Effects of inhibitors of ornithine decarboxylase on the differentiation of mouse neuroblastoma cells

(R, S)-α-Fluoromethylomithine (α-FMO), a catalytic irreversible inhibitor of ornithine decarboxylase (L-omithine carboxy-lyase, EC 4.1.1.17), induced the differentiation of N2a mouse neuroblastoma cells. The effect of α-FMO was concentration dependent; approximately 50% of the cell population exhibited neurite outgrowth in the presence of 1 mM α-FMO, while higher concentrations caused severe growth inhibition and cell death. The effect of 1 mM α-FMO on neuroblastoma differentiation was potentiated greatly by 0.1 to 0.2 mM N⁶O²-dibutyryl adenosine cyclic 3́:5́-monophosphate (Bt2cAMP) causing more than 90% of the cell population to differentiate morphologically with thick and long processes; 0.1 to 0.2 mM Bt₂ cAMP, by itself, had no effect on cell growth and did not induce neurite outgrowth. The effect of α-FMO, either by itself or in combination with 0.1 to 0.2 mM Bt2cAMP, on the morphological differentiation of mouse neuroblastoma cells was reversed by the addition of exogenous putresdne or spermidine. The morphological differentiation of mouse neuroblastoma cells induced by 1 mM α-FMO plus 0.2 mM Bt₂ CAMP was accompanied by increases of the regulatory subunit of the type I cAMP-binding protein and acetylcholinesterase activity. These results indicate that the modulation of cellular polyamine contents may be important in neuroblastoma cell differentiation.