1. Physiological functions of spermidine acetyltransferase in Escherichia coli have been studied using the spermidine acetyltransferase (speG) gene-deficient mutant CAG2242 and the cloned speG gene. The growth of E.coli CAG2242 was normal in the presence and absence of 0.5 mM spermidine. However, cell viability of E.coli CAG2242 at 48 h after the onset of growth decreased greatly by the addition of 0.5 mM spermidine. The amount of spermidine accumulated in the cells was approximately 3-fold that in the cells grown in the absence of spermidine. Transformation of the cloned speG gene to E.coli CAG2242 recovered the cell viability. The accumulation of spermidine caused a decrease in protein synthesis but not in DNA and RNA synthesis at 28 h after the onset of growth. The synthesis of several kinds of proteins was particularly inhibited. They included ribosome mudulation factor and OmpC protein. Since the ribosome modulation factor is essential for cell viability at the stationary phase of
growth, the decrease in the protein was thought to be one of the reasons for the decrease in cell viability. The decrease in the ribosome modulation factor mainly occured at the translational level.
2. Effects of 1,15-bis (ethylamino) -4,8,12-triazapentadecane (BE3333) on the growth of tumor cells were studied in in vitro systems and with tumor xenografts in mice. BE3333 suppressed ornithine decarboxylase and S-adenosylmethionine decarboxylase, induced spermidine/spermine N^1-acetyltransferase, and thus decreased the amount of polyamines. BE3333 accumulated in cells at a concentration 3-5-fold that of spermine in control cells. The accumulated BE3333 inhibited protein synthesis, especially mitochondrial protein synthesis, and decreased the amount of ATP.The inhibition of protein synthesis was correlated with the subsequent inhibition of cell growth. BE3333 showed inhibitory effects in in vitro systems against the growth of mouse FM3A mammary carcinoma cells, human SW480 and SW620 colon tumor cells, Lu-65A and A549 lung tumor cells, MCF-7 breast tumor cells, and MALME-3M and A375 melanoma cells at a range of 0.5-10 muM.Intravenous (30 mg/kg) or i. p. (50 mg/kg) daily injections of BE3333 for 5 days greatly suppressed the growth of human tumor SW620 xenotrasplanted into nude mice. BE3333 also showed inhibitory effects against the growth of lung tumors (Lu-65, Lx-1, Lc-1, and Lu-61), stomach tumors (Sc-6 and St-15), and melanoma (SEKI) xenotransplanted into nude mice. The results indicate that BE3333 is effective against both rapid-and slow-growting tumors, with reasonable short-term host toxicity. Less