Detection and identification of U69 gene mutations encoded by ganciclovir-resistant human herpesvirus 6 using denaturing high-performance liquid chromatography

Antiviral Drugs Against Herpesviruses

The discovery of the nucleoside analogue, acyclovir, represented a milestone in the management of infections caused by herpes simplex virus and varicella-zoster virus. Ganciclovir, another nucleoside analogue, was then used for the management of systemic and organ-specific human cytomegalovirus diseases. The pyrophosphate analogue, foscarnet, and the nucleotide analogue, cidofovir, have been approved subsequently and constitute the second-line antiviral drugs. However, the viral DNA polymerase is the ultimate target of all these antiviral agents with a possible emergence of cross-resistance between these drugs. Recently, letermovir that targets the viral terminase complex was approved for the prophylaxis of human cytomegalovirus infections in hematopoietic stem cell transplant recipients. Other viral targets such as the protein kinase and the helicase-primase complex are also evaluated for the development of novel potent inhibitors against herpesviruses.

Selected nucleos(t)ide-based prescribed drugs and their multi-target activity

Nucleos(t)ide analogues play pivotal roles as antiviral, cytotoxic or immunosuppressive agents. Here, we review recent reports of nucleoside analogues that exhibit broad-spectrum activity towards multiple life-threatening RNA and DNA viruses. We also present a discussion about nucleoside antimetabolites-approved antineoplastic agents-that have recently been shown to have antiviral and/or antibacterial activity. The approved drugs and drug combinations, as well as recently identified candidates for investigation and/or experimentation, are discussed. Several examples of repurposed drugs that have already been approved for use are presented. This strategy can be crucial for the first-line treatment of acute infections or coinfections and for the management of drug-resistant strains.

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. Furthermore, models of β-herpesviruses [Human cytomegalovirus (HCMV) and human herpesvirus-6 (HHV-6)] PKs allow to link amino acid changes with resistance to ganciclovir and/or maribavir, an investigational chemotherapeutic used in patients with multidrug-resistant HCMV. Finally, we set the basis for the understanding of drug-resistance in γ-herpesviruses [Epstein-Barr virus (EBV) and Kaposi's sarcoma associated herpesvirus (KSHV)] TK and PK through the use of animal surrogate models.

High-density lipoprotein therapy inhibits Porphyromonas gingivalis-induced abdominal aortic aneurysm progression

Clinical and experimental studies have highlighted the potential implication of periondontal bacteria contamination in the pathogenesis of abdominal aortic aneurysms (AAA). In addition to their role in reverse cholesterol transport, high-density lipoproteins (HDLs) display multiple functions, including anti-inflammatory and lipopolysaccharide scavenging properties. Low plasma levels of HDL-cholesterol have been reported in AAA patients. We tested the effect of a HDL therapy in Sprague-Dawley rat model of AAA, obtained by intraluminal elastase infusion followed by repeated injections of Porphyromonas gingivalis (Pg). HDLs, isolated by ultracentrifugation of plasma from healthy human volunteers, were co-injected intravenously (10 mg/kg) with Pg (1.107 Colony Forming Unit) one, eight and 15 days after elastase perfusion. Rats were sacrificed one week after the last injection. Our results show that Pg injections promote the formation of a persistent neutrophil-rich thrombus associated with increased aortic diameter in this AAA model. HDLs significantly reduced the increased AAA diameter induced by Pg. Histology showed the onset of a healing process in the Pg/HDL group. HDL injections also reduced neutrophil activation in Pg-injected rats associated with decreased cytokine levels in conditioned media and plasma. Scintigraphic analysis showed an intense uptake of 99mTc-HDL by the AAA suggesting that HDLs could exert their beneficial effect by acting directly on the thrombus components. HDL supplementation may therefore constitute a new therapeutic tool for AAA treatment.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Analysis of ganciclovir-resistant human herpesvirus 6B clinical isolates using quenching probe PCR methodology

Quenching probe PCR (QP-PCR) analysis was used to determine the frequency of ganciclovir (GCV) resistance among clinical isolates of human herpesvirus 6B (HHV-6B) obtained from patients with primary viral infection and viral reactivation. Forty-two HHV-6B clinical isolates were repeatedly recovered from 15 hematopoietic stem cell transplant (HSCT) recipients, and 20 isolates were recovered from 20 exanthem subitum (ES) patients. Of the 15 HSCT recipients, 9 received GCV during the observation period; however, none of the ES patients were treated with GCV. Two established laboratory strains, Z29 and HST, were used as standards in this study. Regions 1 and 2 of the U69 gene of all of the clinical isolates demonstrated the same melting temperature as regions 1 and 2 of the Z29 strain. For region 3, the melting temperatures of all clinical isolates fell between the melting temperature of the plasmid containing the A462D single nucleotide polymorphism (SNP) and the melting temperature of the Z29 strain, and the melting temperatures profiles of all clinical isolates were similar to the melting temperature profile of the Japanese HST strain. As expected, none of the 20 clinical isolates recovered from the ES patients and the 14 isolates recovered from the HSCT recipients who did not receive GCV treatment carried the six known SNPs associated with GCV resistance. Interestingly, these six SNPs were not detected in the 28 clinical isolates recovered from the 9 HSCT recipients who received GCV. Additional sequence analysis of the U69 gene from the 15 representative isolates from the 15 HSCT recipients identified other SNPs. These SNPs were identical to those identified in the HST strain. Therefore, the rate of emergence of GCV-resistant HHV-6B strains appears to be relatively low, even in HSCT recipients treated with GCV.

Analysis of HHV-6 mutations in solid organ transplant recipients at the onset of cytomegalovirus disease and following treatment with intravenous ganciclovir or oral valganciclovir

BACKGROUND

Human herpesvirus 6 (HHV-6) and human cytomegalovirus (HCMV) are major opportunistic pathogens in solid organ transplant (SOT) recipients. The use of antivirals for the treatment of HCMV disease can result in the development of drug resistance mutations in HCMV and also potentially in HHV-6.

OBJECTIVES

The emergence of HHV-6 drug resistance mutations was evaluated in SOT recipients at the onset of HCMV disease and following treatment with ganciclovir (GCV) or valganciclovir (VGCV).

STUDY DESIGN

Detection of HHV-6 was performed by real-time PCR from whole blood samples serially obtained from SOT recipients treated for HCMV disease with an induction dose of intravenous GCV or oral VGCV for 21 days followed by VGCV maintenance for 28 days in both arms. Baseline and last positive HHV-6 samples were tested for mutations in the genes encoding the protein kinase (U69) and the DNA polymerase (U38).

RESULTS

The rate of HHV-6 viraemia among SOT patients with HCMV disease at baseline was 3.2% (5/155). All isolates belonged to the HHV-6B species. Mutations L213I and Y479H were detected at baseline and at later times in the U69 kinase. Mutation L213I was previously reported as polymorphism whereas the role of mutation Y479H in drug resistance is unknown. Mutations D854E and E855Q found in the DNA polymerase were known as natural variants.

CONCLUSIONS

The incidence of HHV-6 viraemia in SOT recipients with established HCMV disease before initiation of antiviral therapy was low. Treatment with GCV or VGCV did not induce the emergence of HHV-6 drug resistance mutations.

Testing the susceptibility of human herpesviruses to antivirals

Herpesviruses cause chronic lifelong infections in humans and may cause life-threatening diseases in immunosuppressed patients. Antiviral drugs targeted to viral DNA polymerase, such as acyclovir, penciclovir, ganciclovir, foscarnet and cidofovir, are currently available and have been proven to be efficient against clinical symptoms of herpesvirus infections. The resistance of herpesviruses to these drugs is associated with specific mutations of viral genes encoding either DNA polymerase or enzymes phosphorylating nucleoside analogs. Resistance is detected and characterized by means of specific susceptibility assays, which can be classified as phenotypic, genetic and functional. These tests are used both to investigate novel antiviral compounds and look for the emergence of resistant viruses in treated patients in case of clinical failure. Although susceptibility assays are often time consuming and present some limitations regarding the interpretation of their results, their use in the monitoring of antiherpetic treatments should be promoted and improved, in parallel to the development of novel efficient drugs.

PCR with quenching probes enables the rapid detection and identification of ganciclovir-resistance-causing U69 gene mutations in human herpesvirus 6

A single-nucleotide polymorphism detection assay using PCR with quenching probes (QP-PCR) was developed for the rapid detection of antiviral drug-resistance mutations of human herpesvirus 6 (HHV-6). The mutations examined were in the HHV-6 U69 gene, and were single-base mutations in sequences known to be associated with ganciclovir (GCV) resistance in HCMV. We previously confirmed that they conferred GCV resistance to recombinant baculoviruses (Nakano et al., J. Virol. Methods 161:223-230, 2009). Six characterized mutations, including a previously reported one that encodes a GCV-sensitive kinase-activity mutant (Isegawa et al., J. Clin. Virol. 44:15-19, 2009), were used. The six mutations were separated into three groups based on their location in the U69 protein, and detected by the hybridization of three probes. We developed and validated a set of assays for these mutations using PCR followed by differential melting of a fluorescently labeled oligo probe, on a Roche Light Cycler platform. Nucleobase quenching was used to detect the hybridized probe. The optimized assay could distinguish the different mutants, and easily detected mutants representing 30% of the DNA in a mixed sample. This QP-PCR assay permitted the rapid (1.5 h), objective, and reproducible detection of drug-resistant mutations of HHV-6.