Cytomegalovirus UL97 mutations associated with ganciclovir resistance in immunocompromised patients from Argentina

Global estimate of phenotypic and genotypic ganciclovir resistance in cytomegalovirus infections among HIV and organ transplant patients; A systematic review and meta-analysis

Human cytomegalovirus (CMV), an opportunistic pathogen belonging to Herpesviridae family, is considered as one of the major causes of morbidity and mortality among wide variety of patients, particularly in transplant recipients and HIV positive patients. As this virus can be resistant to treatment, frequency of CMV in patients who receive organ transplantation and people suffering from AIDS was studied between 1980 and 2019. Medline (via PubMed), Embase, Web of Science, and the Iranian Database were reviewed, and Comprehensive Meta-Analysis (V2.0, Biostat) software analyzed all data. Finally, we used Cochran's Q-statistic to encounter heterogeneity between different studies. Meta-analyses indicated, GCV resistance was 14.1% (95% CI 11.2-17.7); however, in patients suffering from AIDS and organ transplantation were 19.5% (95% CI 14.7-25.4) and 11.4% (95% CI 8.1-15.8), respectively. There were increasing rates in the prevalence of GCV resistance in CMV among transplant recipients, and HIV positive patients. Therefore, evaluation of these refractory infections is beneficial.

Human cytomegalovirus UL97 D605E polymorphism has a high prevalence in immunocompetent Japanese infants and children

There is no existing data on UL97 mutation in human cytomegalovirus (HCMV) isolates obtained from individuals who have never been exposed to ganciclovir (GCV). UL97 codons 439 to 645 from 61 CMV isolates from 61 immunocompetent Japanese infants and children were sequenced directly. No known GCV resistance mutations were found, meaning that the UL97 mutation had resulted from the use of GCV. On the other hand, a mutation at codon 605 (D to E) was frequently identified (56/61: 91.8%). This could be a genetic marker for HCMV in East Asian counties, because of its low prevalence in the strains of HCMV circulating in Western countries.

Genotypic characterization of human cytomegalovirus UL97 phosphotransferase natural polymorphism in the era of ganciclovir and maribavir

The molecular mechanisms of human cytomegalovirus (CMV) resistance to both ganciclovir and maribavir reported so far rely predominantly on the presence of mutations within UL97 phosphotransferase. The accurate interpretation of genotypic antiviral resistance assay results requires the clear distinction between resistance mutations and natural interstrain sequence variations. The objective of this work was to extend the catalog of CMV UL97 phosphotransferase natural polymorphisms. The full-length UL97 gene sequence analysis from 4 laboratory strains and 35 clinical samples from patients who had not received any previous anti-CMV treatment was performed. At the nucleotide level, the interstrain identity was >98%. At the amino acid level, ten natural polymorphisms never previously described were identified. Together with all previous results reported in the literature, a new map of UL97 phosphotransferase natural polymorphism could be settled in the era of ganciclovir and maribavir.

Stereoselective phosphorylation of cyclopropavir by pUL97 and competitive inhibition by maribavir

Human cytomegalovirus (HCMV) is a widespread pathogen that can cause severe disease in immunologically immature and immunocompromised individuals. Cyclopropavir (CPV) is a guanine nucleoside analog active against human and murine cytomegaloviruses in cell culture and efficacious in mice by oral administration. Previous studies established that the mechanism of action of CPV involves inhibition of viral DNA synthesis. Based upon this action and the structural similarity of CPV to ganciclovir (GCV), we hypothesized that CPV must be phosphorylated to a triphosphate to inhibit HCMV DNA synthesis and that pUL97 is the enzyme responsible for the initial phosphorylation of CPV to a monophosphate (CPV-MP). We found that purified pUL97 phosphorylated CPV 45-fold more extensively than GCV, a known pUL97 substrate and the current standard of treatment for HCMV infections. Kinetic studies with CPV as the substrate for pUL97 demonstrated a Km of 1,750+/-210 microM. Introduction of 1.0 or 10 nM maribavir, a known pUL97 inhibitor, and subsequent Lineweaver-Burk analysis demonstrated competitive inhibition of CPV phosphorylation, with a Ki of 3.0+/-0.3 nM. Incubation of CPV with pUL97 combined with GMP kinase [known to preferentially phosphorylate the (+)-enantiomer of CPV-MP] established that pUL97 stereoselectively phosphorylates CPV to its (+)-monophosphate. These results elucidate the mechanism of CPV phosphorylation and help explain its selective antiviral action.

Stability of murine cytomegalovirus genome after in vitro and in vivo passage

While large DNA viruses are thought to have low mutation rates, only a small fraction of their genomes have been analyzed at the single-nucleotide level. Here, we defined the genetic stability of murine cytomegalovirus (MCMV) by whole-genome sequencing. Independently assembled sequences of three sister plaques showed only two single-base-pair substitutions after in vitro passage. In vivo-passaged MCMV likewise demonstrated low mutation rates, comparable to those after in vitro passage, indicating high genome stability of MCMV at the single-nucleotide level in the absence of obvious selection pressure.

Single and multiple mutations in the human cytomegalovirus UL97 gene and their relationship to the enzymatic activity of UL97 kinase for ganciclovir phosphorylation

In this study we determined that the double mutant M460V/D605E in the UL97 gene of an HCMV isolate from an immunocompromised patient (MMT isolate) is related to resistance to ganciclovir (GCV) therapy. Our results suggest that the aspartic acid-to-glutamic acid substitution at codon 605 may be associated with a natural polymorphism of the UL97 gene, and not with positive selection pressure exerted by the antiviral drug. We also determined that GCV resistance due to the M460V mutation in the HCMV UL97 gene is not offset by a second mutation (D605E) at codon 605. Furthermore, we showed that when the two mutations related to GCV resistance were simultaneously detected in the same HCMV construct, virus-drug resistance might be enhanced in comparison to that of the single mutants studied separately. To our knowledge for the first time, seven of 12 amino acid changes (F102L, D118V, M330T, T400A, R507P and C511R and I533V) in the UL97 gene of an isolate are herein reported.

Prevalence of human cytomegalovirus UL97 D605E mutation in transplant recipients in China

Human cytomegalovirus (CMV) resistance to gancyclovir (GCV) occurs via mutation in the UL97 gene, ethylene diamine tetraacetic acid blood samples were obtained from 23 transplant recipients who received a GCV implant. A nested polymerase chain reaction amplifying UL97 codons 450 to 672 was performed. Nested amplifications were sequenced directly. No known UL97 GCV resistance mutations were found. Eighteen of 23 patients (78%) had revealed mutations at codon 605 (D to E). Mutant D605E may reverse to wild-type during the follow-up treatment. We conclude that human CMV UL97 D605E mutation occurred in Chinese transplant recipients. This mutation may be regarded as a natural sequence variant.

Real-time PCR determination of human herpesvirus 6 antiviral drug susceptibility

A quantitative real-time PCR assay was developed to determine the antiviral drug susceptibility of human herpesvirus 6 (HHV-6). After short-term culture of the virus, HHV-6 isolates' susceptibility to the antiviral ganciclovir (GCV) was determined by measuring the HHV-6 variant B (HHV-6B) DNA levels in culture supernatants and infected cells using real-time PCR. A total of 12 well-characterized GCV-sensitive or -resistant strains and clinical isolates were used. This new assay with real-time PCR readout permitted the rapid (3 days), objective, and reproducible determination of HHV-6 drug susceptibilities with no need for stringent control of the initial multiplicity of infection. Furthermore, the real-time PCR assay results showed good correlation (rs=0.95) with those from the conventional TCID50 (50% tissue culture infecting dose) reduction assay (TRA). Thus, the real-time PCR assay described in this report was found to be a suitable quantitative method for determining the susceptibility of HHV-6 to antiviral drugs. It is faster and simpler than the TRA, and it is amenable to use in the routine diagnostic virology laboratory.

Synthesis and screening of bicyclic carbohydrate-based compounds: A novel type of antivirals

A small library of bicyclic carbohydrate derivatives was synthesized and screened. A strong and selective activity against cytomegalovirus was found. Structure-activity relationship for this new type of antivirals is discussed.