ANTIVIRAL ACTIVITY OF INHIBITORS OF PYRIMIDINE DE-NOVO BIOSYNTHESIS

Evaluation of the elevation of host cell biosynthesis of deoxynucleosi de triphosphates (dNTP's) induced by human cytomegalovirus (HCMV) infe ction as a target for antiviral therapeutics was carried out. The conc entrations of all four intracellular dNTP's rose rapidly following HCM V infection, and were markedly above baseline by 8 h post infection (p .i.). All four deoxynucleoside triphosphates remained elevated above b aseline for at least 72 h p.i. The effects of inhibitors of the de-nov o pathway of pyrimidine biosynthesis on HCMV viral replication-were qu antified by DNA dot blot. AII pyrimidine biosynthesis inhibitors exami ned inhibited the HCMV DNA replication at concentrations that were non -toxic to the cell. These drugs were also more effective against HCMV, which is highly dependent on host denovo synthesis, than against HSV- 1 which encodes enzymes capable of increasing the supply of dNTP's. Th e antiviral effect of brequinar, an inhibitor of one of the enzymes of the de-novo pathway (dihydroorotate dehydrogenase), was examined to d etermine if it coincided with a decrease in dNTP's. HCMV-infected fibr oblasts and uninfected control cells were treated with a concentration of brequinar able to inhibit HCMV DNA levels 90%. It was found that b requinar markedly lowered the levels of dTTP found in treated cells co mpared to untreated cells in both HCMV-infected and uninfected cells.