No abstract

SUMMARYThe response to various stimuli of herpes simplex virus-specified deoxypyrimidine kinase activity differs significantly from that of the thymidine kinase and deoxycytidine kinase of mammalian cells. However, the two phosphorylating activities of the HSV deoxypyrimidine kinase are themselves quite distinct in their biochemical behaviour.It has been impossible to separate the HSV-coded thymidine and deoxycytidine phosphorylating activities by their sedimentation, electrophoretic or size characteristics. The evidence suggests that both deoxypyrimidine nucleosides are phosphorylated at the same active site.

1-p-D-Arabinofuranosylthymine (ara-T), a metabolite of the sponge Tethya crypta, has shown selective activity against herpes simplex virus (HSV) replication (G. A. Gentry and J. F. Aswell, Virology 65:294-296, 1975 responsible for the selective antiviral activity of ara-T. This conclusion was further supported by experiments that showed that the replication ofa variety of dPyK-mutants of HSV-1 and HSV-2 were not affected by ara-T and that ara-T inhibited the phosphorylation of deoxycytidine and deoxythymidine by HSV-1 dPyK, but not by host deoxycytidine and deoxythymidine kinases, respectively. Ara-T also selectively inhibited the replication ofequine herpesvirus type 1 (EHV-1) in vitro and was effective against EHV-1 infection in vivo in hamsters. Further, EHV-1 was inhibited by ara-T and by bromodeoxyuridine in LM cells lacking a cytosol thymidine kinase, suggesting that EHV-1 induces a dPyK. Finally, spectrophotometric assay for thymine suggested that ara-T is not a substrate for nucleoside phosphorylase of hamster liver, and a microbiological assay indicated that substantial amounts of ara-T were excreted in the urine of uninfected hamsters that had received a single injection of 5 mg of ara-T, the amount given in each injection in the in vivo experiments with EHV-1.1-p-D-Arabinofuranosylthymine (ara-T; spongothymidine) was first isolated, rather by coincidence, by Bergmann and Feeney (5) in a study of the sterol content (4) of Tethya crypta, a sponge first described as growing almost buried in the ocean floor off the Bahamas (16). Subsequently, ara-T was found to have little effect on the multiplication of tumor cells in culture (11,15) but was later shown to be somewhat inhibitory to herpesvirus replication in vivo (17,18,53,54,56). The demonstration (26) that herpes simplex virus (HSV)-infected cells contain a pyrimidine deoxyribonucleoside kinase (dPyK) with a broad substrate specificity (29,30) suggested that ara-T might be phospho- showing that ara-T at 2 x 10-M completely blocked the replication of HSV type 1 (HSV-1) and HSV type 2 (HSV-2) in BHK cells but had no measurable effect on the multiplication of uninfected BHK cells subcultured at low cell density and followed for several generations (23). It has subsequently been shown that several other deoythymidine (dT) analogs have similar selectivity against HSV, including 5'-amino-2',5'-dideoxy-5-iodouridine, 5-ethyldeoxyuridine, 5-propyldeoxyuridine, 5-allyldeoxyuridine (8, 10); 5-bromodeoxycytidine, 5-iododeoxycytidine (13,20, 24,31); and 5-methoxymethyldeoxyuridine (2,3). This suggests that the HSV-specified dPyK may be a useful tool in