Investigational Drugs Look Promising for Osteoarthritis Pain

WASHINGTON — Investigational treatments aimed specifically at reducing pain in knee osteoarthritis (OA) are moving forward in parallel with disease-modifying approaches.

“We still have very few treatments for the pain of osteoarthritis…It worries me that people think the only way forward is structure modification. I think while we’re waiting for some drugs to be structure modifying, we still need more pain relief. About 70% of people can’t tolerate or shouldn’t be on a [nonsteroidal anti-inflammatory drug], and that leaves a large number of people with pain,” Philip Conaghan, MBBS, PhD, Chair of Musculoskeletal Medicine at the University of Leeds, Leeds, England, told Medscape Medical News.

At the American College of Rheumatology (ACR) 2024 Annual Meeting, Conaghan, who is also honorary consultant rheumatologist for the Leeds Teaching Hospitals NHS Trust, presented new data for two novel approaches, both targeting peripheral nociceptive pain signaling.

In a late-breaking poster, he presented phase 2 trial data on RTX-GRT7039 (resiniferatoxin [RTX]), an agonist of the transient receptor potential vanilloid 1 that is a driver of OA pain. The trial investigated the efficacy and safety of a single intra-articular injection of RTX-GRT7039 in people with knee OA.

And separately, in a late-breaking oral abstract session, Conaghan presented phase 2 trial safety and efficacy data for another investigational agent called LEVI-04, a first-in-class neurotrophin receptor fusion protein (p75NTR-Fc) that supplements the endogenous protein and provides analgesia via inhibition of NT-3 activity.

“I think both have potential to provide good pain relief, through slightly different mechanisms,” Conaghan told Medscape Medical News.

Asked to comment, session moderator Gregory C. Gardner, MD, emeritus professor in the Division of Rheumatology at the University of Washington, Seattle, told Medscape Medical News “I think the results are really exciting terms of the ability to control pain to a significant degree in patients with osteoarthritis.”

However, Gardner also said, “The molecules can be very expensive…so who do we give them to? Will insurance companies pay for this simply for OA pain? They improve function…So clearly, [they] will be a boon to treating osteoarthritis, but do we give them to people with only more advanced forms of osteoarthritis or earlier on?”

Moreover, Gardner said, “One of my concerns about treating osteoarthritis is I don’t want to do too good of a job treating pain in somebody who has a biomechanically abnormal joint…You’ve got a knee that’s worn out some of the cartilage, and now you feel like you can go out and play soccer again. That’s not a good thing. That joint will wear out very quickly, even though it doesn’t feel pain.”

Another OA expert, Matlock Jeffries, MD, director of the Arthritis Research Unit at the Oklahoma Medical Research Foundation, Oklahoma City, told Medscape Medical News, “I think we don’t focus nearly enough on pain, and that’s [partly] because the [US Food and Drug Administration] has defined endpoints for knee OA trials that are radiographic…Patients do not care what their joint space narrowing is. They care what their pain is. And joint space changes and pain do not correlate in knee OA…About 20% or 30% of patients who have completely normal x-rays have a lot of pain…I hope that we’ll have some new OA pain therapeutics in the future because that’s what patients actually care about.”

But Jeffries noted that it will be very important to ensure that these agents don’t produce significant side effects, as had been seen previously in several large industry-sponsored trials of drugs targeting nerve growth factors.

“The big concern that we have in the field…is that the nerve growth factor antibody trials were all stopped because there was a low but persistent risk of rapidly progressive OA in a small percent of patients. I think one of the questions in the field is whether targeting other things having to do with OA pain is going to result in similar bad outcomes. I think the answer is probably not, but that’s one thing that people do worry about, and they never really figured out why the [rapidly progressive OA] was happening.”

‘Potential to Provide Meaningful and Sustained Analgesia’

The phase 2 trial of RTX-GRT7039, funded by manufacturer Grünenthal GmbH, enrolled 40 patients with a baseline visual analog pain score (VAS) of > 40 mm on motion for average joint pain in the target knee over the past 2 days with or without analgesic medication and Kellgren-Lawrence grades 2-4.

They were randomized to receive a single intra-articular injection of 2 mg or 4 mg RTX-GRT7039 within 1 minute after receiving 5 mL ropivacaine (0.5%) or 4 mg or 8 mg RTX-GRT7039 administered 15 minutes after 5 mL ropivacaine pretreatment, or equivalent placebo treatments plus ropivacaine.

Plasma samples were collected for up to 2 hours, and VAS pain scores were collected for up to 3 hours postinjection.

Reductions in VAS scores from baseline in the treated knee were seen in all RTX treatment groups as early as day 8 postinjection and were maintained up to 6 months, while no reductions in VAS pain on motion scores were seen in the placebo group.

At 3 months, the absolute baseline-adjusted reductions in VAS scores were similar for RTX 2 mg (−39.75), RTX 4 mg (−40.20), and RTX 8 mg (−30.25), while the reduction in the placebo group was just −8.50. At 6 months, the mean absolute reduction in VAS score was numerically greater in the RTX 2-mg (−46.49), RTX 4-mg (−43.40), and RTX 8-mg (−38.60) groups vs the group that received RTX 4 mg within 1 minute after receiving ropivacaine (−22.00).

At both 3 and 6 months, a higher proportion of patients receiving any dose of RTX-GRT7039 achieved ≥ 50% and ≥ 70% reduction in pain on motion, compared with those who received placebo. All RTX-GRT7039 treatment groups reported a greater improvement in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) total score than the placebo group at both 3 and 6 months.

Rates of treatment-emergent adverse events were similar between the RTX groups (85.7%-90.9%) and placebo (85.7%) and slightly lower in the group that received RTX 4 mg within 1 minute of receiving ropivacaine (60.0%).

There was a trend toward greater procedural/injection site pain in the RTX treatment groups, compared with placebo, most commonly arthralgia (37.5%), headache (17.5%), and back pain (10%). This tended to peak around 0.5 hours postinjection and resolve by 1.5-3.0 hours.

No treatment-related serious adverse events occurred, and no treatment-emergent adverse events led to discontinuation or death.

“This early-phase trial indicates that RTX-GRT7039 has the potential to provide meaningful and sustained analgesia for patients with knee OA pain,” Conaghan and colleagues wrote in their poster.

The drug is now being evaluated in three phase 3 trials (NCT05248386, NCT05449132, and NCT05377489).

LEVI-04: Modulation of NT-3 Appears to Work Safely

LEVI-04 was evaluated in a phase 2, 20-week, 13-center (Europe and Hong Kong) randomized, double-blind, placebo-controlled trial in 518 people with knee OA who had WOMAC pain subscale scores ≥ 20, mean average daily pain numeric rating scale score of 4-9, and radiographic Kellgren-Lawrence grade ≥ 2.

They were randomized to a total of five infusions of placebo or 0.3 mg/kg, 0.1 mg/kg, or 2 mg/kg LEVI-04 from baseline through week 16, with safety follow-up to week 30.

The primary endpoint, change in WOMAC pain from baseline to weeks 5 and 17, was met for all three doses. At 17 weeks, those were −2.79, −2.89, and −3.08 for 0.3 mg, 1.0 mg, and 2 mg, respectively, vs −2.28 for placebo (all P

Secondary endpoints, including WOMAC physical function, WOMAC stiffness, and Patient Global Assessment, and > 50% pain responders, were also all met at weeks 5 and 17. More than 50% of the LEVI-04–treated patients reported ≥ 50% reduction in pain, and > 25% reported ≥ 75% reduction at weeks 5 and 17.

“So, this modulation of NT-3 is working,” Conaghan commented.

There were no increased incidences of severe adverse events, treatment-emergent adverse events, or joint pathologies, including rapidly progressive OA, compared with placebo.

There were more paresthesias reported with the active drug, 2-4 vs 1 with placebo. “That says to me that the drug is working and that it’s having an effect on peripheral nerves, but luckily these were all mild or moderate and didn’t lead to any study withdrawal or discontinuation,” Conaghan said.

Phase 3 trials are in the planning stages, he noted.

Other Approaches to Treating OA Pain

Other approaches to treating OA pain have included methotrexate, for which Conaghan was also a co-author on one paper that came out earlier in 2024. “This presumably works by treating inflammation, but it’s not clear if that is within-joint inflammation or systemic inflammation,” he told Medscape Medical News.

Another approach, using the weight loss drug semaglutide, was presented in April 2024 at the World Congress on Osteoarthritis 2024 Annual Meeting and published in October 2024 in The New England Journal of Medicine.

The trial involving RTX-GRT7039 was funded by Grünenthal GmbH, and some study co-authors are employees of the company. The trial involving LEVI-04 was funded by Levicept, and some study co-authors are employees of the company. Conaghan is a consultant and/or speaker for Eli Lilly and Company, Eupraxia Pharmaceuticals, Formation Bio, Galapagos, Genascence, GlaxoSmithKline, Grünenthal, Janssen Pharmaceuticals, Kolon TissueGene, Levicept, Medipost, Moebius, Novartis, Pacira, Sandoz, Stryker Corporation, and Takeda. Gardner and Jeffries had no disclosures.

Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape Medical News, with other work appearing in the Washington Post, NPR’s Shots blog, and Diatribe. She is on X @MiriamETucker.