CHICAGO – The phosphoinositide 3-kinase–delta inhibitor ME-401, given with or without rituximab, produced an overall response rate of 80% in a phase 1b trial of patients with relapsed or refractory follicular lymphoma.
Response rates were similar between patients who received ME-401 alone and those who received it in combination with rituximab.
Response rates were also similar between patients on an intermittent dosing schedule and those on a continuous dosing schedule. However, intermittent dosing decreased the rate of delayed grade 3 adverse events (AEs).
“The idea that continuous inhibition of target is absolutely essential for activity of this class of drugs has not been proven,” saidof Memorial Sloan Kettering Cancer Center in New York.
“The promising results of this somewhat novel intermittent schedule that we used with ME-401 suggests to me that we can maintain efficacy and reduce toxicity.”
Dr. Zelenetz and colleagues presented these results in a poster at the annual meeting of the American Society of Clinical Oncology.
Patients and dosing
Data were presented for 54 patients with relapsed/refractory follicular lymphoma enrolled on this. The patients had a median age of 63.5 years, and 80% were male. They had received a median of 2 prior therapies (range, 1-10).
Initially, patients received ME-401 at 60 mg, 120 mg, or 180 mg once daily continuously on a 28-day cycle. However, the dose-escalation portion of the study was closed because response rates were comparable among the three doses, the safety profile was similar, and there were no dose-limiting toxicities.
Two additional groups of patients received ME-401 at 60 mg daily for two cycles, followed by an intermittent schedule (IS) of 60 mg on days 1-7, repeated every 28 days.
The researchers had observed delayed grade 3 AEs on the continuous schedule (CS), and they hypothesized that the IS might prevent these events. Patients could revert to the CS if they had stable disease or progressed on the IS.
“One of the advantages of this particular agent is the very long half-life,” Dr. Zelenetz said. “So, essentially, we have 2 weeks on drug and 2 weeks off [with the IS]. It takes about a week to clear the drug because it has about a 30-hour half-life.”
In all, 40 patients received ME-401 monotherapy, and 14 received ME-401 plus rituximab at 375 mg/m2 weekly for 4 weeks and then on day 1 of cycles 3-6. There were 31 patients who received ME-401 on the CS and 23 who received ME-401 on the IS.
A total of 50 patients were evaluable for efficacy. The overall response rate in these patients was 80% (40/50), and 20% (10/50) achieved a complete response.
The overall response rate was 79% (30/38) in patients who received ME-401 alone, 83% (10/12) in those who received ME-401 plus rituximab, 83% (25/30) in patients on the CS, and 75% (15/20) in those on the IS.
The median duration of response and median progression-free survival have not been reached. The median follow-up for response duration is 8.8 months in the IS group and 8.3 months in the CS group. The median follow-up for progression-free survival is 5.5 months and 6.5 months, respectively.
A total of 18 patients on the IS (78%) were still on therapy at the data cutoff, as were 14 patients (45%) on the CS.
Seven patients (23%) on the CS and two patients (9%) on the IS discontinued treatment due to progression. Four patients in the IS group and two in the CS group who were switched to IS dosing reverted to CS dosing after experiencing progression.
Four CS patients (13%) discontinued treatment because of AEs, but none of the IS patients did.
AEs occurring in at least 15% of patients were diarrhea/colitis (40.7%), fatigue (35.2%), cough (33.3%), rash (24.1%), ALT increase (24.1%), nausea (24.1%), AST increase (22.2%), and decreased appetite (16.7%).
There were no grade 4-5 AEs. Grade 3 drug-related AEs of special interest (in the CS and IS groups, respectively) were diarrhea/colitis (16.1% and 8.7%), rash (12.9% and 0%), ALT increase (6.5% and 4.3%), AST increase (6.5% and 0%), pneumonia (6.5% and 0%), and mucositis (1.9% and 0%).
“[W]hile the grade 3 immune-related events seem to be very consistent in terms of class effects, they did seem to improve with transition to intermittent schedule,” saidof the University of Rochester (N.Y.), who reviewed this study in a poster discussion session.
“And I think that this novel design helps to create an opportunity to limit treatment and mitigate toxicity without necessarily compromising efficacy.”
The phase 1b trial is sponsored by MEI Pharma. Dr. Zelenetz reported relationships with MEI Pharma and several other companies. Dr. Casulo reported relationships with Gilead Sciences, Celgene, and Roche.
SOURCE: Zelenetz A et al. ASCO 2019,