Phase I dose escalation trial evaluating the pharmacokinetics, anti-human cytomegalovirus (HCMV) activity, and safety of 1263W94 in human immunodeficiency virus-infected men with asymptomatic HCMV shedding

Pharmacokinetics and Safety Evaluation of Maribavir in Healthy Japanese and Matched White Participants: A Phase I, Open-Label Study

This phase I study compared pharmacokinetics and safety of maribavir in Japanese and White participants, and evaluated dose proportionality in Japanese participants. Under fasting conditions, 12 healthy adult participants of Japanese descent and 12 matched White participants received a single 400-mg dose of maribavir. Japanese participants received 2 further doses of maribavir: 200 mg and 800 mg, or 800 mg and 200 mg, separated by a ≥72-hour washout period. Serial blood samples were collected up to 24 hours after dosing for pharmacokinetic assessments. Following the 400-mg dose, the geometric mean ratios (90% confidence interval) of Japanese versus White participants were 110% (91.7%-133%) for maximum plasma concentration, 122% (96.8%-155%) for area under the plasma concentration-time curve (AUC) from time of dosing to the last measurable concentration, and 125% (98.0%-160%) for AUC extrapolated to infinity. In Japanese participants, maribavir AUC extrapolated to infinity and AUC from time of dosing to the last measurable concentration increased in a dose-proportional fashion over 200-800 mg; maximum plasma concentration increased less than dose proportionally. Seven participants reported treatment-emergent adverse events (TEAEs; Japanese participants, 400 mg: 2 [16.7%], 200 mg: 1 [8.3%]; White participants, 400 mg: 4 [33.3%]), all mild and most commonly dysgeusia. No serious TEAEs or TEAEs leading to discontinuation were reported. This study demonstrated higher maribavir systemic exposure in Japanese than White participants and similar safety outcomes. This difference in exposure is not considered clinically important and its significance remains to be determined.

New Perspectives on Antimicrobial Agents: Maribavir

Maribavir was approved by the U.S. Food and Drug Administration in November 2021 for the treatment of adult and pediatric patients with post-transplant cytomegalovirus (CMV) infection/disease that is refractory to treatment (with or without genotypic resistance) with ganciclovir, valganciclovir, cidofovir, or foscarnet. Maribavir is an oral benzimidazole riboside with potent and selective multimodal anti-CMV activity. It utilizes a novel mechanism of action which confers activity against CMV strains that are resistant to traditional anti-CMV agents, and also offers a more favorable safety profile relative to the dose-limiting side effects of previously available therapies. Maribavir was initially studied as an agent for CMV prophylaxis in solid organ and hematopoietic stem cell recipients, but initial phase III trials failed to meet clinical efficacy endpoints. It has been more recently studied as a therapeutic agent at higher doses for refractory-resistant (R-R) CMV infections with favorable outcomes. After an overview of maribavir's chemistry and clinical pharmacology, this review will summarize clinical efficacy, safety, tolerability, and resistance data associated with maribavir therapy.

Maribavir for the Management of Cytomegalovirus in Adult Transplant Recipients: A Review of the Literature and Practical Considerations

OBJECTIVE

To review the efficacy and safety of maribavir for management of cytomegalovirus (CMV) in solid organ transplant recipients.

DATA SOURCES

A literature search of PubMed and the Cochrane Controlled Trials Register (1960 to early July 2022) was performed using the following search terms: maribavir, 1263W94, and cytomegalovirus.

STUDY SELECTION AND DATA EXTRACTION

All relevant English-language studies were reviewed and considered, with a focus on phase 3 trials.

DATA SYNTHESIS

Maribavir, an orally available benzimidazole riboside with minimal adverse effects, was originally studied for universal prophylaxis in phase 3 trials but failed to demonstrate noninferiority over placebo and oral ganciclovir. It was effective for preemptive treatment in a dose-finding Phase 2 study. Maribavir is FDA approved for treatment of refractory/resistant CMV infection based on improved response rate at 8 weeks compared with investigator-assigned therapy (IAT) when initiated at median viral loads less than approximately 10 000 IU/mL (55.7% vs 23.9%, P < 0.001). Recurrence after 8-week treatment for refractory/resistant CMV was high (maribavir 50% vs IAT 39%). Significant drug interactions exist and must be managed by a pharmacotherapy expert to prevent harm.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

The addition of maribavir to the antiviral armamentarium should improve the management of refractory/resistant CMV, allowing early transition from toxic, high-cost, intravenous agents such as foscarnet and outpatient management. Optimal timing of initiation, duration, and potential alternative uses are unclear.

CONCLUSION

Future studies are needed to fully elucidate the role of maribavir in the management of CMV after transplant.

Evaluating the Safety of Maribavir for the Treatment of Cytomegalovirus

Purpose of Review

Cytomegalovirus (CMV) infections are a common complication in solid organ (SOT) and hematopoietic stem cell transplant (HSCT) recipients, leading to increased morbidity and mortality. Currently available treatment options have reduced the burden of infection, but utilization of these agents can be limited by toxicities such as nephrotoxicity and/or myelosuppression as well as emergence of resistance. The expansion of our current armamentarium towards CMV infection is crucial. Here, we review an emerging therapy, maribavir, and the safety and efficacy of this potential new agent for the prophylaxis and treatment of CMV infections including resistant/refractory disease.

Recent Findings

Maribavir is a novel agent with CMV activity approved by Federal Food and Drug Administration (FDA) in December 2021 for resistant/refractory disease. Compared to currently available treatment for CMV infection, maribavir has a unique mechanism of action, retains activity against most (val)ganciclovir resistant strains, provides a more predictable pharmacokinetic profile, and fewer severe toxicities. Maribavir has been studied in phase 2 and 3 studies with ongoing phase 3 studies. While maribavir failed to meet the primary endpoints in the initial phase 3 study for prophylaxis therapy in allogeneic-HSCT and liver transplant recipients, results from the phase 2 study when used for pre-emptive therapy after HSCT show similar efficacy to valganciclovir, and results from the phase 3 study examining resistant/refractory disease demonstrate superiority to investigator-initiated therapy of (val)ganciclovir, foscarnet, or cidofovir.

Summary

Maribavir provides a new agent for the management of resistant/refractory CMV infection. Results of the recently published phase 3 study provide further insight into the role of this novel therapy.

Cyclin-Dependent Kinases (CDKs) and the Human Cytomegalovirus-Encoded CDK Ortholog pUL97 Represent Highly Attractive Targets for Synergistic Drug Combinations

Human cytomegalovirus (HCMV) is a pathogenic human herpesvirus associated with serious, potentially life-threatening symptoms in the immunocompromised or immunonaïve host. The limitations encountered by antiviral therapy options currently available include a narrow panel of accessible targets, the induction of viral drug resistance as well as severe drug dosage-mediated side-effects. Improved drug-targeting strategies to resolve these issues are the focus of our investigations. In particular, pharmaceutical kinase inhibitors (PKIs), either directed to host kinases or directed to the viral protein kinase pUL97, have been considered to overcome these restrictions. Recently, we reported the identification of a synergistic combination of two PKIs directed to host cyclin-dependent kinase 7 (CDK7) and viral CDK ortholog pUL97. Here, we substantiate these findings with the following results: (i) true drug synergy was exhibited by various chemical classes of PKI pairs directed to pUL97 and CDK7; (ii) no putative amplification of cytotoxicity by these drug combinations was observed; (iii) a reduction in drug dosage levels for synergistic combinations was defined on a quantitative basis and compared to monotreatments; (iv) the quantities of target proteins CDK7 and pUL97 expressed in HCMV-infected cells were assessed by confocal imaging, indicating a strong down-modulation of CDK7 levels as a result of synergistic drug treatment; (v) the functional importance of these target kinases, both binding to cyclin H, was illustrated by assessing HCMV replication under the viral genomic deletion of ORF-UL97 or cellular cyclin knock-out; (vi) new combinations of HCMV-specific drug synergy were demonstrated for solely host-directed treatments using PKIs against CDK2, CDK7, CDK8 and/or CDK9 and (vii) a triple PKI combination provided further support for the synergy approach. With these combined findings, this study highlights the potential of therapeutic drug combinations of approved, developmental and preclinical PKIs for expanding future options for anti-HCMV therapy.

Advances in the Development of Therapeutics for Cytomegalovirus Infections

The development of therapeutics for cytomegalovirus (CMV) infections, while progressing, has not matched the pace of new treatments of human immunodeficiency virus (HIV) infections; nevertheless, recent developments in the treatment of CMV infections have resulted in improved human health and perhaps will encourage the development of new therapeutic approaches. First, the deployment of ganciclovir and valganciclovir for both the prevention and treatment of CMV infections and disease in transplant recipients has been further improved with the licensure of the efficacious and less toxic letermovir. Regardless, late-onset CMV disease, specifically pneumonia, remains problematic. Second, the treatment of congenital CMV infections with valganciclovir has beneficially improved both hearing and neurologic outcomes, both fundamental advances for these children. In these pediatric studies, viral load was decreased but not eliminated. Thus, an important lesson learned from studies in both populations is the need for new antiviral agents and the necessity for combination therapies as has been shown to be beneficial in the treatment of HIV infections, among others. The development of monoclonal antibodies, sirtuins, and cyclopropovir may provide new treatment options.

Combinatorial Drug Treatments Reveal Promising Anticytomegaloviral Profiles for Clinically Relevant Pharmaceutical Kinase Inhibitors (PKIs)

Human cytomegalovirus (HCMV) is a human pathogenic herpesvirus associated with a variety of clinical symptoms. Current antiviral therapy is not always effective, so that improved drug classes and drug-targeting strategies are needed. Particularly host-directed antivirals, including pharmaceutical kinase inhibitors (PKIs), may help to overcome problems of drug resistance. Here, we focused on utilizing a selection of clinically relevant PKIs and determined their anticytomegaloviral efficacies. Particularly, PKIs directed to host or viral cyclin-dependent kinases, i.e., abemaciclib, LDC4297 and maribavir, exerted promising profiles against human and murine cytomegaloviruses. The anti-HCMV in vitro activity of the approved anti-cancer drug abemaciclib was confirmed in vivo using our luciferase-based murine cytomegalovirus (MCMV) animal model in immunocompetent mice. To assess drug combinations, we applied the Bliss independence checkerboard and Loewe additivity fixed-dose assays in parallel. Results revealed that (i) both affirmative approaches provided valuable information on anti-CMV drug efficacies and interactions, (ii) the analyzed combinations comprised additive, synergistic or antagonistic drug interactions consistent with the drugs’ antiviral mode-of-action, (iii) the selected PKIs, especially LDC4297, showed promising inhibitory profiles, not only against HCMV but also other α-, β- and γ-herpesviruses, and specifically, (iv) the combination treatment with LDC4297 and maribavir revealed a strong synergism against HCMV, which might open doors towards novel clinical options in the near future. Taken together, this study highlights the potential of therapeutic drug combinations of current developmental/preclinical PKIs.

Recent developments in antimicrobial therapy for gastrointestinal infections

PURPOSE OF REVIEW

This focused, narrative review summarizes human clinical trial data for direct-acting antimicrobials in development for the treatment of gastrointestinal infections that were published in the past 18 months (1 January 2019 to 30 June 2020).

RECENT FINDINGS

Antimicrobial agents for Clostridioides difficile infection (n = 6), cryptosporidiosis (n = 1), cytomegalovirus infection (n = 3) and Helicobacter pylori infection (n = 1) have completed and/or are undergoing human clinical trials.

SUMMARY

Although this review highlights significant advances in four disease states, many common gastrointestinal pathogens have no antimicrobials in human clinical trials, emphasizing the need for continued prioritization in this field of study.

Moving Past Ganciclovir and Foscarnet: Advances in CMV Therapy

Purpose of Review

CMV DNA polymerase inhibitors such as ganciclovir and foscarnet have dramatically reduced the burden of CMV infection in the HCT recipient. However, their use is often limited by toxicities and resistance. Agents with novel mechanisms and favorable toxicity profiles are critically needed. We review recent developments in CMV antivirals and immune-based approaches to mitigating CMV infection.

Recent Findings

Letermovir, an inhibitor of the CMV terminase complex, was approved in 2017 for primary CMV prophylaxis in adult seropositive allogeneic HCT recipients. Maribavir, an inhibitor of the CMV UL97 kinase, is currently in two phase 3 treatment studies. Adoptive immunotherapy using third-party T cells has proven safe and effective in preliminary studies. Vaccine development continues, with several promising candidates currently under study.

Summary

No longer limited to DNA polymerase inhibitors, the prevention and treatment of CMV infections in the HCT recipient is a rapidly evolving field which should translate into improvements in CMV-related outcomes.

Maribavir for Refractory or Resistant Cytomegalovirus Infections in Hematopoietic-cell or Solid-organ Transplant Recipients: A Randomized, Dose-ranging, Double-blind, Phase 2 Study

Background

Cytomegalovirus (CMV) infections that are refractory or resistant (RR) to available antivirals ([val]ganciclovir, foscarnet, cidofovir) are associated with higher mortality in transplant patients. Maribavir is active against RR CMV strains.

Methods

Hematopoietic-cell or solid-organ transplant recipients ≥12 years old with RR CMV infections and plasma CMV deoxyribonucleic acid (DNA) ≥1000 copies/mL were randomized (1:1:1) to twice-daily dose-blinded maribavir 400, 800, or 1200 mg for up to 24 weeks. The primary efficacy endpoint was the proportion of patients with confirmed undetectable plasma CMV DNA within 6 weeks of treatment. Safety analyses included the frequency and severity of treatment-emergent adverse events (TEAEs).

Results

From July 2012 to December 2014, 120 patients were randomized and treated (40 per dose group): 80/120 (67%) patients achieved undetectable CMV DNA within 6 weeks of treatment (95% confidence interval, 57–75%), with rates of 70%, 63%, and 68%, respectively, for maribavir 400, 800, and 1200 mg twice daily. Recurrent on-treatment CMV infections occurred in 25 patients; 13 developed mutations conferring maribavir resistance. Maribavir was discontinued due to adverse events in 41/120 (34%) patients, and 17/41 discontinued due to CMV infections. During the study, 32 (27%) patients died, 4 due to CMV disease. Dysgeusia was the most common TEAE (78/120; 65%) and led to maribavir discontinuation in 1 patient. Absolute neutrophil counts <1000/µL were noted in 12/106 (11%) evaluable patients, with rates similar across doses.

Conclusions

Maribavir ≥400 mg twice daily was active against RR CMV infections in transplant recipients; no new safety signals were identified.

Clinical Trials Registration

NCT01611974.

Nuclear Egress Complexes of HCMV and Other Herpesviruses: Solving the Puzzle of Sequence Coevolution, Conserved Structures and Subfamily-Spanning Binding Properties

Herpesviruses uniquely express two essential nuclear egress-regulating proteins forming a heterodimeric nuclear egress complex (core NEC). These core NECs serve as hexameric lattice-structured platforms for capsid docking and recruit viral and cellular NEC-associated factors that jointly exert nuclear lamina as well as membrane-rearranging functions (multicomponent NEC). The regulation of nuclear egress has been profoundly analyzed for murine and human cytomegaloviruses (CMVs) on a mechanistic basis, followed by the description of core NEC crystal structures, first for HCMV, then HSV-1, PRV and EBV. Interestingly, the highly conserved structural domains of these proteins stand in contrast to a very limited sequence conservation of the key amino acids within core NEC-binding interfaces. Even more surprising, although a high functional consistency was found when regarding the basic role of NECs in nuclear egress, a clear specification was identified regarding the limited, subfamily-spanning binding properties of core NEC pairs and NEC multicomponent proteins. This review summarizes the evolving picture of the relationship between sequence coevolution, structural conservation and properties of NEC interaction, comparing HCMV to α-, β- and γ-herpesviruses. Since NECs represent substantially important elements of herpesviral replication that are considered as drug-accessible targets, their putative translational use for antiviral strategies is discussed.

Evaluation of the Effect of Maribavir on Cardiac Repolarization in Healthy Participants: Thorough QT/QTc Study

Maribavir is an orally bioavailable benzimidazole riboside in clinical development for treatment of cytomegalovirus infection in patients who undergo transplantation. Maribavir was evaluated in a thorough QT (TQT) study to determine any effects on cardiac repolarization. The effect of maribavir 100 and 1,200 mg oral doses on the baseline-adjusted and placebo-adjusted corrected QT (QTc) interval (delta delta QTc (ddQTc)) and other electrocardiogram (ECG) parameters was assessed in a randomized, phase I, placebo-controlled, four-period crossover study in healthy participants (men and women ages 18-50 years). Additionally, maribavir pharmacokinetics, safety, and tolerability were investigated. Moxifloxacin (400 mg) was used as a positive control to demonstrate the study's ability to detect QT prolongation. Digital 12-lead Holter ECG monitoring was performed over 22 hours following study drug administration. Individual, Fridericia's, and Bazett's QTc intervals were calculated. Of 52 randomized participants (29 ± 8.1 years old; 31 men (60%)), 50 (96%) completed the study. For both 100-mg and 1200-mg doses of maribavir, analysis of ddQTc demonstrated that the upper bound of the two-sided 90% confidence interval was below the 10-ms threshold at all time points. The concentration-effect analysis demonstrated no relationship between ddQTc and plasma concentrations of maribavir (and its metabolite). There were no clinically meaningful changes in heart rate and systolic blood pressure. The most common adverse event was dysgeusia; no serious adverse events were reported. This TQT study demonstrated that maribavir did not have impact on cardiac repolarization.

The Cytomegalovirus Protein Kinase pUL97:Host Interactions, Regulatory Mechanisms and Antiviral Drug Targeting

Human cytomegalovirus (HCMV) expresses a variety of viral regulatory proteins that undergo close interaction with host factors including viral-cellular multiprotein complexes. The HCMV protein kinase pUL97 represents a viral cyclin-dependent kinase ortholog (vCDK) that determines the efficiency of HCMV replication via phosphorylation of viral and cellular substrates. A hierarchy of functional importance of individual pUL97-mediated phosphorylation events has been discussed; however, the most pronounced pUL97-dependent phenotype could be assigned to viral nuclear egress, as illustrated by deletion of the UL97 gene or pharmacological pUL97 inhibition. Despite earlier data pointing to a cyclin-independent functionality, experimental evidence increasingly emphasized the role of pUL97-cyclin complexes. Consequently, the knowledge about pUL97 involvement in host interaction, viral nuclear egress and additional replicative steps led to the postulation of pUL97 as an antiviral target. Indeed, validation experiments in vitro and in vivo confirmed the sustainability of this approach. Consequently, current investigations of pUL97 in antiviral treatment go beyond the known pUL97-mediated ganciclovir prodrug activation and henceforward include pUL97-specific kinase inhibitors. Among a number of interesting small molecules analyzed in experimental and preclinical stages, maribavir is presently investigated in clinical studies and, in the near future, might represent a first kinase inhibitor applied in the field of antiviral therapy.

Effects of Maribavir on P-Glycoprotein and CYP2D6 in Healthy Volunteers

Maribavir is an investigational drug being evaluated in transplant recipients with cytomegalovirus infection. To understand potential drug-drug interactions, we examined the effects of multiple doses of maribavir on cytochrome P450 (CYP) 2D6 and P-glycoprotein (P-gp) activity using probe substrates in healthy volunteers. During this phase 1 open-label study (NCT02775240), participants received the probe substrates digoxin (0.5 mg) and dextromethorphan (30 mg) before and after maribavir (400 mg twice daily for 8 days). Serial plasma samples were analyzed for digoxin, dextromethorpha, dextrorphan, and maribavir concentrations. Pharmacokinetic parameters were calculated (noncompartmental analysis) and analyzed with a linear mixed-effects model for treatment comparison to estimate geometric mean ratios (GMRs) and 90% confidence intervals (CIs). CYP2D6 polymorphisms were genotyped using polymerase chain reaction. Overall, 17 of 18 participants (94.4%) completed the study. All participants were genotyped as CYP2D6 intermediate/extensive metabolizers. GMR (90%CI) of digoxin Cmax , AUClast , and AUC0-∞ with and without maribavir was 1.257 (1.139-1.387), 1.187 (1.088-1.296), and 1.217 (1.110-1.335), respectively, outside the "no-effect" window (0.8-1.25). GMR (90%CI) of dextromethorphan AUClast and AUClast ratio of dextromethorphan/dextrorphan were 0.877 (0.692-1.112) and 0.901 (0.717-1.133), respectively, marginally outside the no-effect window, although large variability was observed in these pharmacokinetic parameters. Pharmacokinetic parameters of dextrorphan were unaffected. Maribavir inhibited P-gp activity but did not affect CYP2D6 activity. Maribavir's effect on the pharmacokinetics of P-gp substrates should be evaluated individually, and caution should be exercised with P-gp substrates with narrow therapeutic windows.

Maribavir for Preemptive Treatment of Cytomegalovirus Reactivation

BACKGROUND

Maribavir is a benzimidazole riboside with activity against cytomegalovirus (CMV). The safety and efficacy of maribavir for preemptive treatment of CMV infection in transplant recipients is not known.

METHODS

In a phase 2, open-label, maribavir dose-blinded trial, recipients of hematopoietic-cell or solid-organ transplants (≥18 years of age, with CMV reactivation [1000 to 100,000 DNA copies per milliliter]) were randomly assigned to receive maribavir at a dose of 400, 800, or 1200 mg twice daily or the standard dose of valganciclovir for no more than 12 weeks. The primary efficacy end point was the percentage of patients with a response to treatment, defined as confirmed undetectable CMV DNA in plasma, within 3 weeks and 6 weeks after the start of treatment. The primary safety end point was the incidence of adverse events that occurred or worsened during treatment.

RESULTS

Of the 161 patients who underwent randomization, 159 received treatment, and 156 had postbaseline data available - 117 in the maribavir group and 39 in the valganciclovir group. The percentage of patients with postbaseline data available who had a response to treatment within 3 weeks was 62% among those who received maribavir and 56% among those who received valganciclovir. Within 6 weeks, 79% and 67% of patients, respectively, had a response (risk ratio, 1.20; 95% confidence interval, 0.95 to 1.51). The percentages of patients with a response to treatment were similar among the maribavir dose groups. Two patients who had a response to treatment had a recurrence of CMV infection within 6 weeks after starting maribavir at a dose of 800 mg twice daily; T409M resistance mutations in CMV UL97 protein kinase developed in both patients. The incidence of serious adverse events that occurred or worsened during treatment was higher in the maribavir group than in the valganciclovir group (52 of 119 patients [44%] vs. 13 of 40 [32%]). A greater percentage of patients in the maribavir group discontinued the trial medication because of an adverse event (27 of 119 [23%] vs. 5 of 40 [12%]). A higher incidence of gastrointestinal adverse events was reported with maribavir, and a higher incidence of neutropenia was reported with valganciclovir.

CONCLUSIONS

Maribavir at a dose of at least 400 mg twice daily had efficacy similar to that of valganciclovir for clearing CMV viremia among recipients of hematopoietic-cell or solid-organ transplants. A higher incidence of gastrointestinal adverse events - notably dysgeusia - and a lower incidence of neutropenia were found in the maribavir group. (Funded by ViroPharma/Shire Development; EudraCT number, 2010-024247-32.).

Safety considerations with current and emerging antiviral therapies for cytomegalovirus infection in transplantation

Introduction: Human cytomegalovirus (HCMV) is a major contributor of morbidity and mortality, and its management is essential for the successful outcome of solid organ and hematopoietic stem cell transplantation. Areas covered: This review discusses the safety profiles of currently available and emerging antiviral drugs and the other strategies for HCMV prevention and treatment after transplantation. Expert opinion: Strategies for management of HCMV rely largely on the use of antiviral agents that inhibit viral DNA polymerase (ganciclovir/valganciclovir, foscarnet, and cidofovir/brincidofovir) and viral terminase complex (letermovir), with different types and degrees of adverse effects. An investigational agent, maribavir, exerts its anti-CMV effect through UL97 inhibition, and its safety profile is under clinical evaluation. In choosing the antiviral medication to use, it is important to consider these safety profiles in addition to overall efficacy. In addition to antiviral drugs, reduction of immunosuppression is often generally needed in the management of HCMV infection, but with a potential risk of allograft rejection or graft-versus-host disease. The use of HCMV-specific or non-specific intravenous immunoglobulins remains debated, while adoptive HCMV-specific T cell therapy remains investigational, and associated with unique set of adverse effects.

Clinical development of letermovir and maribavir: Overview of human cytomegalovirus drug resistance

The prevention and treatment of human cytomegalovirus (HCMV) infections is based on the use of antiviral agents that currently target the viral DNA polymerase and that may cause serious side effects. The search for novel inhibitors against HCMV infection led to the discovery of new molecular targets, the viral terminase complex and the viral pUL97 kinase. The most advanced compounds consist of letermovir (LMV) and maribavir (MBV). LMV inhibits the cleavage of viral DNA and its packaging into capsids by targeting the HCMV terminase complex. LMV is safe and well tolerated and exhibits pharmacokinetic properties that allow once daily dosing. LMV showed efficacy in a phase III prophylaxis study in hematopoietic stem cell transplant (HSCT) recipients seropositive for HCMV. LMV was recently approved under the trade name Prevymis^™ for prophylaxis of HCMV infection in adult seropositive recipients of an allogeneic HSCT. Amino acid substitutions conferring resistance to LMV selected in vitro map primarily to the pUL56 and rarely to the pUL89 and pUL51 subunits of the HCMV terminase complex. MBV is an inhibitor of the viral pUL97 kinase activity and interferes with the morphogenesis and nuclear egress of nascent viral particles. MBV is safe and well tolerated and has an excellent oral bioavailability. MBV was effective for the treatment of HCMV infections (including those that are refractory or drug-resistant) in transplant recipients in two phase II studies and is further evaluated in two phase III trials. Mutations conferring resistance to MBV map to the UL97 gene and can cause cross-resistance to ganciclovir. MBV-resistant mutations also emerged in the UL27 gene in vitro and could compensate for the inhibition of pUL97 kinase activity by MBV. Thus, LMV and probably MBV will broaden the armamentarium of antiviral drugs available for the prevention and treatment of HCMV infections.

[Modern ethiotropic chemotherapy of human cytomegalovirus infection: clinical effectiveness, molecular mechanism of action, drug resistance, new trends and prospects. Part 2.]

A number of synthetic compounds, such as the nucleoside analog ganciclovir, its L-valine ester (a metabolic precursor of ganciclovir) and pyrophosphate analog foscarnet, are permitted for the treatment of HCMVrelated diseases in the WHO European Region. The viral DNA- polymerase is used by all these drugs as a biotarget. However, the usage of standard anti-CMV therapy is accompanied by severe side effects, as well as the development of drug resistance in the virus, mainly in conditions of immunodefciency. In this review, we focused on viral proteins of interest as new potential targets and their inhibitors, such as the inhibitor of human CMV terminology, lethermovir, which showed great activity in the third phase of clinical trials, inhibitors of viral cyclin-dependent kinase (maribavir, cyclopropavir) and a number of compounds exhibiting anti-HCMV-activity, undergoing only preclinical trials in the experiment. Inclusion of new anti-CMV agents that are active against GСV/PFA/CDV-resistant strains of CMV into standard prophylactic and therapeutic regimens, will allow to increase the effectiveness of anti-CMV therapy, including in cases when standard therapy is ineffective. Areas covered: the international databases such as A MEDLINE, PubMed, eLIBRARY.RU, ClinicalTrials.gov., etc. with the purpose of obtaining information on compounds showing selective action against the human cytomegalovirus, the most promising for the development of drugs.

New therapies for human cytomegalovirus infections

The recent approval of letermovir marks a new era of therapy for human cytomegalovirus (HCMV) infections, particularly for the prevention of HCMV disease in hematopoietic stem cell transplant recipients. For almost 30 years ganciclovir has been the therapy of choice for these infections and by today's standards this drug exhibits only modest antiviral activity that is often insufficient to completely suppress viral replication, and drives the selection of drug-resistant variants that continue to replicate and contribute to disease. While ganciclovir remains the therapy of choice, additional drugs that inhibit novel molecular targets, such as letermovir, will be required as highly effective combination therapies are developed not only for the treatment of immunocompromised hosts, but also for congenitally infected infants. Sustained efforts, largely in the biotech industry and academia, have identified additional highly active lead compounds that have progressed into clinical studies with varying levels of success and at least two have the potential to be approved in the near future. Some of the new drugs in the pipeline inhibit new molecular targets, remain effective against isolates that have developed resistance to existing therapies, and promise to augment existing therapeutic regimens. Here, we will describe some of the unique features of HCMV biology and discuss their effect on therapeutic needs. Existing drugs will also be discussed and some of the more promising candidates will be reviewed with an emphasis on those progressing through clinical studies. The in vitro and in vivo antiviral activity, spectrum of antiviral activity, and mechanism of action of new compounds will be reviewed to provide an update on potential new therapies for HCMV infections that have progressed significantly in recent years.

Treatment of alpha and beta herpesvirus infections in solid organ transplant recipients

INTRODUCTION

Human herpesviruses frequently cause infections in solid organ transplant (SOT) recipients. Areas covered: We provide an overview of the clinical impact of alpha and beta herpesviruses and highlight the mechanisms of action, pharmacokinetics, clinical indications, and adverse effects of antiviral drugs for the management of herpes simplex virus, varicella zoster virus and cytomegalovirus. We comprehensively evaluated key clinical trials that led to drug approval, and served as the foundation for management guidelines. We further provide an update on investigational antiviral agents for alpha and beta herpesvirus infections after SOT. Expert commentary: The therapeutic armamentarium for herpes infections is limited by the emergence of drug resistance. There have been major efforts for discovery of new drugs against these viruses, but the results of early-phase clinical trials have been less than encouraging. We believe, however, that more antiviral drug options are needed given the adverse side effects associated with current antiviral agents, and the emergence of drug-resistant virus populations in SOT recipients. Likewise, optimized use and strategies are needed for existing and novel antiviral drugs against alpha and beta-herpesviruses in SOT recipients.

VP, Dasgupta S, Bose K JC, Mukherjee S, Linert W, Moi SC. Benzimidazole based Pt(ii) complexes with better normal cell viability than cisplatin: synthesis, substitution behavior, cytotoxicity, DNA binding and DFT study

Water soluble Pt(ii) complexes with higher viability towards normal cells and comparable cytotoxicity to cancer cells as compared to cisplatin.

In vitro studies of the impact of maribavir on CMV-specific cellular immune responses

BACKGROUND

Ganciclovir has demonstrated immunosuppressive effects in vitro which may lead to delayed cytomegalovirus (CMV)-specific immune reconstitution when the drug is given prophylactically. Maribavir is a new and more potent anti-CMV drug that is under evaluation for therapeutic use in transplant recipients.

OBJECTIVES

The objective of this study was to evaluate the potential effect of maribavir on CMV-specific T cell function in comparison to ganciclovir.

STUDY DESIGN

In ten immunocompetent CMV seropositive donors, maribavir and ganciclovir were compared over a broad range of concentrations (0.2-500μM) regarding their effects on lymphoproliferation, CMV-specific CD4+ and CD8+ cytokine expression, T cell multifunctionality, degranulation and apoptosis.

RESULTS

Maribavir inhibited lymphocyte proliferation at concentrations of 50μM and above, however, cytokine expression, cellular degranulation and multifunctionality of CD4+ and CD8+ T cells in response to CMV lysate and pp65 peptide mix were not impaired except at the highest concentration of 500μM. Ganciclovir inhibited lymphoproliferative responses starting at 10μM. As with maribavir, other cellular responses following stimulation with CMV lysate and pp65 peptide mix were only impaired at the highest concentration of 500μM of ganciclovir. Neither maribavir nor ganciclovir showed induction of lymphocyte apoptosis.

CONCLUSIONS

Maribavir exhibits a low potential to suppress CMV-specific T cell function. This finding supports the use of higher doses in the prophylactic setting than originally proposed.

Comprehensive Review in Current Developments of Benzimidazole-Based Medicinal Chemistry

The properties of benzimidazole and its derivatives have been studied over more than one hundred years. Benzimidazole derivatives are useful intermediates/subunits for the development of molecules of pharmaceutical or biological interest. Substituted benzimidazole derivatives have found applications in diverse therapeutic areas such as antiulcer, anticancer agents, and anthelmintic species to name just a few. This work systematically gives a comprehensive review in current developments of benzimidazole-based compounds in the whole range of medicinal chemistry as anticancer, antibacterial, antifungal, anti-inflammatory, analgesic agents, anti-HIV, antioxidant, anticonvulsant, antitubercular, antidiabetic, antileishmanial, antihistaminic, antimalarial agents, and other medicinal agents. This review will further be helpful for the researcher on the basis of substitution pattern around the nucleus with an aim to help medicinal chemists for developing an SAR on benzimidazole drugs/compounds.

Overview of congenitally and perinatally acquired cytomegalovirus infections: recent advances in antiviral therapy

Congenital and perinatal infection with human cytomegalovirus (CMV) are commonly encountered in newborns. In recent years there has been increased awareness of the disabilities that result from congenital CMV infection, which in turn has prompted interest in examining the potential efficacy of antiviral agents to prevent or ameliorate neurodevelopmental injury. Currently, there are three licensed systemic antivirals for the treatment of CMV: ganciclovir (Cytovene, Roche] and its prodrug valganciclovir [Valcyte, Roche); foscarnet (Foscavir, AstraZeneca); and cidofovir (Vistide, Pharmacia). A CMV-specific immunoglobulin is also available. Experience with these agents in the setting of congenital and perinatal CMV infection is very limited, but there are encouraging data from a controlled clinical trial indicating that ganciclovir therapy may be of value in limiting one form of neurodevelopmental injury caused by congenital infection, that of sensorineural hearing loss. Licensed antivirals for the treatment of CMV all share the common mechanism of targeting the viral DNA polymerase, but novel therapies that employ alternative modes of action are in development. Ultimately, the problem of perinatal CMV infection may be best controlled by the development of CMV vaccines, which could be administered to young women of childbearing age to help control this important public health problem.

Advances in the antiviral therapy of herpes virus infection in children

Herpes viruses are ubiquitous and primary infections, with many of these viruses common during childhood. In general, children tolerate primary infection well, with only mild symptoms, but in the immunocompromised, including the newborn, infection can be associated with serious morbidity and mortality. Drug treatment for many of the herpes infections is available but is often associated with serious side effects. In the pediatric age group, treatment is further hindered by a lack of information on suitable dosing regimes, unavailability of oral solutions and a lack of clinical trials specifically investigating response to treatment in this group of patients. This article will review current evidence regarding the pharmacokinetics and dosing of the most commonly used antiherpetic agents and will look specifically at the treatment of the more common herpes virus infections in children.

Fast selection of maribavir resistant cytomegalovirus in a bone marrow transplant recipient

BACKGROUND

Human cytomegalovirus infections are still significant causes of morbidity and mortality in transplant recipients. The use of antiviral agents is limited by toxicity and evolving resistance in immunocompromised patients with ongoing viral replication during therapy. Here, we present the first documented case of genotypic resistance against maribavir in a bone marrow transplant (BMT) recipient.

CASE PRESENTATION

The female 13-year-old patient was suffering from a refractory cytopenia. Ganciclovir, foscarnet, cidofovir, leflunomide and maribavir, an inhibitor of the cytomegalovirus UL97 protein, were administered to treat a therapy-resistant cytomegalovirus infection. Viral mutations conferring resistance against nucleotide and pyrophosphate analogs as well as maribavir (MBV) have evolved sequentially. Particularly, impressive was the fast emergence of multiple mutations T409M, H411Y and H411N conferring maribavir resistance after less than 6 weeks.

CONCLUSION

We describe the fast emergence of cytomegalovirus variants with different maribavir resistance associated mutations in a bone marrow transplant recipient treated with MBV 400 mg p.o. twice per day. The results suggest that a high virus load permitted a selection of several but distinct therapy-resistant HCMV mutants. Since a phase II study with MBV is intended for the treatment of resistant or refractory HCMV infections in transplant recipients this has to be kept in mind in patients with high viral loads during therapy (NCT01611974).

Current and emerging antivirals for the treatment of cytomegalovirus (CMV) retinitis: an update on recent patents

Cytomegalovirus (CMV) retinitis is the most common ocular opportunistic complication and a serious cause of vision loss in immunocompromised patients. Even though, a rise in human immunodeficiency virus (HIV) infected individuals seems to be a major factor responsible for the prevalence of CMV retinitis, the introduction of highly active antiretroviral therapy (HAART) significantly reduced the incidence and severity of CMV retinitis. Thorough evaluation of the patient's immune status and an exact classification of the retinal lesions may provide better understanding of the disease etiology, which would be necessary for optimizing the treatment conditions. Current drugs such as ganciclovir, valganciclovir, cidofovir and foscarnet have been highly active against CMV, but prolonged therapy with these approved drugs is associated with dose-limiting toxicities thus limiting their utility. Moreover development of drug-resistant mutants has been observed particularly in patients with acquired immunodeficiency syndrome (AIDS). Continuous efforts by researchers in the industry and academia have led to the development of newer candidates with enhanced antiviral efficacy and apparently minimal side effects. These novel compounds can suppress viral replication and prevent reactivation in the target population. Though some of the novel therapeutics possess potent viral inhibitory activity, these compounds are still in stages of clinical development and yet to be approved. This review provides an overview of disease etiology, existing anti-CMV drugs, advances in emerging therapeutics in clinical development and related recent patents for the treatment of CMV retinitis.

Pharmacokinetics of Maribavir, a Novel Oral Anticytomegalovirus Agent, in Subjects With Varying Degrees of Renal Impairment

The effect of renal function on the pharmacokinetics of maribavir, a novel anticytomegalovirus agent, was evaluated in 12 adults with normal renal function (creatinine clearance [CrCl] >80 mL/min) and 19 adults with renal impairment classified as mild (n = 5), moderate (n = 5), or severe (n = 9), as measured by CrCl 50-80, 30-49, and <30 mL/min, respectively. After a single oral dose of maribavir 400 mg, the pharmacokinetics of maribavir, based on total and unbound plasma concentrations, showed no statistically significant difference between subjects with normal renal function and subjects with mild/moderate or severe renal impairment. Renal impairment was associated with an increase in area under the plasma concentration-time curve (AUC) values for an inactive metabolite of maribavir, VP 44469. Results were consistent with those of previous studies, which showed that very little maribavir was excreted unchanged in urine, whereas about 22% of an oral dose of maribavir is recovered in urine as VP 44469.

Letermovir Treatment of Human Cytomegalovirus Infection Antiinfective Agent

Novel therapies are urgently needed for the management of cytomegalovirus (CMV) disease in high-risk patients. Currently licensed agents target the viral DNA polymerase, and although they are effective, they are fraught with toxicities to patients. Moreover, emergence of antiviral resistance is an increasing problem, particularly for patients on long-term suppressive therapy. A new agent, letermovir (AIC246), shows great promise for the management of CMV infection. Advantages include its good oral bioavailability, its lack of toxicity, and the apparent absence of drug-drug interactions. Letermovir has a novel mechanism of action, exerting its antiviral effect by interfering with the viral pUL56 gene product and in the process disrupting the viral terminase complex. This agent demonstrates substantial promise as an alternative to more toxic antivirals in patients at high risk for CMV disease, particularly in the transplantation setting.

Efficacy and safety of maribavir dosed at 100 mg orally twice daily for the prevention of cytomegalovirus disease in liver transplant recipients: a randomized, double-blind, multicenter controlled trial

Maribavir is an oral benzimidazole riboside with potent in vitro activity against cytomegalovirus (CMV), including some CMV strains resistant to ganciclovir. In a randomized, double-blind, multicenter trial, the efficacy and safety of prophylactic oral maribavir (100 mg twice daily) for prevention of CMV disease were compared with oral ganciclovir (1000 mg three times daily) in 303 CMV-seronegative liver transplant recipients with CMV-seropositive donors (147 maribavir; 156 ganciclovir). Patients received study drug for up to 14 weeks and were monitored for CMV infection by blood surveillance tests and also for the development of CMV disease. The primary endpoint was Endpoint Committee (EC)-confirmed CMV disease within 6 months of transplantation. In a modified intent-to-treat analysis, the noninferiority of maribavir compared to oral ganciclovir for prevention of CMV disease was not established (12% with maribavir vs. 8% with ganciclovir: event rate difference of 0.041; 95% CI: -0.038, 0.119). Furthermore, significantly fewer ganciclovir patients had EC-confirmed CMV disease or CMV infection by pp65 antigenemia or CMV DNA PCR compared to maribavir patients at both 100 days (20% vs. 60%; p < 0.0001) and at 6 months (53% vs. 72%; p = 0.0053) after transplantation. Graft rejection, patient survival, and non-CMV infections were similar for maribavir and ganciclovir patients. Maribavir was well-tolerated and associated with fewer hematological adverse events than oral ganciclovir. At a dose of 100 mg twice daily, maribavir is safe but not adequate for prevention of CMV disease in liver transplant recipients at high risk for CMV disease.

Effects on maribavir susceptibility of cytomegalovirus UL97 kinase ATP binding region mutations detected after drug exposure in vitro and in vivo

Resistance to the experimental human cytomegalovirus (CMV) UL97 kinase inhibitor maribavir has been mapped to UL97 mutations at codons 353, 397, 409 and 411, in the kinase ATP-binding region, and to mutations in the UL27 gene. We studied the maribavir susceptibility phenotypes of additional UL97 mutations observed in vitro and in clinical trials, and the effect of simultaneous mutation in both UL97 and UL27. In vitro selection under maribavir identified a new locus of UL97 mutation within the conserved kinase p-loop (L337M), which conferred low grade maribavir resistance (3.5-fold increased EC50) without ganciclovir cross-resistance. During maribavir Phase III CMV prevention clinical trials, three previously unknown UL97 sequence variants were detected in plasma samples after 27-98 days of drug exposure (I324V, S334G and S386L). These variants did not confer any drug resistance despite proximity to mutations that confer maribavir resistance. The UL27 resistance mutation R233S, when added to strains containing UL97 mutations L337M or V353A, doubled their maribavir EC50s. These results expand the range of UL97 maribavir-resistance mutations into another part of the kinase ATP-binding region, but offer no genotypic evidence that development of drug resistance affected the outcomes of Phase III maribavir clinical trials after drug exposure of up to 14 weeks. There is a potential for increased maribavir resistance in UL27-UL97 double mutants.

Phosphorylation events during viral infections provide potential therapeutic targets

For many medically relevant viruses, there is now considerable evidence that both viral and cellular kinases play important roles in viral infection. Ultimately, these kinases, and the cellular signaling pathways that they exploit, may serve as therapeutic targets for treating patients. Currently, small molecule inhibitors of kinases are under investigation as therapy for herpes viral infections. Additionally, a number of cellular or host-directed tyrosine kinase inhibitors that have been previously FDA approved for cancer treatment are under study in animal models and clinical trials, as they have shown promise for the treatment of various viral infections as well. This review will highlight the wide range of viral proteins phosphorylated by viral and cellular kinases, and the potential for variability of kinase recognition sites within viral substrates to impact phosphorylation and kinase prediction. Research studying kinase-targeting prophylactic and therapeutic treatments for a number of viral infections will also be discussed.

Maribavir and human cytomegalovirus-what happened in the clinical trials and why might the drug have failed?

We summarize the history of the clinical drug development of maribavir for its use as prophylaxis in stem-cell transplant recipients. We highlight key aspects in the design and interpretation of the results of the dose escalation phase II maribavir study that may have contributed to the negative findings on the phase III trials. We discuss key aspects of study design that should be considered in the study of new interventions needed to advance the prevention and treatment of CMV in transplant recipients.

Maribavir prophylaxis for prevention of cytomegalovirus disease in recipients of allogeneic stem-cell transplants: a phase 3, double-blind, placebo-controlled, randomised trial

BACKGROUND

Available drugs against cytomegalovirus have adverse effects that compromise their prophylactic use in recipients of allogeneic stem-cell transplants. We assessed the safety, tolerability, and antiviral activity of oral maribavir in such patients.

METHODS

In this placebo-controlled, randomised, double-blind, multicentre phase 3 study, we enrolled adult patients recipient-seropositive or donor-seropositive for cytomegalovirus who had undergone allogeneic stem-cell transplantation. Patients were recruited from 90 centres in Canada, Europe, and the USA. After engraftment, patients were stratified by recipient cytomegalovirus serostatus and conditioning regimen (myeloablative or reduced-intensity) and assigned (2:1) by masked computer-generated randomisation sequence to receive maribavir 100 mg twice daily or placebo for up to 12 weeks, with weekly blood cytomegalovirus surveillance. If the virus was detected, administration of study drug was stopped and pre-emptive anticytomegalovirus treatment started. The primary endpoint was cytomegalovirus disease within 6 months of transplantation. Analysis was by intention-to-treat. This study is registered with ClinicalTrials.gov, NCT00411645.

FINDINGS

Between December, 2006, and May, 2008, 681 patients were enrolled and assigned to receive maribavir (454) or placebo (227). The incidence of cytomegalovirus disease within 6 months was 20 of 454 (4%) for the maribavir group and 11 of 227 (5%) for the placebo group (OR 0.90; 95% CI 0.42-1.92). During the 100 days following transplantation, cytomegalovirus infection rates as measured by pp65 antigenaemia were lower in the maribavir group (26.4%) than in the placebo group (34.8%; OR 0.67; 0.47-0.95), but not when measured by plasma cytomegalovirus DNA PCR (27.8%vs 30.4%; OR 0·88; 0.62-1.25), nor by initiation of treatment against cytomegalovirus (30.6%vs 37.4%; OR 0.73, 0.52-1.03). Maribavir was well tolerated: most adverse events, including incident acute graft-versus-host disease and neutropenia, affected both groups equally, except for taste disturbance (15% maribavir, 6% placebo).

INTERPRETATION

Compared with placebo, maribavir prophylaxis did not prevent cytomegalovirus disease when started after engraftment. Cytomegalovirus disease as a primary endpoint might not be sufficient to show improvements in cytomegalovirus prevention in recipients of allogeneic stem-cell transplants in the setting of pre-emptive antiviral treatment. Clinical and virological composite endpoints should be used in future trials.

FUNDING

ViroPharma Incorporated.

Antiviral drug resistance of human cytomegalovirus

The study of human cytomegalovirus (HCMV) antiviral drug resistance has enhanced knowledge of the virological targets and the mechanisms of antiviral activity. The currently approved drugs, ganciclovir (GCV), foscarnet (FOS), and cidofovir (CDV), target the viral DNA polymerase. GCV anabolism also requires phosphorylation by the virus-encoded UL97 kinase. GCV resistance mutations have been identified in both genes, while FOS and CDV mutations occur only in the DNA polymerase gene. Confirmation of resistance mutations requires phenotypic analysis; however, phenotypic assays are too time-consuming for diagnostic purposes. Genotypic assays based on sequencing provide more rapid results but are dependent on prior validation by phenotypic methods. Reports from many laboratories have produced an evolving list of confirmed resistance mutations, although differences in interpretation have led to some confusion. Recombinant phenotyping methods performed in a few research laboratories have resolved some of the conflicting results. Treatment options for drug-resistant HCMV infections are complex and have not been subjected to controlled clinical trials, although consensus guidelines have been proposed. This review summarizes the virological and clinical data pertaining to HCMV antiviral drug resistance.