Inhibitors of multidrug resistance

AZT and emodin exhibit synergistic growth-inhibitory effects on K562/ADM cells by inducing S phase cell cycle arrest and suppressing MDR1 mRNA/p-gp protein expression

CONTEXT

Previous studies have demonstrated that both 3'-azido-3'-deoxythymidine (AZT) and emodin, a traditional chemotherapy agent, can inhibit the growth of many types of cancer cells.

OBJECTIVE

This study aimed to evaluate the effect of AZT and emodin on adriamycin-resistant human chronic myelogenous leukemia (K562/ADM) cells, determine the expression of multidrug resistance 1 (MDR1) mRNA/p-glycoprotein (p-gp) protein, a protein known to induce resistance to anticancer agents, and to elucidate the underlying molecular mechanisms.

MATERIALS AND METHODS

K562/ADM cells were treated with AZT (10-160 μM) or emodin (5-80 μM) for 24, 48 and 72 h and cell viability was measured using the MTT assay. The effect of AZT (16.5, 33 and 66 μM) and emodin (6.1, 17.6 and 33.2 μM) on K562/ADM cell cycle distribution was determined by flow cytometry, and MDR1 mRNA/p-gp protein expression was determined by real time RT-PCR and western blotting.

RESULTS

The growth suppression of emodin was dramatically enhanced by AZT in K562/ADM cells. The IC50 of AZT and emodin was lower than that of emodin alone. All examined combinations of AZT and emodin yielded a synergetic effect (CI < 1). Furthermore, AZT and emodin altered the cell cycle distribution and led to an accumulation of cells in S phase. Meanwhile, the expression of MDR1 mRNA/p-gp protein was markedly decreased.

DISCUSSION AND CONCLUSION

These results show a synergistic growth-inhibitory effect of AZT and emodin in K562/ADM cells, which is achieved through S phase arrest. MDR1 might ultimately be responsible for these phenomena.

Ophiobolin-O reverses adriamycin resistance via cell cycle arrest and apoptosis sensitization in adriamycin-resistant human breast carcinoma (MCF-7/ADR) cells

Multidrug-resistance is a major obstacle facing cancer chemotherapy. This paper demonstrates that novel compound Ophiobolin-O reverses MCF-7/ADR resistance to adriamycin (ADM). The IC₅₀ of ADM treated MCF-7 cells was 2.02 ± 0.05 µM and 74.00 ± 0.18 µM treated MCF-7/ADR cells, about 37-fold, compared to the former. However, 0.1 µM Ophiobolin-O (less than 20% inhibition concentration) combined with ADM caused the decreased IC₅₀ of ADM to 6.67 ± 0.98 µM, indicating it reversed ADM resistance of MCF-7/ADR cells (11-fold). Furthermore, Ophiobolin-O increased ADM-induced mitochondrial pathway apoptosis and G2/M phase arrest, which is partly due to the elevation level of ROS in MCF-7/ADR cells. As we described in this paper, the reversal effect of Ophiobolin-O may be due to the reduction of resistance-related protein P-Glycoprotein (P-gp, also known as MDR1) through inhibiting the activity of the multidrug resistance 1 (MDR1) gene promoter, which makes MCF-7/ADR cells more sensitive to ADM treatment. Assays in nude mice also showed that the combination of ADM and Ophiobolin-O significantly improved the effect of ADM.

Role for Class I histone deacetylases in multidrug resistance

Recent reports have showed that histone deacetylase (HDAC) inhibitor resulted in multidrug resistance (MDR) to other chemotherapeutic agents. However, the molecular mechanisms of Class I HDACs on MDR regulation are poorly understood. In this study, HDAC1 and HDAC2 acted as enhancers to intensify the chemosensitivities of anti-cancer drugs via reducing the expression levels of P-gp, MRP1 and MRP2. Furthermore, the dissociation of HDAC1 and HDAC2 led to transcriptional regulation of P-gp expression via the recruitment of p300, PCAF and NF-Y to the P-gp promoter region, which subsequently increased the level of the active gene marker, hyperacetylated histone H3. In parallel, selective inhibition of HDAC1 and HDAC2 induced the recruitment of p300, PCAF, NF-Y via acetylation of Sp1. Thus, our findings showed HDAC1 and 2 regulated P-gp expression through dynamic changes in chromatin structure and transcription factor association within the promoter region.

Anti-proliferative activity and suppression of P-glycoprotein by (-)-antofine, a natural phenanthroindolizidine alkaloid, in paclitaxel-resistant human lung cancer cells

Multidrug resistance (MDR) is a major obstacle in effective chemotherapy for cancer patients. The expression of P-glycoprotein (P-gp) in cancer cells is highly correlated with resistance to chemotherapeutic drugs. (-)-Antofine, a phenanthroindolizidine alkaloid derived from Cynanchum paniculatum, inhibits the growth of various human cancer cells. In this study, we further explored the potential of (-)-antofine to overcome the resistance induced by anti-cancer drugs. To this end, we established the paclitaxel-resistant human lung cancer cell line A549-PA by gradually exposing A549 cells to increasing concentrations of paclitaxel. As a result, the A549-PA cells acquired resistance against paclitaxel treatment and had an IC50 that was more than 200 times that of the parental A549 cells. (-)-Antofine, however, effectively suppressed the growth of both the parental and drug-resistant cells. Additional studies revealed that the anti-proliferative activity of (-)-antofine in A549-PA cells is accompanied by a down-regulation of P-gp mRNA and protein expression. The effect of reversing the multidrug resistance of A549-PA cells via (-)-antofine treatment was demonstrated an increase in intracellular rhodamine-123 accumulation, measured using FACS analysis. These findings suggest an additional chemotherapeutic value of (-)-antofine, that is, regulation of cancer cell drug resistance, in addition to its antitumor effect.

Effects of celecoxib on the reversal of multidrug resistance in human gastric carcinoma by downregulation of the expression and activity of P-glycoprotein

We investigated the effects of celecoxib on the cell proliferation and the expression and activity of P-glycoprotein in the human gastric carcinoma multidrug resistance sublines SGC7901/adriamycin and SGC7901/vincristine. The cell proliferation was measured by [3H]thymidine incorporation assay and MTT test. The expression of the multidrug resistant gene (MDR1) was detected by real-time quantitative reverse transcription-polymerase chain reaction. P-glycoprotein was measured by Western blot analysis. The intracellular rhodamine 123 accumulation was analyzed by flow cytometry to evaluate the activity of P-glycoprotein. After treatment with celecoxib, the proliferation inhibitions of SGC7901 cell line and the SGC7901/adriamycin and SGC7901/vincristine sublines increased linearly in a positive dose-dependent pattern in both the [3H]thymidine incorporation assay and in the MTT test. The IC50 value of the MDR1/GAPDH ratio was 5.50 x 10(-6) mol/l in SGC7901/adriamycin and 3.89 x 10(-6) mol/l in SGC7901/vincristine. P-glycoprotein expression levels in the two multidrug resistance sublines treated with celecoxib were significantly lower than those in control groups, 0.28 vs. 0.71 in the SGC7901/adriamycin subline and 0.21 vs. 0.83 in the SGC7901/vincristine subline, respectively, P<0.05. After treatment with celecoxib, intracellular rhodamine 123 accumulation in the SGC7901/adriamycin and SGC7901/vincristine sublines increased positively in a dose-dependent pattern (P<0.05), and reached more than 50% of that in the SGC7901 cell line at the concentration of 1 x 10(-4) mol/l of celecoxib. In conclusion, celecoxib could inhibit proliferation of multidrug resistance in gastric carcinoma sublines. The reversal of multidrug resistance was caused by downregulation of the expression and activity of P-glycoprotein. The results may suggest a new way to reverse P-glycoprotein-dependent multidrug resistance in human gastric carcinoma.

Mitochondrially targeted effects of berberine [Natural Yellow 18, 5,6-dihydro-9,10-dimethoxybenzo(g)-1,3-benzodioxolo(5,6-a) quinolizinium] on K1735-M2 mouse melanoma cells: comparison with direct effects on isolated mitochondrial fractions

Berberine [Natural Yellow 18, 5,6-dihydro-9,10-dimethoxybenzo(g)-1,3-benzodioxolo(5,6-a)quinolizinium] is an alkaloid present in plant extracts and has a history of use in traditional Chinese and Native American medicine. Because of its ability to arrest the cell cycle and cause apoptosis of several malignant cell lines, it has received attention as a potential anticancer therapeutic agent. Previous studies suggest that mitochondria may be an important target of berberine, but relatively little is known about the extent or molecular mechanisms of berberine-mitochondrial interactions. The objective of the present work was to investigate the interaction of berberine with mitochondria, both in situ and in isolated mitochondrial fractions. The data show that berberine is selectively accumulated by mitochondria, which is accompanied by arrest of cell proliferation, mitochondrial fragmentation and depolarization, oxidative stress, and a decrease in ATP levels. Electron microscopy of berberine-treated cells shows a reduction in mitochondria-like structures, accompanied by a decrease in mitochondrial DNA copy number. Isolated mitochondrial fractions treated with berberine had slower mitochondrial respiration, especially when complex I substrates were used, and increased complex I-dependent oxidative stress. It is also demonstrated for the first time that berberine stimulates the mitochondrial permeability transition. Direct effects on ATPase activity were not detected. The present work demonstrates a number of previously unknown alterations of mitochondrial physiology induced by berberine, a potential chemotherapeutic agent, although it also suggests that high doses of berberine should not be used without a proper toxicology assessment.

Efflux of baicalin, a flavone glucuronide of Scutellariae Radix, on Caco-2 cells through multidrug resistance-associated protein 2

Baicalin and its aglycone, baicalein, being are strong antioxidants and have various pharmacological actions. Baicalein has shown a unique metabolic fate in rat intestine, being excreted into the intestinal lumen from mucosal (epithelial) cells following glucuronidation of baicalein absorbed after oral administration. The purpose of this study was to examine the absorption and excretion of baicalin and baicalein in a Caco-2 cell monolayer model to evaluate the disposition of baicalin and baicalein in the human intestine. When baicalein at 5 microM was loaded on the apical side of the Caco-2 cell monolayer, baicalein was not transferred to the basolateral side, but more baicalin was excreted onto the apical side than was being absorbed onto the basolateral side. The amount of baicalin recovered on both sides accounted for more than 90% of the baicalein absorbed from the apical surface. This was supported by the fact that Caco-2 cell microsomes showed UDP-glucuronate glucuronosyltransferase activity towards baicalein to form baicalin. On the other hand, when baicalein was loaded at higher concentrations, baicalin excretion became saturated, and then baicalein was transferred to the basolateral side. Furthermore, baicalin efflux was not inhibited by MDR1/P-glycoprotein substrates such as ciclosporin and vinblastine, but significantly inhibited by multidrug resistance-associated protein 2 (MRP2, ABCC2) substrates such as probenecid and genistein. MRP2 was also detected in Caco-2 cells by Western blotting using specific antibodies. In addition, baicalin, but not baicalein, enhanced dose-dependently the vanadate-sensitive ATPase activity of human MRP2. These results indicated that, in Caco-2 cells, any baicalein absorbed after loading at low concentrations of baicalein was not transferred to the basolateral side, but was first transformed into baicalin in the cells and excreted through the action of MRP2, mainly to the apical side.

Down-regulation of P-glycoprotein expression in MDR breast cancer cell MCF-7/ADR by honokiol☆

P-glycoprotein accounts for the most intrinsic and acquired cancer multidrug resistance. To inhibit the expression of P-glycoprotein is one of the effective ways to reverse cancer drug resistance. Honokiol, a naturally occurring compound, has been demonstrated to combat cancer through mechanisms including inhibition of angiogenesis and induction of apoptosis. Here, we show that honokiol down-regulated the expression of P-glycoprotein at mRNA and protein levels in MCF-7/ADR, a human breast MDR cancer cell line. The down-regulation of P-glycoprotein was accompanied with a partial recovery of the intracellular drug accumulation, and of the sensitivities toward adriamycin. This study reveals a novel function of honokiol as an anti-cancer agent.

Suppression of P-glycoprotein expression by antipsychotics trifluoperazine in adriamycin-resistant L1210 mouse leukemia cells

Multidrug resistance (MDR) to unrelated chemotherapeutic drugs can be mediated by overexpression of P-glycoprotein (P-gp), the mdr gene product. Trifluoperazine (TFP), a phenothiazine derivative antipsychotics, is known to reverse MDR of tumor cell lines by blocking P-gp efflux function. In the present study, we evaluated the effect of TFP on the expression of P-gp in multidrug-resistant L1210/Adr mouse leukemic cell lines, which are characterized by overexpession of P-gp. We found that TFP induced the downregulation of P-gp protein and mdr1b mRNA in a dose- and time-dependent manner in L1210/Adr cells. TFP reduction of mdr1b mRNA was paralleled by transcriptional suppression of the mdr1b promoter. Moreover, TFP restored the adriamycin-induced apoptosis in L1210/Adr cells. These results suggest that TFP may have utility as an adjuvant in the therapy of leukemia for the reversal of P-gp-dependent MDR as well as for the management of psychological symptoms in the cancer patients.

A Naive Bayes Classifier for Prediction of Multidrug Resistance Reversal Activity on the Basis of Atom Typing

Multidrug resistance (MDR), the ability of cancer cells to become simultaneously resistant to different drugs, remains an unsolved challenge in cancer chemotherapy. The use of MDR reversal (MDRR) agents is a promising approach to overcome this problem. For the design and development of such agents, it would be desirable to have a reliable model to estimate the MDRR activity of compounds. Presented here is a naive Bayes classifier to categorize MDRR agents into active and inactive classes, which uses a universal, generic molecular-descriptor system.(1) The naive Bayes classifier was built from a 424 compound training set, selected from 609 druglike compounds in the publicly available "Klopman set". The model correctly predicted MDRR activities for 82.2% of 185 compounds in a testing set. The cumulative probabilities were proven useful for prioritizing the compounds for testing. The impact of attribute dependences on the performance of the classifier was examined. As an unsupervised learner with no tuning parameters, a naive Bayes classifier is capable of providing an objective comparison of the effectiveness of different molecular descriptors. The relative performance of the classifiers constructed from either an atom-type-based molecular descriptor or the long-range functional-class fingerprint descriptors FCFP_6 or FCFP_2 was compared. Employing an atom typing descriptor with the naive Bayes classification, it enables the interpretability of the resulting model, which offers extra information for the rational design of MDRR agents.

Fluoxetine inhibits multidrug resistance extrusion pumps and enhances responses to chemotherapy in syngeneic and in human xenograft mouse tumor models

Multidrug resistance (MDR) operated by extrusion pumps such as P-glycoprotein and multidrug-resistance-associated-proteins, is a major reason for poor responses and failures in cancer chemotherapy. MDR modulators (chemosensitizers) were found among drugs approved for noncancer indications and their derivatives. Yet toxicity, adverse effects, and poor solubility at doses required for MDR reversal prevent their clinical application. Among newly designed chemosensitizers, some still suffer from toxicity and adverse effects, whereas others progressed to clinical trials. Diversities among tumors and among MDR pumps indicate a need for several clinically approved MDR modulators. Here we report for the first time that fluoxetine (Prozac), the well-known antidepressant, is a highly effective chemosensitizer. In vitro, fluoxetine enhanced (10- to 100-fold) cytotoxicity of anticancer drugs (doxorubicin, mitomycin C, vinblastine, and paclitaxel) in drug-resistant but not in drug-sensitive cells (5 and 3 lines, respectively). Fluoxetine increased drug accumulation within MDR-cells and inhibited drug efflux from those cells. In vivo, fluoxetine enhanced doxorubicin accumulation within tumors (12-fold) with unaltered pharmacokinetics. In four resistant mouse tumor models of both syngeneic and human xenograft, combination treatment of fluoxetine and doxorubicin generated substantial (P < 0.001) improvements in tumor responses and in survivals (2- to 3-fold). Moreover, fluoxetine reversed MDR at doses that are well below its human safety limits, free of the severe dose-related toxicity, adverse effects, and poor solubility that are obstacles to other chemosensitizers. This low-dose range, together with the findings reported here, indicate that fluoxetine has a high potential to join the arsenal of MDR reversal agents that may reach the clinic.

Dying for NF-κB? Control of cell death by transcriptional regulation of the apoptotic machinery

The transcription factor nuclear factor kappaB (NF-kappaB) is a pleiotropic protein complex that is activated from a sequestered, cytoplasmic form by pro-inflammatory extracellular signals and cellular stress. Several hundred cellular genes have been shown to be regulated by NF-kappaB, including cytokines, chemokines and adhesion molecules. Nearly eight years ago, a flurry of publications showed that loss or suppression of NF-kappaB results in an enhanced sensitivity to apoptosis. In the ensuing years, activation of NF-kappaB has become almost synonymous with enhanced cell survival, although more recent data suggests that this transcription factor plays a more complex role in the regulation of cell death.

Drug transport proteins in the liver

Together with drug metabolising enzymes, transmembrane transporters are important determinants of drug metabolism and drug clearance by the liver. Hepatic uptake of organic anions, cations, prostaglandins and bile salts is supported by dedicated transporter proteins in the basolateral (sinusoidal) membrane of hepatocytes: OATPs, OATs, OCTs, PGTs and NTCP, respectively. ATP-binding cassette (ABC) transporter proteins in the canalicular membrane of hepatocytes mediate the hepatic efflux of drugs, bile salts and metabolites against a steep concentration gradient from liver to bile. This transport is driven by ATP hydrolysis. Drugs, endogenous metabolites, bile salts and cytokines affect the expression levels of these transporters. They act through a family of ligand-activated transcription factors, the nuclear hormone receptors. Consequently, the levels of the various transporter proteins are subject to genetic polymorphism in the encoding genes as well as in these transcription factors. Adverse drug reactions may be caused by genetic or disease-induced variations of transporter expression or drug-drug interactions at the level of these transporters.

The impact of efflux transporters in the brain on the development of drugs for CNS disorders

The development of drugs to treat disorders of the CNS requires consideration of achievable brain concentrations. Factors that influence the brain concentrations of drugs include the rate of transport into the brain across the blood-brain barrier (BBB), metabolic stability of the drug, and active transport out of the brain by efflux mechanisms. To date, three classes of transporter have been implicated in the efflux of drugs from the brain: multidrug resistance transporters, monocarboxylic acid transporters, and organic ion transporters. Each of the three classes comprises multiple transporters, each of which has multiple substrates, and the combined substrate profile of these transporters includes a large number of commonly used drugs. This system of transporters may therefore provide a mechanism through which the penetration of CNS-targeted drugs into the brain is effectively minimised. The action of these efflux transporters at the BBB may be reflected in the clinic as the minimal effectiveness of drugs targeted at CNS disorders, including HIV dementia, epilepsy, CNS-based pain, meningitis and brain cancers. Therefore, modulation of these efflux transporters by design of inhibitors and/or design of compounds that have minimal affinity for these transporters may well enhance the treatment of intractable CNS disorders.

In vivo evidence for P-glycoprotein-mediated transport of phenytoin at the blood-brain barrier of rats

PURPOSE

The multidrug transporter P-glycoprotein (P-gp) is expressed at high levels in a variety of tissues such as the endothelial cells of the blood-brain barrier (BBB) capillaries, where it is thought to be involved in the exclusion of various drugs from the capillary endothelial cells, blocking their entry into brain. It was previously shown that pharmacoresistant partial epilepsy is associated with an increased expression of P-gp in brain capillary endothelium and astrocytes, leading to the hypothesis that increased P-gp expression may be involved in medically intractable epilepsy. However, it is not known whether the distribution of antiepileptic drugs (AEDs) into the brain is limited by P-gp. We used in vivo microdialysis in freely moving rats to study whether the concentration of the major AED phenytoin (PHT) in the extra-cellular fluid (ECF) of the cerebral cortex can be enhanced by inhibition of P-gp.

METHODS

Three different P-gp inhibitors, sodium cyanide, verapamil, and PSC 833, were used. These drugs were given via the microdialysis probe in the right frontal cortex, while a probe in the left cortex served as vehicle control side. Perfusion with the inhibitor started 15-60 min before systemic (i.p.) administration of PHT, 50 mg/kg.

RESULTS

PHT rapidly entered the brain ECF compartment, but ECF plasma ratios at time of maximal ECF levels were only approximately 0.04. All P-gp inhibitors significantly increased the ECF concentrations of PHT after local administration, indicating that P-gp in the BBB normally limits the distribution of PHT into the brain parenchyma. Cremorphor EL, the vehicle used to administer PSC, also was able to increase ECF PHT, which is explained by the previously reported inhibitory effect of cremophor on P-gp.

CONCLUSIONS

Provided that multidrug transporters such as P-gp also are involved in the BBB outward transport of other AEDs, increased expression of multidrug transporters, leading to inadequate accumulation of AEDs in the brain, would be a likely explanation for pharmacoresistant epilepsy.

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.

Total Synthesis of Dendroamide A, a Novel Cyclic Peptide That Reverses Multiple Drug Resistance

Dendroamide A (1) was isolated from a blue-green alga on the basis of its ability to reverse drug resistance in tumor cells that overexpress either of the transport proteins, P-glycoprotein or MRP1. Because of this activity, methods for the synthesis of analogues of this oxazole- and thiazole-containing cyclic peptide have been developed, and the total synthesis of 1 has been completed. Highlights of the synthetic strategy are as follows: (1) a dicyclohexylcarbodiimide coupling of D-Ala and L-Thr, followed by reaction with Burgess reagent and DBU-assisted oxidation to form D-Ala-oxazole; (2) formation of D-Val-thiazole and D-Ala-thiazole via modified Hantzsch reactions; and (3) use of molecular modeling to select the preferred precursor for the final cyclization of the peptide analogue. Synthetic 1 demonstrated spectral properties identical to those of the natural product and reversed P-glycoprotein-mediated drug resistance more effectively than MRP1-mediated resistance. Certain of the synthetic precursors had biological activity, indicating that cell permeability and peptide cyclization are necessary for optimal activity. Thus, the structure and the biological activities of the natural product are confirmed, and methods for the synthesis of analogues for further structure-activity explorations are defined.

Potent synergism of the combination of fluconazole and cyclosporine in Candida albicans

Several types of drugs currently used in clinical practice were screened in vitro for their potentiation of the antifungal effect of the fungistatic agent fluconazole (FLC) on Candida albicans. These drugs included inhibitors of multidrug efflux transporters, antimicrobial agents, antifungal agents, and membrane-active compounds with no antimicrobial activity, such as antiarrhythmic agents, proton pump inhibitors, and platelet aggregation inhibitors. Among the drugs tested in an agar disk diffusion assay, cyclosporine (Cy), which had no intrinsic antifungal activity, showed a potent antifungal effect in combination with FLC. In a checkerboard microtiter plate format, however, it was observed that the MIC of FLC, as classically defined by the NCCLS recommendations, was unchanged when FLC and Cy were combined. Nevertheless, if a different reading endpoint corresponding to the minimal fungicidal concentration needed to decrease viable counts by at least 3 logs in comparison to the growth control was chosen, the combination was synergistic (fractional inhibitory concentration index of <1). This endpoint fitted to the definition of MIC-0 (optically clear wells) and reflected the absence of the trailing effect, which is the result of a residual growth at FLC concentrations greater than the MIC. The MIC-0 values of FLC and Cy tested alone in C. albicans were >32 and >10 microg/ml, respectively, and decreased to 0.5 and 0.625 microg/ml when the two drugs were combined. The combination of 0.625 microg of Cy per ml with supra-MICs of FLC resulted in a potent antifungal effect in time-kill curve experiments. This effect was fungicidal or fungistatic, depending on the C. albicans strain used. Since the Cy concentration effective in vitro is achievable in vivo, the combination of this agent with FLC represents an attractive perspective for the development of new management strategies for candidiasis.

Regulation of multidrug resistance 1 (MDR1)/P-glycoprotein gene expression and activity by heat-shock transcription factor 1 (HSF1)

Infection of HeLa cells with adenovirus-carrying HSF1(+) cDNA, which encodes a mutated form of HSF1 with constitutive transactivation capacity, increased multidrug resistance 1 (MDR1) mRNA level and P-glycoprotein (P-gp) cell surface content and stimulated rhodamine 123 accumulation and vinblastine efflux activity. On the other hand, infection with adenovirus-carrying HSP70 and HSP27 cDNAs did not increase MDR1/P-gp expression. HSF1 regulates MDR1/P-gp expression at the transcriptional level, since HSF1(+) bound the heat-shock consensus elements (HSEs) in the MDR1 gene promoter and also activated the expression of an MDR1 promoter-driven reporter plasmid (pMDR1(-1202)). In addition, heat-shock increased pMDR1(-1202) promoter activity but not the activity of a similar reporter plasmid with point mutations at specific HSEs, and the heat-induced increase was totally inhibited by co-transfection with an expression plasmid carrying HSF1(-), a dominant negative mutant of HSF1. The stress inducers arsenite, butyrate, and etoposide also increased pMDR1(-1202) promoter activity, but the increase was not inhibited (in the case of butyrate) or was only partially inhibited (in the case of arsenite and etoposide) by HSF1(-). These results demonstrate that HSF1 regulates MDR1 expression, and that the HSEs present in the -315 to -285 region mediate the heat-induced activation of the MDR1 promoter. However, other factors may also participate in MDR1 induction by stressing agents.

Functional characterization of the carnitine transporter defective in primary carnitine deficiency

Primary carnitine deficiency is an autosomal recessive disorder caused by defective carnitine transport which impairs fatty acid oxidation and manifests as nonketotic hypoglycemia or skeletal or heart myopathy. Here we report the functional characterization of this transporter in human fibroblasts. Carnitine enters normal cells by saturable and unsaturable routes, the latter corresponding to Na+-independent uptake. Saturable carnitine transport was absent in cells from patients with primary carnitine deficiency. In control cells, saturable carnitine transport was energized by the electrochemical gradient of Na+. Carnitine uptake was not inhibited by amino acid substrates of transport systems A, ASC, and X-AG, but was inhibited competitively (in potency order) by butyrobetaine > carnitine > palmitoylcarnitine = acetylcarnitine > betaine. Carnitine uptake was also noncompetitively inhibited by verapamil and quinidine, inhibitors of the multidrug resistance family of membrane transporters, suggesting that the carnitine transporter may share a functional motif with this class of transporters. A high-affinity carnitine transporter was present in kidney 293 cells, but not in HepG2 liver cells, whose carnitine transporter had a Km in the millimolar range. These result indicate the presence of multiple types of carnitine transporters in human cells.