Inhibition of ribonucleotide reductase and growth of human colon carcinoma HT-29 cells and mouse leukemia L1210 cells by N-hydroxy-N′-aminoguanidine derivatives

A series of N-hydroxy-N′-aminoguanidine (HAG) derivatives were studied and compared for their effects on ribonucleotide reductase activity in cell-free extracts; on nucleic acid synthesis and the growth of human colon carcinoma HT-29 cells; and on mouse leukemia L1210 cells in culture. The HAG derivatives [RCHNNHC(NH)NHOH-tosylate] studied could be grouped as; (1) hydroxy-benzylidines; (2) methoxybenzylidines; and (3) nitrobenzylidines substituted at the R position. 2′-Hydroxybenzylidine-HAG, the lead compound, was relatively active in both HT-29 cells and L1210 cells (20 ± 5 and 13 ± 4 μM for 50% inhibition of HT-29 and L1210 cell growth respectively). The monohydroxybenzylidene compounds were generally more active than the dihydroxy- and trihy-droxybenzylidene-HAG derivatives. The methoxybenzylidene-HAGs were as active as the monohy-droxybenzylidene-HAGs. 2′-Hydroxy-4′-methoxybenzylidene-HAG was much more active than 2′,4′-dihydroxybenzylidene-HAG. The mononitrobenzylidene-HAGs were more active than the dinitro-benzylidene-HAG compound. In general, L1210 cells were more sensitive to the effects of the HAG compounds than were HT-29 cells. There was good agreement between the concentration of drug required to inhibit the growth of HT-29 cells and that required to inhibit the growth of L1210 cells. There was also good correlation between the ability of HAG derivatives to inhibit ribonucleotide reductase activity and to inhibit tumor cell growth. Some derivatives, such as 2′,3′,4′- and 3′,4′,5′-trihydroxybenzylidene-HAG inhibited L1210 cell growth by 50% at lower concentrations (7.8 and 11.9 μM respectively) than the concentrations needed for 50% inhibition of HT-29 cell growth (196 and 234 μM respectively) and ribonucleotide reductase activity (122 and 188 μM respectively). The studies of nucleic acid synthesis in L1210 cells using [(3)H]cytidine as a precursor showed that 2′,3′,4′-trihy-droxybenzylidine-HAG inhibited DNA synthesis at a lower concentration (29 μM for 50% inhibition) than was needed for the inhibition of RNA synthesis and formation of [(3)H]deoxycytidine nucleotides in the acid-soluble fraction (320 and 820 μM for 50% inhibition respectively). These results indicate that 2′,3′,4′-trihydroxybenzylidine-HAG inhibits DNA synthesis in L1210 cells through other mechanisms rather than exclusively through the inhibition of ribonucleotide reductase activity.