Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have generated for the first time monoclonal antibodies (mAbs) specific for topoisomerase I (topo I) from scleroderma patients, and tight skin mice which develop a scleroderma-like syndrome. The epitope specificity of these antibodies has been determined using a series of fusion proteins containing contiguous portions of topo I polypeptide. Western blot analysis demonstrated that both human and mouse mAbs bound strongly to fusion protein C encompassing the NH2-terminal portion of the enzyme, and weakly to fusion proteins F and G containing regions close to the COOH-terminal end of the molecule. This crossreactivity is related to a tripeptide sequence homology in F, G, and C fusion proteins. It is interesting that a pentapeptide sequence homologous to that in fusion protein C was identified in the UL70 protein of cytomegalovirus, suggesting that activation of autoreactive B cell clones by molecular mimicry is possible. Both human and mouse mAbs exhibiting the same antigen specificity, also share an interspecies cross-reactive idiotope. These data suggest that B cell clones producing antitopo autoantibodies present in human and mouse repertoire are conserved during phylogeny, and are activated during the development of scleroderma disease.
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PMID:Antitopoisomerase I monoclonal autoantibodies from scleroderma patients and tight skin mouse interact with similar epitopes. 137 44

Irinotecan [7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11)] is a promising water-soluble analogue of camptothecin [S. Sawada et al., Chem. & Pharm. Bull. (Tokyo), 39: 1446-1454, 1991]. We have reported previously the presence of an important polar metabolite, in addition to 7-ethyl-10-hydroxycamptothecin (SN-38) beta-glucuronide, in samples of plasma taken from patients undergoing treatment with CPT-11 (L.P. Rivory and J. Robert, Cancer Chemother. Pharmacol. 36: 176-179, 1995; L. P. Rivory and J. Robert, J. Cromatogr., 661: 133-141, 1994). Plasma samples (0.5 ml) containing comparatively large amounts of this metabolite were extracted by solid-phase columns and subjected to high-performance liquid chromatography and mass spectrometry in parallel to fluorometric detection. The metabolite yielded [M + 1] ions with a m/z of 619, representing the addition of 32 atomic mass units to CPT-11. Purified fractions were subjected to proton nuclear magnetic resonance, and the structure determined, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycampothecin (APC), was further validated following synthesis. Like CPT-11, APC was found to be only a weak inhibitor of the cell growth of KB cells in culture (IC50, 2.1 versus 5.5 micrograms/ml for CPT-11 and 0.01 microgram/ml for SN-38, the active metabolite of CPT-11) and was a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). In contrast to CPT-11, APC was not hydrolyzed to SN-38 by human liver microsomes or purified human liver carboxylesterase. Furthermore, APC did not inhibit the hydrolysis of CPT-11 in these preparations. Interestingly, APC was only a weak inhibitor of acetylcholinesterase in comparison to CPT-11 and neostigmine. It appears likely, therefore, that APC does not contribute directly to the activity and toxicity profile of CPT-11 in vivo.
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PMID:Identification and properties of a major plasma metabolite of irinotecan (CPT-11) isolated from the plasma of patients. 870 9

This article reviews the clinical pharmacokinetics of a water-soluble analogue of camptothecin, irinotecan [CPT-11 or 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptoth eci n]. Irinotecan, and its more potent metabolite SN-38 (7- ethyl-10-hydroxy-camptothecin), interfere with mammalian DNA topoisomerase I and cancer cell death appears to result from DNA strand breaks caused by the formation of cleavable complexes. The main clinical adverse effects of irinotecan therapy are neutropenia and diarrhoea. Irinotecan has shown activity in leukaemia, lymphoma and the following cancer sites: colorectum, lung, ovary, cervix, pancreas, stomach and breast. Following the intravenous administration of irinotecan at 100 to 350 mg/m2, mean maximum irinotecan plasma concentrations are within the 1 to 10 mg/L range. Plasma concentrations can be described using a 2- or 3-compartment model with a mean terminal half-life ranging from 5 to 27 hours. The volume of distribution at steady-state (Vss) ranges from 136 to 255 L/m2, and the total body clearance is 8 to 21 L/h/m2. Irinotecan is 65% bound to plasma proteins. The areas under the plasma concentration-time curve (AUC) of both irinotecan and SN-38 increase proportionally to the administered dose, although interpatient variability is important. SN-38 levels achieved in humans are about 100-fold lower than corresponding irinotecan concentrations, but these concentrations are potentially important as SN-38 is 100- to 1000-fold more cytotoxic than the parent compound. SN-38 is 95% bound to plasma proteins. Maximum concentrations of SN-38 are reached about 1 hour after the beginning of a short intravenous infusion. SN-38 plasma decay follows closely that of the parent compound with an apparent terminal half-life ranging from 6 to 30 hours. In human plasma at equilibrium, the irinotecan lactone form accounts for 25 to 30% of the total and SN-38 lactone for 50 to 64%. Irinotecan is extensively metabolised in the liver. The bipiperidinocarbonylxy group of irinotecan is first removed by hydrolysis to yield the corresponding carboxylic acid and SN-38 by carboxyesterase. SN-38 can be converted into SN-38 glucuronide by hepatic UDP-glucuronyltransferase. Another recently identified metabolite is 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC). This metabolite is a weak inhibitor of KB cell growth and a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). Numerous other unidentified metabolites have been detected in bile and urine. The mean 24-hour irinotecan urinary excretion represents 17 to 25% of the administered dose. Recovery of SN-38 and its glucuronide in urine is low and represents 1 to 3% of the irinotecan dose. Cumulative biliary excretion is 25% for irinotecan, 2% for SN-38 glucuronide and about 1% for SN-38. The pharmacokinetics of irinotecan and SN-38 are not influenced by prior exposure to the parent drug. The AUC of irinotecan and SN-38 correlate significantly with leuco-neutropenia and sometimes with the intensity of diarrhoea. Certain hepatic function parameters have been correlated negatively with irinotecan total body clearance. It was noted that most tumour responses were observed at the highest doses administered in phase I trials, which indicates a dose-response relationship with this drug. In the future, these pharmacokinetic-pharmacodynamic relationships will undoubtedly prove useful in minimising the toxicity and maximise the likelihood of tumour response in patients.
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PMID:Clinical pharmacokinetics of irinotecan. 934 1

Irinotecan (IRN), a topoisomerase I interactive agent, has significant antitumor activity in early Phase I studies in children with recurrent solid tumors. However, the disposition of IRN and its metabolites, SN-38 and APC, in children has not been reported. Children with solid tumors refractory to conventional therapy received IRN by a 1-h i.v. infusion at either 20, 24, or 29 mg/m2 daily for 5 consecutive days for 2 weeks. Serial blood samples were collected after doses 1 and 10 of the first course. IRN, SN-38, and APC lactone concentrations were determined by an isocratic high-performance liquid chromatography assay. A linear four-compartment model was fit simultaneously to the IRN, SN-38, and APC plasma concentration versus time data. Systemic clearance rate for IRN was 58.7 +/- 18.8 liters/h/m2 (mean +/- SD). The mean +/- SD ng/ml x h single-day lactone SN-38 area under the concentration-time curve (AUC(0-->6) was 90.9 +/- 96.4, 103.7 +/- 62.4, and 95.3 +/- 63.9 at IRN doses of 20, 24, and 29 mg/m2, respectively. The relative extent of IRN conversion to SN-38 and metabolism to APC measured after dose 1 were 0.49 +/- 0.33 and 0.29 +/- 0.17 (mean +/- SD). No statistically significant intrapatient difference was noted for SN-38 area under the concentration-time curve. Large interpatient variability in IRN and metabolite disposition was observed. The relative extent of conversion and the SN-38 systemic exposure achieved with this protracted schedule of administration were much greater than reported in adults or children receiving larger intermittent doses.
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PMID:Pharmacokinetics of irinotecan and its metabolites SN-38 and APC in children with recurrent solid tumors after protracted low-dose irinotecan. 1074 1

Irinotecan (CPT-11) is an anticancer prodrug. It is converted by carboxylesterase to yield an active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), which acts as a topoisomerase I inhibitor. Several oxidative metabolites of CPT-11 have been identified in humans, including 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC) and 7-ethyl-10-(4-amino-1-piperidino)carbonyloxycamptothecin (NPC), generated by cytochrome P-450 3A4 (CYP3A4). Other minor metabolites in which metabolic pathways and biologic activities have not been identified also exist. To further investigate the metabolism of CPT-11 in human liver, we analyzed metabolites of CPT-11 in human hepatic microsomes using a high-performance liquid chromatography/mass spectrometry (HPLC/MS) system and detected a new metabolite that was the major one produced in the microsomal system. HPLC-tandem mass spectrometry (HPLC/MS/MS) analysis indicated that this compound was an oxidation product formed by the loss of two hydrogen atoms from the terminal piperidine ring. Kinetic analyses indicated that a single enzyme generated the metabolite, and we have identified this enzyme in two in vitro systems. The formation of the new metabolite was significantly inhibited by SKF525A, ketoconazole, and an anti-CYP3A4 antibody and catalyzed specifically by CYP3A4 expressed in insect microsomes. A significant correlation was observed between the generation of this metabolite and the CYP3A4 content in individual human hepatic microsomes. These findings indicate that this newly detected metabolite is a CYP3A4-generated product that may be produced in hepatic microsomes of patients treated with CPT-11.
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PMID:A new metabolite of irinotecan in which formation is mediated by human hepatic cytochrome P-450 3A4. 1160 29

Irinotecan (CPT-11), a water-soluble topoisomerase I inhibitor, is metabolized by carboxylesterase enzymes to form an active metabolite, SN-38. Recent studies have shown that irinotecan also undergoes oxidative metabolism by the P450 isozyme CYP3A4, leading to the formation of a minor inactive metabolite, 7-ethyl-10-[4-N-[(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC). The elucidation of this metabolic pathway suggests the potential for drug interactions when irinotecan is administered with other inducers or substrates of CYP3A4. In this report, the authors summarize the pharmacokinetic profile of irinotecan and its major metabolites with and without concomitant phenytoin administration in an individual patient. These studies revealed that concomitant phenytoin administration resulted in a marked decrease in the systemic exposure to irinotecan and SN-38 and an increase in the exposure to APC. The area under the curve of irinotecan and SN-38 decreased by 63% and 60%, respectively; the area under the curve of APC increased by approximately 16%. Further detailed pharmacokinetic studies of irinotecan in patients receiving concomitant therapy with enzyme-inducing anticonvulsants are required so that rational dosing recommendations can be provided for this patient population.
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PMID:Influence of phenytoin on the disposition of irinotecan: a case report. 1199 Jun 99

Irinotecan (CPT-11), a camptothecin analog, is metabolized to SN-38, an active topoisomerase I inhibitor, and inactive metabolites, including APC and SN-38 glucuronide (SN-38G). A high-performance liquid chromatographic assay method to simultaneously measure the lactone and carboxylate forms of CPT-11, SN-38, SN-38G, and APC in human plasma was developed. Chromatography was accomplished with a reversed-phase C(8) column and fluorescence detection. A gradient mobile phase system was used. The buffer for mobile phase A consisted of 0.75 M ammonium acetate, 5 mM tetrabutylammonium phosphate (pH 6.0), and acetonitrile (86:14, v/v). The buffer for mobile phase B was identical to mobile phase A with the exception of the concentration (50:50, v/v). Precipitation of plasma proteins was performed with cold methanol. The linear range of detection of the lactone and carboxylate forms of SN-38, SN-38G, and APC was 2-25 ng/ml, and 5-300 ng/ml for CPT-11. The limit of quantitation for the analytes ranged from 0.5 to 5 ng/ml. Analysis of patients' plasma samples obtained before and after CPT-11 administration showed that the assay is suitable for measuring lactone and carboxylate forms of CPT-11, SN-38, SN-38G, and APC in clinical studies.
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PMID:High-performance liquid chromatographic assay with fluorescence detection for the simultaneous measurement of carboxylate and lactone forms of irinotecan and three metabolites in human plasma. 1266 72

Irinotecan (CPT-11) is a semisynthetic derivative of camptothecin, an alkaloid extracted from the Chinese plant Camptotheca acuminata. It bears a bis-piperidine moiety and was selected for its water solubility and promising preclinical antitumor activity in in vitro and in vivo models. The target of drugs of the camptothecin family is DNA topoisomerase I, a nuclear enzyme involved in the relaxation of the DNA double helix required for replication and transcription activities. They stabilize the enzyme-DNA complex and prevent the religation of the single-strand breaks created by the enzyme, which are converted to double-strand breaks upon the collision with a replication fork during the S-phase. Resistance to irinotecan appears not to be mediated by P-glycoprotein, but by qualitative and/or quantitative alterations of its target, topoisomerase I, or by alterations occurring downstream of this interaction. As with all camptothecin derivatives, irinotecan contains a lactone ring that can be spontaneously and reversibly hydrolyzed to a carboxylate open ring form, which predominates at neutral and alkaline pH and is inactive on topoisomerase I-DNA complexes. Irinotecan is, in fact, much less active than its metabolite SN-38 and is generally considered as a prodrug of this compound. The carboxylesterase which carries out this conversion is preferentially active on the lactone form of irinotecan and directly generates the lactone form of SN-38, which may explain the superiority of irinotecan over SN-38 in vivo. Further metabolism of SN-38 to a beta-glucuronide conjugate is a major pathway of detoxification and plays an important role in determining irinotecan toxicity in the clinical setting. Other metabolic pathways of irinotecan involve oxidations occurring on the bis-piperidine rings, which are carried out by cytochrome P450. Irinotecan has shown an important activity in advanced and metastatic colorectal carcinoma and is now used for this indication in several countries, with two different recommended schedules: weekly administration of 125 mg/m(2) with a 2-week drug-free interval every 4 administrations or 3-weekly administration of 350 mg/m(2), a dose that can be increased to 500 mg/m(2) with the support of antidiarrhetics. Other possible indications of irinotecan include lung and cervix cancer, which are presently under investigation. The dose-limiting toxicity of irinotecan is mainly diarrhea, which occurs 7-10 days after treatment and can be life-threatening when associated with neutropenia, another frequent side effect. High-dose loperamide has shown good efficacy for treating this diarrhea and has allowed an increase in irinotecan doses tolerated by patients. The pharmacokinetics of irinotecan are characterized by a 2- or 3-compartment decay, with a terminal half-life of about 10 h, a total volume of distribution of 150 l/m(2) and a total plasma clearance of 15 l/h/m(2). SN-38 AUC is only a small fraction of that of irinotecan (2-4%) and SN-38 is eliminated from plasma with a half-life of about 12 h. SN-38 glucuronide is present in plasma at higher concentrations than SN-38 and is eliminated at the same rate. APC, produced by the action of cytochrome P450, isoenzyme 3A4, is present in plasma at concentrations close to those of irinotecan itself. Only a small fraction of irinotecan and its metabolites is eliminated in urine and a higher proportion in the bile, with an enterohepatic cycle of SN-38 glucuronide and SN-38. Significant relationships have been established between the AUCs of both irinotecan and SN-38 and hematological and intestinal toxicities, suggesting a potential use for monitoring of this drug.
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PMID:Pharmacology of irinotecan. 1498 54

Carboxylesterases metabolize ester, thioester, carbamate, and amide compounds to more soluble acid, alcohol, and amine products. They belong to a multigene family with about 50% sequence identity between classes. CES1A1 and CES2 are the most studied human isoenzymes from class 1 and 2, respectively. In this study, we report the cloning and expression of a new human isoenzyme, CES3, that belongs to class 3. The purified recombinant CES3 protein has carboxylesterase activity. Carboxylesterases metabolize the carbamate prodrug 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11; irinotecan) to its active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), a potent topoisomerase I inhibitor. CYP3A4 oxidizes CPT-11 to two major oxidative metabolites, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin (APC) and 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin (NPC). In this study, we investigate whether these oxidative metabolites, NPC and APC, can be metabolized to SN-38 by purified human carboxylesterases, CES1A1, CES2, and CES3. We find that CPT-11, APC, and NPC can all be metabolized by carboxylesterases to SN-38. CES2 has the highest catalytic activity of 0.012 min(-1) microM(-1) among the three carboxylesterases studied for hydrolysis of CPT-11. NPC was an equally good substrate of CES2 in comparison to CPT-11, with a catalytic efficiency of 0.005 min(-1) microM(-1). APC was a very poor substrate for all three isoenzymes, exhibiting a catalytic activity of 0.015 x 10(-3) min(-1) microM(-1) for CES2. Catalytic efficiency of CES3 for CPT-11 hydrolysis was 20- to 2000-fold less than that of CES1A1 and CES2. The relative activity of the three isoenzymes was CES2 > CES1A1 >> CES3, for all three substrates.
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PMID:Hydrolysis of irinotecan and its oxidative metabolites, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin and 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin, by human carboxylesterases CES1A1, CES2, and a newly expressed carboxylesterase isoenzyme, CES3. 1510 Jan 72

In mammalian cells, Cdt1 activity is strictly controlled by multiple independent mechanisms, implying that it is central to the regulation of DNA replication during the cell cycle. In fact, unscheduled Cdt1 hyperfunction results in rereplication and/or chromosomal damage. Thus, it is important to understand its function and regulations precisely. We sought to comprehensively identify human Cdt1-binding proteins by a combination of Cdt1 affinity chromatography and liquid chromatography and tandem mass spectrometry analysis. Through this approach, we could newly identify 11 proteins, including subunits of anaphase-promoting complex/cyclosome (APC/C), SNF2H and WSTF, topoisomerase I and IIalpha, GRWD1/WDR28, nucleophosmin/nucleoplasmin, and importins. In vivo interactions of Cdt1 with APC/C(Cdh1), SNF2H, topoisomerase I and IIalpha, and GRWD1/WDR28 were confirmed by coimmunoprecipitation assays. A further focus on APC/C(Cdh1) indicated that this ubiquitin ligase controls the levels of Cdt1 during the cell cycle via three destruction boxes in the Cdt1 N-terminus. Notably, elimination of these destruction boxes resulted in induction of strong rereplication and chromosomal damage. Thus, in addition to SCF(Skp2) and cullin4-based ubiquitin ligases, APC/C(Cdh1) is a third ubiquitin ligase that plays a crucial role in proteolytic regulation of Cdt1 in mammalian cells.
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PMID:Identification of novel human Cdt1-binding proteins by a proteomics approach: proteolytic regulation by APC/CCdh1. 1816 79


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