BTK inhibitors
The first-in-class Bruton tyrosine kinase (BTK) inhibitor ibrutinib was the first and thus far only agent approved by the Food and Drug Administration for chronic GVHD. The approval was based on a single-arm, multicenter trial with 42 patients.
The ORR in this trial was 69%, consisting of 31% complete responses and 38% partial responses, with a duration of response longer than 10 months in slightly more than half of all patients. In all, 24% of patients had improvement of symptoms in two consecutive visits, and 29% continued on ibrutinib at the time of the primary analysis in 2017.
Based on these promising results, acalabrutinib, which is more potent and selective for BTK than ibrutinib, with no effect on either platelets or natural killer cells, is currently under investigation in a phase 2 trial in 50 patients at a dose of 100 mg orally twice daily.
JAK1/2 inhibition
The JAK1 inhibitor itacitinib failed to meet its primary ORR endpoint in the phase 3 GRAVITAS-301 study, according to a press release, but the manufacturer (Incyte) said that it is continuing its commitment to JAK inhibitors with ruxolitinib, which has shown activity against acute, steroid-refractory GVHD, and is being explored for prevention of chronic GVHD in the randomized, phase 3 REACH3 study.
The trial met its primary endpoint for a higher ORR at week 24 with ruxolitinib versus best available therapy, at 49.7% versus 25.6%, respectively, which translated into an odds ratio for response with the JAK inhibitor of 2.99 (P < .0001).
Selective T-cell expansion
Efavaleukin alfa is an IL-2-mutated protein (mutein), with a mutation in the IL-2RB-binding portion of IL-2 causing increased selectivity for regulatory T-cell expansion. It is bound to an IgG-Fc domain that is itself mutated, with reduced Fc receptor binding and IgG effector function to give it a longer half life. This agent is being studied in a phase 1/2 trial in a subcutaneous formulation delivered every 1 or 2 weeks to 68 patients.
Monocyte/macrophage depletion
Axatilimab is a high-affinity antibody targeting colony stimulating factor–1 receptor (CSF-1R) expressed on monocytes and macrophages. By blocking CSF-1R, it depletes circulation of nonclassical monocytes and prevents the differentiation and survival of M2 macrophages in tissue.
It is currently being investigated 30 patients in a phase 1/2 study in an intravenous formulation delivered over 30 minutes every 2-4 weeks.
Hedgehog pathway inhibition
There is evidence suggesting that hedgehog pathway inhibition can lessen fibrosis. Glasdegib (Daurismo) a potent selective oral inhibitor of the hedgehog signaling pathway, is approved for use with low-dose cytarabine for patients with newly diagnosed acute myeloid leukemia aged older than 75 years or have comorbidities precluding intensive chemotherapy.
This agent is associated with drug intolerance because of muscle spasms, dysgeusia, and alopecia, however.
The drug is currently in phase 1/2 at a dose of 50 mg orally per day in 20 patients.
ROCK2 inhibition
Belumosudil (formerly KD025) “appears to rebalance the immune system,” Dr. Lee said. Investigators think that the drug dampens an autoaggressive inflammatory response by selective inhibition of ROCK2.
This drug has been studied in a dose-escalation study and a phase 2 trial, in which 132 participants were randomized to receive belumosudil 200 mg either once or twice daily.
At a median follow-up of 8 months, the ORR with belumosudil 200 mg once and twice daily was 73% and 74%, respectively. Similar results were seen in patients who had previously received either ruxolitinib or ibrutinib. High response rates were seen in patients with severe chronic GVHD, involvement of four or more organs and a refractory response to their last line of therapy.
Hard-to-manage patients
“We’re very hopeful for many of these agents, but we have to acknowledge that there are still many management dilemmas, patients that we just don’t really know what to do with,” Dr. Lee said. “These include patients who have bad sclerosis and fasciitis, nonhealing skin ulcers, bronchiolitis obliterans, serositis that can be very difficult to manage, severe keratoconjunctivitis that can be eyesight threatening, nonhealing mouth ulcers, esophageal structures, and always patients who have frequent infections.
“We are hopeful that some these agents will be useful for our patients who have severe manifestations, but often the number of patients with these manifestations in the trials is too low to say something specific about them,” she added.
‘Exciting time’
“It’s an exciting time because there are a lot of different drugs that are being studied for chronic GVHD,” commented Betty Hamilton, MD, a hematologist/oncologist at the Cleveland Clinic.
“I think that where the field is going in terms of treatment is recognizing that chronic GVHD is a pretty heterogeneous disease, and we have to learn even more about the underlying biologic pathways to be able to determine which class of drugs to use and when,” she said in an interview.
She agreed with Dr. Lee that the goals of treating patients with chronic GVHD include improving symptoms and quality, preventing progression, ideally tapering patients off immunosuppression, and achieving a balance between preventing negative consequences of GVHD while maintain the benefits of a graft-versus-leukemia effect.
“In our center, drug choice is based on physician preference and comfort with how often they’ve used the drug, patients’ comorbidities, toxicities of the drug, and logistical considerations,” Dr. Hamilton said.
Dr. Lee disclosed consulting activities for Pfizer and Kadmon, travel and lodging from Amgen, and research funding from those companies and others. Dr. Hamilton disclosed consulting for Syndax and Incyte.