Resistance of human cytomegalovirus to ganciclovir/valganciclovir: A comprehensive review of putative resistance pathways

A UL26-PIAS1 complex antagonizes anti-viral gene expression during Human Cytomegalovirus infection

Viral disruption of innate immune signaling is a critical determinant of productive infection. The Human Cytomegalovirus (HCMV) UL26 protein prevents anti-viral gene expression during infection, yet the mechanisms involved are unclear. We used TurboID-driven proximity proteomics to identify putative UL26 interacting proteins during infection to address this issue. We find that UL26 forms a complex with several immuno-regulatory proteins, including several STAT family members and various PIAS proteins, a family of E3 SUMO ligases. Our results indicate that UL26 prevents STAT phosphorylation during infection and antagonizes transcriptional activation induced by either interferon α (IFNA) or tumor necrosis factor α (TNFα). Additionally, we find that the inactivation of PIAS1 sensitizes cells to inflammatory stimulation, resulting in an anti-viral transcriptional environment similar to ΔUL26 infection. Further, PIAS1 is important for HCMV cell-to-cell spread, which depends on the presence of UL26, suggesting that the UL26-PIAS1 interaction is vital for modulating intrinsic anti-viral defense.

Ganciclovir and maribavir cross-resistance revisited: Relative drug susceptibilities of canonical cytomegalovirus mutants

Therapeutic use of maribavir for human cytomegalovirus infection has renewed attention to the extent of cross-resistance with ganciclovir as the existing standard therapy. Each drug selects in vivo for a characteristic set of resistance mutations in the viral UL97 kinase gene. To improve the calibration of relative susceptibilities to each drug, genetic variants at relevant UL97 codons were extensively phenotyped using the same baseline viral clone, cell culture conditions and growth readout. Ganciclovir-selected mutations at codons 460, 520, 592, 594, 595 and 603 conferred 2.8-fold (C603Y) to 12-fold (M460I) increases in ganciclovir 50% inhibitory concentrations (EC50) over wild type baseline, while conferring maribavir EC50 fold changes ranging from 0.21-fold (M460I) to 1.9-fold (A594V). Maribavir-selected mutations at codons 409, 411 and 480 conferred maribavir EC50 fold changes ranging from 17 (H411Y) to 210 (C480F), while conferring ganciclovir EC50 fold changes ranging from 0.7 (H411Y) to 2.3 (C480F). The P-loop substitution F342Y, selected by either drug, is confirmed to confer 4.7-fold and 6-fold increases in maribavir and ganciclovir EC50s respectively, and suggests this part of the ATP-binding domain of UL97 to be involved in moderate resistance to both drugs. The maribavir hypersensitivity of M460I and M460V may be advantageous.

Development and validation of a next-generation sequencing assay with open-access analysis software for detecting resistance-associated mutations in CMV

Cytomegalovirus (CMV) resistance testing by targeted next-generation sequencing (NGS) allows for the simultaneous analysis of multiple genes. We developed and validated an amplicon-based Ion Torrent NGS assay to detect CMV resistance mutations in UL27, UL54, UL56, and UL97 and compared the results to standard Sanger sequencing. NGS primers were designed to generate 83 overlapping amplicons of four CMV genes (~10 kb encompassing 138 mutation sites). An open-access software plugin was developed to perform read alignment, call variants, and interpret drug resistance. Plasmids were tested to determine NGS error rate and minor variant limit of detection. NGS limit of detection was determined using the CMV WHO International Standard and quantified clinical specimens. Reproducibility was also assessed. After establishing quality control metrics, 185 patient specimens previously tested using Sanger were reanalyzed by NGS. The NGS assay had a low error rate (<0.05%) and high accuracy (95%) for detecting CMV-associated resistance mutations present at ≥5% in contrived mixed populations. Mutation sites were reproducibly sequenced with 40× coverage when plasma viral loads were ≥2.6 log IU/mL. NGS detected the same resistance-associated mutations identified by Sanger in 68/69 (98.6%) specimens. In 16 specimens, NGS detected 18 resistance mutations that Sanger failed to detect; 14 were low-frequency variants (<20%), and six would have changed the drug resistance interpretation. The NGS assay showed excellent agreement with Sanger and generated high-quality sequence from low viral load specimens. Additionally, the higher resolution and analytic sensitivity of NGS potentially enables earlier detection of antiviral resistance.

Efficacy of ganciclovir versus foscarnet in ganciclovir-resistant cytomegalovirus retinitis: A case report

PURPOSE

To report a case of cytomegalovirus (CMV) retinitis improved by treatment with ganciclovir in a patient with ganciclovir-resistant CMV infection associated with Good syndrome.

STUDY DESIGN

Case report.

RESULT

A 52-year-old gentleman with Good syndrome presented with visual disturbance in his right eye. He had a history of receiving intravitreal ganciclovir treatment with CMV retinitis a year ago. During treatment for CMV colitis three months ago, in systemic blood, UL97 mutation was identified and improved after changing treatment from ganciclovir to foscarnet. CMV retinitis recurred, and intravitreal ganciclovir injection was performed but there was no improvement. Therefore, the treatment was changed to foscarnet, but retinal infiltration progressed. Accordingly, it was changed to ganciclovir again and as a result, the progression of retinitis could be stopped.

CONCLUSIONS

Even in the case of CMV retinitis, which has been genetically confirmed to be ganciclovir resistance in systemic blood, ganciclovir treatment can be considered if other anti-CMV agents are not effective.

Factors Associated With Genotypic Resistance and Outcome Among Solid Organ Transplant Recipients With Refractory Cytomegalovirus Infection

Genotypically resistant cytomegalovirus (CMV) infection is associated with increased morbi-mortality. We herein aimed at understanding the factors that predict CMV genotypic resistance in refractory infections and disease in the SOTR (Solid Organ Transplant Recipients) population, and the factors associated with outcomes. We included all SOTRs who were tested for CMV genotypic resistance for CMV refractory infection/disease over ten years in two centers. Eighty-one refractory patients were included, 26 with genotypically resistant infections (32%). Twenty-four of these genotypic profiles conferred resistance to ganciclovir (GCV) and 2 to GCV and cidofovir. Twenty-three patients presented a high level of GCV resistance. We found no resistance mutation to letermovir. Age (OR = 0.94 per year, IC95 [0.089-0.99]), a history of valganciclovir (VGCV) underdosing or of low plasma concentration (OR= 5.6, IC95 [1.69-20.7]), being on VGCV at infection onset (OR = 3.11, IC95 [1.18-5.32]) and the recipients' CMV negative serostatus (OR = 3.40, IC95 [0.97-12.8]) were independently associated with CMV genotypic resistance. One year mortality was higher in the resistant CMV group (19.2 % versus 3.6 %, p = 0.02). Antiviral drugs severe adverse effects were also independently associated with CMV genotypic resistance. CMV genotypic resistance to antivirals was independently associated with a younger age, exposure to low levels of GCV, the recipients' negative serostatus, and presenting the infection on VGCV prophylaxis. This data is of importance, given that we also found a poorer outcome in the patients of the resistant group.

Research for Cytomegalovirus Mutations Associated With Resistance to Antivirals in Kidney Transplant Receptors

Cytomegalovirus (CMV) mutations associated with antiviral resistance have become a major problem related to high mortality in kidney transplant patients. The aim of the study was to investigate mutations in the CMV genes UL97 and UL54 associated with antiviral resistance. A retrospective observational cohort study was carried out at Hospital Ophir Loyola (HOL), a reference in Kidney Transplantation. A total of 81 patients who underwent kidney transplantation were followed up between 2016 and 2018 were monitored for CMV viral load by performing qPCR. Sanger sequencing was performed on 66 patients. All CMV-positive kidney transplant recipients were included. Mutations were observed in 15 samples (22.72%) from patients. Most cases involved UL97 mutations. Mutation in UL54 without mutation in UL97 was detected in only 2 cases. Resistance mutations in UL97 were identified, such as M460V, L595S, H520Q, two co-mutations D465R + Del524 and A594P + D413A and a 3 codon deletion (del598-601). The search for mutations in the CMV genes identified mutations that confer resistance to conventional antivirals, such as ganciclovir and cidofovir, used in the treatment of these patients. Confirmation of the association with increased CMV viral load in transplanted patients, due to mutation in resistance genes, requires phenotypic analysis for confirmation purposes. These were the first findings in patients in northern Brazil that we know of.

[Mutations in the UL97 gene of cytomegalovirus (Herpesvirales: Herpesviridae: Cytomegalovirus: Human betaherpesvirus 5) associated with ganciclovir resistance in recipients of allogeneic hematopoietic stem cells]

INTRODUCTION

Infection caused by cytomegalovirus (CMV) is a serious problem for patients with weakened immunity, including patients with hematopoietic depression. The cases of complications associated with cytomegalovirus require antiviral therapy. However, during the natural mutation process, especially with prolonged use of drugs in suboptimal doses, CMV strains resistant to the action of antiviral drugs (such as ganciclovir, valganciclovir) may occur. Hypothetically, the emergence of resistance in the virus may cause a more aggressive course of infection, the ineffectiveness of antiviral therapy and, as a result, an increase in the number of deaths. In this regard, timely detection of mutations that can potentially lead to the resistance of the virus to antiviral drugs during hematopoietic stem cell transplantation (HSCT), as well as during organ and tissue transplantation, may be important when making a therapeutic decision. We describe three clinical cases for which the dynamics of the appearance of a mutant strain of CMV by the UL97 gene, which correlates with the viral load and clinical picture, is analyzed.The aim of the study was to determine the timing of the occurrence of mutations in CMV phosphotransferase UL97 gene associated with resistance to antiviral drugs in patients with hemoblastoses after allogeneic hematopoietic stem cell (allo-HSCs) transplantation.

MATERIAL AND METHODS

The study included 48 samples of CMV DNA isolated from the peripheral blood of three allo-HSCs recipients with CMV infection who were treated in the clinics of the FSBI «National Medical Research Center for Hematology» of the Ministry of Health of Russia with oncohematological diseases during 2015-2017. Patients received conditional codes (PR, PD, and FS). Mutations associated with antiviral therapy (AVT) resistance were identified in all patients. Sanger sequencing was used for mutation detection. The obtained DNA sequences were analyzed using Nucleotide BLAST and Genome compiler software. Mutations were searched in MRA mutation resistance analyzer software. The nucleotide sequences were compared with the UL97 reference sequence of the Merlin CMV strain using this software environment.

RESULTS AND DISCUSSION

For all patients in whom the virus strains containing C592G (PR), C607F (PD) and C603W (FS) mutations were detected, the timing of the mutation occurrence was determined at days 187, 124 and 1184, respectively. The emergence of mutations with a high resistance factor was shown to be accompanied by an increase in viral load (VL), the appearance of a clinical picture characteristic of CMV infection and a lack of an adequate response to therapy with ganciclovir and its derivatives.

CONCLUSION

Using these results, it is proposed to develop the test system based on random polymerase chain reaction (rPCR) to detect mutations in the most frequently encountered codons: M460I/V, C592G, A591V, A594T/V, L595F/S, C603W. Given that the data on the prevalence of these mutations were obtained from foreign sources, it is advisable to conduct similar studies on the frequency of mutations in the UL97 gene among the population of the Russian Federation in order to improve the quality and accuracy of test systems.

Persistent viremia in an immunocompetent patient with inherited chromosomally integrated HHV-6B

Human herpesvirus-6 (HHV-6), the virus which causes roseola, has traditionally been associated with benign and self-limited childhood illness. However, HHV-6 establishes lifelong latency and can reactivate in immunocompromised adult patients. In about 1% of cases, it integrates into the human genome as inherited chromosomally integrated HHV-6 (iciHHV-6). We report the case of a 70-year-old man presenting with altered mental status and agitation. His infectious workup revealed a cerebrospinal fluid sample positive for HHV-6 with virus detectable in the blood as well. He was subsequently treated with ganciclovir. HHV-6 viremia (DNAemia) persisted, and the antiviral medications were switched to foscarnet under the assumption of treatment failure due to drug resistance. After several admissions to the hospital for the same complaint, and after noticing that DNAemia persisted despite adequate treatment for HHV-6, infectious disease specialists ordered testing for chromosomally integrated virus. Test results confirmed the presence of iciHHV-6, explaining his consistently elevated serum viral load. Primary HHV-6 infection in adults causes a transient increase in viral load with resolution and clearance after a few weeks while iciHHV-6 is characterized by persistent detection of viral DNA at a high copy number. Individuals with iciHHV-6 can develop HHV-6 disease and are at increased risk for active viral replication when treated with immunosuppressive medications, but only mRNA testing, which is not widely available can differentiate between latent and active infection. This makes the decision to treat challenging in this patient population. When faced with a positive HHV-6 DNA result in the setting of equivocal symptoms, clinicians should consider the possibility of chromosomally integrated virus rather than drug-resistant virus in order to reduce exposure to potentially toxic antiviral medications.

Homoseongomycin, a compound isolated from marine actinomycete bacteria K3-1, is a potent inhibitor of encephalitic alphaviruses

Marine microorganisms have been a resource for novel therapeutic drugs for decades. In addition to anticancer drugs, the drug acyclovir, derived from a marine sponge, is FDA-approved for the treatment of human herpes simplex virus-1 infections. Most alphaviruses that are infectious to terrestrial animals and humans, such as Venezuelan and eastern equine encephalitis viruses (VEEV and EEEV), lack efficient antiviral drugs and it is imperative to develop these remedies. To push the discovery and development of anti-alphavirus compounds forward, this study aimed to isolate and screen for potential antiviral compounds from cultured marine microbes originating from the marine environment. Compounds from marine microbes were of interest as they are prolific producers of bioactive compounds across the spectrum of human diseases and infections. Homoseongomycin, an actinobacteria isolated from a marine sponge displayed impressive activity against VEEV from a total of 76 marine bioactive products. The 50% effective concentration (EC₅₀) for homoseongomycin was 8.6 μM for suppressing VEEV TC-83 luciferase reporter virus replication. Homoseongomycin was non-toxic up to 50 μM and partially rescued cells from VEEV induced cell death. Homoseongomycin exhibited highly efficient antiviral activity with a reduction of VEEV infectious titers by 8 log₁₀ at 50 μM. It also inhibited EEEV replication with an EC₅₀ of 1.2 μM. Mechanism of action studies suggest that homoseongomycin affects both early and late stages of the viral life cycle. Cells treated with 25 μM of homoseongomycin had a ~90% reduction in viral entry. In comparison, later stages showed a more robust reduction in infectious titers (6 log₁₀) and VEEV extracellular viral RNA levels (4 log₁₀), but a lesser impact on intracellular viral RNA levels (1.5 log₁₀). In sum, this work demonstrates that homoseongomycin is a potential anti-VEEV and anti-EEEV compound due to its low cytotoxicity and potent antiviral activity.

Frequency of congenital cytomegalovirus infections in newborns in the Sao Paulo State, 2010-2018

Human cytomegalovirus (HCMV) infections remain a neglected public health issue. The aim of the present study was to evaluate the frequency of HCMV congenital infections in newborns up to 1 month in the Sao Paulo State, from 2010 to 2018. The molecular characterization of HCMV-positive samples was also undertaken. Urine samples from 275 potential congenital HCMV-infected patients were tested by real-time Polymerase Chain Reaction (qPCR). HCMV-positive samples were amplified by conventional PCR targeting the UL89 gene, sequenced and searched for mutations. A total of 32 (11.6%) positive-HCMV cases were detected (mean Ct 30.59); mean and median age of 10.3 and 6 days old, respectively. Children aged between 0-3 weeks had higher HCMV detection rates (84.4%; 27/32). UL89 gene was successfully sequenced in two samples, both classified as the human betaherpesvirus 5. No described resistance-associated mutations were identified. A routine screening in newborns coupled with the genetic characterization of key viral genes is vital to decrease sequels associated with congenital HCMV infections.

Definitions of Resistant and Refractory Cytomegalovirus Infection and Disease in Transplant Recipients for Use in Clinical Trials

Despite advances in preventive strategies, cytomegalovirus (CMV) infection remains a major complication in solid organ and hematopoietic cell transplant recipients. CMV infection may fail to respond to commercially available antiviral therapies, with or without demonstrating genotypic mutation(s) known to be associated with resistance to these therapies. This lack of response has been termed "resistant/refractory CMV" and is a key focus of clinical trials of some investigational antiviral agents. To provide consistent criteria for future clinical trials and outcomes research, the CMV Resistance Working Group of the CMV Drug Development Forum (consisting of scientists, clinicians, regulatory officials, and industry representatives from the United States, Canada, and Europe) has undertaken establishing standardized consensus definitions of "resistant" and "refractory" CMV. These definitions have emerged from the Working Group's review of the available virologic and clinical literature and will be subject to reassessment and modification based on results of future studies.

Advances in the genotypic diagnosis of cytomegalovirus antiviral drug resistance

Cytomegalovirus (CMV) drug resistance mutation maps are updated with recent information for polymerase inhibitors, the terminase inhibitor letermovir and the UL97 kinase inhibitor maribavir. Newly mapped mutations and their phenotypes provide more detail on cross-resistance properties and suggest the need to expand the CMV gene regions covered in diagnostic testing. Next-generation deep sequencing technology offers a more sensitive, higher resolution view of emerging antiviral resistance and is recommended for use in clinical trials. Issues of standardization and diagnostic utility in comparison with traditional Sanger sequencing remain unresolved. Quality control is important for the accurate and reproducible detection of mutant viral populations in clinical specimens.

Synthesis and biological evaluation of fluoro-substituted spiro-isoxazolines as potential anti-viral and anti-cancer agents

Electrophilic fluorine-mediated dearomative spirocyclization has been developed to synthesize a range of fluoro-substituted spiro-isoxazoline ethers and lactones. The in vitro biological assays of synthesized compounds were probed for anti-viral activity against human cytomegalovirus (HCMV) and cytotoxicity against glioblastomas (GBM6) and triple negative breast cancer (MDA MB 231). Interestingly, compounds 4d and 4n showed significant activity against HCMV (IC₅₀ ∼ 10 μM), while 4l and 5f revealed the highest cytotoxicity with IC₅₀ = 36 to 80 μM. The synthetic efficacy and biological relevance offer an opportunity to further drug-discovery development of fluoro-spiro-isoxazolines as novel anti-viral and anti-cancer agents.

The synthetic efficacy and biological relevance extend an opportunity to further drug-discovery development of fluoro-spiro-isoxazolines as novel anti-viral and anti-cancer agents.

Analysis of Ganciclovir-Resistant Cytomegalovirus Infection Caused by the UL97 Gene Mutation in Codons 460 and 520 in Pediatric Patients: A Case Series

Background

Drug-resistant cytomegalovirus (CMV) infection has been increasingly recognized. However, there are limited data in pediatric patients. In this study, the prevalence and factors associated with CMV infection with UL97 mutations in pediatric patients treated with ganciclovir but not responding to treatment were evaluated.

Methods

This retrospective study was conducted from January 2013 to December 2017. All patients who were suspected of having ganciclovir-resistant CMV infection and had never had ganciclovir prophylaxis were included. Genotypic assay for UL97 mutations in codons 460 and 520 conferring ganciclovir resistance was performed. Factors associated with the presence of UL97 mutations were analyzed.

Results

Of 34 patients included, 10 patients (29.4%) had a genotypically confirmed UL97 mutation. The median age (interquartile range [IQR]) was 3 (0.85–8.68) years. Ganciclovir resistance was tested at a median time (IQR) of 22.5 (14.3–31) days after initiation of ganciclovir. All resistant isolates harbored a UL97 mutation in codon 460. Compared with patients infected with CMV without UL97 mutation, those infected with UL97 mutation strains were younger (median age [IQR], 3.02 [0.85–8.68] vs 10.45 [2.7–16.4] years) and had a higher maximum viral load (median [IQR], 5.06 [4.74–6.05] vs 4.42 [4.03–4.87] copies/mL). Six of 10 (60%) patients were successfully treated with high-dose ganciclovir (7.5 mg/kg twice daily).

Conclusions

UL97 mutation ganciclovir-resistant CMV infection was not uncommon in the pediatric population. Screening for this mutation should be considered in patients experiencing virological worsening while ganciclovir is given, even if patients have not previously received ganciclovir prophylaxis.

Emergence and Persistence of Letermovir-Resistant Cytomegalovirus in a Patient With Primary Immunodeficiency

Background

Letermovir is a novel cytomegalovirus antiviral that is approved for prophylaxis in hematopoietic stem cell transplantation recipients

Methods

After obtaining informed consent, letermovir prophylaxis was started in a patient with a presumed late-onset primary, combined T- and B-cell immunodeficiency. Plasma CMV DNAemia was monitored with real-time polymerase chain reaction, and letermovir resistance analyses were performed using Sanger sequencing and Illumina MiSeq next-generation sequencing.

Results

A letermovir-resistant cytomegalovirus variant (C325Y mutation in UL56) emerged 17 weeks after start of prophylaxis. The letermovir-resistant variant was able to reactivate without drug selective pressure as this variant was again detected in plasma 20.6 weeks after stopping of letermovir.

Conclusions

This case indicates that the C325Y mutation in UL56 does not significantly alter fitness of cytomegalovirus in vivo.

Design, Synthesis, and Preliminary Studies of Spiro-isoxazoline-peroxides against Human Cytomegalovirus and Glioblastoma ∥

The association between glioblastoma (GBM) and human cytomegalovirus (HCMV) infection has been the intensely debated topic over the decades for developing new therapeutic options. In this regard, the peroxides from natural and synthetic sources served as potential antiviral and anticancer agents in the past. Herein, a concise and efficient strategy has been demonstrated to access a novel class of peroxides containing a spiro-isoxazoline to primarily investigate the biological activities. The synthetic compounds were evaluated for in vitro antiviral and antiproliferative activity against HCMV and glioblastoma cell line (GBM6), respectively. While compound 13m showed moderate anti-CMV activity (IC₅₀ = 19 μM), surprisingly, an independent biological assay for compound 13m revealed its antiproliferative activity against the human glioblastoma cell line (GBM6) with an IC₅₀ of 10 μM. Hence, the unification of an isoxazoline and peroxide heterocycles could be a potential direction to initiate the HCMV-GBM drug discovery program.

[Pharmacological and clinical effects of letermovir (Prevymis®), a novel anti-human cytomegalovirus prophylactic drug]

Letermovir is an anti-human cytomegalovirus (HCMV) drug with a novel mechanism of action. Virological characterization and sequence analysis of resistant viruses indicate that the viral DNA terminase complex is the target of this compound. Unlike currently marketed anti-HCMV drugs, which act via inhibition of the viral DNA polymerase, the terminase inhibitor interferes with viral DNA cleavage and packaging of monomeric genome units into capsids. Letermovir has potent anti-HCMV activity, with 50% effective concentration of single-digit nanomolar against most clinical HCMV isolates in cell-culture models of infection. Besides its excellent in vitro inhibitory activity against laboratory and clinical HCMV isolates, letermovir exhibits activity against virus strains resistant to the currently approved anti-HCMV drugs. Letermovir is specific for human cytomegalovirus but lacks inhibitory activity against major pathogenic viruses including other Herpesviridae. In a xenograft mouse infection model, the 50% and 90% effective doses of the letermovir were 3 and 8 mg/kg/day, respectively. HCMV infection and disease in recipients of allogeneic hematopoietic stem cell transplant (HSCT) is a serious disease leading to significant morbidity and mortality. In the Phase 3 trial, the preventive effect of clinically significant HCMV infection by oral or intravenous administration of letermovir in allogeneic HSCT patients was confirmed, and letermovir was well tolerated with no suggestions of myelotoxicity or nephrotoxicity.

Monocytes Latently Infected with Human Cytomegalovirus Evade Neutrophil Killing

One site of latency of human cytomegalovirus (HCMV) in vivo is in undifferentiated cells of the myeloid lineage. Although latently infected cells are known to evade host T cell responses by suppression of T cell effector functions, it is not known if they must also evade surveillance by other host immune cells. Here we show that cells latently infected with HCMV can, indeed, be killed by host neutrophils but only in a serum-dependent manner. Specifically, antibodies to the viral latency-associated US28 protein mediate neutrophil killing of latently infected cells. To address this mechanistically, a full proteomic screen was carried out on latently infected monocytes. This showed that latent infection downregulates the neutrophil chemoattractants S100A8/A9, thus suppressing neutrophil recruitment to latently infected cells. The ability of latently infected cells to inhibit neutrophil recruitment represents an immune evasion strategy of this persistent human pathogen, helping to prevent clearance of the latent viral reservoir.

The Third International Consensus Guidelines on the Management of Cytomegalovirus in Solid-organ Transplantation

Despite recent advances, cytomegalovirus (CMV) infections remain one of the most common complications affecting solid organ transplant recipients, conveying higher risks of complications, graft loss, morbidity, and mortality. Research in the field and development of prior consensus guidelines supported by The Transplantation Society has allowed a more standardized approach to CMV management. An international multidisciplinary panel of experts was convened to expand and revise evidence and expert opinion-based consensus guidelines on CMV management including prevention, treatment, diagnostics, immunology, drug resistance, and pediatric issues. Highlights include advances in molecular and immunologic diagnostics, improved understanding of diagnostic thresholds, optimized methods of prevention, advances in the use of novel antiviral therapies and certain immunosuppressive agents, and more savvy approaches to treatment resistant/refractory disease. The following report summarizes the updated recommendations.

Treatment and Prevention of CMV Disease in Transplant Recipients: Current Knowledge and Future Perspectives

This review summarizes the significant impact of cytomegalovirus (CMV) infection on solid organ and hematopoietic stem cell transplant recipients. A discussion of the various CMV prevention and treatment strategies is provided, including a detailed description of each of the available CMV antiviral drugs.

Synthesis of new betulinic acid/betulin-derived dimers and hybrids with potent antimalarial and antiviral activities

Severe malaria and viral infections cause life-threatening diseases in millions of people worldwide every year. In search for effective bioactive hybrid molecules, which may possess improved properties compared to their parent compounds, a series of betulinic acid/betulin based dimer and hybrid compounds carrying ferrocene and/or artesunic acid moieties, was designed and, synthesized de novo. Furthermore, they were analyzed in vitro against malaria parasites (growth inhibition of 3D7-strain P. falciparum-infected erythrocytes) and human cytomegalovirus (HCMV). From this series of hybrids/dimers, the betulinic acid/betulin and artesunic acid hybrids 11 and 12 showed the most potent activities against P. falciparum and HCMV. On the strength of results, additive and/or synergistic effects between the natural or semisynthetic products, such as betulinic acid-/betulin- and artesunic acid-derived compounds, are suggested on the basis of putatively complex modes of antimicrobial action. This advantage may be taken into account in future drug development.

Comparison of intravitreal ganciclovir monotherapy and combination with foscarnet as initial therapy for cytomegalovirus retinitis

AIM

To compare the effectiveness between multiple intravitreal injections of ganciclovir alone and combined with foscarnet as initial treatment for patients with newly-onset cytomegalovirus retinitis (CMVR).

METHODS

The retrospective study observed 37 patients (58 eyes) who suffered from CMVR onset between 2013 and 2015. Among them, 35 eyes underwent 4 weekly intravitreal injections of 3.0 mg ganciclovir, and 23 eyes underwent 4 weekly injections of 3.0 mg ganciclovir combined with 2.4 mg foscarnet. Visual acuity, intraocular pressure and viral load of cytomegalovirus (CMV) in aqueous humor measured by real-time polymerase chain reaction were compared before and after each injection.

RESULTS

CMV-DNA copies in aqueous humor decreased remarkably in both groups. The average of CMV-DNA copies in patients' aqueous decreased from 38.3×10⁴ copies/mL at baseline to 2.2×10⁴ copies/mL after the 4^th injection in patients who were treated with ganciclovir monotherapy, and decreased from 76.9×10⁴ copies/mL to 11.3×10⁴ copies/mL after 4 continuous injections of ganciclovir combined with foscarnet. No significant difference was found in reduction of viral load, change of visual acuities or intraocular pressures between monotherapy or combined therapy.

CONCLUSION

Results of this study show that the initial effectiveness of treating CMVR after 4 weekly intravitreal injections is not significantly different from ganciclovir alone or combined with foscarnet. Continuous injection of ganciclovir alone is sufficient in treating immunosuppressive patients with newly-onset CMVR.

Biological relevance of Cytomegalovirus genetic variability in congenitally and postnatally infected children

BACKGROUND

Human cytomegalovirus (HCMV) is the leading cause of congenital infections resulting in severe morbidity and mortality among infected children. Although the virus is highly polymorphic, particularly in genes contributing to immune evasion, the mechanisms underlying its genetic variability and pathogenicity are only partially understood.

OBJECTIVES

We aimed to characterize different HCMV clinical strains isolated from 21 congenitally- or postnatally-infected children for in vitro growth properties and genetic polymorphisms.

STUDY DESIGN

The growth of various HCMV isolates was analyzed in different cell culture models. Genetic polymorphism was assessed by genetic and phylogenetic analysis of viral genes involved in virulence (UL144, US28, and UL18), latency (UL133-138), or drug resistance (UL54 and UL97).

RESULTS

Here, we report a high degree of genetic and phenotypic diversity in distinct HCMV clinical isolates, as shown by their in vitro growth properties. In particular, HCMV isolates displayed the highest degree of genetic variability in the UL144 gene, where we were able to define four distinct genotypes within the cohort based on UL144 heterogeneity. Lastly, among all isolates we were able to identify 36 mutations in UL54 and 2 in UL97.

CONCLUSIONS

Our findings indicate that surprisingly high levels of genetic HCMV variability correlate with a high degree of phenotypic polymorphism, which in turn might differentially influence the growth, fitness, and drug susceptibility of HCMV.

The evolution of nucleoside analogue antivirals: A review for chemists and non-chemists. Part 1: Early structural modifications to the nucleoside scaffold

This is the first of two invited articles reviewing the development of nucleoside-analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. Rather than providing a simple chronological account, we have examined and attempted to explain the thought processes, advances in synthetic chemistry and lessons learned from antiviral testing that led to a few molecules being moved forward to eventual approval for human therapies, while others were discarded. The present paper focuses on early, relatively simplistic changes made to the nucleoside scaffold, beginning with modifications of the nucleoside sugars of Ara-C and other arabinose-derived nucleoside analogues in the 1960's. A future paper will review more recent developments, focusing especially on more complex modifications, particularly those involving multiple changes to the nucleoside scaffold. We hope that these articles will help virologists and others outside the field of medicinal chemistry to understand why certain drugs were successfully developed, while the majority of candidate compounds encountered barriers due to low-yielding synthetic routes, toxicity or other problems that led to their abandonment.

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This is the first of two invited articles reviewing the development of nucleoside-analogue antiviral drugs.

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It is written for a target audience of virologists and other non-chemists, and for chemists unfamiliar with the field.

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Numerous modifications have been made to the nucleoside scaffold in order to impart therapeutic benefits.

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Nucleoside modifications led to the development of potent antivirals such as acyclovir, entecavir, and tenofovir.

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We examine thought processes, progress in synthetic chemistry and results of antiviral testing that led to approved drugs.

Ganciclovir

Ganciclovir is synthetic nucleoside analog of guanine closely related to acyclovir but has greater activity against cytomegalovirus. This comprehensive profile on ganciclovir starts with a description of the drug: nomenclature, formulae, chemical structure, elemental composition, and appearance. The uses and application of the drug are explained. The methods that were used for the preparation of ganciclovir are described and their respective schemes are outlined. The methods which were used for the physical characterization of the dug are: ionization constant, solubility, X-ray powder diffraction pattern, crystal structure, melting point, and differential scanning calorimetry. The chapter contains the spectra of the drug: ultraviolet spectrum, vibrational spectrum, nuclear magnetic resonance spectra, and the mass spectrum. The compendial methods of analysis of ganciclovir include the United States Pharmacopeia methods. Other methods of analysis that were reported in the literature include: high-performance liquid chromatography alone or with mass spectrometry, electrophoresis, spectrophotometry, voltammetry, chemiluminescence, and radioimmunoassay. Biological investigation on the drug includes: pharmacokinetics, metabolism, bioavailability, and biological analysis. Reviews on the methods used for preparation or for analysis of the drug are provided. The stability of the drug in various media and storage conditions is reported. More than 240 references are listed at the end of the chapter.

Design, Synthesis, and the Biological Evaluation of a New Series of Acyclic 1,2,3-Triazole Nucleosides

A new strategy for the synthesis of N3 -benzoylated- and N3 -benzylated N1 -propargylquinazoline-2,4-diones 30a-d and 31a-d from isatoic anhydride 41 is reported. The alkynes 30a-d and 31a-d were applied in the 1,3-dipolar cycloadditions with azides 27 and 28 to synthesize acyclic 1,2,3-triazole nucleosides. The obtained alkynes and 1,2,3-triazole were evaluated for antiviral activity against a broad range of DNA and RNA viruses. The alkyne 30d showed activity against adenovirus-2 (EC50  = 8.3 μM), while compounds 37a and 37d were also active toward herpes simplex virus-1 wild-type and thymidine kinase deficient (HSV-1 TK- ) strains (EC50 values in the range of 4.6-13.8 μM). In addition, compounds 30a, 30b, 37b, and 37c exhibited activity toward varicella-zoster virus (VZV) TK+ and TK- strains (EC50  = 2.1-9.5 μM). The compound 30b proved to be the most selective against VZV and displayed marginal activity against human cytomegalovirus (HCMV). Although the compound 30a had improved anti-HCMV activity, the increase in anti-HCMV activity was accompanied by significant toxicity. Compounds 37a and 37d showed inhibitory effects toward the human T lymphocyte (CEM) cell line (IC50  = 21 ± 7 and 22 ± 1 μM, respectively), while compound 35 exhibited cytostatic activity toward HMEC-1 cells (IC50  = 28 ± 2 μM).

Antibody therapies for the prevention and treatment of viral infections

Antibodies are an important component in host immune responses to viral pathogens. Because of their unique maturation process, antibodies can evolve to be highly specific to viral antigens. Physicians and researchers have been relying on such high specificity in their quest to understand host–viral interaction and viral pathogenesis mechanisms and to find potential cures for viral infection and disease. With more than 60 recombinant monoclonal antibodies developed for human use in the last 20 years, monoclonal antibodies are now considered a viable therapeutic modality for infectious disease targets, including newly emerging viral pathogens such as Ebola representing heightened public health concerns, as well as pathogens that have long been known, such as human cytomegalovirus. Here, we summarize some recent advances in identification and characterization of monoclonal antibodies suitable as drug candidates for clinical evaluation, and review some promising candidates in the development pipeline.

Differentiated Levels of Ganciclovir Resistance Conferred by Mutations at Codons 591 to 603 of the Cytomegalovirus UL97 Kinase Gene

Diagnostic mutations in the cytomegalovirus UL97 kinase gene are used to assess the level of associated ganciclovir resistance and therapeutic options. The best-known mutations at codons 460, 520, or 591 to 607 individually confer 5- to 10-fold-decreased ganciclovir susceptibility, except that a 3-fold decrease occurs in the case of the amino acid substitution C592G. Less common point and in-frame deletion mutations at codons 591 to 603 remain incompletely characterized. The ganciclovir susceptibilities of 17 mutants in this codon range were evaluated by use of the same recombinant phenotyping system and extensive assay replicates in two types of cell cultures. Amino acid substitutions K599E and T601M conferred no ganciclovir resistance, while A591V conferred 3.8-fold-decreased susceptibility. In-frame deletions of three or more codons conferred at least 8-fold-increased ganciclovir resistance, while the level of resistance conferred by one- or two-codon deletions varied from 4- to 10-fold, depending on their location. Measured levels of ganciclovir resistance were closely comparable when assays were performed in either fibroblasts or modified retinal epithelial cells. The significant revision of a few previously published resistance phenotypes and the new data strengthen the interpretation of genotypic testing for cytomegalovirus drug resistance.

Immunotherapy for opportunistic infections: Current status and future perspectives

The outcome after allogeneic haematopoietic stem cell transplantation (allo-HSCT) has significantly improved during the last decades. However, opportunistic infections such as viral and mold infections are still a major obstacle for cure. Within this field, adoptive T cell therapy against pathogens is a promising treatment approach. Recently, the techniques to develop T cell products including pathogen-specific T cells have been sophisticated and are now available in accordance to good manufacturing practice (GMP). Here, we aim to summarize current knowledge about adoptive T cell therapy against viral and mold infections.

Novel Cytomegalovirus UL54 DNA Polymerase Gene Mutations Selected In Vitro That Confer Brincidofovir Resistance

Eight in vitro selection experiments under brincidofovir pressure elicited the known cytomegalovirus DNA polymerase amino acid substitutions N408K and V812L and the novel exonuclease domain substitutions D413Y, E303D, and E303G, which conferred ganciclovir and cidofovir resistance with 6- to 11-fold resistance to brincidofovir or 17-fold when E303G was combined with V812L. The new exonuclease domain I resistance mutations selected under brincidofovir pressure add to the single instance previously reported and show the expected patterns of cross-resistance.

Polyhydroxylated sulfated steroids derived from 5α-cholestanes as antiviral agents against herpes simplex virus

Twelve polyhydroxylated sulfated steroids synthesized from a 5α-cholestane skeleton with different substitutions in C-2, C-3 and C-6 were evaluated for cytotoxicity and antiviral activity against herpes simplex virus (HSV) by a virus plaque reduction assay. Four compounds elicited a selective inhibitory effect against HSV. The disodium salt of 2β,3α-dihydroxy-6E-hydroximine-5α-cholestane-2,3-disulfate, named compound 7, was the most effective inhibitor of HSV-1, HSV-2 and pseudorabies virus (PrV) strains, including acyclovir-resistant variants, in human and monkey cell lines. Preliminary mechanistic studies demonstrated that compound 7 did not affect the initial steps of virus entry but inhibited a subsequent event in the infection process of HSV.

Treatment of CMV infection after allogeneic hematopoietic stem cell transplantation

Despite a remarkable reduction in the past decades, cytomegalovirus (CMV) disease in allogeneic hematopoietic stem cell transplant (HSCT) recipients remains a feared complication, still associated with significant morbidity and mortality. Today, first line treatment of CMV infection/reactivation is still based on dated antiviral compounds Ganciclovir (GCV), Foscarnet (FOS) and Cidofovir (CDF) with their burdensome weight of side effects. Maribavir (MBV), Letermovir (LMV) and Brincidofovir (BDF) are three new promising anti-CMV drugs without myelosuppressive properties or renal toxic effects that are under investigation in randomized phase II and III trials. Adoptive T-cell therapy (ATCT) in CMV infection possesses a strong rationale, demonstrated by several proof of concept studies; its feasibility is currently under investigation by clinical trials. ATCT from third-party and naïve donors could meet the needs of HSCT recipients of seronegative donors and cord blood grafts. In selected patients such as recipients of T-cell depleted grafts, ATCT, based on CMV-specific host T-cells reconstitution kinetics, would be of value in the prophylactic and/or preemptive CMV treatment. Vaccine-immunotherapy has the difficult task to reduce the incidence of CMV reactivation/infection in highly immunocompromised HSCT patients. Newer notions on CMV biology may represent the base to flush out the Troll of transplantation.

Approach to drug-resistant cytomegalovirus in transplant recipients

PURPOSE OF REVIEW

The purpose of this study is to provide updated information on diagnosis of cytomegalovirus (CMV) drug resistance, treatments for drug-resistant infection and potential uses of experimental antiviral compounds.

RECENT FINDINGS

For established CMV antivirals, uncommon viral UL97 kinase and UL54 DNA polymerase drug resistance mutations are sporadically described that expand an extensive existing database. Some novel mutations reported from treated patients have no drug-resistant phenotype and may be genotyping artefacts. Next-generation sequencing technology may enable earlier detection of emerging resistance mutations in treated patients. Management options for drug-resistant infection include optimization of host defenses, antiviral dose escalation, substitutions or combinations of standard or experimental antivirals. Maribavir and letermovir have antiviral targets distinct from the classic DNA polymerase. UL97 mutations elicited by ganciclovir and maribavir are different, although a single p-loop mutation can confer significant cross-resistance. High-grade resistance mutations in the UL56 terminase gene are readily selected in vitro under letermovir and await clinical correlation.

SUMMARY

Technical advancements can enhance the accurate and timely genotypic detection of drug resistance. Antivirals undergoing clinical trial offer the prospect of new viral targets and drug combinations, but unresolved issues exist with regard to their therapeutic potential for drug-resistant CMV and their genetic barriers to resistance.

Overcoming drug resistance in HSV, CMV, HBV and HCV infection

Although vaccination has provided as a very efficient preventive tool, antiviral therapy is still needed to control viral infections not avoidable by prophylaxis with vaccines; those caused by viruses for which a vaccine is available, but vaccination is not universally implemented or does not result in complete, long-term protection; and in immunocompromised individuals with reduced immune control of viral replication. After more than 50 years of the first licensing for an antiherpetic drug, novel compounds for herpes-simplex viruses and human cytomegalovirus will open new strategies for better control and management of these two recurrent viral infections. Besides, the development and use of antiviral drugs for hepatitis viruses causing chronic liver disease has evolved from the unavailability of compounds targeting virus-specific pathways, to the generalization of different treatment regimes based on specific antiviral drugs, both for hepatitis B and C viruses. However, due to the nature of the viral genomes and their replication, in the face of the selective pressure imposed by antiviral drugs viral-resistant variants inevitably emerge, and specific strategies are needed to avoid, or reduce, their clinical and public health impact.

Phosphonylated Acyclic Guanosine Analogues with the 1,2,3-Triazole Linker

A novel series of {4-[(2-amino-6-chloro-9H-purin-9-yl)methyl]-1H-1,2,3-triazol-1-yl}alkylphosphonates and {4-[(2-amino-6-oxo-1,6-dihydro-9H-purin-9-yl)methyl]-1H-1,2,3-triazol-1-yl}alkylphosphonates as acyclic analogues of guanosine were synthesized and assessed for antiviral activity against a broad range of DNA and RNA viruses and for their cytostatic activity toward three cancerous cell lines (HeLa, L1210 and CEM). They were devoid of antiviral activity; however, several phosphonates were found slightly cytostatic against HeLa cells at an IC₅₀ in the 80–210 µM range. Compounds (1R,2S)-17k and (1S,2S)-17k showed the highest inhibitory effects (IC₅₀ = 15–30 µM) against the proliferation of murine leukemia (L1210) and human T-lymphocyte (CEM) cell lines.

Intermolecular Complementation between Two Varicella-Zoster Virus pORF30 Terminase Domains Essential for DNA Encapsidation

The herpesviral terminase complex is part of the intricate machinery that delivers a single viral genome into empty preformed capsids (encapsidation). The varicella-zoster virus (VZV) terminase components (pORF25, pORF30, and pORF45/42) have not been studied as extensively as those of herpes simplex virus 1 and human cytomegalovirus (HCMV). In this study, VZV bacterial artificial chromosomes (BACs) were generated with small (Δ30S), medium (Δ30M), and large (Δ30L) ORF30 internal deletions. In addition, we isolated recombinant viruses with specific alanine substitutions in the putative zinc finger motif (30-ZF3A) or in a conserved region (region IX) with predicted structural similarity to the human topoisomerase I core subdomains I and II (30-IXAla, 30-620A, and 30-622A). Recombinant viruses replicated in an ORF30-complementing cell line (ARPE30) but failed to replicate in noncomplementing ARPE19 and MeWo cells. Transmission electron microscopy of 30-IXAla-, 30-620A-, and 30-622A-infected ARPE19 cells revealed only empty VZV capsids. Southern analysis showed that cells infected with parental VZV (VZVLUC) or a repaired virus (30R) contained DNA termini, whereas cells infected with Δ30L, 30-IXAla, 30-620A, or 30-622A contained little or no processed viral DNA. These results demonstrated that pORF30, specifically amino acids 619 to 624 (region IX), was required for DNA encapsidation. A luciferase-based assay was employed to assess potential intermolecular complementation between the zinc finger domain and conserved region IX. Complementation between 30-ZF3A and 30-IXAla provided evidence that distinct pORF30 domains can function independently. The results suggest that pORF30 may exist as a multimer or participate in higher-order assemblies during viral DNA encapsidation.

IMPORTANCE

Antivirals with novel mechanisms of action are sought as additional therapeutic options to treat human herpesvirus infections. Proteins involved in the viral DNA encapsidation process have become promising antiviral targets. For example, letermovir is a small-molecule drug targeting HCMV terminase that is currently in phase III clinical trials. It is important to define the structural and functional characteristics of proteins that make up viral terminase complexes to identify or design additional terminase-specific compounds. The VZV ORF30 mutants described in this study represent the first VZV terminase mutants reported to date. Targeted mutations confirmed the importance of a conserved zinc finger domain found in all herpesvirus ORF30 terminase homologs but also identified a novel, highly conserved region (region IX) essential for terminase function. Homology modeling suggested that the structure of region IX is present in all human herpesviruses and thus represents a potential structurally conserved antiviral target.

Potential Antiviral Agents from Marine Fungi: An Overview

Biodiversity of the marine world is only partially subjected to detailed scientific scrutiny in comparison to terrestrial life. Life in the marine world depends heavily on marine fungi scavenging the oceans of lifeless plants and animals and entering them into the nutrient cycle by. Approximately 150 to 200 new compounds, including alkaloids, sesquiterpenes, polyketides, and aromatic compounds, are identified from marine fungi annually. In recent years, numerous investigations demonstrated the tremendous potential of marine fungi as a promising source to develop new antivirals against different important viruses, including herpes simplex viruses, the human immunodeficiency virus, and the influenza virus. Various genera of marine fungi such as Aspergillus, Penicillium, Cladosporium, and Fusarium were subjected to compound isolation and antiviral studies, which led to an illustration of the strong antiviral activity of a variety of marine fungi-derived compounds. The present review strives to summarize all available knowledge on active compounds isolated from marine fungi with antiviral activity.