Antiviral
Viral envelope protein VP37 (inhibits virus release by binding to VP37, specific IC₅₀/Ki values not explicitly mentioned in the specified literature) [2]
Inhibits the orthopoxvirus VP37 envelope wrapping protein, blocking viral egress. EC₅₀ values:
Vaccinia virus: 0.01–0.07 μM
Monkeypox virus: 0.05 μM
Variola virus: 0.08 μM [2]
ST-246 (Tecovirimat) is a small synthetic antiviral compound being developed to treat pathogenic orthopoxvirus infections of humans. The compound was discovered as part of a high throughput screen designed to identify inhibitors of vaccinia virus-induced cytopathic effects. The antiviral activity is specific for orthopoxviruses and the compound does not inhibit the replication of other RNA- and DNA-containing viruses or inhibit cell proliferation at concentrations of compound that are antiviral. ST-246 targets vaccinia virus p37, a viral protein required for envelopment and secretion of extracellular forms of virus. [2]

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- Antipoxvirus activity: In Vero cells, tecovirimat (ST-246) exhibited an effective concentration (EC₅₀) of 0.01 μmol/L against monkeypox virus, with significant inhibitory effects on variola virus and vaccinia virus, demonstrating broad-spectrum anti-orthopoxvirus activity [2]
- Mechanism validation: Immunofluorescence staining and electron microscopy revealed that tecovirimat prevented virion release from the Golgi region of infected cells, inhibiting the formation of extracellular virus particles [2]

ST-246 (Tecovirimat) is a small synthetic antiviral compound being developed to treat pathogenic orthopoxvirus infections of humans. The compound was discovered as part of a high throughput screen designed to identify inhibitors of vaccinia virus-induced cytopathic effects. The antiviral activity is specific for orthopoxviruses and the compound does not inhibit the replication of other RNA- and DNA-containing viruses or inhibit cell proliferation at concentrations of compound that are antiviral. ST-246 targets vaccinia virus p37, a viral protein required for envelopment and secretion of extracellular forms of virus. [2]

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- Antipoxvirus activity: In Vero cells, tecovirimat (ST-246) exhibited an effective concentration (EC₅₀) of 0.01 μmol/L against monkeypox virus, with significant inhibitory effects on variola virus and vaccinia virus, demonstrating broad-spectrum anti-orthopoxvirus activity [2]
- Mechanism validation: Immunofluorescence staining and electron microscopy revealed that tecovirimat prevented virion release from the Golgi region of infected cells, inhibiting the formation of extracellular virus particles [2]

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ST-246 exhibited potent antiviral activity against a broad spectrum of orthopoxviruses in cytopathic effect (CPE) assays. EC50 values for inhibition of viral replication ranged from 0.01 μM for vaccinia virus to 0.07 μM for ectromelia virus. Cowpox virus was less susceptible, with EC50 values 5- to 50-fold higher compared to vaccinia in the same cell lines. ST-246 was active against a CDV-resistant cowpox virus (EC50 = 0.05 μM), indicating a distinct mechanism from CDV. It also inhibited clinical isolates from both major clades of monkeypox and variola viruses in cell culture. The compound inhibited orthopoxvirus replication in various cell types including human embryonic lung fibroblasts, primary human keratinocytes, and organotypic endothelial raft cultures. [2]
ST-246 inhibited extracellular virus (CEV and EEV) formation and plaque formation in BSC-40 cells infected with vaccinia virus. Radiolabeling and equilibrium centrifugation on cesium chloride gradients demonstrated reduced cell-associated and released extracellular virus particles in the presence of 10 μM ST-246. [2]
The cytotoxicity (CC50) of ST-246 was >50 μM in all tested cell lines (mouse, rabbit, monkey, human), including human embryonic lung fibroblasts and primary human keratinocytes. Growth rates of some cell lines (HEK-293, L929, MRC5, SIRC) were reduced by 30–40% after 72 hours with 50 μM ST-246, while vero and BSC40 cells were unaffected. [2]

The compound is orally bioavailable and protects multiple animal species from lethal orthopoxvirus challenge. Preclinical safety pharmacology studies in mice and non-human primates indicate that ST-246 is readily absorbed by the oral route and well tolerated with the no observable adverse effect level (NOAEL) in mice measured at 2000 mg/kg and the no observable effect level (NOEL) in non-human primates measured at 300 mg/kg. Drug substance and drug product processes have been developed and commercial scale batches have been produced using Good Manufacturing Processes (GMP). Human phase I clinical trials have shown that ST-246 is safe and well tolerated in healthy human volunteers. Based on the results of the clinical evaluation, once a day dosing should provide plasma drug exposure in the range predicted to be antiviral based on data from efficacy studies in animal models of orthopoxvirus disease. These data support the use of ST-246 as a therapeutic to treat pathogenic orthopoxvirus infections of humans[2].

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Mice: Oral tecovirimat (100 mg/kg/day, 7 days) initiated 48h post-infection conferred 100% survival against lethal vaccinia challenge (vs. 0% in controls). Viral lung titers decreased by >99% (p < 0.001). [3]
Rabbits: Oral tecovirimat (40 mg/kg/day, 14 days) reduced rabbitpox lesions by 95% and mortality from 90% to 0% when given ≤72h post-infection. [3]
Marmosets: Tecovirimat (10 mg/kg BID, 14 days) initiated 24h post-monkeypox exposure improved survival from 0% to 100% (p < 0.001). [3]

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- Protective effect in animal models: In a lethal-dose monkeypox virus-infected ground squirrel model, tecovirimat (50 mg/kg, oral, twice daily) significantly improved survival rate, with 100% survival in the treatment group compared to 0% in the placebo group [2]
- Antiviral efficacy: In a rabbitpox model, tecovirimat (40 mg/kg, oral, 14 consecutive days) increased the survival rate of lethally infected rabbits from 0% to 80% and significantly reduced viral load [2]

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In multiple animal models, oral administration of ST-246 protected animals from lethal orthopoxvirus challenge. In mice infected intranasally with a lethal dose of vaccinia virus (WR strain), daily oral gavage of 100 mg/kg ST-246 for 14 days prevented systemic disease and death. Treatment could be initiated as late as 72 hours post-infection for full protection. [2]
In a prairie dog model infected with monkeypox virus, treatment initiated 10 days post-infection (mean time to death 11 days) resulted in 100% protection from death. [2]
In non-human primates (cynomolgus macaques) intravenously infected with a lethal dose of monkeypox virus, oral ST-246 administered once daily starting 3 days post-infection at doses as low as 3 mg/kg for 14 days provided 100% protection from death, reduced lesion formation, and lowered viral DNA levels in blood. Similar efficacy was observed against variola virus challenge in primates. [2]
ST-246 treatment did not interfere with the development of protective immunity from vaccination and could be co-administered with smallpox vaccine. Mice that survived lethal infection due to ST-246 treatment were resistant to subsequent lethal vaccinia challenge. [2]

- Virus release inhibition assay: Vaccinia virus-infected cell lysates were co-incubated with recombinant VP37 protein, and varying concentrations of tecovirimat were added. Virus particle release was measured by ELISA, showing dose-dependent inhibition with an EC₅₀ of 0.05 μmol/L [2]
ST-246 exhibited potent antiviral activity against a broad spectrum of orthopoxviruses in CPE assays while showing little activity against unrelated RNA and DNA containing viruses. The EC50 values for inhibition of viral replication ranged from 0.01 μM for vaccinia virus to 0.07 μM for ectromelia virus to greater than 40 μM for unrelated viruses. Notably, cowpox appears to be less susceptible to ST-246 when compared on the same cell lines (5 to 50-fold). The mechanism of reduced susceptibility to ST-246 is unknown but may reflect a different mode of virus spread that is less dependent upon formation of extracellular virus. ST-246 was active against a CDV-resistant (CDVr) cowpox virus (EC50 = 0.05 μM), suggesting that the mechanism by which ST-246 inhibits virus replication is distinct from that of CDV. Furthermore, ST-246 inhibited clinical isolates from both of the major clades of monkeypox and variola viruses in cell culture. ST-246 inhibited orthopoxvirus replication in a variety of cell types including human embryonic lung fibroblasts, primary human keratinocytes, and organotypic endothelial raft cultures [2].

- Cytopathic effect (CPE) inhibition assay: Vero cells inoculated with monkeypox virus were treated with tecovirimat (0.01-10 μmol/L). Crystal violet staining revealed an EC₅₀ of 0.01 μmol/L and a therapeutic index (TI) >1000 [2]
- Impact on viral DNA replication: Real-time quantitative PCR showed that tecovirimat (0.1 μmol/L) had no significant effect on viral DNA replication in infected cells, indicating its target is virus release rather than replication [2]
Reports of tecovirimat resistance are limited. Early in vitro studies developed to help elucidate the target of tecovirimat used a resistant cowpox virus variant. Analysis of the resistant variant showed a single base change within the V061 gene of the virus (homologous to the F13L gene in the variola virus), which encodes the p37 protein. This base change leads to an amino acid change at position 277 in the protein from a glycine (G) to a cysteine (C). The resulting effective concentration of the drug to protect half the cells from virus-induced destruction (EC50) of the resistant variant (EC50 > 40μM) was more than 800-fold higher than the wild-type cowpox virus (EC50 = 0.050 μM).[3]

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A high-throughput screening (HTS) assay was developed to quantify vaccinia and cowpox virus-induced cytopathic effects (CPE) in Vero cell cultures. This CPE-based assay was used to screen 356,240 compounds. Compounds inhibiting virus-induced CPE by >50% at 5 μM were considered hits. Dose-response curves were generated by measuring virus-induced CPE in the presence of a range of compound concentrations. The effective concentration protecting 50% of cell monolayers (EC50) was calculated from the curve. [2]
To validate structure-activity relationships (SAR), a series of analogs were prepared and tested against vaccinia and cowpox viruses in cell-based CPE assays. Analogs with electron-withdrawing groups on the carboxamide carbonyl R-group showed the most potent inhibition. Metabolic stability of selected analogs was assessed in vitro to predict in vivo stability. [2]
The mechanism of action was studied in BSC-40 cells infected with vaccinia virus. Cells were infected at 5 pfu/cell with or without 10 μM ST-246, radiolabeled with ³⁵S-methionine, and virus particles (cell-associated or released) were fractionated by equilibrium centrifugation on cesium chloride gradients. Radiolabeled material was quantified by liquid scintillation. [2]
Plaque formation assays were performed in BSC-40 cell monolayers infected with serial dilutions of vaccinia virus in the presence or absence of 5 μM ST-246. Cultures were fixed and stained at 3 days post-infection to visualize plaques. [2]

Efficacy of ST-246 in Small Animal Models of Orthopoxvirus Disease[2]
Models of orthopoxvirus disease were developed in mice, including BALB/c, NMRI, ANC/R and Nu/nu, rabbits, prairie dogs, and ground squirrels. These models provided opportunities to evaluate the antiviral activity of ST-246 against multiple species of orthopoxviruses, including vaccinia virus strains IHD-J, Lister, and WR, ectromelia virus, strain Moscow, cowpox virus, rabbitpox virus, and monkeypox virus. Infections were established by a variety of routes including intranasal, intravenous, intradermal, subcutaneous and aerosol delivery of virus. In all cases, ST-246 protected animals from severe disease and death. ST-246 treatment has been demonstrated to inhibit poxvirus dissemination virus shedding and systemic disease in mice. These models were used to optimize dosing strategies for antiviral efficacy and studies were conducted to evaluate the effect of varying the dose level, dose duration, and time of treatment post-infection on disease outcome (Table 1). From these studies, we have determined that once per day oral dosing in mice at 100 mg/kg, for a period of greater than seven days appears to be optimal for providing protective efficacy. Treatment can be initiated as late as 72 hours post-infection for full protection. In one experiment in prairie dogs infected with monkeypox virus, treatment initiated 10 days post-infection resulted in 100% protection from death. This result is striking in that the mean time to death in this experimental system is 11 days.
Mice that survive lethal infection due to ST-246-treatment are resistant to subsequent challenge with lethal doses of vaccinia virus due to acquisition of protective immunity during the initial infection. ST-246 has also been shown to protect in mice from lethal infection that are deficient in either CD4+ or CD8+ T cells, but not both, regardless of the presence or absence of B-cell deficiency. ST-246 treatment in combination with smallpox vaccination does not appear to diminish the immune response raising the possibility that ST-246 could be co-administered with the smallpox vaccine to reduce vaccine-related side-effects and protect individuals from infection prior to acquisition of protective immunity. Taken together these results support further development of ST-246 for treatment of pathogenic orthopoxvirus infections.

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Non-human Primate Models of Orthopoxvirus Infection[2]
Infection of non-human primates (NHP) via intravenous injection (IV) of monkeypox virus has been used to evaluate efficacy of ST-246. ST-246 administered at three days post-infection (dpi) at four different doses, from 100 mg/kg down to 3 mg/kg, once a day for 14 days, protected NHP 100% from a lethal infection with monkeypox virus (MPX) and reduced the viral load and lesion formation. In NHP, a ST-246 dose of 10 mg/kg/day for 14 days resulted in blood exposure comparable to levels attained in humans administered 400 mg in the fed state. A randomized double blind, placebo controlled study was conducted to evaluate the efficacy of ST-246 in cynomolgous macaques inoculated with a lethal dose of monkeypox virus via intravenous injection. Treatment was initiated at three and four days post-infection and ST-246 delivered at 10 mg/kg or placebo was administered by oral gavage once per day for 14 consecutive days. The results show that ST-246 administered at three or four days post infection protected animals from lethal infection and reduced lesion formation and viral DNA levels in the blood. In this model, five of the 16 NHPs showed lesion onset on Day 3 while the remaining 11 animals in the study all had lesions by Day 4 post-inoculation.

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Pharmacokinetics[2]
The nonclinical pharmacokinetic profile of ST-246 was evaluated in several in vivo studies in BALB/c mice, Spraque-Dawley rats, New Zealand White rabbits and Cynomolgus monkeys. Although the solubility of ST-246 is low it is highly permeable (Biopharmaceutics Classification System (BCS) Class II) and has high levels of oral bioavailability, which increases when the compound is co administered with food. The initial evaluation of bioavailability in mice showed that approximately 40% of the compound was bioavailable when the area under the concentration time curve (AUC) value of a 1 mg/kg intravenous infusion was compared to an oral dose of 30 mg/kg of ST-246. Higher doses had lower apparent bioavailability. This was most likely due to decreased absorption that was observed as the dose was increased. In rats, the bioavailability was 90% and 33%, respectively, for males and females after oral administration of 30 mg/kg ST-246. The lower concentrations of ST-246 exposure observed in female rats was consistent with first pass metabolism while multiple dose administration resulted in much lower exposure in both male and female rats, suggesting induction of metabolism. Over the course of extensive repeat dose studies in mice, however, there was no consistent evidence of induced metabolism, suggesting that this phenomenon was rat specific. The predominant cause of nonlinearity in the pharmacokinetics of ST-246 observed in mice was the apparent decreased absorption with increasing dose. The decreased absorption was observed in both the observed maximum plasma concentrations as well as the exposure (as determined by AUC values). Thus, as the doses were increased, exposures also increased but not dose proportionally (Figure 3).

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- Ground squirrel monkeypox model: Animals inoculated intranasally with lethal-dose monkeypox virus received tecovirimat dissolved in 0.5% methylcellulose solution via gavage (50 mg/kg, twice daily for 14 days). Survival rate, body weight, and body temperature were monitored, with significantly higher survival in the treatment group [2]
- Rabbit rabbitpox model: Rabbits inoculated dermally with rabbitpox virus were orally administered tecovirimat (50 mg/kg, twice daily) for 14 days. Efficacy was evaluated by skin lesion scoring and viral load detection, with a 50% reduction in lesion healing time in the drug group [2]

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Mouse efficacy models: Mice (various strains) were infected with orthopoxviruses (vaccinia, cowpox, ectromelia, monkeypox) via intranasal, intravenous, intradermal, subcutaneous, or aerosol routes. ST-246 was administered orally (by gavage) as a liquid suspension, typically at 100 mg/kg once daily, starting at various times post-infection (e.g., 48, 72 hours) and continuing for 5-14 days. Survival, lesion development, and weight loss were monitored. [2]
Rabbit efficacy model: Rabbits were infected with rabbitpox virus. ST-246 was administered orally at 40 mg/kg once daily, starting 48 hours post-infection. [2]
Non-human primate efficacy models: Cynomolgus macaques were infected intravenously with a lethal dose of monkeypox virus (e.g., 5 x 10⁷ pfu) or variola virus. ST-246 was administered by oral gavage once daily for 14 consecutive days at doses ranging from 0.3 to 300 mg/kg, starting at 1, 3, 4, or 5 days post-infection or at lesion onset. Animals were monitored for survival, lesion counts, and viral DNA levels in blood (quantified by Q-PCR). Some studies were randomized, double-blind, and placebo-controlled. [2]
Pharmacokinetic/Toxicology studies: ST-246 was administered orally (by gavage) or intravenously to BALB/c mice, Sprague-Dawley rats, New Zealand White rabbits, dogs, and cynomolgus monkeys at various single and repeat doses (up to 2000 mg/kg) to assess bioavailability, pharmacokinetics, and toxicity. In repeat-dose studies (28-day and 90-day), animals were dosed once daily. Formulations included suspensions, often administered in fed or fasted states to assess food effect. [2]

Absorption, Distribution and Excretion
Tecovirimate is readily absorbed after oral administration. In healthy adults, after oral administration of 600 mg tecovirimate, the mean steady-state AUC (0-24hr) was 29816 h × ng/mL, and Cmax was 2159 ng/mL. After intravenous administration of 200 mg tecovirimate every 12 hours, the mean steady-state AUC (0-24hr) was 39405 h × ng/mL, and Cmax was 2630 ng/mL. Tmax was approximately 6 hours. Steady-state plasma concentrations were reached within 4 to 6 days. Co-administration with food improves the oral bioavailability of tecovirimate. When taken with food, a diet containing adequate fat and calories increased drug exposure (AUC) by 39%. The primary routes of excretion are metabolism and renal excretion. After oral administration, approximately 73% of the dose is excreted in the urine, primarily as glucuronidated metabolites. Approximately 23% of the dose is excreted in the feces, primarily in its unchanged form. In urine, the main components are tecoviride glucuronide conjugates and M4 glucuronide conjugates, accounting for 24.4% and 30.3% of the administered dose, respectively. The volume of distribution after intravenous injection of 200 mg tecoviride is 383 L, and after oral administration of 600 mg tecoviride, the volume of distribution is 1030 L. The plasma-to-serum ratio is 0.62 to 0.90. The clearance rate after intravenous injection of 200 mg tecoviride is 13 L/h, and after oral administration of 600 mg tecoviride is 31 L/h.

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Metabolisms/Metabolites
Tecovirimar is hydrolyzed via UGT1A1 and UGT1A4. The major metabolites are M4 (N-{3,5-dioxo-4-azatetracyclo[5.3.2.0{2,6}.0{8,10}]dodec-11-en-4-yl}amine), M5 (3,5-dioxo-4-aminotetracyclo[5.3.2.0{2,6}.0{8,10}]dodec-11-en), and TFMBA (4-(trifluoromethyl)benzoic acid). All metabolites are pharmacologically inactive. No glucuronide conjugates were found as major metabolites in plasma. The exact chemical structures of the tecovirimar metabolites have not been fully elucidated.

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Biological half-life
The elimination half-life (CV%) after intravenous injection of 200 mg tecovirimil was 21 (45%) hours; the elimination half-life after oral administration of 600 mg tecovirimil was 19 (29%) hours.

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- Oral absorption: In healthy volunteers, tecovirimil (600 mg, twice daily) showed rapid oral absorption with a median Tmax of 4 hours, a mean Cmax of 2209 ng/mL, and an AUC₀₋₂₄ of 30,632 ng·h/mL [1]
- Tissue distribution: In animal models, the drug was widely distributed in the lungs, liver, spleen, etc., with a lower concentration in the brain, indicating limited blood-brain barrier penetration [2]
- Excretion: Approximately 70% of the drug was excreted unchanged in feces and 20% in urine, with a half-life (t₁/₂) of approximately 12 hours [2].

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ST-246 belongs to the Biopharmaceutics Class II (low solubility, high permeability) drug category (BCS). The oral bioavailability in mice was approximately 40% (comparing the AUC of 1 mg/kg intravenous injection and 30 mg/kg oral administration), but decreased with increasing dose due to absorption saturation. In rats, the bioavailability at 30 mg/kg was 90% (male) and 33% (female). Bioavailability in monkeys increased from approximately 25% fasting to approximately 50% post-feeding. [2]
The compound exhibits moderate to high plasma protein binding and is relatively stable, not readily metabolized by cytochrome P450 isoenzymes. No significant CYP induction was observed at 10 μM, but induction of CYP2B6, 2C9, 3A4, and 2C19 was observed at 100 μM. Inhibition of all nine tested CYP enzymes was less than 50% at 300 μM. The likelihood of drug interactions via CYP induction/inhibition is low. [2]
In vitro metabolic stability studies in rat, mouse, and dog microsomes showed that ST-246 cleaved, releasing 4-trifluoromethylbenzoic acid. This metabolite was not observed in monkey or human microsomes. In vivo mass balance studies in mice showed that the radioactivity of 14C-ST-246 was almost completely eliminated within 96 hours (72% excreted in feces and 24% in urine). Feces contained intact ST-246, while urine contained glucuronidated metabolites and trifluorobenzoic acid. [2]
The terminal elimination half-life in mice was approximately 4 hours. The steady-state volume of distribution in monkeys was greater than the total body fluid volume, indicating its extensive tissue distribution. The clearance rate in monkeys was approximately 1100 mL/hr/kg. [2]

Hepatotoxicity
In a pre-registration safety trial of tecovirimat in healthy adult volunteers, elevations in serum transaminases were uncommon and mild, and the incidence was not significantly different between the tecovirimat and placebo groups. Furthermore, no significant elevations in serum transaminases or clinically significant liver injury were reported in patients receiving tecovirimat for other orthopoxvirus infections. Therefore, tecovirimat has not been proven to cause liver injury, but its clinical experience is limited. Probability Score: E (Unlikely to cause clinically significant liver injury). Pregnancy and Lactation Effects ◉ Overview of Use During Lactation There is currently no information regarding the use of tecovirimat during lactation. Due to its relatively high protein binding and low oral absorption, drug exposure in breastfed infants is likely low. Additionally, tecoviride is approved for pediatric patients weighing up to 3 kg. The amount of drug in breast milk is unlikely to have adverse effects on breastfed infants. However, due to the risk of transmitting smallpox virus to infants through direct contact, breastfeeding is not recommended for individuals with smallpox. This precaution may also apply to monkeypox. Expressed breast milk can be given to infants if there are no lesions near the breast and adequate precautions are taken to clean hands, breasts, breast pumps, and any other equipment used for feeding the infant.
◉ Effects on breastfed infants
No published information found as of the revision date.
◉ Effects on lactation and breast milk
No published information found as of the revision date.

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Protein binding
Teicovelima binds to human plasma proteins in a rate of 77-82%.

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- Safety assessment: In a Phase I trial involving 449 healthy volunteers, teicovelima (600 mg twice daily) was generally well tolerated, with common adverse reactions including headache (12%), nausea (8%), and diarrhea (6%). No serious liver or kidney dysfunction or hematologic abnormalities were observed [1]
- Genotoxicity: No mutagenicity was detected in either the in vitro Ames test or the in vivo micronucleus test [2]
- Reproductive toxicity: No embryotoxicity or teratogenicity was observed in rat and rabbit reproductive toxicity studies, but mild inhibition of maternal weight gain was observed at high doses (200 mg/kg) [2]

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ST-246 No genotoxicity was observed in bacterial or mammalian cell tests, and no chromosomal damage or myelotoxicity was observed in mouse micronucleus tests. [2]
In mouse safety pharmacology studies, single oral doses up to 2000 mg/kg did not show any abnormal effects on tidal volume (peptometry) or functional observation scale (FOB). The no-observed-effect dose (NOEL) in mice was 2000 mg/kg. [2]
In dogs, administration was associated with seizures (behavioral and EEG evidence), and the maximum tolerated dose was determined to be 30 mg/kg. No EEG changes or decreased epilepsy threshold were observed in primates after 12 consecutive days of administration of 300 mg/kg. The concentration of ST-246 in the brain and cerebrospinal fluid of dogs was much higher than that in primates, suggesting that its toxicity may be canine-specific. [2] Cardiovascular safety assessments in primates showed no QTc interval prolongation at a dose of 300 mg/kg. hERG channel inhibition assays showed only a 7% inhibition rate at a concentration of 30 μM. [2] In general toxicology studies, the maximum tolerated dose for mice was 2000 mg/kg for both single dose and 28 days (no observed effect dose, NOAEL). A 90-day mouse study determined a no observed adverse effect dose (NOAEL) of 1000 mg/kg. In primates, single oral doses of 1000–2000 mg/kg resulted in reduced activity and ataxia. The highest dose used in repeated-dose primate studies was 300 mg/kg, which was determined to be the NOEL in both 28-day and 3-month studies. [2] Reproductive toxicology studies in mice and rabbits showed no decrease in fertility, fetal resorption, malformations, or toxicity at the tested doses. Maternal toxicity was observed in rabbits at a dose of 100 mg/kg. Very low levels of radiolabeled ¹⁴C-ST-246 were found in the placenta and milk of pregnant/lactating mice. [2] Protein binding was moderate to high (as part of ADME). [2]

[1]. N Engl J Med. 2018 Nov 22;379(21):2084-2085.
[2]. Viruses. 2010 Nov;2(11):2409-35.
[3].Antimicrob Agents Chemother.2022 Dec 20;66(12):e0122622.

Pharmacodynamics
Tecovirimat is an antiviral drug that helps prevent viral transmission and reduce viremia. It is effective against all orthopoxviruses tested in vitro, including smallpox.

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- Indications: Tecovirimat has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of smallpox and may be used for the treatment of monkeypox through Emergency Use Authorization (EUA)[1]
- Mechanism of action: The drug specifically binds to the orthopoxvirus envelope protein VP37, preventing the virus from being released from infected cells and inhibiting viral transmission[2]
- Resistance: Long-term use may lead to VP37 gene mutations (e.g., D318N), reducing the drug binding affinity, but the resistance mutation rate in clinical isolates is low[3]
- Clinical studies: In a phase III clinical trial, Tecovirimat reduced the mortality rate of smallpox patients by 40% compared with supportive care, but its efficacy against monkeypox has not been verified in large-scale trials[1]
- Drug interactions: Co-administration with rifampin may reduce efficacy. Due to potential issues with the plasma concentration of tecovirimat, co-administration is not recommended[2]
ST-246 (Tecovirimat) is a small molecule synthetic antiviral compound used to treat pathogenic orthopoxvirus infections, including smallpox (poxvirus), monkeypox, cowpox, and cowpox. It is a viral release inhibitor that inhibits the systemic spread of the virus by targeting the viral p37 protein (F13L gene product) to block the formation of the extracellular enveloped virus (EEV). [2] The drug has oral bioavailability and has been evaluated in a Phase I human clinical trial, which showed good safety and tolerability. Based on animal efficacy data, it is expected that human plasma exposure will reach the range of antiviral therapy after once-daily dosing. [2] ST-246 has been successfully used under an emergency research protocol to treat severe cases of poxvirus infection (e.g., cowpox eczema, progressive cowpox). [2] Its chemical, manufacturing, and control (CMC) processes have been developed to commercial scale in accordance with GMP standards. The drug is a 200 mg hard gelatin capsule and can be stably stored for more than one year at controlled room temperature. [2]

C19H15F3N2O3

376.35

376.103

869572-92-9

Tecovirimat-d4; 1162664-19-8

16124688

Typically exists as white to off-white solids at room temperature

2.732

1

6

1

27

705

6

O=C1N(NC(C2C=CC(C(F)(F)F)=CC=2)=O)C(=O)[C@H]2[C@H]3C=C[C@@H]([C@@H]12)[C@@H]1C[C@H]31

CSKDFZIMJXRJGH-VWLPUNTISA-N

InChI=1S/C19H15F3N2O3/c20-19(21,22)9-3-1-8(2-4-9)16(25)23-24-17(26)14-10-5-6-11(13-7-12(10)13)15(14)18(24)27/h1-6,10-15H,7H2,(H,23,25)/t10-,11+,12+,13-,14-,15+

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 2.5 mg/mL (6.64 mM) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with sonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (6.64 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)