Inhibition of polyamine synthesis and proliferation in mouse L cells by DL-α-hydrazino-δ-aminovaleric acid, an inhibitor of ornithine decarboxylase

The role of polyamine in the proliferation of cultured mouse L cells was investigated using DL-α-hydrazino-δ-aminovaleric acid (DL-HAVA), a potent and competitive inhibitor of ornithine decarboxylase [EC 4.1.1.17].When confluent mouse L cells were reseeded, the intracellular concentration of polyamines increased sharply, and the maximal levels of putrescine, spermidine, and spermine were 3.3, 2.2, and 1.8 times their initial values, respectively, one or two days after inoculation. DL-HAVA produced prompt depletion of the intracellular putrescine and spermidine contents and a further increase of the spermine level to 30-90% more than that of the control throughout the experiment. The total level of the three polyamines was reduced to a great extent in DL-HAVA-treated cells. Concomitant with the disappearance of the two polyamines, cell proliferation, measured as the total cell number and DNA accumulation, was greatly suppressed by the inhibitor. Addition of exogenous putrescine or spermidine with or after DL-HAVA restored the inhibited cell growth in a dose-dependent manner. Putrescine administered to inhibitor-treated cultures was rapidly incorporated into the cells and effectively converted to spermidine. Addition of spermidine to the culture medium also normalized the intracellular spermidine content, but the putrescine level remained unchanged. Neither cadaverine nor 1,3-diaminopropane, structural analogs of putrescine, overcame the inhibition under the same conditions.Thymidine kinase [EC 2.7.1.21] activity and the pools of tnphosphates of thymidine and deoxyadenosine were appreciably reduced in DL-HAVA-treated cells, whereas DNA polymerase [EC 2.7.7.7] activity was not changed significantly.These findings suggest that spermidine might play essential roles in the metabolism of deoxyribonucleoside tnphosphates and growth of mouse L cells in culture.