Long chain diamines inhibit growth of C6 glioma cells according to their hydrophobicity. An in vitro and molecular modeling study

A series of diamines with the general structure NH2(CH2)(x)NH2, x=2-12, was tested for their potential effects on cell proliferation of cultured rat C 6 glioma cells in comparison to natural polyamines. Long chain diamines red uced cell number after 48 h in culture with a sequence of 1,12-diaminododec ane (1,12-DD) >1,10-diaminodecane >1,9-diaminononane. Polyamines (putrescin e, spermidine and spermine) as well as diamines up to a CH2-chain length of x=8 were found to be ineffective. The spermine analogue 1,12-DD was the mo st effective molecule in reducing cell number in an irreversible, dose-depe ndent manner (EC50=3 mu M under serum-free conditions). In further experiments we investigated the mechanisms of action of 1,12-DD. The compound had only a minor effect on cell cycle and did not affect free internal calcium concentration. Under physiological conditions 1,12-DD int eracts with tripler DNA but not with duplex DNA. Ornithine decarboxylase ac tivity as well as the concentration of internal polyamines were found to be reduced by 1,12-DD. Polyamine application, however, was not able to revers e the effect of 1,12-DD, indicating a polyamine-independent or non-competit ive mechanism of action. 1,12-DD reduced cell number by induction of apopto sis as well as necrosis. In molecular modeling studies it was found that a minimal hydrophobic inter segment of at least 4 Angstrom was required to make a diamine an effective drug in respect to cellular growth. A hydrophobic gap of this size fits the minimum requirement expected from molecular modeling to provide space for hydrophobic interactions with parts of proteins like a CH3-group. Our resul ts show that 1,12-DD acts as a potent drug, reducing the number of C6 gliom a cells, and suggest that its spatial and hydrophobic properties are respon sible for its mechanism of action.