Time dependence of the in vitro cytotoxicity of hexamethylmelamine and its metabolites.

The cytotoxicity of hexamethylmelamine (HMM) and its metabolites pentamethylmelamine (PMM), N,2,2,4,6-tetramethylmelamine (TMM) and hydroxymethylpentamethylmelamine (HMPMM) and of the alkylating agent triethylenemelamine (TEM) were studied on a cell line derived from a human ovarian cancer, by measuring [3H]TdR uptake. After 24 h of incubation all the tested compounds inhibited [3H]TdR uptake, but only at a concentration of 100 micrograms/ml. However, after 120 h incubation, concentrations of 0.1--10 micrograms/ml resulted in highly significant cytotoxicity. HMPMM and TEM were the most active and their effect was not reversed 72 h after their removal. In our in vitro system no metabolism of HMM was observed.