The effect of ion channel blockers, immunosuppressive agents, and other drugs on the activity of the multi-drug transporter

Isobavachalcone as an Active Membrane Perturbing Agent and Inhibitor of ABCB1 Multidrug Transporter

Isobavachalcone (IBC) is an active substance from the medicinal plant Psoralea corylifolia. This prenylated chalcone was reported to possess antioxidative, anti-inflammatory, antibacterial, and anticancer activities. Multidrug resistance (MDR) associated with the over-expression of the transporters of vast substrate specificity such as ABCB1 (P-glycoprotein) belongs to the main causes of cancer chemotherapy failure. The cytotoxic, MDR reversing, and ABCB1-inhibiting potency of isobavachalcone was studied in two cellular models: human colorectal adenocarcinoma HT29 cell line and its resistant counterpart HT29/Dx in which doxorubicin resistance was induced by prolonged drug treatment, and the variant of MDCK cells transfected with the human gene encoding ABCB1. Because MDR modulators are frequently membrane-active substances, the interaction of isobavachalcone with model phosphatidylcholine bilayers was studied by means of differential scanning calorimetry. Molecular modeling was employed to characterize the process of membrane permeation by isobavachalcone. IBC interacted with ABCB1 transporter, being a substrate and/or competitive inhibitor of ABCB1. Moreover, IBC intercalated into model membranes, significantly affecting the parameters of their main phospholipid phase transition. It was concluded that isobavachalcone interfered both with the lipid phase of cellular membrane and with ABCB1 transporter, and for this reason, its activity in MDR cancer cells was presumptively beneficial.

Effective MDR reversers through phytochemical study of Euphorbia boetica

INTRODUCTION

Macrocyclic diterpenes from Euphorbia species were found to be promising modulators of multidrug resistance (MDR), a complex phenomenon that hampers the effectiveness of cancer therapy.

OBJECTIVE

To find new effective MDR reversers through the phytochemical study of E. boetica, including isolation and molecular derivatisation.

MATERIAL AND METHODS

The phytochemical study of E. boetica was performed through chromatographic techniques. Preliminary analysis of crude chromatographic fractions from the methanol extract was carried out by ¹ H-NMR in order to prioritise the study of those having macrocyclic diterpenes. Polyamide resin was used to remove chlorophylls. Molecular derivatisation of isolated compounds comprised hydrolysis, reduction and acylation reactions. The structural identification of compounds was performed through analysis of spectroscopic data, mainly one-dimensional- and two-dimensional-NMR. The MDR reversing activity was assessed using a combination of transport and chemosensitivity assays, in mouse lymphoma (L5178Y-MDR) and Colo320 cell models.

RESULTS

The ¹ H-NMR study of crude fractions and application of a straightforward method to remove chlorophylls, allowed the effortless isolation of two lathyrane-type diterpenes in large amounts, including the new polyester, euphoboetirane B (1). Taking advantage of the chemical functions of 1, 13 new derivatives were prepared. Several compounds showed to be promising modulators of P-glycoprotein (P-gp), in resistant cancer cells. Most of the compounds tested revealed to interact synergistically with doxorubicin.

CONCLUSION

These results corroborate the importance of macrocyclic lathyrane diterpenes as effective lead compounds for the reversal of MDR.

In vitro evaluation of antimicrobial agents on Acanthamoeba sp. and evidence of a natural resilience to amphotericin B

The free-living amoeba (FLA) Acanthamoeba sp. is an opportunistic pathogen that can cause amoebic keratitis (AK) or granulomatous amoebic encephalitis (GAE). While current treatments of AK are long with some relapses, no consensus therapy has been developed for GAE remaining lethal in 90% of the cases. In this context, efficient antiacanthamoebal drugs have to be identified. In this work, 15 drugs used in the treatment of AK or GAE or in other parasitic diseases were evaluated for their in vitro activity on A. castellanii. Hexamidine, voriconazole and clotrimazole exhibited the highest activities with IC₅₀ values at 0.05 μM, 0.40 μM and 0.80 μM, respectively, while rifampicin, metronidazole and cotrimoxazole were inactive. Among 15 drug associations evaluated, no synergistic effect was observed, and one antagonism was determined between hexamidine and chlorhexidine. Interestingly, amphotericin B was the only drug presenting an increase of IC₅₀ as a function of treatment duration. The amoebae susceptibility to amphotericin B cultured in the presence of 250 μM of the drug was similar to the one of a naive control, revealing that no resistant strain could be selected. However, the amoebae susceptibility always returned to an initial level at each passage. This natural and non-acquired adaptation to amphotericin B, qualified as resilience, was observed in several strains of A. castellanii and A. polyphaga. Using a pharmacological approach with effectors of different cellular mechanisms or transports, and an ultrastructural analysis of amphotericin B-treated amoebae, the involvement of several mitochondria-dependent pathways as well as multidrug resistant transporters was determined in amphotericin B resilience. Based on the observations from this study, the relevance of using amphotericin B in GAE treatments may be reconsidered, while the use of some other drugs, such as rifampicin or cotrimoxazole, is not relative to intrinsic antiacanthamoebal activity.

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In vitro evaluation of 15 antimicrobial agents on Acanthamoeba castellanii.

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Best activity for hexamidine and inefficiency of rifampicin and cotrimoxazole.

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Antagonism of the combination chlorhexidine/hexamidine.

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Natural resilience of Acanthamoeba sp. for amphotericin B.

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Involvement of mitochondria-dependent pathways and MDR in amphotericin B resilience.

Fluorimetric Methods for Analysis of Permeability, Drug Transport Kinetics, and Inhibition of the ABCB1 Membrane Transporter

The cell membrane P-glycoprotein (P-gp; MDR1, ABCB1) is an energy-dependent efflux pump that belongs to the ATP-binding cassette (ABC) family of transporters, and has been associated with drug resistance in eukaryotic cells. Multidrug resistance (MDR) is related to an increased expression and function of the ABCB1 (P-gp) efflux pump that often causes chemotherapeutic failure in cancer. Modulators of this efflux pump, such as the calcium channel blocker verapamil (VP) and cyclosporine A (CypA), can reverse the MDR phenotype but in vivo studies have revealed disappointing results due to adverse side effects. Currently available methods are unable to visualize and assess in a real-time basis the effectiveness of ABCB1 inhibitors on the uptake and efflux of ABCB1 substrates. However, predicting and testing ABCB1 modulation activity using living cells during drug development are crucial. The use of ABCB1-transfected mouse T-lymphoma cell line to study the uptake/efflux of fluorescent probes like ethidium bromide (EB), rhodamine 123 (Rh-123), and carbocyanine dye DiOC2, in the presence and absence of potential inhibitors, is currently used in our laboratories to evaluate the ability of a drug to inhibit ABCB1-mediated drug accumulation and efflux. Here we describe and compare three in vitro methods, which evaluate the permeability, transport kinetics of fluorescent substrates, and inhibition of the ABCB1 efflux pump by drugs of chemical synthesis or extracted from natural sources, using model cancer cell lines overexpressing this transporter, namely (1) real-time fluorimetry that assesses the accumulation of ethidium bromide, (2) flow cytometry, and (3) fluorescent microscopy using rhodamine 123 and DiOC2.

Epoxylathyrol Derivatives: Modulation of ABCB1-Mediated Multidrug Resistance in Human Colon Adenocarcinoma and Mouse T-Lymphoma Cells

Epoxyboetirane A (1), a macrocyclic diterpene that was found to be inactive as an ABCB1 modulator, was submitted to several chemical transformations, aimed at generating a series of compounds with improved multidrug resistance (MDR)-modifying activity. Overall, 23 new derivatives were prepared, in addition to the already reported epoxylathyrol (2) and methoxyboetirol (3). Their anti-MDR potential was assessed through both functional and chemosensitivity assays on resistant human colon adenocarcinoma and human ABCB1-gene transfected L5178Y mouse lymphoma cells. Structure-activity relationship analysis showed that different substitution patterns led to distinct ABCB1 inhibitory activities, although intrinsic cellular characteristics seemed to influence the modulatory behavior. A considerable enhancement in MDR-modifying activity was observed for aromatic compounds in both cell lines, particularly in 3,17-disubstituted esters derived from 3, a Payne-rearranged Michael adduct of 2. All compounds tested were revealed to interact synergistically with doxorubicin, and ATPase inhibition by three representative MDR-modifying compounds was also investigated. On account of its outstanding ABCB1 inhibitory activity at 0.2 μM and overall remarkable bioactive profile, methoxyboetirane B (22) was found to be a new promising lead for MDR-reversing anticancer drug development.

Development of small-molecule P-gp inhibitors of the N-benzyl 1,4-dihydropyridine type: novel aspects in SAR and bioanalytical evaluation of multidrug resistance (MDR) reversal properties

Novel series of N-benzyl 1,4-dihydropyridines have been prepared by facile syntheses. All relevant substituents of the molecular scaffold have been varied. The resulting compounds were biologically evaluated as P-glycoprotein (P-gp) inhibitors. Substitutions of the N-benzyl residue favour biological activity beside respective 3-ester functions. Most active compounds were further evaluated as multidrug resistance (MDR) modulators to restore the cytotoxic properties of varying daunorubicin applications.

A novel approach for predicting P-glycoprotein (ABCB1) inhibition using molecular interaction fields

P-glycoprotein (Pgp or ABCB1) is an ABC transporter protein involved in intestinal absorption, drug metabolism, and brain penetration, and its inhibition can seriously alter a drug's bioavailability and safety. In addition, inhibitors of Pgp can be used to overcome multidrug resistance. Given this dual purpose, reliable in silico procedures to predict Pgp inhibition are of great interest. A large and accurate literature collection yielded more than 1200 structures; a model was then constructed using various molecular interaction field-based technologies, considering pharmacophoric features and those physicochemical properties related to membrane partitioning. High accuracy was demonstrated internally with two different validation sets and, moreover, using a number of molecules, for which Pgp inhibition was not experimentally available but was evaluated in-house. All of the validations confirmed the robustness of the model and its suitability to help medicinal chemists in drug discovery. The information derived from the model was rationalized as a pharmacophore for competitive Pgp inhibition.

Transporters as mediators of drug resistance in Plasmodium falciparum

Drug resistance represents a major obstacle in the radical control of malaria. Drug resistance can arise in many different ways, but recent developments highlight the importance of mutations in transporter molecules as being major contributors to drug resistance in the human malaria parasite Plasmodium falciparum. While approximately 2.5% of the P. falciparum genome encodes membrane transporters, this review concentrates on three transporters, namely the chloroquine resistance transporter PfCRT, the multi-drug resistance transporter 1 PfMDR1, and the multi-drug resistance-associated protein PfMRP, which have been strongly associated with resistance to the major antimalarial drugs. The studies that identified these entities as contributors to resistance, and the possible molecular mechanisms that can bring about this phenotype, are discussed. A deep understanding of the underpinning mechanisms, and of the structural specificities of the players themselves, is a necessary basis for the development of the new drugs that will be needed for the future armamentarium against malaria.

Multidrug resistance in a urothelial cancer cell line after 1-hour mitomycin C exposure

PURPOSE

A factor pertinent to the design of cancer chemotherapy is multidrug resistance. Research in this area conventionally involves in vitro models using resistant cell lines generated by continuous low dose drug exposure for many months, unlike the exposure experienced by residual superficial bladder cancer cells during chemotherapy adjuvant to resection. Recently we noted a measure of multidrug resistance induced by 3 short exposures to mitomycin C during 10 weeks. We currently report detectable functional resistance after a single 1-hour insult.

MATERIALS AND METHODS

RT112 bladder cancer cells (Catalog No. ACC 418, Deutsche Sammlung von Mikroorganismen und Zellkulturen, Braunschweig, Germany) were exposed to a range of mitomycin C concentrations for 1 hour. Cells regrew in 3 of 24 cultures at 15.6, 3.91 and 0.98 mg/ml exposure. These cells were subjected to 3 functional tests of cross resistance to epirubicin, including MTT cytotoxicity assay, quantitative accumulation by flow cytometry and nuclear uptake or exclusion by live cell fluorescence microscopy.

RESULTS

MTT assay and flow cytometry revealed clear indications of resistance. Intracellular distribution, in which nuclear exclusion indicates resistance, was distinctively resistant in 1 subline and another 2 were equivocal.

CONCLUSIONS

Results indicate that some multidrug resistance potential exists even in a cloned cell line that is capable of surviving 1 short drug exposure and expanding after that insult. The exposures used are consistent with those probably experienced by many superficial transitional cell carcinoma cells during an intravesical chemotherapy application. The result gives added weight to considering multidrug resistance induction in dose scheduling or drug combinations for topical chemotherapy.

Tabernines A-C, beta-carbolines from the leaves of Tabernaemontana elegans

Three novel beta-carboline indole alkaloids (1-3) have been isolated from a MeOH extract of the leaves of Tabernaemontana elegans. The structures were established by means of spectroscopic techniques including 2D NMR experiments. Compounds 1 and 2 contain a two-carbon unit, attached to a structurally related beta-carboline skeleton, as part of an additional six-membered ring in 1 and a seven-membered ring in 2. To the best of our knowledge, this is the first report of beta-carboline indole alkaloids from the genus Tabernaemontana. Compounds 1-3 were evaluated for their ability to modulate multidrug resistance in mouse lymphoma cell lines. Compounds 1 and 3 exhibited a weak activity.

Plasmodium falciparum Na+/H+ exchanger 1 transporter is involved in reduced susceptibility to quinine

Polymorphisms in the Plasmodium falciparum crt (Pfcrt), Pfmdr1, and Pfmrp genes were not significantly associated with quinine (QN) 50% inhibitory concentrations (IC(50)s) in 23 strains of Plasmodium falciparum. An increased number of DNNND repeats in Pfnhe-1 microsatellite ms4760 was associated with an increased IC(50) of QN (P = 0.0007). Strains with only one DNNND repeat were more susceptible to QN (mean IC(50) of 154 nM). Strains with two DNNND repeats had intermediate susceptibility to QN (mean IC(50) of 548 nM). Strains with three DNNND repeats had reduced susceptibility to QN (mean IC(50) of 764 nM). Increased numbers of NHNDNHNNDDD repeats were associated with a decreased IC(50) of QN (P = 0.0020). Strains with profile 7 for Pfnhe-1 ms4760 (ms4760-7) were significantly associated with reduced QN susceptibility (mean IC(50) of 764 nM). The determination of DNNND and NHNDNHNNDDD repeats in Pfnhe-1 ms4760 could be a good marker of QN resistance and provide an attractive surveillance method to monitor temporal trends in P. falciparum susceptibility to QN. The validity of the markers should be further supported by analyzing more isolates.

Polymorphisms within PfMDR1 alter the substrate specificity for anti-malarial drugs in Plasmodium falciparum

Resistance to several anti-malarial drugs has been associated with polymorphisms within the P-glycoprotein homologue (Pgh-1, PfMDR1) of the human malaria parasite Plasmodium falciparum. Pgh-1, coded for by the gene pfmdr1, is predominately located at the membrane of the parasite's digestive vacuole. How polymorphisms within this transporter mediate alter anti-malarial drug responsiveness has remained obscure. Here we have functionally expressed pfmdr1 in Xenopus laevis oocytes. Our data demonstrate that Pgh-1 transports vinblastine, an established substrate of mammalian MDR1, and the anti-malarial drugs halofantrine, quinine and chloroquine. Importantly, polymorphisms within Pgh-1 alter the substrate specificity for the anti-malarial drugs. Wild-type Pgh-1 transports quinine and chloroquine, but not halofantrine, whereas polymorphic Pgh-1 variants, associated with altered drug responsivenesses, transport halofantrine but not quinine and chloroquine. Our data further suggest that quinine acts as an inhibitor of Pgh-1. Our data are discussed in terms of the model that Pgh-1-mediates, in a variant-specific manner, import of certain drugs into the P. falciparum digestive vacuole, and that this contributes to accumulation of, and susceptibility to, the drug in question.

Dissecting the components of quinine accumulation in Plasmodium falciparum

Although quinine, the active ingredient of chinchona bark, has been used in the treatment of malaria for several centuries, there is little information regarding the interactions of this drug with the human malaria parasite Plasmodium falciparum. To better understand quinine's mode of action and the mechanism underpinning reduced responsiveness, we have investigated the factors that contribute to quinine accumulation by parasites that differ in their susceptibility to quinine. Interestingly, passive distribution, in accordance with the intracellular pH gradients, and intracellular binding could account for only a small fraction of the high amount of quinine accumulated by the parasites investigated. The results of trans-stimulation kinetics suggest that high accumulation of quinine is brought about by a carrier-mediated import system. This import system seems to be weakened in parasites with reduced quinine susceptibility. Other data show that polymorphisms within PfCRT are causatively linked with an increased verapamil-sensitive quinine efflux that, depending on the genetic background, resulted in reduced quinine accumulation. The polymorphisms within PfMDR1 investigated did not affect quinine accumulation. Our data are consistent with the model that several factors, including acidotropic trapping, binding to intracellular sites and carrier-mediated import and export transport systems, contribute to steady-state intracellular quinine accumulation.

Structure–activity relationships of novel N-acyloxy-1,4-dihydropyridines as P-glycoprotein inhibitors

Series of novel N-acyloxy-1,4-dihydropyridines have been synthesized and evaluated as P-glycoprotein inhibitors in an in vitro assay to estimate their potential to act as multidrug resistance modulators in cancer cells. Structure-activity relationships are discussed and prove a significant and regiospecific influence of certain functional groups.

Furosemide reverses multidrug resistance status in bladder cancer cells in vitro

BACKGROUND

Multidrug resistance (MDR) has a potentially serious influence on cancer treatment and should be taken into consideration in the design and application of therapeutic regimens. It is mediated through the activity of cellular pumps.

AIM

To investigate whether furosemide, itself a pump-blocker, reverses MDR in an in vitro model.

MATERIALS AND METHODS

An MDR bladder cancer cell line (MGH-u 1R) and its parental (drug sensitive) clone were exposed to epirubicin and furosemide, with the concentration of one drug fixed and that of the other serially diluted in a 96-well plate format. Both drugs formed the variable component in separate experiments. After a 1-h exposure, the cells were washed and replenished with fresh medium. To examine the toxicity of epirubicin and furosemide separately and in combination, monotetrazolium-based assays were carried out. Intracellular epirubicin distribution was assessed by confocal microscopy as a second index of resistance status after in vitro exposure.

RESULTS

MGH-u 1R cells incubated with furosemide showed distribution of drug similar to that in the parental cells (MGH-u 1 sensitive). Controls (without furosemide) continued to show a resistant pattern of fluorescence. In cytotoxicity assays furosemide appeared substantially non-toxic. Resistant cells in the toxicity titration experiments showed increased resistance to levels of furosemide over 500 mug/ml. Parental cells were made only marginally more sensitive against increased background toxicity.

CONCLUSION

Furosemide is effective in reversing MDR status in bladder cancer cell lines in vitro. It may also have an increment of intrinsic cytotoxicity, but only at higher concentrations. We propose a potential for further investigation of furosemide as an adjunct to chemotherapy for superficial bladder cancer.

Biological activity of carotenoids in red paprika, Valencia orange and Golden delicious apple

Carotenoid fractions were extracted from red paprika, Valencia orange peel and the peel of Golden delicious apple. Thus, hypophasic carotenoids of paprika (PM1), orange (PM3) and apple (PM4), and epiphasic extractions of paprika (PM2) and apple (PM5) were obtained by extraction, saponification and partition between MeOH-H(2)O (9:1) (hypophasic) and hexane (epiphasic). A high content of capsanthin was quantified in hypophasic carotenoids (PM1) from red spice paprika, whereas the hypophasic fractions from orange (PM3) and apple (PM4) were mainly composed of violaxanthin, zeaxanthin and lutein. On the other hand, a high content of beta,beta-carotene and beta-cryptoxanthin was found in epiphasic fractions (PM2 and PM5). The extracts were studied for their anti-Helicobacter pylori (H. pylori), anti-human immunodeficiency virus (HIV), cytotoxic, multidrug resistance (MDR) reversal and radical scavenging activity. Among five PM extracts and beta,betacarotene, PM4 showed potent anti-H. pylori activity (MIC(50) = 36 microg/mL), comparable to metronidazole (MIC(50) = 45 microg/mL). The extracts were inactive against HIV. PM3 and PM4 showed slightly higher cytotoxic activity against three human tumor cell lines (squamous cell carcinoma HSC-2, HSC-3, submandibular gland carcinoma HSG) and human promyelocytic leukemic HL-60 cells than against three normal human oral cells (gingival fibroblast HGF, pulp cell HPC, periodontal ligament fibroblast HPLF), suggesting a tumor-specific cytotoxic activity. PM1, PM3 and PM4 displayed much higher MDR-reversing activity than (+/-)-verapamil. ESR spectroscopy demonstrated that PM1-5 and beta,beta-carotene produced little or no detectable radical under alkaline conditions and did not scavenge the O(2) (-) produced by the hypoxanthine and xanthine oxidase reaction. On the other hand, PM1 and PM2 scavenged efficiently 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, whereas singlet oxygen was also quenched efficiently by PM5 and PM2. The data suggest the potential importance of carotenoids as possible anti-H. pylori and MDR reversal agents. The active principles in the carotenoid extract might differ, depending upon the types of fruits and vegetables.

Lamellarin D: a novel pro-apoptotic agent from marine origin insensitive to P-glycoprotein-mediated drug efflux

Lamellarin D (LAM-D) is a marine alkaloid endowed with potent cytotoxic activities against various tumor cells, in particular human prostate cancer cells and leukemia cells. Its cytotoxic action is dependent, at least in part, to its capacity to inhibit topoisomerase I. P388CPT5 murine leukemia cells resistant to the reference topoisomerase I poison camptothecin (CPT) are cross-resistant to LAM-D but the relative resistance index (RRI) is significantly reduced with LAM-D (RRI=21) compared to CPT (RRI=103). To comprehend further the mechanism of action of this novel marine antitumor agent, we have investigated the influence of the P glycoprotein (Pgp) on the cytotoxicity of LAM-D and the proapoptotic effects induced by the alkaloid. P388CPT5 cells, expressing a mutated top1 gene, display a functional Pgp, as judged from cytometry experiments performed with cells treated with rhodamine 123 or calcein-ester whereas no Pgp activity was detected with the parental P388 cells. P388CPT5 cells are also cross-resistant to the topoisomerase II poisons doxorubicin and etoposide but the resistance is abolished in the presence of verapamil or quinine (at non toxic concentrations) which reverse the multidrug resistance (MDR) phenotype. In contrast, the RRI measured with LAM-D and CPT remain unchanged in the presence of the two MDR reversal agents. The effects of LAM-D on the cell cycle progression were different in the parental P388 cells compared with the CPT-resistant which were blocked in the S and subsequently G2-M phases of the cell cycle. Cytometry experiments with the JC-1 fluorescent marker revealed that LAM-D and CPT promoted apoptosis in parental P388 cells via an activation of the mitochondrial pathway. In contrast, a massive depolarisation of the mitochondrial membrane potential and a nuclear fragmentation were detected only with LAM-D on P388CPT5 cells. This in vitro work identifies LAM-D as a potent pro-apoptotic agent and its cytotoxic action is fully maintained in multidrug-resistant cells compared to the sensitive parental cell line.

Biological activity of barbados cherry (acerola fruits, fruit of Malpighia emarginata DC) extracts and fractions

Fractionation of barbados cherry (acerola fruit, a fruit of Malpighia emarginata DC.) extracts were performed by organic solvent extractions and column chromatographies, using two extraction methods. Higher cytotoxic activity was concentrated in fractions A4 and A6 (acetone extract), and H3 and HE3 (hexane extract). These four fractions showed higher cytotoxic activity against tumor cell lines such as human oral squamous cell carcinoma (HSC-2) and human submandibular gland carcinoma (HSG), when compared with that against normal cells such as human periodontal ligament fibroblasts (HPLF) and human gingival fibroblasts (HGF). HE2 (hexane extract), AE2 (ethyl acetate extract), AE3, AE4, AE5, A8, A9 and A10 showed some relatively higher anti-bacterial activity on the Gram-positive Staphylococcus epidermidis ATCC 1228 but were ineffective on the representative Gram-negative species E. coli and Ps. aeruginosa. The fractions were inactive against Helicobacter pylori, two representative Candida species, and human immunodeficiency virus (HIV). H3, H4 and HE3, which displayed higher tumor-specific cytotoxicity also showed higher multidrug resistance (MDR) reversal activity, than (+/-)-verapamil as positive control. ESR spectroscopy shows that the radical-mediated oxidation is not involved in the induction of tumor-specific cytotoxic activity. The tumor specific cytotoxic activity and MDR reversal activity of barbados cherry may suggest its possible application for cancer therapy.

3,5-Dibenzoyl-4-(3-phenoxyphenyl)-1,4-dihydro-2,6-dimethylpyridine (DP7) as a new multidrug resistance reverting agent devoid of effects on vascular smooth muscle contractility

The aim of this study was to investigate the effects of 3,5-diacetyl- (DP1-DP5) and 3,5-dibenzoyl-1,4-dihydropyridines (DP6-DP11) on vascular functions in vitro, by comparing their mechanical and electrophysiological actions in rat aorta rings and single rat tail artery myocytes, respectively, and to quantify their multidrug resistance (MDR)-reversing activity in L5178 Y mouse T-lymphoma cells transfected with MDR1 gene. In rat aorta, the 11 compounds tested, but 3,5-dibenzoyl-4-(3-phenoxyphenyl)-1,4-dihydro-2,6-dimethylpyridine (DP7), 3,5-dibenzoyl-4-(3-chlorophenyl)-1,4-dihydro-2,6-dimethylpyridine (DP9), 3,5-dibenzoyl-4-(4-chlorophenyl)-1,4-dihydro-2,6-dimethylpyridine (DP10) and 3,5-dibenzoyl-4-phenyl-1,4-dihydro-2,6-dimethylpyridine (DP11), antagonized 60 mm K+ (K60)-induced contraction in a concentration-dependent manner, with IC50 (m) values ranging between 5.65 x 10(-7) and 2.23 x 10(-5). The 11 dihydropyridines tested, but DP7, inhibited L-type Ca2+ current recorded in artery myocytes in a concentration-dependent manner, with IC50 (M) values ranging between 1.12 x 10(-6) and 6.90 x 10(-5). The K+ -channel opener cromakalim inhibited the Ca2+ -induced contraction in K30 but not that evoked in K60. On the contrary, DP7 was ineffective in both experimental conditions. When the rings were preincubated with 1 mm Ni2+ plus 1 microm nifedipine, the response to phenylephrine was significantly reduced by 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), a well-known endoplasmic reticulum Ca2+ -ATPase inhibitor. DP7 had no effects on this model system. In L5178 MDR cell line, the 11 dihydropyridines tested, but 3,5-diacetyl-4-(2-nitrophenyl)-1,4-dihydro-2,6-dimethylpyridine (DP1), 3,5-diacetyl-4-(3-phenoxyphenyl)-1,4-dihydro-2,6-dimethylpyridine (DP2) and 3,5-diacetyl-4-(3-chlorophenyl)-1,4-dihydro-2,6-dimethylpyridine (DP4), exhibited an MDR-reversing activity, with IC50 values ranging between 3.02 x 10(-7) and 4.27 x 10(-5), DP7 being the most potent. In conclusion, DP7 may represent a lead compound for the development of potent dihydropyridine MDR chemosensitizers devoid of vascular effects. British Journal of Pharmacology (2004) 141, 415-422. doi:10.1038/sj.bjp.0705635

New phenothiazine-type multidrug resistance modifiers: anti-MDR activity versus membrane perturbing potency

The phenothiazine multidrug resistance (MDR) modulators are chemically diversified but share the common feature to be hydrophobic cationic molecules. Molecular mechanisms of their action may involve interactions with either P-glycoprotein or membrane lipid matrix. In the present work we study the anti-MDR and biophysical membrane effects of new phenothiazine derivatives differing in the type of group substituting phenothiazine ring at position 2 (H-, Cl-, CF(3)-) and in the side chain group (NHCO(2)CH(3) or NHSO(2)CH(3)). Within each phenothiazine subset we found that anti-MDR activity (determined by P-glycoprotein inhibition assessed by flow cytometry) correlates with the theoretically calculated hydrophobicity value (logP) and experimental parameters (determined by calorimetry and fluorescence spectroscopy) of lipid bilayers. It is concluded that the biological and biophysical activity of phenothiazine derivatives depends more on the type of ring substitution than on the nature of the side chain group.

Biological activity of persimmon (Diospyros kaki) peel extracts

Fractionated extracts of persimmon (Diospyros kaki) peels were studied for cytotoxic activity, multidrug resistance (MDR) reversal activity, anti-human immunodeficiency virus (HIV) activity and anti-Helicobacter pylori (H. pylori) activity. The potent cytotoxic activity against human oral squamous cell carcinoma cells (HSC-2) and human submandibular gland tumor (HSG) cells was found in the acetone fractions (A4 and A5) with IC(50) ranging from 21 to 59 micro g/mL. However, the cytotoxic activity was not correlated with the radical intensity of the fractions. Three 70% MeOH extract fractions (70M2-4) produced radical and efficiently scavenged the O(2)(-) produced by hypoxanthine and xanthine oxidase reaction. All of the fractions tested were not effective for anti-H. pylori and anti-HIV. Fractions H3 and H4 of hexane extract, and M2 and M3 of MeOH extract showed a remarkable MDR reversal activity comparable with that of (+/-)-verapamil (a positive control). These results indicate the therapeutic value of persimmon peel extracts as potential antitumor and MDR-reversing agents.

Effects of a series of dihydroanthracene derivatives on drug efflux in multidrug resistant cancer cells

A set of 9,10-dihydro-9,10-ethano and ethenoanthracene derivatives was tested with the aim to quantify the effect observed on drug efflux. Structure activity relationships and molecular modeling studies allowed to define topological display of pharmacophoric groups for these reversal agents.

Neither lipophilicity nor membrane-perturbing potency of phenothiazine maleates correlate with the ability to inhibit P-glycoprotein transport activity

Although phenothiazines are known as multidrug resistance modifiers, the molecular mechanism of their activity remains unclear. Since phenothiazine molecules are amphiphilic, the interactions with membrane lipids may be related, at least partially, to their biological effects. Using the set of phenothiazine maleates differing in the type of phenothiazine ring substitution at position 2 and/or in the length of the alkyl bridge-connecting ring system and side chain group, we investigated if their ability to modulate the multidrug resistance of cancer cells correlated with model membrane perturbing potency. The influence exerted on lipid bilayers was determined by liposome/buffer partition coefficient measurements (using the absorption spectra second-derivative method), fluorescence spectroscopy and calorimetry. Biological effects were assessed by a flow cytometric functional test based on differential accumulation of fluorescent probe DiOC(2)(3) by parental and drug-resistant cells. We found that all phenothiazine maleates were incorporated into lipid bilayers and altered their biophysical properties. With only few exceptions, the extent of membrane perturbation induced by phenothiazine maleates correlated with their lipophilicity. Within the group of studied derivatives, the compounds substituted with CF(3)- at position 2 of phenothiazine ring were the most active membrane perturbants. No clear relation was found between effects exerted by phenothiazine maleates on model membranes and their ability to modulate P-glycoprotein transport activity.

Pervilleines B and C, new tropane alkaloid aromatic esters that reverse the multidrug-resistance in the hollow fiber assay

P-Glycoprotein (Pgp)-mediated drug efflux can yield a multidrug-resistance phenotype that is associated with poor response to cancer chemotherapy. Pervilleines B and C (PB and PC), two new tropane alkaloid aromatic esters obtained from a chloroform extract of the roots of Erythroxylum pervillei as the result of bioactivity-guided fractionation, were found to restore the vinblastine (VLB) sensitivity of cultured multidrug-resistant KB-V1 cells, with 50% inhibitory concentration values of 0.17 microM in each case. To explore the potential relevance of this response, KB-V1 cells were placed in hollow fibers and implanted into NCr nu/nu mice. Cell growth was not significantly inhibited when VLB or PB or PC were administered as single agents, but when used in combination with vinblastine inhibition of up to 77.7% was observed. Equimolar doses of verapamil were less effective. These data suggest that PB and PC are effective inhibitors of Pgp and should be further evaluated for clinical utility.

3,5-dibenzoyl-1,4-dihydropyridines: synthesis and MDR reversal in tumor cells

Fifteen 4-phenyl-3,5-dibenzoyl-1,4-dihydropyridines (BzDHPs) (1-15) substituted at the 4-phenyl ring were synthesized and compared to their cytotoxic activity and multidrug resistance (MDR)-reversing activity in in vitro assay systems. Among them, 2-CF3 (5) (IC50=8.7 microM), 2-Cl (11) (IC50=7.0 microM) and 3-Cl (12) (IC50=7.0 microM) derivatives showed the highest cytotoxic activity against human oral squamous carcinoma (HSC-2) cells. The activity of P-glycoprotein (Pgp) response for MDR in tumor cells was reduced by some of derivatives (3, 4, 8, 12), verapamil (VP) and nifedipine (NP). These data suggest that 3,5-dibenzoyl-4-(3-chlorophenyl)-1,4-dihydro-2,6-dimethylpyridine (12) can be recommended as a new drug candidate for MDR cancer treatment.

Ellipticine analogues and related compounds as inhibitors of reverse transcriptase and as inhibitors of the efflux pump

Ten polycyclic derivatives related to ellipticine have been synthesised and tested for their intercalating, reverse transcriptase (RT) inhibitory and multidrug resistance efflux pump inhibitory properties. The intercalating activity and the RT inhibitory activity of the derivatives suggest that ellipticine analogues bind at an allosteric binding site on RT or that this inhibition could be controlled at the DNA level. The MDR efflux pump inhibitory activities of these derivatives, however, appears to be unrelated to the DNA binding ability.

Mechanisms and clinical implications of renal drug excretion

The body defends itself against potentially harmful compounds like drugs, toxic compounds, and their metabolites by elimination, in which the kidney plays an important role. Renal clearance is used to determine renal elimination mechanisms of a drug, which is the result of glomerular filtration, active tubular secretion and reabsorption. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine. Renal secretory mechanisms exists for, anionic compounds and organic cations. Both systems comprises several transport proteins, and knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past decade. Due to overlapping specificities of the transport proteins, drug interactions at the level of tubular secretion is an event that may occur in clinical situation. This review describes the different processes that determine renal drug handling, the techniques that have been developed to attain more insight in the various aspects of drug excretion, the functional characteristics of the individual transport proteins, and finally the implications of drug interactions in a clinical perspective.

Biological activity of kiwifruit peel extracts

Various bioactive substances in kiwifruit extracts were fractionated by organic solvent extractions, followed by silica gel and ODS chromatographies. Both cytotoxic activity and multi-drug resistance reversal activity were found in the less polar fractions. Cytotoxic activity was not always parallel the radical intensity. Antibacterial activity was distributed into various fractions and all fractions were inactive against Candida albicans and H. pylori. Only 70% methanol extracts showed anti-human immunodeficiency virus activity, and produced a broad ESR signal under alkaline conditions, in a fashion similar to lignin. These fractions also effectively scavenged O(2)(-) produced by the xanthine-xanthine oxidase reaction, suggesting a bimodal (pro-oxidant and antioxidant) action. These data suggest a medicinal efficacy of kiwifruit peel extracts.

Modulation by LY335979 of P-glycoprotein function in multidrug-resistant cell lines and human natural killer cells

Resistance to chemotherapy by some human tumors may be due to overexpression of membrane-associated transport proteins. The best characterized of these is the multidrug resistance (MDR) transporter, P-glycoprotein (Pgp). The aim of this study was to measure the inhibitory effects of a potent new MDR modulator, (2R)-anti-5-(3-[4-(10,11-difluoromethanodibenzo-suber-5-yl) piperazin-1-yl]-2-hydroxypropoxy)quinoline trihydrochloride (LY335979), in the drug-resistant cell line HL60/VCR and in normal, human CD56(+) lymphocytes. We used flow cytometric methods to detect the accumulation of rhodamine 123 and daunorubicin, fluorescent MDR substrates, in these cells. Our results indicate that LY335979 was 500-1500 times more potent than cyclosporin A or verapamil in restoring Pgp substrate accumulation in the MDR cell line HL60/VCR. Moreover, LY335979 could effectively block Pgp function on isolated CD56(+) lymphocytes (IC(50) = 1.2 nM) or CD56(+) lymphocytes in whole blood (IC(50) = 174 nM). We conclude that LY335979 is among the most potent Pgp inhibitors described and that it maintains significant potency in whole-human blood. These latter findings are important for establishing the dosing regimens of LY335979 for future clinical studies.

Modulation of Multidrug Resistance in Cancer by Immunosuppresive Agents. Preclinical Studies

This is a brief summary of the status of known immunosuppressive drugs describing their potential and mode of action to reverse the function of the MDR1 gene product, the P glycoprotein. Different aspects of these immunosuppressors have been reviewed in the recent literature. This summary will focus only on those studies which relate to the effect of these drugs on the P-glycoprotein. In addition, studies which may explain the mode of action, but do not deal directly with P-glycoprotein, are also summarized.

High multidrug resistance (P-glycoprotein 170) expression in inflammatory bowel disease patients who fail medical therapy

BACKGROUND & AIMS

The multidrug resistance (MDR) gene codes for a drug efflux pump P-glycoprotein 170 (Pgp-170) expressed on the surface of lymphocytes and intestinal epithelial cells. Inflammatory bowel disease (IBD) poorly responsive to medical therapy may relate to MDR expression because glucocorticoids are known Pgp-170 substrates.

METHODS

Using flow cytometry, we measured peripheral blood lymphocyte (PBL) MDR in 153 IBD patients and 50 healthy volunteers, and assessed the relationship between PBL, mucosal intraepithelial lymphocyte (IEL), and mucosal epithelial cell (EC) MDR expression in a further 20 IBD patients and 19 controls.

RESULTS

Compared with controls, PBL MDR was significantly elevated in patients with Crohn's disease who required bowel resection for failed medical therapy (mean +/- SEM, 26.7 +/- 2.8 vs. 11.9 +/- 1.0; P <0.0001) and patients with ulcerative colitis who required proctocolectomy for failed medical therapy (20.3 +/- 2.5 vs. 11.9 +/- 1.0; P = 0.001). PBL MDR remained stable over time and was not influenced by disease activity or glucocorticoid therapy. Both PBL and mucosal MDR expression appeared independent of disease activity, and there was a significant correlation between PBL MDR expression and both IEL expression (r = 0.92; P < 0.0001) and EC expression (r = 0.54; P < 0.001).

CONCLUSIONS

PBL and mucosal MDR expression may play an important role in determining the response of IBD patients to glucocorticoid therapy.

Mechanism of action of P-glycoprotein in relation to passive membrane permeation

This review presents a survey of studies of the movement of chemotherapeutic drugs into cells, their extrusion from multidrug-resistant (MDR) cells overexpressing P-glycoprotein (Pgp), and the mode of sensitization of MDR cells to anticancer drugs by Pgp modulators. The consistent features of the kinetics from studies of the operation of Pgp in cells were combined in a computer model that enables the simulation of experimental scenarios. MDR-type drugs are hydrophobic and positively charged and as such bind readily to negatively charged phospholipid head groups of the membrane. Transmembrane movement of MDR-type drugs, such as doxorubicin, occurs by a flip-flop mechanism with a lifetime of about 1 min rather than by diffusion down a gradient present in the lipid core. A long residence time of a drug in the membrane leaflet increases the probability that P-glycoprotein will remove it from the cell. In a manner similar to ion-transporting ATPases, such as Na+,K(+)-ATPase, Pgp transports close to one drug molecule per ATP molecule hydrolyzed. Computer simulation of cellular pharmacokinetics, based on partial reactions measured in vitro, show that the efficiency of Pgp, in conferring MDR on cells, depends on the pumping capacity of Pgp and its affinity toward the specific drug, the transmembrane movement rate of the drug, the affinity of the drug toward its pharmacological cellular target, and the affinity of the drug toward intracellular trapping sites. Pgp activities present in MDR cells allow for the efficient removal of drugs, whether directly from the cytoplasm or from the inner leaflet of the plasma membrane. A prerequisite for a successful modulator, capable of overcoming cellular Pgp, is the rapid passive transbilayer movement, allowing it to reenter the cell immediately and thus successfully occupy the Pgp active site(s).

Biochemical, cellular, and pharmacological aspects of the multidrug transporter

Considerable evidence has accumulated indicating that the multidrug transporter or P-glycoprotein plays a role in the development of simultaneous resistance to multiple cytotoxic drugs in cancer cells. In recent years, various approaches such as mutational analyses and biochemical and pharmacological characterization have yielded significant information about the relationship of structure and function of P-glycoprotein. However, there is still considerable controversy about the mechanism of action of this efflux pump and its function in normal cells. This review summarizes current research on the structure-function analysis of P-glycoprotein, its mechanism of action, and facts and speculations about its normal physiological role.

Anti-psychotic drugs reverse multidrug resistance of tumor cell lines and human AML cells ex-vivo

Anti-psychotic drugs are used in cancer patients undergoing chemotherapy frequently and the concomitantly used drugs may alter the pharmacokinetics of each other. One reason for the alteration of pharmacokinetics may be the modulation of the function of P-glycoprotein, whose efflux pump occurs in resistant cancer cells, in human intestine and in the blood-brain barrier. For this reason we tested the effect of several anti-psychotic drugs on the multidrug-resistant pump, P-glycoprotein. We found that in the MDR gene transfected L121C MDR, L5178 MDR and in the KB-V-1 cells selected for resistance some antipsychotic drugs block the function of P-glycoprotein. Blood cells of two treatment-resistant leukemic patients also showed increased uptake of daunorubicin if treated ex vivo with the anti-psychotic drugs. Our results suggest that pharmacokinetic studies should be performed prior to concomitant clinical use of such drugs which block P-glycoprotein function.

Structure-activity relationships of P-glycoprotein interacting drugs: kinetic characterization of their effects on ATPase activity

We have determined the kinetic parameters for stimulation and inhibition by 34 drugs of the P-glycoprotein ATPase in membranes derived from CR1R12 Chinese hamster ovary cells. The drugs chosen were sets of calmodulin antagonists, steroids, hydrophobic cations, hydrophobic peptides, chemotherapeutic substrates of P-glycoprotein, and some other drugs with lower affinity for P-glycoprotein. We studied how these kinetic parameters correlated with the partition coefficient and the Van der Waals surface area of the drugs. The maximum velocity of ATPase stimulation decreased with surface area and showed a suggestion of a maximum with increasing partition coefficient. The affinity of these drugs for P-glycoprotein showed no significant correlation with partition coefficient but was highly correlated with the surface area suggesting that binding between modulators and P-glycoprotein takes place across a wide interaction surface on the protein.

Molecular Events as Targets of Anticancer Drug Therapy

The aim of this review is to introduce some molecular targets for cancer chemotherapy, with comments on their mode of action, preclinical and clinical results. The representatives of the following groups are covered: phosphorylation inhibitors, protein kinase modulators, receptor antagonists, immunomodulators, differentiating agents, multidrug resistance modulation, telomerase inhibitors, and bioreductive agents.

Bisphenolic compounds that enhance cell cation transport are found in commercial phenol red

We have isolated two bisphenolic compounds (4 and 5) that have a marked effect on K+ and Na+ concentrations in human cells from commercial preparations of the pH indicator dye phenol red (phenolsulfonphthalein). We used a bioassay to identify active chromatographic fractions from the lipophilic impurities present in phenol red, and we determined the structure of two active components (4 and 5) by 1H and 13C NMR and mass spectrometry. When added to human fibroblasts in serum-free medium, the bisphenol fluorene derivative 9,9-bis(4'-hydroxyphenyl)-3-hydroxyfluorene (5) produced a rapid loss of K+ and a gain of Na+, at low concentrations, with an EC50 between 30 and 60 ng/mL (80-160 nM). The 2- and 4-hydroxy isomers of the fluorene 5 (i.e., compounds 6 and 7), prepared by synthesis, had similar activity, although compound 6 was somewhat less potent. The bisphenol xanthene derivative 9,9-bis(4'-hydroxyphenyl)xanthene (4) elicited a similar biological response but was less potent than 5-7; it also had a strong effect on cell adhesion, causing release of cells from the plastic substrate at concentrations as low as 2-5 microg/mL (5.5-14 microM). The structures of xanthene (4) and fluorene (5) bisphenols have been confirmed by synthesis from xanthone and hydroxyfluorenone, respectively, by Friedel-Crafts alkylation with phenol. In the latter case, the desired 3-hydroxyfluorene isomer was formed in situ by rearrangement of the 1-hydroxy isomer.

P-glycoprotein and multidrug resistance

Although the phenomenon of simultaneous resistance to multiple cytotoxic drugs (multidrug resistance) in cancer cells has been discussed for more than two decades, and the human and mouse genes encoding an energy-dependent transporter (the multidrug transporter or P-glycoprotein) responsible for multidrug resistance were cloned 10 years ago, there is still considerable controversy about the mechanism of action of this efflux pump and its true biological function. This review summarizes the current research on the mechanism of action of the multidrug transporter, including the hydrophobic cleaner and altered partitioning models, the possible function of P-glycoprotein as a chloride and/or ATP channel, the role of phosphorylation in its function and fact and speculation about its physiological role.

Intracellular pH does not affect drug extrusion by P-glycoprotein

The intracellular pH (pH(i)) of cells exhibiting multidrug resistance (MDR) related to the expression of the P-glycoprotein (Pgp) is often more alkaline than that of the parental cells, as also observed for the KB-V1/KB-3-1 system in this paper. The possible role of an elevated pH(i) in Pgp-related MDR has been investigated by shifting back the pH(i) of the MDR+ cells to a more acidic value using the mobile proton ionophore carbonylcyanide m-chlorophenylhydrazone (CCCP). The influence of CCCP-evoked delta pH(i) on relative daunorubicin (DNR) accumulation was similar in the case of several Pgp positive and negative cell lines, in view of flow cytometric and radioactive drug accumulation studies and measuring DNR levels in the medium in a flow-through system. Our data argue against a significant effect of pH(i) on Pgp pumping efficiency. However, an indirect connection between pH(i) regulation and the MDR phenotype is suggested by the fact that acidification of the external medium in the presence of verpamil could be observed exclusively in MDR+ cells.

MDR1/P-glycoprotein function. I. Effect of hypotonicity and inhibitors on rhodamine 123 exclusion

The MDR1 protein (P-glycoprotein) is a membrane ATPase whose expression results in resistance to several anti-tumor drugs. It has been proposed that the MDR1 protein, in addition to its pumplike properties, can function as (Gill et al. Cell 71: 23-32, 1992; Altenberg et al. Cancer Res. 54:618-622, 1994) or mediate the activity of (Hardy et al. EMBO J. 14: 68-75, 1995) a hypotonic stress-induced Cl- current. In addition, one study found that drug transport and Cl- channel-associated functions of MRD1 were separable and mutually exclusive and that, when cells were swelled, the MDR1 protein could not transport substrate. This hypothesis was tested in four pairs of isogenic cell lines with MDR1 transfectants expression 8,000-55,000 MDR1 antibody binding sites per cell. Cytoplasmic exclusion of rhodamine 123 was used as an indicator of MDR1 function to measure the effect of hypotonic stress, MDR1 inhibitors, and Cl- channel blockers on MRD1 transport function. It was found that MDR1 activity and its inhibition by cyclosporine A or flufenamic acid were unaffected by hypotonicity alone or in combination with Cl- channel blockers.