ObjectivesBaloxavir marboxil (formerly S-033188) is a first-in-class, orally available, cap-dependent endonuclease inhibitor licensed in Japan and the USA for the treatment of influenza virus infection. We evaluated the efficacy of delayed oral treatment with baloxavir marboxil in combination with a neuraminidase inhibitor in a mouse model of lethal influenza virus infection.MethodsThe inhibitory potency of baloxavir acid (the active form of baloxavir marboxil) in combination with neuraminidase inhibitors was tested in vitro. The therapeutic effects of baloxavir marboxil and oseltamivir phosphate, or combinations thereof, were evaluated in mice lethally infected with influenza virus A/PR/8/34; treatments started 96 h post-infection.ResultsCombinations of baloxavir acid and neuraminidase inhibitor exhibited synergistic potency against viral replication by means of inhibition of cytopathic effects in vitro. In mice, baloxavir marboxil monotherapy (15 or 50 mg/kg twice daily) significantly and dose-dependently reduced virus titre 24 h after administration and completely prevented mortality, whereas oseltamivir phosphate treatments were not as effective. In this model, a suboptimal dose of baloxavir marboxil (0.5 mg/kg twice daily) in combination with oseltamivir phosphate provided additional efficacy compared with monotherapy in terms of virus-induced mortality, elevation of cytokine/chemokine levels and pathological changes in the lung.ConclusionsBaloxavir marboxil monotherapy with 96 h-delayed oral dosing achieved drastic reductions in virus titre, inflammatory response and mortality in a mouse model. Combination treatment with baloxavir acid and oseltamivir acid in vitro and baloxavir marboxil and oseltamivir phosphate in mice produced synergistic responses against influenza virus infections, suggesting that treating humans with the combination may be beneficial.

The repeated-dose liver micronucleus (RDLMN) assay using young adult rats has the potential to detect hepatocarcinogens. We conducted a collaborative study to assess the performance of this assay and to evaluate the possibility of integrating it into general toxicological studies. Twenty-four testing laboratories belonging to the Mammalian Mutagenicity Study Group, a subgroup of the Japanese Environmental Mutagen Society, participated in this trial. Twenty-two model chemicals, including some hepatocarcinogens, were tested in 14- and/or 28-day RDLMN assays. As a result, 14 out of the 16 hepatocarcinogens were positive, including 9 genotoxic hepatocarcinogens, which were reported negative in the bone marrow/peripheral blood micronucleus (MN) assay by a single treatment. These outcomes show the high sensitivity of the RDLMN assay to hepatocarcinogens. Regarding the specificity, 4 out of the 6 non-liver targeted genotoxic carcinogens gave negative responses. This shows the high organ specificity of the RDLMN assay. In addition to the RDLMN assay, we simultaneously conducted gastrointestinal tract MN assays using 6 of the above carcinogens as an optional trial of the collaborative study. The MN assay using the glandular stomach, which is the first contact site of the test chemical when administered by oral gavage, was able to detect chromosomal aberrations with 3 test chemicals including a stomach-targeted carcinogen. The treatment regime was the 14- and/or 28-day repeated-dose, and the regime is sufficiently promising to incorporate these methods into repeated-dose toxicological studies. The outcomes of our collaborative study indicated that the new techniques to detect chromosomal aberrations in vivo in several tissues worked successfully.

A new anthraquinone, 1,5,15-tri-O-methylmorindol (1), and two new saccharide fatty acid esters, 2-O-(beta-D-glucopyranosyl)-1-O-hexanoyl-beta-D-gluropyranose (4) and 2-O-(beta-D-glucopyranosyl)-1-O-octanoyl-beta-D-gluropyranose (5), have been isolated from a methanol extract of the fruits of Morinda citrifolia (noni) along with 10 known compounds, namely, two anthraquinones (2, 3), six saccharide fatty acid esters (6-11), an iridoid glycoside (12), and a flavanol glycoside (13). Upon evaluation of six compounds (5-7, 9, 10, and 13) for inhibitory activity against 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation (1 microg/ear) in mice, four saccharide fatty acid esters, 5-7 and 9, exhibited potent anti-inflammatory activity, with ID50 values of 0.46-0.79 mg per ear. In addition, when compounds 1-13 were evaluated against the Epstein-Barr virus early antigen (EBV-EA) activation induced by TPA, all of the compounds exhibited moderate inhibitory effects (IC50 values of 386-578 mol ratio/32 pmol TPA).

Objectives Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become established in the human population, making the need to develop safe and effective treatments critical. We have developed the small-molecule antiviral ensitrelvir, which targets the 3C-like (3CL) protease of SARS-CoV-2. This study evaluated the in vitro and in vivo efficacy of ensitrelvir compared with that of another SARS-CoV-2 3CL PI, nirmatrelvir. Methods Cultured cells, BALB/cAJcl mice and Syrian hamsters were infected with various SARS-CoV-2 strains, including the ancestral strain WK-521, mouse-adapted SARS-CoV-2 (MA-P10) strain, Delta strain and Omicron strain. Ensitrelvir efficacy was compared with that of nirmatrelvir. Effective concentrations were determined in vitro based on virus-induced cytopathic effects, viral titres and RNA levels. Lung viral titres, nasal turbinate titres, body-weight changes, and animal survival were also monitored. Results Ensitrelvir and nirmatrelvir showed comparable antiviral activity in multiple cell lines. Both ensitrelvir and nirmatrelvir reduced virus levels in the lungs of mice and the nasal turbinates and lungs of hamsters. However, ensitrelvir demonstrated comparable or better in vivo efficacy than that of nirmatrelvir when present at similar or slightly lower unbound-drug plasma concentrations. Conclusions Direct in vitro and in vivo efficacy comparisons of 3CL PIs revealed that ensitrelvir demonstrated comparable in vitro efficacy to that of nirmatrelvir in cell culture and exhibited equal to or greater in vivo efficacy in terms of unbound-drug plasma concentration in both animal models evaluated. The results suggest that ensitrelvir may become an important resource for treating individuals infected with SARS-CoV-2.