Prophylactic effect of ensitrelvir in mice infected with SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiological cause of coronavirus disease 2019 (COVID-19) and continues to be a major health concern worldwide. Strategies to protect individuals at high risk of COVID-19 are critical but are currently a largely unmet need. We evaluated the oral antiviral drug ensitrelvir, which specifically targets the SARS-CoV-2 3CL protease, for its efficacy as a pre-exposure prophylactic treatment. Aged BALB/c mice were subcutaneously treated with various doses of ensitrelvir 24 h prior to a lethal SARS-CoV-2 challenge infection. Mouse body weight changes, survival rates, and viral titers in the lungs were evaluated, and plasma concentrations of ensitrelvir were determined. A single subcutaneous administration of ensitrelvir at 64 mg/kg or greater 24 h prior to SARS-CoV-2 challenge infection significantly protected aged mice against lethality and inhibited body weight loss. Pharmacokinetic analysis of ensitrelvir in the aged mice suggested that plasma concentrations ≥2.99 µg/mL resulted in a significant prophylactic effect against SARS-CoV-2 infection. In the aged mouse prophylaxis model, SARS-CoV-2 titers were suppressed in the lungs of mice treated with ensitrelvir 24 h prior to challenge infection, suggesting that the prophylactic administration of ensitrelvir exerted its prophylactic effect by suppressing viral proliferation. These findings suggest that ensitrelvir is a candidate drug for pre-exposure prophylactic treatment of individuals at high risk of COVID-19.

In Vivo Antiviral Activity of Baloxavir against PA/I38T-Substituted Influenza A Viruses at Clinically Relevant Doses.

Although the prevalence of polymerase acidic (PA)/I38T strains of influenza virus with reduced susceptibility to baloxavir acid is low, there is a possibility of emergence under selective pressure. Furthermore, the virus may be transmitted between humans. We investigated the in vivo efficacy of baloxavir acid and oseltamivir phosphate against influenza A subtypes H1N1, H1N1pdm09, and H3N2, with PA/I38T substitution, at doses simulating human plasma concentrations. A pharmacokinetic/pharmacodynamic analysis was performed to strengthen the validity of the findings and the applicability in a clinical setting. Although the antiviral effect of baloxavir acid was attenuated in mice infected with PA/I38T-substituted viral strains compared with the wild type (WT), baloxavir acid significantly reduced virus titers at higher-but clinically relevant-doses. The virus titer reduction with baloxavir acid (30 mg/kg subcutaneous single dose) was comparable to that of oseltamivir phosphate (5 mg/kg orally twice daily) against H1N1 and H1N1pdm09 PA/I38T strains in mice, as well as the H3N2 PA/I38T strain in hamsters. Baloxavir acid demonstrated an antiviral effect against PA/I38T-substituted strains, at day 6, with no further viral rebound. In conclusion, baloxavir acid demonstrated dose-dependent antiviral effects comparable to that of oseltamivir phosphate, even though the degree of lung virus titer reduction was diminished in animal models infected with PA/I38T-substituted strains.

Efficacy comparison of 3CL protease inhibitors ensitrelvir and nirmatrelvir against SARS-CoV-2 in vitro and in vivo.

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.

S-217622, a SARS-CoV-2 main protease inhibitor, decreases viral load and ameliorates COVID-19 severity in hamsters.

In parallel with vaccination, oral antiviral agents are highly anticipated to act as countermeasures for the treatment of the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Oral antiviral medication demands not only high antiviral activity but also target specificity, favorable oral bioavailability, and high metabolic stability. Although a large number of compounds have been identified as potential inhibitors of SARS-CoV-2 infection in vitro, few have proven to be effective in vivo. Here, we show that oral administration of S-217622 (ensitrelvir), an inhibitor of SARS-CoV-2 main protease (Mpro; also known as 3C-like protease), decreases viral load and ameliorates disease severity in SARS-CoV-2-infected hamsters. S-217622 inhibited viral proliferation at low nanomolar to submicromolar concentrations in cells. Oral administration of S-217622 demonstrated favorable pharmacokinetic properties and accelerated recovery from acute SARS-CoV-2 infection in hamster recipients. Moreover, S-217622 exerted antiviral activity against SARS-CoV-2 variants of concern, including the highly pathogenic Delta variant and the recently emerged Omicron BA.5 and BA.2.75 variants. Overall, our study provides evidence that S-217622, an antiviral agent that is under evaluation in a phase 3 clinical trial (clinical trial registration no. jRCT2031210350), has remarkable antiviral potency and efficacy against SARS-CoV-2 and is a prospective oral therapeutic option for COVID-19.

Generation of Human-Induced Pluripotent Stem Cell-Derived Functional Enterocyte-Like Cells for Pharmacokinetic Studies.

We aimed to establish an in vitro differentiation procedure to generate matured small intestinal cells mimicking human small intestine from human-induced pluripotent stem cells (iPSCs). We previously reported the efficient generation of CDX2-expressing intestinal progenitor cells from embryonic stem cells (ESCs) using 6-bromoindirubin-3'-oxime (BIO) and (3,5-difluorophenylacetyl)-L-alanyl-L-2-phenylglycine tert-butyl ester (DAPT) to treat definitive endodermal cells. Here, we demonstrate the generation of enterocyte-like cells by culturing human iPSC-derived intestinal progenitor cells on a collagen vitrigel membrane (CVM) and treating cells with a simple maturation medium containing BIO, DMSO, dexamethasone, and activated vitamin D3. Functional tests further confirmed that these iPSC-derived enterocyte-like cells exhibit P-gp- and BCRP-mediated efflux and cytochrome P450 3A4 (CYP3A4)-mediated metabolism. We concluded that hiPS cell-derived enterocyte-like cells can be used as a model for the evaluation of drug transport and metabolism studies in the human small intestine.

Generation of intestinal organoids derived from human pluripotent stem cells for drug testing.

Drug absorption via the intestinal tissue is modulated by membrane permeability and metabolism in intestinal epithelial cells (IECs). In drug discovery research, using human IECs to evaluate membrane permeability and metabolic stability can offer very useful information when exploring for drug candidate compounds that have good bioavailability and when trying to predict the fraction absorbed and intestinal availability in humans. Here, we evaluated the pharmacokinetic functions of human IECs differentiated from human induced pluripotent stem cells (hiPSCs) in 3D cultures. As human IECs differentiated in 3D cultures form intestinal organoids and spheroids (herein termed organoids), their morphology makes it difficult to evaluate their pharmacokinetic functions. Therefore, we dissociated intestinal organoids into single cells and attempted to purify human IECs. We found that hiPSC-derived IECs (hiPSC-IECs) expressed the epithelial cell adhesion molecule (EpCAM) and could be highly purified by sorting EpCAM+ cells. The hiPSC-IEC monolayer showed a high TEER value (approximately 350 Ω × cm2). In addition, hiPSC-IECs oxidatively metabolized terfenadine (CYP3A and CYP2J2 substrate) and midazolam (CYP3A substrate). These results indicated that hiPSC-IECs form tight-junction and have cytochrome P450 enzymatic activities. In conclusion, we developed a novel application of hiPSC-derived intestinal organoids for drug testing.

The elucidation of key factors for oral absorption enhancement of nanocrystal formulations: In vitro-in vivo correlation of nanocrystals.

Nanocrystal formulation is a well-established approach for improving oral absorption of poorly water-soluble drugs. However, it is difficult to predict the in vivo performance of nanocrystal formulations from in vitro dissolution studies. The object of the present study was to investigate the in vitro-in vivo correlation of nanocrystal formulations of different particle sizes. A microsuspension and three nanosuspensions with different particle sizes for model drugs, fenofibrate and megestrol acetate, were prepared. In the comparison between the microsuspension and the nanosuspension having the smallest particle sizes, drug permeation rates from the nanosuspension were about 3-fold higher in the dissolution-permeation study. On the other hand, the solubility enhancement effect due to nanocrystal formation was only up by 1.4-fold, suggesting that nanocrystal formulations dramatically improved not the solubility but the apparent permeability. The oral absorption rate in rats increased with particle size reduction. There were positive and very strong correlations (R2 > 0.95) between the in vitro permeation rate and in vivo maximum absorption rate. We concluded that the enhanced permeability rate due to nanocrystal formation is the main factor for improving oral absorption, and the in vitro dissolution-permeation study could be useful for predicting oral absorption enhancement of nanocrystal formulations.

Application of Intestinal Epithelial Cells Differentiated from Human Induced Pluripotent Stem Cells for Studies of Prodrug Hydrolysis and Drug Absorption in the Small Intestine.

Cell models to investigate intestinal absorption functions, such as those of transporters and metabolic enzymes, are essential for oral drug discovery and development. The purpose of this study was to generate intestinal epithelial cells from human induced pluripotent stem cells (hiPSC-IECs) and then clarify whether the functions of hydrolase and transporters in them reflect oral drug absorption in the small intestine. The hiPSC-IECs showed the transport activities of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and peptide transporter 1 (PEPT1), revealed by using their probe substrates ([3H]digoxin, sulfasalazine, and [14C]glycylsarcosine), and the metabolic activities of CYP3A4, CES2, and CES1, which were clarified using their probe substrates (midazolam, irinotecan, and temocapril). The intrinsic clearance by hydrolysis of six ester prodrugs into the active form in hiPSC-IECs was correlated with the plasma exposure (Cmax , AUC, and bioavailability) of the active form after oral administration of these prodrugs to rats. Also, the permeability coefficients of 14 drugs, containing two substrates of P-gp (doxorubicin and [3H]digoxin), one substrate of BCRP (sulfasalazine), and 11 nonsubstrates of transporters (ganciclovir, [14C]mannitol, famotidine, sulpiride, atenolol, furosemide, ranitidine, hydrochlorothiazide, acetaminophen, propranolol, and antipyrine) in hiPSC-IECs were correlated with their values of the fraction of intestinal absorption (Fa) in human clinical studies. These findings suggest that hiPSC-IECs would be a useful cell model to investigate the hydrolysis of ester prodrugs and to predict drug absorption in the small intestine.