Ornithine decarboxylase activity and the growth of neuroblastoma cells. The effects of bromoacetylcholine, bromoacetate and 1,3-diaminopropane

Partial purification and characterization of ornithine decarboxylase from Entamoeba histolytica

Multiplication of E. histolytica was accompanied by a parallel increase in ornithine decarboxylase (ODC) specific activity up to 72 h of cultivation in TYI-S-33 medium. Thereafter, activity rapidly decayed whereas growth continued for another 24 h before entering into the stationary growth phase. ODC was very unstable. Partial purification (14-fold) of the enzyme was achieved by a three-step procedure involving high-speed centrifugation, gel filtration and adsorption to hydroxylapatite. The partially purified enzyme (Mr 211 kDa) revealed maximum activity at pH 8.5-9.0 and a sigmoidal response to substrate concentration. An S0.5 value of 1.0 mM ornithine was estimated. Although ODC did not exhibit an absolute dependence on pyridoxal phosphate (PLP), addition of PLP increased catalytic activity about 4-fold, with an S0.5 value of 45 microM. Evolution of 14CO2 from ornithine was markedly inhibited by polyamines in the following increasing order of effectiveness: putrescine > spermidine > spermine. The substrate analogs alpha-methylornithine and alpha-difluoromethylornithine had no effect on enzyme activity and cell growth. In contrast, 1,3-diaminopropane and 2,4-diamino-2-butanone, 2 putrescine analogs, severely inhibited both enzyme activity and amoeba multiplication. Results are discussed in terms of the role of ODC in the amoeba proliferation.

Effects of glucose on neuroblastoma in vitro and in vivo

Because neuroblastoma cells in vitro are sensitive to changes in glucose levels in growth media, the effects of glucose levels and dietary carbohydrate on the sensitivity of neuroblastoma cells to chemotherapy were studied. In vitro, 20 microM bromoacetylcholine, 3mM 1,3-diaminopropane, and 5 mM 5-fluorouracil were added to the growth medium of strain N2a neuroblastoma cells cultured in Dulbecco's modified Eagle medium with high glucose (4.5 g/L, HG), normal glucose (1.0 g/L, NG), or low glucose (0.1 g/L, LG). Diaminopropane and 5-fluorouracil had some cytotoxic effect on cells in all media. Bromoacetylcholine killed cells in all media, but at a concentration of 20 microM was most effective in LG medium. Mice (A/Jax) were inoculated with neuroblastoma cells for in vivo studies. Mice could not tolerate a carbohydrate-free diet, while a high-carbohydrate diet caused no change in survival time. When mice on a high carbohydrate diet were treated with cyclophosphamide (100 mg/kg, ip) or 5-fluorouracil (125 mg/kg, ip) they died faster than drug-treated mice on a normal diet. Oral chlorpropamide or cimetidine did not prolong survival time. Analysis of blood glucose levels showed neuroblastoma significantly lowered blood glucose levels (p less than 0.05), while chlorpropamide had no significant effect. It is proposed that manipulation of plasma glucose to lower levels will not be effective in enhancing the chemotherapy of neuroblastoma.

Effects of the spermine analogue canavalmine on proliferation of murine erythroleukemia cells in culture

The effects of canavalmine, a structural analogue of spermine, were studied in cultured murine erythroleukemia cells 745A. Canavalmine exerted an inhibition on murine erythroleukemia cell growth at concentrations over 50 microM. The cell proliferation was, however, restored when canavalmine was removed from the culture medium after 24 h. Treatment of the cells with 500 microM canavalmine blocked the accumulation of intracellular polyamines. Especially, both spermine and spermidine levels were reduced below 50% of those in control cells after 48 h and below 30% after 96 h. The decreased contents of spermine and spermidine were compensated for by the increased content of canavalmine incorporated within the cells. In these cells, RNA and protein contents also decreased. The degree of growth inhibition by canavalmine during the cell cycle was examined using synchronized cells. Serum-induced growth stimulation was inhibited by canavalmine most effectively in the cells at G1 phase prior to DNA synthesis. The antiproliferative effect decreased when canavalmine was added to the cells after commencement of DNA synthesis. The results suggest that the growth-inhibitory action of canavalmine on murine erythroleukemia cells is most likely due to an inhibition of early events of the cell cycle, possibly due to the interference of a structure-specific function of spermidine and/or spermine on DNA replication.

Antiproliferative effects of retinoids related to the cell cycle-specific inhibition of ornithine decarboxylase

The induction of ornithine decarboxylase (ODC) during G1 phase of the cell cycle appears to be universal and essential for cell cycle progression. This induction has been demonstrated in at least 23 cell types in response to various growth stimuli. Further, specific inhibitors of ODC added to several of these cell lines resulted in inhibition of cell proliferation. The studies of the effects of retinoids to inhibit Chinese hamster ovary (CHO) cell growth indicate that the cells are blocked in G1 of cell cycle, and that there is a concentration-dependent inhibition of ODC induction. Retinoids only inhibit the induction of ODC activity when added in the first 2-3 hr of G1 progression. It is postulated that ODC induction is a requirement for G1 progression and that the antiproliferative properties of retinoids are related to the specific ability to inhibit this expression. Since retinoids do not dramatically alter the rate of protein synthesis, their ability to inhibit ODC may be related to their ability to inhibit messenger RNa synthesis for ODC.

The increase in putrescine content in the gastric mucosa of rats with ulcerations induced by restraint-immersion stress

By means of high-performance liquid-chromatography, the putrescine, spermidine and histamine contents in the gastric mucosa were examined during the course of ulceration in rats by the restraint-immersion stress. (1) The putrescine content increased progressively during the course of ulceration with the continuing stress whereas after being released from the stress the content decreased gradually to a significantly lower level than that immediately after 12 hours of the stress. (2) The spermidine content in the gastric mucosa was unchanged during the course of ulceration with continuing stress nor after being released from the stress. (3) The mucosal histamine content decreased significantly after 4 hours under the continuing stress. (3) Extensive histological examination revealed the appearance of regenerating epithelium 36 hours after being released from the stress whereas no such finding was seen before that period. From the above findings, it has been speculated that the increase in the gastric mucosal putrescine content during the course of ulceration induced by restraint-immersion stress is probably due to the stimulated adrenal function by the stress, independently of the regeneration of gastric mucosa.

Antiproliferative effects of inhibitors of polyamine synthesis in tumors of neural origin

The antiproliferative properties of inhibitors of polyamine synthesis were evaluated in cultured neuroblastoma and glioma cells. The diamines (1,3-propanediamine, 1,5-pentanediamine, and 1,6-hexanediamine) dramatically decreased neuroblastoma replication and inhibited the rate-limiting enzyme, ornithine decarboxylase. Glioma cells were less sensitive to the diamines in spite of significant drug-induced decreases in enzyme activity. The fact that ornithine decarboxylase was inhibited in both cell lines with different effects on proliferation suggests that the activity of other enzymes in polyamine biosynthesis may be altered selectively by these inhibitors.

Chemotherapy of neuroblastoma in mice with anticancer agents

Neuroblastoma-inoculated A/J mice were treated with various anticancer chemotherapeutic agents, including cyclophosphamide, daunorubicin, vincristine, alpha-bungarotoxin, dihydroxytryptamine, and diaminopropane. Cyclophosphamide and diaminopropane inhibited neuroblastoma as effectively as bromoacetylcholine and bromacetate. The effectiveness of these drugs could be related to the inhibition of ornithine decarboxylase, a rate-limiting enzyme for the synthesis of polyamines.

Inhibition of polyamine accumulation and cell proliferation by derivatives of diaminopropane in Ehrlich ascites cells grown in culture

1. 1,3-Diaminopropane and some of its derivatives are potent inhibitors of ornithine decarboxylase (EC 4.1.1.17) in Ehrlich ascites cells grown in suspension culture. Among the amine derivatives tested, 1,3-diamino-2-propanol most effectively prevented any accumulation of spermidine and spermine in ascites cells when the proliferation was stimulated by diluting the cells with fresh medium. 2. The effectiveness of diaminopropanol in abolishing polyamine accumulation was primarily based on a rapid decay of ornithine decarboxylase activity following the exposure of the cells to the drug. 3. The mechanism of action of diaminopropanol on ornithine decarboxylase apparently involved a formation of macromolecular inhibitors or 'antizymes' to the enzyme. 4. Even though the inhibitory effect of 1,3-diaminopropane on polyamine accumulation approached that of diaminopropanol, the former compound only marginally inhibited the incorporation of [3H]thymidine into DNA and that of [14C]leucine into protein, in contrast to the marked depression of macromolecular synthesis produced by diaminopropanol. The apparent dissociation of polyamine depletion brought about by 1,3-diaminopropane from an antiproliferative action was apparently due to the fact that diaminopropane, unlike diaminopropanol, was partially capable of taking over the function of natural polyamines. 5. The inhibition of DNA and protein synthesis as well as the prevention of increase in cell number by diaminopropanol was closely associated with polyamine depletion and was fully comparable, as regards timing and magnitude, with that achieved with difluoromethylornithine. The antiproliferative effect of diaminopropanol, however, was only partly reversed by a simultaneous addition of putrescine (or spermidine) into the culture medium. The lack of a complete reversal of the action of diaminopropanol on cell growth by natural polyamines was apparently due to the fact that it was remarkably difficult or even impossible to increase intracellular polyamine concentrations by exogenous polyamines in the presence of diaminopropanol. Nevertheless, the diaminopropanol-induced arrest of growth was reversible as judged by a rapid increase in ornithine decarboxylase activity followed by restoration of DNA synthesis.