Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nuclear enzyme topoisomerase I (topo I) has been recently recognized as the target for the anticancer drug camptothecin (CPT) and its derivatives. Two of the agents that target this enzyme--topotecan (TPT) and CPT-11--appear to be active against a broad range of human tumors. In the following presentation, we review 1) the role of topo I in normal cells, 2) the chemistry and proposed mechanism of action of CPT and its analogues, 3) the results of preclinical and clinical testing of TPT and CPT-11, and 4) mechanisms of resistance to these agents. In normal cells, topo I is thought to be involved in gene transcription and DNA replication. During the course of its normal catalytic cycle, topo I transiently forms a covalent bond with DNA. CPT and its derivatives slow the religation step of the enzyme and stabilize the covalent adduct between topo I and DNA. In S-phase cells, advancing replication forks convert these topo I-DNA adducts into double-strand breaks that appear to be responsible for the cytotoxicity of these agents. Preclinical studies demonstrate antineoplastic activity for TPT and CPT-11 in a variety of tumor models. Phase I studies have identified neutropenia as the dose-limiting toxicity for both drugs. Gastrointestinal effects might also be dose-limiting for CPT-11 administered on some schedules. CPT-11 has shown antitumor activity in phase II trials for patients with carcinomas of lung, cervix, ovary, colon, and rectum and for patients with non-Hodgkin's lymphoma. Phase II studies of TPT are in progress. Resistance to the cytotoxic effects of these agents might result from decreased production of topo I or from production of a mutated form of topo I. In addition, decreased metabolic activation of CPT-11 (which is a pro-drug) and active efflux of TPT by P-glycoprotein-mediated transport might contribute to resistance. As agents with a novel mechanism of action, tolerable toxicity, and encouraging antitumor activity in early clinical trials, TPT and CPT-11 are undergoing further clinical development. If these agents can be successfully combined with other active chemotherapy agents, the topo I-directed agents offer the potential for significant advances in the treatment of patients with a variety of malignancies.
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PMID:The current status of camptothecin analogues as antitumor agents. 838 Nov 86

The overexpression of the multidrug resistance (mdr1) gene and its product, P-glycoprotein (P-gp), is thought to limit the successful chemotherapy of human tumors. Recent studies demonstrate that SN-38, a metabolite of the camptothecin (CPT) derivative CPT-11, has antitumor effects on several tumors, but the mechanisms responsible for its cytotoxicity remain unclear. We therefore determined whether SN-38 has cytotoxic effects on MDR human glioblastoma GB-1 cells and non-MDR human glioblastoma U87-MG cells. Furthermore, we determined what role SN-38 plays in the induction of cytotoxicity in these tumor cells. In this study, we demonstrated that SN-38 had significantly stronger antitumor effects on GB-1 and U-87MG cells than did CPT (P < 0.01 and P < 0.05, respectively). In addition, findings obtained using a DNA fragmentation assay, Hoechst 33258 staining, in situ end-labeling and cell cycle analysis demonstrated that SN-38 induced apoptosis in these tumors. Our results suggest that SN-38 has a stronger antitumor effect on malignant glioma cells regardless of MDR expression than does CPT, and therefore can be considered a new chemotherapeutic agent potentially effective in the treatment of human primary or recurrent malignant gliomas resistant to chemotherapy.
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PMID:Induction of apoptosis in multi-drug resistant (MDR) human glioblastoma cells by SN-38, a metabolite of the camptothecin derivative CPT-11. 905 55

Irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin, (CPT-11) resistance was overcome by using a biscoclaurine alkaloid, cepharanthine, in CPT-11- and multidrug-resistant 50MT-1 cells. 50MT-1 cells were established from a mouse breast-cancer cell line, FM3A, by subjecting the cells to a low dose of CPT-11 continuously. 50MT-1 cells exhibited resistance to CPT-11 (40-fold in colony-formation assay) and to other drugs such as doxorubicin (11.7-fold) and etoposide (VP-16) (16.8-fold). The plasma trans-membrane potential was lower in 50MT-1 cells than in FM3A cells, although there were no differences in expressions of P-glycoprotein and of DNA topoisomerase-I and -II proteins. The lower membrane potential in 50MT-1 cells was augmented by co-treatment with a non-toxic dose of cepharanthine. CPT-11 resistance in 50MT-1 cells was overcome (5.0- to 1.4-fold, 6-hr exposure) by the co-treatment with cepharanthine through increasing intracellular accumulation of CPT-11. Resistance to doxorubicin and VP-16 was also overcome by cepharanthine treatment (2.5- to 0.69-fold and 4.2- to 1.4-fold respectively). We conclude that the modification of plasma trans-membrane potential by cepharanthine should be effective in overcoming CPT-11 and multidrug resistance in 50MT-1 cells.
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PMID:Overcoming CPT-11 resistance by using a biscoclaurine alkaloid, cepharanthine, to modulate plasma trans-membrane potential. 921 36

A frequent dose-limiting effect of irinotecan (CPT-11) is its gastrointestinal toxicity (diarrhea), which is thought to be related to biliary excretion of CPT-11 and its metabolites. Accordingly, we have investigated the mechanism of biliary excretion of these compounds. In vivo pharmacokinetic studies revealed that the biliary excretion of the four anionic forms of CPT-11 and its metabolites was reduced in Eisai hyperbilirubinemic rats, which carry a mutation of the hepatic canalicular multispecific organic anion transporter (cMOAT) gene. The protein encoded by this gene is expressed on the bile canalicular membrane and is responsible for the transport of organic anions into bile. Detailed analysis using isolated liver bile canalicular membrane vesicles to identify transport systems showed that cMOAT is responsible for biliary excretion of the low-affinity component of the carboxylate form of CPT-11 and the high-affinity component of both the lactone and carboxylate forms of SN-38 glucuronide. The carboxylate form of SN-38 is transported by cMOAT alone. Transport of the high-affinity component of CPT-11 was inhibited by verapamil and PSC-833, but their effect on the transport of its low-affinity component was minimal. In addition, ATP dependence in the uptake of CPT-11 by membrane vesicles obtained from a P-glycoprotein (P-gp)-overexpressing cell line was observed. Thus P-gp may be responsible for transport of the high-affinity component of the carboxylate form of CPT-11.
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PMID:Multiplicity of biliary excretion mechanisms for the camptothecin derivative irinotecan (CPT-11), its metabolite SN-38, and its glucuronide: role of canalicular multispecific organic anion transporter and P-glycoprotein. 975 28

To investigate the possible involvement of P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and/or other glutathione S-conjugate export pump (GS-X pump) family members on the active efflux of irinotecan [(7-ethyl-10-[4-(1-piperidino)-1-pipertidino)-1-piperidino]carb onylox y camptothecin (CPT-11)] and its metabolites, as well as their contribution to the acquisition of resistance, we studied the uptake of CPT-11, its active metabolite SN-38, and glucuronide conjugate (SN38-Glu) using membrane vesicles from human epidermoid KB-3-1-derived cell lines. These lines included KB-C2, C-A500, and KCP-4, which overexpress P-gp, MRP, and the unidentified GS-X pump, respectively. The carboxylate form of SN-38 exhibited significant ATP-dependent transport, with a Michaelis constant of 17 microM, into membrane vesicles from C-A500 but not from other cell lines. Among these KB-derived cells, significant ATP-dependent uptake of the carboxylate form of CPT-11 was only observed in KB-C2 vesicles. In addition, the uptake of the lactone and carboxylate forms of SN38-Glu into membrane vesicles from C-A500 and KB-C2, but not KCP-4, was ATP dependent, although the transport activity in C-A500 was much higher than that in KB-C2. The 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay revealed that the resistance of KB-C2 to CPT-11 and SN-38, compared with that of KB-3-1, was 6.3- and 6.8-fold, respectively; the corresponding figures for C-A500 were 12- and 27-fold, respectively, whereas those for KCP-4 were 2.3- and 20-fold, respectively. These results suggest that MRP and P-gp are involved in the active efflux of SN-38 and CPT-11, respectively, from human KB-derived cells. In addition, a difference in substrate specificity among GS-X pump members was demonstrated.
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PMID:Active efflux of CPT-11 and its metabolites in human KB-derived cell lines. 991 83

In our previous work, we found that the biliary excretion of the carboxylate form of irinotecan, CPT-11, on rat bile canalicular membrane consists of two components, the low-affinity one being canalicular multispecific organic anion transporter (cMOAT). In the present study, we have investigated the high-affinity component by studying the uptake in canalicular membrane vesicles. The ATP-dependent uptake of the carboxylate form of CPT-11 was inhibited significantly by several substrates and/or modulators of P-glycoprotein, including PSC-833, verapamil, and cyclosporin A, at a substrate concentration of 5 microM, at which the high-affinity component is involved predominantly in CPT-11 transport. When the concentration of the carboxylate form of CPT-11 was 250 microM, at which the low-affinity component (cMOAT) is involved predominantly in its transport, the inhibitory effect of the above compounds was reduced greatly. Similarly, there was also much lower inhibition of the ATP-dependent uptake of S-(2,4-dinitrophenyl)-glutathione, a substrate of cMOAT, by the above compounds. Taurocholic acid, a substrate of canalicular bile acid transporter, failed to inhibit the uptake of CPT-11 at the substrate concentration of both 5 and 250 microM. These results suggest that P-glycoprotein may act as the high-affinity component in the biliary excretion of the carboxylate form of CPT-11 in rats.
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PMID:Possible involvement of P-glycoprotein in biliary excretion of CPT-11 in rats. 1010 Nov 37

Non-P-glycoprotein-mediated multidrug-resistant C-A120 cells that overexpressed multidrug resistance protein (MRP) were 10.8- and 29. 6-fold more resistant to 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) and SN-38, respectively, than parental KB-3-1 cells. To see whether MRP is involved in CPT-11 and SN-38 resistance, MRP cDNA was transfected into KB-3-1 cells. The transfectant, KB/MRP, which overexpressed MRP, was resistant to both CPT-11 and SN-38. 2-[4-Diphenylmethyl)-1-piperazinyl]ethyl-5-(trans-4,6-dimethyl-1,3 , 2-dioxaphosphorinan-2-yl)-2, 6-dimethyl-4-(3-nitrophenyl)-3-pyridinecarboxylate P-oxide (PAK-104P) and MK571, which reversed drug resistance in MRP overexpressing multidrug-resistant cells, significantly increased the sensitivity of C-A120 and KB/MRP cells, but not of KB-3-1 cells, to CPT-11 and SN-38. The accumulation of both CPT-11 and SN-38 in C-A120 and KB/MRP cells was lower than that in KB-3-1 cells. The treatment with 10 microM PAK-104P increased the accumulation of CPT-11 and SN-38 in C-A120 and KB/MRP cells to a level similar to that found in KB-3-1 cells. The ATP-dependent efflux of CPT-11 and SN-38 from C-A120 and KB/MRP cells was inhibited by PAK-104P. DNA topoisomerase I expression, activity, and sensitivity to SN-38 were similar in the three cell lines. Furthermore, the conversion of CPT-11 to SN-38 in KB-3-1 and C-A120 cell lines was similar. These findings suggest that MRP transports CPT-11 and SN-38 and is involved in resistance to CPT-11 and SN-38 and that PAK-104P reverses the resistance to CPT-11 and SN-38 in tumors that overexpress MRP.
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PMID:ATP-Dependent efflux of CPT-11 and SN-38 by the multidrug resistance protein (MRP) and its inhibition by PAK-104P. 1022 May 71

Cisplatin-resistant KCP-4 cells were 12.4- and 31.6-fold more resistant to CPT-11 and SN-38 than parental KB-3-1 cells, respectively. We studied the mechanism of cross-resistance to CPT-11 and SN-38. Our previous study showed that multidrug resistance protein (MRP), canalicular multispecific organic anion transporter (cMOAT) and P-glycoprotein (P-gp) were not expressed in KCP-4 cells (Chen, Z.-S. et al., Exp. Cell Res., 240 (1998) 312-320, and Chuman, Y. et al., Biochem. Biophys. Res. Commun., 226 (1996) 158-165). The accumulation of both CPT-11 and SN-38 in KCP-4 cells was lower than that in KB-3-1 cells. The ATP-dependent efflux of CPT-11 and SN-38 from KCP-4 cells was enhanced compared with that from KB-3-1 cells. DNA topoisomerase (topo) I expression, topo I activity, topo I-mediated cleavable complex, and the sensitivity to SN-38 of DNA topo I in KCP-4 were similar to those in KB-3-1 cells. Furthermore, the conversion of CPT-11 to SN-38 in the two cell lines was also similar. The transport of LTC4 in KCP-4 membrane vesicles was competitively inhibited by bis-(glutathionato)-platinum (II) (GS-Pt), CPT-11 and SN-38. These findings suggested that an unknown transporter distinct from P-gp, MRP or cMOAT is expressed in KCP-4 cells and transports CPT-11 and SN-38.
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PMID:An enhanced active efflux of CPT-11 and SN-38 in cisplatin-resistant human KB carcinoma cells. 1037 68

20 (S) Camptothecin was discovered in the early 60's as a result of the intensive screening of natural products by the NCI. Camptothecin lactone was poorly water soluble and was administered as the sodium salt in phase I trials. Despite some encouraging responses in early studies, continued evaluation of this compound revealed severe and unpredictable toxicities such as haemorrhagic cystitis and diarrhoea. The reversible opening of the lactone ring of a camptothecin is pH-dependent and yields a ring-opened carboxylate form which has greatly reduced activity in vivo and in vitro. Under physiological conditions, the carboxylate form predominates, but the exact position of this equilibrium in vivo also depends on other factors such as protein-binding and differential metabolism and elimination. The site of action of camptothecin is a complex formed by the nuclear enzyme topoisomerase I and DNA, which represents a novel target for cancer chemotherapy. The principal role of topoisomerase I is the relaxation of DNA required for transcription and replication. The transient covalent complexes formed by the linking of the enzyme and the 3' extremity of a nicked DNA strand are stabilised in the presence of camptothecin and involved in collisions with replication forks. The ensuing arrest of the fork is accompanied by the generation of permanent double-strand breaks which are thought to be responsible for the antiproliferative properties of camptothecin. The acquisition of resistance to camptothecin in cell culture appears, in general, to be due to a reduction in content and activity of topo-isomerase I. Single-point mutations of the gene of the enzyme have been detected in a number of these resistant variants. Camptothecin appears to be a poor substrate of P-glycoprotein and its intracellular accumulation is not appreciably reduced in cells expressing the multidrug-resistant phenotype. Several water soluble and active derivatives of camptothecin have been synthetized of which CPT-11 and topotecan are the most advanced in clinical trials. These compounds represent two different approaches to the problem of the poor water solubility of camptothecin lactone. CPT-11 is a soluble prodrug which is converted in vivo to the highly active SN-38, whereas topotecan itself is water-soluble due to the presence of a tertiary amine substitution which is charged at physiological pH. These two compounds present different pharmacological properties in the clinical setting.
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PMID:[Pharmacology of camptothecin and its derivatives]. 1084 37

DX-8951f, a new water-soluble camptothecin (CPT) derivative, has been reported to show potent antitumor effects against various tumors in vitro and in vivo. We further evaluated the cytotoxic effect of DX-8951f against eight drug-resistant sublines derived by stepwise exposure of human oat cell carcinoma PC-6 to various drugs. In paclitaxel-, adriamycin-, vincristine- and etoposide-resistant cells, overexpression of P-glycoprotein (P-gp) and a correlative reduction in drug accumulation and typical drug-sensitivity pattern were confirmed. The etoposide-resistant line with the highest P-gp level was cross-resistant also to SN-38, CPT-11 and topotecan (TPT), but not to 9-aminocamptothecin (9-AC), CPT and DX-8951f. SN-38- and CPT-11-resistant cells, of which topoisomerase I activities and levels were similar to those of the parent cells, showed cross-resistance clearly to TPT, 9-AC and mitoxantrone, but hardly to DX-8951f. In these two resistant sublines, the intracellular topotecan level was significantly lower than that in parental PC-6 and the reduced accumulation was found to be mediated by breast cancer resistant protein (BCRP). The cisplatin-resistant variant, which had a 2-fold increase in glutathione content, showed no cross-resistance and the 5-fluorouracil-resistant variant, which had a 50% decrease in glutathione content, exhibited collateral sensitivity to most of the other anticancer agents including DX-8951f. We concluded that DX-8951f showed a potent cytotoxic effect on various types of drug-resistant cells.
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PMID:Growth inhibitory effect of a new camptothecin analog, DX-8951f, on various drug-resistant sublines including BCRP-mediated camptothecin derivative-resistant variants derived from the human lung cancer cell line PC-6. 1091 51


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