INHIBITION OF HUMAN CYTOMEGALOVIRUS IN CULTURE BY ALKENYL GUANINE ANALOGS OF THE THIAZOLO[4,5-D]PYRIMIDINE RING-SYSTEM

A series of alkyl and alkenyl guanine analogs containing a thiazolo[4, 5-d]pyrimidine ring system were prepared by reaction of the appropriat e alkyl halide,vith the sodium salt of the heterocycle. In preliminary antiviral efficacy evaluations against laboratory strains of both hum an cytomegalovirus (HCMV) and herpes simplex virus types 1 and 2, it w as determined that two of the compounds (T70072 and T01132) were more active and less toxic in stationary-phase cell monolayers than were th e other derivatives tested. T01132 and T70072, which have 2-pentenyl a nd 3-methyl-2-butenyl moieties attached to position 3 of the 5-aminoth iazolo [4,5-d] pyrimidine 2,7-dione, respectively, were then more exte nsively evaluated for anti-HCMV activity. The concentrations of T01132 and T70072 required to inhibit HCMV by 50% in plaque reduction assays were similar to 0.5 and 6.8 mu M, respectively. These two compounds i nhibited the growth of KB, MRC-5, or Vero cells at concentrations of 7 5 to 150 mu M, depending upon the cell line. In bone marrow progenitor cells T01132 was slightly less toxic than ganciclovir (DHPG). The 50% inhibitory concentrations of T01132 against clinical isolates and DHP G-resistant strains of HCMV were approximately the same as those obtai ned for laboratory strains of HCMV (similar to 0.5 mu M). When tested in combination with DHPG, the resultant antiviral activity was determi ned to be additive but not synergistic. Experiments performed using va riations of the viral multiplicity of infection (MOI) demonstrated tha t T01132 was more active than DHPG at a low MOI (0.002 or 0.02). Howev er, when a higher MOI (0.2 or 2.0) was used, DHPG was more efficacious than T01132. In experiments in which drug was added at various times post-viral infection, T01132 was most effective when added within the first 24 h post-HCMV infection while DHPG was able to protect cells in this assay system when added up to 48 h postinfection, indicating tha t T01132 is exerting its antiviral effect on events leading up to and possibly including viral DNA synthesis. The data presented in this rep ort suggest that the antiviral activity of alkenyl-substituted thiazol opyrimidine derivatives may represent a mechanism of action against he rpesviruses alternative to that of classical nucleoside analogs such a s acyclovir or DHPG.