Efficacy of (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine and 9-(1,3-dihydroxy-2-propoxymethyl)guanine for the treatment of murine cytomegalovirus infection in severe combined immunodeficiency mice

HPMPC (cidofovir), PMEA (adefovir) and Related Acyclic Nucleoside Phosphonate Analogues: A Review of their Pharmacology and Clinical Potential in the Treatment of Viral Infections

The acyclic nucleoside phosphonate (ANP) analogues are broad-spectrum antiviral agents, with potent and selective antiviral activity in vitro and in vivo. The prototype compounds are: ( S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC, cidofovir), which is active against a wide variety of DNA viruses; 9-(2-phosphonylmethoxyethyl)adenine (PMEA, adefovir), which is active against retro-, herpes- and hepadnaviruses, and ( R)-9-(2-phosphonylmethoxypropyl) adenine (PMPA), which is active against retro- and hepadnaviruses. The antiviral action of the ANP analogues is based on a specific interaction of the active diphosphorylated metabolite with the viral DNA polymerase. The long intracellular half-life of the active metabolite accounts for the optimal efficacy in infrequent dosing schedules. The potential of HPMPC as a broad-spectrum anti-DNA virus agent, as originally observed in vitro and in vivo, has been confirmed in clinical trials. HPMPC has recently been commercially released in the USA for the treatment of cytomegalovirus retinitis in AIDS patients. In addition, topical systemic HPMPC is being (or will be) explored for use against other herpesviruses (i.e. herpes simplex virus, Epstein-Barr virus, or varicella-zoster virus), by adenoviruses, or by human papilloma- or polyomaviruses. Intravenous HPMPC is associated with dose-dependent nephrotoxicity, that should be counteracted by prehydration and concomitant administration of probenecid, and by the application of an infrequent dosing schedule. The oral prodrug of PMEA, bis(pivaloyloxymethyl)-PMEA, is currently being evaluated in patients infected with human immunodeficiency virus (HIV) or hepatitis B virus. Finally, preclinical data on the efficacy of PMPA in animal retrovirus models point to its potential usefulness against HIV infections, when given either prophylactically or therapeutically in the treatment of established HIV infections.

Comparative Anti-Retrovirus and Anti-Hepadnavirus Activity of Three Different Classes of Nucleoside Phosphonate Derivatives

The prototype compounds of three different classes of nucleoside phosphonates [i.e. 9-(2-phosphonomethoxyethyl)adenine (PMEA), 9-(2-phosphonomethoxyethoxy)adenine (PMEoA) and 9-[(2R,5R)-2,5-dihydro-5-(phosphonomethoxy)-2-furanyl]adenine (D4API)] were investigated and compared for their antiviral activities. The three test compounds showed a marked inhibition of human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) in CEW and MT-4 cell cultures [50% effective concentration (EC50): 0.8-14μm]. D4API was 2- and 15-fold more inhibitory than PMEA and PMEoA, respectively. In contrast, the activity of PMEA against human hepatitis B virus (HHBV) in human hepatoma Hep G2 2.2.15 cells was 5- and 10-fold more pronounced than the activities of PMEoA and D4API, respectively (EC50 1.2μm versus 10 and 6 μm, respectively). The inhibitory activity of D4API against Moloney murine sarcoma virus (MSV)-induced C3H/3T3 cell transformation was superior to the activities of PMEA and PMEoA by at least one order of magnitude (EC50 for D4API 1.3μM, versus 2.8 and 14 μM for PMEA and PMEoA, respectively). The markedly greater inhibitory effect of D4API on MSV in vitro was in agreement with our In vivo findings that D4API inhibited MSV-induced tumour formation in newborn mice and delayed the MSV-associated animal death at a lower dose than PMEA or PMEoA. Both PMEA and D4API emerged as promising compounds that warrant further investigation for their anti-retrovirus and anti-hepadnavirus activities in vivo.

Cidofovir, a New Agent with Potent Anti-Herpesvirus Activity

Cidofovir is a potent, broad spectrum antiviral agent with activity in vitro and in vivo against cytomegalovirus and other members of the herpesvirus family, as well as certain other DNA viruses. After uptake into cells it is converted enzymatically to cidofovir diphosphate, a structural analogue of deoxycytidine triphosphate, which selectively inhibits viral DNA polymerases relative to host cell polymerases. Cross-resistance to cidofovir is not usually seen with human cytomegalovirus isolates that are foscarnet-resistant, or isolates that are ganciclovir-resistant due to a deficiency in ganciclovir phosphorylation. Cross-resistance is seen, however, with isolates that are ganciclovir resistant due to polymerase mutations. A prolonged elimination phase seen in vivo, correlates with a long intracellular half-life seen in vitro and allows for efficacy in animal models of virus infection with infrequent dosing or prophylaxis. Clinical studies of intravenous cidofovir in cytomegalovirus retinitis in patients with AIDS are claimed to show delay of retinitis progression with maintenance doses given once every 2 weeks.

Dipyridamole Potentiates the Activity of Various Acyclic Nucleoside Phosphonates against Varicella-Zoster Virus, Herpes Simplex Virus and Human Cytomegalovirus

Dypiridamole (DPM) is widely used in the treatment of cardiovascular diseases as a coronary vasodilator and inhibitor of platelet aggregation. Phosphonylmethoxyethyl (PME) and 3-hydroxy-2-phosphonylmethoxypropyl (HPMP) derivatives of purines and pyrimidines are potent and selective inhibitors of varicella-zoster virus (VZV), herpes simplex virus (HSV) and human cytomegalovirus (HCMV). We have found that DPM markedly potentiates the antiviral effects of the PME derivatives of adenine (PMEA) and 2,6-diaminopurine (PMEDAP), and of the HPMP derivatives of adenine (HPMPA), 3-deazaadenine (HPMPc3A) and cyclic HPMPA (cHPMPA). This was reflected by a significant decrease in the 50% inhibitory concentration of the acyclic nucleoside phosphonates for VZV-, HSV- and HCMV-induced cytopathic effect or plaque formation. DPM did not enhance the activity of vidarabine, acyclovir or ganciclovir. These results were confirmed by virus yield assays (for HSV and HCMV) and flow cytometry (for VZV).

Transporter-targeted lipid prodrugs of cyclic cidofovir: a potential approach for the treatment of cytomegalovirus retinitis

Cidofovir (CDF) and its cyclic analogue (cCDF) have shown potential in vitro and in vivo antiviral activity against cytomegalovirus (CMV) retinitis. However, hydrophilic nature of CDF may affect cell permeation across lipophilic epithelium and thus limit its effectiveness in the treatment of CMV retinitis. In the present study, we have tested a novel hypothesis, which involves chemical derivatization of cCDF into lipophilic transporter-targeted prodrug [via conjugation with different carbon chain length of lipid raft and targeting moiety (biotin) for sodium-dependent multivitamin transporter (SMVT)]. We have synthesized and characterized three derivatives of cCDF including biotin B-C2-cCDF, B-C6-cCDF, and B-C12-cCDF. Physicochemical properties such as solubility, partition coefficient (n-octanol/water and ocular tissue), bioreversion kinetics, and interaction with SMVT transporter have been determined. Among these novel conjugates, B-C12-cCDF has shown higher interaction to SMVT transporter with lowest half maximal inhibitory concentration value, higher cellular accumulation, and high tissue partitioning. Improvement in physicochemical properties, lipophilicity, and interaction with transporter was observed in the trend of increasing the lipid chain length, that is, B-C12-cCDF > B-C6-cCDF > B-C2-cCDF. These results indicate that transporter-targeted lipid analogue of cCDF exhibits improved cellular accumulation along with higher transporter affinity and hence could be a viable strategy for the treatment of CMV retinitis.

Pivotal role of animal models in the development of new therapies for cytomegalovirus infections

Since human cytomegalovirus (CMV) is extremely species specific and does not replicate in experimental animal tissues, animal models for the evaluation of antiviral agents for these infections have utilized surrogate animal viruses including murine CMV, rat CMV and guinea pig CMV. Murine CMV and rat CMV infections in normal and immunocompromised animals provide models of disseminated infection and are ideal for screening of new agents. While guinea pig CMV infection in immunocompromised animals also provides a model for disseminated disease, the model for congenital CMV is unique among all the experimental models. While these models have played a major role in the development of ganciclovir, foscarnet and cidofovir, they do not provide information directly related to human CMV, nor are they useful for evaluation of agents that are active only against human CMV. The SCID-hu mouse models in which human tissue is infected with human CMV has been very useful in the development of new antiviral agents such as maribavir and cyclopropavir. Collectively these experimental CMV infections provide a variety of models representing various aspects of CMV infection in humans that are highly predictive for antiviral efficacy in humans.

Oral activity of a methylenecyclopropane analog, cyclopropavir, in animal models for cytomegalovirus infections

We reported previously that purine 2-(hydroxymethyl)methylenecyclopropane analogs have good activity against cytomegalovirus infection. A second-generation analog, (Z)-9-[[2,2-bis-(hydroxymethyl)cyclopropylidene]methyl]guanine (ZSM-I-62, cyclopropavir [CPV]), has particularly good activity against murine and human cytomegaloviruses (MCMV and HCMV) in vitro. To determine the oral activity of this compound in vivo, BALB/c or severe combined immunodeficient (SCID) mice infected with MCMV and two models using SCID mice implanted with human fetal tissue and subsequently infected with HCMV were used. In MCMV-infected normal mice, CPV at 10 mg/kg of body weight was highly effective in preventing mortality when administered at 24, 48, or 72 h post-viral inoculation and reduced titers of virus in tissues of SCID mice by 2 to 5 log10. In one HCMV model, human fetal retinal tissue was implanted into the anterior chamber of the mouse eye and inoculated with the Toledo strain of HCMV, and in the second, human fetal thymus and liver tissues were implanted under the kidney capsule of mice and then inoculated with HCMV. In general, replication of HCMV in both types of implant tissue increased from 7 through 21 to 28 days and then gradually decreased to undetectable levels by 8 weeks postinfection. Oral treatment with 45 or 15 mg of CPV/kg initiated 24 h after infection was highly effective in reducing replication to undetectable levels in both models and was generally more effective than ganciclovir. These data indicate that the methylenecyclopropane analog, CPV, was highly efficacious in these four animal models and should be evaluated for use in HCMV infections in humans.

In vitro efficacy of ganciclovir, cidofovir, penciclovir, foscarnet, idoxuridine, and acyclovir against feline herpesvirus type-1

OBJECTIVE

To establish the in vitro efficacy of 4 novel drugs (ie, ganciclovir, cidofovir, penciclovir, and foscarnet) against feline herpesvirus type-1 (FHV-1) and compare their antiviral efficacy with that of acyclovir and idoxuridine.

SAMPLE POPULATION

Cultured Crandell-Reese feline kidney (CRFK) cells and FHV-1 strain 727

PROCEDURE

For each drug, antiviral effect was estimated by use of conventional plaque-reduction assays, and inhibitory concentration 50 (IC50; drug concentration at which plaque numbers were reduced by 50% relative to the number of plaques for nontreated control wells) was calculated. To determine whether observed antiviral effects were related to alterations in the number or viability of CRFK cells, cytotoxicity assays were performed at 1, 2, and 10 times the median IC50 for each antiviral drug.

RESULTS

Median IC50 for each drug was as follows: ganciclovir, 5.2 microM; cidofovir, 11.0 microM; penciclovir, 13.9 microM; foscarnet, 232.9 microM; idoxuridine, 4.3 microM; and acyclovir, 57.9 microM. Obvious changes in morphologic characteristics, confluence, or viability of CRFK cells were not observed at concentrations up to and including 2 times the IC50 for each drug.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro efficacy of idoxuridine and ganciclovir against FHV-1 was approximately equivalent and about twice that of cidofovir and penciclovir. Foscarnet appeared to be comparatively ineffective. Given the reasonable clinical efficacy of idoxuridine in cats infected with FHV-1, clinical trials of ganciclovir, cidofovir, and penciclovir or their prodrug forms appear to be warranted.

Activities of benzimidazole D- and L-ribonucleosides in animal models of cytomegalovirus infections

Since human cytomegalovirus (HCMV) does not infect or replicate in nonhuman cells and tissues, there are few animal models currently available for evaluation of antiviral therapies for these infections. In the present studies, we utilized two different models in which severe combined immunodeficient (SCID) mice were implanted with human fetal tissue that was subsequently infected with HCMV. In one model, human fetal retinal tissue was implanted into the anterior chamber of the SCID mouse eye, and in the second, human fetal thymus and liver (thy/liv) tissues were implanted under the kidney capsule. After the implants were established, they were infected with 2,000 to 9,000 PFU of HCMV. To determine the efficacy of three benzimidazole nucleosides, 2-bromo-5,6-dichloro-(1-beta-D-ribofuranosyl)benzimidazole (BDCRB), GW275175X (175X), and GW257406X (1263W94, maribavir [MBV]) treatment was initiated 24 h after infection of the implants and continued for 28 days. Treatment consisted of either placebo, 25 mg of ganciclovir (GCV)/kg of body weight administered intraperitoneally (i.p.) twice daily, 33 or 100 mg of BDCRB/kg administered i.p. twice daily, or 75 mg of either MBV or 175X/kg administered orally twice daily. GCV was effective in both models, inhibiting HCMV infection by 5- to 3,000-fold. In the retinal tissue model, MBV and BDCRB reduced HCMV replication about fourfold through 21 days postinfection compared with results for the vehicle control. In the thy/liv tissue model, all three benzimidazole nucleosides were effective in inhibiting HCMV replication by approximately 30- to 3,000-fold in comparison to the vehicle control. These data indicate that the benzimidazole nucleosides were efficacious in these animal models and suggest that this class of compounds should be active against the various HCMV infections that occur in the immunocompromised host.

Clinical potential of the acyclic nucleoside phosphonates cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates HPMPC (cidofovir), PMEA (adefovir), and PMPA (tenofovir) have proved to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections: cidofovir against herpesvirus (herpes simplex virus types 1 and 2 varicella-zoster virus, cytomegalovirus [CMV], Epstein-Barr virus, and human herpesviruses 6, 7, and 8), polyomavirus, papillomavirus, adenovirus, and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus, and orf virus) infections; adefovir against herpesvirus, hepadnavirus (human hepatitis B virus), and retrovirus (human immunodeficiency virus types 1 [HIV-1] and 2 [HIV-2], simian immunodeficiency virus, and feline immunodeficiency virus) infections; and tenofovir against both hepadnavirus and retrovirus infections. Cidofovir (Vistide) has been officially approved for the treatment of CMV retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) has been approved for the treatment of HIV infections (i.e., AIDS), and adefovir dipivoxil (Hepsera) has been approved for the treatment of chronic hepatitis B. Nephrotoxicity is the dose-limiting side effect for cidofovir (Vistide) when used intravenously (5 mg/kg); no toxic side effects have been described for adefovir dipivoxil and tenofovir disoproxil fumarate, at the approved doses (Hepsera at 10 mg orally daily and Viread at 300 mg orally daily).

HPMPC therapy of MCMV-induced retinal disease in the SCID mouse measured by electroretinography, a non-invasive technique

The purpose of these studies was to investigate the use of non-invasive electroretinography for the evaluation of retinal disease and its treatment in an ocular murine cytomegalovirus (MCMV) disease model. While under anesthesia, 10(2.6)plaque forming units (pfu) of salivary gland passaged, Smith strain MCMV was injected in the anterior chamber of 6- to 8-week-old severe combined immunodeficiency (SCID) mice. At various times post-inoculation, bright-flash scotopic electroretinogram, viral titer, and histology were obtained from the injected eye. Antiviral therapy was tested using 0.1 and 5mg/kg/day subcutaneous injections of HPMPC (Cidofovir) once daily for 5 consecutive days. In infected animals, the a- and b-waves of the electroretinographic (ERG) signal were significantly reduced as of 10 days post-inoculation when compared to control animals. Therapy with HPMPC 0.1mg/kg/day subcutaneously (s.c.) once daily for 5 consecutive days was able to delay the decrease in ERG wave amplitude and inhibit viral replication, whereas 5mg/kg/day s.c. significantly protected the ERG, completely inhibited viral replication, and maintained ocular viral titer below the limit of detection for up to 17 days post-infection. The reduction of ERG activity during progression of retinal disease correlated well with reduction of disease pathology. ERG recording represents a valuable non-invasive technique to measure the progression of the retinal disease induced by MCMV and the efficacy of antiviral treatment in the ocular MCMV disease model.

Antiviral and immunomodulatory activity of the metal chelator ethylenediaminedisuccinic acid against cytomegalovirus in vitro and in vivo

Antiviral activity of the metal chelator ethylenediaminedisuccinic acid (EDDS) was examined in vitro against human cytomegalovirus (HCMV) wild type strains and strains that are resistant against ganciclovir (GCV) and cidofovir (HPMPC). EDDS inhibited the replication of wild-type as well as GCV- and HPMPC-resistant strains with a 50% effective concentration of 7.4-12 microg/ml. At concentrations of 100 microg/ml EDDS, unlike GCV or HPMPC, suppressed HCMV-induced up-regulation of intercellular adhesion molecule-1 (ICAM-1) and reduced T-cell adhesion to HCMV-infected cells in a monolayer adhesion model. In vitro EDDS inhibited murine cytomegalovirus (MCMV) replication (EC50 8.6 microg/ml) and caused in mice some protection against MCMV induced mortality at a non-toxic dose. Since immunopathological factors may play a significant role in HCMV disease it will be of interest to further study whether EDDS is effective in terms of modulation of inflammatory responses to HCMV infections.

Sulphated and sulphonated polymers inhibit the initial interaction of hepatitis B virus with hepatocytes

The initial step during hepatitis B virus (HBV) infection is the specific attachment of the virus to the hepatocyte. Here we studied whether the binding of HBV to hepatocytes can, as is the case with most other enveloped viruses, be blocked by polyanionic compounds. Viral particles produced by HepAD38 cells were used as inoculum and HBV-negative HepG2 cells, as well as primary human hepatocytes, as target cells. Three sulphated polymers, that is, PAVAS (a co-polymer of acrylic acid with vinyl alcohol sulphate), heparin and dextran sulphate (DS) (MW 5000), and the sulphonated polymer PAMPS [poly(2-acryl-amido-2-methyl-1-propanesulfonic acid] (MW approximately 7000-12000), proved strong inhibitors of the binding of HBV to HepG2 cells and primary hepatocytes. The 50% effective concentration (EC50) for inhibition of HBV binding to HepG2 cells by PAVAS, heparin, DS and PAMPS was 1.3 microg/ml, 1.6 microg/ml, 1.8 microg/ml and 3.3 microg/ml, respectively, and to primary hepatocytes 1.6 microg/ml (PAVAS), 1.6 microg/ml (heparin), 2.6 microg/ml (DS) and 4.1 microg/ml (PAMPS). These values are in the same range as the concentrations required for these compounds to prevent such viruses as herpesviruses and HIV from binding to cells. These findings may be helpful in elucidating the mechanism of the initial interaction of HBV with hepatocytes.

Inhibition of murine cytomegalovirus and human cytomegalovirus by a novel non-nucleosidic compound in vivo

Novel non-nucleosidic compounds have recently been identified as potent inhibitors of the human cytomegalovirus (HCMV) and murine cytomegalovirus (MCMV) in vitro. We have now investigated the antiviral activity of these compounds in MCMV-infected NOD/LtSz-scid/j mice that lack functional T, B and, in contrast to C.B-17/Icr scid/scid mice, natural killer cells, and represent a novel model for cytomegalovirus infection in immunocompromised hosts. BAY 38-4766 (3-hydroxy-2,2-dimethyl-N-[4(([5-(dimethylamino)-1-naphthyl]sulfonyl)amino)- phenyl]propanamide) was identified as the most potent representative of this class of antiviral compounds. Per os administration of BAY 38-4766 at dosages > or = 10 mg/kg body weight led to antiviral effects that were comparable to ganciclovir 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (Cymevene) as measured by survival and levels of viral DNA in organs of infected mice. In order to assess the anti-HCMV activity of BAY 38-4766 in vivo, we used a model, in which HCMV-infected human cells were entrapped in hollow fibers and subsequently transplanted into immunodeficient mice. Using this model, we demonstrated antiviral activity of BAY 38-4766 similar to that of ganciclovir. We conclude that BAY 38-4766 shows potential as an anti-HCMV drug.

Cyclic HPMPC is safe and effective against systemic guinea pig cytomegalovirus infection in immune compromised animals

Cidofovir (HPMPC) is licensed for the treatment of cytomegalovirus (CMV) retinitis in patients with AIDS but its use is limited by nephrotoxicity. We evaluated the safety and efficacy of 1-[((s)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosi ne dihydrate (CHPMPC) the cyclic congener of cidofovir. Treatment was well tolerated both in normal guinea pigs and in animals immune compromised with cyclophosphamide. Further, blood chemistry analysis showed no adverse effects of CHPMPC treatment on kidney or liver function. In efficacy studies in immune compromised guinea pigs challenged with a virulent salivary gland passaged guinea pig CMV, CHPMPC treatment significantly reduced mortality resulting from disseminated virus infection. Quantitative culture showed that treatment also significantly reduced virus replication in the liver and spleen, but not the lungs of infected animals. The efficacy of CHPMPC combined with its improved safety profile appear to make it an attractive alternative to cidofovir for the treatment of herpesvirus infections. Further evaluation is warranted.

In vitro activities of methylenecyclopropane analogues of nucleosides and their phosphoralaninate prodrugs against cytomegalovirus and other herpesvirus infections

Human cytomegalovirus (HCMV) infection does not generally cause problems in the immunocompetent adult but can result in severe clinical disease in the fetus, neonate, and immunocompromised host. Ganciclovir (GCV), the agent currently used to treat most HCMV infections, has resulted in much therapeutic success; however, efficacy remains suboptimal. Therefore, there is still a need to develop new compounds for use against HCMV infections. In the present study, several Z- and E-series methylenecyclopropane analogues and their phosphoroalaninate prodrugs were tested initially for activity against HCMV, strain AD169, and murine cytomegalovirus (MCMV) in vitro. Many were found to exhibit efficacy comparable to that of GCV against HCMV in plaque assays and were active against MCMV as well. The compounds were also tested for efficacy against herpes simplex virus types 1 and 2, varicella-zoster virus, and Epstein-Barr virus, and some had levels of activity that were comparable to that of acyclovir. In addition, the compounds synguanol (QYL-438) and 2-amino-6-cyclopropylamino analogue (QYL-769) were chosen for further evaluation and were found to be effective against additional laboratory and clinical isolates of HCMV and GCV-resistant isolates. QYL-438 and QYL-769 were found to be nontoxic in human and mouse fibroblasts and were considerably less toxic than GCV in granulocyte macrophage CFUs and erythroid burst-forming units. These results provide evidence for the high activity of some of these methylenecyclopropane analogues against various herpesviruses, particularly HCMV, in tissue culture and suggest that further evaluation is warranted to determine their potential for use in future clinical studies.

A novel peptide aldehyde with activity against human cytomegalovirus in two different in vivo models

Novel peptide aldehydes (PAs) were identified as potent inhibitors of human cytomegalovirus (HCMV) in vitro. Although these compounds were highly effective against HCMV, they did not exhibit any activity against murine cytomegalovirus (MCMV). The purpose of this study was to test the antiviral activity of PA 8 as a representative of this novel class of inhibitors against HCMV in vivo. Because of the strict species specificity of HCMV we had to use two artificial animal models. In the first model, HCMV-infected human cells were entrapped into agarose plugs and transplanted into mice. In the second model, SCID mice were transplanted with human tissues that were subsequently infected with a clinical isolate of HCMV. In these two models the antiviral activity of PA 8 was clearly demonstrated, ganciclovir only being slightly superior in its in vivo antiviral activity.

Acute murine cytomegalovirus infection: a model for determining antiviral activity against CMV induced hepatitis

Acute intraperitoneal infection of weanling BALB/c mice with murine cytomegalovirus (MCMV) resulted in an inoculum titer-dependent weight loss, mortality and elevation of plasma transaminases (ALT: alanine transaminase and AST: aspartate transaminase). Three days post infection (p.i.) with 10(4.85) plaque forming units (pfu) there was 90% mortality with a mean death day p.i. of 4.1 +/- 0.2. Plasma levels of ALT and AST were elevated 24- and 15-fold, respectively. Organ titers of virus (log10 pfu/g tissue) were 6.16 in the liver, 6.05 in the spleen, 4.0-4.7 in the lung, heart, kidney and intestine and undetectable in the muscle and brain. Organ concentrations (units/g wet-weight) of ALT were highest in the liver, whilst for AST the highest levels were found in the heart. The concentrations of ALT but not AST were reduced (35-55%) in the infected liver; the concentrations of ALT and AST were not changed in other infected organs. There were excellent correlations (r > 0.95) between viral titers in the liver, increases of plasma ALT and depletion of liver ALT. HPMPC and ganciclovir administered either p.o. or s.c. reduced mortality, increases in plasma transaminases and viral burdens in the liver and prevented depletion of liver ALT. HPMPC was approximately 10-fold more potent than ganciclovir. These results strongly suggest that intraperitoneal infection of the BALB/c mouse with MCMV represents an animal model of CMV hepatitis that can be monitored by measuring plasma ALT.

Effect of desferrioxamine (DFO) and calcium trinatrium diethylenetriaminepentaacetic acid (DTPA) on rat cytomegalovirus replication in vitro and in vivo

Cytomegalovirus (CMV) infection is a major problem in the immunosuppressed patient. It is thought that besides direct CMV induced cell lysis, immunological damage is part of CMV pathogenesis. New antiviral drugs, which combine immunomodulating and antiviral qualities, could be beneficial. Recently, it has been described that desferrioxamine (DFO) and calcium trinatrium diethylenetriaminepentaacetic acid (DTPA) exhibit both properties. In this report the antiviral effects of both compounds against rat CMV (RCMV) are described in vitro and in vivo using a generalised and local infection model. In vitro, both compounds exhibited a significant antiviral effect, DTPA being more potent than DFO. However, in the generalised infection model no effect was seen on mortality, morbidity or presence of virus in internal organs. In rats infected subcutaneously in the hind paw, no effect was seen locally on paw thickness, presence of viral antigens and inflammatory response. In addition, these rats suffered from a generalised infection of low magnitude at 15 days post infection, although both DFO and DTPA were able to lower the level of viral replication. In conclusion, our data indicate that despite in vitro activity, in vivo usage of DFO or DTPA for acute CMV infection is not warranted.

Effective treatment of murine cytomegalovirus infections with methylenecyclopropane analogues of nucleosides

A number of new nucleoside analogues with a Z- or E-methylenecyclopropane structure exhibited significant activity against human and murine cytomegaloviruses (HCMV, MCMV) in tissue culture that was generally comparable to, or greater than, 9-[(1-3-dihydroxy-2-propoxy)methyl]guanine (ganciclovir, GCV). Several of these analogues were chosen for further evaluation of therapeutic efficacy utilizing a MCMV infection. Intraperitoneal (i.p.) inoculation of 3-week-old Balb/c mice with 2.0 x 10(5) plaque forming units (pfu) of MCMV results in an acute, lethal infection with rapid virus replication in visceral and glandular tissue, thus, making it an ideal model for identifying compounds that have potential for use in humans. Synadenol (QYL-284A) and synguanol (QYL-438) were administered i.p. once daily for 5 days initiated 6, 24, or 48 h post-viral infection. Significant protection was demonstrated at 50 and 16.7 mg/kg compared to placebo, with efficacy comparable to GCV. When delivered orally once or twice daily at 100 mg/kg per day, QYL-438 was active, but less effective than GCV. In addition, 2-amino-6-methoxypurine analogue (QYL-941) was active at 60 mg/kg administered orally twice daily, comparable to GCV, while it's prodrug (QYL-972) was as effective as GCV at 40 mg/kg when delivered twice daily for 5 days. Additionally, analogue 2-amino-6-cyclopropylaminopurine (QYL-769) was found to be highly efficacious when given orally twice daily for 5 days. Mortality of 0% and 13% was observed at 60 and 20 mg/kg, respectively, which was similar to GCV. Oral treatment with QYL-769 or GCV reduced virus replication in target organs, but neither resulted in complete clearance of MCMV. These data indicate that these new analogues have activity comparable to GCV when given orally to mice and should be evaluated further to assess their potential for use in humans.

Dose and duration-dependence of ganciclovir treatment against murine cytomegalovirus infection in severe combined immunodeficient mice

The present study investigates the full dose-response curve and treatment duration dependence of ganciclovir (GCV) against murine cytomegalovirus (MCMV) infection in severe combined immunodeficiency (SCID) mice. Animals inoculated intraperitoneally with 6.3 x 10(3) pfu of MCMV per mouse developed typical wasting syndrome rapidly and died around day 12 post-inoculation. Once-daily treatment with subcutaneous GCV for 5 days dose dependently delayed MCMV-induced wasting syndrome and mortality at a dose range of 1-80 mg/kg per day, whereas a dose of 160 mg/kg per day induced reversible side-effects. The effect of GCV treatment on mean death day (MDD) was significantly correlated to reductions of viral titers in the lung (r = 0.969, P < 0.05). Treatment duration dependence was examined at the dose of GCV at 80 mg/kg per day for 1, 5, 8 and 12 days. The protective duration, over vehicle-treated mice, was constantly 3-4 days plus the duration of GCV treatment, as evidenced by the delay of viral replication, wasting syndrome and death. At a sub-optimally effective dose of 10 mg/kg per day of GCV, maximum protection was achieved with a 8-day treatment regimen. Prolongation of this treatment to 12 days failed to further delay mean death day and wasting syndrome that started on day 10, indicative of insufficient suppression of viral replication. Treatment with a single dose of GCV failed to show a complete dose-response curve since only minimal protective effects were observed at the dose of 80 mg/kg while side-effects were associated with the dose of 160 mg/kg. The treatment duration dependence and requirement for sufficient dosage of GCV against CMV infection observed in the current model are consistent with clinical observations. It also suggests that 5 8 days treatment duration may be a good balance considering the opportunity for identifying active compounds and speeding up the turnaround time in drug evaluations.

Intraocular pressure and aqueous humor dynamics in patients with AIDS treated with intravitreal cidofovir (HPMPC) for cytomegalovirus retinitis

PURPOSE

To evaluate the decrease in intraocular pressure associated with cidofovir (1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine dihydrate; HPMPC) intravitreal injections.

METHODS

We followed up 97 eyes of 63 patients with acquired immunodeficiency syndrome (AIDS) who had cytomegalovirus retinitis and had been treated with up to nine 20-microgram intravitreal cidofovir injections. Measurements were taken at baseline, between 2 and 3 weeks, and at 5 to 6 weeks after injections. Anterior chamber fluorophotometry was studied in seven eyes (four patients) before and after injections. Ciliary body anatomy was evaluated in two patients.

RESULTS

After the first intravitreal injection, mean intraocular pressure was 2.2 mm Hg lower than that at baseline at 2 to 3 weeks (P < .001) and 1.3 mm Hg lower than at baseline at 5 to 6 weeks (P = .0025). After the second injection, mean pressure was 2.6 mm Hg lower at 2 to 3 weeks (P = .0013) and 1.5 mm Hg lower at 5 to 6 weeks (P = .043). After subsequent injections, however, the decrease was less than 1 mm Hg, suggesting that a plateau had been reached. Pressure in eyes with anterior uveitis after the first injection was lower than that in eyes without anterior uveitis (P < .0001). The mean rate of aqueous flow decreased from 2.8 to 1.9 microliters per minute 2 to 4 weeks after injection (P < .015). Ultrasound biomicroscopy disclosed that severe hypotony after cidofovir injections is associated with ciliary body atrophy.

CONCLUSIONS

Intraocular pressure decreases after the initial 20-microgram cidofovir intravitreal injection. However, eyes stabilize (pressure plateaus) after three injections. Effects on the ciliary body are the main cause of the decrease after cidofovir injections.

Effective treatment of experimental cytomegalovirus-induced encephalo-meningitis in immunocompromised rats with HPMPC

Cytomegalovirus (CMV)-induced encephalomeningitis is a dramatic complication in patients with the acquired immunodeficiency syndrome (AIDS) and treatment of this infection remains a major clinical problem. In order to study the pathogenesis and treatment of CMV-induced encephalomeningitis, we experimentally induced intracranial rat CMV (RCMV) infection in rats that were immunosuppressed by total body X-irradiation. CMV infection was monitored by viral plaque assay for estimation of the viral load. CMV-induced pathology, the presence of CMV-infected cells, as well as the presence of T-lymphocytes and monocytes/macrophages were studied by histopathologic and immunohistochemical staining techniques. The meninges showed CMV infection in mononuclear infiltrative cells and in endothelium of small blood vessels 8 days after intracerebral inoculation. This was accompagnied by multiple haemorraghes and inflammatory cell infiltration. The infection and inflammatory response persisted for at least 21 days p.i. Animals were treated with (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC), 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG), hyperimmune serum (HIS) and both DHPG and HIS combined. Treatment with one dosage of HPMPC at 20 mg/kg effectively reduced virus titers. However, all other treatment modalities were not effective. In conclusion, the pathology of RCMV-induced encephalomeningitis in immunocompromised rats closely resembles that of AIDS patients. The infection is effectively treated by HPMPC.

Analysis of the complete DNA sequence of murine cytomegalovirus

The complete DNA sequence of the Smith strain of murine cytomegalovirus (MCMV) was determined from virion DNA by using a whole-genome shotgun approach. The genome has an overall G+C content of 58.7%, consists of 230,278 bp, and is arranged as a single unique sequence with short (31-bp) terminal direct repeats and several short internal repeats. Significant similarity to the genome of the sequenced human cytomegalovirus (HCMV) strain AD169 is evident, particularly for 78 open reading frames encoded by the central part of the genome. There is a very similar distribution of G+C content across the two genomes. Sequences toward the ends of the MCMV genome encode tandem arrays of homologous glycoproteins (gps) arranged as two gene families. The left end encodes 15 gps that represent one family, and the right end encodes a different family of 11 gps. A homolog (m144) of cellular major histocompatibility complex (MHC) class I genes is located at the end of the genome opposite the HCMV MHC class I homolog (UL18). G protein-coupled receptor (GCR) homologs (M33 and M78) occur in positions congruent with two (UL33 and UL78) of the four putative HCMV GCR homologs. Counterparts of all of the known enzyme homologs in HCMV are present in the MCMV genome, including the phosphotransferase gene (M97), whose product phosphorylates ganciclovir in HCMV-infected cells, and the assembly protein (M80).

New antiherpesvirus agents. Their targets and therapeutic potential

Of the large number of agents under development for the treatment of herpes virus infections [herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), cytomegalovirus (CMV), Epstein-Barr virus (EBV)], only ten have apparently reached clinical development. Aciclovir was approved for the treatment of HSV infections over 10 years ago, and it remains an important and reliable antiviral agent. Recent approvals in some countries of valaciclovir for VZV infection and famciclovir for both HSV and VZV infections demonstrate the rapidity of change in this field. Intravenous ganciclovir and foscarnet are approved for the treatment of CMV infection in the immunocompromised patient. Five of the antiherpetic drugs under current clinical development are nucleoside analogues or their prodrugs; another is a phosphorylated nucleoside (nucleotide). Four of the nucleoside agents-penciclovir, famciclovir, valaciclovir and lobucavir-are being developed for the management of HSV and VZV infections. Valaciclovir is also being developed for the prevention of CMV infections and famciclovir and lobucavir for the treatment of hepatitis B virus infection. Oral ganciclovir, lobucavir, ISIS 2922 and cidofovir are being developed for the suppression of CMV infections in immunocompromised patients. Sorivudine has been studied in VZV infections. n-Docosanol is under development for HSV infections, and cidofovir is being developed for both HSV and CMV infections, as well as for treatment of other viral diseases. Traditionally, the adverse effects associated with anti-CMV compounds have been more difficult to manage and are acceptable clinically only because of the severity of the underlying infection and lack of safer therapeutic alternatives. In general, toxicity issues continue to be problematic in the anti-CMV arena, although newer agents have improved the situation to some extent. In contrast, the safety of anti-HSV compounds has traditionally been excellent, establishing a safety standard that must be met by newer agents entering the field.

Patterns of resistance and sensitivity to antiviral compounds of drug-resistant strains of human cytomegalovirus selected in vitro

Drug-resistant human cytomegalovirus (HCMV) strains were selected in human embryonic lung (HEL) fibroblasts under pressure of the (S)-3-hydroxy-2-phosphonylmethoxypropyl (HPMP) derivatives of cytosine (HPMPC) and adenine (HPMPA), the 2-phosphonylmethoxyethyl (PME) derivative of 2,6-diaminopurine (PMEDAP), ganciclovir (GCV), acyclovir (ACV), and foscarnet (PFA). Drug susceptibility profiles of the different drug-resistant (i.e., GCVr, HPMPCr, HPMPAr, PFAr, ACVr, and PMEDAPr) strains were determined in HEL cells. A considerable degree of cross-resistance against GCV, HPMPC, and HPMPA occurred with GCVr, HPMPCr, and HPMPAr strains. No changes in susceptibility to 9-(2-phosphonylmethoxyethyl)adenine (PMEA), PMEDAP, ACV, or PFA were detected for the HPMPCr, HPMPAr, and GCVr strains when compared to the wild-type virus. On the other hand, a significant degree of cross-resistance was noted with the PMEDAPr, PFAr, and ACVr strains against PMEA, PMEDAP, PFA, and ACV. NO differences in susceptibility to HPMPC, HPMPA and GCV were observed for the ACVr, PFAr, and PMEDAPr strains relative to the wild type. The drug susceptibility profiles of the different resistant strains point to a common mechanism of HCMV resistance to PFA and the PME derivatives that is different from the mechanism of HCMV resistance to the HPMP derivatives.

Evaluation of Cidofovir (HPMPC, GS-504) against adenovirus type 5 infection in vitro and in a New Zealand rabbit ocular model

The antiviral inhibitory activity of Cidofovir [1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine dihydrate, HPMPC, GS-504] against adenovirus type 5 (Ad5) in the New Zealand rabbit ocular replication model was evaluated. The 50% inhibitory dose (ID50) of Cidofovir was determined to be 4.7-9.5 micrograms/ml against four adenoviruses (two Ad5, Ad8 and Ad14) by plaque reduction assay in A549 cells. Twenty-four New Zealand rabbits received intrastromal inoculation and topical application of 2 x 10(6) plaque-forming units (PFU) per eye of Ad5 McEwen, a clinical isolate. Cidofovir was administered topically at three different concentrations twice per day, beginning 16 h postinoculation and continuing for 20 consecutive days. The inhibitory effects were determined by measuring suppression of virus replication and by observation of the clinical effects. Compared to the placebo group, the 1% and 0.5% Cidofovir-treated groups showed significantly reduced Ad5 ocular titers, fewer days of viral shedding and less severe subepithelial opacities (P = 0.0001). The 1% Cidofovir group had the lowest humoral antibody titer against adenovirus antigens, but the difference was not significant (P = 0.24). Cidofovir proved to have potent antiviral activity against adenovirus replication and may have great promise for the treatment of adenovirus infection. Further investigation is recommended.

Efficacy of BMS-180194 against experimental cytomegalovirus infections in immunocompromised mice

A new antiviral nucleoside, BMS-180194 [1R-(1 alpha, 2 beta, 3 alpha)]- 2-amino-9[2,3-bis(hydroxymethyl)cyclobutyl]-1,9dihydro-6H-purin-6- one, is a broad spectrum antiviral agent. The antiviral effectiveness of BMS-180194 against murine cytomegalovirus (MCMV) infection in immunocompromised C57BL/6 mice was investigated and was compared to that of ganciclovir (GCV). LP-BM5 murine retrovirus complex-induced immunocompromised C57BL/6 mice were challenged with MCMV then treated intraperitoneally or per os with various doses of BMS-180194 ranging from 30 to 3 mg/kg/day. When administered intraperitoneally, BMS-180194 was effective against MCMV-mediated mortality in a dose-dependent manner demonstrating a 50% protective dose (PD50) of 3.12 mg/kg/day which was comparable to that of GCV. There was a marked reduction in organ MCMV titers in BMS-180194-treated animals (10-10,000- fold lower than the placebo controls). Similar findings were observed when the compound was administered orally. Interestingly, oral BMS-180194 demonstrated a similar antiviral efficacy as that obtained by the parental route of administration suggesting a high oral bioavailability of the compound. Oral ganciclovir treatment, however, required more than a 4-fold higher amount of GCV to confer the same degree of protection obtained by a parenteral route of administration. Oral BMS-180194 was also effective in reducing the organ MCMV titer in genetically severe combined immunodeficient (SCID) mice. The parenteral or oral antiviral efficacy of BMS-180194 was comparable to that of parenteral ganciclovir against MCMV infection in the present study. Doses of BMS-180194 employed in the present study showed no toxicity to mice. These results suggest that BMS-180194 may be of value as an oral antiviral agent for treatment of opportunistic CMV infections in immunocompromised individuals.

Safety of 9-(2-phosphonylmethoxyethyl)adenine (PMEA) in patients with human immunodeficiency virus infection: a pilot study

The compound 9-(2-phosphonylmethoxyethyl)adenine (PMEA) is a potent inhibitor of a number of viruses in vitro such as human immunodeficiency virus types 1 and 2, herpes simplex virus types 1 and 2, hepatitis B virus, cytomegalovirus, and Epstein-Barr virus. PMEA also proved to be effective in vivo against feline immunodeficiency virus in cats and simian immunodeficiency virus in rhesus monkeys. In an open, non-placebo-controlled trial, the safety of weekly doses of PMEA in 10 patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex was studied for a period of 11 weeks. CD4+ T-cell counts at baseline were between 10 and 450/mm(3). The drug was administered intravenously at a dose of 1000 mg. No serious side-effects were seen. On one occasion one patient showed alanine aminotransferase and aspartate aminotransferase levels 5 times higher than the upper limit of normal and another patient showed on one occasion aspartate aminotransferase levels 5 times higher than the upper limit of normal. In another patient serum amalyse levels increased, on one occasion 1.5 times above the upper limit of normal. An improvement in general well-being was reported by all patients. For patients with a CD4+ T-cell count > 100/mm(3) at baseline, the CD4+ T-cell count increased from a mean of 283/mm(3) at baseline to a mean of 448/mm(3) at the end of the study. Repeat infusions of PMEA at a dose of 1000 mg were safe and well tolerated. Our results suggest that PMEA, administrated according to this treatment schedule, may be effective in treating patients with human immunodeficiency virus infection.

Antiviral activity of 9-[[(ethoxyhydroxyphosphinyl)-methoxy]methoxy] guanine against cytomegalovirus and herpes simplex virus

An isosteric analog of 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG), 9-[[(ethoxyhydroxyphosphinyl)methoxy]methoxy]guanine (SKI 1008), was evaluated for its in vitro antiviral activity against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), murine cytomegalovirus (MCMV), and human cytomegalovirus (HCMV), and its in vivo antiviral efficacy against MCMV in mice. The in vitro anti-HSV activity of SKI 1008 was much lower than that of acyclovir, even though SKI 1008 showed similar antiviral activity against thymidine kinase positive (TK+) and thymidine kinase negative (TK-) strains. Like ganciclovir and PMEG, SKI 1008 selectively inhibited plaque formation of MCMV; the 50% effective concentration (EC50) and the 50% cytotoxic concentration (CC50) of SKI 1008, ganciclovir, and PMEG being 0.51 and 600, 1.65 and 461, and 0.06 and 12.1 micrograms/ml, respectively. The in vitro EC50 value of SKI 1008 against HCMV was comparable to that of ganciclovir (0.24 vs 0.16 microgram/ml) and was 12-fold higher than that of PMEG in a plaque reduction assay, but the therapeutic indices (the ratios of CC50 to EC50) of SKI 1008 and ganciclovir were higher than that of PMEG. The in vivo antiviral efficacy of SKI 1008 in MCMV-infected normal BALB/c and severe combined immunodeficiency (SCID) mice was lower than that of ganciclovir in terms of mortality and mean survival time.

Antiviral agents in dermatology: current status and future prospects

The majority of current antiviral agents have become available only during the past decade. The above mentioned antiviral drugs, especially the viral-TK-specific agents have attempted to bring antiviral therapy on par with antimicrobial therapy. The fact, that cells infected with viruses can be selected against the relatively low toxicity to the patient, highlights the present state of antiviral therapy. Since viral infection can be viewed as an integral component of the self (i.e., a condition that cannot simply be surgically eliminated), the science of medicine is turning to the components of the self to overcome such conditions. By administering immune-system-derived agents (e.g., interferons) or compounds that stimulate the immune system (e.g., adjuvants like imiquimod), previously unmanageable conditions become manageable. The future of antiviral therapy will undoubtedly be at the molecular level. With greater understanding of the virus and the immune system with which it interacts, more specific and efficacious antiviral agents will be added to the arsenal of the clinician.

Phase I/II study of intravitreal cidofovir for the treatment of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome

PURPOSE

In this study we evaluated the safety and efficacy of the nucleoside phosphonate analogue intravitreal cidofovir to treat cytomegalovirus retinitis in humans.

METHODS

We conducted a phase I/II unmasked consecutive case series in a single-center institutional referral practice. Eligible patients with the acquired immunodeficiency syndrome had active cytomegalovirus retinitis in at least one eye, despite adequate intravenous therapy with ganciclovir or foscarnet, were intolerant to intravenous therapy, were noncompliant with intravenous therapy, or refused intravenous therapy. In a preliminary safety study (Group 1), ten eyes of nine patients received 14 injections of cidofovir while being treated concurrently with intravenous ganciclovir. In a dose-escalating efficacy study (Group 2), eight eyes of seven patients received 11 injections of cidofovir as sole treatment for cytomegalovirus retinitis. The primary outcome was time to retinitis progression.

RESULTS

In the Group 1 eyes receiving 20 micrograms of cidofovir, the median time to retinitis progression was between 49 and 92 days (mean, 78 days). In Group 2 eyes treated with 20 micrograms cidofovir, the median time to retinitis progression was 64 days (mean, 63 days). Hypotony occurred in the two eyes treated with a 100-micrograms dose of cidofovir and in one of three eyes receiving a 40-micrograms dose. No adverse effects resulted from the remaining 20 cidofovir injections.

CONCLUSIONS

Cidofovir (also known as HPMPC) appears to be safe and effective for the local treatment of cytomegalovirus retinitis, providing a long duration of antiviral effect. These preliminary results indicate that additional studies should be performed to investigate more fully this promising medication.

In vivo antiherpesvirus activity of N-7-substituted acyclic nucleoside analog 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine

The efficacy of 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (S2242) was evaluated in several animal models for herpesvirus infections. Compound S2242 was more effective than acyclovir (i) when administered subcutaneously in a model for herpes simplex virus type 1 (HSV-1)-induced mortality in immunocompetent mice and (ii) when applied topically to hairless (hr/hr) mice that had been infected intracutaneously with HSV-2. In SCID (severe combined immune deficient) mice that had been infected with a thymidine kinase-deficient HSV-1 strain, S2242 (administered subcutaneously at a dosage of 50 mg/kg/day) completely protected against virus-induced mortality whereas foscarnet was less effective and acyclovir had no or little protective effect. Compound S2242 was far more effective than ganciclovir in preventing or delaying murine cytomegalovirus-induced mortality in immunocompetent and SCID mice. The compound was more effective when a given dose was fractionated and administered on subsequent days than when this dose was administered in one single injection. A 5-day treatment course with S2242 (10 and 50 mg/kg/day) for newborn mice that had been infected with a lethal dose of murine cytomegalovirus suppressed virus-induced mortality. Compound S2242 had no inhibitory effect on the growth of weanling (at 50 mg/kg for 5 days) and 3- to 4-week-old mice (at doses of 50 to 200 mg/kg for 6 weeks). However, akin to ganciclovir, compound S2242 significantly reduced testicle weight, testicle morphology, and spermatogenesis.

The N-7-substituted acyclic nucleoside analog 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine is a potent and selective inhibitor of herpesvirus replication

2-Amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (compound S2242) represents the first antivirally active nucleoside analog with the side chain attached to the N-7 position of the purine ring. Compound S2242 strongly inhibits the in vitro replication of both herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) (50% effective concentration [EC50], 0.1 to 0.2 microgram/ml), varicella-zoster virus (EC50, 0.01 to 0.02 microgram/ml) and thymidine kinase (TK)-deficient strains of HSV (EC50, 0.4 microgram/ml) and varicella-zoster virus (EC50, 0.2 to 0.5 microgram/ml). Potent activity was also observed against murine cytomegalovirus (EC50, 1 microgram/ml), human cytomegalovirus (HCMV) (EC50, 0.04 to 0.1 microgram/ml), and human herpesvirus 6 (EC50, 0.0005 microgram/ml). Compound S2242 (i) was not cytotoxic to confluent Vero, HeLa, or human fibroblast cells at concentrations of > 100 micrograms/ml, (ii) proved somewhat more cytostatic to Vero, HEL, HeLa, and C127I cells than ganciclovir, and (iii) was markedly more cytostatic than ganciclovir to the growth of the human lymphocytic cell lines HSB-2 and CEM degrees. In contrast to ganciclovir, (i) compound S2242 proved not to be cytocidal to murine mammary carcinoma (FM3A) cells transfected with the HSV-1 or HSV-2 TK gene, (ii) exogenously added thymidine had only a limited effect on its anti-HSV-1 activity, and (iii) the compound was not phosphorylated by HSV-1-encoded TK derived from HSV-1 TK-transfected FM3A cells, indicating that the compound is not activated by a virally encoded TK. Compound S2242 inhibited (i) the expression of late HCHV antigens at an EC50 of 0.07 microgram/ml (0.6 microgram/ml for ganciclovir) and (ii) HCMV DNA synthesis at an EC50 of 0.1 microgram/ml (0.32 microgram/ml for ganciclovir), i.e., values that are close to the EC50S for inhibition of HCMV-induced cytopathogenicity. Neither ganciclovir nor S2242 had any effect on the expression of immediate-early HCMV antigens, which occurs before viral DNA synthesis. In time-of-addition experiments, S2242 behaved like ganciclovir and acyclovir; i.e., the addition of the drugs could be delayed until the onset of viral DNA synthesis.

Nucleotide analogs related to acyclovir and ganciclovir are effective against murine cytomegalovirus infections in BALB/c and severe combined immunodeficient mice

Acyclovir phosphonate [9-(3-phosphono-propyloxymethyl)guanine; SR3722] and the S enantiomer (SR3772), R enantiomer (SR3773), and R,S enantiomeric mixture (SR3745A) of ganciclovir phosphonate (9-[((+/-)-1-hydroxymethyl-3-phosphono)propyloxymethyl]guanine) were evaluated for their antiviral activities against murine cytomegalovirus. In severe combined immunodeficient mice infected with murine cytomegalovirus, SR3773 and SR3745A (12.5, 25, and 50 mg/kg of body weight per day) were superior to ganciclovir in extending the mean time to death, whereas SR3722 and SR3772 was less potent than ganciclovir. In normal BALB/c mice, SR3773 and ganciclovir were approximately equally active in preventing death. SR3773 caused renal tubular damage when administered at 50 mg/kg/day for 15 days. These results suggest that SR3773 may have potential for use in the treatment of human cytomegalovirus infections, but it may also exhibit renal toxicity.

Mechanism of action of acyclic nucleoside phosphonates against herpes virus replication

Foremost among the acyclic nucleoside phosphonates currently pursued for their potential in the treatment of herpes and retrovirus infections are (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC) and 9-(2-phosphonylmethoxyethyl)adenine (PMEA). These compounds are as such taken up by the cells and then phosphorylated by cellular enzymes to their diphosphoryl derivatives HPMPCpp and PMEApp. The main target for the antiviral action of HPMPCpp and PMEApp is the viral DNA polymerase. Whereas PMEApp has been shown to interact as a DNA chain terminator with both retro- and herpes viruses, the mechanism by which HPMPCpp inhibits herpes viral DNA synthesis remains the subject of further study.

Efficacy of (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine for the treatment of lethal vaccinia virus infections in severe combined immune deficiency (SCID) mice

Severe combined immune deficient (SCID) mice inoculated intravenously with vaccinia virus (VV) became sick within 6-8 days and died 10-12 days after infection. Tail lesions developed and the number depended on the virus inoculum. Age-matched immunocompetent NMRI mice similarly infected also developed tail lesions but did not become sick. When the infected SCID mice were treated with the acyclic nucleoside phosphonate HPMPC [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine], either for 5 consecutive days starting on the day of infection or for 5 consecutive days starting on day 2, 4, or 6 post infection, or as a single dose at 7 days or 1 day before infection, VV-associated death was significantly delayed. VV-infected SCID mice that received two doses of 20 mg/kg of HPMPC every week survived the infection for about 130 days. The period during which the mice remained disease-free following HPMPC treatment correlated with the absence of detectable virus in their organs. The VV/SCID mouse model employed here may be useful for determining whether (attenuated) recombinant VV (carrying HIV genes) may have detrimental effects in the immunodeficient host. HPMPC may be considered as a drug candidate for the treatment and prophylaxis of such complications.

Inhibitory activity of S-adenosylhomocysteine hydrolase inhibitors against human cytomegalovirus replication

Various acyclic and carbocyclic adenosine analogues, which are apparently targeted at the S-adenosylhomocysteine (AdoHcy) hydrolase have been reported to inhibit the replication of a number of pox-, rhabdo-, paramyxo-, arena-, and reoviruses. Here we show that this activity spectrum extends to human cytomegalovirus (HCMV). Of the compounds tested, neplanocin A, 3-deazaneplanocin A, 6'-C-methylneplanocin A and 5'-noraristeromycin were found to be the most potent inhibitors of HCMV replication in vitro. Their 50% inhibitory concentration ranged from 0.05 to 1.35 micrograms/ml. In general, the anti-HCMV activity of the adenosine analogues correlated well with their affinity (Ki) for AdoHcy hydrolase, suggesting that AdoHcy hydrolase may be considered as a target enzyme for anti-HCMV agents. For four compounds (3-deazaneplanocin A, 6'-C-methylneplanocin A (isomers I and II) and 3-deazaadenosine), anti-HCMV potency was greater than could be expected solely from their interaction with AdoHcy hydrolase, suggesting that these compounds may be functioning by an additional mechanism.

Protective activity of lipid A analogue GLA-60 against murine cytomegalovirus infection in mice

A chemically synthesized lipid A subunit analogue, GLA-60 (2-deoxy-4-O-phosphono-2-[(3R)-3-hydroxytetradecanamido]-3-O-[(3R) - 3-tetradecanoyloxytetradecanoyl]-D-glucose), has many of the activities of endotoxins but little, if any, toxicity. We investigated the protective activity of GLA-60 against murine cytomegalovirus (MCMV) infection in NMRI mice. Intraperitoneal administration of GLA-60 at 1 day before MCMV infection at doses of 1, 10, or 100 micrograms per mouse significantly reduced mortality. GLA-60 stimulated peritoneal natural killer (NK) cell and macrophage activities, and these activities were abolished by in vitro treatment with anti-asialo GM1 antibody and anti-Mac1 antibody, respectively. GLA-60 proved also protective against MCMV infection in mice in which either NK cells or macrophages were depleted by in vivo treatment with anti-asialo GM1 or anti-Mac1 antibody. The anti-MCMV activity of GLA-60 can at least be partially attributed to activation of NK cells and macrophages.

Activity of the anti-HIV agent 9-(2-phosphonyl-methoxyethyl)-2,6-diaminopurine against cytomegalovirus in vitro and in vivo

9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP), a potent inhibitor of human immunodeficiency virus (HIV) replication, was evaluated for its activity against human cytomegalovirus (HCMV) in vitro, and murine cytomegalovirus (MCMV) and rat CMV (RCMV) in vivo. PMEDAP strongly inhibited HCMV-induced cytopathicity in human embryonic lung (HEL) cell cultures (EC50 11 microM) and caused a concentration-dependent suppression of viral DNA synthesis (IC50 20 microM) [corrected]. PMEDAP had no effect on the expression of HCMV-specific immediate early antigens (IEA) as measured on day 1 post-infection, but inhibited the expression of HCMV late antigens as measured on day 6 post-infection (EC50 20 microM) [corrected]. The diphosphate derivative of PMEDAP (PMEDAPpp) selectively inhibited HCMV-induced DNA polymerase (IC50 0.1 microM). PMEDAP proved markedly effective in reducing the mortality rate of NMRI mice that had been infected intraperitoneally or intracerebrally with a lethal dose of MCMV. PMEDAP exhibited greater anti-MCMV activity when administered as a single dose immediately after infection than when this dose was divided over repeated administrations. 9-(2-phosphonylmethoxyethyl)-adenine (PMEA) also prevented MCMV-induced mortality, but only at a dose ten-fold higher than that of PMEDAP. PMEDAP also delayed death in severe combined immune deficiency (SCID) mice that had been infected with MCMV. The effect of PMEDAP on RCMV infections in rats was less pronounced.

Evaluation of HPMPC therapy for primary and recurrent genital herpes in mice and guinea pigs

The nucleoside analogue (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC) inhibited the replication of herpes simplex virus (HSV) types 1 and 2 in tissue culture cells at about 1.0 micrograms/ml, whereas Acyclovir (ACV) had an EC50 of about 0.10-0.50 micrograms/ml. The purpose of these studies was to evaluate the efficacy of topically applied HPMPC in animal models of primary and recurrent genital HSV-2 infections. Mice treated with 5%, 1% or 0.5% HPMPC three times daily, beginning 6 or 24 h after virus inoculation had reduced vaginal viral replication regardless of time of initiation of therapy. ACV at 5% also reduced vaginal viral replication, but not as effectively as HPMPC. In primary infection of guinea pigs, therapy with 5% or 1% HPMPC beginning at 24 h but not 72 h significantly altered lesion development. However, 5% HPMPC was highly toxic to guinea pigs. Vaginal viral replication was reduced significantly with either 1% or 0.3% HPMPC initiated at 24 h. In these studies, HPMPC was also more efficacious than 5% ACV. Topical treatment with 1% HPMPC did not reduce the incidence or severity of spontaneous or UV-induced recurrent genital lesions. These results indicate that topical therapy with 1%, 0.5% or 0.3% HPMPC was more effective than 5% ACV in the treatment of primary genital HSV-2 infections of guinea pigs and mice and suggest that HPMPC should be considered for topical use in humans.

Efficacy of (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)-cytosine and 9-(1,3-dihydroxy-2-propoxymethyl)-guanine in the treatment of intracerebral murine cytomegalovirus infections in immunocompetent and immunodeficient mice

The efficacy of HPMPC and DHPG against systemic and intracerebral murine cytomegalovirus (MCMV) infections was examined in immunocompetent NMRI mice and in mice with severe combined immunodeficiency (SCID). HPMPC proved to be far superior to DHPG in preventing mortality and growth retardation in MCMV-infected NMRI mice even when given as a single dose on the day of infection. In intraperitoneally infected SCID mice, HPMPC administered as a single dose of 2, 10, 20 or 50 mg/kg per week increased the survival period of the mice by 22, 49, 77 and 156 days, respectively. In contrast, DHPG at daily doses of 10, 20 or 50 mg/kg for five consecutive days every week did not delay death by more than 13, 17 and 21 days, respectively. About one week before the MCMV-infected SCID mice (treated with either DHPG or HPMPC) died, they developed signs of neurological disease and intranuclear inclusion-bearing cells were found in their brains. The virus that was recovered from the brains of these mice did not prove to be resistant to HPMPC or DHPG. Only the virus recovered from the brains of mice treated with HPMPC at a dosage of 50 mg/kg/week had a slightly decreased susceptibility to HPMPC. When HPMPC (50 mg/kg for 4 consecutive days) was administered to SCID mice at the time when neurological symptoms became apparent, death of the animals could be delayed by another 35 to 40 days.

Efficacy of oral 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP) in the treatment of retrovirus and cytomegalovirus infections in mice

9-(2-Phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP) is a broad-spectrum antiviral agent with potent activity against DNA viruses and retroviruses. We now demonstrate that PMEDAP is highly efficacious when given orally to mice infected with either Moloney murine sarcoma virus (MSV), Friend leukemia virus (FLV), or murine cytomegalovirus (MCMV). PMEDAP markedly delayed MSV-induced tumor initiation when administered orally at 50, 100, or 250 mg/kg/day during 5 subsequent days. At the highest dose (250 mg/kg/day), PMEDAP completely prevented tumor formation in the MSV-infected animals. PMEDAP also caused 84-96% inhibition of FLV-induced splenomegaly when given orally to FLV-infected mice at 50-250 mg/kg/day. These PMEDAP treatment regimens were also markedly effective in increasing the survival rate of MCMV-infected mice. Intraperitoneal PMEDAP achieved a comparable antiviral activity at 2- to 5-fold lower doses than oral PMEDAP. However, the therapeutic index (ratio of the toxic dose to the antivirally effective dose) of oral PMEDAP was substantially higher than that of intraperitoneal PMEDAP. Oral PMEDAP at doses of 100, 250, or 500 mg/kg resulted in plasma PMEDAP levels of 0.5-2.5 micrograms/ml, which were sustained for 3 or 6 hours after administration and may account for the high antiviral efficacy achieved.

Rat cytomegalovirus-induced pneumonitis after allogeneic bone marrow transplantation: effective treatment with (S)-1-(3-hydroxy-2-phosphonyl-methoxypropyl)cytosine

Two antiviral compounds, (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC) and 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG), were evaluated for their effects on rat cytomegalovirus (RCMV)-induced interstitial pneumonitis after allogeneic bone marrow transplantation (BMTx). Eight-week-old Brown Norway rats immunosuppressed by a lethal dose of total body irradiation were inoculated with RCMV and received allogeneic bone marrow cells from Lewis rats. Animals were treated with either HPMPC (20 mg/kg of body weight as a single dose) or DHPG (20 mg/kg as two daily doses for 5 days). The effect of antiviral therapy was monitored by measuring RCMV titers in different organs and the histopathologic changes in lungs at 8 to 10 days postinfection. In RCMV-infected allogeneic BMTx recipients, severe diffuse thickening of alveolar septa (6.02 microns) with a diffuse infiltration of mononuclear cells occurred, whereas in the noninfected allogeneic BMTx recipients, the septal width was on the order of 2 microns (P < 0.01). Treatment with DHPG (20 mg/kg in two daily doses for 5 days) resulted in a decrease in virus titers (log10 PFU per gram of tissue) in lungs and spleens from 3.81 +/- 0.34 and 4.29 +/- 1.07 (untreated animals) to 1.26 +/- 0.53 and 3.22 +/- 0.27 (treated animals), respectively. Treatment with HPMPC (20 mg/kg as a single dose) resulted in a complete reduction of virus titers in all organs to below the detection level (P < 0.01). Furthermore, antiviral treatment resulted in a reduction of the alveolar septal width from 6.02 +/- 1.59 microns (untreated animals) to 4.67 +/- 1.70 and 3.32 +/- 0.63 microns after DHPG and HPMPC treatment, respectively. Treatment with HPMPC (20 mg/kg as a single dose) resulted in a complete reduction of virus titers in all organs to below the detection level (P <0.01). Furthermore, antiviral treatment resulted in a reduction of the alveolar septal width from 6.02 +/- 1.59 micrometre (untreated animals) to 4.67 +/- 0.63 micrometre after DHPG and HPMPC treatment, respectively. Furthermore, the influx of mononuclear cells in the alveolar septa was significantly impaired after treatment with HPMPC (P <0.01). We conclude that in the described rat model, HPMPC is highly effective in suppressing RCMV-induced interstitial pneumonitis after allogeneic BMTx.

Activity of different antiviral drug combinations against human cytomegalovirus replication in vitro

The effects of different antiviral drug combinations on the replication of various human cytomegalovirus (CMV) strains in human embryonic lung (HEL) fibroblasts were evaluated. HPMPC combined with either ganciclovir, foscarnet or acyclovir showed additive to synergistic inhibition of CMV replication. Combinations of zidovudine with HPMPC, ganciclovir, foscarnet or acyclovir also resulted in additive to synergistic inhibition of CMV replication. Synergism tended to be higher for the clinical CMV isolates than for the reference strains AD-169 and Davis. Suppression of CMV replication was obtained at lower drug concentrations when the drugs were combined than when the drugs were used alone. At the highest drug concentrations used in the antiviral activity experiments, neither drug alone nor its combination suppressed host cell growth. If higher drug concentrations were used, zidovudine increased the inhibitory effects of ganciclovir, acyclovir and foscarnet but not of HPMPC, on cell proliferation. Use of combinations in the therapy of CMV infections may be considered to enhance drug efficacy, to reduce toxicity and, possibly, to diminish the risk of emergence of drug-resistant virus strains.