Novel DNA polymerase mutations conferring cytomegalovirus resistance: input of BAC-recombinant phenotyping and 3D model.

Long-term exposure to antiviral therapy in immunocompromised patients favors emergence of human cytomegalovirus (HCMV) resistance mutations. Two new UL54 DNA polymerase mutations (deletion of codon 524 and N408S substitution) identified in a kidney recipient and a bone marrow recipient respectively were characterized. Marker transfer experiment through recombination into a HCMV AD169 BAC demonstrated del524 and mutation N408S confer GCV and CDV resistance. These results suggest continued mutation of UL54 under selective antiviral pressure. Characterization of each new mutation is thus required to inform genotypic assays and to better understand the functional regions of UL54 for the development of novel antivirals.

Eight flavonoids and their potential as inhibitors of human cytomegalovirus replication.

The drugs currently available for treatment of severe human cytomegalovirus (HCMV) infections suffer from many drawbacks, particularly toxicity, and potential teratogenicity contraindicating their use in target populations such as pregnant women. The emergence of drug-resistant strains is still a problem for disease management, particularly in immunosuppressed populations where antivirals are used for extended periods of time. The flavonoid family of drugs contains promising candidates as they have low toxicity and inhibit different targets to currently available antivirals. We report here that, unlike their chalcon homologs, four flavonoids (baicalein, quercetin, quercetagetin and naringenin) inhibit various stages of HCMV replication, the most active anti-HCMV compound being baicalein and the less active and less selective being quercetagetin. These drugs could provide potential inhibitors of virus replication alone or in combination, without increased toxicity.

Drug-resistant cytomegalovirus in transplant recipients: a French cohort study.

OBJECTIVES: Cytomegalovirus (CMV) drug resistance is a therapeutic challenge in the transplant setting. No longitudinal cohort studies of CMV resistance in a real-life setting have been published in the valganciclovir era. We report findings for a French multicentre prospective cohort of 346 patients enrolled at initial diagnosis of CMV infection (clinical trial registered at clinicaltrials.gov: NCT01008540). PATIENTS AND METHODS: Patients were monitored for detection of CMV infection for ≥2 years. Real-time detection of resistance by UL97 and UL54 gene sequencing and antiviral phenotyping was performed if viral replication persisted for >21 days of appropriate antiviral treatment. Plasma ganciclovir assays were performed when resistance was suspected. RESULTS: Resistance was suspected in 37 (10.7%) patients; 18/37 (5.2% of the cohort) had virological resistance, associated with poorer outcome. Most cases involved single UL97 mutations, but four cases of multidrug resistance were due to UL54 mutations. In solid organ transplant recipients, resistance occurred mainly during primary CMV infection (odds ratio 8.78), but also in two CMV-seropositive kidney recipients. Neither CMV prophylaxis nor antilymphocyte antibody administration was associated with virological resistance. CONCLUSIONS: These data show the feasibility of surveying resistance. Virological resistance was frequent in patients failing antiviral therapy. More than 1/5 resistant isolates harboured UL54 mutations alone or combined with UL97 mutations, which conferred a high level of resistance and sometimes were responsible for cross-resistance, leading to therapeutic failure.

Conserved domains and structure prediction of human cytomegalovirus UL27 protein.

BACKGROUND: The human cytomegalovirus (HCMV) nuclear UL27 protein (pUL27) could be involved at the stage of nuclear egress. Maribavir is a new anti-HCMV drug that targets nuclear egress through direct inhibition of the HCMV serine-threonine kinase, UL97 protein (pUL97). Because maribavir-resistance-related mutations are observed in both proteins, pUL27 is thought to interfere with pUL97 activity; however, its mechanism of action remains unclear. METHODS: As there is no available crystal structure for pUL27 or any known structures of its homologous proteins, we attempted to identify pUL27 functional domains by sequence analysis, identification of conserved domains, structure prediction and matching with previously known maribavir resistance mutations. RESULTS: The UL27 sequence analysis of 20 HCMV wild-type strains and 8 ganciclovir-resistant HCMV strains allowed us to describe four conserved domains, to localize the putative phosphorylation sites and to identify protein-protein interface domains, suggesting that pUL27 could interact with either pUL97 or itself. CONCLUSIONS: Although the function of pUL27 is still unknown in the HCMV replication cycle, our approach identified target domains that appeared to be essential to the function of pUL27. This work provides a better understanding on the relative importance of each pUL27 mutation and could form the basis of later comparison analyses, when a three-dimensional structure of a pUL27 homologue will be available.

[cytomegalovirus; resistance; antiviral therapy; UL97 kinase; polymerase]. / Résistance du Cytomégalovirus aux antiviraux.

Antiviral resistance of cytomegalovirus strains is a growing problem in the transplant setting as it can concern 5% of patients with CMV replication. It is a consequence of the intensive and prolonged use of the three clinically approved inhibitors of the viral polymerase UL54, ganciclovir cidofovir and foscarnet. Resistance to ganciclovir can result from either mutations of the UL97 kinase, dispensable for its activation, which may appear within one month of therapy, or later from mutations in the UL54 viral polymerase, that can confer resistance to all antivirals. Screening for resistance is based on genotyping from clinical sample or isolates, and has to be associated whenever isolates are obtained to phenotype to evaluate the fitness of the virus and to test new drugs in the pipeline. Plasmatic dosage of the molecules, available for ganciclovir, reduction of immunosuppression, and if necessary modification of the antiviral regimen guided by genotype and/or phenotype are associated to control CMV infection in case of resistance.