Inhibition of transforming growth factor-induced cell growth in soft agar by oxidized polyamines

An inhibitor of the transforming growth factor-induced growth in soft agar of normally anchorage-dependent rat kidney fibroblasts has been detected in the acid-ethanol extracts of human placenta, bovine lung and kidney, and human rhabdomyosarcoma cells (A673). The inhibitor has been purified from human placenta by gel-filtration and cation-exchange chromatography followed by acetylation and HPLC. Acetylation destroys inhibitory activity and deacetylation, by treatment with 6 N HCl at 110 degrees C for 16 h, restores full activity. The purified compound has been identified as spermine by mass spectral and NMR analyses and by cochromatography on HPLC of the acetylated material with acetylated spermine. Both the compound isolated from the placenta and spermine and spermidine show approximately equal activity in inhibiting the transforming growth factor-induced growth of cells in soft agar with an ED50 of 0.7-1.1 microM, while putrescine displays no inhibitory activity. Evidence suggests that the polyamines must first be oxidized by serum polyamine oxidase before inhibition will occur. Acrolein, a product of polyamine oxidation, will also inhibit cell growth in soft agar with an ED50 of 6.8 microM. It is concluded that an oxidation product of spermine is responsible for the previously reported inhibition of colony growth in soft agar following treatment of normal fibroblasts with transforming growth factors.