Phase 1 trial results suggest umbralisib, a PI3Kδ/CK1ε inhibitor, can be safe and active in patients with relapsed or refractory B-cell malignancies.
Researchers said the safety profile of umbralisib “was distinct from that of other PI3Kδ inhibitors,” as it produced few immune-mediated adverse events (AEs).
Umbralisib also produced an objective response rate of 37% in the entire study cohort, 80% in patients with chronic lymphocytic leukemia (CLL), 53% in patients with follicular lymphoma (FL), and 31% in patients with diffuse large B-cell lymphoma (DLBCL).
These results were published in The Lancet Oncology. The study was sponsored by TG Therapeutics, Inc.
The trial enrolled 90 patients between January 17, 2013, and January 14, 2016.
There were 24 patients with CLL, 22 with FL, 16 with DLBCL, 11 with Hodgkin lymphoma, 6 with mantle cell lymphoma, 5 with marginal zone lymphoma, 3 with Waldenstrom’s macroglobulinemia, 2 with T-cell lymphoma, and 1 with hairy cell leukemia.
The median number of prior therapies was 3 (range, 2-5), and 49% of patients were refractory to previous therapy.
Patients took umbralisib once daily in 28-day cycles until disease progression, unacceptable toxicity, or withdrawal of consent.
Initially, patients took the drug in a fasting state at doses of 50 mg, 100 mg, 200 mg, 400 mg, 800 mg, 1200 mg, or 1800 mg.
In April 2014, the researchers did a second dose-escalation with a micronized formulation of umbralisib, taken with food, at doses of 200 mg, 400 mg, 800 mg, 1200 mg, or 1800 mg.
In August, 2014, all patients who were still on the study transitioned to the 800 mg dose of the micronized formulation. This was the recommended phase 2 dose.
At the data cutoff in November 2016, 44 patients (49%) had received umbralisib for more than 6 cycles, and 23 (26%) had received the drug for more than 12 cycles. Thirteen patients (14%) were still taking umbralisib at the end of the study.
Most patients who stopped treatment did so because of disease progression (n=50, 56%) or AEs (n=9, 10%).
“We are pleased to have treated the first patient ever with umbralisib over 5 years ago and believe it has an important place in the treatment landscape for patients with hematologic malignancies,” said study author Howard A. Burris, MD, of the Sarah Cannon Research Institute in Nashville, Tennessee.
“Several patients from this phase 1 study are still on study today, approaching 5 years of continuous daily therapy, speaking to both the safety and efficacy profile of this unique agent.”
Dose-limiting toxicities (DLTs) occurred in 4 patients. One DLT was grade 3 maculopapular rash in a patient receiving the 800 mg dose of the initial formulation.
Another DLT was grade 3 hypokalemia in a patient receiving 1800 mg of the initial formulation. A third DLT was grade 3 fatigue, which occurred in 2 patients receiving 1800 mg of the micronized formulation.
Because of these toxicities, the maximum tolerated dose was 1200 mg of the micronized formulation.
The most common treatment-emergent AEs were diarrhea (43%), nausea (42%), and fatigue (31%). The most common grade 3/4 AEs were neutropenia (13%), anemia (9%), and thrombocytopenia (7%).
Serious AEs considered at least possibly related to umbralisib were pneumonia (3%), lung infection (1%), febrile neutropenia (1%), and colitis (2%).
Treatment discontinuation due to AEs considered at least possibly related to umbralisib occurred in 6 patients (7%). Two patients had grade 3 colitis, 2 had increased ALT/AST (grade 1 and grade 4), 1 had grade 2 diarrhea, and 1 had grade 3 fatigue.
There were no treatment-related deaths.
The researchers said the safety profile of umbralisib was distinct from that of other PI3Kδ inhibitors, as patients in this trial had fewer occurrences of autoimmune-like toxicities, such as colitis.
“Preclinically, umbralisib has a very unique profile, selectively inhibiting both PI3Kδ and CK1ε,” said study author Owen O’Connor, MD, PhD, of Columbia Presbyterian Medical Center in New York, New York.
“The clinical results in this paper support our thesis that the differentiated preclinical profile explains the differences seen in the clinic between umbralisib and the other PI3Kδ inhibitors.”
The objective response rate was 37%, with 33 patients achieving a response and 3 patients having a complete response (CR).
Sixteen CLL patients responded (80%), all with partial responses (PRs). Four DLBCL patients responded (31%), all with PRs. And 9 FL patients responded (53%), 2 with CRs.
The remaining CR occurred in a Hodgkin lymphoma patient, and this was the only response in this patient group.
One patient with marginal zone lymphoma had a PR, as did 1 patient with mantle cell lymphoma. All other patients had stable disease or progressed.
The mean duration of response was 13.4 months in the CLL patients, 6.4 months in the DLBCL patients, and 9.3 months in the FL patients.