A Herpes Simplex Virus 1 DNA Polymerase Multidrug Resistance Mutation Identified in a Patient With Immunodeficiency and Confirmed by Gene Editing.

Background: Herpes simplex virus 1 can cause severe infections in individuals who are immunocompromised. In these patients, emergence of drug resistance mutations causes difficulties in infection management.

Methods: Seventeen herpes simplex virus 1 isolates were obtained from orofacial/anogenital lesions in a patient with leaky severe combined immunodeficiency over 7 years, before and after stem cell transplantation.

Synergistic targeting of the PI3K/mTOR and MAPK/ERK pathways in Merkel cell carcinoma.

Merkel cell carcinoma (MCC) is an aggressive type of skin cancer, which is caused either by integration of the oncogenic Merkel cell polyomavirus (MCPyV) or by accumulation of UV-light induced mutations. Since the response to immune-checkpoint inhibitors is limited, new therapeutic agents need to be explored. Previous studies have shown that MCC cell lines and xenografts are sensitive to MLN0128, a dual mTOR1/2 inhibitor.

Poxviruses Bearing DNA Polymerase Mutations Show Complex Patterns of Cross-Resistance.

Despite the eradication of smallpox four decades ago, poxviruses continue to be a threat to humans and animals. The arsenal of anti-poxvirus agents is very limited and understanding mechanisms of resistance to agents targeting viral DNA polymerases is fundamental for the development of antiviral therapies. We describe here the phenotypic and genotypic characterization of poxvirus DNA polymerase mutants isolated under selective pressure with different acyclic nucleoside phosphonates, including HPMPC (cidofovir), cHPMPC, HPMPA, cHPMPA, HPMPDAP, HPMPO-DAPy, and PMEO-DAPy, and the pyrophosphate analogue phosphonoacetic acid.

Organotypic Epithelial Raft Cultures as a Three-Dimensional In Vitro Model of Merkel Cell Carcinoma.

Merkel cell carcinoma (MCC) is a rare type of skin cancer for which an in vitro model is still lacking. MCC tumorigenesis is associated either with the integration of Merkel cell polyomavirus into the host genome, or with the accumulation of somatic mutations upon chronic exposure to UV light. Transgenic animals expressing the viral oncoproteins, which are constitutively expressed in virus-related MCC, do not fully recapitulate MCC.

An MHV-68 Mutator Phenotype Mutant Virus, Confirmed by CRISPR/Cas9-Mediated Gene Editing of the Viral DNA Polymerase Gene, Shows Reduced Viral Fitness.

Drug resistance studies on human γ-herpesviruses are hampered by the absence of an in vitro system that allows efficient lytic viral replication. Therefore, we employed murine γ-herpesvirus-68 (MHV-68) that efficiently replicates in vitro as a model to study the antiviral resistance of γ-herpesviruses. In this study, we investigated the mechanism of resistance to nucleoside (ganciclovir (GCV)), nucleotide (cidofovir (CDV), HPMP-5azaC, HPMPO-DAPy) and pyrophosphate (foscarnet (PFA)) analogues and the impact of these drug resistance mutations on viral fitness.

[Herpes simplex virus resistance to antivirals].

Herpes simplex virus (HSV) infections remain an important cause of morbidity among immunocompromised patients, such as transplant recipients and human immunodeficiency virus [HIV]-infected individuals. Only few antiviral drugs are available to treat HSV infections: (val)acyclovir, foscarnet, and cidofovir. Prophylactic and curative antiviral treatments administered during prolonged periods among patients with altered T-cell immunity may lead to the emergence of HSV resistance to antivirals, contributing to a challenging therapeutic management of viral infection.

Viral fitness of MHV-68 viruses harboring drug resistance mutations in the protein kinase or thymidine kinase.

Murine γ-herpesvirus-68 (MHV-68), genetically and biologically related to human γ-herpesviruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, can be easily propagated in vitro allowing drug resistance studies. Previously, we described specific changes in MHV-68 protein kinase (PK) or thymidine kinase (TK) associated with resistance to various purine or pyrimidine nucleoside analogues, respectively. To investigate how specific TK and PK mutations affect viral replication capacity, we performed dual infection competition assays in which wild-type and drug-resistant virus compete in absence or presence of antivirals in Vero cells.

BKTyper: Free Online Tool for Polyoma BK Virus VP1 and NCCR Typing.

Human BK polyomavirus (BKPyV) prevalence has been increasing due to the introduction of more potent immunosuppressive agents in transplant recipients, and its clinical interest. BKPyV has been linked mostly to polyomavirus-associated hemorrhagic cystitis, in allogenic hematopoietic stem cell transplant, and polyomavirus-associated nephropathy in kidney transplant patients. BKPyV is a circular double-stranded DNA virus that encodes for seven proteins, of which Viral Protein 1 (VP1), the major structural protein, has been extensively used for genotyping.

CRISPR/Cas9 Editing of the Polyomavirus Tumor Antigens Inhibits Merkel Cell Carcinoma Growth In Vitro.

Merkel cell carcinoma (MCC) is an aggressive type of skin cancer whose main causative agent is Merkel cell polyomavirus (MCPyV). MCPyV is integrated into the genome of the tumor cells in most MCCs. Virus-positive tumor cells constitutively express two viral oncoproteins that promote cell growth: the small (sT) and the large (LT) tumor antigens (TAs).

Monitoring of phosphorylation using immobilized kinases by on-line enzyme bioreactors hyphenated with High-Resolution Mass Spectrometry.

Nucleosides analogues are the cornerstone of the treatment of several human diseases. They are especially at the forefront of antiviral therapy. Their therapeutic efficiency depends on their capacity to be converted to the active nucleoside triphosphate form through successive phosphorylation steps catalyzed by nucleoside/nucleotide kinases.

Investigation of tumor-tumor interactions in a double human cervical carcinoma xenograft model in nude mice.

Tumor-tumor distant interactions within one organism are of major clinical relevance determining clinical outcome. To investigate this poorly understood phenomenon, a double human cervical xenograft model in nude mice was developed. A first tumor was induced subcutaneously by injection of human papillomavirus positive cervical carcinoma cells into the mouse lower right flank and 3 weeks later, animals were challenged with the same tumor cell line injected subcutaneously into the upper left flank.

Thymidine kinase and protein kinase in drug-resistant herpesviruses: Heads of a Lernaean Hydra.

Herpesviruses thymidine kinase (TK) and protein kinase (PK) allow the activation of nucleoside analogues used in anti-herpesvirus treatments. Mutations emerging in these two genes often lead to emergence of drug-resistant strains responsible for life-threatening diseases in immunocompromised populations. In this review, we analyze the binding of different nucleoside analogues to the TK active site of the three α-herpesviruses [Herpes Simplex Virus 1 and 2 (HSV-1 and HSV-2) and Varicella-Zoster Virus (VZV)] and present the impact of known mutations on the structure of the viral TKs.

The Anti-Human Immunodeficiency Virus Drug Tenofovir, a Reverse Transcriptase Inhibitor, Also Targets the Herpes Simplex Virus DNA Polymerase.

Background: Genital herpes is an important cofactor for acquisition of human immunodeficiency virus (HIV) infection, and effective prophylaxis is a helpful strategy to halt both HIV and herpes simplex virus (HSV) transmission. The antiretroviral agent tenofovir, formulated as a vaginal microbicide gel, was shown to reduce the risk of HIV and HSV type 2 (HSV-2) acquisition.

Methods: HSV type 1 (HSV-1) and HSV-2 mutants were selected for resistance to tenofovir and PMEO-DAPy (6-phosphonylmethoxyethoxy-2,4-diaminopyrimidine, an acyclic nucleoside phosphonate with dual anti-HSV and anti-HIV activity) by stepwise dose escalation.

Distribution and effects of amino acid changes in drug-resistant α and β herpesviruses DNA polymerase.

Emergence of drug-resistance to all FDA-approved antiherpesvirus agents is an increasing concern in immunocompromised patients. Herpesvirus DNA polymerase (DNApol) is currently the target of nucleos(t)ide analogue-based therapy. Mutations in DNApol that confer resistance arose in immunocompromised patients infected with herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV), and to lesser extent in herpes simplex virus 2 (HSV-2), varicella zoster virus (VZV) and human herpesvirus 6 (HHV-6).

Resistance to the nucleotide analogue cidofovir in HPV(+) cells: a multifactorial process involving UMP/CMP kinase 1.

Human papillomavirus (HPV) is responsible for cervical cancer, and its role in head and neck carcinoma has been reported. No drug is approved for the treatment of HPV-related diseases but cidofovir (CDV) exhibits selective antiproliferative activity. In this study, we analyzed the effects of CDV-resistance (CDVR) in two HPV(+) (SiHaCDV and HeLaCDV) and one HPV(-) (HaCaTCDV) tumor cell lines.

ST-246 is a key antiviral to inhibit the viral F13L phospholipase, one of the essential proteins for orthopoxvirus wrapping.

Objectives: ST-246 is one of the key antivirals being developed to fight orthopoxvirus (OPV) infections. Its exact mode of action is not completely understood, but it has been reported to interfere with the wrapping of infectious virions, for which F13L (peripheral membrane protein) and B5R (type I glycoprotein) are required. Here we monitored the appearance of ST-246 resistance to identify its molecular target.

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.

Spectrum of activity and mechanisms of resistance of various nucleoside derivatives against gammaherpesviruses.

The susceptibilities of gammaherpesviruses, including Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), and animal rhadinoviruses, to various nucleoside analogs was investigated in this work. Besides examining the antiviral activities and modes of action of antivirals currently marketed for the treatment of alpha- and/or betaherpesvirus infections (including acyclovir, ganciclovir, penciclovir, foscarnet, and brivudin), we also investigated the structure-activity relationship of various 5-substituted uridine and cytidine molecules. The antiviral efficacy of nucleoside derivatives bearing substitutions at the 5 position was decreased if the bromovinyl was replaced by chlorovinyl.

Reduced tumorigenicity and pathogenicity of cervical carcinoma SiHa cells selected for resistance to cidofovir.

Background: Insights into the mechanisms associated with chemotherapy-resistance are important for implementation of therapeutic strategies and for unraveling the mode of action of chemotherapeutics. Although cidofovir (CDV) has proven efficacious in the treatment of human papillomavirus (HPV)-induced proliferation, no studies concerning the development of resistance to CDV in HPV-positive tumor cells have been performed yet.

Methods: From the cervical carcinoma SiHa cells (SiHaparental), which are HPV-16 positive, cidofovir-resistant cells (SiHaCDV) were selected, and differential gene expression profiles were analyzed by means of microarrays.

Cidofovir selectivity is based on the different response of normal and cancer cells to DNA damage.

Background: Cidofovir (CDV) proved efficacious in treatment of human papillomaviruses (HPVs) hyperplasias. Antiproliferative effects of CDV have been associated with apoptosis induction, S-phase accumulation, and increased levels of tumor suppressor proteins. However, the molecular mechanisms for the selectivity and antitumor activity of CDV against HPV-transformed cells remain unexplained.

Heterogeneity and evolution of thymidine kinase and DNA polymerase mutants of herpes simplex virus type 1: implications for antiviral therapy.

Background: Infections caused by acyclovir-resistant isolates of herpes simplex virus (HSV) after hematopoietic stem cell transplantation (HSCT) are an emerging concern. An understanding of the evolutionary aspects of HSV infection is crucial to the design of effective therapeutic and control strategies.

Methods: Eight sequential HSV-1 isolates were recovered from an HSCT patient who suffered from recurrent herpetic gingivostomatitis and was treated alternatively with acyclovir, ganciclovir, and foscavir.

The large tumor antigen: a "Swiss Army knife" protein possessing the functions required for the polyomavirus life cycle.

The SV40 large tumor antigen (L-Tag) is involved in the replication and cell transformation processes that take place during the polyomavirus life cycle. The ability of the L-Tag to interact with and to inactivate the tumor suppressor proteins p53 and pRb, makes this polyfunctional protein an interesting target in the search for compounds with antiviral and/or antiproliferative activities designed for the management of polyomavirus-associated diseases. The severe diseases caused by polyomaviruses, mainly in immunocompromised hosts, and the absence of licensed treatments, make the discovery of new antipolyomavirus drugs urgent.

Cidofovir treatment improves the pathology caused by the growth of human papillomavirus-positive cervical carcinoma xenografts in athymic nude mice.

Cidofovir has shown antiproliferative effects against human papillomavirus (HPV)-positive cells and successfully suppressed the growth of HPV-positive xenografts in athymic nude mice. The present study evaluated the effect of cidofovir on several disease parameters in this animal model. Intratumoral administration of cidofovir resulted in a beneficial effect on body weight gain, a reduction in splenomegaly, a partial restoration of tryptophan catabolism, and diminished the inflammatory state induced by the xenografts.