Clinical uses of cidofovir

Ganciclovir and cidofovir treatment of cytomegalovirus-induced myocarditis in mice

The cardiovascular disease myocarditis is characterized by inflammation and necrosis of cardiac muscle. This disease has been associated with various viral etiologies, including cytomegalovirus (CMV). Murine CMV (MCMV) infection of adult BALB/c mice produces a disease with acute and chronic phases similar to that found in humans. In our murine model, we have investigated the therapeutic efficacy of antiviral drug administration on myocarditis. Two drugs commonly used for CMV treatment, ganciclovir and cidofovir, were subjected to trials, with both drugs showing potent antiviral activity against MCMV both in vitro and in vivo. The acute phase of myocarditis was significantly reduced when antiviral therapy commenced 24 h postinfection. Such treatment also reduced the severity of the chronic phase of myocarditis. In contrast, antiviral treatment commencing after the acute phase had no effect on chronic myocarditis. Reinfection of mice with MCMV caused exacerbation of myocardial inflammation. Such an increase in severity of myocarditis could be prevented with either ganciclovir or cidofovir treatment, but the preexisting inflammation and necrosis of the myocardium persisted. These data highlight possible therapeutic uses of antiviral drugs in viral myocarditis as well as further elucidating the pathogenic nature of the disease.

Vaccinia virus inhibitors as a paradigm for the chemotherapy of poxvirus infections

Poxviruses continue to pose a major threat to human health. Monkeypox is endemic in central Africa, and the discontinuation of the vaccination (with vaccinia virus) has rendered most humans vulnerable to variola virus, the etiologic agent of smallpox, should this virus be used in biological warfare or terrorism. However, a large variety of compounds have been described that are potent inhibitors of vaccinia virus replication and could be expected to be active against other poxviruses as well. These compounds could be grouped in different classes: (i) IMP dehydrogenase inhibitors (e.g., EICAR); (ii) SAH hydrolase inhibitors (e.g., 5'-noraristeromycin, 3-deazaneplanocin A, and various neplanocin A derivatives); (iii) OMP decarboxylase inhibitors (e.g., pyrazofurin) and CTP synthetase inhibitors (e.g., cyclopentenyl cytosine); (iv) thymidylate synthase inhibitors (e.g., 5-substituted 2'-deoxyuridines); (v) nucleoside analogues that are targeted at viral DNA synthesis (e.g., Ara-A); (vi) acyclic nucleoside phosphonates [e.g., (S)-HPMPA and (S)-HPMPC (cidofovir)]; and (vii) polyanionic substances (e.g., polyacrylic acid). All these compounds could be considered potential candidate drugs for the therapy and prophylaxis of poxvirus infections at large. Some of these compounds, in particular polyacrylic acid and cidofovir, were found to generate, on single-dose administration, a long-lasting protective efficacy against vaccinia virus infection in vivo. Cidofovir, which has been approved for the treatment of cytomegalovirus retinitis in immunocompromised patients, was also found to protect mice, again when given as a single dose, against a lethal aerosolized or intranasal cowpox virus challenge. In a biological warfare scenario, it would be advantageous to be able to use a single treatment for an individual exposed to an aerosolized poxvirus. Cidofovir thus holds great promise for treating human smallpox, monkeypox, and other poxvirus infections. Anecdotal experience points to the efficacy of cidofovir in the treatment of the poxvirus infections molluscum contagiosum and orf (ecthyma contagiosum) in immunosuppressed patients.

Antiviral agents

The potential severity of many viral infections and the lack of appropriate treatment for these diseases have been a source of endless frustration and helplessness for clinicians. The newly developed field of antiviral therapy is expanding at an astounding rate, with new discoveries each day. Although physicians are not yet able to cure many of the viral infections, such as HSV, HIV, and CMV, a means of controlling them is available. It is hoped that the research and investigations currently under way will lead to a future era of antiviral drugs that will be able to eradicate these diseases.

An overview of sexually transmitted diseases. Part III. Sexually transmitted diseases in HIV-infected patients

The HIV epidemic has dramatically altered the field of sexually transmitted diseases (STDs). HIV infection is unique among sexually transmitted diseases because it can modify the clinical presentation and features of other STDs. Conversely, other STDs can affect the transmission of HIV. This review is the third part of a series that has provided a general overview of STDs. In this article, genital ulcer diseases (genital herpes, syphilis, chancroid, lymphogranuloma venereum, and granuloma inguinale), human papillomavirus infection (anogenital warts and subclinical infections), molluscum contagiosum, human herpesvirus 8 infection, viral hepatitis, and ectoparasitic infestations (scabies and pediculosis pubis) are discussed as they occur in HIV-infected hosts. Additional features as they relate to HIV-infected patients, such as epidemiology and transmission, are discussed when applicable.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should improve their understanding of sexually transmitted diseases in the HIV-infected host.

Progressive multifocal leukoencephalopathy treated with cidofovir in HIV-infected patients receiving highly active anti-retroviral therapy

Progressive multifocal leukoencephalopathy (PML) has been a devastating disease for HIV-1-infected patients since the beginning of the AIDS pandemic. Currently, highly active antiretroviral therapy (HAART) seems to improve the outcome of PML in many patients. We describe two cases of PML whose course worsened in spite of HAART, but had a good response to cidofovir.

Novel agents for the therapy of varicella-zoster virus infections

Varicella-zoster virus (VZV), a member of the herpesvirus family, is responsible for both primary (varicella or chickenpox) as well as recurrent (zoster or shingles) infections. Acyclovir has been the mainstay for treating VZV infections in both immunocompetent and immunocompromised patients. Recently, newer anti-VZV drugs, i.e., valaciclovir (the oral prodrug form of acyclovir) and famciclovir (the oral prodrug form of penciclovir) have been developed and have enlarged the therapeutic options to treat VZV infections. Both acyclovir and penciclovir are dependent on the virus-encoded thymidine kinase (TK) for their intracellular activation. Although emergence of drug-resistant strains does not occur in immunocompetent patients, several reports have documented the isolation of drug-resistant VZV strains following long-term acyclovir therapy in immunocompromised patients. Mutations at the level of the TK are responsible for development of resistance to drugs that depend on the viral TK for their phosphorylation (i.e., acyclovir and penciclovir). Foscarnet, a direct inhibitor of the viral DNA polymerase, which does not require activation by the viral TK, is the drug of choice for the treatment of TK-deficient VZV mutants emerging under acyclovir therapy. Recently, emergence of foscarnet-resistant strains has also been reported. Both TK-deficient strains and foscarnet-resistant mutants are sensitive to the acyclic nucleoside phosphonate cidofovir, CDV, HPMPC, (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine. This agent does not depend on the virus-encoded TK, but on cellular enzymes for its conversion to the diphosphoryl derivative, which then inhibits the viral DNA polymerase.

Prediction of cytomegalovirus load and resistance patterns after antiviral chemotherapy

Cytomegalovirus (CMV) replicates rapidly in its human host with a doubling time of approximately 1 day. Using simple mathematical models we show that the efficacy of the anti-CMV drug ganciclovir (GCV) against wild-type strains is 91.5% [95% confidence interval (CI) 89-94%] when given i.v. (5 mg/kg twice a day) but only 46.5% (95% CI 45-47.5%) when given orally (1 g three times a day) whereas the corresponding figures for a typical GCV-resistant virus are 62% (95% CI 57-66%) and 35% (95% CI 33-37%), respectively. During prolonged periods of GCV therapy we show that the apparent sudden appearance of GCV resistance is explained by the combination of two exponentially increasing populations (wild type and mutant) at doses of GCV that do not completely inhibit CMV replication. Cell culture methods to assess CMV drug resistance in vivo will underestimate its prevalence because of the fitness loss of resistant virus in the absence of therapy. The parameters determined from these models then were used to predict the likely viral load and resistance patterns in patients on prolonged therapy with GCV. The modeled and experimental data showed excellent agreement over extended time periods (up to 270 days of therapy) and provide a framework to predict the virologic course of patients at therapeutic initiation.

Resistance of herpes simplex virus type 1 against different phosphonylmethoxyalkyl derivatives of purines and pyrimidines due to specific mutations in the viral DNA polymerase gene

Drug-resistant strains of herpes simplex virus type 1 (HSV-1) were selected under the pressure of (S)-3-hydroxy-2-phosphonylmethoxypropyl (HPMP) derivatives of cytosine (HPMPC, cidofovir) and adenine (HPMPA) and 2-phosphonylmethoxyethyl (PME) derivatives of adenine (PMEA, adefovir) and 2,6-diaminopurine (PMEDAP). HPMPC-resistant (HPMPC(r)) and HPMPA(r) strains were cross-resistant to one another, but they remained sensitive to foscarnet (PFA), acyclovir (ACV) and the PME derivatives, while the PMEA(r) and PMEDAP(r) strains showed cross-resistance to PFA and ACV. The PMEA(r), PMEDAP(r) and PFA(r) mutants all revealed a single nucleotide change resulting in a Ser-724 to Asn mutation within the conserved region II of the DNA polymerase. Two HPMPA(r) clones and one HPMPC(r) clone possessed single amino acid changes in the DNA polymerase (HPMPA(r) clone D1, Leu-1007 to Met; HPMPA(r) clone B5, Ile-1028 to Thr; HPMPC(r) clone C3, Val-573 to Met). The HPMPC(r) clone A4 contained two mutations, Ala-136 to Thr and Arg-700 to Met. The mutation at position 136, located outside the catalytic domain of the enzyme, was not detected in other HPMPC(r) clones, suggesting that this mutation may not be responsible for the resistant phenotype. Residue 573 is located within the 3'-->5' exonuclease editing domain close to the catalytically important residues Tyr-577 and Asp-581. Similarly, residue 700 is located in the palm subdomain of the catalytic domain, adjacent to the Asp residues 717, 886 and 888 that are vital for polymerase activity. The HPMPA(r) mutations at residues 1007 and 1028, beyond the last conserved region, still fall within the thumb subdomain of the catalytic domain. The different drug-resistant mutants varied in neurovirulent behaviour, the HPMPC(r) strains showing reduced neurovirulence compared with the wild-type.

Cidofovir, a new approach for the treatment of cervix intraepithelial neoplasia grade III (CIN III)

Cervix intraepithelial neoplasia grade III (CIN III) is an intraepithelial proliferative process with different levels of severity depending on both the extension of the proliferation in the epithelium and the presence of cellular atypia. Human papillomavirus (HPV) has been clearly associated with such lesions. The results of a preliminary study are described on the local application of cidofovir, an acyclic nucleoside phosphonate derivative with broad-spectrum anti-DNA virus activity for the treatment of CIN III. Cidofovir 1% in gel was applied three times, every other day, on the cervix of each of 15 women with biopsy proven CIN III. Within 1 month after the start of treatment, the cervix was removed surgically. Histology and human papillomavirus polymerase chain reaction (HPV-PCR) were carried out. In 7 of the 15 patients the histology showed a complete response, whereas 5 patients had a partial response characterized by the persistence of CIN II-III lesions, 1 patient had a dysplasia of lower grade (CIN I), and 2 patients did not show differences in the histology. Complete response was confirmed by PCR in 4 of the 7 patients, with complete response histologically. Cidofovir was not toxic to the normal epithelium. Cidofovir 1% gel was able to inhibit partially or completely cervical dysplasia lesions after only three applications (every other day). This effect was specific and tissue other than the dysplastic epithelium was not affected by the treatment.

Human herpesvirus 7

Human herpesvirus 7, reported in 1990 is a lymphotropic member of the betaherpesvirus subfamily of herpesviruses. The virus is highly seroprevalent, primary infection usually occurs during childhood, and it has been associated with cases of exanthem subitum, pityriasis rosea, neurological manifestations and transplant complications. The latter two may warrant antiviral intervention, in vitro studies have shown that HHV-7 is susceptible to several nucleoside phosphonate compounds. In vitro, the virus has approximately a 5 day growth cycle in cultured lymphocytes; in vivo, latency is established in peripheral blood T-cells and a persistent infection is established in salivary gland tissue from which infectious virus is constitutively shed in saliva. The HHV-7 genome is approximately 145 kb and encodes at least 84 different proteins. Studies characterising HHV-7 gene products and the required interactions between viral and cellular genes necessary for virus replication, persistence and latency are in their infancy. HHV-7 infection has a variety of effects on host cells including upregulation of interleukin 15 and down-modulation of the cell surface molecule CD4; the latter serves as the cellular membrane receptor for HHV-7. Since HIV also infects T-cells via the CD4 molecule, the interactions of these viruses within T-cells during the course of AIDS are important areas of investigation.

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.

Management of CMV retinitis in the era of highly active antiretroviral therapy

Although the epidemiological features of CMV retinitis is changing in patients receiving highly active antiretroviral therapy (HAART), continued attention must be paid to detect and treat earlier CMV infections in AIDS patients to prevent severe ophthalmic complications. Initial therapy must be based on characteristics of the CMV retinitis and patient conditions. Long term therapy of HAART must be pursued, even in patients with increased CD4 and undetectable HIV viral load, until results from large controlled studies are available. reserved.

The dynamics of human cytomegalovirus replication in vivo

Cytomegalovirus (CMV) is generally described as a slowly replicating virus. During studies of immunocompromised patients, we observed rapid changes in the quantity of CMV DNA present in serial blood samples by quantitative-competitive polymerase chain reaction commensurate with a doubling time of <2 d. To further investigate the dynamics of replication in vivo, patients in three distinct situations were studied in detail: (a) those receiving intravenous ganciclovir; (b) those in whom ganciclovir-resistant strains appeared during long-term therapy; and (c) those in whom ganciclovir-resistant strains disappeared with alternative drug therapy. In all cases, it was possible to provide accurate estimates of the doubling time of CMV and its half-life of disappearance after antiviral chemotherapy. The results from all three approaches demonstrated that the doubling time/half-life of CMV in blood is approximately 1 d when frequent samples are collected. These results show that CMV DNA replication in vivo is a highly dynamic process. We conclude that the reputation of CMV as a slowly replicating virus based on the time taken to produce cytopathic effects in vitro is unwarranted. These findings have implications for the potency, dose, and duration of antiviral chemotherapy needed for the effective treatment of this important human pathogen.

In vitro sensitivity of Kaposi's sarcoma cells to various chemotherapeutic agents including acyclic nucleoside phosphonates

The involvement of a viral agent in the pathogenesis of Kaposi's sarcoma (KS) points to antiviral agents as possible therapeutic and/or prophylactic options in the management of the disease. In the present study we investigated the antiproliferative effects of various chemotherapeutic agents, including acyclic nucleoside phosphonates, on the growth of KS-derived cells. Nested PCR amplification demonstrated that these cells do not contain human herpesvirus 8 (HHV-8) DNA sequences. The cytotoxicity of the chemotherapeutic compounds was less pronounced in KS cells than in human dermal microvascular endothelial cells, which are considered to be the normal counterpart of KS cells. Stimulation of KS cells with basic fibroblast growth factor (bFGF) and correction of the IC50 values by the doubling times revealed that the apparent chemotherapeutic resistance of KS cells could mainly be attributed to the long doubling times of these cells. bFGF-stimulated KS cells still exhibited no particular sensitivity to the acyclic nucleoside phosphonates whose activity extends to HHV-8, which is consistent with the absence of linear HHV-8 DNA synthesis in these cells. Our data suggest that neither anti-cancer agents nor antiviral agents such as the acyclic nucleoside phosphonates can discriminate efficiently between KS cells and normal endothelial cells.

Current pharmacological approaches to the therapy of varicella zoster virus infections: a guide to treatment

Varicella zoster virus (VZV), a member of the herpesvirus family, is responsible for both primary (varicella, chickenpox) as well as reactivation (zoster, shingles) infections. In immunocompetent patients, the course of varicella is generally benign. For varicella zoster, post-herpetic neuralgia is the most common complication. In immunocompromised patients (particularly those with AIDS), transplant recipients and cancer patients, VZV infections can be life-threatening. For these patients and also for immunocompetent patients at risk such as pregnant women or premature infants, the current treatment of choice is based on either intravenous or oral aciclovir (acyclovir). The low oral bioavailability of aciclovir, as well as the emergence of drug-resistant virus strains, have stimulated efforts towards the development of new compounds for the treatment of individuals with VZV infections. Among these new compounds, penciclovir, its oral prodrug form famciclovir and the oral pro-drug form of aciclovir (valaciclovir), rank among the most promising. As with aciclovir itself, all of these drugs are dependent on the virus-encoded thymidine kinase (TK) for their intracellular activation (phosphorylation), and, upon conversion to their triphosphate form, they act as inhibitors/alternative substrate of the viral DNA polymerase. Therefore, cross-resistance to these drugs may be expected for those virus mutants that are TK-deficient and thus resistant to aciclovir. Other classes of nucleoside analogues dependent for their phosphorylation on the viral TK that have been pursued for the treatment of VZV infections include sorivudine, brivudine, fialuridine, fiacitabine and netivudine. Among oxetanocins, which are partially dependent on viral TK, lobucavir is now under clinical evaluation. Foscarnet, which does not require any previous metabolism to interact with the viral DNA polymerase, is used in the clinic when TK-deficient VZV mutants emerge during aciclovir treatment. TK-deficient mutants are also sensitive to the acyclic nucleoside phosphonates (i.e. [s]-1-[3-hydroxy-2-phosphonylmethoxypropyl]cytosine; HPMPC); these agents do not depend on the virus-encoded TK for their phosphorylation but depend on cellular enzymes for conversion to their diphosphoryl derivatives which then inhibit viral DNA synthesis. Vaccination for VZV has now come of age. It is recommended for healthy children, patients with leukaemia, and patients receiving immunosuppressive therapy or those with chronic diseases. The protection induced by the vaccine seems, to some extent, to include zoster and associated neuralgia. Passive immuniatin based on specific immunoglobulins does not effectively prevent VZV infection and is therefore restricted to high risk individuals (i.e. immunocompromised children and pregnant women).

A multicenter phase I/II dose escalation study of single-dose cidofovir gel for treatment of recurrent genital herpes

A randomized, double-blind, clinic-initiated, sequential dose-escalation pilot study was performed to compare the safety and efficacy of single applications of 1, 3, and 5% cidofovir gel with placebo in the treatment of early, lesional, recurrent genital herpes at five Canadian outpatient sites. Ninety-six patients began treatment within 12 h of lesion appearance and were evaluated twice daily until healing of the lesion occurred. Cidofovir gel at all strengths significantly decreased the median time to negative virus culture in a dose-dependent fashion (3.0 days in the placebo group versus 2.2, 1.3, and 1.1 days in the 1, 3, and 5% cidofovir gel treatment groups, respectively; P = 0.02, 0.0001, and 0.0003, respectively). A trend toward a reduction in the median time to complete healing in association with treatment was present, but the differences were not statistically significant (5.0 days in the placebo group versus 4.3, 4.1, and 4.6 days in the 1, 3, and 5% cidofovir gel treatment groups, respectively). Application site reactions occurred in 3, 5, 19, and 22% of the patients in these four groups, respectively. Treatment-associated lesion recrudescence with delayed healing, which is suggestive of local toxicity, was observed in three patients treated with 5% cidofovir gel and one patient treated with 3% cidofovir gel. In summary, single-dose application of cidofovir gel confers a significant antiviral effect on lesions of recurrent genital herpes. Additional studies are warranted to further identify the optimal efficacious dose of cidofovir in association with the maximum gel strength that can be tolerated.

Virus infections of the eye

In reviewing the clinical features, diagnostic evaluations and therapies of the most common ocular viral infections we attempt to whet your appetite for attacking the numerous challenges in diagnosis and treatment of viral eye disease. The herpes viruses, HSV, VZV and CMV are the cause of significant ocular morbidity. HSV most commonly affects the cornea producing keratitis that can be recurrent and may lead to corneal clouding and neovascularisation. Manifestations can be purely infectious or immunological and treatment options must be tailored to the underlying pathophysiology. Herpes zoster ophthalmicus, caused by VZV infection of the first branch of the trigeminal nerve, produces a characteristic rash and can progress to keratitis and uveitis. HSV and VZV can cause retinitis in both immunocompetent and immunocompromised individuals. There has been a significant increase in the incidence of CMV retinitis since the beginning of the AIDS epidemic. We review the numerous new treatments, diagnostic tests and treatment strategies which have been developed in response to this potentially blinding retinal infection. Adenovirus produces an epidemic conjunctivitis and epidemic keratoconjunctivitis which are severe and extremely contagious conjunctival infections. HIV, molluscum contagiosum, EBV and rubeola also cause ocular diseases which are described.Copyright 1998 John Wiley & Sons, Ltd.

New antivirals - mechanism of action and resistance development

In recent years, several novel treatment modalities emerged for a number of virus infections, including lamivudine for hepatitis B virus, abacavir, adefovir dipivoxyl and apropovir disprometil for human immunodeficiency virus, cidofovir for cytomegalovirus, and famciclovir (the oral prodrug of penciclovir) and cidofovir for other herpesviruses (i.e. herpes simplex virus and varicella-zoster virus). For all drugs, resistance eventually develops upon prolonged administration to the infected individuals, albeit at a varying extent. In addition, new mutations related to multidrug resistance have recently been identified.

Predicting and preventing the emergence of antiviral drug resistance in HSV-2

Genital herpes, caused by herpes simplex virus, is the most prevalent sexually transmitted disease worldwide. In many developing countries genital herpes is untreated, and in the United States only 10% of cases are treated. We present a mathematical model that we use as a health policy tool to predict the levels of antiviral drug resistance that would emerge, if treatment rates were increased, and to identify the key factors in determining the emergence of drug resistance. We use our results to suggest control measures for herpes epidemics that would prevent the emergence of substantial levels of antiviral drug resistance.