Acute and Delayed Toxicity Studies on the Antiherpesvirus Agents 5-Methoxymethyl-2′-Deoxycytidine and 5-Methoxymethyl-2′-Deoxyuridine

Abstract

Summary5-Methoxymethyl-2'-deoxycytidine (MMdCyd) and the corresponding deoxyuridine analogue, 5-methoxymethyl-2'-deoxyuridine (MMdUrd) are selective antiherpesvirus agents. MMdCyd (ED 50 1.5~lM) is a more potent inhibitor of herpes simplex virus replication than MMdUrd (ED 5o 30~lM) when maintained in the deoxycytidine form (deamination prevented). The 5'-triphosphates, MMdCTP and MMdUTP, were synthesized, and incorporation into DNA. by mitochondrial DNA polymerase y was investigated. MMdcTPand MMdUTP were incorporated into DNA in place of dCTP and dTTP, respectively. The effect of MMdCyd and MMdUrd on cell growth (acute toxicity) and proloriged exposure (delayed cytotoxicity) in CEM cells was investigated. The two analogues did not exhibit acute or delayed toxicity (2 weeks exposure) up to 1000~lM. In contrast, at a concentration as low as 0.125~lM of 2' )'-dideoxycytidine (ddC; control druq], the doubling time of the cells increased after 10 days. At higher concentrations, a very marked increase in doubling time was observed from 6 days onward with ddC treatment. The data suggest that in uninfected cells neitherMMdUrd nor MMdCyd are anabolized to the triphosphate Form in signiFicant amounts. As a result, little or no MMdCTP or MMdUTP builds up in the mitochondria and thus delayed toxicity is not observed.