Inhibitory and lethal concentrations of 9-beta-D-arabinofuranosyladenine and its hypoxanthine-derivative versus herpes simplex virus, type 1.

Minimum inhibitory concentrations of 9-beta-D-arabinofuranosyladenine (ara-A, adenine arabinoside, vidarabine) and a purified preparation of 9-beta-D-arabinofuranosylhypoxanthine (arabinoslhypoxanthine, ara-Hx) at end points of 50% MIC50) and 100% (MIC100) reduction to challenges of approximately 50 p.f.u. of herpes simplex virus, type 1 (HSV-1) were determined in vero renal tissue cultures. Adenosine deaminase is universally present in tissue cultures and serum. These same tests were repeated in the presence of a potent inhibitor of adenosine deaminase, R-3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3,6,7,8-tetrahydroimidazo-4,5-d)-(1,3)-diazepin-8-ol (co-vidarabine, co-ara-A). Addition of co-ara-A to assays of MIC50 or MIC100 for ara-A ensures standard reproducible results which can be compared in different laboratories. After incubations of HSV-1 in infected cultures for 96 hours, 35 degrees C., with concentrations of ara-A or ara-Hx at the MIC100 and over, cells were scraped and sonicated. Supernates were then reinoculated into vero flasks free of antiviral agents to determine minimum lethal concentrations (MLC's). Standard values (microng/ml.) for ara-A with co-ara-A are 11.3 (MIC50), 17.0 (MIC100), and 34.0 (MLC) but are 68.1 (MIC50), 170.4 (MIC100) and 375 (MLC) for ara-Hx. These data confirm that as a virustatic agent (MIC100) ara-A is 10 times more active than ara-Hx. Ara-A and ara-Hx have virucidal potentials which require approximately two times the respective MIC100.