The antiviral activity of 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine (BRL 39123) was assessed in several animal models of herpes simplex virus (HSV) infection. BRL 39123 was as active as acyclovir (ACV) when applied topically to guinea pigs with a cutaneous HSV type 1 (HSV-1) infection and was also active topically in an HSV-2 genital infection. Before systemic administration to infected animals, BRL 39123 and ACV were administered orally and subcutaneously to mice, and the blood was assayed for each compound by high-pressure liquid chromatography. When given systemically to mice infected cutaneously with HSV-1, BRL 39123 was as active as ACV. In mice infected intranasally with HSV-1 or HSV-2, single daily subcutaneous doses of BRL 39123 were more effective than equivalent treatment with ACV, reflecting the more persistent activity seen in cell culture and a more stable triphosphate within the infected cell. When the compounds were supplied in drinking water for this infection, BRL 39123 and ACV had similar potencies against HSV-1, although ACV was more active against an HSV-2 infection than BRL 39123 was. In mice infected intraperitoneally with HSV-1, BRL 39123 was 10-fold more potent than ACV and a single dose of BRL 39123 reduced virus replication within the peritoneal cavity more effectively than 3 doses of ACV given 1, 5, and 20 h after infection. Although BRL 39123 failed to eradicate the virus from mice latently infected with HSV-1, treatment initiated 5 h after infection of the ear pinna reduced the numbers of mice that developed latent infections.The activity of 9-(4-hydroxy-3-hydroxymethylbut-1-yl) guanine (BRL 39123) against members of the herpesvirus family in cell culture has been described by Boyd et al. (4). In virus yield reduction assays, it was shown that BRL 39123 was more active than acyclovir (ACV) against herpes simplex virus type 1 (HSV-1) and of equal activity against HSV-2, although in plaque reduction assays BRL 39123 was less active than ACV against HSV-1 and HSV-2. It was demonstrated that treatment of HSV-infected MRC-5 cells with BRL 39123 for short periods inhibited virus replication much more effectively than similar treatment with ACV and that, in addition, virus replication remained depressed for prolonged periods after treatment with BRL 39123 (4). It was suggested that these results reflected different rates of phosphorylation for BRL 39123 and ACV and that the phosphorylated form of BRL 39123 was trapped efficiently within the infected cell.Since BRL 39123 is a potent inhibitor of HSV in vitro, the antiviral activity of this compound was studied in several animal models of HSV infection. Moreover, since cell culture studies showed that the continuous presence of BRL 39123 in the extracellular medium was not necessary for the maintenance of viral inhibition, it was predicted that persistent activity would be observed in infected animals. In this report, results of experiments are described in which BRL 39123 was tested for efficacy in several HSV infections in animals and i...

The in vitro antihepadnavirus activities of the purine nucleoside analogs ganciclovir {9-[2-hydroxy-1-(hydroxymethyl)ethoxymethyl]guanine} and penciclovir [9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine; BRL 39123] were compared in primary duck hepatocyte cultures congenitally infected with the duck hepatitis B virus (DHBV). Both compounds inhibited DHBV DNA replication to a comparable extent during continuous short-term treatment of the cultures. However penciclovir was more active both during longer-term continuous treatment (50% inhibitory concentrations: penciclovir, 0.7 ± 0.1 ,uM; ganciclovir, 4.0 ± 0.2 ,uM) and in washout experiments (50% inhibitory concentrations: penciclovir, 3.0 ± 0.4 ,uM; ganciclovir, 46 ± 1.5 ,uM) designed to compare the persistence of inhibitory activity after removal of the extracellular compound. The effects on viral protein synthesis were similar to the effects on viral DNA replication. These data suggest that penciclovir or its oral form, famciclovir, may have clinical utility in the treatment of chronic hepatitis B virus infection.Attempts to develop therapy against hepatitis B virus (HBV) have been hampered by its extremely narrow host range (only humans and chimpanzees are susceptible to HBV infection) and by the inability of cell lines to support complete autonomous HBV replication (22). These problems have been overcome to some extent by the recent development of assay systems for identifying potential antihepadnavirus agents. Animal models of HBV infection, particularly those of the woodchuck and duck, have been used for in vivo testing and evaluation, while continuous HBV-transfected cell lines and primary hepatocytes have been used for in vitro screening. The utilities and validities of these systems seem to have been vindicated by findings that agents previously found to be active in clinical studies (2,19,20) are generally active in the test systems (8,21,23,33,34) MATERLILS AND METHODSAnimals. One-day-old Pekin-Aylesbury cross ducks congenitally infected with an Australian strain of DHBV were obtained from a commercial supplier (33). Viremia was monitored by dot blot hybridization of serum, and 7-to 14-day-old ducklings with stable viral titers of 5 x 108 to 10 x 108 viral genome equivalents per ml were selected for hepatocyte isolation.Cell culture. Primary cultures of duckling hepatocytes were prepared as described previously (5, 30), except that feeder cell layers (a potential source of competing nucleosides) were not used. Six-well plastic culture plates (Greiner, Frickenhausen, Germany) were seeded with 2 x 106 to 2.5 x 106 hepatocytes per well, and cells were allowed to attach overnight before the first medium change (on day 1 postplating) and were maintained with medium changes every second day. Antiviral drug treatment. For each experiment, triplicate sets of PDH monolayers were exposed to drug concentrations in the range 0 to 500 ,uM beginning on day 1 postplating. One set was harvested after 5 days of drug treatment. Treatment of the second set was stopped aft...

The activity of 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine (BRL 39123) against several herpesviruses was compared with that of acyclovir (ACV). In plaque reduction tests with clinical isolates of herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), and varicella-zoster virus, mean 50% inhibitory concentrations (IC50s) (n = number tested) for BRL 39123 were 0.4 (n = 17), 1.5 (n = 13), and 3.1 (n = 5) ,ug/ml, respectively. Corresponding IC50s for ACV were 0.2, 0.6, and 3.8 ,ig/ml. Cytomegalovirus was relatively resistant to BRL 39123 (IC50, 51 ,ug/ml), but equid herpesvirus 1, bovid herpesvirus 2, and felid herpesvirus 1 were susceptible (IC50s, 1.6, 1.2, and 0.9 ,ug/ml, respectively). BRL 39123 was inactive against an HSV-1 strain which does not express thymidine kinase activity, but a DNA polymerase mutant selected for resistance to ACV was sensitive to BRL 39123 (IC50, 1.5 ,ug/ml). In contrast to the results from plaque reduction tests, BRL 39123 was more active than ACV against HSV-1 and of equal activity against HSV-2 in virus yield reduction assays in MRC-5 cells. After treatment of HSV-infected cultures for short periods, BRL 39123 was considerably more effective than ACV at reducing virus replication, and furthermore, after removal of extracellular BRL 39123, virus replication remained depressed for long periods, whereas such persistent activity was not observed with ACV. Neither compound significantly affected MRC-5 cell replication at 100 ,ug/mI, but at 300 ,ug/ml BRL 39123 was more inhibitory than ACV.Since the discovery of acyclovir (ACV) and its introduction as an effective treatment for herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) and varicella-zoster virus (VZV) infections in humans, several laboratories have been searching for acyclic purine nucleosides with improved properties. ACV is a highly selective antiviral agent which is activated by the virus-induced thymidine kinase and inhibits susceptible viruses at concentrations which do not affect cell replication (9). Several other guanine derivatives have been described and evaluated as inhibitors of herpesviruses in cell culture and in animal infections (1,10,13,14,(22)(23)(24). Many publications show that 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) is beneficial in the treatment of severe cytomegalovirus (CMV) infections in humans, but because of adverse toxicity its use in less serious infections may be limited (20).Pandit et al. (18) first claimed to have synthesized 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine, but the compound was not fully characterized and no biological properties were given. The synthesis and isolation of pure compound have since been reported by Harnden and Jarvest (12), who found that the experimental conditions originally described provided a mixture of products. In the present paper, the activity of 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine (BRL 39123; Fig. 1

The antiherpesvirus agent penciclovir has been evaluated extensively in cell culture. The spectrum of activity of penciclovir against human herpesviruses is similar to that of acyclovir, both compounds having good activity against herpes simplex viruses types 1 and 2 (HSV-1, HSV-2), varicella-zoster virus (VZV), and Epstein-Barr virus (EBV). Like acyclovir, penciclovir has slight activity against cytomegalovirus (CMV). The susceptibility of recent clinical isolates was not influenced by geographical origin. The activity of penciclovir was examined in several antiviral assays (plaque reduction, virus antigen, virus yield, and viral DNA inhibition) and in many different host cells (fibroblast, epithelial-like, keratinocyte). The comparative activity of penciclovir and acyclovir depended on both the host cell and the assay and, while in certain circumstances penciclovir was more active than acyclovir, overall the activities of the two compounds were considered comparable. Both compounds were highly selective antiviral agents with minimal effects on a wide range of representative, proliferating human cells. The inhibition of a variety of acyclovir-resistant strains has been examined and, as expected, thymidine kinase-negative strains were resistant to both penciclovir and acyclovir. The majority of acyclovir-resistant HSV and VZV clinical strains were cross-resistant to penciclovir. However, certain acyclovir-resistant strains, some of which were of clinical origin and all of which expressed altered thymidine kinase or DNA polymerase, were susceptible to penciclovir. In addition, a series of foscarnet-resistant HSV isolates appeared to be susceptible to both penciclovir and acyclovir. These results led to the evaluation of penciclovir in further cell culture studies, and also in animal models. Furthermore, the mechanism of action of penciclovir has also been investigated. Since the oral absorption of penciclovir in animals was poor, an oral form, famciclovir, was selected which gave improved oral bioavailability of penciclovir.

The novel phorbol ester 12-deoxyphorbol 13-(3E,5E-decadienoate) [1] was isolated as the anti-HIV principle of Excoecaria agallocha leaves and stems collected in northwest Australia. The structure was determined by spectral means. Compound 1 was also a potent displacer of [3H]-phorbol dibutyrate from rat brain membranes.