Maribavir

Maribavir is a potent inhibitor of histone phosphorylation catalyzed by wild-type pUL97 in vitro, with an IC50 of 3 nM. Maribavir has potent antiviral activity against HCMV and Epstein-Barr virus (EBV).

In Vitro:Maribavir is a potent inhibitor of the autophosporylation of the wild type and all the major Ganciclovir (GCV) resistant UL97 mutants analysed with a mean IC50 of 35 nM. The M460I mutation results in hypersensitivity to Maribavir with an IC50 of 4.8 nM. A Maribavir resistant mutant of UL97 (L397R) is functionally compromised as both a Ganciclovir kinase and a protein kinase (~ 10% of wild type levels). Enzyme kinetic experiments demonstrate that Maribavir is a competitive inhibitor of ATP with a Ki of 10 nM[1]. Maribavir (1263W94) inhibits viral replication in a dose-dependent manner, with IC50 of 0.12±0.01 μM as measured by a multicycle DNA hybridization assay. The pUL97 protein kinase is strongly inhibited by Maribavir, with 50% inhibition occurring at 3 nM[2].

References:
[1]. Shannon-Lowe CD, et al. The effects of Maribavir on the autophosphorylation of ganciclovir resistant mutants of the cytomegalovirus UL97 protein. Herpesviridae. 2010 Dec 7;1(1):4. [2]. Biron KK, et al. Potent and selective inhibition of human cytomegalovirus replication by 1263W94, a benzimidazole L-riboside with a unique mode of action. Antimicrob Agents Chemother. 2002 Aug;46(8):2365-72.

Detection of Low Frequency Multi-Drug Resistance and Novel Putative Maribavir Resistance in Immunocompromised Pediatric Patients with Cytomegalovirus.[Pubmed:27667983]

Front Microbiol. 2016 Sep 9;7:1317.

Human cytomegalovirus (HCMV) is a significant pathogen in immunocompromised individuals, with the potential to cause fatal pneumonitis and colitis, as well as increasing the risk of organ rejection in transplant patients. With the advent of new anti-HCMV drugs there is therefore considerable interest in using virus sequence data to monitor emerging resistance to antiviral drugs in HCMV viraemia and disease, including the identification of putative new mutations. We used target-enrichment to deep sequence HCMV DNA from 11 immunosuppressed pediatric patients receiving single or combination anti-HCMV treatment, serially sampled over 1-27 weeks. Changes in consensus sequence and resistance mutations were analyzed for three ORFs targeted by anti-HCMV drugs and the frequencies of drug resistance mutations monitored. Targeted-enriched sequencing of clinical material detected mutations occurring at frequencies of 2%. Seven patients showed no evidence of drug resistance mutations. Four patients developed drug resistance mutations a mean of 16 weeks after starting treatment. In two patients, multiple resistance mutations accumulated at frequencies of 20% or less, including putative Maribavir and ganciclovir resistance mutations P522Q (UL54) and C480F (UL97). In one patient, resistance was detected 14 days earlier than by PCR. Phylogenetic analysis suggested recombination or superinfection in one patient. Deep sequencing of HCMV enriched from clinical samples excluded resistance in 7 of 11 subjects and identified resistance mutations earlier than conventional PCR-based resistance testing in 2 patients. Detection of multiple low level resistance mutations was associated with poor outcome.

In vitro studies of the impact of maribavir on CMV-specific cellular immune responses.[Pubmed:26780109]

J Clin Virol. 2016 Feb;75:53-9.

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 (0.2-500muM) 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 50muM 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 500muM. Ganciclovir inhibited lymphoproliferative responses starting at 10muM. As with Maribavir, other cellular responses following stimulation with CMV lysate and pp65 peptide mix were only impaired at the highest concentration of 500muM 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.

Maribavir is a potent inhibitor of histone phosphorylation catalyzed by wild-type pUL97 in vitro, with an IC50 of 3 nM. Maribavir has potent antiviral activity against HCMV and Epstein-Barr virus (EBV).

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