Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.1.1.17 (ornithine decarboxylase)
 6,351 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Treatment of 9L cells with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) depletes cells of putrescine and spermidine and sensitizes cells to the cytotoxic effects of the alkylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea. Because depletion of intracellular levels of the sulfhydryl compound glutathione also increases the cytotoxicity of alkylating agents, the effect of DFMO on intracellular glutathione content was investigated to determine whether DFMO-induced sensitization could be explained by a sulfhydryl-related mechanism. Treatment of 9L cells with 1 mM DFMO caused no change in the glutathione concentration within 48 h; sensitization of cells to 1,3-bis(2-chloroethyl)-1-nitrosourea is generally studied after 48 h of treatment with DFMO. Incubation of cells with DFMO for longer periods caused an increase in glutathione that is related to the depletion of polyamines and not to a decrease in growth rate or a cell cycle effect. Increased glutathione content is not due to a decrease in glutathione catabolism, but rather to an apparent increase in the rate of synthesis of the tripeptide.
 ...
PMID:Changes in the glutathione content of rat 9L cells induced by treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine. 311 62

We have investigated the effect of pretreatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) on the cytocidal efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in a series of five cultured human adenocarcinoma cell lines. Plating efficiency assays were used to generate BCNU dose-response survival curves for DFMO-treated and control cells. The cell lines varied in their sensitivity to BCNU, with A-427 (lung) and HuTu-80 (duodenum) cells being most sensitive, HT-29 (colon) and ME-180 (cervix) most resistant, and MCF-7 (breast) showing intermediate sensitivity. For all five cell lines, a 48-h pretreatment with 5 mM DFMO reduced intracellular putrescine and spermidine content to less than 10% of control levels and decreased spermine content to between 60 and 70% of controls. This pretreatment resulted in a shift of the BCNU survival curves for each of the five cell lines downward and to the left, indicating that the cells were sensitized to the lethal effects of BCNU. Dose enhancement ratios for DFMO-induced chemosensitization ranged from 1.2 (HuTu-80 cells at the 1% survival level) to 1.9 (HT-29 cells at the 10% survival level). The cell lines most resistant to BCNU appeared to give the greatest degree of potentiation by DFMO pretreatment. For four of the five cell lines, addition of 50 to 100 microM exogenous putrescine to DFMO-pretreated cultures 12 to 24 h before BCNU addition reversed the chemosensitization. ME-180 cells were the sole exception. Exogenous putrescine did not increase the surviving fraction after BCNU of any cells not pretreated with DFMO. These results suggest that DFMO-induced chemosensitization to BCNU in the four cell lines other than ME-180 is a specific consequence of the inhibition of ornithine decarboxylase by DFMO and the resulting depletion of intracellular polyamine content.
 ...
PMID:Chemosensitization of cultured human carcinoma cells to 1,3-bis(2-chloroethyl)-1-nitrosourea by difluoromethylornithine-induced polyamine depletion. 392 Dec 37

alpha-Difluoromethylornithine, an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, inhibited the growth of both chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro. After 48 hr of treatment with 10 mM alpha-difluoromethylornithine, the putrescine and spermidine contents of both resistant and sensitive cells were less than 5% of control levels, but the spermine level was slightly elevated. The cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea, as measured by a colony-forming efficiency assay, was significantly increased in alpha-difluoromethylornithine-pretreated sensitive cells but not in resistant cells treated with this polyamine inhibitor. With the sister chromatid exchange assay, we found that alpha-difluoromethylornithine pretreatment increased 1,3-bis(2-chloroethyl)-1-nitrosourea-induced damage to chromosomes in sensitive but not in resistant cells.
 ...
PMID:Differential potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea by alpha-difluoromethylornithine in chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro. 640 51

Polyamine depletion by pretreatment with alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase, potentiates the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in L1210 leukemia cells grown in a modified soft agar system. The dose enhancement ratio was 1.97 at a control colony formation level of 5%. The basis for this enhancement was investigated at the level of DNA damage using a modified fluorometric assay to quantitate the production of alkaline-labile strand breaks per relative DNA molecular mass. Pretreatment of cultured L1210 cells for 48 hr with 5 mM DFMO depleted intracellular putrescine and spermidine (but not spermine) pools and resulted in a 2.3-fold increase in BCNU-induced (10 micrograms/ml, 2 hr) DNA strand breaks per relative DNA molecular mass. The inclusion of 10 microM spermidine during the DFMO pretreatment fully prevented growth inhibition and enhancement of BCNU-induced DNA damage while maintaining cellular spermidine pools at control levels. The inclusion of 2 microM putrescine or spermidine also prevented growth inhibition and enhancement of DNA damage while maintaining spermidine pools at only 25 to 35% of control. Thus, the portion of spermidine essential for cell growth appears to be associated with DNA. BCNU itself was found to reduce cellular polyamine levels by causing their leakage from cells. In addition, BCNU was found to react directly with spermidine in a cell-free system, resulting in a major reaction product detectable by high-performance liquid chromatography. While decreased interaction of BCNU with polyamines could account, in part, for enhancement effects of DFMO, it is more probable that alterations in DNA structure secondary to polyamine depletion are responsible for these effects.
 ...
PMID:Enhancement of 1,3-bis(2-chloroethyl)-1-nitrosourea-induced cytotoxicity and DNA damage by alpha-difluoromethylornithine in L1210 leukemia cells. 643 May 55

alpha-Difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase, was used alone and in combination with various single doses of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to treat animals bearing murine glioma 26 and rat 9L gliosarcoma intracerebral tumors. Used as a single agent, DFMO has little or no effect against these tumors. However, in both intracerebral tumor models, pretreatment with DFMO p.o. before i.p. administration of BCNU potentiates the effect of BCNU without increasing toxicity. The effects of DFMO administered p.o. after BCNU or before and after various doses of BCNU indicate that DFMO may also effectively slow the repopulation of these tumors after BCNU therapy.
 ...
PMID:Potentiation of the antitumor therapeutic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea by alpha-difluoromethylornithine, an ornithine decarboxylase inhibitor. 679 58

O6-Alkylguanine-DNA alkyltransferase (AGT) activity is associated with resistance of brain tumor cell lines to the cytotoxic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). SF-763 cells exhibit high AGT activity and are resistant to BCNU. In this study, we compared the effects of the AGT inhibitor O6-benzylguanine (BG) on the cytotoxicity of BCNU in oxic and hypoxic SF-763 cells; we also measured AGT activity, ornithine decarboxylase (ODC) activity, and polyamine levels to determine if there was any correlation with cell survival as determined by colony-forming efficiency assay. Exponentially growing monolayer cells were pretreated with 10 microM BG for 2 h under oxic or hypoxic (95% nitrogen/5% CO2) conditions and then exposed to graded concentrations of BCNU for 1 h. BG significantly lowered AGT activity but had no cytotoxic effect in oxic or hypoxic cells; hypoxia alone was not cytotoxic. The cytotoxicity of BCNU was 4 times higher in BG-treated hypoxic cells than in oxic cells treated with BCNU alone; the BCNU doses required for a 1-log cell kill were 75 and 300 microM, respectively. ODC activity was lowered by hypoxia alone but was not significantly affected by BG in either hypoxic or oxic cells. Polyamine levels were not significantly affected by hypoxia or BG. These results indicate that pretreatment with BG dramatically lowers AGT activity and increases the cytotoxicity of BCNU in both oxic and hypoxic SF-763 cells. The mechanism of this enhanced cytotoxicity is apparently unrelated to ODC activity or polyamine levels.
 ...
PMID:The effects of O6-benzylguanine and hypoxia on the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea in nitrosourea-resistant SF-763 cells. 825 97

Inhibitors of ornithine decarboxylase (ODC), such as alpha-difluoromethylornithine (DFMO), may influence the cytotoxicity of anti-tumour agents that interact with DNA. Intracellular levels of putrescine and spermidine were markedly reduced by ODC inhibitors while the level of spermine, which is the main polyamine in nuclei, was unchanged. By combining a novel inhibitor of ODC, such as (2R, 5R)-6-heptyne-2,5-diamine (MDL 72.175, MAP), with an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), such as 5'-[[(Z)-4-aminobut-2-enyl]methylamino]-5'-deoxyadenosine (MDL 73.811, AbeAdo), spermine was selectively depleted in a human ovarian cancer cell line OVCAR-3 (i.e. spermine became almost undetectable whereas the levels of spermidine and putrescine were not affected). The depletion of spermine blocked DNA synthesis with a consequent accumulation of cells in the G1 phase of the cell cycle. Pretreatment with MAP plus AbeAdo did not change the cytotoxicity of alkylating agents, such as L-phenylalanine mustard (L-PAM), 1,4-bis(2'-chloroethyl)-1,4-diazabicyclo-[2.2.1] heptane diperchlorate (DABIS), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), cis-diamminedichloroplatinum (II) (cis-DDP), N-deformyl-N-[4-N-N,N-bis (2-chloroethylamino)benzoyl] (tallimustine) or CC-1065, whereas it markedly reduced the cytotoxicity of DNA topoisomerase II inhibitors, such as doxorubicin (DX) and 4'-demethylepipodophyllotoxin-5-(4,6-O)-ethylidene- beta-D-glycopyranoside (VP-16). The addition of spermine before drug treatment restored the sensitivity to the DNA topoisomerase II inhibitors, thus indicating that the reduced effect was related to the intracellular spermine level. The reason for the reduction in cytotoxicity is unclear, but it does not appear to be related to a cell cycle effect or to a decrease in the intracellular level of DNA topoisomerase II. Drugs that modify polyamine biosynthesis are under early clinical development as potential new anti-tumour agents. These findings illustrate the need for caution in combining such drugs with DNA topoisomerase II inhibitors.
 ...
PMID:Treatment with inhibitors of polyamine biosynthesis, which selectively lower intracellular spermine, does not affect the activity of alkylating agents but antagonizes the cytotoxicity of DNA topoisomerase II inhibitors. 908 39