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)

Topoisomerase (topo) inhibitors induce enzyme-linked DNA breaks. Resulting DNA damage can lead to cell cycle arrest and/or cell death by apoptosis. The sensitivity of five human leukemic cell lines to topo I (camptothecin or CPT) and topo II (etoposide or VP-16) inhibitors varied widely (100-fold for CPT and 30-fold for VP-16). Three cell lines were more sensitive (BV173, HL60, U937) and two cell lines were resistant (K562, KCL22) to both drugs. None of these cell lines were selected for drug resistance and overexpressed mdr1 gene. Their sensitivity was not related to their doubling time nor to cell cycle repartition. The initial DNA damage (cleavable complexes) induced by topo I and II inhibitors was measured as DNA-protein crosslinks (DPC) using alkaline elution. Neither DPC level induced by 30-min treatment with CPT or VP-16 nor the levels of topo 1, topo II alpha and topo II beta mRNA were related to sensitivity. Electron microscopy and DNA fragmentation measured by filter elution and agarose gel electrophoresis demonstrated that apoptosis was induced by both drugs in the five cell lines. The kinetics of DNA fragmentation was related to cell sensitivity. At drug concentrations higher than IC50, DNA fragmentation increased very rapidly in the three sensitive, compared with the two resistant, cell lines. Continuous exposure to both drugs induced cell cycle arrest in either G2 or S phase that was related both to cell sensitivity and drug concentration. Comparison between cell lines indicated that the ability of cells to arrest cell cycle in G2 or S phase was related to their drug sensitivity and increased with cell resistance. In a given cell line, cell cycle progression was observed to be progressively inhibited by increasing drug concentrations. Treatment of synchronized cells demonstrated that highly cytotoxic drug concentration induced a complete inhibition of cell cycle progression. Altogether, these data suggest that the ability of leukemic cell lines to regulate cell cycle progression and to trigger apoptosis is more indicative of their sensitivity to topoisomerase poisons than cleavable complexes induced by these drugs.
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PMID:The role of cell cycle regulation and apoptosis triggering in determining the sensitivity of leukemic cells to topoisomerase I and II inhibitors. 759 66

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

Telomerase, a ribonucleoprotein that adds telomeric repeats onto chromosome ends, is involved in telomere length maintenance and permits unlimited cell proliferation. We examined the possibility that higher telomerase activity is associated with the replicative phase of the cell cycle using gastric cancer cell lines treated with anticancer drugs. Telomerase activity increased at the time point of S-phase accumulation in NUGC-3 cells (5 x 10(5) cells/ml) incubated with CDDP (0.5 microgram/ml), paclitaxel (0.01 microM), or VP-16 (1 microM) and in MKN-28 cells incubated with CDDP. When these cell lines were incubated with 5-fluorouracil (10 microM) or CPT (0.1 microM), the increase of telomerase activity preceded the S-phase accumulation. Our results suggest that telomerase activity be regulated by the cell cycle.
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PMID:[Telomerase activity during the cell cycle in gastric cancer cell lines]. 961 22

TAS-103 is a novel anticancer agent targeting both topoisomerase (Topo) I and Topo II, that stabilizes cleavable complexes of Topo-DNA at the cellular level. In this study, the in vitro antitumor effects of TAS-103 were compared with those of other known Topo I and Topo II inhibitors. TAS-103 inhibited DNA synthesis more strongly than RNA and protein synthesis, and induced an increase of cell population in the S-G2/M phase. The cytotoxicity of TAS-103 was strongest against S-phase cells, but its cell cycle phase specificity was not clear, and depended on drug concentration and exposure time. The cytotoxicity of TAS-103 (IC50: 0.0030-0.23 microM) against various tumor cell lines was much stronger than that of VP-16 and comparable to that of SN-38. The cytotoxicity of TAS-103 seemed to be more related to the amount of protein-DNA complexes than to the accumulation of TAS-103 in the cells. P-Glycoprotein (P-gp)-mediated MDR, CDDP-resistant and 5-FU-resistant cell lines did not show cross-resistance to TAS-103. Although PC-7/CPT cells bearing a Topo I gene mutation showed cross-resistance to TAS-103, the sensitivity of P388/CPT, HT-29/CPT and St-4/CPT cells, showing decreased Topo I expression, was not changed. KB/VM4 and HT-29/Etp cells, showing decreased Topo II expression, were slightly cross-resistant to TAS-103. These results suggest that TAS-103 may act as an inhibitor of both Topo I and Topo II at the cellular level. This property may be responsible for its strong antitumor effect and broad-spectrum, growth-inhibitory effect on drug-resistant cell lines.
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PMID:In vitro antitumor activity of TAS-103, a novel quinoline derivative that targets topoisomerases I and II. 1039 Oct 99