Biological activity and mode of action of some dihydroorotic and dihydroazaorotic acid derivatives.

The conversion of six dihydroorotate analogues by the dihydroorotate dehydrogenase (DHO-DH) of plant and animal mitochondria was studied. In the case of plant DHO-DH the dehydrogenation of analogues was as follows: Dihydroorotic acid (DHO) (control, 100%), DHO-hydrazide (40%), azaDHO (13%), azaDHO-ethyl ester (23%), azaDHO-hydrazide (11%), dihydrouracil (0%), dihydrothymine (0%). When animal DHO-DH was used the analogues were practically not dehydrogenated. These compounds were also tested as inhibitors of DHO-dehydrogenation. AzaDHO, azaDHO-hydrazide and azaDHO-ethylester inhibited this reaction by 75, 70% and 60%, respectively, for plant DHO-DH. AzaDHO and azaDHO-ethylester inhibited this reaction to 90% and 70%, respectively, for animal enzyme. The other analogues had no effect. The compounds showed a moderate antibacterial activity. AzaDHO was more active than azaDHO-ethyl ester and azaDHO-hydrazide. A considerable inhibitory effect of azaDHO and azaDHO-ethyl ester was observed on the growth of St. aureus mutant UV-2 and S. lutea. The analogues were little active against the experimental mouse tumors leukemia L 1210, Lewis lung carcinoma (LLC) and B-16 melanoma. AzaDHO-ethyl ester and azaDHO-hydrazide inhibited the growth of LLC by 59% and 56%, respectively. In addition, the effect of analogues on the growth of plant cells was studied. AzaDHO and azaDHO-ethyl ester inhibited the growth of tomato cells in suspension culture by 10% and 41%, respectively.

Lack of genotoxic and cytotoxic effects of the herbicide lenacil on mouse tumor cells and on some Salmonella typhimurium strains.

The effects of 3-cyclohexyl-6,7-dihydro-1H-cyclopentapyrimidine-2,4(3H,5H)-dione (lenacil) on macromolecular synthesis, thymidilate synthetase activity, viability and cell cycle progression were studied using Friend leukemia (FL). P388 and Ehrlich ascites tumor cells in suspension, and its cytogenetic effects were studied in a Salmonella/mammalian microsome assay using both frameshift and base-substitution tester strains. At a concentration of 0.5 mmol/l lenacil inhibited 45 to 70% thymidine incorporation into DNA fraction, while incorporations of uridine into RNA and leucine into protein were less affected. Thymidilate synthetase activity in P388 cells as assayed by the release of tritiated water from 5-3H-deoxyuridine was inhibited by the compound to about 20%. Lenacil neither showed an in vivo inhibitory action on thymidine incorporation into acid-insoluble material in P388 cells, nor on thymidilate synthetase activity after a 24 or 48 h treatment. The compound did not change the melting temperature of isolated DNA. Studies of lenacil's effect on cell cycle kinetics of FL cells demonstrated that 48 h treatment increased the percentage of S-phase cells. Lenacil exerted a weak cytotoxic effect on FL cells. At concentrations above 0.1 mmol/l it inhibited cell growth the effect being nonlethal. Cytogenetic studies of lenacil revealed no indication of its mutagenicity against Salmonella typhimurium TA97, TA98, TA100 and TA102.

Inhibitory effects of pyruvic acid semi- and thiosemicarbazones on the growth of bacteria, yeasts, experimental tumours and plant cells.

Pyruvic acid semi- and thiosemicarbazones (1 and 2, respectively) were tested as inhibitors of bacterial, fungal, experimental tumour and plant cell growth. 1 and 2 displayed a growth-inhibitory effect in vitro against different bacterial strains, and especially against St. aureus mutant UV-2 and S. lutea. The compounds proved to have low activity in vivo against L 1210 and P 388 leukemia, adenocarcinoma 755 and melanoma B 16. 2 inhibited strongly the growth of cultured cells of Lycopersicon esculentum (100% inhibition at a concentration of 1,5 mumol/ml) while 1 was not active.

Cyanopyrazoles as analogs of purine precursors--II. Effects on macromolecular synthesis and cell cycle progression.

The cytotoxic and cytokinetic effects, and in vitro inhibition of macromolecular synthesis by cyanopyrazoles were studied using Friend leukemia and Ehrlich ascites tumor cells. At concentrations in the range of 2.5 mM to 50 microM analog 3(5)-amino-4-cyano-5(3)-trichloromethylpyrazole (I) was highly cytotoxic and completely inhibited thymidine, uridine and leucine incorporation into macromolecular material. 24 hr incubation of FL cells with cytostatic concentrations of compound I (in the range of 2 to 0.5 microM) resulted in an accumulation of cells in the G2 + M phase. Analogs N-hydroxyethyl-3(5)-amino-4-cyano-5(3)-trichloromethylpyrazole (II) and 3(5)-amino-4-cyanopyrazole (III) were not cytotoxic at concentrations up to 5 mM and did not substantially inhibit precursor incorporation into macromolecules but exhibited a cytostatic activity. These compounds caused a decrease of FL cells in the G2 + M phase and an accumulation in the S phase. Analogs I and II displayed a similar in vivo inhibitory effect on thymidine incorporation into DNA in EAT cells. The results indicate that the cytotoxicity of cyanopyrazoles correlates with their ability to inhibit precursor incorporation into macromolecular material. On the other hand, the cytostatic action of compound I is not coupled to a block of nucleic acid synthesis.