Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.31 (beta-glucuronidase)
 7,680 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Irinotecan (7-ethyl-10-[4-[1-piperidino]-1-piperidino]carbonyloxycampothecin) , also known as CPT-11, is a promising semi-synthetic derivative of camptothecin with significant activity against a range of tumor types. The pharmacokinetic behaviour of its principal and presumedly active metabolite, SN-38 (7-ethyl-10-hydroxy-camptothecin), displays wide inter-patient variation. During the high-performance liquid chromatographic (HPLC) analysis of plasma samples collected from a patient given CPT-11, we observed several unidentified peaks that were not present in pre-infusion samples. In this paper we describe the manner in which one of these was determined to be a beta-glucuronide of SN-38. The total plasma concentrations of this metabolite were quantified following digestion with beta-glucuronidase and were found to be greater than those of SN-38 in the patient studied. The elimination phases of the plasma concentration profile of SN-38 and its glucuronide were parallel, suggesting that the transformation of SN-38 to the glucuronide is the rate-limiting step in the elimination of SN-38 and could play a key role in its pharmacokinetics.
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PMID:Identification and kinetics of a beta-glucuronide metabolite of SN-38 in human plasma after administration of the camptothecin derivative irinotecan. 776 55

Irinotecan (CPT-11 [Camptosar]), a semisynthetic derivative of the plant alkaloid camptothecin, is bioactivated by carboxylesterases (EC3.1.1-) to the topoisomerase I inhibitor SN-38, a minor metabolite. Bioactivation of intravenously administered irinotecan by carboxylesterases occurs predominantly in the liver. Two human carboxylesterase isoforms responsible for SN-38 formation have been characterized. At relevant hepatic irinotecan concentrations up to 12 micrograms/mL, a low-Km isoform is responsible for irinotecan bioactivation. High concentrations of drugs commonly coadministered with irinotecan do not inhibit carboxylesterase activity. Intestinal carboxylesterases can also generate SN-38, followed by subsequent oral absorption. A second major polar metabolite of irinotecan, aminopentanecarboxylic acid (APC), is the product of CYP3A4-mediated oxidation of the terminal piperidine ring. APC is 100-fold less active than SN-38 as a topoisomerase I inhibitor and is a relatively weak inhibitor of acetylcholinesterase. SN-38 is eliminated mainly through conjugation by hepatic uridine glucuronosyltransferase (UGT*1.1), the same isoezyme responsible for glucuronidation of bilirubin. Grade 4 irinotecan-related toxicity (ie, neutropenia, diarrhea) has recently been reported in two patients with deficient UGT*1.1 activity. SN-38 glucuronide (SN-38G), which has only 1/100th the antitumor activity of SN-38, is actively secreted into the bile by a canalicular multispecific organic anion transporter. Deconjugation of SN-38G to SN-38 by beta-glucuronidase produced by the intestinal flora may contribute to enterohepatic recirculation of SN-38 and delayed intestinal toxicity.
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PMID:Pharmacology of irinotecan. 972 89

Irinotecan (CPT-11) is a prodrug that is used to treat metastatic colorectal cancer. It is activated to the topoisomerase poison SN-38 by carboxylesterases. SN-38 is subsequently metabolised to its inactive glucuronide, SN-38G, which can however be reactivated to SN-38 by beta-glucuronidase. The purpose of this study was to examine the role of carboxylesterases and beta-glucuronidase in the in vitro production of SN-38 in human colorectal tumours. The production of SN-38 from CPT-11 and SN-38G was measured by HPLC in human colorectal tumour homogenates. Carboxylesterase and beta-glucuronidase activities were found to be lower in tumour tissues compared to matched normal colon mucosa samples. In colorectal tumour, beta-glucuronidase and carboxylesterase-mediated SN-38 production rates were comparable at clinically relevant concentrations of SN-38G and CPT-11, respectively. Therefore, tumour beta-glucuronidase may play a significant role in the exposure of tumours to SN-38 in vivo, particularly during prolonged infusions of CPT-11.
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PMID:The relative contributions of carboxylesterase and beta-glucuronidase in the formation of SN-38 in human colorectal tumours. 1453 29

Irinotecan (CPT-11) is a clinically important anticancer prodrug that requires enzymatic hydrolysis by carboxyesterase to generate the active metabolite SN-38. However, SN-38 is further metabolized to inactive SN-38 glucuronide (SN-38G), thus diminishing the levels of active SN-38. Although exogenously administered glucuronide drugs are being investigated for cancer therapy, it is unknown if endogenously generated camptothecin glucuronide metabolites can be used for tumor therapy. Here, we tested the hypothesis that tumor-located hydrolysis of endogenously generated SN-38G can enhance the antitumor efficacy of CPT-11 therapy. EJ human bladder carcinoma cells expressing membrane-tethered beta-glucuronidase (EJ/mbetaG cells) were used to selectively hydrolyze SN-38G to SN-38. Parental EJ and EJ/mbetaG cells displayed similar in vitro and in vivo growth rates and sensitivities to CPT-11 and SN-38. By contrast, EJ/mbetaG cells were more than 30 times more sensitive than EJ cells to SN-38G, showing that SN-38 could be generated from SN-38G in vitro. Systemic administration of CPT-11 resulted in tumor-located hydrolysis of SN-38G and accumulation of SN-38 in EJ/mbetaG subcutaneous tumors. Importantly, systemic administration of CPT-11, which itself is not a substrate for beta-glucuronidase, dramatically delayed the growth of EJ/mbetaG xenografts without increased systemic toxicity. Thus, the anticancer activity of CPT-11 can be significantly enhanced by converting the relatively high levels of endogenously generated SN-38G to SN-38 in tumors. The high concentrations of SN-38G found in the serum of patients treated with CPT-11 suggest that clinical response to CPT-11 may be improved by elevating beta-glucuronidase activity in tumors.
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PMID:Local enzymatic hydrolysis of an endogenously generated metabolite can enhance CPT-11 anticancer efficacy. 1937 67

Chemotherapy-induced diarrhoea is a major oncological problem, caused by the cytotoxic effects of cancer chemotherapy. Irinotecan is linked with severe mucositis and diarrhoea, the mechanisms of which remain poorly understood. Bacterial beta-glucuronidase is thought to be involved in the metabolism of irinotecan, implicating the intestinal flora. Intestinal mucins may also be implicated in the development of chemotherapy-induced diarrhoea. Rats were treated with 200 mg/kg of irinotecan and killed at 96, 120 and 144 h. The rats were monitored for diarrhoea. Pathology and immunohistochemical staining was performed. The samples were cultured and faecal DNA was analysed using real-time polymerase chain reaction. Severe diarrhoea was observed from 72 to 96 h. A decrease in body mass was also observed after treatment. Significant changes in goblet cell numbers (both complete and cavitated cells) were observed in the small and large intestines. Changes in MUC gene expression were observed in the small intestine only. Modifications were observed to the intestinal flora profile, especially Escherichia coli, and an increase in the expression of beta-glucuronidase was detected. In conclusion, irinotecan-induced diarrhoea may be caused by an increase in some beta-glucuronidase-producing bacteria, especially E. coli, exacerbating the toxicity of active metabolites. Accelerated mucous secretion and mucin release may also contribute to the delayed onset of diarrhoea.
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PMID:Irinotecan-induced mucositis manifesting as diarrhoea corresponds with an amended intestinal flora and mucin profile. 1976 3