good performance status, early stage and ≥3g/dl albumin level were found to be the most important prognostic factors for overall survival and progression-free survival.

Antimalarial Drug Sensitivity Profile of Western Kenya Plasmodium falciparum Field Isolates Determined by a SYBR Green I in vitro Assay and Molecular Analysis

In vitro drug sensitivity and molecular analyses of Plasmodium falciparum track drug resistance. DNA-binding fluorescent dyes like SYBR Green I may allow field laboratories, proximal to P. falciparum collection sites, to conduct drug assays. In 2007-2008, we assayed 121 P. falciparum field isolates from western Kenya for 50% inhibitory concentrations (IC(50)) against 6 antimalarial drugs using a SYBR Green I in vitro assay: 91 immediate ex vivo (IEV) and 30 culture-adapted, along with P. falciparum reference clones D6 (chloroquine [CQ] sensitive) and W2 (CQ resistant). We also assessed P. falciparum mdr1 (Pfmdr1) copy number and single nucleotide polymorphisms (SNPs) at four codons. The IC(50)s for IEV and culture-adapted P. falciparum isolates were similar, and approximated historical IC(50)s. For Pfmdr1, mean copy number was 1, with SNPs common at codons 86 and 184. The SYBR Green I assay adapted well to our field-based laboratory, for both IEV and culture-adapted P. falciparum, warranting continued use.

Polymorphisms and haplotypes in multidrug resistance 1 gene are not associated with chronic lymphocytic leukemia susceptibility and prognostic parameters of chronic lymphocytic leukemia in Chinese population

The human multidrug resistance (MDR1, ABCB1) gene encodes P-glycoprotein (P-gp), which affects the pharmacokinetics of many drugs. Here, we investigated whether common MDR1 single nucleotide polymorphisms (SNPs) (C1236T, C3435T, and G2677T/A) affect predisposition to chronic lymphocytic leukemia (CLL). Genotyping was performed in 150 patients with CLL and 117 controls using polymerase chain reaction (PCR)-based assays. Haplotypes were inferred using the PHASE algorithm. We found comparable allele and genotype frequencies among patients with CLL and controls. Moreover, patient and control groups did not differ regarding MDR1 haplotype distribution (p = 0.97). Furthermore, no correlation was shown between the MDR1 1236, 3435, or 2677 genotypes and Binet stage, unmutated immunoglobulin heavy-chain variable region (IGHV) status, CD38 expression, ZAP-70 expression, and p53 deletion. In conclusion, our results do not support a major influence of MDR1 variants on the risk of CLL, and these genomic polymorphisms are not associated with clinical prognostic factors in Chinese patients with CLL.

Over-expression of MDR1 in amrubicinol-resistant lung cancer cells

Amrubicin, a totally synthetic 9-aminoanthracycline anticancer drug, has shown promising activity for lung cancer, but little is known about the mechanism of resistance for this agent. This study was aimed to clarify the role of P-glycoprotein (P-gp) in amrubicinol, an active metabolite of amrubicin, resistance in lung cancer cells. Amrubicinol-resistant cell line PC-6/AMR-OH was developed by continuously exposing the small-cell lung cancer cell line PC-6 to amrubicinol. Gene expression level of MDR1, which encodes P-gp, and intracellular accumulation of amrubicinol were evaluated by PC-6 and PC-6/AMR-OH cells. The involvement of MDR1 in amrubicinol resistance was evaluated by treatment with P-gp inhibitor verapamil and small interfering RNA (siRNA) against MDR1. Also, expression levels and single-nucleotide polymorphisms (SNPs) of MDR1 in 22 lung cancer cell lines were examined, and the relationships between these factors and sensitivity to amrubicinol were evaluated. The MDR1 gene was increased approximately 4,500-fold in PC-6/AMR-OH cells compared with PC-6 cells, and intracellular accumulation of amrubicinol in PC-6/AMR-OH cells was decreased to about 15 percent of that in PC-6 cells. Treatment with verapamil and siRNA against MDR1 significantly increased the sensitivity to amrubicinol in PC-6/AMR-OH cells with increased cellular accumulation of amrubicinol. Meanwhile, neither MDR1 gene expression levels nor SNPs of the gene were associated with amrubicinol sensitivity. Results of this study indicate that increased MDR1 expression and P-gp activity confer acquired resistance to amrubicinol. In contrast, neither expression level nor SNPs of MDR1 are likely to be predictive markers for amrubicin activity.

Genetic variants in MDR1 and CYP3A5 and vincristine toxicity in children with acute lymphoblastic leukemia.

9526 Background: Vincristine plays a key role in the treatment of acute lymphoblastic leukemia (ALL) in children. Constipation and peripheral or central neurotoxicity's are the most common side effects. Pharmacokinetic parameters are unreliable to determine which patients are at risk for developing these side effects. Pharmacogenetic studies might help to identify those patients at risk. Therefore we investigated the role of functional single nucleotide polymorphisms (SNPs) in two genes encoding enzymes that play an important role in the metabolism of vincristine, namely the multi-drug resistance (MDR1) gene and the cytochrome P450 enzyme (CYP3A5). Methods: We genotyped 105 children with ALL. In each patient, vincristine toxicity was graded retrospectively according to the National Cancer Institute toxicity scale. SNPs were genotyped by TaqMan SNP genotyping assays. The association between vincristine toxicity and each SNP was estimated using logistic regression models. Two-way interactions between the MDR1 and CYP3A5 were investigated using multivariate logistic models. Results: Elevated liver enzymes were associated with a variant in CYP3A5, namely rs776746 (CYP3A5*3; p=0.040). Peripheral polyneuropathy was associated with the 3435C>T polymorphism in MDR1 (rs1128503; p=0.025). Interaction between 3435C>T and 2677C>T (rs2032582) in MDR1 showed a significant relationship with CNS toxicity (p=0.044). Conclusions: This study shows that genetic variations in genes involved in vincristine metabolism are probably related with toxicity. Future studies are necessary to determine whether these SNPs in MDR1 and CYP3A5 can be used for adjustment of vincristine treatment. No significant financial relationships to disclose.

MDR1 3435T and 1236T alleles delay disease progression to pediatric AIDS but have no effect on HIV-1 vertical transmission

Single nucleotide polymorphisms (SNPs) in the MDR1 gene, coding for the drug transporter P-glycoprotein, may modulate the response to antiretroviral therapy and susceptibility to HIV-1 infection. We investigated whether the MDR1 SNPs C1236T (exon 12) and C3435T (exon 26) affect HIV-1 vertical transmission and progression to pediatric AIDS. The MDR1 genotypes were identified by PCR-restriction fragment length polymorphism (RFLP) assays in 219 HIV-infected, 128 exposed uninfected children and 231 HIV-seronegative blood donors. Genotype and haplotype frequencies were estimated in the different groups. The median follow-up time of the infected cohort was 108 months and AIDS-free time was evaluated for the different MDR1 genotypes in 171 HIV-infected children. We found that both C1236T and C3435T polymorphisms were highly frequent in the studied groups (approximately 0.44) and showed strong linkage disequilibrium. There was no association between MDR1 genotypes and HIV-1 vertical transmission. However, a protective effect against progression to AIDS was associated with MDR1 3435CT, 1236CT and 1236TT genotypes (P = 0.005, P = 0.024 and P = 0.026, respectively). Moreover, haplotype pairs' analysis showed that the 3435CT/1236CT and 3435CT/1236TT exerted a significant protection against progression to pediatric AIDS (P = 0.0025 and P = 0.006, respectively). We conclude that in Argentinean children, MDR1 genotypes are associated with progression to AIDS, but they do not affect HIV-1 susceptibility by vertical transmission. These results support the notion that P-glycoprotein plays a role in HIV-1 infection independently from its role in drug transport.

Multidrug resistance gene (MDR1) polymorphisms correlate with imatinib response in chronic myeloid leukemia

The human multidrug resistance gene (MDR1, ABCB1) codes for P-glycoprotein (P-gp) that affects the pharmacokinetics of many drugs. MDR1 single nucleotide polymorphisms (SNPs) are associated with drug clearance. Imatinib is a substrate of P-gp-mediated efflux. We investigated the MDR1 T1236C, G 2677T/A, and C3435T polymorphism in 52 patients with chronic myeloid leukemia treated with imatinib. The distribution of MDR1 1236, 2677, or 3435 genotypes was significantly different between the resistance patients and sensitivity patients. The resistance incidence correlated with the number of T alleles at locus 1236 and 3435. Resistance was higher for patients homozygous for the 1236T allele when compared to patients with CT/CC genotype groups (75% vs. 31.3%, P = 0.004). For the G2677T/A polymorphism, a better complete cytogenetic remission was observed for patients with genotype AG/AT/AA, when compared to other genotype groups (TT/GT/GG, P = 0.02). Patients with 3435 TT/CT genotypes showed a higher resistance when compared with patients with CC genotype (59.4% vs. 25%, P = 0.023). In conclusion, determination of 1236T, C3435T, and G2677T MDR1 polymorphisms might be useful in response prediction to therapy with imatinib in patients with CML.