A Phase I/II Study of Ibrutinib and Ixazomib in Relapsed/Refractory Mantle Cell Lymphoma: PrE0404

Background:

The Bruton's tyrosine kinase inhibitor ibrutinib is highly effective as a monotherapy in relapsed/refractory mantle cell lymphoma (MCL) with an overall response rate of 68% (Wang et al, NEJM 2013), but the duration of response is shorter than what is seen in chronic lymphocytic leukemia, and the survival of patients who progress after receiving ibrutinib is as short as 3 months (Martin et al, Blood, 2016). In addition, the complete response (CR) rate is only 21%. Ibrutinib-containing combinations may improve depth and duration of response in patients with relapsed/refractory MCL. While use of the proteasome inhibitor, bortezomib, can be limited due to the development of peripheral neuropathy, it has an ORR of 33% (CR rate 8%) in MCL, and preclinical models suggest a synergism between proteasome inhibitors and ibrutinib in MCL cell lines (Axelrod et al, Leukemia 2014). We developed a phase 1/2 trial of ibrutinib combined with the oral proteasome inhibitor ixazomib in patients with relapsed/refractory MCL.

Methods:

PrE0404 will be open at 18 sites nationwide and is registered at clinicaltrials.gov (NCT03323151). It is currently enrolling patients with relapsed/refractory MCL who have received at least 1 prior line of combination therapy. Patients receiving prior BTK or proteasome inhibitors are eligible, and patients may have received prior autologous or allogeneic transplantation as long as they do not have active graft versus host disease. Patients must have ≤ grade 1 peripheral neuropathy. For phase 1, patients are required to have been off of a BTK inhibitor for 3 months. Starting dose of ibrutinib for all patients is 560mg daily, and dose levels of ixazomib for the phase 1 trial range from 3mg to 4mg days 1, 8, and 15 of a 28 day cycle. Patients continued therapy until disease progression or unacceptable toxicity. For the phase 1 portion of the study, patients are monitored for a dose limiting toxicity (DLT) during cycle 1, defined as grade 3 thrombocytopenia with significant bleeding, select grade 3 non-hematologic toxicities, grade 4 thrombocytopenia, grade 4 febrile neutropenia, grade 4 non-hematologic toxicity, or any grade 5 toxicity. In addition, any toxicity-related dose delay > 7 days of ibrutinib or ixazomib or an inability to receive all 3 doses of ixazomib during cycle 1 are considered DLT's. The maximum tolerated dose/recommended phase 2 dose will be the dose at which fewer than 1/6 patients experience a DLT, with the maximum dose of ixazomib will be 4mg.

The primary endpoint for the phase 2 portion of the study is CR rate, and patients will be assigned to one of two cohorts based on prior BTK-inhibitor exposure. For ibrutinib-naïve patients, we will target a CR rate of 40% (based on a historical CR rate of 21% for ibrutinib), and for ibrutinib-pretreated patients, we will target a CR rate of 23% (based on a historical CR rate of 8% for bortezomib). There is 86% statistical power & a one-sided 10% alpha to test each hypothesis. We will accrue 31 patients to each cohort in order to detect this difference. Secondary and exploratory endpoints will include progression-free and overall survival, overall response, toxicity, frequency of BTK mutations, and response based on molecular risk stratification. As of July 2019 the study is open to accrual at 14 sites and is expected to move to phase 2 in fall 2019, at which time it will be expanded to 18 sites.