Influence of ABCB1 gene polymorphisms on the pharmacokinetics of verapamil among healthy Chinese Han ethnic subjects

Genetic and clinical predictors of rifapentine and isoniazid pharmacokinetics in paediatrics with tuberculosis infection

OBJECTIVES

Twelve weekly doses of rifapentine and isoniazid (3HP regimen) are recommended for TB preventive therapy in children with TB infection. However, they present with variability in the pharmacokinetic profiles. The current study aimed to develop a pharmacokinetic model of rifapentine and isoniazid in 12 children with TB infection using NONMEM.

METHODS

Ninety plasma and 41 urine samples were collected at Week 4 of treatment. Drug concentrations were measured using a validated HPLC-UV method. MassARRAY® SNP genotyping was used to investigate genetic factors, including P-glycoprotein (ABCB1), solute carrier organic anion transporter B1 (SLCO1B1), arylacetamide deacetylase (AADAC) and N-acetyl transferase (NAT2). Clinically relevant covariates were also analysed.

RESULTS

A two-compartment model for isoniazid and a one-compartment model for rifapentine with transit compartment absorption and first-order elimination were the best models for describing plasma and urine data. The estimated (relative standard error, RSE) of isoniazid non-renal clearance was 3.52 L·h-1 (23.1%), 2.91 L·h-1 (19.6%), and 2.58 L·h-1 (20.0%) in NAT2 rapid, intermediate and slow acetylators. A significant proportion of the unchanged isoniazid was cleared renally (2.7 L·h-1; 8.0%), while the unchanged rifapentine was cleared primarily through non-renal routes (0.681 L·h-1; 3.6%). Participants with the ABCB1 mutant allele had lower bioavailability of rifapentine, while food prolonged the mean transit time of isoniazid.

CONCLUSIONS

ABCB1 mutant allele carriers may require higher rifapentine doses; however, this must be confirmed in larger trials. Food did not affect overall exposure to isoniazid and only delayed absorption time.

Pharmacogenomic study-A pilot study of the effect of pharmacogenomic phenotypes on the adequate dosing of verapamil for migraine prevention

OBJECTIVE

To investigate factors affecting the efficacy and tolerability of verapamil for migraine prevention using individual pharmacogenomic phenotypes.

BACKGROUND

Verapamil has a wide range of dosing in headache disorders without reliable tools to predict the optimal doses for an individual.

METHODS

This is a retrospective chart review examining adults with existing pharmacogenomic reports at Mayo Clinic who had used verapamil for migraine. Effects of six cytochrome P450 phenotypes on the doses of verapamil for migraine prevention were assessed.

RESULTS

Our final analysis included 33 migraine patients (82% with aura). The mean minimum effective and maximum tolerable doses of verapamil were 178.2(20-320) mg and 227.9(20-480) mg. A variety of CYP2C9, CYP2D6, and CYP3A5 phenotypes were found, without significant association with the verapamil doses after adjusting for age, sex, body mass index, and smoking status.

CONCLUSIONS

We demonstrated a wide range of effective and tolerable verapamil doses used for migraine in a cohort with various pharmacogenomic phenotypes.

A Dose-Finding Study to Guide Use of Verapamil as an Adjunctive Therapy in Tuberculosis

Induction of mycobacterial efflux pumps is a cause of Mycobacterium tuberculosis (Mtb) drug tolerance, a barrier to shortening antitubercular treatment. Verapamil inhibits Mtb efflux pumps that mediate tolerance to rifampin, a cornerstone of tuberculosis (TB) treatment. Verapamil's mycobacterial efflux pump inhibition also limits Mtb growth in macrophages in the absence of antibiotic treatment. These findings suggest that verapamil could be used as an adjunctive therapy for TB treatment shortening. However, verapamil is rapidly and substantially metabolized when co-administered with rifampin. We determined in a dose-escalation clinical trial of persons with pulmonary TB that rifampin-induced clearance of verapamil can be countered without toxicity by the administration of larger than usual doses of verapamil. An oral dosage of 360 mg sustained-release (SR) verapamil given every 12 hours concomitantly with rifampin achieved median verapamil exposures of 903.1 ng.h/mL (area under the curve (AUC)0-12 h ) in the 18 participants receiving this highest studied verapamil dose; these AUC findings are similar to those in persons receiving daily doses of 240 mg verapamil SR but not rifampin. Moreover, norverapamil:verapamil, R:S verapamil, and R:S norverapamil AUC ratios were all significantly greater than those of historical controls receiving SR verapamil in the absence of rifampin. Thus, rifampin administration favors the less-cardioactive verapamil metabolites and enantiomers that retain similar Mtb efflux inhibitory activity to verapamil, increasing overall benefit. Finally, rifampin exposures were 50% greater after verapamil administration, which may also be advantageous. Our findings suggest that a higher dosage of verapamil can be safely used as adjunctive treatment in rifampin-containing treatment regimens.

P-glycoprotein mechanical functional analysis using in silico molecular modeling: Pharmacokinetic variability according to ABCB1 c.2677G > T/A genetic polymorphisms

P-glycoprotein (P-gp) is a widely membrane-expressed multi-drug transporter. It is unclear whether the pharmacokinetic diversity of P-gp substrates is highly dependent on ABCB1 polymorphisms encoding P-gp. The purpose of this study is to analyze the mechanistic function of P-gp through in silico molecular modeling and to approach the resolution of controversy over pharmacokinetic differences according to ABCB1 polymorphisms. P-gp conformations of apo, ligand-docked, and outward-facing states can be modeled based on structural information of human P-gp. And polymorphic P-gp structures were constructed through homology modeling. ABCB1 c.2677G > T/A (Ala893Ser/Thr), did not correspond to P-gp's nucleotide-binding-domain (NBD) or drug-binding-pocket (DBP) or involve mechanical conformational changes. Although amino acid substitution by ABCB1 c.2677G > T/A caused a 30 % increased strain in an α-helix hinge between the NBD and DBP in P-gp's internal tunnel, there were no overall structural changes compared to wild-type. ABCB1 c.2677G > T/A may increase torsional energy, impacting conformational change rate, but this does not significantly affect P-gp's general functioning. Fexofenadine docking into P-gp's DBP explained the substrate interaction, but no effect by ABCB1 c.2677G > T/A was confirmed. Our findings provide additional insights useful in resolving the debate about the influence of ABCB1 polymorphisms on the interindividual pharmacokinetic variability of P-gp substrates.

A dose-finding study to guide use of verapamil as an adjunctive therapy in tuberculosis

Induction of mycobacterial efflux pumps is a cause of Mycobacterium tuberculosis (Mtb) drug tolerance, a barrier to shortening antitubercular treatment. Verapamil inhibits Mtb efflux pumps that mediate tolerance to rifampin, a cornerstone of tuberculosis treatment. Verapamil's mycobacterial efflux pump inhibition also limits Mtb growth in macrophages in the absence of antibiotic treatment. These findings suggest that verapamil could be used as an adjunctive therapy for TB treatment shortening. However, verapamil is rapidly and substantially metabolized when co-administered with rifampin. We determined in a dose-escalation clinical trial that rifampin-induced clearance of verapamil can be countered without toxicity by the administration of larger than usual doses of verapamil. An oral dosage of 360 mg sustained-release (SR) verapamil given every 12 hours concomitantly with rifampin achieved median verapamil exposures of 903.1 ng.h/ml (AUC 0-12h), similar to those in persons receiving daily doses of 240 mg verapamil SR but not rifampin. Norverapamil:verapamil, R:S verapamil and R:S norverapamil AUC ratios were all significantly greater than those of historical controls receiving SR verapamil in the absence of rifampin, suggesting that rifampin administration favors the less-cardioactive verapamil metabolites and enantiomers. Finally, rifampin exposures were significantly greater after verapamil administration. Our findings suggest that a higher dosage of verapamil can be safely used as adjunctive treatment in rifampin-containing treatment regimens.

Genetic variants related to successful migraine prophylaxis with verapamil

BACKGROUND

Currently, there is no biologically based rationale for drug selection in migraine prophylactic treatment.

METHODS

To investigate the genetic variation underlying treatment response to verapamil prophylaxis, we selected 225 patients from a longitudinally established, deeply phenotyped migraine database (N = 5983), and collected uninterrupted quantitated verapamil treatment response data and DNA for these 225 cases. We recorded the number of headache days in the four weeks preceding treatment with verapamil and for four weeks, following completion of a treatment period with verapamil lasting at least five weeks. Whole-exome sequencing (WES) was applied to a discovery cohort consisting of 21 definitive responders and 14 definitive non-responders, and the identified single nucleotide polymorphisms (SNPs) showing significant association were genotyped in a separate confirmation cohort (185 verapamil treated patients). Statistical analysis of the WES data from the discovery cohort identified 524 SNPs associated with verapamil responsiveness (p < 0.01); among them, 39 SNPs were validated in the confirmatory cohort (n = 185) which included the full range of response to verapamil from highly responsive to not responsive.

RESULTS

Fourteen SNPs were confirmed by both percentage and arithmetic statistical approaches. Pathway and protein network analysis implicated myo-inositol biosynthetic and phospholipase-C second messenger pathways in verapamil responsiveness, emphasizing the earlier pathogenic understanding of migraine. No association was found between genetic variation in verapamil metabolic enzymes and treatment response.

CONCLUSION

Our findings demonstrate that genetic analysis in well-characterized subpopulations can yield important pharmacogenetic information pertaining to the mechanism of anti-migraine prophylactic medications.

Effects of ABCB1 rs1045642 polymorphisms on the efficacy and safety of amlodipine therapy in Caucasian patients with stage I-II hypertension

PURPOSE

The aim of this study was to determine the impact of ABCB1 (MDR1) rs1045642 polymorphisms on the efficacy and safety of amlodipine in Caucasian patients.

PATIENTS AND METHODS

The 12-week study included 100 patients. Patients with the newly diagnosed stage I-II hypertension (HT) were recruited to complete genotyping of the rs1045642 single-nucleotide polymorphism (SNP). The study design did not include a control group. Before treatment, all patients either did not undergo antihypertensive treatment at all or did not receive regular antihypertensive therapy. The initial dose was 5 mg/day. Four office blood pressure measurements, two 24-hour noninvasive ambulatory blood pressure measurements, and questionnaires of Tsvetov were used to evaluate the efficacy and safety of amlodipine.

RESULTS AND CONCLUSION

The highest antihypertensive effect in combination with the lowest incidence of adverse reactions was observed in the TT group, while patients with the CC genotype showed a low antihypertensive effect and the highest incidence of adverse effects. Patients with the CC genotype presented with adverse effects predominantly in the form of edema. A total of 33 patients reached the target blood pressure (SBP <140 mmHg; DBP <90 mmHg): two patients with the CC genotype (12%); 18 patients with the CT genotype (34%); and 13 patients with the TT genotype (43%). The intergroup differences were: CC vs CT, P=0.02; CC vs TT, P=0.02; and CT vs TT, P=0.05. The results of this study indicate the potential of pharmacogenetic testing for rs1045642 SNP when prescribing amlodipine for the first time in Caucasian patients with stage I-II arterial HT.

Gambogic acid as a non-competitive inhibitor of ATP-binding cassette transporter B1 reverses the multidrug resistance of human epithelial cancers by promoting ATP-binding cassette transporter B1 protein degradation

Gambogic acid (GA) is known for its anti-cancer activity in a phase II clinical trial. However, the detailed molecular mechanisms of its anti-multidrug resistance remain unclear. The present study was designed to study the relationship between GA and multidrug-resistant protein ATP-binding cassette transporter B1 (ABCB1). GA dose dependently inhibited ABCB1 activity levels in the in vitro Pgp-Glo assay system and increased the cellular accumulation of ABCB1 substrate adriamycin. Although GA had no significant influence on ABCB1 mRNA in the real-time PCR assay, Western blot detection indicated the compound reduced ABCB1 protein levels. Further study showed the proteasome inhibitor MG-132 reversed the GA-decreased ABCB1 level and prolonged half-life of ABCB1. It was also found that GA coordinated with other anti-cancer drugs (such as adriamycin, docetaxel, verapamil and protopanaxadiol) to enhance cellular cytotoxicity on human epithelial cancer cell lines with higher ABCB1 expression levels. These data suggest that GA functions as a non-competitive inhibitor of ABCB1 by directly inhibiting and reducing its expression levels by promoting protein degradation through post-translational proteasome pathway. The results of this study will aid in the understanding of the synergistic effects of combining GA with other drugs as a new anti-multidrug-resistant agent.

Functional significance of genetic polymorphisms in P-glycoprotein (MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2)

Recent pharmacogenomic/pharmacogenetic (PGx) studies have disclosed important roles for drug transporters in the human body. Changes in the functions of drug transporters due to drug/food interactions or genetic polymorphisms, for example, are associated with large changes in pharmacokinetic (PK) profiles of substrate drugs, leading to changes in drug response and side effects. This information is extremely useful not only for drug development but also for individualized treatment. Among drug transporters, the ATP-binding cassette (ABC) transporters are expressed in most tissues in humans, and play protective roles; reducing drug absorption from the gastrointestinal tract, enhancing drug elimination into bile and urine, and impeding the entry of drugs into the central nervous system and placenta. In addition to PK/pharmacodynamic (PD) issues, ABC transporters are reported as etiologic and prognostic factors (or biomarkers) for genetic disorders. Although a consensus has not yet been reached, clinical studies have demonstrated that the PGx of ABC transporters influences the overall outcome of pharmacotherapy and contributes to the pathogenesis and progression of certain disorders. This review explains the impact of PGx in ABC transporters in terms of PK/PD, focusing on P-glycoprotein and breast cancer resistance protein (BCRP).