Saquinavir induces stable and functional expression of the multidrug transporter P-glycoprotein in human CD4 T-lymphoblastoid CEMrev cells

Ecdysteroid Derivatives that Reverse P-Glycoprotein-Mediated Drug Resistance

The expression of multidrug resistance P-glycoprotein (P-gp) by cancer cells represents one of the major drawbacks to successful cancer therapy. Accordingly, the development of drugs that inhibit the activity of this transporter remains a major challenge in cancer drug discovery. In this context, several new ecdysteroid derivatives have been synthesized and evaluated as P-gp inhibitors. Two of them (compounds 9 and 14) were able to resensitize CEM^Vbl100 and LoVo^Doxo resistant cell lines to vinblastine and doxorubicin, respectively. Indeed, both compounds 9 and 14 increased the cellular accumulation of rhodamine 123 in cells expressing P-gp and stimulated basal P-glycoprotein-ATPase activity at a 1 μM concentration, demonstrating their interference with the transport of other substrates in a competitive mode. Moreover, in a medulloblastoma cell line (DAOY), compounds 9 and 14 reduced the side population representing cancer stem cells, which are characterized by a high expression of ABC drug transporters. Further, in DAOY cells, the same two compounds synergized with cisplatin and vincristine, two drugs used commonly in the therapy of medulloblastoma. Molecular docking studies on the homology-modeled structure of the human P-glycoprotein provided a rationale for the biological results, validating the binding mode within the receptor site, in accordance with lipophilicity data and observed structure-activity relationship information. Altogether, the present results endorse these derivatives as promising P-gp inhibitors, and they may serve as candidates to reverse drug resistance in cancer cells.

Colchicine-Binding Site Inhibitors from Chemistry to Clinic: A Review

It is over 50 years since the discovery of microtubules, and they have become one of the most important drug targets for anti-cancer therapies. Microtubules are predominantly composed of the protein tubulin, which contains a number of different binding sites for small-molecule drugs. There is continued interest in drug development for compounds targeting the colchicine-binding site of tubulin, termed colchicine-binding site inhibitors (CBSIs). This review highlights CBSIs discovered through diverse sources: from natural compounds, rational design, serendipitously and via high-throughput screening. We provide an update on CBSIs reported in the past three years and discuss the clinical status of CBSIs. It is likely that efforts will continue to develop CBSIs for a diverse set of cancers, and this review provides a timely update on recent developments.

Design, synthesis and biological evaluation of novel vicinal diaryl-substituted 1H-Pyrazole analogues of combretastatin A-4 as highly potent tubulin polymerization inhibitors

A series of 3-(3',4',5'-trimethoxyphenyl)-4-substituted 1H-pyrazole and their related 3-aryl-4-(3',4',5'-trimethoxyphenyl)-1-H-pyrazole regioisomeric derivatives, prepared as cis-rigidified combretastatin A-4 (CA-4) analogues, were synthesized and evaluated for their in vitro antiproliferative against six different cancer cell lines and, for selected highly active compounds, inhibitory effects on tubulin polymerization, cell cycle effects and in vivo potency. We retained the 3',4',5'-trimethoxyphenyl moiety as ring A throughout the present investigation, and a structure-activity relationship (SAR) information was obtained by adding electron-withdrawing (OCF₃, CF₃) or electron-releasing (alkyl and alkoxy) groups on the second aryl ring, corresponding to the B-ring of CA-4, either at the 3- or 4-position of the pyrazole nucleus. In addition, the B-ring was replaced with a benzo[b]thien-2-yl moiety. For many of the compounds, their activity was greater than, or comparable with, that of CA-4. Maximal activity was observed with the two regioisomeric derivatives characterized by the presence of a 4-ethoxyphenyl and a 3',4',5'-trimethoxyphenyl group at the C-3 and C-4 positions, and vice versa, of the 1H-pyrazole ring. The data showed that the 3',4',5'-trimethoxyphenyl moiety can be moved from the 3- to the 4-position of the 1H-pyrazole ring without significantly affecting antiproliferative activity. The most active derivatives bound to the colchicine site of tubulin and inhibited tubulin polymerization at submicromolar concentrations. In vivo experiments, on an orthotopic murine mammary tumor, revealed that 4c inhibited tumor growth even at low concentrations (5 mg/kg) compared to CA-4P (30 mg/kg).

Pharmacokinetic interactions of herbs with cytochrome p450 and p-glycoprotein

The concurrent use of drugs and herbal products is becoming increasingly prevalent over the last decade. Several herbal products have been known to modulate cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp) which are recognized as representative drug metabolizing enzymes and drug transporter, respectively. Thus, a summary of knowledge on the modulation of CYP and P-gp by commonly used herbs can provide robust fundamentals for optimizing CYP and/or P-gp substrate drug-based therapy. Herein, we review ten popular medicinal and/or dietary herbs as perpetrators of CYP- and P-gp-mediated pharmacokinetic herb-drug interactions. The main focus is placed on previous works on the ability of herbal extracts and their phytochemicals to modulate the expression and function of CYP and P-gp in several in vitro and in vivo animal and human systems.

Natural daucane esters induces apoptosis in leukaemic cells through ROS production

Continuing our research on antiproliferative agents from plants, we extended our interest on further compounds isolated from Ferula communis and Ferulago campestris. One new daucane (DE-20) and one new phenol derivative (PH-3) were isolated and characterized in addition to six daucane, three coumarins and four simple phenolics. The cytotoxic activity was evaluated against a panel of six human tumor cell lines. The derivative DE-17 that resulted moderately active on all the studied cell lines was studied to evaluate its possible mechanism of action. DE-17 was able to induce apoptosis in a time and concentration-dependent manner in SEM and Jurkat cell lines. We observed that DE-17 just after 1h of treatment increased the reactive oxygen species (ROS) production and that the co-incubation of DE-17 with ROS scavengers significantly increased cell viability suggesting that ROS-mediated downstream signaling is essential for the antiproliferative effects of DE-17. At later times of incubation DE-17 induced mitochondrial depolarization, as well as caspase-3 and -9 activation suggesting that apoptosis follow the mitochondrial pathway. Concomitantly to ROS induction, a remarkable decrease of mRNA expression of several antioxidant enzymes and intracellular GSH content was detected in treated cells compared to controls further indicative of oxidative stress. Taken together our results showed for the first time that daucane esters induces apoptotic cell death through a ROS-mediated mechanism in human leukemia cells.

Synthesis, antimitotic and antivascular activity of 1-(3',4',5'-trimethoxybenzoyl)-3-arylamino-5-amino-1,2,4-triazoles

A new class of compounds that incorporated the structural motif of the 1-(3',4',5'-trimethoxtbenzoyl)-3-arylamino-5-amino-1,2,4-triazole molecular skeleton was synthesized and evaluated for their antiproliferative activity in vitro, interactions with tubulin, and cell cycle effects. The most active agent, 3c, was evaluated for antitumor activity in vivo. Structure-activity relationships were elucidated with various substituents on the phenyl ring of the anilino moiety at the C-3 position of the 1,2,4-triazole ring. The best results for inhibition of cancer cell growth were obtained with the p-Me, m,p-diMe, and p-Et phenyl derivatives 3c, 3e, and 3f, respectively, and overall, these compounds were more or less as active as CA-4. Their vascular disrupting activity was evaluated in HUVEC cells, with compound 3c showing activity comparable with that of CA-4. Compound 3c almost eliminated the growth of syngeneic hepatocellular carcinoma in Balb/c mice, suggesting that 3c could be a new antimitotic agent with clinical potential.

Design, synthesis and biological evaluation of arylcinnamide hybrid derivatives as novel anticancer agents

The combination of two pharmacophores into a single molecule represents one of the methods that can be adopted for the synthesis of new anticancer molecules. A series of novel antiproliferative agents designed by a pharmacophore hybridization approach, combining the arylcinnamide skeleton and an α-bromoacryloyl moiety, was synthesized and evaluated for its antiproliferative activity against a panel of seven human cancer cell lines. In addition, the new derivatives were also active on multidrug-resistant cell lines over-expressing P-glycoprotein. The biological effects of various substituents on the N-phenyl ring of the benzamide portion were also described. In order to study the possible mechanism of action, we observed that 4p slightly increased the Reactive Oxygen Species (ROS) production in HeLa cells, but, more importantly, a remarkable decrease of intracellular reduced glutathione content was detected in treated cells compared with controls. These results were confirmed by the observation that only thiol-containing antioxidants were able to significantly protect the cells from induced cell death. Altogether our results indicate that the new derivatives are endowed with good anticancer activity in vitro, and their properties may result in the development of new cancer therapeutic strategies.

Raltegravir does not revert efflux activity of MDR1-P-glycoprotein in human MDR cells

Background

Raltegravir (Isentress®)(RALT) has demonstrated excellent efficacy in both treatment-experienced and naïve patients with HIV-1 infection, and is the first strand transfer integrase inhibitor to be approved for use in HIV infected adults worldwide. Since the in vivo efficacy of this class of antiviral drugs depends on their access to intracellular sites where HIV-1 replicates, we analyzed the biological effects induced by RALT on human MDR cell systems expressing multidrug transporter MDR1-P-glycoprotein (MDR1-Pgp).

Methods

Our study about RALT was performed by using a set of consolidated methodologies suitable for evaluating the MDR1-Pgp substrate nature of chemical and biological agents, namely: i) assay of drug efflux function; ii) analysis of MDR reversing capability by using cell proliferation assays; iii) monoclonal antibody UIC2 (mAb) shift test, as a sensitive assay to analyze conformational transition associated with MDR1-Pgp function; and iv) induction of MDR1-Pgp expression in MDR cell variant subjected to RALT exposure.

Results

Functional assays demonstrated that the presence of RALT does not remarkably interfere with the efflux mechanism of CEM-VBL100 and HL60 MDR cells. Accordingly, cell proliferation assays clearly indicated that RALT does not revert MDR phenotype in human MDR1-Pgp expressing cells. Furthermore, exposure of CEM-VBL10 cells to RALT does not induce MDR1-Pgp functional conformation intercepted by monoclonal antibody (mAb) UIC2 binding; nor does exposure to RALT increase the expression of this drug transporter in MDR1-Pgp expressing cells.

Conclusions

No evidence of RALT interaction with human MDR1-Pgp was observed in the in vitro MDR cell systems used in the present investigation, this incorporating all sets of studies recommended by the FDA guidelines. Taken in aggregate, these data suggest that RALT may express its curative potential in all sites were HIV-1 penetrates, including the MDR1-Pgp protected blood/tissue barrier. Moreover RALT, evading MDR1-Pgp drug efflux function, would not interfere with pharmacokinetic profiles of co-administered MDR1-Pgp substrate antiretroviral drugs.

Synthesis and biological evaluation of 2-(alkoxycarbonyl)-3-anilinobenzo[b]thiophenes and thieno[2,3-b]pyridines as new potent anticancer agents

Two new series of inhibitors of tubulin polymerization based on the 2-(alkoxycarbonyl)-3-(3',4',5'-trimethoxyanilino)benzo[b]thiophene and thieno[2,3-b]pyridine molecular skeletons were synthesized and evaluated for antiproliferative activity on a panel of cancer cell lines, inhibition of tubulin polymerization, cell cycle effects, and in vivo potency. Antiproliferative activity was strongly dependent on the position of the methyl group on the benzene portion of the benzo[b]thiophene nucleus, with the greatest activity observed when the methyl was located at the C-6 position. Also, in the smaller thieno[2,3-b]pyridine series, the introduction of the methyl group at the C-6 position resulted in improvement of antiproliferative activity to the nanomolar level. The most active compounds (4i and 4n) did not induce cell death in normal human lymphocytes, suggesting that the compounds may be selective against cancer cells. Compound 4i significantly inhibited in vivo the growth of a syngeneic hepatocellular carcinoma in Balb/c mice.

Synthesis and biological evaluation of 2-substituted-4-(3',4',5'-trimethoxyphenyl)-5-aryl thiazoles as anticancer agents

Antitumor agents that bind to tubulin and disrupt microtubule dynamics have attracted considerable attention in the last few years. To extend our knowledge of the thiazole ring as a suitable mimic for the cis-olefin present in combretastatin A-4, we fixed the 3,4,5-trimethoxyphenyl at the C4-position of the thiazole core. We found that the substituents at the C2- and C5-positions had a profound effect on antiproliferative activity. Comparing compounds with the same substituents at the C5-position of the thiazole ring, the moiety at the C2-position influenced antiproliferative activities, with the order of potency being NHCH(3) > Me >> N(CH(3))(2). The N-methylamino substituent significantly improved antiproliferative activity on MCF-7 cells with respect to C2-amino counterparts. Increasing steric bulk at the C2-position from N-methylamino to N,N-dimethylamino caused a 1-2 log decrease in activity. The 2-N-methylamino thiazole derivatives 3b, 3d and 3e were the most active compounds as antiproliferative agents, with IC(50) values from low micromolar to single digit nanomolar, and, in addition, they are also active on multidrug-resistant cell lines over-expressing P-glycoprotein. Antiproliferative activity was probably caused by the compounds binding to the colchicines site of tubulin polymerization and disrupting microtubule dynamics. Moreover, the most active compound 3e induced apoptosis through the activation of caspase-2, -3 and -8, but 3e did not cause mitochondrial depolarization.

Discovery and optimization of a series of 2-aryl-4-amino-5-(3',4',5'-trimethoxybenzoyl)thiazoles as novel anticancer agents

A new series of tubulin polymerization inhibitors based on the 2-aryl/heteroaryl-4-amino-5-(3',4',5'-trimethoxybenzoyl)thiazole scaffold was synthesized and evaluated for growth inhibition activity on a panel of cancer cell lines, cell cycle effects, and in vivo potency. Structure-activity relationships were elucidated with various substitutions at the 2-position of the thiazole skeleton. Hydrophobic moieties, such as phenyl and 3-thienyl, were well tolerated at this position, and variation of the phenyl substituents had remarkable effects on potency. The most active compound (3b) induced apoptosis through the mitochondrial pathway with activation of caspase-3. We also showed that it has potential antivascular activity since it reduced in vitro endothelial cell migration and disrupted capillary-like tube formation at noncytotoxic concentrations. Furthermore, compound 3b significantly reduced the growth of the HT-29 xenograft in a nude mouse model, suggesting that 3b is a promising new antimitotic agent with clinical potential.

Synthesis and evaluation of 1,5-disubstituted tetrazoles as rigid analogues of combretastatin A-4 with potent antiproliferative and antitumor activity

Tubulin, the major structural component of microtubules, is a target for the development of anticancer agents. Two series of 1,5-diaryl substituted 1,2,3,4-tetrazoles were concisely synthesized, using a palladium-catalyzed cross-coupling reaction, and identified as potent antiproliferative agents and novel tubulin polymerization inhibitors that act at the colchicine site. SAR analysis indicated that compounds with a 4-ethoxyphenyl group at the N-1 or C-5 position of the 1,2,3,4-tetrazole ring exhibited maximal activity. Several of these compounds also had potent activity in inhibiting the growth of multidrug resistant cells overexpressing P-glycoprotein. Active compounds induced apoptosis through the mitochondrial pathway with activation of caspase-9 and caspase-3. Furthermore, compound 4l significantly reduced in vivo the growth of the HT-29 xenograft in a nude mouse model, suggesting that 4l is a promising new antimitotic agent with clinical potential.

One-pot synthesis and biological evaluation of 2-pyrrolidinyl-4-amino-5-(3',4',5'-trimethoxybenzoyl)thiazole: a unique, highly active antimicrotubule agent

A wide variety of small molecules with diverse molecular scaffolds inhibit microtubule formation. In this article we report a one-pot procedure for the preparation of a novel 2-(N-pyrrolidinyl)-4-amino-5-(3',4',5'-trimethoxybenzoyl)thiazole in which the size of the substituent at the C-2 position of the thiazole ring plays an essential role in compound activity. The most active agent (3f) inhibited at submicromolar concentrations the growth of tumor cell lines. It also inhibited tubulin polymerization with an activity quantitatively similar to that of CA-4, and treatment of HeLa cells resulted in their arrest at the G2-M phase of the cell cycle. Furthermore, 3f was effective against multidrug resistant cancer cells and inhibited the growth of the HT-29 xenograft in a nude mouse model. This indicated that 3f is a promising new antimitotic agent with encouraging preclinical potential.

Exposure to HIV-protease inhibitors selects for increased expression of P-glycoprotein (ABCB1) in Kaposi's sarcoma cells

Background:

Given that HIV-protease inhibitors (HIV-PIs) are substrates/inhibitors of the multidrug transporter ABCB1, can induce ABCB1 expression, and are used in combination with doxorubicin for AIDS-Kaposi's Sarcoma (KS) treatment, the role that ABCB1 plays in mediating multidrug resistance (MDR) in a fully transformed KS cell line (SLK) was explored.

Methods:

The KS cells were exposed to both acute and chronic treatments of physiological concentrations of different HIV-PIs (indinavir, nelfinavir, atazanavir, ritonavir, or lopinavir), alone or together with doxorubicin. The ABCB1 mRNA and protein expression levels were then assessed by qRT–PCR and western blotting, flow cytometry, and immunofluorescence.

Results:

Chronic treatment of SLK cells with one of the five HIV-PIs alone or together resulted in increased resistance to doxorubicin. Co-treatment with one of the HIV-PIs in combination with doxorubicin resulted in a synergistic increase in resistance to doxorubicin, and the degree of resistance was found to correlate with the expression of ABCB1. The SLK cells were also revealed to be cross-resistant to the structurally unrelated drug paclitaxel.

Conclusion:

These studies suggest that ABCB1 is primarily responsible for mediating MDR in SLK cells selected with either HIV-PIs alone or in combination with doxorubicin. Therefore, the roles that ABCB1 and drug cocktails play in mediating MDR in KS in vivo should be evaluated.

Convergent synthesis and biological evaluation of 2-amino-4-(3',4',5'-trimethoxyphenyl)-5-aryl thiazoles as microtubule targeting agents

Combretastatin A-4, a potent tubulin polymerization inhibitor, caused us to synthesize a novel series of 2-amino-4-(3',4',5'-trimethoxyphenyl)-5-aryl thiazoles with the goal of evaluating the effects of substituents on the phenyl at the 5-position of the thiazole skeleton on biological activities. An ethoxy group at the para-position produced the most active compound in the series, with IC(50) values of 0.03-0.9 nM against five of seven cancer cell lines. The most active compounds retained full activity in multidrug resistant cancer cells and acted through the colchicine site of tubulin. Treated cells were arrested in the G2/M phase of the cell cycle, with cell death proceeding through an apoptotic pathway that was only partially caspase-dependent. Preliminary results suggest that, in addition to cell death by apoptosis, cells were also killed via mitotic catastrophe as an alternative cell death mechanism.

Impact of drug transporters on cellular resistance towards saquinavir and darunavir

OBJECTIVES

Highly active antiretroviral therapy is complicated by drug-drug interactions and the development of viral resistance. Drug interactions involve transporters that may critically affect the pharmacokinetics of many antiretroviral drugs and contribute to the formation of functional sanctuary sites. We therefore investigated the effect of saquinavir and darunavir on drug transporter expression and functional consequences for cellular resistance towards these compounds.

METHODS

Induction of transporters was investigated in LS180 cells over a period of 4 weeks by means of RT-PCR, and for some transporters also at the protein and functional levels. Cellular resistance was measured by growth inhibition assays.

RESULTS

Incubation with 10 µM darunavir for 1 week significantly increased mRNA expression of P-glycoprotein (P-gp/MDR1/ABCB1) 3.8-fold and of organic anion-transporting polypeptide 2B1 (SLCO2B1) 1.9-fold. In contrast, 10 µM saquinavir significantly increased mRNA expression of P-gp 5.7-fold, multidrug resistance-associated protein 1 (MRP1/ABCC1) 2.3-fold, MRP2/ABCC2 4.5-fold, MRP3/ABCC3 2.0-fold, MRP4/ABCC4 1.8-fold, MRP5/ABCC5 3.8-fold, breast cancer resistance protein (BCRP/ABCG2) 4.1-fold, SLCO1B1 4.6-fold, SLCO2B1 1.8-fold and SLCO3A1 1.8-fold. P-gp induction was also confirmed at the protein and functional levels. Induction by darunavir caused an increase in cellular resistance towards this compound, as measured in growth inhibition assays; however, saquinavir treatment did not cause reduced sensitivity of cells, indicating unchanged intracellular concentration. Hence, induction by darunavir increased drug efflux and might therefore lead to a suboptimal intracellular concentration of darunavir.

CONCLUSIONS

The study revealed substantial induction of several drug transporters by saquinavir and darunavir, possibly leading to decreased efficacy of antiretrovirals and drugs used to treat co-morbidity.

ABC transporters in human lymphocytes: expression, activity and role, modulating factors and consequences for antiretroviral therapies

IMPORTANCE OF THE FIELD

ATP-binding cassette (ABC) transporters are a superfamily of efflux pumps that transport numerous compounds across cell membranes. These transporters are located in various human tissues including peripheral blood cells, in particular lymphocytes, and present a high variability of expression and activity. This variability may affect the intracellular concentrations and efficacy of drugs acting within lymphocytes, such as antiretroviral drugs.

AREAS COVERED IN THIS REVIEW

This review focuses on the current knowledge about the expression, activity, roles and variability of ABC drug transporters in human lymphocytes. The identified modulating factors and their impact on the intracellular pharmacokinetics and efficacy of antiretroviral drugs are also detailed.

WHAT THE READER WILL GAIN

Controversial data regarding the expression, activity and sources of variability of ABC transporters in lymphocytes are discussed. The modulating factors and their pharmacological consequences regarding antiretroviral therapies are also provided.

TAKE HOME MESSAGE

Numerous studies have reported conflicting results regarding the expression and activity of ABC drug transporters in lymphocytes. Despite these discrepancies, which may partly result from heterogeneous analytical methods, ABCC1 appears to have the highest expression in lymphocytes and may thus play a predominant role in the resistance to antiretroviral drugs, particularly to protease inhibitors.

Lack of P-glycoprotein induction by rifampicin and phenobarbital in human lymphocytes

The efficacy of drugs acting within lymphocytes depends on their intracellular concentrations, which could be modulated by membrane efflux transporters including P-glycoprotein (P-gp), encoded by the MDR1 gene. In particular, P-gp induction may compromise the efficacy of its substrates. Rifampicin and phenobarbital have been shown to induce P-gp in hepatic and intestinal cells through the activation of the nuclear receptors PXR and CAR. However, controversial data exist in human lymphocytes. We investigated the effect of these drugs on P-gp activity and expression in lymphocytes in vitro and ex vivo. CCRF-CEM cells and peripheral blood mononuclear cells (PBMCs) from healthy volunteers were incubated in the presence of rifampicin, phenobarbital, or without any drug. P-gp activity was measured by flow cytometry using DiOC(6) efflux. MDR1, PXR and CAR mRNA expression were measured by quantitative RT-PCR. Neither P-gp activity nor MDR1 mRNA expression were modified by rifampicin or phenobarbital both in CCRF-CEM cells and PBMCs. Moreover, P-gp protein expression at the membrane was neither detectable nor induced. The very weak PXR and CAR mRNA expression levels in these cells could partly explain these results. Therefore, P-gp induction by rifampicin and phenobarbital may play a negligible role in drug interactions occurring within lymphocytes.

P-glycoprotein, multidrug resistance-associated proteins and human organic anion transporting polypeptide influence the intracellular accumulation of atazanavir

BACKGROUND

Drug efflux (for example, P-glycoprotein [P-gp], multidrug resistance-associated proteins [MRPs] and breast cancer resistance protein [BCRP]) and influx (for example, human organic anion transporting polypeptide [hOCTP] or human organic anion transporting polypeptide [hOATP]) transporters alter the cellular concentrations of some HIV protease inhibitors (HPIs). Here, we studied the lipophilicity and uptake of [(3)H]-atazanavir (ATV) in CEM (parental), CEM(VBL) (P-gp-overexpressing), CEM(E1000) (MRP1-overexpressing) and peripheral blood mononuclear cells (PBMCs), and evaluate the effects of modulators of drug transporters on uptake.

METHODS

Lipophilicity was measured by octanol/saline partition method. The influence of influx/efflux transporters on uptake was evaluated in the absence and presence of inhibitors of P-gp (GPV031), P-gp/BCRP (tariquidar and GF120918), P-gp/MRP1 (dipyridamole and daidzein), MRP1/2 (frusemide and genistein), hOATP/hOCTP (estrone-3-sulfate [E-3-S]) and hOATP/hOCTP/MRP (probenecid). The effects of a number of HPIs on uptake were also evaluated. Data from digitonin permeabilized cells allowed the evaluation of the contribution of cellular binding to total drug uptake, whereas the inhibitory effect of ATV on P-gp was assessed by daunomycin efflux/uptake assays.

RESULTS

[(3)H]-ATV is lipophilic and accumulates in the cultured cells as follows: CEM>CEM(E1000)>CEM(VBL). Tariquidar, GF120918 and daidzein significantly increased the uptake of [(3)H]-ATV in the cultured cells. By contrast, only daidzein and tipranavir significantly increased uptake in PBMCs, with tariquidar and frusemide devoid of effects, whereas dipyridamole, E-3-S, GPV031 and genistein significantly decreased accumulation. ATV inhibits P-gp activity; manipulation of uptake with digitonin suggests binding of [(3)H]-ATV to P-gp.

CONCLUSIONS

[(3)H]-ATV is lipophilic, a P-gp, MRP and hOATP substrate and an inhibitor of P-gp. Concomitant administration of ATV with drugs and dietary components (for example, daidzein and genistein) that interact with these transporters could alter its pharmacokinetics.

Pyrrolotetrazinones deazaanalogues of temozolomide induce apoptosis in Jurkat cell line: involvement of tubulin polymerization inhibition

PURPOSE

Pyrrolotetrazinones are a new class of azolotetrazinones endowed with a high, remarkable antiproliferative activity in human tumor cultured cells. They hold the deaza skeleton of the antitumor drug temozolomide, although preliminary investigations indicated a different mechanism of action. To understand their mechanism(s) of action along with their target at molecular level, four derivatives were selected on the basis of their activity on a panel of human tumor cell lines and they were investigated in depth in a T leukemia cell line (Jurkat).

METHODS AND RESULTS

Flow cytometric analysis of cell cycle after treatment with pyrrolotetrazinones has demonstrated that they were able to induce an arrest of the cell cycle in G2/M phase. This effect was accompanied by apoptosis of the treated cells which is further characterized by exposure of phosphatidylserine on the external surface of the cell membranes. Mitochondria were strongly involved in the apoptotic pathway as demonstrated by the induced mitochondrial depolarization, generation of reactive oxygen species, and activation of caspase-3. Western blot analysis showed that Bcl-2 expression was down regulated whereas the proapototic protein Bax was upregulated in a time dependent manner. Moreover, these compounds induced a clear increase in the mitotic index, and inhibited microtubule assembly in vitro indicating that pyrrolotetrazinones, at variance with temozolomide, involved an efficacious inhibition of tubulin polymerization in their mechanism of action. Interestingly compound 3 at the concentration of 50 mg/kg body weight significantly inhibited in vivo the growth of a syngeneic hepatocellular carcinoma in Balb/c mice.

CONCLUSION

These results suggest that pyrrolotetrazinones inhibit microtubule polymerization, induce G2/M arrest of cell cycle and cause apoptosis through the mitochondrial pathway identifying them as novel effective antimitotic agents with potential for clinical development.

Stronger activity of human immunodeficiency virus type 1 protease inhibitors against clinical isolates of Plasmodium vivax than against those of P. falciparum

Recent studies using laboratory clones have demonstrated that several antiretroviral protease inhibitors (PIs) inhibit the growth of Plasmodium falciparum at concentrations that may be of clinical significance, especially during human immunodeficiency virus type 1 (HIV-1) and malaria coinfection. Using clinical isolates, we now demonstrate the in vitro effectiveness of two HIV-1 aspartic PIs, saquinavir (SQV) and ritonavir (RTV), against P. vivax (n = 30) and P. falciparum (n = 20) from populations subjected to high levels of mefloquine and artesunate pressure on the Thailand-Myanmar border. The median 50% inhibitory concentration values of P. vivax to RTV and SQV were 2,233 nM (range, 732 to 7,738 nM) and 4,230 nM (range, 1,326 to 8,452 nM), respectively, both within the therapeutic concentration range commonly found for patients treated with these PIs. RTV was fourfold more effective at inhibiting P. vivax than it was at inhibiting P. falciparum, compared to a twofold difference in SQV sensitivity. An increased P. falciparum mdr1 copy number was present in 33% (3/9) of isolates and that of P. vivax mdr1 was present in 9% of isolates (2/22), but neither was associated with PI sensitivity. The inter-Plasmodium sp. variations in PI sensitivity indicate key differences between P. vivax and P. falciparum. PI-containing antiretroviral regimens may demonstrate prophylactic activity against both vivax and falciparum malaria in HIV-infected patients who reside in areas where multidrug-resistant P. vivax or P. falciparum is found.

Interindividual variability in the effect of atazanavir and saquinavir on the expression of lymphocyte P-glycoprotein

OBJECTIVES

ABCB1 encodes the efflux transporter P-glycoprotein (P-gp), which regulates the intracellular concentration of many xenobiotics, including several HIV protease inhibitors (PIs). Exposure to some xenobiotics, such as the antibiotic rifampicin, increases P-gp expression. In the present study, we investigated the effect of the HIV PIs saquinavir and atazanavir on the expression and function of ABCB1 and P-gp in primary and cultured lymphocytes, as well as the molecular interactions between these drugs and P-gp. ABCB1 and P-gp expression and function were examined in lymphocyte samples from healthy subjects before and after atazanavir-boosted saquinavir treatment. Expression and function were also studied in CEM cells following exposure to atazanavir and saquinavir. The inhibitory effects of these drugs were investigated in ABCB1-transfected HEK293T cells.

METHODS

P-gp expression and function were measured by flow cytometry. ABCB1 mRNA expression was evaluated using quantitative RT-PCR.

RESULTS

There were no overall changes in ABCB1 or P-gp expression or function after saquinavir-atazanavir treatment in primary lymphocyte samples. However, there was considerable interindividual variability in baseline lymphocyte ABCB1 expression, as well as in the degree of change in ABCB1 expression after saquinavir-atazanavir administration. In cell culture, 5 microM saquinavir increased ABCB1 levels, although it did not affect P-gp expression. Atazanavir inhibited P-gp function at concentrations above therapeutic levels.

CONCLUSIONS

Differences in lymphocyte ABCB1 expression, which may be caused by genetic polymorphisms in ABCB1 or its regulatory partners, are a likely cause of interindividual variation in the disposition and efficacy of clinically relevant P-gp substrates, including HIV PIs.

HIV-1 integrase inhibitors are substrates for the multidrug transporter MDR1-P-glycoprotein

Background

The discovery of diketoacid-containing derivatives as inhibitors of HIV-1 Integrase (IN) (IN inhibitors, IINs) has played a major role in validating this enzyme as an important target for antiretroviral therapy. Since the in vivo efficacy depends on access of these drugs to intracellular sites where HIV-1 replicates, we determined whether the IINs are recognized by the multidrug transporter MDR1-P-glycoprotein (P-gp) thereby reducing their intracellular accumulation. To address the effect of IINs on drug transport, nine quinolonyl diketo acid (DKA) derivatives active on the HIV-1 IN strand transfer (ST) step and with EC50 ranging from 1.83 to >50 μm in cell-based assays were tested for their in vitro interaction with P-gp in the CEM-MDR cell system. IINs were investigated for the inhibition and induction of the P-gp function and expression as well as for multidrug resistance (MDR) reversing ability.

Results

The HIV-1 IINs act as genuine P-gp substrates by inhibiting doxorubicin efflux and inducing P-gp functional conformation changes as evaluated by the modulation of UIC2 mAb epitope. Further, IINs chemosensitize MDR cells to vinblastine and induce P-gp expression in drug sensitive revertants of CEM-MDR cells.

Conclusion

To our knowledge, this is the first demonstration that HIV-1 IINs are P-gp substrates. This biological property may influence the absorption, distribution and elimination of these novels anti HIV-1 compounds.

TNF activates P-glycoprotein in cerebral microvascular endothelial cells

BACKGROUND/AIMS

Multidrug resistance proteins (MDRs, including P-glycoproteins) are efflux pumps that serve important biological functions but hinder successful drug delivery to the CNS. Many chemotherapeutic agents, anti-epileptics, anti-HIV drugs, and opiates are substrates for MDRs. Therefore, understanding the regulation of MDRs in the endothelial cells composing the blood-brain barrier has therapeutic implications.

METHODS

We used microarray, real time RT-PCR, Western blotting, and uptake of vinblastine by RBE4 cerebral endothelial cells to test the effects of tumor necrosis factor alpha (TNF) on the expression and functions of P-glycoprotein (MDR1).

RESULTS

The proinflammatory cytokine TNF specifically induced the expression and enhanced the function of MDR1 in RBE4 cells. The persistent upregulation of MDR1 mRNA was shown by cDNA microarray at 6, 12, and 24 h after TNF treatment. This was confirmed by real-time RT-PCR between 2 and 24 h. MDR1 protein expression was increased 6 to 24 h after TNF treatment and resulted in a significant reduction in the cellular uptake of (3)H-vinblastine.

CONCLUSION

The drug efflux transporter in cerebral endothelial cells can be upregulated by TNF. This suggests that adjunctive anti-TNF treatment has novel therapeutic potential in conditions such as brain cancer, epilepsy, neuroAIDS, and chronic pain.

HIV/AIDS: Interactions between Natural Health Products and Antiretroviral Drugs: Pharmacokinetic and Pharmacodynamic Effects

Concurrent use of natural health products (NHPs) with antiretroviral drugs (ARVs) is widespread among human immunodeficiency virus-infected patients. This article reviews the clinical pharmacokinetic and pharmacodynamic interactions between NHPs and ARVs. Many NHPs are complex mixtures and are likely to contain organic compounds that may induce and/or inhibit drug metabolizing enzymes and drug transporters. Although the weight of evidence for the effects of certain NHPs varies and many studies of these products lack scientific rigor, it has been observed that St. John's wort clearly induces cytochrome P450 3A4 and P-glycoprotein and reduces protease inhibitor and nonnucleoside reverse-transcriptase inhibitor concentrations, thereby increasing the likelihood of therapeutic failure. Limited clinical research suggests that intake of garlic and vitamin C results in reductions in ARV concentrations. The intake of milk thistle, Echinacea species, and goldenseal inhibits cytochrome P450 enzymes in vitro and may increase ARV concentrations, but by clinically unimportant amounts. Intake of fish oil reduces ARV-induced hypertriglyceridemia without significantly affecting lopinavir concentrations. Before recommending the use of NHPs as adjuncts to ARV use, studies should first exclude significant pharmacokinetic interactions and ensure that ARV efficacy is maintained.

MDR1 G1199A polymorphism alters permeability of HIV protease inhibitors across P-glycoprotein-expressing epithelial cells

OBJECTIVE

To evaluate the impact of the human multidrug resistance gene (MDR1) G1199A polymorphism (amino acid change Ser400Asn) on P-glycoprotein (P-gp)-dependent transepithelial permeability and uptake kinetics of HIV protease inhibitors (PI), by using recombinant epithelial cells expressing wild-type MDR1 (MDR1wt) or the G1199A variant (MDR1(1199A)).

METHODS

Using a recombinant expression system developed previously, the transepithelial permeability and uptake kinetic parameters of five PI, amprenavir, indinavir, lopinavir, ritonavir, and saquinavir were estimated across polarized epithelial cells.

RESULTS

For all PI, the transepithelial permeability ratio (basolateral-to-apical transport divided by apical-to-basolateral transport) was significantly greater in MDR1(1199A) cells than MDR1wt cells: amprenavir (1.7-fold), indinavir (1.8-fold), lopinavir (1.5-fold), ritonavir (2.8-fold), and saquinavir (2.1-fold). However, the impact of G1199A on P-gp activity appeared to primarily influence drug permeability in the apical-to-basolateral direction. Kinetic analysis of ritonavir and saquinavir uptake by MDR1wt- and MDR1(1199A)-expressing cells showed that Vmax was similar, while uptake Km was significantly higher in cells expressing the G1199A variant suggesting that alterations in P-gp-dependent efflux mediated by G1199A were due to changes in transporter affinity.

CONCLUSIONS

Alterations in transepithelial permeability of HIV PI due to the G1199A polymorphism may impact oral bioavailability of PI and penetration into cells and tissues of the lymphoid and central nervous systems.

Transport of HIV protease inhibitors through the blood-brain barrier and interactions with the efflux proteins, P-glycoprotein and multidrug resistance proteins

HIV protease inhibitors (HPIs) have limited penetration into the brain. This poor transport through the blood-brain barrier is mainly due to active efflux by proteins such as P-glycoprotein (P-gp) preventing drugs from clearing the brain of the virus. The present paper focuses on cerebral uptake of HPIs and interactions between HPIs and efflux proteins, either as substrates or modulators. Most of the studies described HPIs as P-gp substrates. Studies are more controversial when investigating HPIs as inhibitors of P-gp. HPIs seem to be able to inhibit efflux proteins of in vitro cell models but with limited consequences in vivo. Moreover, after repeated administrations of HPIs, most of them are also able to induce the expression and functionality of P-gp. For these reasons, certain combinations of HPIs may not efficiently increase brain uptake of HPIs as would combinations of more potent efflux inhibitors.

The implications of P-glycoprotein in HIV: friend or foe?

P-glycoprotein (P-gp), coded by the ABCB1 gene, has a wide tissue distribution. The drug transporter is known to limit the bioavailability of a plethora of drugs and xenobiotics including the human immunodeficiency virus (HIV) protease inhibitors. There remains a considerable degree of debate in the literature with respect to the role of ABCB1 polymorphisms in HIV-treatment outcome and some studies have also implicated antiretroviral drugs as inducers of P-gp. Recent evidence indicates a role for P-gp in the inhibition of viral infectivity and/or release and cellular relationships with other infection-related proteins (and cholesterol). It is becoming increasingly clear that future studies on P-gp in HIV should consider both pharmacological and virological issues.