Efficacy of Tilorone Dihydrochloride against Ebola Virus Infection

Abstract

Tilorone dihydrochloride (tilorone) is a small-molecule, orally bioavailable drug that is used clinically as an antiviral outside the United States. A machinelearning model trained on anti-Ebola virus (EBOV) screening data previously identified tilorone as a potent in vitro EBOV inhibitor, making it a candidate for the treatment of Ebola virus disease (EVD). In the present study, a series of in vitro ADMET (absorption, distribution, metabolism, excretion, toxicity) assays demonstrated the drug has excellent solubility, high Caco-2 permeability, was not a P-glycoprotein substrate, and had no inhibitory activity against five human CYP450 enzymes (3A4, 2D6, 2C19, 2C9, and 1A2). Tilorone was shown to have 52% human plasma protein binding with excellent plasma stability and a mouse liver microsome half-life of 48 min. Dose range-finding studies in mice demonstrated a maximum tolerated single dose of 100 mg/kg of body weight. A pharmacokinetics study in mice at 2-and 10-mg/kg dose levels showed that the drug is rapidly absorbed, has dosedependent increases in maximum concentration of unbound drug in plasma and areas under the concentration-time curve, and has a half-life of approximately 18 h in both males and females, although the exposure was ϳ2.5-fold higher in male mice. Tilorone doses of 25 and 50 mg/kg proved efficacious in protecting 90% of mice from a lethal challenge with mouse-adapted with once-daily intraperitoneal (i.p.) dosing for 8 days. A subsequent study showed that 30 mg/kg/day of tilorone given i.p. starting 2 or 24 h postchallenge and continuing through day 7 postinfection was fully protective, indicating promising activity for the treatment of EVD.

Tilorone: a Broad-Spectrum Antiviral Invented in the USA and Commercialized in Russia and beyond

“…HIV, HBV, influenza etc., there are currently no broad-spectrum antivirals approved in the USA. In contrast, tilorone has been widely used outside the USA for several decades and recent data suggests efficacy in an animal model of EBOV infection (36) while additional in vitro activities from several groups support the use of this molecule as a broad-spectrum treatment of various viral infections. The preclinical data around this compound and all available data allows a candidate product profile to be generated (Table III).…”

“…This model predicted Ebola inhibitory activity for tilorone, which was then tested using an in vitro anti-Ebola assay for activity. Tilorone gave a 50% effective concentration (EC 50 ) in this assay of 230 nM (Table II), making it one of the most potent small-molecule inhibitors of EBOV reported at the time (31,35,36). After a series of toxicity and pharmacokinetic studies, the compound was tested in a mouse model of EBOV infection where it was associated with 90-100% survival in a mouse EBOV efficacy study at three different doses.…”

“…After a series of toxicity and pharmacokinetic studies, the compound was tested in a mouse model of EBOV infection where it was associated with 90-100% survival in a mouse EBOV efficacy study at three different doses. For comparison, the vehicle-treated group had only 10% survival (36). Interestingly, tilorone was either comparable or had significantly reduced survival rates as compared to the vehicle in guinea pigs infected with EBOV (33).…”

Perspectives towards antiviral drug discovery against Ebola virus

“…Among various FDA screens, multiple compounds including amodiaquine, diphenylpyraline, ketotifen, diphenoxylate were reported to inhibit EBOV replication, while others including, verapamil, dronedarone, sertraline, toremifene, chloroquine, teicoplanin, and amiodarone were considered EBOV entry inhibitors . Very recently, tilorone (EC 50 = 0.23 μM) was reported to be the most potent small‐molecule inhibitor with a single‐daily dose of 25 and 50 mg/kg intraperitoneal and proved efficacious in protecting 90% of mice from a lethal EBOV challenge . Some of these inhibitors are shown in Figure .…”

Déjà vu: Stimulating open drug discovery for SARS-CoV-2

“…We also leveraged NIH support to a collaborator to test the other two compounds as well. These molecules were then each tested in the mouse model for Ebola infection and demonstrated significant efficacy [29][30][31]. Pyronaridine is currently being pursued in larger animal models of Ebola virus infection.…”