ORLANDO – An experimental combination of obinutuzumab and venetoclax appears safe as frontline therapy for patients with active, untreated chronic lymphocytic leukemia and comorbidities.
In the safety run-in portion of a phase 3, open-label trial comparing the combination of obinutuzumab (Gazyva) and the investigational Bcl-2 inhibitor venetoclax with obinutuzumab and its usual partner chlorambucil in 12 patients, only two of seven patients classified as being at high risk for the tumor lysis syndrome (TLS) developed laboratory-defined TLS, and no patients had clinical TLS.
The combination did not meet any of the pre-specified stopping criteria, and early data hinted at efficacy for the combination, said Dr. Kirsten Fischer, from the Center for Integrated Oncology at University Hospital Cologne in Germany.
Dr. Kirsten Fischer
“As with previous reports, our data confirm rapid and profound reduction in lymphocyte counts after the first dose obinutuzumab in all 12 [evaluable] patients,” she said at the American Society of Hematology annual meeting.
In the CLL 11 trial, investigators in the German CLL group previously showed that the combination of the anti-CD20 antibody obinutuzumab and chlorambucil resulted in improved overall survival compared to chlorambucil alone in patients with previously untreated CLL and coexisting medical conditions. The combination is approved in the United States for adults with treatment-naïve CLL.
Venetoclax has been shown to have good efficacy against relapsed/refractory CLL both as monotherapy and in combination with rituximab, prompting the investigators to explore it in combination with the rituximab follow-on drug obinutuzumab.
In the safety run-in phase of the CLL 14 trial, the investigators enrolled 13 adults (median age 75, range 59-88 years) with newly diagnosed, active confirmed CLL and coexisting medical conditions as determined either by a score greater 6 on the cumulative illness rating scale (CIRS) or by estimated creatinine clearance less than 70 mL/min.
The patients were treated with 6 cycles of obinutuzumab and venetoclax followed by 6 additional cycles of venetoclax. Obinutuzumab was administered intravenously 100 mg on day 1 and 900 mg on day 2, with the option to deliver 1,000 mg on day 1 instead, then 1,000 mg on days 8 and 15 of cycle 1, and 1,000 mg on day 1 for cycles 2-6.
The dose of venetoclax was titrated upward gradually, with doses of 20 mg, 50 mg, 100 mg, 200 mg, and up to 400 mg administered starting on day 22 of cycle 1.
Planned stopping criteria were one treatment-related death or a grade 4 adverse event related to clinical TLS despite prophylaxis as specified by the protocol.
At the time of data cutoff (October 2015), 12 patients had been on treatment for at least 4 weeks and had reached the maximum venetoclax dose. Two patients had reached 11 cycles, three had reached 10 cycles, and seven had reached 8 cycles.
Grade 1 or 2 adverse events in all 13 enrolled patients included infusion-related reactions in 8; infections in 6; diarrhea, hyperkalemia, and constipation in 5; nausea, dizziness and cough in 4; and fatigue, headache and pruritus in 3.
Grade 3 or 4 adverse events were neutropenia in five patients; infusion related reactions; syncope, thrombocytopenia and laboratory-defined TLS in two patients; and bradycardia, hyperglycemia, influenza, leucopenia, pyrexia, respiratory tract infection, and elevated transaminases in one patient each.
As noted, all 12 evaluable patients had rapid drops in absolute lymphocyte counts, and all but one had complete resolution of lymphadenopathy after three cycles, with the improvement maintained after six cycles. The remaining patient had a decrease to near normal after both three and six cycles.
Of the 12 patients, 11 had a partial response after three cycles, and the remaining patient had stable disease, for an overall response rate of 92%. The overall response rate after six cycles was 100%, with all patients having a partial response.
The data were sufficiently good to justify continuing with the randomized phase, which began in August 2015, Dr. Fischer noted.
The study is sponsored by Hoffman-La Roche and AbbVie. Dr. Fischer disclosed receiving travel grants from Hoffman-La Roche.