EFFECT OF INCORPORATION OF CIDOFOVIR INTO DNA BY HUMAN CYTOMEGALOVIRUS DNA-POLYMERASE ON DNA ELONGATION

Cidofovir (CDV) (HPMPC) has potent in vitro and in vivo activity again st human cytomegalovirus (HCMV), CDV diphosphate (CDVpp), the putative antiviral metabolite of CDV, is an inhibitor and an alternate substra te of HCMV DNA polymerase, CDV is incorporated with the correct comple mentation to dGMP in the template, and the incorporated CDV at the pri mer end is not excised by the 3'-to-5' exonuclease activity of HCMV DN A polymerase. The incorporation of a CDV molecule causes a decrease in the rate of DNA elongation for the addition of the second natural nuc leotide from the singly incorporated CDV molecule, The reduction in th e rate of DNA (36-mer) synthesis from an 18-mer by one incorporated CD V is 31% that of the control, However, the fidelity of HCMV DNA polyme rase is maintained for the addition of the nucleotides following a sin gle incorporated CDV molecule, The rate of DNA synthesis by HCMV DNA p olymerase is drastically decreased after the incorporation of two cons ecutive CDV molecules; the incorporation of a third consecutive CDV mo lecule is not detectable, Incorporation of two CDV molecules separated by either one or two deoxynucleoside monophosphates (dAMP, dGMP, or d TMP) also drastically decreases the rate of DNA chain elongation by HC MV DNA polymerase. The rate of DNA synthesis decreases by 90% when a t emplate which contains one internally incorporated CDV molecule is use d, The inhibition by CDVpp of DNA synthesis by HCMV DNA polymerase and the inability of HCMV DNA polymerase to excise incorporated CDV from DNA may account for the potent and long-lasting anti-CMV activity of C DV.