Ribavirin mitigates wart growth in rabbits at early stages of infection with cottontail rabbit papillomavirus

In vitro and Animal Models for Antiviral Therapy in Papillomavirus Infections

The need for antiviral therapies for papillomavirus infections is well recognized but the difficulties of reproducing the infectious cycle of papillomaviruses in vitro has hindered our understanding of virus-cell interactions and the regulation of viral gene expression during permissive growth. Recent advances in understanding the temporal expression and function of papillomavirus proteins has enabled consideration of a targeted approach to papillomavirus chemotherapy and in particular the inhibition of viral replication by targeting the E1 and E2 proteins. There are in vitro culture systems available for the screening of new chemotherapeutic agents, since significant advances have been made with culture systems which promote epithelial differentiation in vitro. However, to date, there are no published data which show that virions generated in vitro can infect keratinocytes and initiate another round of replication in vitro. In vivo animal models are therefore necessary to assess the efficacy of antivirals in preventing and treating viral infection, particularly for the low-risk genital viruses which are on the whole refractory to culture in vitro. Although papillomaviruses affect a wide variety of hosts in a species-specific manner, the animals most useful for modelling papillomavirus infections include the rabbit, ox, mouse, dog, horse, primate and sheep. The ideal animal model should be widely available, easy to house and handle, be large enough to allow for adequate tissue sampling, develop lesions on anatomical sites comparable with those in human diseases and these lesions should be readily accessible for monitoring and ideally should yield large amounts of infectious virus particles for use in both in vivo and in vitro studies. The relative merits of the various papillomavirus animal models available in relation to these criteria are discussed.

Formulation of cidofovir improves the anti-papillomaviral activity of topical treatments in the CRPV/rabbit model

Current topical treatments for papillomas use ablative, cytotoxic and immunomodulating strategies and reagents. However, the effectiveness of topical treatments using different formulations has not been examined in preclinical models or clinical trials. The purpose of this study was to determine whether formulation of the small molecule acyclic nucleoside, cidofovir (CDV), could lead to improved therapeutic endpoints following topical treatment of papillomas using the cottontail rabbit papillomavirus (CRPV)/rabbit model. Different formulations with a set dose of 1% cidofovir were tested to establish comparative data. The results demonstrated that anti-papilloma treatments with topical CDV were greatly enhanced when formulated versus unformulated. Best results were obtained with CDV formulated in cremophor, then in Carbomer 940, and then in DMSO. Further studies indicated that effective formulations led to complete cures of papillomas at dilutions less than 0.3% CDV. These studies together with previous observations demonstrated that unformulated CDV under the same treatment regime required doses of 2% to achieve cures demonstrating that much less compound can be used when properly formulated.

Antiviral agents for the treatment of recurrent respiratory papillomatosis: a systematic review of the English-language literature

OBJECTIVE

To determine the efficacy of antiviral agents for recurrent respiratory papillomatosis (RRP) in children and adults.

STUDY DESIGN

Systematic review to include randomized controlled trials (RCTs), comparative studies (historical and/or nonrandomized), case series, and case reports.

RESULTS

Twenty-six original studies were included (one case-control series, 21 noncomparative trials, four case reports, and no RCTs). Meta-analysis was not possible. The antiviral modalities included acyclovir, ribavirin, intravenous cidofovir, and intralesional cidofovir injections. The strongest evidence was for intralesional cidofovir, with 17 studies including 158 patients. Of these, 90 patients (57%) demonstrated complete resolution, 55 patients (35%) a partial response, and 13 patients (8%) showed no improvement.

CONCLUSIONS

Insufficient evidence from controlled trials exists for reliable conclusions, but several series indicate intralesional cidofovir may have some efficacy. A well-designed placebo-controlled, double-blinded, randomized controlled trial is needed.

SIGNIFICANCE

This study provides the background for future study design and a comprehensive review of the available evidence.

Cottontail rabbit papillomavirus (CRPV) model system to test antiviral and immunotherapeutic strategies

The cottontail rabbit papillomavirus (CRPV)/rabbit model has proven to be the most versatile preclinical model to test antiviral, immunopotentiating and immunotherapeutic strategies for papilloma-virus infections. We have utilized this model for many years and have recently observed significant improvements in the utility of the model. Improvements have included various techniques to infect rabbit skin sites with strains of wild-type and mutant CRPV DNA prepared using standard molecular biological procedures. A better understanding of the virus life cycle in vivo has been gained also from these studies such that we now have several defined strains of CRPV including i) antigenically diverse strains of CRPV, ii) mutant strains of CRPV with reduced growth rates, and iii) mutant strains of CRPV that demonstrate accelerated malignant progression rates. Collectively, these mutant genomes provide laboratories with a powerful pre-clinical model to assess a variety of antiviral therapies. Many of the treatments already tested in the CRPV/rabbit model have shown parallel efficacy against HPV infections in a clinical setting. Some of our recent experiences with the CRPV/rabbit model are outlined in this brief overview.

Estudo do efeito do Cidofovir na papilomatose laríngea recorrente em crianças: relato preliminar

OBJETIVO: Demonstrar o efeito do uso do Cidofovir (aplicações locais) em crianças com papilomatose laríngea recorrente (PLR), respeitando um protocolo adotado desde 2002 na Disciplina de Otorrinolaringologia Pediátrica da UNIFESP. FORMA DE ESTUDO: Preliminar/clínico-prospectivo. MATERIAL E MÉTODO: Foram incluídas inicialmente 5 crianças portadoras de PLR acompanhadas no nosso ambulatório de laringologia pediátrica. Estas já haviam sido submetidas há no mínimo 3 cirurgias prévias ao uso do Cidofovir, com confirmação anatomopatológica de papilomatose (critérios inclusão) e não apresentavam alterações renais ou hepáticas (critérios de exclusão). O protocolo consistia em exérese das lesões e aplicação de até 3ml Cidofovir (7,5mg/ml). O ciclo de tratamento consistia de, no mínimo, 3 aplicações, e a qualquer sinal de recidiva iniciava-se novo ciclo de aplicações. RESULTADOS: Observamos nas 5 crianças estudadas que as recidivas das lesões (antes do Cidofovir) ocorreram em intervalos muito curtos (1 a 3 meses) necessitando de intervenção cirúrgica. Após inclusão no protocolo ocorreu mudança na evolução da doença nas 5 crianças, pois permanecem por período de no mínimo 1 ano sem necessidade de cirurgia. Nenhuma criança apresentou nenhum tipo de alteração nos exames laboratoriais, e nenhum tipo de efeito colateral local ou sistêmico com a injeção local de Cidofovir. Os resultados deste estudo preliminar nos permitem observar que a aplicação local de cidofovir utilizado em crianças com PLR, respeitando o protocolo adotado, demonstrou um bom controle das recidivas das lesões durante o período estudado.

Pharmacotherapy of recurrent respiratory papillomatosis

Recurrent respiratory papillomatosis (RRP) is a disease which affects both children (juvenile-onset RRP) and adults (adult-onset RRP). While a greater amount of information is known about the epidemiology of juvenile-onset than adult-onset RRP, fundamental work is still needed to more fully describe areas such as the mode of transmission. The primary management approach focuses on the removal of the papillomas by surgical debulking, although persistence of the human papillomavirus genome and subsequent recurrence of disease is the typical outcome. In a minority of patients, surgical management must be supplemented with adjuvant medical therapy, with IFN being the best studied and most commonly used. Other adjuvant treatments being employed include photodynamic therapy, indole-3-carbinol, ribavirin and cidofovir. Large controlled trials are lacking for all but IFN, making it extremely difficult to assess clinical benefit and risk in a systematic fashion at the current time. As with surgical management, viral persistence occurs following treatment with these adjuvant modalities, further contributing to the challenge of managing patients with this potentially devastating disease.

Xenograft model for identifying chemotherapeutic agents against papillomaviruses

The report describes the establishment and characterization of a mouse xenograft transplantation model for the study of papillomavirus infection of bovine skin. Calf scrotal skin was inoculated with bovine papillomavirus type 2 before grafting it to the dorsum of severe combined immunodeficient mice. The grafted skin contained epidermis, dermis, and a thin layer of fat. After 5 months the induced warts not only showed histological features of papillomavirus infections but also tested positive for viral DNA and papillomavirus capsid antigen. The formation of infectious virions was demonstrated by inoculation of new transplants with crude extract from the induced warts as well as in a cell culture focus assay. Topical application of bromovinyl-2'-deoxyuridine led to a reduction in viral DNA content in the developing wart. This small-animal xenograft model should be useful for characterizing antiviral compounds and providing an understanding of the regulation of papillomavirus infections.

In vivo anti-papillomavirus activity of nucleoside analogues including cidofovir on CRPV-induced rabbit papillomas

A series of nucleoside analogues were tested for in vivo anti-papillomavirus activity using the cottontail rabbit papillomavirus (CRPV) domestic rabbit model. Compounds were delivered either topically, injected into growing papillomas, or delivered subcutaneously at a site remote from the papillomas. Compounds tested included cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine] (HPMPC); cyclic HPMPC (cHPMPC); cyclopentenylcytosine (CPE-C); lobucavir [1R(1alpha,2beta,3alpha)]-9-[2, 3-bis(hydroxymethyl)cyclobutyl]guanine; 9-((2-phosphonylmethoxy)propyl)adenine (PMPA); adefovir 9-((2-phosphonylmethoxy)ethyl)adenine(PMEA) and cyclopropyl 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (cyclopropylPMEDAP). Dose response curves and time-course treatments were included for most compounds tested. Strong anti-viral activity was detected using cidofovir and cHPMPC when delivered either topically or by the intralesional route. Complete cures were obtained using 1% (w/v) topical cidofovir at dosing schedules of twice daily for 8 weeks beginning at 4 weeks after CRPV infection, which represents a time when papillomas were clearly visible. Complete cures of large established papillomas were obtained by intralesional injection of 1% cidofovir three times per week for 8 weeks. Topical treatments with adefovir had strong anti-viral activity, cyclopropyl PMEDAP had moderate anti-viral activity, and CPE-C, PMPA and lobucavir showed no effects. These data indicate that certain nucleoside analogues have strong in vivo anti-papillomavirus activity and that the CRPV/rabbit model is a good model for assessing clinical responses of anti-viral treatments for patients with HPV disease.

Recent advances in diagnosis and therapy of human papillomaviruses

Infection with human papillomavirus is extremely common throughout the world. Almost 50% of sexually active young women are infected with human papillomavirus and although most infections are transient, a subset has the potential to progress to invasive cancer. During the last 20 years, our understanding of the human papillomavirus life cycle and the role of human papillomavirus in human cancer has dramatically increased. Recent technological advances in human papillomavirus detection have provided the means to detect the presence of human papillomavirus with great sensitivity. In the context of patient care, there is still substantial debate regarding the optimal diagnostic and prognostic use of information derived from hybrid capture or polymerase chain reaction-based detection. The inventory of available treatment options is growing somewhat slowly. The most promising advances are being made in the clinical evaluation of candidates for prophylactic vaccination. This review is focused on the current status and future directions of prevention, diagnosis and therapy.

Topical effects of cidofovir on cutaneous rabbit warts: treatment regimen and inoculum dependence

The present study examined topical effects of cidofovir on cutaneous rabbit warts. Based on an inoculum-dependency study, each New Zealand White rabbit was inoculated with a high and low titer of cottontail rabbit papillomavirus (CRPV) at four sites on each dorsolateral area. Inoculation with 50 ID(50) induced papillomas at 100% of the inoculation sites within 16+/-1 days, and the wart growth curve plateaued within approximately 7 weeks. With an inoculum of 5 ID(50), 80% of the inoculated sites developed papillomas within 21+/-1 days and their size plateaued at a later time. Cidofovir was applied topically twice daily on the inoculated sites at a concentration of 1% for 18 days, starting at three different time points. In the first experiment, treatment was initiated 7 days post-inoculation. One of the inoculated sides received cidofovir or the vehicle, PBS, while the other side was left untreated. With this treatment regimen, cidofovir significantly delayed the time of onset and the growth rate of papillomas induced with the high titer of inoculum. It completely prevented papilloma-induction on the sites inoculated with the low titer of CRPV. Reversible side-effects of cidofovir were observed on the directly treated area including erythema, necrosis, and flaking. Both therapeutic and side-effects were limited to the sites of direct exposure. In the second experiment, one of the two sides in each group of rabbits received cidofovir or vehicle starting on day 29 post-inoculation. With this treatment regimen, cidofovir significantly reduced wart growth against the low titer only. Topical treatment initiated on day 49 post-inoculation was not effective on warts initiated with either viral titer. These results demonstrated that topical cidofovir could be very effective against papillomavirus-induced wart growth if it is initiated early during the infection, especially against low titers of inoculum.

Juvenile onset recurrent respiratory papillomatosis: possibilities for successful antiviral therapy

Recurrent respiratory papillomatosis (RRP) is a potentially devastating disease that can have significant morbidity, and can even result in mortality due to airway compromise or, less commonly, malignant transformation. Two distinct types of RRP exist: adult-onset RRP (AO-RRP) and juvenile-onset RRP (JO-RRP). Acquisition of human papillomavirus (HPV), the causative agent of RRP, is believed to occur in the peripartum period in the case of JO-RRP, with disease symptoms (primarily hoarseness) becoming apparent during the first several years of life. Treatment currently consists of surgical debulking of the papillomas to relieve airway obstruction. However, numerous antiviral therapies have also been evaluated, albeit primarily under uncontrolled settings. This article will review the biology, natural history and management of HPV infection, with particular emphasis on JO-RRP.

Therapeutic evaluation of compounds in the SCID-RA papillomavirus model

A previous study by Kreider (Kreider et al., 1979) indicated that rabbit skin, which had been transplanted to immunodeficient nude mice, could be successfully infected with cottontail rabbit papillomavirus (CRPV). We have extended this observation in developing a rodent model for evaluation of compounds for activity against the papillomaviruses. In this model (called the SCID-Ra model), rabbit ear skin is transplanted to the dorsum of SCID mice and allowed to heal for 3 weeks. Infection with CRPV by scarification leads to the growth of warty lesions within 2 3 weeks in >95% of the animals. Topical and/or systemic therapy can be initiated at various times post infection (PI). Weekly lesion scores are recorded and compounds are evaluated for their ability to suppress wart growth when compared to untreated control mice. Ribavirin, which has had a suppressive effect both in the clinic for the treatment of respiratory papillomatosis and on the growth of warts in the rabbit back model, was evaluated and showed significant anti-proliferative activity with oral dosing. Both antiviral and antiproliferative compounds including podophyllin and 5-fluorouracil, which have been used clinically for the treatment of human papillomavirus (HPV) infections, were evaluated in this model. The anti-mitotic compound, Navelbine (vinorelbine tartrate), which is used for the treatment of non-small cell lung carcinoma was evaluated in this system and showed significant inhibition of wart growth with somewhat less topical cytotoxicity when compared to podophyllotoxin.

Treatment of severe laryngeal papillomatosis with intralesional injections of cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine]

Respiratory papillomatosis is a rare and often severe disease, usually localized in the larynx. It may cause respiratory distress and even life-threatening obstruction of the airways. Treatment is generally based on the evaporation of the lesions with a CO2 laser, but microsurgery, cytotoxic and/or cytostatic drugs, interferons, and vaccines are also used. Cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine] (HPMPC) was shown to suppress the growth of tumors induced by rabbit papillomavirus as well as human papillomavirus (HPV). The efficacy of cidofovir was assessed in 17 patients with severe respiratory papillomatosis. Cidofovir at a concentration of 2.5 mg/ml was injected directly in the different laryngeal papillomatous lesions during microlaryngoscopy under general anesthesia. Biopsies were taken before the treatment was started both for anatomopathology and viral typing. HPMPC kinetics in serum was monitored in three patients, the drug levels being determined by high-performance liquid chromatography. Complete disappearance of the papillomatosis was observed in 14 patients. Four patients relapsed and were successfully treated again with cidofovir. Of the three remaining patients, one progressed while under treatment with cidofovir, after an initial marked response. One patient had a partial remission and remained stable for more than 1 year after the last injection. He had a very aggressive and extensive disease originally. Finally, one patient was lost to follow-up after four injections. Intratumoral injections of cidofovir for the treatment of severe laryngeal papillomatosis is a powerful new therapeutic approach for this disease. Treatment was well tolerated, and no significant side effects were noted.

HPV replication in experimental models: effects of interferon

Preclinical evaluation of the effectiveness of interferon (IFN) therapy on human papillomaviruses (HPV) has been hampered by the inability to propagate these viruses in cell culture. Nonetheless, interferon is used extensively in the treatment of HPV infections. Alpha interferons in particular have found a place in the treatment of anogenital disease, plantar warts, and laryngeal papillomas. While their is significant clinical evidence to suggest that interferon is useful in therapy of disease, the cellular mechanism(s) (i.e., antiviral, antiproliferative, immunomodulatory) by which IFN is able to control HPV-induced pathology is not well understood. This review focuses on experimental animal and cell culture models which are currently being used to help identify the antiviral, antiproliferative and immunomodulatory effects of IFN on HPV infection.

Topical CTC-96 accelerates wart growth in rabbits infected with cottontail rabbit papillomavirus

CTC-96, a cobalt containing complex, was tested as a putative topical therapeutic agent for the treatment of papillomavirus-induced tumors in our cottontail rabbit papillomavirus (CRPV)-rabbit model system. Following experimental infection of domestic rabbits with CRPV, CTC-96 was applied to infection sites twice daily, 5 days a week for a total of 8 weeks. Two levels of concentrations of aqueous CTC-96 were compared to placebo control-treated animals. With increasing dose of CTC-96 we observed tumors earlier, larger, and more often across eight infected sites on each animal.

Pilot trial of ribavirin for the treatment of laryngeal papillomatosis

The antiviral drug ribavirin was used as an adjunct to laser surgery for the treatment of patients with laryngeal papillomatosis (LP). An uncontrolled clinical trial for four patients with ribavirin treatment at a daily dose of 23 mg/kg was performed. Three adults received drug prior to laser surgery and continuing orally for 6 months. One infant was treated for 3 months. Two adults achieved complete remissions for at least 2 consecutive months, and both patients developed only minimal recurrent disease in 4 months of follow-up. The other adult and the child sustained a partial response and an increased interval between the required surgeries. Ribavirin caused only a mild, reversible reduction in hemoglobin and reticulocytosis. This preliminary trial shows that ribavirin may be an effective therapy in combination with surgery for LP in a larger controlled clinical trial.