Moving into Phase III trials, our lead drug targets chronic pain and inflammation arising from a wide range of conditions ...

ATB-346 is a novel anti-inflammatory drug that releases hydrogen sulfide. It has shown unequivocal superiority to naproxen in gastrointestinal safety in a large Phase IIB clinical trial. Recently, it demonstrated efficacy at a high degree of statistical significance, also in a large Phase IIB clinical trial. At the two-week mark, ATB-346 exceeded the efficacy of the average NSAID at 12+ weeks.1,2,3  These strong safety and efficacy data reflect the results of earlier clinical and preclinical studies.

Beginning in the first half of 2021, we anticipate conducting an adaptive Phase II/III pivotal trial to set the minimum effective dose—this study will also constitute one of the efficacy trials in ATB-346’s Phase III program.

Addressing a Clear Unmet Medical Need

As the standard first-line treatment for osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, and general pain reduction, naproxen and other NSAIDs are effective, but can induce ulceration and bleeding of the digestive tract, with much higher incidence in patients with co-morbidities and in the elderly. In these patients, COX-2 selective NSAIDs (e.g., celecoxib) offer only a modest improvement in terms of gastrointestinal safety (especially when co-administered with aspirin), but their use is associated with significant cardiovascular toxicity. 

Preclinical Studies

ATB-346 demonstrates significant safety advantage

ATB-346 remained gastrointestinal-safe when given to animals with compromised mucosal defence or pre-existing ulcers—situations in which selective COX-2 inhibitors cause ulcers and bleeding in humans. It also remained safe when co-administered with aspirin, which markedly elevates the risk of damage when taken to address the cardiovascular risks of COX-2 inhibitors. ATB-346 also did not elevate blood pressure when administered acutely to hypertensive rats, in contrast to a significant hypertensive effect with naproxen.

Human Trials

Profound Phase IIB gastrointestinal safety results

In 2018, Antibe completed a Phase IIB gastrointestinal safety trial of ATB-346 in 244 healthy volunteers. The study was designed to demonstrate the superiority of ATB-346 compared to naproxen, the most prescribed NSAID in the US. One group was treated for fourteen days with ATB-346 (250 mg once daily), while the other group was treated for the same period with the standard prescription dose of naproxen (500 mg twice daily, totaling 1,000 mg per day). The primary endpoint for the study was the incidence of gastric or duodenal ulcers of at least 3 mm diameter with unequivocal depth, considered the “gold standard” in assessing the gastrointestinal safety of NSAIDs. ATB-346 successfully met the primary endpoint in the study.

Subjects on ATB-346 exhibited an ulceration rate of 2.5% (3/118) versus an ulceration rate of 42.1% (53/126) for subjects on naproxen at the end of the treatment period, with a very high degree of statistical significance (p<0.0001). ATB-346 was also well tolerated.


Strong Phase IIB efficacy results

In June 2020, Antibe reported positive top-line results from its Phase IIB efficacy study designed to validate the efficacy of ATB-346 in reducing pain. This was a large study, involving 39 sites and 381 participants with osteoarthritis of the knee. Subjects were randomized to placebo or one of three doses of ATB-346 administered once daily: 150 mg, 200 mg or 250 mg. The primary endpoint was the change in the WOMAC pain subscale score (the standard in clinical pain assessment) over a fourteen-day treatment period. As measured by their respective p-values, the WOMAC results showed a high degree of statistical significance, thereby demonstrating substantial efficacy in pain reduction.

Complementing this pain efficacy, the WOMAC results for the therapeutic benefits of stiffness and difficulty in performing daily activities (DPDA) showed efficacy at a very high degree of statistical significance.


The chart above depicts the strong efficacy of ATB-346: The vertical bars depict the improvement in WOMAC pain subscale score delivered by each of three doses on ATB-346 after two weeks of administration. (Further information about WOMAC scores is available in our Investor Presentation.) The horizontal dotted-line indicates the average efficacy of NSAIDs after twelve (or more) weeks, as set out in Comparative Pain Reduction of Oral Non-steroidal Anti-inflammatory Drugs and Opioids for Knee Osteoarthritis: Systematic Analytic Review; S.R. Smith et al, 2016.

This Phase IIB study replicates the success of an earlier Phase IIA open label, efficacy study that concluded in August 2016. The primary endpoint of that study was the clinical assessment of pain over the ten-day course of treatment at 250 mg once daily (n = 12). This produced a WOMAC pain score reduction on day 10, at a very high level of statistical significance in comparison to baseline pain (p<0.001).

1. Post Hoc analysis. Results do not necessarily predict future efficacy results.
2. WOMAC pain subscale scores based on 500-point Likert scale; figures normalized to 100mm scale; shown with 95% confidence interval.
3. NSAID study data drawn from Comparative Pain Reduction of Oral Non-steroidal Anti-inflammatory Drugs and Opioids for Knee Osteoarthritis: Systematic Analytic Review; Smith; S.R., Deshpande, B.R., Collins, J.E., Katz, J.N., Losina, E.; Osteoarthritis and Cartilage; 24: 962-972, 2016.
4. Adjusted mean change from baseline computed with assumption that subjects who withdrew early due to insufficient efficacy had zero (0) change from baseline WOMAC pain subscale score.


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