Depletion of intracellular putrescine and spermidine by alpha-difluromethylornithine does not inhibit proliferation of 9L rat brain tumor cells.

Incubation of 9L rat brain tumor cells with 25 mM DL-α-difluoromethylornithine inhibits cell proliferation, while treatment with 10 mM and 1 mM do not. All three concentrations cause equal degrees of depletion of intracellular putrescine and spermidine content, but have no effect on spermine content. These observations show that 9L cells can continue to proliferate in spite of significant polyamine depletion and leads one to question the role of polyamines in 9L cell replication. These observations also suggest that inhibition of 9L cell proliferation by 25 mM DL-α-difluormethylornithine is probably not due to its effect on ornithine decarboxylase or on intracellular polyamine content.