by about 30%, according to early results of a clinical trial scheduled to be presented at the American Academy of Allergy, Asthma, and Immunology annual meeting. The AAAAI canceled the meeting and provided abstracts and access to presenters for press coverage.
Dr. Cem Akin
“This correlates with reduction from very severe to moderate or from moderate to mild category, and all the reductions in symptoms were statistically significant,” Cem Akin, MD, of the University of Michigan, Ann Arbor, said in an interview. He reported on part 1 of the phase 2 PIONEER trial of the kinase inhibitor avapritinib, described as a potent and highly selective inhibitor of the KIT D816V mutation that affects 90% of patients with systemic mastocytosis.
Currently, Dr. Akin noted, patients with indolent or smoldering systemic mastocytosis must rely on over-the-counter antihistamines used for seasonal allergies. “These patients use antihistamines in higher doses because mastocytosis patients have higher counts of mast cells that release histamines that cause a variety of symptoms,” he said. Symptoms, which can occur suddenly, include flushing and reactions that resemble allergic or anaphylactic reactions.
The purpose of the part 1 study was to evaluate three different dosing levels of avapritinib vs. placebo: 25, 50, and 100 mg. Ten patients were in each dosing group and nine were in the placebo group. The primary outcome was reduction in total symptom scores at 16 weeks as measured by the Indolent SM Symptom Assessment Form. “All three dose groups showed significant reductions in total symptom scores as well as specific symptoms that were most bothersome to the patient, whether skin symptoms or GI or neurocognitive symptoms,” Dr. Akin said. “All three doses were effective; the average reduction was about 30% compared to baseline.” Specifically, 25-mg dosing showed an average 30% reduction, 50-mg dosing showed an average 19% reduction, and 100-mg dosing showed an average 35% reduction.
The researchers determined that the 25-mg daily dose was the most effective and safest, with no patients on the dose reporting grade 3 adverse events, Dr. Akin said. In total 20% and 40% of the 50- and 100-mg dose groups, respectively, reported grade 3 AEs, according to study results.* The 25-mg daily dose will be evaluated in part 2 of the trial. The trial is estimated to enroll 112 total patients, according to the ClinicalTrials.gov filing. In part 3, patients who complete parts 1 or 2, including those initially randomized to placebo, may participate in a long-term open-label extension, receiving 25 mg avapritinib plus best supportive care.
“This is targeting a population whose symptoms are not controlled by antihistamines, based on a minimum total symptom score according to diaries they fill out, and they have to be on at least two different systemic medications – antihistamine or proton-pump inhibitor and leukotriene inhibitor – and they still have significant symptoms,” Dr. Akin said. He estimated that this describes about two-thirds of his patients with indolent or smoldering systematic mastocytosis.
“This is a disease that also takes a psychological toll,” he said. “This is a problem that starts in the bone marrow; it is similar to a hematological stem-cell disorder that affects the mast cell progenitor and it’s caused by a mutation that has not been particularly targeted until this drug,” he said. While most of these patients live with a benign mastocytosis their entire lives, the symptoms can be debilitating to the point where the disease disrupts and restricts social activities and comprises their quality of life, he said.
“This is a groundbreaking therapy that will change the way we think about mastocytosis treatment going forward,” Dr. Akin said. “It’s the first time we are actually targeting the underlying mutation that’s causing the disease, in terms of reducing directly that mutation as opposed to just treating the symptoms in indolent disease.”
Scheduled session moderator Anil Nanda, MD, of the Asthma and Allergy Center in Lewisville, Texas, said the findings are encouraging. “As a practicing allergist and immunologist in the community, it is very exciting to have a potential new treatment option for indolent or smoldering systemic mastocytosis,” he said via email. “Patients appreciate new options in therapy.”
Dr. Akin, the primary investigator, receives funding from and serves as a consultant for Blueprint Medicines, which sponsored the trial. He also disclosed a financial relationship with Novartis.
SOURCE: Akin C et al. AAAAI 2020, Presentation L5.
*Correction, 4/6/2020: An earlier version of this story misstated the percentage of grade 3 adverse events. In total 20% and 40% of the 50- and 100-mg dose groups, respectively, reported grade 3 adverse events.