Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.21 (CPT)
 4,580 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

CPT-11, a recently developed topoisomerase I (Topo I) inhibitor, attracts the attention not only of basic researchers but also of clinicians because of its high antitumor activity. The CPT-11 resistant human lung cancer cell line, PC-7/CPT, showed 10-fold resistance compared to parental cell line, PC-7. The total activity of Topo I in the resistant cell line was one fourth that of the parental sensitive cell line. The Topo I from the resistant cells was also 5-fold more resistant to the inhibitory effect of CPT-11 than that of the parental cells. We speculated that the alteration of the Topo I gene may be responsible for the change in topoisomerase activity of the CPT-11 resistant cell line. Therefore, we analyzed the mutation of Topo I gene using the method of single strand conformation polymorphism of polymerase chain reaction and the reverse transcriptase. We divided Topo I cDNA into ten fragments which overlapped each other and covered whole coding sequences of the Topo I cDNA. We observed mobility shift of two fragments in the PC-7/CPT, suggesting the presence of some mutations in these fragments. We performed the direct-sequencing of these portions by the dideoxy chain termination method and observed an altered sequence having a G to A base change in PC-7/CPT. This base substitution results in replacement of the conserved threonine at 729 position with alanine. These results suggest that the point mutation of Topo I gene is related to the decreases of Topo I activity and the sensitivity to Topo I inhibitor in PC-7/CPT cells.
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PMID:Detection of topoisomerase I gene point mutation in CPT-11 resistant lung cancer cell line. 133 3

Camptothecin-11 (CPT-11) is a new derivative of camptothecin, a plant alkaloid antitumor agent, and a good candidate for clinical trials because of higher antitumor activity, less toxicity, and high aqueous solubility. CPT-11 is known to be altered into an active form, SN-38, by esterase in in vivo. CPT-11-resistant cells (PC-7/CPT) established from a human non-small cell lung cancer cell (PC-7) by stepwise, continuous treatment with CPT-11 exhibit about a 10-fold increase in resistance to the drug. CPT-11-resistant cells show a moderate cross-resistance to camptothecin (x8.6) and SN-38 (x8.6), and weak cross-resistance to Adriamycin (x2.2) and 5-fluorouracil (x2.4). The comparative studies between the parent (PC-7) and resistant (PC-7/CPT) cell lines with respect to their growth characterization shows a longer cell doubling time (45.8 versus 35.5 h), a lower cloning efficiency (3.2 versus 7.1%), and a lower population of S-phase cells (26.4 versus 36.0%) in the CPT-11-resistant cells. This observation may partly explain the resistance to CPT-11, a drug whose activity is cell cycle specific. Accumulation of CPT-11 is nearly the same in both cell lines. However, the intracellular concentration of SN-38 formed in the parent cells was 2-fold greater than in the CPT-11-resistant cells. This alteration may affect to some extent to the resistance. As assayed by relaxation of supercoiled plasmid DNA, the total activity of DNA topoisomerase I from the CPT-11-resistant cells was shown to be reduced to one-fourth its level in sensitive cells. The reduced activity was caused by a reduction of amount of DNA topoisomerase I. Furthermore, the enzyme from the resistant cells was shown to be 5-fold more resistant to CPT-11 than the enzyme from the parent cells. Thus, decreased total activity of topoisomerase I may play an important role in cellular resistance to CPT-11, and it appears that this decreased activity is due to a resistant form of topoisomerase I in CPT-11 resistant cells.
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PMID:Establishment of a camptothecin analogue (CPT-11)-resistant cell line of human non-small cell lung cancer: characterization and mechanism of resistance. 216 85

A camptothecin-resistant subline of P388 leukemia (P388/CPT) was developed by repeated transplantation of P388 cells in mice treated with therapeutic doses of camptothecin. In mice bearing the resistant tumor, a maximally tolerated dose of camptothecin produced no net reduction in tumor cell burden, in contrast to a 5-log cell kill in the parental P388 (P388/S). The IC50 of camptothecin, as determined by colony formation assays of cultured cells, was 8 times greater for the cloned P388/CPT cell line than for P388/S. P388/CPT cells were not cross-resistant to other antineoplastic agents, including topoisomerase II inhibitors. The type I topoisomerases purified from P388/CPT and P388/S cells were identical with respect to molecular weight, specific activity, in vitro camptothecin sensitivity, and DNA cleavage specificity. Camptothecin induced fewer protein-associated DNA single-strand breaks in the resistant cells than in the wild-type P388 cells. Topoisomerase I mRNA, immunoreactivity, and extractable enzymatic activity were 2-4 times lower for P388/CPT cells than for P388/S cells. As resistance to camptothecin developed, topoisomerase I extractable activity decreased, concomitant with an increase in topoisomerase II extractable activity. Furthermore, the appearance of camptothecin resistance was associated with specific rearrangements of the topoisomerase I gene. These results suggest that development of resistance to inhibitors of topoisomerase I can occur by down-regulation of the target enzyme, thus reducing the production of lethal enzyme-mediated DNA damage. The enhanced topoisomerase II activity in these cells suggests that resistance to camptothecin may be overcome by co-treatment with topoisomerase II inhibitors.
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PMID:Development of a stable camptothecin-resistant subline of P388 leukemia with reduced topoisomerase I content. 217 65

The synthesis and pharmacological activity of a series of terbenzimidazoles are described. The ability of these derivatives to induce DNA cleavage in the presence of topoisomerase I was evaluated in vitro. These analogs were also assayed for their cytotoxicity in RPMI 8402 cells and the camptothecin-resistant CPT-K5 cells. In addition the potential for these compounds to serve as substrates for MDR1 was also determined. Several terbenzimidazoles exhibited similar cytotoxicity against variants of human tumor cells that either overexpress MDR1 or are camptothecin-resistant.
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PMID:Synthesis and evaluation of terbenzimidazoles as topoisomerase I inhibitors. 765 51

The nuclear enzyme topoisomerase I (topo I) has been recently recognized as the target for the anticancer drug camptothecin (CPT; NSC 94600) and its derivatives. This drug has been reported to display effective antitumor effects on a variety of human tumor models xenografted in nude mice. However clinical studies of sodium CPT have revealed that the open-ring form of the drug is a poor inhibitor of topo I and much less potent antitumor agent than CPT lactone. However, the insolubility of CPT lactone makes it difficult to devise a suitable formulation for further clinical testing. In view of these observations, we report here the successful incorporation of CPT into a liposome-based drug delivery system (LCPT) composed of DPPC:Sph:CHOL:PI (2.4:6.6:1.0:0.05 M ratio) that can be used as a suitable formulation for clinical testing of the drug. Higher incorporation efficiency was observed when the total phospholipids:drug ratio = 40 and the cholesterol content = 1%. Image analysis of the CPT-containing liposomes with freeze-fracture electron microscopy has indicated that CPT significantly increased the interlamellar space of the vesicles as a result of its intercalation between lipid bilayers. This has occurred with no major disruptive effects on the bilayer structure. The in vitro drug release study in human serum was characterized by an initial rapid loss-of 50% of contents during 4 h, followed by a slow leakage of the remaining 50% of the total drug over a 20 h period. When tested for its antitumor activity on nude mice xenografted with human malignant melanoma and breast carcinoma, LCPT displayed effective antitumor activity with minimal host toxicity. For example, single i.m. injection of LCPT at 10 mg/kg has produced complete tumor regression to nude mice xenografted with CLO breast carcinoma. Likewise, similar results were obtained with the nude mice xenografted with human malignant BRO cells melanoma. These results appear to suggest that i.m. administration of liposome-incorporated CPT has considerable potential for the treatment of human neoplastic diseases, especially lymph node metastases.
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PMID:Antitumor effect of liposome-incorporated camptothecin in human malignant xenografts. 775 88

The kinetics of the in vivo interconversion of the carboxylate and lactone forms of the prodrug irinotecan, 7-ethyl-10-[4-(1-piperidino)-1- piperidino]carbonyloxycamptothecin (CPT-11), and its active metabolite SN-38 were studied in five patients using a HPLC method that allows the simultaneous determination of all four compounds and detects any hydrolysis of lactones due to inadequate sample handling and storage. The apparent conversion of CPT-11 lactone to the carboxylate in vivo was rapid with a mean half-life of 9.5 min; the carboxylate became the predominant form of plasma CPT-11 soon after the end of the infusion. The ratio of the area under the plasma concentration-time curves of the lactone to total CPT-11 was 36.8 +/- 3.5% (SD). In contrast, SN-38 was present predominantly as the lactone at all times and with little interpatient variability (lactone/total area under the plasma concentration-time curve ratio, 64.0 +/- 3.4%). This may explain in part the promising activity of CPT-11 because CPT derivatives are active against their target, topoisomerase I, only in their lactone form.
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PMID:Kinetics of the in vivo interconversion of the carboxylate and lactone forms of irinotecan (CPT-11) and of its metabolite SN-38 in patients. 798 23

Two sublines of LY murine lymphoma, differing in sensitivity to CPT, served as source of topoisomerase I in order to compare the enzyme's properties. The activity of topoisomerase I isolated from LY-S cells of reduced sensitivity to CPT increased about 2-times more upon phosphorylation with casein kinase but was inhibited to a lesser extent upon dephosphorylation with alkaline phosphatase than the enzyme from the CPT-sensitive LY-R cells. The in vitro phosphorylation of LY-S enzyme restored its sensitivity to CPT. The in vitro incorporation of 32P into topoisomerase protein was about 1.7-times higher in LY-S than in LY-R enzyme. A reversed incorporation ratio was observed upon metabolic labelling. The level of topoisomerase I protein, determined by Western blot analysis using scleroderma anti-topoisomerase I antibodies, was about 1.5-times higher in LY-S than in LY-R cells. The level of topoisomerase I mRNA was similar in both sublines. These results indicate that the reduced sensitivity of LY-S cells to CPT is based on the lowered phosphorylation of topoisomerase I protein but does not depend on the expression of topoisomerase I gene.
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PMID:Topoisomerase I is differently phosphorylated in two sublines of L5178Y mouse lymphoma cells. 799 92

A camptothecin analog, ((4s)-4,11-diethyl-4-hydroxy-9-[(4- piperidinopiperidino)carbonyloxy]dione hydrochloride trihydrate), (CPT-11), is a recently developed topoisomerase I (Topo I) inhibitor which attracts the attention of clinicians because of its high antitumor activity. We established a CPT-11-resistant human ovarian cell line, HAC2/CPT, from the parental HAC2 cell line. An in vitro drug sensitivity assay revealed that HAC2/CPT was 9.7 and 4.7 times as resistant as HAC2 to CPT-11 and 7-ethyl-10-hydroxy-CPT-11 (SN-38), an active metabolite of CPT-11, respectively. HAC2/CPT showed no cross-resistance to other drugs tested (adriamycin, etoposide, cisplatin and Taxol), suggesting that HAC2/CPT acquired a phenotype specifically resistant to the Topo I inhibitor. In order to elucidate the mechanism of the resistance, we measured Topo I activity of HAC2 and HAC2/CPT. The activity of Topo I of HAC2/CPT was reduced to half of that of the parental HAC2 cells. To determine the cause of the decreased activity of Topo I, the mutation of the Topo I gene was searched for by the polymerase chain reaction and the reverse transcriptase analysis. Topo I gene mutation was not detected. The amount of Topo I protein was measured by immunoblotting and a marked decrease of Topo I protein was observed in HAC2/CPT. These results suggest that the decreased protein content of Topo I causes the decreased activity of Topo I and the decreased sensitivity of HAC2/CPT to Topo I inhibitors.
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PMID:Establishment of a CPT-11-resistant human ovarian cancer cell line. 807 81

Hoechst dye 33342 (Ho33342), like many other DNA minor groove binding ligands and its parent compound Hoechst dye 33258 (Ho33258), nonspecifically inhibits the catalytic activities of many DNA enzymes. However, both Ho33258 and Ho33342 also specifically interrupt the breakage/reunion reaction of mammalian DNA topoisomerase I by trapping reversible topoisomerase I cleavable complexes. The enhanced membrane permeability of Ho33342 over its parent compound Ho33258 has allowed studies of the cellular action of Ho33342. Our results suggest that Ho33342 also traps topoisomerase I but not topoisomerase II into reversible cleavable complexes in human KB cells. Although Ho33342 shares a similar mechanism of action with camptothecin, a prototypic topoisomerase I poison, in trapping topoisomerase I cleavable complexes, Ho33342 differs from camptothecin in its effect on drug-resistant cells. Different from camptothecin, Ho33342 was shown to be about 200-fold less cytotoxic in MDR1-overexpressing human KB V1 cells relative to parental human KB 3-1 cells. Ho33342 is only 5-fold less cytotoxic for camptothecin-resistant CPT-K5 cells, which expresses a highly camptothecin-resistant from of topoisomerase I, than for the wild type human lymphoblast RPMI 8402 cells. Our studies suggest a potential use of Hoechst 33342 as a new topoisomerase I poison in antitumor chemotherapy.
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PMID:A new mammalian DNA topoisomerase I poison Hoechst 33342: cytotoxicity and drug resistance in human cell cultures. 838 8

Suramin, a highly sulfonated drug, has been reported to be effective against several human malignancies in vitro and in vivo, and currently is undergoing clinical trials against prostate tumors. The biochemical and molecular mechanisms for suramin's antiproliferative activity are not clear. In order to define the biochemical basis for its antitumor activity and to enhance suramin's chemotherapeutic potential while decreasing its toxicity, we have examined interactions of suramin with topoisomerase I and II and several clinically active anticancer drugs against the human prostate (PC3 and LNCaP) cancer cell line. While etoposide, m-AMSA, camptothecin, and SN-38 (the active metabolite of CPT-11) were active in killing prostate cells as single agents, combinations of suramin and these agents were antagonistic against these cells. We found that suramin inhibited activities of purified topoisomerase I and II in vitro as measured by relaxation and cleavage assays. Further studies indicated that suramin also inhibited the drug-induced DNA damage in vitro and in isolated nuclei. These findings indicate that combinations of suramin with topoisomerase inhibitors, for example, VP-16, m-AMSA, or CPT, may not be beneficial to patients receiving suramin-containing chemotherapy.
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PMID:Suramin inhibits DNA damage in human prostate cancer cells treated with topoisomerase inhibitors in vitro. 839 91


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