Local administration of cidofovir for human papilloma virus associated skin lesions in transplant recipients

Cutaneous Applications of the Antiviral Drug Cidofovir: A Review

Background/Objectives: Cidofovir, an antiviral drug approved for cytomegalovirus retinitis, has emerged as an alternative treatment option for virally induced cutaneous and mucocutaneous conditions, as well as being trialed as a treatment for select neoplasms. In this review, we highlight the existing evidence, clinical uses, and rationale of using cidofovir for the treatment of cutaneous pathologies. Methods: A PubMed database literature search was conducted to identify relevant articles for inclusion in this review. Results: Cidofovir has several cutaneous applications in various formulations including intravenous, topical, and subcutaneous administrations. Primarily through case reports, case series, and retrospective reviews, cidofovir has demonstrated efficacy in treating a variety of virally induced conditions-verruca vulgaris, herpes simplex virus, molluscum contagiosum-as well as in adjuvant treatment for select neoplasms. The drug has shown efficacy in immunocompromised and immunocompetent adults and children alike. Conclusions: The body of literature supports the use of cidofovir as an effective and well-tolerated treatment for many viral cutaneous pathologies, and encourages further study for its use as an adjuvant therapy for neoplastic disease.

Towards Formulation of Highly Acidic Active Ingredients: Development of Clinically Effective Concentrated Trichloroacetic Acid Gel for Wart Management

Common warts are benign skin lesions caused by the human papillomavirus. Although they are usually not harmful, they can cause pain, depending on their location. While many modalities are available for treatment of warts, none is a gold standard, and many are not affordable and/or have suboptimal outcomes. Trichloroacetic acid (TCA) is a chemical tissue-destroying agent used as a highly concentrated solution for wart management. While available and efficient, it is difficult to handle as the solution spreads to tissue surrounding the wart causing pain and burning. Hence, we developed a new polymer-based gel of high TCA content (100% w/v). Gels were formed successfully as hydroxyethyl cellulose (HEC) and chitosan were used to impart viscosity and bioadhesion. Formulae of different concentrations were tested for their physical properties, and the optimal formulation was selected for clinical evaluation. A combination of 3% HEC and 2% chitosan provided optimal viscosity and limited water content and have acceptable stability. The efficacy and safety of the biweekly application of TCA gel were evaluated in 30 patients. The clinical study revealed gel's efficacy and tolerability; half of the patients showed a complete cure, and 90% showed improvement within 6 weeks. Only 10-12% of the patients reported side effects. In summary, transforming TCA solution into a gel enabled its application and handling in a practical manner by physicians and patients alike, while maintaining its efficacy as a tissue-destroying agent. Moreover, it is economic and easy to apply, rendering it a promising formulation for similar conditions requiring controlled tissue ablation.

Intralesional cidofovir for the management of refractory cutaneous verrucae: a review of applications and opportunities

Viral warts - manifestations of cutaneous infection by human papilloma virus - can be a significant physical and emotional burden for patients when common treatments fail, particularly for individuals who are immunocompromised or with multiple lesions. Cidofovir, an antiviral agent typically used for the treatment of cytomegalovirus infection, has emerged as an alternative treatment option for viral warts when administered topically or intralesionally. In this review, we highlight the scientific rationale, published evidence, and practical clinical uses of intralesional cidofovir for the management of cutaneous warts as well as ongoing questions requiring further research and exploration of this emerging therapy for refractory verrucae.

Skin conditions in liver transplant recipients in a Singapore academic medical center: A retrospective cohort study

Background

Liver transplant recipients are at lifelong risk of immunosuppression-related cutaneous complications, such as malignancy and infection.

Objective

Our study aims to assess the epidemiology of dermatologic conditions among liver transplant recipients in an academic medical center in Singapore.

Methods

Medical records of liver transplant recipients on follow-up with gastroenterology and dermatology departments at the Singapore General Hospital between 2006 and 2021 were retrospectively reviewed. A literature review was subsequently performed on the keywords “liver transplant” and “dermatology.”

Results

A total of 99 liver transplant recipients were identified in this study. Sixty-nine patients (70%) had at least 1 dermatologic condition. Inflammatory skin conditions were the most common (53%), followed by cutaneous infection (36%) and benign cutaneous tumors (30%). Malignant and premalignant lesions were the least common skin conditions reported (10%). Our study results concurred with many other studies reported worldwide, demonstrating a low cutaneous malignancy burden after liver transplantation.

Limitations

The study included a small population size in a single center and did not have a pre-existing protocol for pretransplant dermatologic surveillance.

Conclusion

Although the incidence of skin cancer after liver transplant in Singapore is low, the patients will benefit from long-term dermatology surveillance, given the long-term risks of infection and malignant skin conditions.

Infectious complications of vascularized composite allograft transplantation

PURPOSE OF REVIEW

Vascularized composite allograft (VCA) transplants constitute multiple tissues transplanted together as one functional unit. These procedures are increasing in frequency and complexity, yet data about graft survival, quality of life, and infection risk remain limited.

RECENT FINDINGS

Informative guidance for this patient population is often inferred from the solid organ transplantation literature. Yet, it is important to understand that VCA transplantation additionally carries its own significant and distinctive risk factors for infection.

SUMMARY

In this review, we give an overview of previously described infectious complications of VCA transplantation in the literature, discuss risk factors for future infection in these patients, and discuss how to manage such obstacles.

Long-term outcome after hand and forearm transplantation - a retrospective study

Between 2000 and 2014, five patients received bilateral hand (n = 3), bilateral forearm (n = 1), and unilateral hand (n = 1) transplants at the Innsbruck Medical University Hospital. We provide a comprehensive report of the long-term results at 20 years. During the 6-20 years follow-up, 43 rejection episodes were recorded in total. Of these, 27.9% were antibody-related with serum donor-specific alloantibodies (DSA) and skin-infiltrating B-cells. The cell phenotype in rejecting skin biopsies changed and C4d-staining increased with time post-transplantation. In the long-term, a change in hand appearance was observed. The functional outcome was highly depending on the level of amputation. The number and severity of rejections did not correlate with hand function, but negatively impacted on the patients´ well-being and quality of life. Patient satisfaction significantly correlated with upper limb function. One hand allograft eventually developed severe allograft vasculopathy and was amputated at 7 years. The patient later died due to progressive gastric cancer. The other four patients are currently rejection-free with moderate levels of immunosuppression. Hand transplantation remains a therapeutic option for carefully selected patients. A stable immunologic situation with optimized and individually adopted immunosuppression favors good compliance and patient satisfaction and may prevent development of DSA.

Successful treatment of genital warts with cidofovir cream in a pediatric patient with Fanconi anemia

INTRODUCTION

Patients with Fanconi anemia have an increased susceptibility to malignancies associated with human papillomavirus, and thus prevention and early management of human papillomavirus infections in this patient population are crucial.

CASE REPORT

A nine-year-old girl with Fanconi anemia developed genital warts about three years after undergoing haplo-identical stem cell transplant. The transplant was complicated by chronic graft-versus-host disease, and the patient had therefore received multiple immunosuppressants. The genital warts were treated with several creams, but minimal improvement was reported.

MANAGEMENT AND OUTCOME

Cidofovir was extemporaneously compounded into an unscented 1% moisturizing cream and applied daily at bedtime to the genital warts. By the end of treatment, the warts had been successfully treated, and no adverse events were reported. The patient is still free of any lesions at six months after completing treatment.

DISCUSSION

Although reports have been published on the use of cidofovir cream, most were in adults with non-genital warts. Cidofovir cream may be considered as a treatment option for refractory genital warts in pediatric patients. However, further studies are needed to better define the optimal preparation and dosing for such patient population.

Treatment of intraurethral condylomata acuminata with surgery and cidofovir instillations in two immunocompromised patients and review of the literature

Condylomata acuminata (CA) or anogenital warts are benign proliferative lesions caused by low-risk human papillomaviruses (HPV). Treating CA can be very frustrating for patients and clinicians due to the high recurrence rates. Immunosuppression is associated with larger size of CA that are more frequently resistant to treatment. Surgical approaches tend to be poorly effective in the long-term because of high recurrence rates related to the persistence of HPV-infected cells. In our search to find an agent to treat intraurethral CA with minor or no side effects, we evaluated intraurethral cidofovir in two male patients, who were under immunosuppressing therapy due to organ transplantation and suffered from extensive urethral HPV lesions. Both patients underwent biopsy of the lesions and initial transurethral resection. In our first case, intraurethral cidofovir instillations were started after 2 months due to recurrence after surgical treatment. In our second case, intraurethral cidofovir was administered after surgery because of incomplete resection of extensive lesions. Because of persistent or rapidly recurrent lesions despite intraurethral cidofovir instillations, the first patient needed two additional surgical interventions while the second patient underwent one additional surgical intervention. After surgical intervention, both patients received again adjuvant cidofovir instillations without side effects. Over a period of 56 weeks, both patients received each a total of 28 instillations with cidofovir. Following 3.5 years (patient 1) of the last cidofovir instillation, no recurrences were observed in our first patient. Following 6 months of the last cidofovir instillation (patient 2), two very small recurrent lesions in the most distal part of the urethra were observed in our second patient for which he will receive a cycle of 6 cidofovir instillations in the near future. Intraurethral cidofovir is a safe, easy-to-use, well-tolerated and an effective adjuvant to surgery for extensive intraurethral CA in immunocompromised patients.

Topical Cidofovir for Recalcitrant Verrucae in Individuals with Severe Combined Immunodeficiency After Hematopoietic Stem Cell Transplantation

Verrucae vulgaris in patients with severe combined immunodeficiency (SCID) after hematopoietic stem cell transplantation (HCST) can be challenging to manage. We describe two brothers with X-linked SCID who had severe, persistent verrucae that did not respond to traditional topical therapies, including liquid nitrogen, imiquimod, salicylic acid, sinecatechins, 40% urea, and 5-fluorourcil. Both brothers had full response to topical 3% cidofovir, which should be considered in recalcitrant warts in individuals with SCID after HSCT.

Vascularized Composite Allotransplantation: Medical Complications

The objective of this review is to summarize the collective knowledge regarding the risks and complications in vascularized composite tissue allotransplantation (VCA), focusing on upper extremity and facial transplantation. The field of VCA has entered its second decade with an increasing experience in both the impressive good outcomes, as well as defining challenges, risks, and experienced poor results. The limited and selective publishing of negative outcomes in this relatively new field makes it difficult to conclusively evaluate outcomes of graft and patient survival and morbidities. Therefore, published data, conference proceedings, and communications were summarized in an attempt to provide a current outline of complications. These data on the medical complications of VCA should allow for precautions to avoid poor outcomes, data to better provide informed consent to potential recipients, and result in improvements in graft and patient outcomes as VCA finds a place as a therapeutic option for selected patients.

HPV Carcinomas in Immunocompromised Patients

Human papillomavirus (HPV) infection is the most common sexually transmitted disease worldwide and can result in pre-malignancies or overt malignancies of the skin and mucosal surfaces. HPV-related illnesses are an important personal and public health problem causing physical, mental, sexual and financial detriments. Moreover, this set of malignancies severely affects the immunosuppressed population, particularly HIV-positive patients and organ-transplant recipients. There is growing incidence of HPV-associated anogenital malignancies as well as a decrease in the average age of affected patients, likely related to the rising number of high-risk individuals. Squamous cell carcinoma is the most common type of HPV-related malignancy. Current treatment options for HPV infection and subsequent disease manifestations include imiquimod, retinoids, intralesional bleomycin, and cidofovir; however, primary prevention with HPV vaccination remains the most effective strategy. This review will discuss anogenital lesions in immunocompromised patients, cutaneous warts at nongenital sites, the association of HPV with skin cancer in immunocompromised patients, warts and carcinomas in organ-transplant patients, HIV-positive patients with HPV infections, and the management of cutaneous disease in the immunocompromised patient.

Insights into the mechanism of action of cidofovir and other acyclic nucleoside phosphonates against polyoma- and papillomaviruses and non-viral induced neoplasia

Acyclic nucleoside phosphonates (ANPs) are well-known for their antiviral properties, three of them being approved for the treatment of human immunodeficiency virus infection (tenofovir), chronic hepatitis B (tenofovir and adefovir) or human cytomegalovirus retinitis (cidofovir). In addition, cidofovir is mostly used off-label for the treatment of infections caused by several DNA viruses other than cytomegalovirus, including papilloma- and polyomaviruses, which do not encode their own DNA polymerases. There is considerable interest in understanding why cidofovir is effective against these small DNA tumor viruses. Considering that papilloma- and polyomaviruses cause diseases associated either with productive infection (characterized by high production of infectious virus) or transformation (where only a limited number of viral proteins are expressed without synthesis of viral particles), it can be envisaged that cidofovir may act as antiviral and/or antiproliferative agent. The aim of this review is to discuss the advances in recent years in understanding the mode of action of ANPs as antiproliferative agents, given the fact that current data suggest that their use can be extended to the treatment of non-viral related malignancies.

Effect of maintenance immunosuppressive drugs on virus pathobiology: evidence and potential mechanisms

Recent evidence suggesting a potential anti-CMV effect of mTORis is of great interest to the transplant community. However, the concept of an immunosuppressant with antiviral properties is not new, with many accounts of the antiviral properties of several agents over the years. Despite these reports, to date, there has been little effort to collate the evidence into a fuller picture. This manuscript was developed to gather the evidence of antiviral activity of the agents that comprise a typical immunosuppressive regimen against viruses that commonly reactivate following transplant (HHV1 and 2, VZV, EBV, CMV and HHV6, 7, and 8, HCV, HBV, BKV, HIV, HPV, and parvovirus). Appropriate immunosuppressive regimens posttransplant that avoid acute rejection while reducing risk of viral reactivation are also reviewed. The existing literature was disparate in nature, although indicating a possible stimulatory effect of tacrolimus on BKV, potentiation of viral reactivation by steroids, and a potential advantage of mammalian target of rapamycin (mTOR) inhibition in several viral infections, including BKV, HPV, and several herpesviruses.

Castleman disease in a pediatric liver transplant recipient: a case report and literature review

Castleman disease is a rare hematologic disorder, closely linked to the HHV-8, and most commonly observed in immunocompromised individuals. Thirteen months following a liver transplant for CPS-1 defect, a 15-month-old boy presented with fevers, anemia, and growth retardation. Abdominal CT scan showed splenomegaly and generalized lymphadenopathy. Histology of chest wall lymph nodes revealed a mixed CD3+ T-cell and CD20+ B-cell population with atretic germinal centers consistent with multicentric Castleman disease. Qualitative DNA PCR detected HHV-8 in the resected lymph node and in the blood, supporting the diagnosis. Immunosuppression was tapered, and he was transitioned from tacrolimus to sirolimus. His graft function remained stable, and repeat imaging showed regression of the lymphadenopathy. The child is living one yr after Castleman disease diagnosis with a well-functioning graft. Castleman disease is a potential complication of solid organ transplant and HHV-8 infection. Reduction in immunosuppression and switch to sirolimus may be an effective strategy to treat this condition.

Radiotherapy for nasopharyngeal carcinoma and combined capecitabine and nimotuzumab treatment for lung metastases in a liver transplantation recipient: a case experience of sustained complete response

The primary treatment for nasopharyngeal carcinoma (NPC) is external beam radiotherapy. However, until now, there is little experience with the management of NPC occurred after solid organ transplantation. In this report, a 60-year-old man was found to have NPC (T2N1M0; stage III) 3 years after orthotopic liver transplantation treatment for hepatocellular carcinoma. Intensity-modulated radiotherapy (IMRT) was performed for NPC. One month after IMRT, complete response of NPC was achieved. However, multiple lung metastases occurred 18 months after the IMRT with the largest lesion measuring 4.1×5.5 cm and confirmed to be originated from NPC. Combined chemo-/targeted therapy consisted of capecitabine, and nimotuzumab was administered for four cycles. One month after initiation of capecitabine plus nimotuzumab treatment, a near-complete response was achieved for lung metastases. A repeat CT scan 1 year later showed sustained resolution of the lung metastases. The patient is still alive 16 months after the combined chemo-/targeted therapy.

Human papillomavirus-related genital disease in the immunocompromised host: Part II

Human papillomavirus is responsible for common condyloma acuminata and a number of premalignant and malignant anogenital lesions. The immunocompromised population is at particular risk because of a higher incidence of malignant transformation. Lesions in this population may prove refractory to standard treatment. This is part II of a two-part review that will discuss the treatment of condyloma acuminata and vaginal, vulvar, penile, and anal intraepithelial neoplasias. This article will provide an updated review of available treatments, with a focus on recent advances and the challenges faced in successfully treating human papillomavirus lesions in the immunocompromised host.

Acyclic nucleoside phosphonates: An unfinished story

While cidofovir, adefovir and tenofovir are the three acyclic nucleoside phosphonates (ANPs) that have been licensed for clinical use (the latter as a single-, double- and triple-drug combination), there are many more ANPs that await their application for medical or veterinary use: (S)-HPMPA, (S)-HPMPDAP, cPrPMEDAP, (R)-HPMPO-DAPy, PMEO-DAPy, 5-X-PMEO-DAPy, (R)-PMPO-DAPy, (S)-HPMP-5-azaC, and cyclic (S)-HPMP-5-azaC, and alkoxyalkyl prodrugs thereof.

Novel treatment of atypical human papillomavirus-associated epithelial hyperplasia with cidofovir

PURPOSE

We report a severe case of human papillomavirus-associated epithelial hyperplasia in a man infected with human immunodeficiency virus. These lesions were recalcitrant to treatment with surgical modalities and were eventually controlled with the daily application of a topical cidofovir gel.

PATIENT AND METHODS

A single case is presented, along with a relevant review of the published data.

RESULTS

Before the initiation of cidofovir treatment, the patient had approximately 80% of his gingiva and buccal mucosa engrossed by confluent papillomatous lesions. At 2 weeks after cidofovir treatment, the lesions had markedly regressed, and by 4 weeks, they were almost fully resolved. No untoward adverse reactions occurred.

CONCLUSIONS

Cidofovir formulated as a gel can be safe and effective for the treatment of epithelial hyperplasia in those with human immunodeficiency virus infection.

Yet another ten stories on antiviral drug discovery (part D): paradigms, paradoxes, and paraductions

This review article presents the fourth part (part D) in the series of stories on antiviral drug discovery. The stories told in part D focus on: (i) the cyclotriazadisulfonamide compounds; (ii) the {5-[(4-bromophenylmethyl]-2-phenyl-5H-imidazo[4,5-c]pyridine} compounds; (iii) (1H,3H-thiazolo[3,4-a]benzimidazole) derivatives; (iv) T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) and (v) its structurally closely related analogue pyrazine 2-carboxamide (pyrazinamide); (vi) new strategies for the treatment of hemorrhagic fever virus infections, including, as the most imminent, (vii) dengue fever, (viii) the veterinary use of acyclic nucleoside phosphonates; (ix) the potential (off-label) use of cidofovir in the treatment of papillomatosis, particularly RRP (recurrent respiratory papillomatosis); and (x) finally, the prophylactic use of tenofovir to prevent HIV infections.

Colorectal and anal neoplasms following liver transplantation

OBJECTIVE

Liver transplantation (LT) is the treatment of choice for end-stage liver disease. The required immunosuppression increases the risk for developing malignancies. Some viruses play a crucial role. Data on neoplasms of the colon, rectum and anus in LT are limited.

METHOD

A retrospective evaluation of the incidence and clinical course of colorectal and anal malignancies and colonic polyps in a series of 467 consecutive LTs in 402 individuals between 1998 and 2001 was performed. Standard immunosuppression included Tacrolimus, Mycophenolic acid and steroids.

RESULTS

During a median follow up of 5.2 years, three colon adenocarcinomas, one EBV associated cecal posttransplant lymphoproliferative tumour and two HPV associated anal tumours were identified. Pre-LT colonoscopy was performed in 161 patients (40%), and of 153 evaluable individuals, 53 (34.9%) had polyps. Colonoscopy was performed in 186 patients (46.3%) median 14.8 (range 0.2-77.8) months post-LT and 55 (29.3%) had polyps. Post-LT adenomatous polyps were detected in 47.3% of patients with pre-LT polyps vs 6.7% of patients without pre-LT polyps (P < 0.001). Patients with alcoholic liver disease had a significantly higher rate of adenoma formation (50.0% vs 11.1%, P < 0.001). No patient died from colorectal/anal malignancy.

CONCLUSION

The incidence of metachronous and new polyp formation in our study is similar to people who are not immunocompromised, but subgroups are at increased risk. Viral-associated malignancies, including post-transplant lymphoproliferative disorders and anal cancer, are important entities in the LT population suggesting that complete screening of the colon, rectum and anus including pre-LT and post-LT colonoscopy should be utilized.

[Human papillomavirus-associated warts in organ transplant recipients. Incidence, risk factors, management]

Human papillomaviruses infect the squamous epithelia of the skin and cause warts, and are occasionally found in squamous cell carcinomas. Since cell-mediated immunity plays a crucial role in the control of HPV-infections, organ transplant recipients, unable to mount an adequate T-helper 1 cell-mediated immune surveillance, frequently develop widespread and resistant induced warts. Skin tumors, especially squamous cell carcinomas, are the most common post-transplantation neoplasm. Warts, actinic keratoses and invasive squamous cell carcinomas are known to develop at the same time in the areas. The role of HPV in the development of invasive squamous cell carcinoma under immunosuppression, remains to be elucidated in respect to common risk factors and increased numbers of warts potentially identifying patients at increased risk for carcinoma. We prospectively studied 1690 organ transplant recipients in the dermatology clinic at the Charité University Hospital in Berlin, to evaluate risk factors being involved in the development of HPV-induced warts and to assess a potential association of with the development of non-melanoma skin cancers in this population. The cumulative incidence of warts steadily increased throughout the post-transplant years. The presence of more than 10 verrucae was associated with the development of actinic keratoses, invasive squamous cell carcinoma and basal cell carcinoma. This study shows clear evidence that certain risk factors of skin carcinogenesis in organ transplant recipient such as increased age at transplantation, a high dose of immunosuppression related to a specific type of graft and use of azathioprine or cyclosporine are strongly associated with an increased incidence of warts. Furthermore, HPV-induced verrucae vulgares could be used as a potential predictor for the development of coincidental non melanoma skin cancer in organ transplant recipients and therefore could serve as an early identification marker of skin cancer high-risk patients. The challenging management of warts in organ transplantation patients is reviewed.

Cutaneous warts in children before and after renal transplantation

Cutaneous warts occur in 3.9-4.9% of children in the UK. The incidence is increased in organ transplant recipients and may be increased in patients with chronic kidney disease (CKD), since uraemia reduces the immune system's function. We surveyed the records from our CKD and renal transplant clinic to ensure patients with warts were identified and appropriately treated. Data were collected by questionnaire. The presence of warts, location, treatment, levels of pain and emotional upset were recorded. Nine of 49 (18.4%) pre-transplantation patients (33 male, median age 12.1 years) were currently suffering from warts compared with 17 of 60 (28.3%) post-transplantation patients (34 male, median age 13.9 years). A further 14 pre-transplantation and 16 post-transplantation patients had previously suffered from warts which had resolved. Forty-one patients had sought treatment for warts, mainly from primary care. Five patients, all having received transplants, were seen by a dermatologist. Self-rated levels of pain and emotional upset were generally low, apart from those of four adolescent patients who expressed significant emotional upset. We concluded that cutaneous warts are more common among CKD patients. Appropriate information and treatment are required before and after transplantation. The majority of warts can be treated in primary care, but selected patients with extensive warts that cause distress need early referral for dermatology opinion.

Cidofovir: clinical experience and future perspectives on an acyclic nucleoside phosphonate analog of cytosine in the treatment of refractory and premalignant HPV-associated anal lesions

BACKGROUND

Cidofovir, a nucleotide analog with antiviral activity against a broad range of DNA viruses including human papilloma viruses (HPV), is available off label to clinicians.

OBJECTIVE

To provide a better knowledge of pharmacology and effects when topically applied.

METHODS

After reviewing the chemistry, physiology, and animal studies, an overview of clinical studies is provided.

RESULTS/CONCLUSIONS

Cidofovir, as a result of its antiviral and antiproliferative activity and its ability to induce apoptosis, can offer a solution for the treatment of severe recurrent HPV-induced lesions. It can also be used to attempt to treat dysplastic lesions and as an adjuvant treatment. The long-lasting antiviral activity allows infrequent dosing. As a rule, cidofovir applied on the skin is well tolerated, even in long-term treatment. The dose-limiting nephrotoxicity of the drug is not a concern in patients with a glomerular filtration rate within the normal range. Cidofovir has clearly influenced the landscape of refractory and dysplastic anogenital condylomata acuminata and its use has increased over the last decade. However, further controlled clinical trials are needed to assess the role of cidofovir and its derivatives.

Antiviral agents acting as DNA or RNA chain terminators

Nucleoside or nucleotide analogue inhibitors of viral replication almost act as chain terminators during DNA (DNA- and retroviruses) or RNA (RNA viruses) synthesis. Following intracellular phosphorylation, by viral and/or cellular kinases, the 5'-triphosphate metabolites (or 2'-diphosphate metabolites in the case of acyclic nucleoside phosphonate analogues) compete with the natural substrate in the DNA or RNA polymerization reaction. Obligatory chain terminators (e.g., acyclovir) do not offer the 3'-hydroxyl function at the riboside moiety of the molecule. Nucleoside analogues that possess a hydroxyl function at a position equivalent of the 3'-hydroxyl position may act as chain terminators if this hydroxyl group is conformationally constrained (e.g., ganciclovir) or sterically hindered to enter into a phosphodiester linkage with the incoming nucleotide. In case that the 3'-hydroxylgroup is correctly positioned, chain elongation may be hampered through steric hindrance from neighboring substituents (e.g., 2'-C-methyl or 4'-azido nucleoside inhibitors of HCV replication). Here, we review the molecular mechanism of action and the clinical applications of the nucleosides and nucleotides acting as chain terminators. A further discussion of clinical applications in combination therapy can be found in Chap. 12.

Cell-permeable artificial zinc-finger proteins as potent antiviral drugs for human papillomaviruses

Human papillomavirus (HPV) is one of the important pharmaceutical targets because infection of the high-risk types causes invasive cervical cancer. However, effective antiviral drugs for HPV have not been developed so far. In the present study, we constructed cell-permeable artificial zinc-finger proteins (AZPs) by fusing an AZP previously generated for inhibition of HPV-18 DNA replication with a cell-penetrating peptide (CPP) as candidates for new antiviral drugs against HPV. We confirmed that these CPP-AZP fusions reduced the replication rate in transient replication assays when added to the culture medium. In particular, 250 nM CPP-AZP (designated AZP-R9) containing a 9-mer of arginine as the CPP reduced HPV-18 DNA replication to 3% of that of a control, and the 50% effective concentration (EC50) was <31 nM. Furthermore, a cytotoxicity assay revealed that the 50% inhibitory concentration (IC50) of AZP-R9 was >10 microM. Therefore, the selectivity index, defined as IC50/EC50, was >300, which is better than that of the antiviral cidofovir for HPVs. Thus, our results demonstrate that cell-permeable AZPs could serve as potent protein-based antiviral drugs.

Activities of several classes of acyclic nucleoside phosphonates against camelpox virus replication in different cell culture models

Camelpox virus (CMLV) is the closest known virus to variola virus. Here we report on the anti-CMLV activities of several acyclic nucleoside phosphonates (ANPs) related to cidofovir [(S)-1-(3-hydroxy-2-phosphonomethoxypropyl)cytosine (HPMPC; Vistide)] against two CMLV strains, CML1 and CML14. Cytopathic effect (CPE) reduction assays performed with human embryonic lung fibroblast monolayers revealed the selectivities of the first two classes of ANPs (cHPMPA, HPMPDAP, and HPMPO-DAPy) and of the hexadecyloxyethyl ester of 1-{[(5S)-2-hydroxy-2-oxido-1,4,2-dioxaphosphinan-5-yl]methyl}-5-azacytosine (HDE-cHPMP-5-azaC), belonging to the newly synthesized ANPs, which are HPMP derivatives containing a 5-azacytosine moiety. The inhibitory activities of ANPs against both strains were also confirmed with primary human keratinocyte (PHK) monolayers, despite the higher toxicity of those molecules on growing PHKs. Virus yield assays confirmed the anti-CML1 and anti-CML14 efficacies of the compounds selected for the highest potencies in CPE reduction experiments. Ex vivo studies were performed with a 3-dimensional model of human skin, i.e., organotypic epithelial raft cultures of PHKs. It was ascertained by histological evaluation, as well as by virus yield assays, that CMLV replicated in the human skin equivalent. HPMPC and the newly synthesized ANPs proved to be effective at protecting the epithelial cells against CMLV-induced CPE. Moreover, in contrast to the toxicity on PHK monolayers, signs of toxicity in the differentiated epithelium were seen only at high ANP concentrations. Our results demonstrate that compounds belonging to the newly synthesized ANPs, in addition to cidofovir, represent promising candidates for the treatment of poxvirus infections.

First forearm transplantation: outcome at 3 years

We here report on the surgical procedure, postoperative course and functional results at 3 years following the first bilateral forearm transplantation. A 41-year-old male underwent bilateral forearm transplantation on February 17, 2003. After ATG induction therapy, tacrolimus, prednisone and MMF were given for maintenance immunosuppression. At 16 months, MMF was switched to everolimus. Hand function, histology, immunohistochemistry, radiomorphology, motor and nerve conduction and somatosensory-evoked potentials were investigated at frequent intervals. A total of six rejection episodes required treatment with either steroids, basiliximab, ATG, alemtuzumab or tacrolimus dose augmentation. At 3 years, the patient is free of clinical signs of rejection despite a persisting minimal perivascular lymphocytic dermal infiltrate. No signs of myointimal proliferation in graft vessels were seen. Motor function continuously improved, resulting in satisfactory hand function. Intrinsic hand muscle function was first observed at 16 months and continues to improve. Although discrimination of hot and cold recovered, overall sensitivity remains poor. The patient is satisfied with the outcome. Bilateral forearm transplantation represents a novel therapeutic option after loss of forearms.