EFFECTS OF DL-ALPHA-METHYLORNITHINE ON PROLIFERATION AND POLYAMINE CONTENT OF 9L RAT-BRAIN TUMOR-CELLS

Abstract

Treatment of 9L rat brain tumor cells with 10 mM DL-.alpha.-methylornithine (.alpha.MO) resulted in cytostasis when cells were plated in monolayer culture at an initial cell density of 5 .times. 105/flask but not 1 .times. 106. Fifty mM caused cytostasis at both initial densities, but more effectively at the lower one. Cytocidal effects measured by a colony-forming efficiency assay were observed at 100 mM, but not at 75 mM or less. Both concentrations at both initial cell densities depleted intracellular putrescine content to < 5% of control by 12 h and spermidine content to < 20% of control by 48 post-treatment. Intracellular spermine content increased between 1.5- and 2-fold with either concentration of .alpha.MO and at both densities. Flow cytometry revealed no differences in cell cycle distribution between controls and cells treated with 10 mM .alpha.MO. The cytostatic effect of 10 mM .alpha.MO on 9L cultures of lower initial density appeared to be a specific result of polyamine depletion since it was reversible by exogenous putrescine added 24 h after treatment. The effect of 50 mM .alpha.MO was not reversible by exogenous putrescine or pyridoxal added simultaneously or 24 h after treatment. Treatment of 9L cells with 50 mM DL- or L-ornithine caused growth inhibition equal to that produced by 50 mM .alpha.MO. The effect of 50 mM .alpha.MO is not attributable to polyamine depletion.