In patients with newly diagnosed or relapsing pemphigus vulgaris, an update of the phase 2 BELIEVE study with the Bruton tyrosine kinase (BTK) inhibitor rilzabrutinib has raised hopes that the ongoing phase 3 trial will confirm that this drug is a breakthrough therapy, according to an investigator who presented the data at the American Academy of Dermatology Virtual Meeting Experience.
Dr. Dedee F. Murrell
Among the highlights of the phase 2 data presented during a late-breaking research session was that a substantial minority of patients achieved a complete response within 12 weeks of starting treatment with rilzabrutinib. Treatment was associated with mostly mild and transient adverse events, according to Dedee F. Murrell, MD, director of dermatology, St. George Hospital, University of New South Wales, Sydney.
Many of the phase 2 results have been presented previously and the phase 3 trial, called PEGASUS, has now completed enrollment.
Focusing on part A of the BELIEVE study, Dr. Murrell reported that about one-third of the 27 patients enrolled had newly diagnosed pemphigus. The remaining patients had relapsing disease after a mean 8.9 years after diagnosis. The disease was judged moderate to severe in 59%. The daily oral dose of rilzabrutinib ranged from 400 mg to 600 mg twice daily.
For the primary endpoint of control of disease activity (CDA), meaning no formation of new lesions with diminishing activity of existing lesions, 52% had responded by week 4 and 70% had responded by week 12, which was the end of active treatment. Responses at both time points were comparable among patients with newly diagnosed disease (56% at week 4 and 67% at week 12) relapsing disease (50% and 72%, respectively), moderate disease severity at baseline (55% and 64%, respectively) and more severe disease (50% and 75%, respectively), Dr. Murrell noted.
“A complete response was achieved by 22% of patients at week 4 and nearly 30% by the end of the study,” she said.
These response rates were reflected in the Pemphigus Disease Area Index (PDAI) and the Autoimmune Bullous Disease Quality of Life (ABQOL) Score. From a baseline score of 20, the PDAI fell to 10 at 4 weeks and then to 6 at 12 weeks in the newly diagnosed cohort. In the relapsing cohort, the score fell from a baseline of 18 to 13 at week 4 and then to 7 at week 12.
“The improvement corresponded to a reduction in steroid doses,” Dr. Murrell reported. By the end of the study, the mean daily dose of corticosteroids fell to 10 mg from a baseline of 20 mg. In a 12-week follow-up, corticosteroid doses rose slowly and did not reach baseline levels until about eight weeks after rilzabrutinib was discontinued.
The ABQOL scores fell most rapidly in the newly diagnosed cohort. By week 12, there was about a 6.6-point reduction. In the relapsing group, the score fell by 3.7 points from a similar baseline level. Both reductions are considered highly clinically meaningful, according to Dr. Murrell. At the end of the 12 weeks of follow-up after the drug was discontinued, ABQOL scores had increased but remained below the baseline.
Nausea was reported by 15% of patients, making it the most commonly reported adverse event. All cases were grade 1 severity. Three patients had grade 2 abdominal pain. The only grade 3 event in this series was a case of cellulitis in a patient who had developed steroid-induced diabetes mellitus. With treatment, the cellulitis resolved, and the patient completed the study.
Data from part B of the BELIEVE study, which was similarly designed and enrolled 15 patients with newly diagnosed or relapsing pemphigus vulgaris, was not updated by Dr. Murrell at the meeting, but these data have been presented before and showed similar results, including achievement of CDA in the majority of patients accompanied by a reduction in corticosteroid doses.
“In summary, rilzabrutinib produced a rapid clinical effect with an overall favorable benefit-to-risk profile,” said Dr. Murrell, who reiterated that the improvement in quality of life underscored meaningful activity.
Three BTK inhibitors, ibrutinib, acalabrutinib, and zanubrutinib, have been approved for the treatment of hematologic malignancies. These have also been well tolerated. The shared mechanism of action of these drugs is a reduction in B-cell activity achieved by blocking BTK enzyme signaling. The autoimmune activity of pemphigus vulgaris is at least partially mediated by B cells.
“Rilzabrutinib is the first BTK inhibitor tried in pemphigus,” said Dr. Murrell, who cited evidence that pemphigus is at least partially mediated by B-cell activity. The proof-of-concept phase 2 study has increased expectations for the phase 3 PEGASUS trial, which is scheduled for completion in about 1 year, she said.
Dr. Murrell reports financial relationship with multiple pharmaceutical companies, including Principia Biopharma, a Sanofi subsidiary that is developing rilzabrutinib and sponsored the BELIEVE trial.