A preclinical and clinical overview of the nucleotide-based antiviral agent cidofovir (HPMPC)

Murine Gammaherpesvirus 68 Efficiently Infects Myeloid Cells Resulting In An Atypical, Restricted Form Of Infection

The gammaherpesviruses (γHVs) establish a lifelong infection in their hosts, with the cellular outcome of infection intimately regulated by target cell type. Murine gammaherpesvirus 68 (MHV68), a small animal model of γHV infection, infects macrophages in vivo, resulting in a range of outcomes, from lytic replication to latent infection. Here, we have further investigated the nature of MHV68 macrophage infection using reductionist and primary in vivo infection studies. While MHV68 readily infected the J774 macrophage cell line, viral gene expression and replication were significantly impaired relative to a fully permissive fibroblast cell line. Lytic replication only occurred in a small subset of MHV68-infected J774 cells, despite the fact that these cells were fully competent to support lytic replication following pre-treatment with interleukin-4, a known potentiator of replication in macrophages. In parallel, we harvested virally-infected macrophages at 16 hours after MHV68 infection in vivo and analyzed gene expression by single cell RNA-sequencing. Among virally infected macrophages, only rare (0.25%) cells had lytic cycle gene expression, characterized by detection of multiple lytic cycle RNAs. In contrast, ~50% of virally-infected macrophages were characterized by expression of ORF75A, ORF75B and/or ORF75C, in the absence of other detectable viral RNAs. Selective transcription of the ORF75 locus also occurred in MHV68-infected J774 cells. In total, these studies indicate that MHV68 efficiently infects macrophages, with the majority of cells characterized by an atypical state of restricted viral transcription, and only rare cells undergoing lytic replication.

Kaposi's sarcoma herpesvirus lytic replication compromises apoptotic response to p53 reactivation in virus-induced lymphomas

Primary effusion lymphomas (PELs) are aggressive Kaposi's sarcoma herpesvirus (KSHV)-induced malignancies with median survival time <6 months post-diagnosis. Mutations in the TP53 gene seldom occur in PELs, suggesting that genetic alterations in the TP53 are not selected during PEL progression. We have reported that p53 reactivation by an inhibitor of the p53-MDM2 interaction, Nutlin-3, induces selective and massive apoptosis in PEL cells leading to efficient anti-tumor activity in a subcutaneous xenograft model for PEL. Here, we show compelling anti-tumor activity of Nutlin-3 in the majority of intraperitoneal PEL xenografts in vivo. Interestingly, our results demonstrate that spontaneous induction of viral lytic replication in tumors could drastically attenuate the p53-dependent apoptotic response to Nutlin-3. Moreover, viral reactivation compromised p53-dependent apoptosis in PEL cells treated with genotoxic anti-cancer agents doxorubicin and etoposide. We have recently demonstrated that the Ser/Thr kinases Pim 1 and 3 are required to trigger induction of the lytic replication cascade of KSHV. We have now assessed the ability of a novel Pim kinase inhibitor to restore the Nutlin-3-induced cytotoxicity in lytic PEL cells. PEL cells induced to lytic replication by phorbol esters showed 50% inhibition of active viral replication following treatment with the Pim kinase inhibitor. Importantly, co-treatment of these cells with the kinase inhibitor and Nutlin-3 resulted in a robust restoration of the Nutlin-3-induced cell death. These results highlight the potential impact of activation of viral lytic replication on disease progression and response to treatment in KSHV-induced lymphomas.

Anticytomegaloviral activity of esterified milk proteins and L-polylysines

MRC-5 fibroblasts infected with human cytomegalovirus (HCMV) reference strain AD 169 were treated with different concentrations of methylated alpha-lactalbumin (Met-ALA) or methylated beta-lactoglobulin (Met-BLG), as well as with their peptic hydrolysates, and with the highly basic polypeptides such as are L-polylysines (4-15 kDa). The antiviral activity was calculated by comparing the number of infected cells in the presence and absence of the tested substances. Both Met-ALA and Met-BLG, as well as their peptic hydrolysates, decreased the infectious activity of cytomegalovirus in fibroblast cells. As expected, L-polylysines showed the highest antiviral activity. However, the tested basic proteins and polypeptides despite their lower antiviral activities might be potentially quite useful in fight of arising drug resistance activities and the persistence capacities of this virus.

Emerging therapies for herpes viral infections (types 1 – 8)

There are eight members of the herpesviridae family: herpes simplex virus-1 (HSV-1), HSV-2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, human herpes virus-6, human herpes virus-7 and human herpes virus-8. The diseases caused by viruses of the herpesviridae family are treated with and managed by systemic and topical antiviral therapies and immunomodulating drugs. Because these viruses establish a latent state in hosts, antiherpetic agents, such as nucleoside analogues, only control symptoms of disease or prevent outbreaks, and cannot cure the infections. There is a need for treatments that require less frequent dosing, can be taken even when lesions are more advanced than the first signs or symptoms, and can treat resistant strains of the viruses without the toxicities of existing therapies. Immunomodulating agents, such as resiquimod, can act on the viruses indirectly by inducing host production of cytokines, and can thereby reduce recurrences of herpes. The new helicase primase inhibitors, which are the first non-nucleoside antiviral compounds, are being investigated for treatment of HSV disease, including infections resistant to existing therapy.

A novel nonnucleoside inhibitor specifically targets cytomegalovirus DNA maturation via the UL89 and UL56 gene products

3-Hydroxy-2,2-dimethyl-N-[4([[5-(dimethylamino)-1-naphthyl]sulfonyl]amino)-phenyl]propanamide (BAY 38-4766) is a novel selective nonnucleoside inhibitor of cytomegalovirus (CMV) replication with an excellent safety profile. This compound and structural analogues inhibit neither viral DNA synthesis nor viral transcription and translation. Accumulation of dense bodies and noninfectious enveloped particles coincides with inhibition of both concatemer processing and functional cleavage at intergenomic transitions, pointing to interference with viral DNA maturation and packaging of monomeric genome lengths. Resistant virus populations, including a murine CMV (MCMV) isolate with 566-fold-decreased drug sensitivity, were selected in vitro. Sequencing of the six open reading frames (ORFs) known to be essentially involved in viral DNA cleavage and packaging identified mutations in ORFs UL56, UL89, and UL104. Construction of MCMV recombinants expressing different combinations of murine homologues of mutant UL56, UL89, and UL104 and analysis of drug susceptibilities clearly demonstrated that mutant ORFs UL89 exon II (M360I) and M56 (P202A I208N) individually confer resistance to BAY 38-4766. A combination of both mutant proteins exhibited a strong synergistic effect on resistance, reconstituting the high-resistance phenotype of the in vitro mutant. These findings are consistent with genetic mapping of resistance to TCRB (2,5,6-trichloro-1-beta-D-ribofuranosyl benzimidazole) (P. M. Krosky et al., J. Virol. 72:4721-4728, 1998) and provide further indirect evidence that proteins encoded by UL89 and UL56 function as two subunits of the CMV terminase. While these studies also suggest that the molecular mechanism of BAY 38-4766 is distinct from that of benzimidazole ribonucleosides, they also offer an explanation for the excellent specificity and tolerability of BAY 38-4766, since mammalian DNA does not undergo comparable maturation steps.

Successful preemptive cidofovir treatment for CMV antigenemia after dose-reduced conditioning and allogeneic blood stem cell transplantation

BACKGROUND

Cidofovir (CDV) is a nucleotide analogue with proven in vitro effects against cytomegalovirus (CMV) and adenovirus and has been successfully used in the treatment of CMV retinitis in AIDS patients.

METHODS

We performed a prospective study to evaluate the efficacy of CDV in 17 patients with hematological malignancies after allogeneic blood stem cell transplantation from related (n=3) and unrelated (n=14) donors. Dose-reduced conditioning (DRC) regimen consisted of busulfan (Bu)/fludarabine (Flu) (n=9) and idarubicin/cytosine arabinoside/Flu (n=1). Myeloablative conditioning (MC) was performed with Bu/cyclophosphamide (Cy)/etoposide (Eto) (n=4), Bu/Cy (n=2), and total body irradiation (TBI)/Cy/Eto (n=1). Antithymocyte globulin (ATG) was used in seven patients with DRC and in six patients with MC. In all patients, either the donor, host, or both were CMV IgG positive pretransplant. Indication for therapy was preemptive treatment of primary CMV antigenemia defined as two consecutive positive tests of pp65 antigenemia assay after transplant. In case of response with a decreasing number of pp65-positive leukocytes, CDV was scheduled in a dosage of 5 mg/kg body weight once a week for 2 weeks followed by maintenance therapy every 2 weeks in an outpatient setting. All patients received probenecid and prehydration as recommended. Patients were monitored using an immunostaining assay for pp65 antigen and a qualitative and quantitative CMV polymerase chain reaction (PCR). Success of treatment was defined as negativity for the pp65 antigen.

RESULTS

After DRC, nine of ten patients (90%) showed a response with seven of nine revealing a complete clearance of the virus (pp65 negative, qualitative PCR negative). In the remaining two responders, treatment was changed to ganciclovir because of either renal impairment or slow clearance of antigenemia. Only one of seven patients in the MC group experienced a temporary clearance of pp65 antigen. After MC, two patients experienced CMV disease. Treatment-related toxicity rate was moderate with four patients developing reversible renal impairment (creatinine 133-180 micromol/L); one patient with proteinuria and three patients with complaints of nausea and vomiting.

CONCLUSION

Our data suggest the feasibility of CDV administration in patients after allogeneic transplantation. In the recommended dose, it might be used successfully for low-risk patients, e.g., after DRC or organ transplantation, in an outpatient setting.

Human papillomavirus infections: epidemiology, pathogenesis, and therapy

BACKGROUND

Human papillomaviruses (HPV) are common human pathogens and are classified into more than 80 different types. These viruses produce benign warts in many cases and aggressive squamous cell carcinomas in other cases.

OBJECTIVE

The goal of this review is to update the reader on the epidemiology, pathogenesis, and therapy of HPV infections. Nonanogenital warts are transmitted by skin-to-skin contact while anogenital warts are usually transmitted sexually. Both types of warts produce much morbidity but rarely undergo malignant transformation. They are commonly treated with surgical or cytodestructive therapy, but immunomodulatory agents, such as imiquimod, have been proven to be very effective in anogenital warts and are being evaluated in nonanogenital warts. Other types of HPV have marked oncogenic potential such that over 99% of all cervical cancers and over 50% of other anogenital cancers are due to infection with oncogenic HPV. Many cofactors, such as cigarette smoking, genetics, and helper viruses, have potential roles in HPV oncogenesis, but their relative contributions are poorly understood. Other control measures for warts and HPV-associated cancers are under study, but the greatest future potential may be from the development of prophylactic and therapeutic vaccines.

CONCLUSIONS

Infection with HPV is very prevalent as are the clinical manifestations of this family of pathogens. Improved therapies for warts (e.g., imiquimod) have recently become available. Vaccines for HPV offer hope for future interventions for warts as well as for prevention of anogenital malignancies.

Human papillomavirus infections: epidemiology, pathogenesis, and host immune response

Human papillomaviruses (HPVs) are ubiquitous and often cause lesions on the skin that come to the attention of the dermatologist. Skin lesions, or warts, often occur on the hands or soles of the feet and can cause embarrassment or discomfort. Genital HPV infections are transmitted by sexual contact. Infections associated with some HPV types have a high risk of progressing to carcinoma. This review discusses the molecular biology and genetics of human papillomaviruses and provides an overview of the virology, pathology, clinical manifestations, and host immune response to infection.

Iritis associated with intravenous cidofovir

OBJECTIVE

To report two patients with AIDS and cytomegalovirus retinitis who developed iritis after receiving intravenous cidofovir. Both experienced recurrent symptoms upon rechallenge.

CASE SUMMARIES

Two HIV-positive patients with cytomegalovirus retinitis infections previously controlled with intravenous ganciclovir or foscarnet were treated with intravenous cidofovir. Symptoms of iritis developed after the second or third dose of cidofovir. One patient experienced symptoms unilaterally, while the other patient had bilateral symptoms. In both patients, the iritis resolved with topical ophthalmic therapy, but recurred following subsequent infusions of cidofovir. Therapy with cidofovir was discontinued, and no further recurrences of iritis were noted. One patient had post-inflammatory fixed dilated pupils.

CONCLUSIONS

Iritis can uncommonly occur in patients receiving intravenous cidofovir and oral probenecid. With prompt drug discontinuation and administration of topical corticosteroids and/or mydriatic agents, symptoms are usually reversible.

New antiviral agents for dermatologic disease

The topic of antiviral agents for dermatologic disease is an area that is rapidly changing and expanding as our knowledge of herpes viruses, HIV, and human papilloma viruses continues to expand. New drugs are continuing to make therapy for these viruses more efficacious day by day. This review will discuss the recent advances in antiviral therapy, new therapies currently being developed or studied, and the future of antiviral vaccines.

An in vivo model of human cytomegalovirus retinal infection

PURPOSE

To develop an animal model system in which human retina implanted in the anterior chamber of the eyes of rats would support human cytomegalovirus replication. Cytomegalovirus retinitis currently represents the most common cause of posterior uveitis in many urban areas in North America. Despite the tremendous interest in cytomegalovirus retinitis as a result of the acquired immunodeficiency syndrome (AIDS) epidemic, human cytomegalovirus infection has been difficult to model in vivo because of its extreme species-specificity.

METHODS

Human retina was introduced into the anterior chamber of athymic rats and allowed to attach to the rat iris. A human cytomegalovirus mutant carrying a beta-galactosidase indicator gene was then injected into the anterior chamber to infect the implanted tissue. After 4 weeks, the eyes were removed, sectioned, and developed with a chromogenic substrate to demonstrate the presence and location of beta-galactosidase expression.

RESULTS

Multiple spreading foci of beta-galactosidase expression were found in the retinal implants, indicating that human cytomegalovirus replication had occurred within the human tissue. There was no infection of rat tissue.

CONCLUSIONS

This model allows human cytomegalovirus infection of human retina to be established in vivo and sustained long enough to permit multiple cycles of viral replication to occur. The model thus has potential for evaluating antiviral therapies directed against human cytomegalovirus retinal disease.