Cyclosporins: structure-activity relationships for the inhibition of the human MDR1 P-glycoprotein ABC transporter

Taming Conformational Heterogeneity on Ion Racetrack to Unveil Principles that Drive Membrane Permeation of Cyclosporines

Our study reveals the underlying principles governing the passive membrane permeability in three large N-methylated macrocyclic peptides (N-MeMPs): cyclosporine A (CycA), Alisporivir (ALI), and cyclosporine H (CycH). We determine a series of conformers required for robust passive membrane diffusion and those relevant to other functions, such as binding to protein targets or intermediates, in the presence of solvent additives. We investigate the conformational interconversions and establish correlations with the membrane permeability. Nuclear magnetic resonance (NMR) and cyclic ion-mobility spectrometry-mass spectrometry (cIMS-MS) are employed to characterize conformational heterogeneity and identify cis-amides relevant for good membrane permeability. In addition, ion mobility selected cIMS-MS and infrared (IR) multiple-photon dissociation (IRMPD) spectroscopy experiments are conducted to evaluate the energy barriers between conformations. We observe that CycA and ALI, both cyclosporines with favorable membrane permeabilities, display multiple stable and well-defined conformers. In contrast, CycH, an epimer of CycA with limited permeability, exhibits fewer and fewer stable conformers. We demonstrate the essential role of the conformational shift from the aqueous cis MeVal11-MeBmt1 state (A1) to the closed conformation featuring cis MeLeu9-MeLeu10 (C1) in facilitating membrane permeation. Additionally, we highlight that the transition from A1 to the all-trans open conformation (O1) is specifically triggered by the presence of CaCl2. We also capture a set of conformers with cis Sar3-MeLeu4, MeLeu9-MeLeu10, denoted as I. Conformationally selected cIMS-MS and IRMPD data of [CycA+Ca]2+ show immediate repopulation of the original population distribution, suggesting that CaCl2 smooths out the energy barriers. Finally, our work presents an improved sampling molecular dynamics approach based on a refined force field that not only consistently and accurately captures established conformers of cyclosporines but also exhibits strong predictive capabilities for novel conformers.

Design and Synthesis of Cyclolipopeptide Mimics of Dysoxylactam A and Evaluation of the Reversing Potencies against P-Glycoprotein-Mediated Multidrug Resistance

Inspired by the structure of dysoxylactam A (DLA) that has been demonstrated to reverse P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) effectively, 61 structurally simplified cyclolipopeptides were thus designed and synthesized via an effective method, and their reversing P-gp-mediated MDR potentials were evaluated, which provided a series of more potent analogues and allowed us to explore their structure-activity relationship (SAR). Among them, a well-simplified compound, 56, with only two chiral centers that all derived from amino acids dramatically reversed drug resistance in KBV200 cells at 10 μM in combination with vinorelbine (VNR), paclitaxel (PTX), and adriamycin (ADR), respectively, which is more promising than DLA. The mechanism study showed that 56 reversed the MDR of tumor cells by inhibiting the transport function of P-gp rather than reducing its expression. Notably, compound 56 effectively restored the sensitivity of MDR tumors to VNR in vivo at a dosage without obvious toxicity.

The mechanisms of multidrug resistance of breast cancer and research progress on related reversal agents

Chemotherapy is the mainstay in the treatment of breast cancer. However, many drugs that are commonly used in clinical practice have a high incidence of side effects and multidrug resistance (MDR), which is mainly caused by overexpression of drug transporters and related enzymes in breast cancer cells. In recent years, researchers have been working hard to find newer and safer drugs to overcome MDR in breast cancer. In this review, we provide the molecule mechanism of MDR in breast cancer, categorize potential lead compounds that inhibit single or multiple drug transporter proteins, as well as related enzymes. Additionally, we have summarized the structure-activity relationship (SAR) based on potential breast cancer MDR modulators with lower side effects. The development of novel approaches to suppress MDR is also addressed. These lead compounds hold great promise for exploring effective chemotherapy agents to overcome MDR, providing opportunities for curing breast cancer in the future.

Binding of Different Cyclosporin Variants to Micelles Evidenced by NMR and MD Simulations

Peptides play a critical role in the life of organisms, performing completely different functions. The biological activity of some peptides, such as cyclosporins, can be determined by the degree of membrane permeability. Thus, it becomes important to study how the molecule interacts with lipid bilayers. Cyclosporins C, E, H and L were characterised molecular dynamics simulation; NMR spectroscopy studies were also carried out for cyclosporins C and E. The comparison of one- and two-dimensional spectra revealed certain similarities between spatial structures of the studied cyclosporin variants. Upon dissolving in water containing DPC micelles, which serve as model membranes, subtle changes in the NMR spectra appear, but in a different way for different cyclosporins. In order to understand whether observed changes are related to any structural modifications, simulation of the interaction of the peptide with the phospholipid micelle was performed. The onset of the interaction was observed, when the peptide is trapped to the surface of the micelle. Simulations of this kind are also of interest in the light of the well-known membrane permeability of cyclosporin, which is important for its biological action.

Non-Immunosuppressive Cyclophilin Inhibitors

Cyclophilins, enzymes with peptidyl-prolyl cis/trans isomerase activity, are relevant to a large variety of biological processes. The most abundant member of this enzyme family, cyclophilin A, is the cellular receptor of the immunosuppressive drug cyclosporine A (CsA). As a consequence of the pathophysiological role of cyclophilins, particularly in viral infections, there is a broad interest in cyclophilin inhibition devoid of immunosuppressive activity. This Review first gives an introduction into the physiological and pathophysiological roles of cyclophilins. The presentation of non-immunosuppressive cyclophilin inhibitors will commence with drugs based on chemical modifications of CsA. The naturally occurring macrocyclic sanglifehrins have become other lead structures for cyclophilin-inhibiting drugs. Finally, de novo designed compounds, whose structures are not derived from or inspired by natural products, will be presented. Relevant synthetic concepts will be discussed, but the focus will also be on biochemical studies, structure-activity relationships, and clinical studies.

Atomic View of Aqueous Cyclosporine A: Unpacking a Decades-Old Mystery

An atomic view of a main aqueous conformation of cyclosporine A (CycA), an important 11-amino-acid macrocyclic immunosuppressant, is reported. For decades, it has been a grand challenge to determine the conformation of free CycA in an aqueous-like solution given its poor water solubility. Using a combination of X-ray and single-crystal neutron diffraction, we unambiguously resolve a unique conformer (A1) with a novel cis-amide between residues 11 and 1 and two water ligands that stabilize hydrogen bond networks. NMR spectroscopy and titration experiments indicate that the novel conformer is as abundant as the closed conformer in 90/10 (v/v) methanol/water and is the main conformer at 10/90 methanol/water. Five other conformers were also detected in 90/10 methanol/water, one in slow exchange with A1, another one in slow exchange with the closed form and three minor ones, one of which contains two cis amides Abu2-Sar3 and MeBmt1-MeVal11. These conformers help better understand the wide spectrum of membrane permeability observed for CycA analogues and, to some extent, the binding of CycA to protein targets.

Cyclosporin Structure and Permeability: From A to Z and Beyond

Cyclosporins are natural or synthetic undecapeptides with a wide range of actual and potential pharmaceutical applications. Several members of the cyclosporin compound family have remarkably high passive membrane permeabilities that are not well-described by simple structural metrics. Here we review experimental studies of cyclosporin structure and permeability, including cyclosporin-metal complexes. We also discuss models for the conformation-dependent permeability of cyclosporins and similar compounds. Finally, we identify current knowledge gaps in the literature and provide recommendations regarding future avenues of exploration.

A nanomedicine approach enables co-delivery of cyclosporin A and gefitinib to potentiate the therapeutic efficacy in drug-resistant lung cancer

Drug resistance, accounting for therapeutic failure in the clinic, remains a major challenge to effectively manage cancer. Cyclosporin A (CsA) can reverse multidrug resistance (MDR), especially resistance to epidermal growth factor receptor tyrosine kinase inhibitors. However, the application of both drugs in cancer therapies is hampered by their poor aqueous solubility and low bioavailability due to oral administration. CsA augments the potency of gefitinib (Gef) in both Gef-sensitive and Gef-resistant cell lines. Here, we show that the simultaneous encapsulation of CsA and Gef within polyethylene glycol-block-poly(_{D, L}-lactic acid) (PEG-PLA) produced a stable and systemically injectable nanomedicine, which exhibited a sub-50-nm diameter and spherical structures. Impressively, the co-delivery of therapeutics via single nanoparticles (NPs) outperformed the oral administration of the free drug combination at suppressing tumor growth. Furthermore, in vivo results indicated that CsA formulated in NPs sensitized Gef-resistant cells and Gef-resistant tumors to Gef treatment by inactivating the STAT3/Bcl-2 signaling pathway. Collectively, our nanomedicine approach not only provides an alternative administration route for the drugs of choice but also effectively reverses MDR, facilitating the development of effective therapeutic modalities for cancer.

Injection of nanoparticles containing the anticancer drug gefitinib and the immunosuppressant cyclosporin A reverses drug-resistant cancer growth in mice. The development of multidrug resistance is the main reason why many forms of chemotherapy fail. Cyclosporin A, a drug used to prevent immune rejection after organ transplantation, has previously been shown to enhance the potency of gefitinib. Hangxiang Wang and colleagues at Zhejiang University, Hangzhou, China, have successfully combined cyclosporin A and gefitinib, two poorly water-soluble and slowly absorbed drugs, into stable injectable nanoparticles that delay the growth of gefitinib resistant human lung cancer cells as well as the growth of drug resistant tumors in mice. Importantly, this novel co-formulation was more effective than oral co-administration of the two drugs. Further investigation into this drug delivery route could yield much needed alternative treatments for patients with multidrug-resistant cancers.

Past, Current, and Future Developments of Therapeutic Agents for Treatment of Chronic Hepatitis B Virus Infection

For decades, treatment of hepatitis B virus (HBV) infection has been relying on interferon (IFN)-based therapies and nucleoside/nucleotide analogues (NAs) that selectively target the viral polymerase reverse transcriptase (RT) domain and thereby disrupt HBV viral DNA synthesis. We have summarized here the key steps in the HBV viral life cycle, which could potentially be targeted by novel anti-HBV therapeutics. A wide range of next-generation direct antiviral agents (DAAs) with distinct mechanisms of actions are discussed, including entry inhibitors, transcription inhibitors, nucleoside/nucleotide analogues, inhibitors of viral ribonuclease H (RNase H), modulators of viral capsid assembly, inhibitors of HBV surface antigen (HBsAg) secretion, RNA interference (RNAi) gene silencers, antisense oligonucleotides (ASOs), and natural products. Compounds that exert their antiviral activities mainly through host factors and immunomodulation, such as host targeting agents (HTAs), programmed cell death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) inhibitors, and Toll-like receptor (TLR) agonists, are also discussed. In this Perspective, we hope to provide an overview, albeit by no means being comprehensive, for the recent development of novel therapeutic agents for the treatment of chronic HBV infection, which not only are able to sustainably suppress viral DNA but also aim to achieve functional cure warranted by HBsAg loss and ultimately lead to virus eradication and cure of hepatitis B.

Semi-synthesis of cyclosporins

BACKGROUND

Since its isolation in 1970, and discovery of its potent inhibitory activity on T-cell proliferation, cyclosporin A (CsA) has been shown to play a significant role in diverse fields of biology. Furthermore, chemical modification of CsA has led to analogs with distinct biological activities associated with its protein receptor family, cyclophilins.

SCOPE OF REVIEW

This review systematically collates the synthetic chemistry performed at each of the eleven amino acids, and provides examples of the utility of such transformations. The various modifications of CsA are traced from early, modest chemistry performed at the unique Bmt residue, through the remarkable use of a polyanion enolate that can be stereoselectively manipulated, and onto application of more recently developed olefin metathesis chemistry to prepare new CsA derivatives with unexpected biological activity.

MAJOR CONCLUSIONS

The myriad biological activities of CsA and its synthetic derivatives have inspired the development of new approaches to modify the CsA ring. In turn, these new CsA derivatives have served as tools in the discovery of new roles for cyclophilins.

GENERAL SIGNIFICANCE

This review provides information on the types of cyclosporin derivatives that are available to the many biologists working in this field, and should be of value to the medicinal chemist trying to discover drugs based on CsA. This article is part of a Special Issue entitled Proline-directed foldases: Cell signaling catalysts and drug targets.

Biosynthesis of cyclosporins and other natural peptidyl prolyl cis/trans isomerase inhibitors

BACKGROUND

Peptidyl-prolyl-cis/trans-isomerases (PPIases) are ubiquitously expressed and have been implicated in a wide range of biological functions. Their inhibition is beneficial in immunosuppression, cancer treatment, treatment of autoimmune diseases, protozoan and viral infections.

SCOPE OF REVIEW

Three classes of PPIases are known, each class having their own specific inhibitors. This review will cover the present knowledge on the biosynthesis of the natural PPIase inhibitors. These include for the cyclophilins: the cyclosporins, the analogues of peptolide SDZ 214-103 and the sanglifehrins; for the FKBPs: ascomycin, rapamycin and FK506 and for the parvulins the naphtoquinone juglone.

MAJOR CONCLUSIONS

Over the last thirty years much progress has been made in understanding PPIase function and the biosynthesis of natural PPIase inhibitors. Non-immunosuppressive analogues were discovered and served as lead compounds for the development of novel antiviral drugs. There are, however, still unsolved questions which deserve further research into this exciting field.

GENERAL SIGNIFICANCE

As all the major natural inhibitors of the cyclophilins and FKBPs are synthesized by complex non-ribosomal peptide synthetases and/or polyketide synthases, total chemical synthesis is not a viable option. Thus, fully understanding the modular enzyme systems involved in their biosynthesis may help engineering enzymes capable of synthesizing novel PPIase inhibitors with improved functions for a wide range of conditions. This article is part of a Special Issue entitled Proline-directed Foldases: Cell signaling catalysts and drug targets.

Potent nonimmunosuppressive cyclophilin inhibitors with improved pharmaceutical properties and decreased transporter inhibition

Nonimmunosuppressive cyclophilin inhibitors have demonstrated efficacy for the treatment of hepatitis C infection (HCV). However, alisporivir, cyclosporin A, and most other cyclosporins are potent inhibitors of OATP1B1, MRP2, MDR1, and other important drug transporters. Reduction of the side chain hydrophobicity of the P4 residue preserves cyclophilin binding and antiviral potency while decreasing transporter inhibition. Representative inhibitor 33 (NIM258) is a less potent transporter inhibitor relative to previously described cyclosporins, retains anti-HCV activity in cell culture, and has an acceptable pharmacokinetic profile in rats and dogs. An X-ray structure of 33 bound to rat cyclophilin D is reported.

From chemical tools to clinical medicines: nonimmunosuppressive cyclophilin inhibitors derived from the cyclosporin and sanglifehrin scaffolds

The cyclophilins are widely expressed enzymes that catalyze the interconversion of the cis and trans peptide bonds of prolines. The immunosuppressive natural products cyclosporine A and sanglifehrin A inhibit the enzymatic activity of the cyclophilins. Chemical modification of both the cyclosporine and sanglifehrin scaffolds has produced many analogues that inhibit cyclophilins in vitro but have reduced immunosuppressive properties. Three nonimmunosuppressive cyclophilin inhibitors (alisporivir, SCY-635, and NIM811) have demonstrated clinical efficacy for the treatment of hepatitis C infection. Additional candidates are in various stages of preclinical development for the treatment of hepatitis C or myocardial reperfusion injury. Recent publications suggest that cyclophilin inhibitors may have utility for the treatment of diverse viral infections, inflammatory indications, and cancer. In this review, we document the structure-activity relationships of the nonimmunosuppressive cyclosporins and sanglifehrins in clinical and preclinical development. Aspects of the pharmacokinetic behavior and chemical biology of these drug candidates are also described.

Cyclosporin A and its analogs inhibit hepatitis B virus entry into cultured hepatocytes through targeting a membrane transporter, sodium taurocholate cotransporting polypeptide (NTCP)

Chronic hepatitis B virus (HBV) infection is a major public health problem worldwide. Although nucleos(t)ide analogs inhibiting viral reverse transcriptase are clinically available as anti-HBV agents, emergence of drug-resistant viruses highlights the need for new anti-HBV agents interfering with other targets. Here we report that cyclosporin A (CsA) can inhibit HBV entry into cultured hepatocytes. The anti-HBV effect of CsA was independent of binding to cyclophilin and calcineurin. Rather, blockade of HBV infection correlated with the ability to inhibit the transporter activity of sodium taurocholate cotransporting polypeptide (NTCP). We also found that HBV infection-susceptible cells, differentiated HepaRG cells and primary human hepatocytes expressed NTCP, while nonsusceptible cell lines did not. A series of compounds targeting NTCP could inhibit HBV infection. CsA inhibited the binding between NTCP and large envelope protein in vitro. Evaluation of CsA analogs identified a compound with higher anti-HBV potency, having a median inhibitory concentration <0.2 μM.

CONCLUSION

This study provides a proof of concept for the novel strategy to identify anti-HBV agents by targeting the candidate HBV receptor, NTCP, using CsA as a structural platform.

Mass spectrometry reveals synergistic effects of nucleotides, lipids, and drugs binding to a multidrug resistance efflux pump

Multidrug resistance is a serious barrier to successful treatment of many human diseases, including cancer, wherein chemotherapeutics are exported from target cells by membrane-embedded pumps. The most prevalent of these pumps, the ATP-Binding Cassette transporter P-glycoprotein (P-gp), consists of two homologous halves each comprising one nucleotide-binding domain and six transmembrane helices. The transmembrane region encapsulates a hydrophobic cavity, accessed by portals in the membrane, that binds cytotoxic compounds as well as lipids and peptides. Here we use mass spectrometry (MS) to probe the intact P-gp small molecule-bound complex in a detergent micelle. Activation in the gas phase leads to formation of ions, largely devoid of detergent, yet retaining drug molecules as well as charged or zwitterionic lipids. Measuring the rates of lipid binding and calculating apparent KD values shows that up to six negatively charged diacylglycerides bind more favorably than zwitterionic lipids. Similar experiments confirm binding of cardiolipins and show that prior binding of the immunosuppressant and antifungal antibiotic cyclosporin A enhances subsequent binding of cardiolipin. Ion mobility MS reveals that P-gp exists in an equilibrium between different states, readily interconverted by ligand binding. Overall these MS results show how concerted small molecule binding leads to synergistic effects on binding affinities and conformations of a multidrug efflux pump.

Intestinal ciprofloxacin efflux: the role of breast cancer resistance protein (ABCG2)

Intestinal secretory movement of the fluoroquinolone antibiotic, ciprofloxacin, may limit its oral bioavailability. Active ATP-binding cassette (ABC) transporters such as breast cancer resistance protein (BCRP) have been implicated in ciprofloxacin transport. The aim of this study was to test the hypothesis that BCRP alone mediates intestinal ciprofloxacin secretion. The involvement of ABC transport proteins in ciprofloxacin secretory flux was investigated with the combined use of transfected cell lines [bcrp1/BCRP-Madin-Darby canine kidney II (MDCKII) and multidrug resistance-related protein 4 (MRP4)-human embryonic kidney (HEK) 293] and human intestinal Caco-2 cells, combined with pharmacological inhibition using 3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6, 7,12,12a-octahydropyrazino[1',2':1,6]pyrido[3,4-b]indol-3-yl)-propionic acid tert-butyl ester (Ko143), cyclosporine, 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK571), and verapamil as ABC-selective inhibitors. In addition, the regional variation in secretory capacity was investigated using male Han Wistar rat intestine mounted in Ussing chambers, and the first indicative measurements of ciprofloxacin transport by ex vivo human jejunum were made. Active, Ko143-sensitive ciprofloxacin secretion was observed in bcrp1-MDCKII cell layers, but in low-passage (BCRP-expressing) Caco-2 cell layers only a 54% fraction was Ko143-sensitive. Ciprofloxacin accumulation was lower in MRP4-HEK293 cells than in the parent line, indicating that ciprofloxacin is also a substrate for this transporter. Ciprofloxacin secretion by Caco-2 cell layers was not inhibited by MK571. Secretory flux showed marked regional variability in the rat intestine, increasing from the duodenum to peak in the ileum. Ciprofloxacin secretion was present in human jejunum and was reduced by Ko143 but showed marked interindividual variability. Ciprofloxacin is a substrate for human and rodent BCRP. An additional pathway for ciprofloxacin secretion exists in Caco-2 cells, which is unlikely to be MRP(4)-mediated. BCRP is likely to be the dominant transport mechanism for ciprofloxacin efflux in both rat and human jejunum.

Molecular aspects of cyclophilins mediating therapeutic actions of their ligands

Cyclosporine A (CsA) is an immunosuppressive cyclic peptide that binds with a high affinity to 18 kDa human cyclophilin-A (hCyPA). CsA and its several natural derivatives have some pharmacological potential in treatment of diverse immune disorders. More than 20 paralogues of CyPA are expressed in the human body while expression levels and functions of numerous ORFs encoding cyclophilin-like sequences remain unknown. Certain derivatives of CsA devoid of immunosuppressive activity may have some potential in treatments of Alzheimer diseases, Hepatitis C and HIV infections, amyotrophic lateral sclerosis, congenital muscular dystrophy, asthma and various parasitic infections. Here, we discuss structural and functional aspects of the human cyclophilins and their interaction with various intra-cellular targets that can be under the control of CsA or its complexes with diverse cyclophilins that are selectively expressed in different cellular compartments. Some molecular aspects of the cyclophilins expressed in parasites invading humans and causing diseases were also analyzed.

N-(3,4-dimethoxyphenethyl)-4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2[1H]-yl)-6,7-dimethoxyquinazolin-2-amine (CP-100,356) as a "chemical knock-out equivalent" to assess the impact of efflux transporters on oral drug absorption in the rat

The utility of the diaminoquinazoline derivative CP-100,356 as an in vivo probe to selectively assess MDR1/BCRP-mediated drug efflux was examined in the rat. CP-100,356 was devoid of inhibition (IC(50) >50 microM) against major human P450 enzymes including P4503A4. In human MDR1-transfected MDCKII cells, CP-100,356 inhibited acetoxymethyl calcein (calcein-AM) uptake (IC(50) approximately 0.5 +/- 0.07 microM) and digoxin transport (IC(50) approximately 1.2 +/- 0.1 microM). Inhibition of prazosin transport (IC(50) approximately 1.5 +/- 0.3 microM) in human BCRP-transfected MDCKII cells by CP-100,356 confirmed the dual MDR1/BCRP inhibitory properties. CP-100,356 was a weak inhibitor of OATP1B1 (IC(50) approximately 66 +/- 1.1 microM) and was devoid of MRP2 inhibition (IC(50) >15 microM). In vivo inhibitory effects of CP-100,356 in rats were examined after coadministration with MDR1 substrate fexofenadine and dual MDR1/BCRP substrate prazosin. Coadministration with increasing doses of CP-100,356 resulted in dramatic increases in systemic exposure of fexofenadine (36- and 80-fold increase in C(max) and AUC at a CP-100,356 dose of 24 mg/kg). Significant differences in prazosin pharmacokinetics were also discernible in CP-100,356-pretreated rats as reflected from a 2.6-fold increase in AUC. Coadministration of CP-100,356 and P4503A substrate midazolam did not result in elevations in systemic exposure of midazolam in the rat. The in vivo methodology should have utility in drug discovery in selective and facile assessment of the role of MDR1 and BCRP efflux transporters in oral absorption of new drug candidates.

Cyclosporin A decreases apolipoprotein E secretion from human macrophages via a protein phosphatase 2B-dependent and ATP-binding cassette transporter A1 (ABCA1)-independent pathway

Cyclosporin A (CsA) is an immunosuppressant that inhibits protein phosphatase 2B (PP2B/calcineurin) and is associated with hyperlipidemia, decreased cholesterol efflux via ATP-binding cassette transporter A1 (ABCA1), and increased risk of atherosclerosis. Apolipoprotein E (apoE) is an important regulator of lipid metabolism and atherosclerosis, the secretion of which from human macrophages is regulated by the serine/threonine protein kinase A (PKA) and intracellular calcium (Ca(2+)) (Kockx, M., Guo, D. L., Huby, T., Lesnik, P., Kay, J., Sabaretnam, T., Jary, E., Hill, M., Gaus, K., Chapman, J., Stow, J. L., Jessup, W., and Kritharides, L. (2007) Circ. Res. 101, 607-616). As PP2B is Ca(2+)-dependent and has been linked to PKA-dependent processes, we investigated whether CsA modulated apoE secretion. CsA dose- and time-dependently inhibited secretion of apoE from primary human macrophages and from Chinese hamster ovary cells stably transfected with human apoE and increased cellular apoE levels without affecting apoE mRNA. [(35)S]Met kinetic modeling studies showed that CsA inhibited both secretion and degradation of apoE, increasing the half-life of cellular apoE 2-fold. CsA also inhibited secretion from primary human Tangier disease macrophages and from mouse macrophages deficient in ABCA1, indicating that the effect is independent of the known inhibition of ABCA1 by CsA. The role of PP2B in mediating apoE secretion was confirmed using additional peptide and chemical inhibitors of PP2B. Importantly, kinetic modeling, live-cell imaging, and confocal microscopy all indicated that CsA inhibited apoE secretion by mechanisms quite distinct from those of PKA inhibition, most likely inducing accumulation of apoE in the endoplasmic reticulum compartment. Taken together, these results establish a novel mechanism for the pro-atherosclerotic effects of CsA, and establish for the first time a role for PP2B in regulating the intracellular transport and secretion of apoE.

Advances in genomic research on hepatitis C virus with a useful tool, replicon system

The research for hepatitis C virus (HCV) has long delayed by missing of in vitro culture system. Since the development of replicon system, a replication system of subgenomic HCV RNAs in a hepatoma cell line, has been reported, many virological and clinical findings have been discovered. Recently, in addition of subgenomic replication system, hepatitis C virus full-length RNA replication has been possible, and a few cell culture systems producing viral particles have been produced. These developments enabled us to investigate the life cycle or intracellular circumstance of HCV production. By screening of newly synthesized drugs with this replicon system, several possible medicines have been established and clinical researches are now running. Among them, VX950 and SCH503034 are nearest to clinical use. Other possible agents for reducing viral replication such as cyclophyllin inhibitors, inhibitors of sphingomyelin synthesis, HMG-CoA reductase inhibitors, or RNA-dependent RNA polymerase inhibitors have been also investigated. Furthermore the mechanism for development of hepatocellular carcinoma in the HCV infected liver has been vigorously studied using the HCV replicon system.

Cyclosporine stimulates the renal epithelial sodium channel by elevating cholesterol

Cyclosporine A (CsA) is an efficient immunosuppressant used for reducing allograft rejection but with a severe side effect of causing hypertension. We hypothesize that the renal epithelial sodium channel (ENaC) may participate in CsA-induced hypertension. In the present study, we used the patch-clamp cell-attached configuration to examine whether and how CsA stimulates ENaC in A6 distal nephron cells. The data showed that CsA significantly increased ENaC open probability. Since CsA is an inhibitor of the ATP-binding cassette A1 (ABCA1) transporter, we employed 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), another ABCA1 inhibitor, and found that DIDS mimicked the effects of CsA on ENaC basal and cholesterol-induced activity but without any additive effect if combined with CsA. CsA and DIDS also had an identical effect on reduced ENaC activity caused by cholesterol extraction. ABCA1 protein was detected in A6 cells by Western blot analysis. Confocal microscopy data showed that both CsA and DIDS facilitated A6 cells to uptake cholesterol. Since enhanced ENaC activity is known to cause hypertension, these data together suggest that CsA may cause hypertension by stimulating ENaC through a pathway associated with inhibition of ABCA1 and consequent elevation of cholesterol in the cells.

Chalcogenopyrylium dyes as inhibitors/modulators of P-glycoprotein in multidrug-resistant cells

A series of chalcogenopyrylium dyes were evaluated as modulators/inhibitors of P-glycoprotein (Pgp). Their ability to inhibit verapamil (VER)-dependent ATPase activity (IC(50) values) in lipid-activated, mouse Cys-less mdr3 Pgp was determined. Their ability to promote calcein-AM (CAM) uptake in MDCKII-MDR1 cells and their capacity to be transported by Pgp in monolayers of MDCKII-MDR1 cells were also evaluated. The chalcogenopyrylium dyes promoted CAM uptake with values of EC(50) between 5 x 10(-6) and 3.5 x 10(-5)M and 7 of the 9 dyes examined in transport studies were substrates for Pgp with efflux ratios (P(BA/AB)) between 14 and 390. Binding of three compounds (1-S, 3-S, and 4-S) to Pgp was also assessed by fluorescence. These three thiopyrylium dyes showed increased fluorescence upon binding to Pgp, giving apparent binding constants, K(app), on the order of 10(-7) to 10(-6)M. Compound 8-Te was particularly intriguing since it appeared to influence Pgp at low micromolar concentrations as evidenced by its influence on VER-stimulated ATPase activity (IC(50) of 1.2 x 10(-6)M), CAM uptake (EC(50) of 5.4 x 10(-6)M), as well as [(3)H]-vinblastine transport by Pgp in cells (IC(50) of 4.3 x 10(-6)M) and within inside-out membrane vesicles (IC(50) of 9.6 x 10(-6)M). Yet, Pgp did not influence the distribution of 8-Te in MDCKII-MDR1 monolayers suggesting that 8-Te may bind to an allosteric site.

Development of predictive in silico model for cyclosporine- and aureobasidin-based P-glycoprotein inhibitors employing receptor surface analysis

P-glycoprotein (Pgp) is implicated in multiple drug resistance (MDR) exhibited by several types of cancer against a multitude of anticancer chemotherapeutic agents. This problem prompted several research groups to search for effective P-gp inhibitors. Cyclosporine A (CsA), aureobasidin A (AbA) and related analogues were reported to possess potent inhibitory actions against Pgp. In this work we employed receptor surface analysis (RSA) to construct two satisfactory receptor surface models (RSMs) for cyclosporine- and aureobasidin-based Pgp inhibitors. These pseudoreceptors were combined to achieve satisfactory three-dimensional quantitative structure activity relationship (3D-QSAR) for 68 different cyclosporine and aureobasidin derivatives. Upon validation against an external set of 16 randomly selected Pgp inhibitors, the optimal 3D-QSAR was found to be self-consistent and predictive (r(LOO)(2)=0.673, r(PRESS)(2)=0.600). The resulting 3D-QSAR was employed to probe the structural factors that control the inhibitory activities of cyclosporine and aureobasidin analogues against Pgp.

The Effects of Crinum asiaticum on the Apoptosis Induction and the Reversal of Multidrug Resistance in HL-60/MX2

The present study investigated the anti-proliferative and chemosensitizing effects of Crinum asiaticum var. japonicum against multi-drug resistant (MDR) cancer cells. The 80% methanol extract, chloroform (CHCI₃) fraction and butanol (BuOH) fraction of C asiaticum inhibited the growth of mitoxantrone (MX) resistant HL-60 (HL-60/MX2) cells. When HL-60/MX2 cells were treated with the CHCI₃ and BuOH fractions, DNA ladder and sub-G1 hypodiploid cells were observed. Furthermore, the fractions reduced Bcl-2 mRNA levels, whereas Bax mRNA levels were increased. These results suggest that the inhibitory effect of C. asiaticum on the growth of the HL-60/MX2 cells might arise from the induction of apoptosis. Treatment of HL-60/MX2 cells with the fractions markedly decreased the mRNA levels of the multi-drug resistance protein-1 and breast cancer resistance protein. The CHCI3 fraction and hexane fraction increased MX accumulation in HL-60/MX2 cells. These results imply that the CHCI₃ fraction of C asiaticum plays a pivotal role as a chemosensitizer. We suggest that components of C asiaticum might have a therapeutic potential for the treatment of MDR leukemia.

Unconjugated bilirubin efflux by bovine brain microvascular endothelial cells in vitro

OBJECTIVES

The passage of unconjugated bilirubin (UCB) across the blood-brain barrier into the central nervous system is a crucial first step in the development of kernicterus. The objective of the current study was to characterize the passage of UCB across primary bovine brain microvascular endothelial cell (BBMVEC) monolayers in vitro.

DESIGN

Experimental study.

SETTING

Research institute.

SUBJECTS

BBMVECs.

INTERVENTIONS

Tritiated UCB (H-UCB) transport at 60, 80, 100, 200, 300, and 400 nM concentrations was tested in both the apical to basolateral (A--> B) and basolateral to apical (B-->A) directions in BBMVEC monolayers in vitro with or without preincubation with pharmacologic active transport inhibitors cyclosporine A, indomethacin, or MK571.

MEASUREMENTS AND MAIN RESULTS

The rate of H-UCB transport in the B-->A direction was 6.2- to 7.3-fold higher than in the A-->B direction, suggesting active efflux of UCB. Cyclosporine A (5 microM), a model inhibitor of P-glycoprotein, enhanced A-->B while decreasing B-->A UCB transport, resulting in an overall decrease in BBMVEC UCB efflux of between 46% and 54%. Indomethacin (10 microM) and MK-571 (50 microM), respectively a substrate and potent inhibitor of multidrug resistance-associated protein-1, had no effect.

CONCLUSIONS

We conclude that 1) UCB is transported by BBMVEC monolayers in vitro in a net B-->A direction (i.e., active efflux); and 2) cyclosporine A partially inhibits such transport. We speculate that the blood-brain barrier limits the passage and central nervous system retention of UCB by active transport and that this may be accounted in part by P-glycoprotein.

Chemical genetics approach to hepatitis C virus replication: cyclophilin as a target for anti-hepatitis C virus strategy

Hepatitis C virus (HCV) is a major causative agent of liver diseases such as chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Because the current standard therapy, interferon (IFN) or pegylated-IFN alone or in combination with ribavirin, is ineffective on approximately half of the HCV-infected patients, alternative therapeutics are greatly needed. The chemical genetics method is a useful strategy to elucidate molecular mechanisms of the viral life cycle and screen for anti-viral agents. This review focuses on the use of chemical genetics approach to virology, which could be called 'chemical virology', and introduces an example of such analysis. From a cell culture-based screening, an immunosuppressant cyclosporin A (CsA) was identified as an anti-HCV compound. Analysis using CsA as a bioprobe showed that cyclophilin (CyP) B, a cellular target of CsA, regulates the function of HCV RNA polymerase NS5B, which is essential for efficient viral genome replication. By targeting CyP, HCV genome replication was drastically suppressed. Thus, chemical genetics analysis identified CyPB as a cellular cofactor of HCV genome replication and a target for novel anti-HCV agents.

Novel targeted therapies in epithelial ovarian cancer: from basic research to the clinic

The development of new molecularly targeted therapies represents a high priority for the treatment of epithelial ovarian cancer. P-glycoprotein overexpression has been associated with multidrug resistance, and the use of multidrug resistance modulators, such as valspodar, is being explored in combination with chemotherapy. Human epidermal receptor (HER) family members are attractive targets for biological therapies. The addition of erlotinib or cetuximab to first-line paclitaxel- plus carboplatin-based chemotherapy is feasible and well tolerated. Gefitinib is able to inhibit the proliferation of ovarian clear-cell carcinoma in in vitro and in vivo experimental models. Single-agent trastuzumab has a limited value for recurrent epithelial ovarian cancer owing to the low frequency of HER2 overexpression and the low rate of objective responses among HER2-overexpressing patients. A Gynecologic Oncology Group Phase II trial of the proteasome inhibitor bortezomib in recurrent epithelial ovarian cancer is currently ongoing, and the combination of bortezomib and chemotherapeutic agents should be assessed. The mammalian target of rapamycin (mTOR) plays an important role in stimulating the translation of mRNAs encoding key proteins for cell growth and angiogenesis, and mTOR inhibitors, such as AP-23573 (ARIAD), deserve to be tested in selected epithelial ovarian cancer patients. The addition of intraperitoneal treatment with adenovirus containing human wild-type p53 to standard paclitaxel- plus carboplatin-based chemotherapy failed to improve the clinical outcome of patients with mutated p53 epithelial ovarian cancer. The Gynecologic Oncology Group is conducting a Phase II trial of single-agent bevacizumab (antivascular endothelial growth factor monoclonal antibody) in platinum-resistant disease. In conclusion, emerging drugs for epithelial ovarian cancer include agents designed to overcome chemoresistance, HER-targeting agents, proteasome inhibitors, mTOR inhibitors and angiogenesis inhibitors. A new paradigm of treatment could consist of chemotherapy combined with a biological agent for six cycles, and followed by chronic maintenance therapy with the biological agent alone. Advances in genomics and proteomics will elucidate the molecular mechanisms of ovarian carcinogenesis, which will hopefully lead to individualized molecular medicine in the next years.

Functional studies on the activity of efflux transporters in an ex vivo model with chicken splenocytes and evaluation of selected fluoroquinolones in this model

The efflux proteins P-glycoprotein (P-gp), BCRP and members of the MRP-family (MRPs) are increasingly recognized as determinants of the absorption, tissue distribution and excretion of numerous drugs. A widely applied in vitro screening method, to assess the effect of these efflux transporters in transmembrane transport of drugs is based on the use of peripheral blood mononuclear cells (PBMC), in which the efflux of fluorescent dye Rhodamine 123 (Rh-123) can be easily measured. In avian species, the isolation of PBMCs is compromised by the presence of thrombocytes having approximately the same size. As an alternative, we validated the use of isolated splenocytes to assess Rhodamine 123 transport in the presence and absence of specific inhibitors for P-gp, MRPs and BCRP. Rh-123 efflux was concentration-dependent with the percentage of efflux that decreased with increasing concentrations. P-gp inhibitors, PSC833 and GF120918, significantly inhibit Rh-123 efflux, whereas inhibitors for MRPs and BCRP, MK571 and Ko-143, respectively, have a limited inhibitory effect. However, the effect of GF120918 was more pronounced as compared to PSC833, suggesting an additional role for BCRP next to P-gp in Rh-123 efflux. Moreover, fluoroquinolones were selected to test the applicability of the described model. None of these fluoroquinolones significantly inhibit P-gp function at concentrations up to 50 microM, with exception of danofloxacin and danofloxacin mesylate that were found to reduce Rh-123 efflux by approximately 15%.

A cationic chalcogenoxanthylium photosensitizer effective in vitro in chemosensitive and multidrug-resistant cells

Pentacyclic thio- (1) and seleno- (2) analogues of tetramethylrosamine (TMR) were prepared with a julolidyl fragment replacing the 3-dimethylamino substituent in the xanthylium core. The pentacylic structure increases the lipophilicity of 1 and 2 relative to TMR-S and TMR-Se and locks the lone-pair of electrons on the julolidyl N atom into conjugation with the xanthylium core. This conformational rigidization leads to longer wavelengths of absorption, but has little impact on other photophysical properties such as quantum yields for fluorescence and singlet-oxygen generation and fluorescence lifetimes in 1 and 2 relative to TMR-S and TMR-Se. Both 1 and 2 are effective photosensitizers against chemosensitive AUXB1 cells in vitro at 1x10(-7)M and compound 2 is an effective photosensitizer against multidrug-resistant CR1R12 cells in vitro at 1x10(-7)M. While the uptake TMR-S into CR1R12 cells as measured by fluorescence is significantly lower than uptake into chemosensitive AUXB1 cells, there is no significant difference in the uptake of 1 into either AUXB1 or CR1R12 cells. The addition of 2x10(-4)M verapamil to the cells prior to treatment with 1 had no significant effect on the uptake of 1 into either AUXB1 or CR1R12 cells. Treating lipid-activated, purified Pgp with 2 and light gave complete inhibition of Pgp ATPase activity.

The Immunosuppressant Cyclosporin A Antagonizes Human Formyl Peptide Receptor through Inhibition of Cognate Ligand Binding

Cyclosporin A (CsA) is a fungus-derived cyclic undecapeptide with potent immunosuppressive activity. Its analog, cyclosporin H (CsH), lacks immunosuppressive function but can act as an antagonist for the human formyl peptide receptor (FPR). More recent studies have shown that CsA also inhibits fMLF-induced degranulation in differentiated HL-60 promyelocytic leukemia cells. However, it is unclear whether CsA interferes with ligand-receptor interaction, G protein activation, or other downstream signaling events. In this study we used human neutrophils, differentiated HL-60 cells, and rat basophilic leukemia (RBL)-2H3 cells expressing human FPR (RBL-FPR) to identify the action site of CsA. In functional assays, CsA inhibited fMLF-stimulated degranulation, chemotaxis, calcium mobilization, and phosphorylation of the MAPKs ERK 1/2 and the serine/threonine protein kinase Akt. CsA also blocked Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm)-induced functions in RBL-FPR cells. Concentrations for half-maximal inhibition with CsA are generally 6- to 50-fold higher than that of CsH. CsA was compared with another immunosuppressant, ascomycin, relative to the inhibitory effects on FPR-mediated chemotaxis, calcium mobilization, and degranulation. In these experiments, ascomycin produced no inhibitory effects at low micromolar concentrations (1-4 microM), whereas the inhibitory effects of CsA were prominent at comparable concentrations. Finally, CsA dose-dependently inhibited the uptake of fNle-Leu-Phe-Nle-Tyr-Lys-fluoresceine and [3H]fMLF or [125I]WKYMVm binding to FPR. However, CsA and CsH did not show any obvious inhibitory effect on FPR-like 1-mediated cellular functions. These results demonstrate that CsA is a selective antagonist of FPR and that its inhibition of fMLF-stimulated leukocyte activation is at the level of cognate ligand binding.

The role of transporters in drug interactions

Transport proteins play an important role in the adsorption, distribution and elimination of a wide variety of drugs. Therefore, it is not surprising that transporter-based drug interactions can occur in the clinic. These interactions can lead to changes in toxicity and/or efficacy of the affected drug. Here, we review such interactions and ask if these interactions could have been predicted from in vitro data. Conducting such in vitro-in vivo correlation is important for predicting future transporter-based drug interactions.

Genotype-dependent Down-regulation of Gene Expression and Function of MDR1 in Human Peripheral Blood Mononuclear Cells under Acute Inflammation

Recent advances in pharmacogenomics have suggested the association of clinical outcome of glucocorticoid-based anti-inflammatory therapy with a single nucleotide polymorphism at position 3435 in exon 26 (C3435T) of the MDR1 gene. In the present study, the effects of the MDR1 C3435T genotype on the time-dependent profiles of gene expression and function of MDR1/P-glycoprotein were evaluated in peripheral blood mononuclear cells (PBMCs) under lipopolysaccharide (LPS)-induced experimental acute inflammation. LPS treatment resulted in the rapid elevation of IL-1beta and TNF-alpha mRNA levels relative to beta-actin mRNA at 1 h, with a subsequent slight decrease at 3 h after the treatment, while the down-regulation of the relative concentration of MDR1 mRNA was found at 3 h, not at 1 h, after LPS treatment. Here, the C3435T genotype-dependent down-regulations of MDR1 mRNA level were found for CC(3435) and CT(3435), but not for TT(3435), and were 64.1+/-10.1%, 71.4+/-5.9% and 100.0+/-22.5% (+/-S.D.), respectively, of their respective baseline levels, which were independent of C3435T (0.010+/-0.005, 0.011+/-0.013 and 0.009+/-0.006 (+/-S.D.), respectively). The C3435T genotype-dependent down-regulation was supported by the increase of the intracellular accumulation of calcein in PBMCs treated with LPS for 72 h, and the increase was more predominant for CC(3435) than TT(3435). These data suggested that glucocorticoid-based anti-inflammatory therapy might be more effective for C(3435)-allele carriers than non-carriers.

Pharmacological targeting of catalyzed protein folding: the example of peptide bond cis/trans isomerases

Peptide bond isomerases are involved in important physiological processes that can be targeted in order to treat neurodegenerative disease, cancer, diseases of the immune system, allergies, and many others. The folding helper enzyme class of Peptidyl-Prolyl-cis/trans Isomerases (PPIases) contains the three enzyme families of cyclophilins (Cyps), FK506 binding proteins (FKBPs), and parvulins (Pars). Although they are structurally unrelated, all PPIases catalyze the cis/trans isomerization of the peptide bond preceding the proline in a polypeptide chain. This process not only plays an important role in de novo protein folding, but also in isomerization of native proteins. The native state isomerization plays a role in physiological processes by influencing receptor ligand recognition or isomer-specific enzyme reaction or by regulating protein function by catalyzing the switch between native isomers differing in their activity, e.g., ion channel regulation. Therefore elucidating PPIase involvement in physiological processes and development of specific inhibitors will be a suitable attempt to design therapies for fatal and deadly diseases.

Cyclophilin B is a functional regulator of hepatitis C virus RNA polymerase

Viruses depend on host-derived factors for their efficient genome replication. Here, we demonstrate that a cellular peptidyl-prolyl cis-trans isomerase (PPIase), cyclophilin B (CyPB), is critical for the efficient replication of the hepatitis C virus (HCV) genome. CyPB interacted with the HCV RNA polymerase NS5B to directly stimulate its RNA binding activity. Both the RNA interference (RNAi)-mediated reduction of endogenous CyPB expression and the induced loss of NS5B binding to CyPB decreased the levels of HCV replication. Thus, CyPB functions as a stimulatory regulator of NS5B in HCV replication machinery. This regulation mechanism for viral replication identifies CyPB as a target for antiviral therapeutic strategies.

PK11195, a peripheral benzodiazepine receptor (pBR) ligand, broadly blocks drug efflux to chemosensitize leukemia and myeloma cells by a pBR-independent, direct transporter-modulating mechanism

The peripheral benzodiazepine receptor (pBR) ligand, PK11195, promotes mitochondrial apoptosis and blocks P-glycoprotein (Pgp)-mediated drug efflux to chemosensitize cancer cells at least as well or better than the Pgp modulator, cyclosporine A (CSA). We now show that PK11195 broadly inhibits adenosine triphosphate (ATP)-binding cassette (ABC) transporters in hematologic cancer cell lines and primary leukemia-cell samples, including multidrug resistance protein (MRP), breast cancer resistance protein (BCRP), and/or Pgp. Ectopic expression models confirmed that pBR can directly mediate chemosensitizing by PK11195, presumably via mitochondrial activities, but showed that pBR expression is unnecessary to PK11195-mediated efflux inhibition. PK11195 binds plasma-membrane sites in Pgp-expressing cells, stimulates Pgp-associated adenosine triphosphatase (ATPase) activity, and causes conformational changes in Pgp, suggesting that PK11195 modulates Pgp-mediated efflux by direct transporter interaction(s). PK11195 and CSA bind noncompetitively in Pgp-expressing cells, indicating that PK11195 interacts with Pgp at sites that are distinct from CSA-binding sites. Importantly, PK11195 concentrations that were effective in these in vitro assays can be safely achieved in patients. Because PK11195 promotes chemotherapy-induced apoptosis by a pBR-dependent mitochondrial mechanism and broadly blocks drug efflux by an apparently pBR-independent, ABC transporter-dependent mechanism, PK11195 may be a useful clinical chemosensitizer in cancer patients.

[Current approaches for developing new anti-HCV agents and analyses of HCV replication using anti-HCV agents]

Currently, patients with hepatitis C virus (HCV) are mainly treated with interferon alone or in combination with ribavirin. However, because the virus is not eliminated from approximately one half of the patients by this treatment, alternative approaches to the treatment of HCV infection are needed. Recently, an HCV subgenomic replicon system has been established in which an HCV subgenomic replicon autonomously replicated in cultured cells. It enables us to screen for anti-HCV agents in cell culture system. Taking advantage of this system, we examined the effects of various types of compounds on the replication of HCV. Consequently, we found that a well-known immunosuppressant, cyclosporin A (CsA), had a strong suppressive activity on HCV replication, at least in cell culture system. This anti-HCV activity did not require the immunosuppressive feature of CsA. Through the investigation into the mechanism of anti-HCV effect of CsA, it was suggested that cyclophilin B, one of the cellular target molecules of CsA, played a significant role in HCV replication. Thus, searching for anti-HCV agents may lead to the elucidation of one of the mechanisms of HCV replication.

Inhibition of P-glycoprotein transport function and reversion of MDR1 multidrug resistance by cnidiadin

PURPOSE

Overexpression of P-glycoprotein (Pgp) encoded by the MDR1 gene is one of the major obstacles to successful cancer chemotherapy. The goal of this study was to evaluate if, among other natural coumarins, cnidiadin, a furanocoumarin present in traditional Chinese medications and in a spice commonly used in Greek food, inhibits Pgp transport activity and has the potential to reverse MDR1 multidrug resistance.

METHODS

Using MDR1-transfected Madin-Darby canine kidney (MDCK-MDR1) cells as a model of cells expressing the human MDR1 phenotype, and verapamil or CsA or both as positive control, we tested the capacity of six natural coumarins (umbelliferone, esculin, esculetin, cnidiadin, angelicin and psoralen) to induce the accumulation of rhodamine-123 (R-123) and [3H]-vinblastine ([3H]-VBL) and to modulate the photolabeling of Pgp by SDZ 212-122, a diazirin cyclosporin A. The growth-inhibitory effect of cnidiadin and its capacity to enhance the cell toxicity of vinblastine (VBL) or vincristine (VCR) was then evaluated by the WST-1 assay in two cell lines overexpressing Pgp (MDCK-MDR1 and vincristine-resistant KB/VCR).

RESULTS

Cnidiadin was the only tested coumarin capable of significantly accumulating R-123 and [3H]-VBL and inhibiting Pgp photolabeling in MDCK-MDR1 cells. The dose-dependent increase in [3H]-VBL uptake (IC50 26.5 microM) induced by cnidiadin in the dose range 1-100 microM correlated with inhibition of Pgp photolabeling. At 10 microM cnidiadin inhibited photolabeling by 59% and sensitized both MDCK-MDR1 and KB/VCR cells to vinca alkaloids.

CONCLUSION

Cnidiadin is a cytotoxic agent capable in vitro of competitively inhibiting the binding and efflux of drug by Pgp and of enhancing the cell toxicity of vinca alkaloids in two cell lines (MDCK-MDR1 and mutant human carcinoma KB/VCR) overexpressing Pgp. This suggests that diet or traditional preparation containing cnidiadin may contribute to the reversal of MDR1 multidrug resistance and may affect the bioavailability of Pgp substrates orally administered. However, due to its cell toxicity, clinical interest in cnidiadin as a chemosensitizer appears to be limited.

EFFECT OF THE MODULATION OF THE MEMBRANE LIPID COMPOSITION ON THE LOCALIZATION AND FUNCTION OF P-GLYCOPROTEIN IN MDR1-MDCK CELLS

Multidrug resistance (MDR) is a major obstacle in cancer therapy. It results from different mechanisms; among them is P-glycoprotein (P-gp)-mediated drug efflux out of cells. The mechanism of action remains elusive. The membrane lipid surrounding of P-gp, especially cholesterol, has been postulated to play an important role. To determine the effect of cholesterol depletion on P-gp, Madin Darby canine kidney (MDCK) cells, transfected with the mdr1 gene (MDR1-MDCK cells), were treated with methyl-beta-cyclodextrin (MbetaCD). The localization and function of P-gp were analyzed using confocal laser scanning microscopy. Treatment with 100 mM MbetaCD did not affect viability but altered the structural appearance of the cells and abolished efflux of rhodamine 123, a P-gp substrate. The MbetaCD treatment released P-gp from intact cells into the supernatant and reduced the amount of P-gp in total membrane preparations. The P-gp was shifted from the raft fractions (1% Triton X-100, 4 degrees C) to higher density fractions in MbetaCD-treated cells. The amount of cholesterol was significantly decreased in the raft fractions. Treatment of cells with 1-phenyl-2-decanoylamino-3-morpholino-1-propanol, a glucosylceramide synthase inhibitor, also led to a shift of P-gp to higher density fractions. These results show that removal of cholesterol modulates the membrane lipid composition, changes the localization of P-gp, and results in loss of P-gp function.

Cyclosporin A traps ABCA1 at the plasma membrane and inhibits ABCA1-mediated lipid efflux to apolipoprotein A-I

OBJECTIVE

ABCA1 mediates cellular cholesterol and phospholipid efflux to apolipoprotein A-I and other apolipoprotein acceptors. In this study, we analyzed the effect of the immunosuppressant cyclosporin A on the ABCA1-mediated lipid effluxes reactions.

METHODS AND RESULTS

Cyclosporin A acted as a potent inhibitor of ABCA1 activity in several cell lines. Using the RAW264.7 mouse macrophage cell line, in which ABCA1 and its associated cholesterol efflux activity are inducible by cAMP analogues, cyclosporin A inhibition of cholesterol efflux to apolipoprotein A-I was rapidly reversible after its removal from the culture media, implying that ABCA1 levels were not drastically reduced by cyclosporin A. In fact, cyclosporin A treatment decreased ABCA1 turnover and yielded a 2-fold increase in cell-surface ABCA1. Despite the increase in cell-surface ABCA1, cyclosporin A decreased apolipoprotein A-I uptake, resecretion, and degradation in RAW cells. Finally, consistent with the inhibition of ABCA1 in vitro, cyclosporin A treatment induced a 33% reduction of high-density lipoprotein (HDL) levels in mice.

CONCLUSIONS

ABCA1 inhibition by cyclosporin A supports a role for ABCA1 endocytic trafficking in ABCA1-mediated lipid efflux and could explain in part the low HDL levels observed in some patients with transplants.

Analogues of tetramethylrosamine as transport molecules for and inhibitors of P-glycoprotein-mediated multidrug resistance

Tetramethylrosamine and its thio- and seleno- analogues (TMR-O, TMR-S, and TMR-Se, respectively) were examined for their ability to be transported by Pgp into chemo-resistant CR1R12 cells. Verapamil (7 x 10(-6)M) enhanced the uptake of TMR-O and TMR-S into CR1R12 cells compared to those cultures not previously exposed to verapamil. The uptake of TMR-O and TMR-S in CR1R12 cells in the presence of 7 x 10(-6)M verapamil was equivalent to its uptake in the chemo-sensitive parent cell line AUXB1 in the absence or presence of verapamil. None of the TMR analogues were effective alone as photosensitizers of CR1R12 cells. However, when either TMR-S or TMR-Se was added to CR1R12 cells after 7 x 10(-6)M verapamil exposure for 2h, irradiation of cultures with 5.0J cm(-2) of 350-750 nm light caused significant phototoxicity. TMR-O showed no significant phototoxicity in the presence of verapamil. Chemo-sensitive AUXB1 cells are equally susceptible to phototoxicity using TMR-Se with or without previous exposure to verapamil. The Pgp modulators verapamil and CsA increased the uptake of CAM into CR1R12. Exposure of CR1R12 cells to TMR-S or TMR-Se for 2h in the dark resulted in no significant change in the intracellular accumulation of CAM. However, 1h of light exposure after incubation of cells with TMR-S or TMR-Se resulted in an up to 2-fold increase in CAM uptake.