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Upamostat at specified doses used was well tolerated, without significant side effects.
Entry criteria enhanced the hospitalization rate in the placebo group.
Dose-dependent increased international normalized ratio and partial thromboplastin time and decreased d-dimer levels were observed.
Upamostat speeded resolution and decreased the incidence of new severe symptoms.
No upamostat patients were hospitalized because of COVID-19.
We performed a pilot study of upamostat, a serine protease inhibitor, in outpatients with symptomatic COVID-19 before a pivotal trial.
SARS-CoV-2 patients with ≥2 moderate-severe symptoms onset within 5 days were randomized to oral upamostat 200 or 400 mg or placebo daily for 14 days. Patients completed COVID-19 symptom questionnaires daily for 28 days, then thrice weekly for 4 weeks, and underwent physical and laboratory examinations periodically.
A total of 61 patients enrolled of which 20 received a placebo or upamostat 200 mg daily; 21 received upamostat 400 mg daily. Treatment was well tolerated; only one patient (upamostat 400) reported a drug-related adverse event, mild skin rash; no patient discontinued owing to a drug-related adverse event. The median time to a sustained recovery from severe symptoms was 8, 4, and 3 days for the three treatment groups, respectively. New severe symptoms developed in 20% of the placebo group vs 2.4% in the combined upamostat groups, (P = 0.036). Three placebo patients (15%) versus no upamostat patients were hospitalized for worsening COVID (P= 0.03). The mean d-dimer level remained constant in placebo patients but decreased by 38% and 48% in upamostat 200 and 400 patients, respectively.
Upamostat was well tolerated, shortened recovery time, and decreased new severe symptoms and hospitalization.
All COVID-19 therapeutics available to date target the virus directly rather than host factors. Host cell proteases, primarily transmembrane serine protease 2, are responsible for the cleavage of SARS-CoV-2 spike protein [
]. Upamostat inhibits cell surface proteases required to cleave viral spike protein, blocking attachment and uptake of the virus into host cells. In vitro, it inhibits SARS-CoV-2 replication in Calu-3 cells and in a human bronchial epithelium organoid model; it may also act via cathepsin-L (data on file, RedHill Biopharma). In addition, inhibition of trypsins and related enzymes may block tissue damage caused by excessive enzyme release due to infection. In healthy volunteers (data on file, RedHill Biopharma) and cancer patients [
], upamostat was well tolerated at the doses chosen for this study.
The primary objective of this pilot study was the determination of the safety and tolerability of two dose levels of upamostat, in comparison with placebo, before the conduct of a pivotal efficacy study. Efficacy parameters to be used in the main study were followed to provide preliminary evidence of their utility and, for the patient-reported symptom questionnaire, to assess its validity.
Adults diagnosed with COVID-19 and who did not require hospitalization were included. At baseline, patients had to have at least two moderate to severe symptoms, from a total of 17 symptoms elicited in a questionnaire. Symptom onset and initial positive polymerase chain reaction (PCR) or rapid antigen test had to be ≤5 days before the start of treatment. Additional entry requirements were baseline oxygen saturation ≥92% on room air, negative pregnancy test for women of childbearing potential, and no immediate requirement for antiviral, anticytokine, or corticosteroid therapy. Patients could be of any risk category, could have received vaccination for COVID-19, and were allowed to receive monoclonal antibody therapy for COVID-19. All patients gave informed consent electronically before any study-specific procedures. Additional entry criteria are in the protocol, which accompanies this paper online. After consent, patients completed the questionnaire, which determined qualification for the study based on baseline symptoms, underwent physical examination and electrocardiogram, and were provided a nasal swab for SARS-CoV-2 PCR and viral typing and blood for safety laboratories and disease markers.
Patients were stratified by age (<65 or ≥65 years) and randomized to one of three treatment groups: once-daily oral treatment with placebo, upamostat 200 mg, or upamostat 400 mg for 14 days. Patients were randomized centrally in computer-generated blocks of three or six, in random order. The randomization system assigned a treatment kit to each patient entered. All study personnel and participants were blinded to treatment.
Patients completed the symptom questionnaire daily for 28 days and then thrice weekly for the next 4 weeks using a smartphone app (ObvioHealth, Orlando FL). In addition to questions about symptoms of COVID-19, patients were to note other events, compliance with study medication administration, and use of concomitant medication. The symptom questionnaire and accompanying additional questions can be found in the protocol, as Appendix 2.
Patients were seen on days 1 (baseline) and 57 of the study in the clinic, and on days 8, 15, and 29 either at home or in the clinic, with televisits on days 3 and 43. At each in-person visit, vital signs were taken, patients were questioned regarding adverse events, administration of study medication and concomitant medications, nasal swabs for SARS-CoV-2 PCR test, and blood for safety laboratory tests and disease markers were taken. Six-lead electrocardiograms (KardiaMobile® 6L, Alivecor, Mountain View, CA) were performed on days 1, 8, 15, and 29 of the study.
Temperature and oxygen saturation data were collected for the first several weeks of the study using electronic thermometers and pulse oximeters, which were connected via Bluetooth to the smartphone.
Adverse event data were collected throughout the study. Investigators classified events as either related or unrelated to COVID; those events related to COVID, whether from the questionnaire or elicited separately, were analyzed together. Events deemed by the investigator unrelated to COVID were analyzed as adverse events. Events were coded according to Medical Dictionary for Regulatory Activities (MedDRA) version 24.0 and graded using National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) version 5.
Laboratory abnormalities were graded using NCI CTCAE version 5. Any laboratory abnormality that developed in the study, i.e., went from normal to abnormal or worsened in the study by at least one grade, was considered an adverse event, regardless of clinical significance. Laboratory abnormalities for which there is no NCI CTCAE version 5 grade were graded 1 unless there were clinical sequelae that prompted a higher grading.
Assessment of the safety and tolerability of the two dose levels of upamostat for determination of the dose to use for the main efficacy study was the primary objective of this pilot study. The sample size, 20 per treatment group, was felt to be adequate to detect clinically relevant differences in safety and tolerability for purposes of determination of dose for the pivotal study. Given the small sample sizes, statistically significant differences in safety parameters were not expected. A data and safety monitoring board reviewed the results of the study and determined, based on overall clinical and laboratory data, including the incidence of adverse events, serious adverse events, and discontinuation of treatment due to adverse events, whether there were clinically meaningful differences in tolerability between the two dose levels.
As all patients randomized received at least one dose of study medication, the intent to treat and safety populations are the same and comprise all randomized patients in the treatment groups to which they were randomized.
Recovery from COVID-19 was defined in the protocol as:
afebrile (<38.0°C core temperature) for at least 48 hours without the use of antipyretics;
all symptoms resolved or returned to pre-illness levels (e.g., if the patient had respiratory compromise prior to the onset of COVID-19), except for
fatigue, anosmia, ageusia, or dysgeusia, which may be persistent at a level similar to that during the acute illness, i.e., the same level per symptom questionnaire;
chest pain, cough, or dyspnea which if persistent must be at least one grade lower than at the start of treatment and no worse than grade 1 (mild).
Sustained recovery was recovery continuing for at least 14 days or until l last observation of the study, whichever came first. The above exclusions to complete resolution of all symptoms were to allow for patients who might have ongoing symptoms at end of the study but who would generally be considered to have recovered from the acute illness. These were based on early reports of long COVID-19 symptoms [
]. As a sensitivity analysis, a more stringent definition of recovery was set before data unblinding, in which recovery was defined as the 1st day at which there were no symptoms, other than preexisting symptoms, which were no worse than mild, for at least 14 days or until last observation on the study, whichever came first. A post hoc analysis of the time to recover from severe symptoms was also performed. Time to a sustained recovery from severe symptoms was defined as the time from the start of therapy until the 1st day at which no severe symptoms were present for at least 14 days or until the last available diary, whichever came first.
A total of 61 patients were randomized between February 16 and November 12, 2021, at seven investigative sites, six in the United States and one in South Africa. Overall, 74 patients gave informed consent; 13 patients failed to meet all inclusion and exclusion criteria. Figure 1, the Consolidated Standards of Reporting Trials (CONSORT) diagram, shows the disposition of patients. All randomized patients received at least one dose of study medication and all are analyzed for both safety and efficacy in the groups to which they were randomized. Twenty patients each were randomized to placebo and upamostat 200 mg daily; 21 to upamostat 400 mg daily.
Patient characteristics are shown in Table 1. The mean ages of the groups were in their 40’s; 10% of patients entered were age 65 or over. Overall, 27 patients (44%) were male; 36 patients (59%) had one or more high-risk characteristics, most commonly hypertension, diabetes, or obesity.Overall, 9 patients (15%) had received at least one vaccination against COVID-19; seven patients (12%) received monoclonal antibody infusions at the start of the study treatment.
As shown in Table 2, the number of baseline symptoms ranged from 5-17, with a median of 11, 10, and nine in the placebo, upamostat 200 mg, and upamostat 400 mg groups, respectively. The mean time from the onset of symptoms to the start of treatment was similar for each treatment group. No patient started treatment more than 5 days after the onset of symptoms or positive virologic determination. Across treatment groups, the most common symptoms of any severity were fatigue (58 patients, 95%), myalgias/body aches (57 patients, 93%), anorexia (51 patients, 84%), chills (50 patients, 82%), and fever/feeling feverish (49 patients, 80%). At baseline, 61% had decreased or absent sense of smell and 59% had decreased or absent sense of taste. Overall, 29 patients (48%) reported at least one severe symptom at baseline.
Table 2Baseline symptomatology
Upamostat 200 mg
Upamostat 400 mg
Number of symptoms per subject
11.0 (8.0 to 14.0)
10.0 (7.5 to 12.0)
9.0 (8.0 to 13.0)
Days from onset of symptoms to first dose
Number of symptoms reported
Fever or feeling feverish
Decreased or absent sense of smell
Decreased or absent sense of taste
Number (percent) of subjects with any severe symptoms
aSymptoms collected: chills or shivering, feeling hot or feverish, muscle or body aches, headaches, tiredness or feeling low of energy, chest pain, difficulty breathing, cough, abdominal pain, nausea, loss of appetite, diarrhea, vomiting, sore throat, stuffy or runny nose, change in sense of smell, change in sense of taste.
Viral typing was obtained on 24 patients (39%), eight in the early part of the study in late winter and spring, 2021, and the rest in the fall of 2021; 10 patients entered the study in the early part of the study and the balance in the fall of 2021. Of the specimens typed, 62% were delta variants. Assuming most untyped specimens, obtained in fall, 2021, were delta, the percentage of patients with the delta variant would be approximately 85% across all treatment groups.
Across all treatment groups, 54 patients (89%) took the full course of treatment. In total, 5 patients in the placebo group and one each in the upamostat group took less than the full course of therapy. Treatment was stopped at hospitalization for three patients in the placebo group and one in the upamostat 400 mg group who did not complete treatment.
Several parameters studied show the efficacy of upamostat against COVID-19, despite the small number of patients in each treatment group.
Table 3 shows the time to sustained recovery by the three definitions used. As shown in the table and in Figure 2a, upamostat was not effective in decreasing time to sustained recovery per protocol definition. Using a more stringent definition of recovery, the absence of all symptoms other than those present before the onset of COVID, the median time to sustained recovery in the placebo group was twice as long as for the original protocol definition, 38 rather than 19 days, as shown in Figure 2b. However, there was no substantial improvement in time to recovery in the upamostat groups as compared to the placebo.
Table 3Time to sustained recovery
Days to sustained recovery, median (interquartile)
Severe symptoms: time until no severe symptoms present.
All analyses performed on mITT population: placebo: 20 patients total; 10 with severe symptoms; upamostat 200 mg: 20 patients total, 8 with severe symptoms; upamostat 400 mg: 21 patients total, 11 with severe symptoms.
Definitions of sustained recovery: recovery as defined below with no new or recurrent symptoms for at least 14 days or until the last questionnaire is completed, whichever came first.
a Protocol: the resolution of all symptoms except those specified in the protocol, as described in text.
b All symptoms: the resolution of all symptoms except for preexisting symptoms present as mild.
c Severe symptoms: time until no severe symptoms present.
The overall incidence of new symptoms of any grade was similar across treatment groups, but on-study development of new severe symptoms was substantially lower in the active treatment groups as compared to the placebo group, as shown in Figure 3. The incidence of any new severe symptom was 20% in the placebo group compared to 2.4% in the upamostat groups combined (nominal P = 0.036, Fisher's exact test). No patient in the upamostat 400 mg group developed a new severe symptom in the study, nor did any patient in either active treatment group develop severe gastrointestinal or respiratory signs or symptoms in the study. New severe symptoms experienced by patients in the placebo group were (n = 1 except where otherwise indicated): abdominal pain, nausea, COVID-19 pneumonia (n = 2), decreased appetite, acute respiratory insufficiency, chest pain (n = 2), cough, dyspnea, hypoxia (n = 2), and oropharyngeal pain. The only new severe symptom experienced by an upamostat recipient was severe anorexia in one patient in the upamostat 200 mg group.
In the subgroup of patients with severe baseline symptoms, the incidences of new severe symptoms were 30% (3/10) in the placebo group, 12% (1/8) in the upamostat 200 mg group, and 0% (0/11) in the upamostat 400 mg group.
In a post hoc analysis of time to resolution of severe symptoms, there was a substantial difference favoring the upamostat groups, as shown in Table 3 and Figure 4: median of 8 days to the sustained resolution of severe symptoms in the placebo group compared to 4 and 3 in the upamostat 200 and upamostat 400 mg groups, respectively.
The incidence of hospitalization paralleled that of the development of new severe symptoms in the study. Overall, 3 patients in the placebo group (15%) were hospitalized, all for worsening respiratory COVID-19 symptoms, on study days 3, 4, and 6. No patient in the upamostat group was hospitalized for COVID-19. One patient in the upamostat 400 mg group was hospitalized for acute alcohol intoxication, with a very high blood alcohol level on admission. This was deemed by the investigator, prior to unblinding, as related neither to COVID-19 nor to study medication but rather represented the recurrence of a chronic condition. Thus, the incidence of hospitalization for COVID-19 was 15% in the placebo group as compared to 0% in the upamostat groups combined (nominal P = 0.032, Fisher's exact test). Characteristics of the hospitalized patients are shown in Table 4.
As shown in Figure 5, mean d-dimer levels increased 1.7% over time in the placebo group but decreased in the upamostat groups, with decreases over the course of the study of 38% and 48% in the upamostat 200 and upamostat 400 mg groups, respectively. In the upamostat 200 mg group, the mean d-dimer level at day 29 was markedly affected by one aberrantly high value; values for that patient were below the limit of detection on subsequent evaluations.
No differences among treatment groups were noted for C-reactive protein or lymphocyte counts.
Due to the way viral load data were reported, with titers over 25,000 copies/µl reported as >25,000 copies/µl, we were unable to calculate mean viral titers. There was a small difference among treatment groups in the proportion of patients who were PCR negative at day 8: 41%, 47%, and 53% in the placebo, upamostat 200 mg, and upamostat 400 mg groups. At subsequent time points, differences between active and placebo were minimal. We did not obtain viral titers between baseline and day 8.
Both upamostat dose levels were well tolerated. Most patients developed adverse events: 85% in the placebo group and 95% in each upamostat group. Adverse events other than laboratory abnormalities were experienced by 30% of the placebo group, 25% of the upamostat 200 mg groups, and 29% of upamostat 400 mg patients.
The most commonly involved system organ classes (SOCs) across treatment groups (other than investigations) were infections and infestations (n = 6), nervous system disorders (n = 4), and gastrointestinal and skin disorders (n = 3 each). Most adverse events other than those in the SOC investigations were experienced by only one patient, and none by more than two patients. Those events experienced by two patients each were headaches unrelated to COVID-19 (both upamostat 200 mg patients, both mild), hypertension (one placebo, one upamostat 200 mg patient; both mild), rash (both upamostat 400 mg patients, one mild, one moderate), and sinusitis (both placebo patients, one mild, one moderate). Only one adverse event, a mild skin rash lasting one week in a patient in the 400 mg group, was felt by an investigator to be associated with the study medication. No patient discontinued treatment because of an adverse event.
All clinical adverse events were mild or moderate in severity.
Laboratory abnormalities classified as adverse events were noted in 85% of placebo patients, 90% of patients in the upamostat 200 mg group, and 95% of patients in the upamostat 400 mg group. Supplemental Table 1 shows the incidence of each laboratory adverse event by treatment group. The most common laboratory abnormalities across treatment groups were increased international normalized ratio (INR) (24 patients, 39%), increased partial thromboplastin time (PTT) (22 patients, 36%); increased d-dimer (19 patients, 31%), and increased chloride and decreased total protein (14 patients each, 23%). INR and/or PTT increased in the study in 25%, 50%, and 62% of patients in the placebo, upamostat 200 mg, and upamostat 400 mg groups, respectively. Platelet increases were noted in five (25%), two (10%), and one (5%) placebo, upamostat 200, and upamostat 400 mg patients, respectively. Other laboratory abnormalities did not exhibit a dose-response relationship. No clinical bleeding events were noted in the study.
One patient in the placebo group, two in the upamostat 200 mg group, and three in the upamostat 400 mg group developed grade 3 or 4 laboratory abnormalities, none of which had clinical sequelae. These included the placebo group: grade 3 lymphocyte count decreased in one patient; upamostat 200 mg group: grade 4 potassium increased and grade 3 INR increased (one patient), grade 3 PTT prolonged (one patient); upamostat 400 mg group: grade 3 potassium increased, neutrophil count decreased, PTT prolonged (one patient each). All grade 3 or 4 laboratory abnormalities were noted at only one time point, other than for one patient in the upamostat 400 mg group, who had no baseline coagulation profile and persistently elevated PTT values at all times on study.
No effects on liver or renal function were noted in the study.
We conducted a pilot outpatient study of upamostat, a serine protease inhibitor targeting host cell enzymes, in COVID-19 patients not requiring hospitalization but who were experiencing at least two moderate or severe symptoms at baseline. The study was open to adults regardless of age, prior vaccination, or the presence of coexisting medical conditions considered to put them at higher risk of hospitalization or death. Participants could receive monoclonal antibody infusions for COVID-19 in addition to study medication.
Upamostat is a prodrug of WX-UK1, originally expected to act as a thrombin antagonist [
The primary objective of this study, the determination of the safety and tolerability of upamostat in patients with COVID-19, was met: both dose levels were very well tolerated. There was no effect on liver, renal or hematologic parameters. Although mean and median INR and PTT were unchanged among treatment groups over the course of treatment, minor increases in each parameter were more common in upamostat-treated patients than in the placebo group. No bleeding events were noted in any patient. Mean d-dimer levels remained constant over the course of the study in the placebo group but decreased by 38% and 48% in the upamostat 200 mg and 400 mg groups, respectively. Taken together, these data suggest a modest anticoagulant effect of treatment, a potentially beneficial property in patients with COVID-19.
The incidence of hospitalization in the placebo group in this study, 15%, was more than twice that noted in recently published studies of monoclonal antibodies, nirmatrelvir, and remdesivir in outpatients with COVID-19 [
]. Although the number of patients in our study is small, this suggests that by selecting patients with significant symptomatology regardless of risk category or prior vaccination, we were able to accrue a group of patients with a substantial risk of hospitalization.
Several parameters suggested that upamostat is effective in the treatment of COVID-19. The median time to resolution of severe symptoms among upamostat recipients was less than half that in placebo patients. Similarly, the decrease in new severe symptoms in upamostat recipients as compared to placebo recipients was quite marked. The absence of hospitalizations for COVID-19 among upamostat-treated patients paralleled the decrease in severe symptoms and the absence of new severe respiratory symptoms among these patients, further suggesting that this was not just a random finding but rather a treatment effect. The decrease in d-dimer levels in the upamostat groups as compared to the stable levels in the placebo group strongly suggested a pharmacologic effect of treatment. This effect may be complementary to the increased incidence of mild elevations in INR and PTT in upamostat-treated patients as compared to controls.
Limitations of the study are the small group sizes and the preponderance of patients with the SARS-CoV-2 delta variant. The efficacy evaluations, intended to aid in the finalization of the design of a larger, pivotal study, are understood to be preliminary.
In summary, upamostat was well tolerated. Entry criteria for the study resulted in a placebo population with a hospitalization rate higher than that in several other studies in which symptom severity was not considered, providing a basis for patient selection in future studies. Biologic effects of the compound, dose-dependent increased INR and PTT, and decreased mean d-dimer levels, were observed in our study. Upamostat-treated patients had a more rapid resolution of severe symptoms and a lower incidence of new severe symptoms as compared to placebo recipients; no upamostat patients were hospitalized due to COVID-19. These data strongly support a larger, pivotal trial of upamostat for the treatment of symptomatic outpatients with COVID-19.
The study was financed solely by the sponsor, RedHill Biopharma, Ltd.
The protocol (NCT04723537) was approved by a central independent review board and, in some cases, individual institutional review boards. It was allowed to proceed by the U.S. Food and Drug Administration and the South African Health Products Regulatory Authority (SAHPRA).
Declaration of competing interest
Drs. Plasse, Abramson, and Fathi, and Ms. Fehrmann were contractors to RedHill Biopharma, Ltd, the sponsor of the study. Drs. Delgado, Potts, and McComsey were investigators whose organizations or institutions were paid by the sponsor to conduct the study.
The authors would like to thank all the investigators who participated in the study, Belkis Delgado, MD, South Florida Research, Miami FL; Chrisette Dharma, Southwest Family Medical Associates, Dallas TX; Grace A McComsey, MD, University Hospitals of Cleveland and Case Western Reserve University, Cleveland OH; Joseph Miller, MD, Henry Ford Health Systems, Detroit, MI; Dr. Larisha Pillay-Ramaya, Global Clinical Trials, Pretoria, South Africa; Yanely Pineiro MD, Angels Clinical Research, Miami, FL; Jeffrey Potts, MD, Great Lakes Research Group, Bay City, MI; research coordinators at several of the sites, Melinda Caraballo, Kyle Cunningham, Caren Kolb, Lisbelle Revoredo, Heather Tribaut, Terri Vittitow, and all the staff members at Obvio Health and FHI Clinical, the contract research organizations which managed the study, and to all the patients and caregivers who participated.