Modeling of drug-transporter interactions using structural information

Drug-transporter interactions have recently been demonstrated to play an important part in multidrug resistance, drug-drug interactions and drug disposition. Such interactions can occur as inhibition of transport, efflux out of cellular systems or enhanced transport into cellular systems. Modeling efforts are currently being undertaken using both ligand- and transporter-based methods, such as (3D) quantitative structure-activity relationship studies, pharmacophore modeling, homology modeling and molecular dynamics studies. The aim of these efforts is to explain how differences in chemical structures either enhance or weaken interactions with the transporter, or to elucidate how the transporter functions in general. This review summarizes recent modeling efforts in the light of difficulties such as the lack of X-ray crystal structures and the complexity and inconsistency of available experimental data on drug-transporter interactions.     

Evaluation of drug-transporter interactions using in vitro and in vivo models

Drug transporters, including efflux transporters (the ATP binding cassette (ABC) proteins) and uptake transporters (the solute carrier proteins (SLC)), have an important impact on drug disposition, efficacy, drug-drug interactions and toxicity. Identification of the interactions of chemical scaffolds with transporters at the early stages of drug development can assist in the optimization and selection of new drug candidates. In this review, we discuss current in vitro and in vivo models used to investigate the interactions between drugs and transporters such as P-gp, MRP, BCRP, BSEP, OAT, OATP, OCT, NTCP, PEPT1/2 and NT. In vitro models including cell-based, cell-free, and yeast systems as well as in vivo models such as genetic knockout, gene deficient and chemical knockout animals are discussed and compared. The applications, throughput, advantages and limitations of each model are also addressed in this review.     

Small-molecule inhibitors of protein-protein interactions

Protein-protein interactions regulate almost all aspects of cellular signaling and aberrant protein-protein interactions have the potential to cause or contribute to human disease. The modulation of these interactions by drug-like molecules would offer previously unavailable opportunities to explore the relevance of pre-selected protein-protein interactions for cellular signaling, as well as benefits to patients. After an initial period of skepticism with regards to feasibility, there is now an encouraging set of data indicating that the effective and selective modulation of protein-protein interactions by drug-like molecules is attainable. This review highlights selected areas of current research that are aimed at identifying potent inhibitors of disease-relevant protein-protein interactions.     

Clinical reappraisal of the influence of drug-transporter polymorphisms in epilepsy

Introduction: Although novel antiepileptic drugs (AEDs) have been recently released, the issue of drug resistance in epileptic patients remains unsolved and largely unpredictable.

Areas covered: We aim to assess the clinical impact of genetic variations that may influence the efficacy of medical treatment in epilepsy patients. Indeed, many genes, including genes encoding drug transporters (ABCB1), drug targets (SCN1A), drug-metabolizing enzymes (CYP2C9, CYP2C19), and human leucocyte antigen (HLA) proteins, may regulate the mechanisms of drug resistance in epilepsy. This review specifically focuses on the ABC genes, which encode multidrug resistance-associated proteins (MRPs) and may reduce the blood–brain barrier penetration of anticonvulsant AEDs.

Expert opinion: Drug resistance remains a crucial problem in epilepsy patients. Pharmacogenomic studies may improve our understanding of drug responses and drug resistance by exploring the impact of gene variants and predicting drug responses and tolerability.     

Drug interactions with cholinesterase inhibitors

Cholinesterase inhibitors are used for the symptomatic treatment of patients with Alzheimer's disease. This population often has numerous comorbidities and receives treatment with multiple medications. The astute clinician should remain mindful of possible drug interactions, both pharmacokinetic and pharmacodynamic, that may occur with concomitant treatment. Although pharmacokinetic interactions have been reported, pharmacodynamic interactions play a far greater role in the significance of drug interactions, with anticholinergic medications being most concerning. Commonly prescribed medications, such as antihistamines and tricyclic antidepressants, often have anticholinergic properties that alone or in combination with one another can antagonise the effects of cholinesterase inhibitors. Other medication classes such as antipsychotics and cholinergic agents may also result in pharmacodynamic interactions. However, for the most part, cholinesterase inhibitors can be used safely in combination with other medications.     

Interfacial inhibitors of protein-nucleic acid interactions

This essay develops the paradigm of "Interfacial Inhibitors" (Pommier and Cherfils, TiPS, 2005, 28: 136) for inhibitory drugs beside orthosteric (competitive or non-competitive) and allosteric inhibitors. Interfacial inhibitors bind with high selectivity to a binding site involving two or more macromolecules within macromolecular complexes undergoing conformational changes. Interfacial binding traps (generally reversibly) a transition state of the complex, resulting in kinetic inactivation. The exemplary case of interfacial inhibitor of protein-DNA interface is camptothecin and its clinical derivatives. We will also provide examples generalizing the interfacial inhibitor concept to inhibitors of topoisomerase II (anthracyclines, ellipticines, epipodophyllotoxins), gyrase (quinolones, ciprofloxacin, norfloxacin), RNA polymerases (alpha-amanitin and actinomycin D), and ribosomes (antibiotics such as streptomycin, hygromycin B, tetracycline, kirromycin, fusidic acid, thiostrepton, and possibly cycloheximide). We discuss the implications of the interfacial inhibitor concept for drug discovery.     

Pharmacokinetic interactions between HIV-protease inhibitors in rats

The interactions of four HIV-protease inhibitors, ritonavir (RIT), saquinavir (SAQ), indinavir (IND) and nelfinavir (NEL), were examined by in vitro metabolic studies using rat liver microsomal fractions. The substrate concentrations employed were 0.75 approximately 12 microM, and the inhibitor concentrations were 2.5 approximately 60 microM. The metabolic clearance rates of SAQ, NEL and IND as determined by V(max)/K(m) were 170.9+/-10.9, 126.0+/-4.4 and 73.0+/-2.0 microL/min/mg protein, respectively. RIT was a potent inhibitor of the other three protease inhibitors, and the inhibition constants (K(i)) were 1.64 microM for SAQ, 0.95 microM for IND and 1. 01 microM for NEL. NEL was the second strongest inhibitor with a K(i) for NEL inhibition of IND metabolism of 2.14 microM. IND was the third strongest inhibitor with K(i)s of 2.76 microM for inhibition of NEL and 3.55 microM for inhibition of SAQ. As SAQ has the highest metabolic clearance rate, the K(i) for the SAQ inhibition of IND metabolism was high, 9.50 microM. Based on these in vitro results, drug interactions between NEL and IND or RIT were studied after oral administration to rats where the dose of each drug was 20 mg/kg. The C(max) and AUC of NEL were increased 3.6- and 8.5-fold by the co-administration with RIT. However, in contrast to co-administration of NEL and RIT, the effect of IND on the pharmacokinetics of NEL was negligible and the t(1/2) of NEL was not significantly increased by IND. Therefore, the combination of NEL and IND is recommended as a combination therapy for AIDS patients.     

HIV蛋白酶抑制剂的药代动力学相互作用

艾滋病的治疗是一个长期的过程,HIV蛋白酶抑制剂是此类病人最常选用的抗病毒药物。在治疗过程中,病人很可能患其它疾病,艾滋病自身也常伴随众多并发症,使得临床上不可避免的需要联用其它药物。由于HIV蛋白酶抑制剂对药物代谢酶和转运体有广泛的作用,因此探索HIV蛋白酶抑制剂的药物相互作用问题显得十分必要。本文重点从药代相互作用机制的角度综述了HIV蛋白酶抑制剂在临床上可能出现的药物相互作用方面的研究文献,包括HIV蛋白酶抑制剂与其它药物的相互作用以及蛋白酶抑制剂之间的相互作用及机制等,期望对于临床给药方案的设计和提高临床用药的安全性和有效性提供有价值的参考和借鉴。     

Influence of drug-transporter polymorphisms on the pharmacokinetics of fexofenadine enantiomers

1. This study investigated an association of SLCO (encoding organic anion-transporting polypeptides (OATP), 1B1, 1B3, and 2B1), ABCB1 (P-glycoprotein (P-gp)), ABCC2 multidrug resistance protein 2 (MRP2), and ABCG2 (breast cancer resistance protein (BCRP)) polymorphisms with fexofenadine enantiomer pharmacokinetics after an oral dose of fexofenadine (60?mg) in 24 healthy subjects.

2. The area under the plasma concentration-time curve (AUC_0–24) of S-fexofenadine, but not R-fexofenadine, was significantly lower in subjects with a SLCO2B1*1/*1 allele as compared to subjects with a *3 allele (p?=?0.031).

3. The AUC_0–24 of S-fexofenadine was significantly lower in subjects with a wild-type combination of SLCO2B1*1/*1/ABCB1 1236CC, SLCO2B1*1/*1/ABCB1 3435CC, SLCO2B1*1/*1/ABCC2 -24CC, and ABCB1 1236CC/3435CC/ABCC2 -24CC compared to other polymorphic genotypes (p?=?0.010, 0.033, 0.022, and 0.036, respectively), whereas there was no difference in the AUC_0–24 between the SLCO1B1/1B3 plus ABCB1 and ABCC2 groups.

4. The pharmacokinetic properties of S-fexofenadine are affected by a single polymorphism of SLCO2B1 in combination with several polymorphisms of ABCB1 C1236T, C3435T, and ABCC2 C-24T. However, the ABCG2 polymorphism was not associated with fexofenadine pharmacokinetics.

5. These findings suggest that a combination of multiple transporters, including OATP, P-gp, and MRP2, reacts strongly to fexofenadine exposure in the small intestine and liver, resulting in different dispositions of both enantiomers.

     

Computational identification of inhibitors of protein-protein interactions

The ability to control protein-protein interactions (PPIs) for therapeutic purposes is attractive since many processes in cells involve such interactions. Recent successes in the discovery of small molecules that target protein-protein interactions for drug development have shown that targeting these interactions is indeed feasible. In the present review the use of computer-aided drug design (CADD) via database screening or docking algorithms for identifying inhibitors of protein-protein interactions is introduced. The principles of database screening and a practical protocol for targeting PPIs are described. The recent applications of these approaches to different systems involving protein-protein interactions, including BCL-2, S100B, ERK and p56lck, are presented and provide valuable examples of inhibitor discovery and design.     

Histone acetyltransferase inhibitors and preclinical studies

Background: Drugs able to regulate the histone modifier enzymes are very promising tools for the treatment of several diseases, such as cancer. Histone acetyltransferase (HAT) inhibitors are compounds able to inhibit the catalytic activity of HATs reported to be active in cancer, or in several other diseases, such as Alzheimer (AD), diabetes and hyperlipidaemia. Objectives: Here we review the status and the rationale for the use of HAT inhibitors in the treatment of various diseases. Methods: Patents have been found on the espacenet database; the clinical trials have been reported as in the clinicaltrial.gov website. Results and conclusion: Despite the fact that other drugs able to regulate the histone modifier enzymes (such as histone deacetylase inhibitors) have been already approved for the treatment of cancer, HAT inhibitors seem promising for the treatment of human diseases such as AD and diabetes, although side effects and toxicity need to be investigated.     

脂加氧酶及其抑制剂研究进展

脂加氧酶(lipoxygenase,LO)途径参与高血压、动脉粥样硬化和血管成型术后再狭窄等疾病的病理过程,并在诸疾病发展中起关键作用。LO抑制剂能明显降低血管收缩性,降低血压,抑制血管平滑肌细胞迁移,降低动脉损伤后新内膜增厚速率,减少活性氧(reactiveoxygenspecies,ROS)的生成,阻断细胞间结合反应。LO抑制剂的作用与阻断MAPK通路有关。阻断LO途径为防治心血管疾病提供了新的策略,因此LO可望成为防治心血管疾病药物的重要靶点。     

Monolayer studies of insulin-lipid interactions

The interactions between insulin and various lipids were studied by monolayer penetration experiments at constant surface area. The increase in surface pressure, delta II, of a lipid film depended upon the particular lipid used and the concentration of insulin in the subphase. For all lipids studied, delta II was dependent on the initial surface pressure of the lipid film. Evidence of the interaction between insulin and the lipids was found in the ability of insulin to penetrate lipid films with initial pressures greater than 16 dynes/cm, the maximum surface pressure obtained by insulin alone. For phospholipids, both the nonpolar and polar regions influenced the degree of interaction with insulin. Saturated chain lecithins exhibited less penetration than phospholipids with unsaturated hydrocarbon chains. The net charge of the lipid was not found to be an important determinant of penetration; however, the structure of the polar group can have a dramatic effect. Insulin penetration of mixed lipid films cannot be predicted by the penetration characteristics of the pure components. The possible role of these interactions in determining the geography of the insulin molecule within the liposome and its resultant effects on the stability is discussed.     

Pharmacokinetic-pharmacodynamic drug interactions with HMG-CoA reductase inhibitors

The HMG-CoA reductase inhibitors (statins) are effective in both the primary and secondary prevention of ischaemic heart disease. As a group, these drugs are well tolerated apart from two uncommon but potentially serious adverse effects: elevation of liver enzymes and skeletal muscle abnormalities, which range from benign myalgias to life-threatening rhabdomyolysis. Adverse effects with statins are frequently associated with drug interactions because of their long-term use in older patients who are likely to be exposed to polypharmacy. The recent withdrawal of cerivastatin as a result of deaths from rhabdomyolysis illustrates the clinical importance of such interactions. Drug interactions involving the statins may have either a pharmacodynamic or pharmacokinetic basis, or both. As these drugs are highly extracted by the liver, displacement interactions are of limited importance. The cytochrome P450 (CYP) enzyme system plays an important part in the metabolism of the statins, leading to clinically relevant interactions with other agents, particularly cyclosporin, erythromycin, itraconazole, ketoconazole and HIV protease inhibitors, that are also metabolised by this enzyme system. An additional complicating feature is that individual statins are metabolised to differing degrees, in some cases producing active metabolites. The CYP3A family metabolises lovastatin, simvastatin, atorvastatin and cerivastatin, whereas CYP2C9 metabolises fluvastatin. Cerivastatin is also metabolised by CYP2C8. Pravastatin is not significantly metabolised by the CYP system. In addition, the statins are substrates for P-glycoprotein, a drug transporter present in the small intestine that may influence their oral bioavailability. In clinical practice, the risk of a serious interaction causing myopathy is enhanced when statin metabolism is markedly inhibited. Thus, rhabdomyolysis has occurred following the coadministration of cyclosporin, a potent CYP3A4 and P-glycoprotein inhibitor, and lovastatin. Itraconazole has been shown to increase exposure to simvastatin and its active metabolite by at least 10-fold. Pharmacodynamically, there is an increased risk of myopathy when statins are coprescribed with fibrates or nicotinic acid. This occurs relatively infrequently, but is particularly associated with the combination of cerivastatin and gemfibrozil. Statins may also alter the concentrations of other drugs, such as warfarin or digoxin, leading to alterations in effect or a requirement for clinical monitoring. Knowledge of the pharmacokinetic properties of the statins should allow the avoidance of the majority of drug interactions. If concurrent therapy with known inhibitors of statin metabolism is necessary, the patient should be monitored for signs and symptoms of myopathy or rhabdomyolysis and the statin should be discontinued if necessary.     

Pharmacokinetic interactions between cyclosporine and protease inhibitors in HIV+ subjects

With advances in antiretroviral therapy, many HIV+ individuals are living longer lives and some are developing end-stage renal and/or hepatic disease requiring transplantation. These patients require concomitant use of immunosuppressants (e.g., cyclosporine [CsA]) and antiretrovirals (e.g., protease inhibitors [PIs]), which exhibit narrow therapeutic windows and are substrates and inhibitors of cytochrome P450 3A enzymes and the cellular transporter P-glycoprotein. In this pilot study, HIV+ subjects on either oral nelfinavir (NFV) or indinavir (IND) with nondetectable viral loads and normal renal and hepatic function had 12 hour pharmacokinetic (PK) studies on 3 separate days: PIs alone, PIs+intravenous CsA, and PIs+oral CsA to determine the extent of PK interactions between these medications. PIs and CsA concentrations were measured by LC/MS in plasma and whole blood, respectively. Nine subjects (n=7 on NFV, n=2 on IND) completed the study. Only the results of those subjects taking NFV are reported. Oral co-administration of CsA increased NFV T(max) from 2.6+/-0.9 to 3.2+/-0.8 h (p<0.05), and AUC(0-infinity) from 27.9+/-15.2 to 43.2+/-27.1 mg(*)h/mL (p=0.06). Intravenous CsA did not appreciably alter oral pharmacokinetics of NFV. Both CsA and NFV PK parameters exhibited a high degree of intersubject variability, underscoring the need for routine therapeutic drug monitoring of both CsA and PIs in HIV+ subjects undergoing transplantation.     

mTOR inhibitors in pancreas transplant: adverse effects and drug-drug interactions

Introduction: Patient and pancreas allograft survival improved following reductions in surgical complications, tighter donor selection and optimization in immunosuppressive protocols. However, long-term survival of pancreas allografts is adversely affected by rejection and immunosuppressive regimen toxicity.

Areas covered: This article reviews the existing literature and knowledge of mammalian target of rapamycin inhibitors (mTORi). Some clinically relevant drug-drug interactions are highlighted. We summarize the nephrotoxic and diabetogenic mechanisms of mTORi after pancreas transplant, the alternatives to minimize these effects, and report on other adverse events.

Expert opinion: Calcineurin inhibitor (CNI)-based regimens remain the mainstay treatment after pancreas-kidney transplant. However, long-term use of CNIs may be associated with nephrotoxicity. Switching from CNIs to mTORi (sirolimus/SRL and everolimus/EVR) may preserve kidney function, mainly EVR conversion. However, mTORi promote an imbalance of mTOR signaling during long-term follow-up and may ultimately contribute to proteinuria and hyperglycemia. These drugs disrupt autophagy, inhibit cell proliferation, and downregulate VEGF. Therefore, it is important to comprehend and interpret the experimental data. It is equally important to critically analyze clinical studies. Of importance, minimization of side effects, based on safe approaches, can prolong kidney allograft survival. Additional randomized-controlled studies are required to assess the impact of mTORi on pancreas allograft survival.