Novel knee osteoarthritis drugs target pain, joint space narrowing

MADRID – Two independently conducted, randomized, phase 2 trials of novel agents for moderate to severe knee osteoarthritis have produced promising results, as reported at the European Congress of Rheumatology.

In the 24-week, dose-ranging TRIUMPH trial involving 175 patients, treatment with the synthetic trans-capsaicin CNTX-4975 was associated with improvements in several clinical parameters, such as pain when walking, knee stiffness, and physical function, as well as being generally well tolerated.

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These findings suggest that both could be future alternatives to using nonsteroidal anti-inflammatory drugs (NSAIDs), injected corticosteroids, and opioid analgesics, which are currently used to help manage knee OA.

Synthetic trans-capsaicin CNTX-4975

“Few effective pharmacologic therapies are available to manage the chronic pain of OA,” said Randall Stevens, MD, chief medical officer for Centrexion Therapeutics (Boston), the company developing CNTX-4975. Both NSAIDs and corticosteroids are associated with substantial toxicities, he argued, and opioid analgesics are not ideal to use long term because of the risk of side effects and addiction.

CNTX-4975 is a nonopioid analgesic that acts directly on the pain fibers in the knee, Dr. Stevens explained. Specifically, after a single injection, it targets the capsaicin receptor (transient receptor potential vanilloid 1, TRPV1) to inactivate only the local fibers transmitting pain signals to the brain. It does not affect other sensory fibers involved in sensation to touch or pressure, he said.

The aim of the phase 2b TRIUMPH trial was to examine the efficacy and safety of two doses (0.5 mg and 1.0 mg) of the synthetic trans-capsaicin versus placebo in patients with chronic, stable, moderate to severe knee OA who had been experiencing knee pain for at least 2 months or more. For inclusion, patients could be aged between 45 and 80 years, have a body mass index of up to 45 kg/m², and had to have failed treatment or not be able to tolerate oral or intra-articular analgesics. Patients who had undergone recent knee surgery were excluded.

The primary endpoint was the change in pain with walking from baseline to week 12 measured as the area under the curve (AUC) for daily Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) A1 score. Significant improvements were seen, with a least squares mean difference (LSMD) of –0.8 (P = .07) and –1.6 (P less than .0001) with the 0.5 mg and 1.0 mg doses of CNTX-4975, respectively, versus placebo.

The effects of CNTX-4975 were maintained to 24 weeks, Dr. Stevens reported, with significant improvements in pain with walking, comparing the 1.0-mg dose with placebo (LSMD, –1.35; P = .0002).

“These are the largest effect sizes I’ve seen with osteoarthritis knee pain,” Dr. Stevens said.

The investigators saw improvements in other efficacy endpoints, such as the weekly pain with walking (WOMAC A1) score and the change in weekly average joint stiffness (WOMAC B subscale, LSMD: −2.5; P = .0013) and physical function (WOMAC C subscale, LSMD: −18.3; P = .004) versus placebo at week 12. Numerically greater improvements occurred at week 24.

A similar percentage of patients experienced any treatment-emergent adverse events in the 1.0-mg (29.6%) CNTX-4975 treated and placebo groups (30%). Although a higher percentage of patients given the lower CNTX-4975 dose reported side effects (47.1%), most were mild to moderate and were considered unrelated to study treatment. Arthralgia was the most common side effect with CNTX-4975 1.0 mg versus placebo (7% vs. 5.7%).

“With these findings, we are moving in to phase 3 with the 1.0-mg dose,” Dr. Stevens said.

Wnt inhibitor SM04690

Promising data from the phase 2 trial of the Wnt inhibitor SM04690 also suggest that it, too, could soon be heading into phase 3 trials.

Several early clinical studies have been completed already, noted Yusuf Yazici, MD, chief medical officer of Samumed (San Diego), the California-based company that is developing SMO4690.

SM04690 is a small molecule inhibitor of the Wnt pathway, which is involved in increased bone formation and turnover, he explained. The hypothesis is that by blocking this pathway, the joint can be protected and cartilage could perhaps be regenerated.

Dr. Yazici presented radiographic outcomes at 26 weeks from a 52-week trial that “demonstrated SM04690 treatment maintained or increased medial joint space width compared to placebo.” This is important, as “joint space narrowing is indicative of OA progression and is predictive of knee surgery,” and radiographic progression remains a “gold standard” for assessing potential disease modification in OA, said Dr. Yazici, who is also clinical associate professor and director of the Seligman Center for Advanced Therapeutics at New York University.

In the phase 2 trial he presented, three doses of SM04690 (0.03 mg, 0.07 mg, and 0.23 mg), given as one 2-mL intra-articular injection into a single target knee, were tested and compared against placebo. The target knee was the knee designated as causing the patient the most pain, according to the study investigator.

Radiographs of both knees were taken at the start of treatment, at week 26, and again at week 52, with the change in medial joint space width analyzed. Clinical assessments included changes in WOMAC total, function, and pain subscale scores, and patients’ and physicians’ global assessments.

A total of 455 subjects, mean age 60 years, were randomized into the trial.

Considering all patients, the mean increase in medial joint space width from baseline to 26-week assessment versus placebo was –0.07 mm in the SM04690 0.03-mg group, –0.16 mm in the SM04690 0.07-mg group, and –0.03 mm in the SM04690 0.23-mg group.

An improvement in mean medial joint space narrowing was observed in 47.6% with SM04690 0.03 mg, 40.5% with 0.07 mg, 39.6% with 0.23 mg, and 30.5% with placebo. There was no change in a respective 7.6%, 9%, 17.8%, and 11.4%, and narrowing in the remainder (44.8%, 50.5%, 42,6%, and 58.1%) in this intent-to-treat population.

The investigators conducted prespecified subanalyses in a “unilateral symptomatic” population of 164 patients, and this showed slightly better results, with a higher probability of improved medial joint space width with SM04690 than with placebo (odds ratio, 5.2; 95% confidence interval, 2.1-12.8; P less than .001).

However, an important limitation of the study is that it was not formerly powered to look at radiographic progression, Dr. Yazici said. Nevertheless, radiographs were centrally read and high intra- and inter-observer reproducibility was observed.

Safety and clinical outcomes from the trial, which were reported separately in a poster at the meeting, showed no undue concerns and clinically meaningful improvements in both patients’ and physicians’ global assessments of pain with SM04690 versus placebo.

“Radiographic and clinical outcomes from this 26-week interim analysis of a 52-week trial suggest that SM04690 has potential as a disease-modifying osteoarthritis drug (DMOAD) for knee OA,” Dr. Yazici concluded.

The studies were supported by Samumed and by Centrexion Therapeutics. Dr. Yazici is an employee and shareholder of Samumed. Dr. Stevens is an employee and shareholder of Centrexion Therapeutics.