Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The emergence of drug resistance is a major obstacle to effective cancer chemotherapy. The identification of novel agents that serve as selective, potent and nontoxic modulators of drug resistance is thus an important goal for improving the success of cancer treatment. Thaliblastine (TBL), a plant alkaloid and P-glycoprotein (P-gp) inhibitor, is presently shown to fully reverse 490-fold resistance to Adriamycin (AdR) in a multidrug-resistant (MDR) human breast cancer cell line (MCF/AdR) that overexpresses P-gp, whereas the same treatment had no effect on AdR cytotoxicity in the drug-sensitive parental MCF-7 cells. Mechanistic studies showed that this striking resistance reversal was achieved without alteration of cellular levels of glutathione and without inhibition of glutathione S-transferase, glutathione peroxidase or P450 reductase by TBL, each of which is significantly altered in MCF/AdR cells, and each of which has been proposed to contribute to AdR resistance in this MDR line. Rather, resistance reversal by TBL can be entirely explained by this drug's capacity to restore the intracellular accumulation of AdR in the resistant cells. These results establish that MDR associated with P-gp overexpression can be fully reversed by the potent P-gp inhibitor TBL. They further indicate that although changes in multiple drug-metabolizing enzymes may accompany the development of MDR, these multiple biochemical alterations need not correspond to multiple functional determinants for drug resistance.
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PMID:Complete reversal by thaliblastine of 490-fold adriamycin resistance in multidrug-resistant (MDR) human breast cancer cells. Evidence that multiple biochemical changes in MDR cells need not correspond to multiple functional determinants for drug resistance. 756 98

Xenobiotics frequently induce proteins involved in their detoxification. Because many drugs that are metabolized by human cytochromes P450 (CYP) 3A4 and 3A5 are also transported by the drug efflux pump P-glycoprotein, we determined whether expression of these proteins was altered by a variety of drugs in a cell line derived from a human colon adenocarcinoma, LS180/WT, and its adriamycin-resistant subline, LS180/AD50. P-glycoprotein and CYP3A4 were constitutively expressed in both LS180/AD50 and LS180/WT cells, and both proteins were up-regulated after treatment with many drugs, including rifampicin, phenobarbital, clotrimazole, reserpine, and isosafrole. However, there were some exceptions because P-glycoprotein was up-regulated by midazolam and nifedipine, whereas CYP3A4 was not. CYP3A5, which is also constitutively expressed in these cells, remained unchanged with most drug treatments but was up-regulated by reserpine and clotrimazole. The apparent coordinated coexpression of the CYP3A gene family and P-glycoprotein in the LS180 cells suggests that for common orally administered drugs, P-glycoprotein may play an important role in net drug absorption and drug/drug interactions of shared CYP3A4/P-glycoprotein substrates.
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PMID:Modulators and substrates of P-glycoprotein and cytochrome P4503A coordinately up-regulate these proteins in human colon carcinoma cells. 863 64

P-glycoprotein, the MDR1 gene product which confers multidrug resistance to tumor cells and transports cationic or neutral compounds with high lipophilicity outward from the cells, excretes xenobiotics into the lumen in the kidney, small intestine and liver. The expression of P-glycoprotein is enhanced by stresses including exposure to various xenobiotics, while the activity is regulated to some extent by the phosphorylation. P-glycoprotein and P450 3A have similar substrate specificities and inducers, which may suggest they have complementary roles in the liver. The other subclass, MDR3, which does not show the multidrug resistance, translocates phosphatidyl choline selectively into the outer leaflet of the liver canalicular membrane, and may protect the liver from the detergent effect of bile acids.
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PMID:[The role of P-glycoprotein in the liver]. 915 55

The role of protein kinase C and protein phosphatases was examined in the control of mutagenic metabolites of aromatic amines. Various metabolic activating systems derived from rat liver were treated with: 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C modulator; okadaic acid (OA), a potent inhibitor of serine/threonine protein phosphatases (PP1 and PP2A); and ortho-vanadate (OV), an inhibitor of tyrosine phosphatases. TPA used over a wide concentration range (10(-9)-10(-6) M) did not affect the bacterial mutagenicity of the aromatic amines and of the aromatic amide investigated, 2-aminoanthracene, 2-aminofluorene and 2-acetylaminofluorene (2AAF). At the molecular level, TPA did not affect the function of cytochrome P450s 1A1 or 1A2, which are known key factors for the activation and inactivation of aromatic amines/amides. By contrast the OA and OV treatment of rat hepatocytes, rat liver homogenate, fraction S9 and the nuclear fraction drastically reduced (by > 80%) the mutagenicity of the aromatic amines/amide investigated. This is by far the most pronounced change in genotoxicity observed to date via modulation of phosphorylation. Whilst the mutagenicity of the primary toxication product 2-N-OH-acetylaminofluorene (2-N-OH-AAF) in the presence of exogenous activating systems (hepatocytes, S9-fraction, nuclear fraction) was also reduced by OV, OA had no influence. Thus the tyrosine protein phosphatase inhibitor and the serine/threonine protein phosphatase inhibitor influence the genotoxicity of aromatic amines/amides on different levels. Moreover, this shows that the drastic reduction in mutagenicity by OA was due to its influence on a step prior to the presence of the primary toxication product 2-N-OH-AAF. This reduction could be due to changes in the activity of cytochrome P4501A1 and/or 1A2. However, no incorporation of 32P-labelled phosphate from intracellularly prelabelled [32P]-ATP into cytochromes P450 1A1 or 1A2 nor any change in their catalytic activities was observed in the presence of OA. Furthermore, a phosphorylation dependent change in the function of P-glycoprotein (known for its role in the transport of diverse xenobiotic substances and their metabolites) was shown not to contribute to the observed decrease in mutagenicity. Our results reveal an important role for protein phosphatase 1 and/or 2A and tyrosine phosphatase(s) in the control of the genotoxicity of aromatic amines and amides. However, the present study does not distinguish between effects mediated by individual proteins affected by these protein phosphatases.
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PMID:Control of the mutagenicity of aromatic amines by protein kinases and phosphatases. I. The protein phosphatase inhibitors okadaic acid and ortho-vanadate drastically reduce the mutagenicity of aromatic amines. 933 96

The metabolism of valspodar (PSC 833; PSC), which is developed as a multidrug resistance-reversing agent, was investigated to assess the potential for drug-drug interactions and the pharmacological activity of major metabolites. The primary metabolites of PSC produced by human liver microsomes were monohydroxylated, as revealed by LC/MS. The major site of hydroxylation was at amino acid 9, resulting in M9, as determined by cochromatography with synthetic M9. Dihydroxylated and N-demethylated metabolites were also detected. PSC metabolism in two human livers exhibited KM values of 1.3-2.8 microM. The intrinsic clearance was 9-36 ml/min/kg of body weight. PSC biotransformation was cytochrome P450 (CYP or P450) 3A dependent, based on chemical inhibition and on metabolism by Chinese hamster ovary cells expressing CYP3A. Ketoconazole was a competitive inhibitor (Ki = 0.01-0.04 microM). The inhibition by 27 compounds, including four antineoplastic agents, corresponded to the inhibitory potentials of these compounds toward CYP3A. For vinblastine, paclitaxel, doxorubicin, and etoposide, the IC50 values were 5, 12, 20, and 150 microM, respectively. M9 was also an inhibitor, with a lower apparent affinity for CYP3A (IC50 = 21 microM), compared with that of PSC. M9 was also less active as a multidrug resistance-reversing agent. M9 demonstrated low potency in sensitizing resistant cells to paclitaxel and was a poor inhibitor of rhodamine-123 efflux from paclitaxel-resistant cells. In addition, compared with PSC, a higher concentration of M9 was needed to compete with the photoaffinity labeling of P-glycoprotein. Conversely, PSC inhibited only reactions catalyzed by CYP3A, including cyclosporine A metabolism (IC50 = 6.5 microM) and p-hydroxyphenyl-C3'-paclitaxel formation (Ki = 1.2 microM). Thus, PSC behaves in a manner very similar to that of other cyclosporines, and a comparable drug-drug interaction profile is expected.
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PMID:The multidrug resistance modulator valspodar (PSC 833) is metabolized by human cytochrome P450 3A. Implications for drug-drug interactions and pharmacological activity of the main metabolite. 969 96

We investigated the effects of ketoconazole on the oral bioavailability of morpholine-urea-phenylalanine-homophenylalanine-vinylsulfone-phenyl (K02), a vinylsulfone peptidomimetic cysteine protease inhibitor, and a P450 3A (CYP3A) and P-glycoprotein dual substrate, in male Sprague-Dawley rats, so as to evaluate the roles of CYP3A and P-gp in K02 disposition. Male Sprague-Dawley rats (8-10 wk old, n = 3-6) were administered a single dose of K02 (10 mg/kg) i.v. or (30 mg/kg) p.o. with or without a concomitant oral dose of ketoconazole (20 mg/kg). Blood samples were collected from 2 min to 8 h after administration through a implanted jugular vein cannula. K02 plasma concentrations were determined by liquid chromatography/mass spectrometer/mass spectrometer analysis. Ketoconazole markedly raised the area under the curve of orally administered K02 from 9.4 +/- 4.4 to 102 +/- 24 mg . min/liter and decreased K02 oral plasma clearance from 3810 +/- 1620 to 306 +/- 60 ml/min/kg. With concomitant ketoconazole dosing, the changes of AUC of i.v. administered K02 (from 94 +/- 17 to 107 +/- 14 mg . min/liter) and clearance (from 110 +/- 22 to 95 +/- 13 ml/min/kg) were not significant, although K02 oral bioavailability increased from 2.9 +/- 1.4 to 31.0 +/- 7.5% (P < .001). In summary, ketoconazole, a dual inhibitor of CYP3A and P-glycoprotein, can effectively increase K02 oral bioavailability by inhibiting the CYP3A/P-gp absorption barrier in the small intestine.
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PMID:Effects of ketoconazole on the intestinal metabolism, transport and oral bioavailability of K02, a novel vinylsulfone peptidomimetic cysteine protease inhibitor and a P450 3A, P-glycoprotein dual substrate, in male Sprague-Dawley rats. 976 44

Oral paclitaxel is not inherently bioavailable because of the overexpression of P-glycoprotein by intestinal cells and the significant first-pass extraction by cytochrome P450-dependent processes. This study sought to simulate the toxicological and pharmacological profile of a clinically relevant schedule of paclitaxel administered on clinically relevant i.v. dosing schedules in patients with advanced solid malignancies using oral paclitaxel administered with cyclosporin A, an inhibitor of both P-glycoprotein and P450 CYP3A. Nine patients were treated with a single course of oral paclitaxel in its parenteral formulation at a paclitaxel dose level of 180, 360, or 540 mg. Cyclosporin A was administered at a dose of 5 mg/kg p.o. 1 h before and concurrently with oral paclitaxel. Blood sampling was performed to evaluate the pharmacokinetics of paclitaxel, 6-alpha-hydroxypaclitaxel, 3-p-hydroxypaclitaxel, and cyclosporin A. The pharmacokinetic behavior of paclitaxel was characterized using both compartmental and noncompartmental methods. Model-estimated parameters were used to simulate paclitaxel concentrations after once daily and twice daily oral administration of paclitaxel and cyclosporin A. Aside from an unpleasant taste, the oral regimen was well tolerated, and there were no grade 3 or 4 drug-related toxicities. The systemic exposure to paclitaxel, as assessed by maximum plasma concentration (Cmax) and area under the plasma concentration versus time curve (AUC) values, did not increase as the dose of paclitaxel was increased from 180 to 540 mg, and there was substantial interindividual variability (4-6-fold) at each dose level. Mean paclitaxel Cmax values approached plasma concentrations achieved with clinically relevant parenteral dose schedules, averaging 268+/-164 ng/ml. AUC values averaged 3306+/-1977 ng x h/ ml, which was significantly lower than AUC values achieved with clinically relevant i.v. paclitaxel dose schedules. However, computer simulations using pharmacokinetic parameters derived from the present study demonstrated that pharmacodynamically relevant steady-state plasma paclitaxel concentrations of at least 0.06 microM would be achieved after protracted once daily and twice daily dosing with oral paclitaxel and cyclosporin A. Paclitaxel metabolites were detectable in three patients, and the 6-alpha-hydroxypaclitaxel: paclitaxel and 3-p-hydroxypaclitaxel:paclitaxel AUC ratios averaged 0.63 and 0.86, respectively; these values were substantially higher than values reported in patients treated with i.v. paclitaxel. Oral paclitaxel was bioavailable in humans when administered in combination with oral cyclosporin A 5 mg/kg 1 h before and concurrently with paclitaxel treatment, and plasma paclitaxel concentrations achieved with this schedule were biologically relevant and approached concentrations attained with clinically relevant parenteral dose schedules. However, treatment of patients with oral paclitaxel using a single oral dose administration schedule failed to achieve sufficiently high systemic drug exposure and pharmacodynamic effects. In contrast, computer simulations demonstrated that clinically relevant pharmacodynamic effects are likely to be achieved with multiple once daily and twice daily oral paclitaxel-cyclosporin A dosing schedules.
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PMID:Oral paclitaxel and concurrent cyclosporin A: targeting clinically relevant systemic exposure to paclitaxel. 1099 29

The recent clinical development of a number of migraine specific 5-HT1B/1D agonist triptans with enhanced lipophilicity (TELs), relative to the first drug of this class sumatriptan, and with a range of different metabolic, pharmacokinetic and receptor affinity profiles, provides the potential for critically different clinical profiles. Eletriptan, naratriptan, rizatriptan and zolmitriptan display both increased stability to first pass metabolic inactivation by monoamine oxidase (MAO-A) and enhanced lipophilicity (4- to > 120-fold more than sumatriptan), leading to increased oral bioavailability (2- to 5-fold more than the 14% reported for oral sumatriptan). Central penetration and increased receptor affinity and selectivity for the neuronal (5-HT1D) receptor also combine to allow for lower total oral dosing (i.e., unit doses of 15 mg or less compared with 50-300 mg doses of sumatriptan) and reduced peripheral exposure to the coronary vasoconstrictor (5-HT1B) receptor. The notable exception being eletriptan, where an active P-glycoprotein blood-brain barrier efflux system effectively negates these benefits and requires an 80 mg oral dose. Differences in the metabolic balance between hepatic P450 (especially CYP 1A2) and MAO-A inactivation lead to potential drug interactions for all TELs with the oral contraceptive pill (OCP), fluvoxamine and the quinilone antibiotics (with increased triptan levels). An important but complex MAO-A interaction between a metabolite of propranolol and rizatriptan mandates dosage reduction (to 5 mg) for rizatriptan in the presence of propranolol treatment. There is also an absolute contraindication for the concurrent administration of the MAO-A inhibitor moclobemide and rizatriptan. All the new-marketed TELs have potential clinical benefits and were well-tolerated relative to sumatriptan. Both rizatriptan (10 mg) and zolmitriptan (2.5 mg and 5 mg) demonstrate at least equivalent efficacy to sumatriptan 25, 50 and 100 mg, respectively, making them suitable first line agents for moderate or severe migraine headaches. Rizatriptan has the fastest onset of effect of the TELs. Naratriptan would appear to have lower recurrent headache rate than sumatriptan, rizatriptan or zolmitriptan. Therefore, for headaches of long duration and with a tendency to recur naratriptan may be the most appropriate treatment. Thus, knowledge of the metabolic, pharmacokinetic and clinical profiles of the TELs facilitates the selection of a triptan which allows optimisation of the clinical benefits for individual patients, minimising the risk of drug interactions and a minimally effective dose to reduce potential adverse events (AEs).
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PMID:Migraine pharmacotherapy with oral triptans: a rational approach to clinical management. 1124 25

Chlorpheniramine (CPAM) is a chiral antihistaminic drug commercialized as a racemic mixture. The intestinal absorption and metabolism of CPAM have been investigated in rat using in vivo (oral and IV administration), in situ (intestinal loop model), and in vitro (everted sac model) experiments. Oral and IV administrations of 20 mg/kg of the racemic mixture show that the pharmacokinetics of CPAM are stereoselective, with higher AUCs for the (+)-S-enantiomer compared to its antipode. The monodesmethyl metabolite (DCPM) was quantifiable in blood and its pharmacokinetics are stereoselective after oral but not after IV administration. Experiments using intestinal loops and everted sacs showed that the absorption is not stereoselective and that in vivo stereoselective formation of DCPM is presumably due to stereoselective hepatic metabolism. Moreover, the in vitro and in situ absorption of CPAM are not modified by modulators of P-glycoprotein and cytochromes P450 (cyclosporin A, ketoconazole).
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PMID:Intestinal absorption and metabolism of chlorpheniramine enantiomers in rat. 1128 26

1. UK-343,664 is a potent and specific PDE5 inhibitor. Following single oral doses to human volunteers, it exhibited non-proportional pharmacokinetics over the dose range 30-800 mg. Over this 27-fold dose range, Cmax and AUCt increased 247- and 287-fold respectively. The half-life (4-6 h) was similar at all doses. No systemic exposure was quantifiable at doses <10 mg. 2. UK-343,664 is a lipophilic molecule (log D7.4 = 3.1) and as such is expected to be cleared mainly by metabolism. Based on studies with expressed human P450 enzymes it was concluded that the metabolism of UK-343,664 was predominantly mediated by CYP3A4. With a moderate Km = 76 microM for this enzyme, saturation of first-pass metabolism alone was considered unlikely to account for the non-proportional pharmacokinetics. 3. UK-343,664 showed high affinity for P-glycoprotein in vitro, with a Km = 7.3 microM. In transport studies in LLC-PK1 cell monolayers transfected with P-glycoprotein, UK343,664 showed marked polarized transport which was concentration dependent. 4. The high affinity of UK-343,664 for P-glycoprotein is considered to be the primary source of the non-proportional pharmacokinetic profile observed in man.
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PMID:Potential role for P-glycoprotein in the non-proportional pharmacokinetics of UK-343,664 in man. 1156 32


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