5,6-Dihydro-5-azathymidine

The plasma kinetics of 5,6-dihydro-5-azacytidine (DHAC) was determined in mice using an HPLC method following an intravenous dose of 2000 mg/kg (LD10). Pharmacokinetic parameters calculated from these single dose data were sufficient to predict steady state plasma concentrations produced by s.c. infusion of DHAC. Lethal toxicity (LD66) occurred at an infusion rate of 37 mg/kg/h (111mg/m2/h), corresponding to a plasma steady-state DHAC concentration 38 +/- 14 micrograms/ml when the infusion time was 96 h; no lethality occurred at infusion times of 72 h or less. In vitro clonogenic assays and in vivo therapeutic experiments with L1210 tumor indicated that increasing the exposure time at concentrations near 25 micrograms/ml from 24 to 72 h increased the cell kill only slightly. The maximum log cell kill of L1210 estimated from either in vitro or in vivo data was 1.5 logs.

5,6-Dihydro-5-azathymidine (DHAdT), a nucleoside antibiotic inhibitory for herpes simplex virus (HSV) in cell cultures (H. E. Renis, Antimicrob. Agents Chemother. 13: 613-617, 1978), was evaluated in mice with experimental HSV infections. DHAdT protected mice infected with HSV type 1 (HSV-1) when the virus was inoculated intravenously and the drug was given by subcutaneous or oral routes. The activity observed was dependent on the dose and schedule of treatment. Doses of 100 to 400 mg/kg given three to four times daily (at 4-h intervals) for 4 to 5 days gave greater protection than less frequent treatment for shorter time intervals. DHAdT treatment reduced the rate of isolation as well as the HSV-1 titers in homogenates prepared from spinal cords and brains, whereas the titers in kidney homogenates were only marginally affected. The above treatment regime with DHAdT afforded only partial protection to mice infected intracerebrally with HSV-1 or mice inoculated intravaginally with HSV-1 or HSV-2. The antiviral activity of DHAdT was reversed by the co-administration of thymidine. Under these conditions, DHAdT was not toxic in mice.

5,6-Dihydro-5-azathymidine (DHAdT), a novel water-soluble nucleoside antibiotic, inhibits herpes simplex virus type 1 (HSV-1) in appropriately infected cell cultures to a greater extent than herpes simplex virus type 2 (HSV-2). Vaccinia virus was less susceptible than HSV-2, and pseudorabies virus yields were not reduced at the concentrations studied. Plaque formation by varicella-zoster virus was suppressed by DHAdT. DHAdT was slightly toxic to cells at concentrations that were inhibitory for HSV-1 and varicella-zoster virus. Thymidine and deoxyuridine completely reversed the anti-HSV-1 activity of DHAdT, whereas deoxycytidine was partially effective. Compared with other nucleoside analogs with activity for HSV-1, DHAdT was less active than 5-iodo-2'-deoxyuridine or 1-beta-d-arabinofuranosylcytosine and nearly equipotent with 9-beta-d-arabinofuranosyladenine.