Ublituximab (TG-1101), a Novel Glycoengineered Anti-CD20 Monoclonal Antibody, in Combination with Ibrutinib Is Highly Active in Patients with Relapsed and/or Refractory CLL and MCL; Results of a Phase II Trial

Introduction: Ublituximab (UTX) is a novel, chimeric monoclonal antibody (mAb) which targets a unique epitope on the CD20 antigen and has been glycoengineered to enhance affinity for all variants of FcγRIIIa receptors, demonstrating greater antibody-dependent cellular cytotoxicity (ADCC) activity than rituximab and ofatumumab, particularly against cells that express low CD20 levels. Two Phase I trials of single agent UTX in relapsed/refractory CLL reported significant response rates with rapid and sustained lymphocyte depletion and a manageable safety profile. Ibrutinib, a novel oral BTK inhibitor approved for patients with previously treated CLL and MCL, displays high single agent activity and has reported increased activity in combination with non-glycoengineered anti-CD20 mAbs. Herein we report safety and efficacy data on the first combination of ibrutinib with a glycoengineered anti-CD20 mAb, UTX, from an ongoing Phase 2 trial.

Methods: Eligible patients have relapsed or refractory CLL/SLL or MCL with an ECOG PS ≤ 2. The study was designed to assess safety, tolerability, and early overall response rate, with an initial safety run-in period consisting of 6 patients followed by open enrollment. UTX (Cohorts of 600 and 900 mg for CLL and at 900 mg for MCL patients) is administered on Days 1, 8, and 15 in Cycle 1 followed by Day 1 of Cycles 2 - 6. Ibrutinib is started on Day 1 and continues daily at 420 mg and 560 mg for CLL and MCL patients respectively. Following Cycle 6, patients come off study but remain on ibrutinib. Primary endpoint for safety: Adverse Events and Dose Limiting Toxicities (DLT) during safety run-in. Phase II primary efficacy endpoint: ORR with an emphasis on early activity with response assessments by CT scan scheduled prior to cycles 3 and 6 only.

Results: 40 patients (33 CLL/ 7 MCL) have been enrolled to date with enrollment continuing. 23 M/17 F, median age 72 yr (range 52-86), ECOG 0/1/2: 20/19/1, median prior Tx = 2 (range 1-6), 38% with ≥ 2 prior anti-CD20 therapies; prior purine analog = 43%; prior alkylating agent = 68%; and prior purine and alkylating agent = 43%. No DLTs were observed during the safety run-in. Gr 3/4 AE’s occurring in at least 5% of patients and at least possibly related to UTX and/or ibrutinib included: neutropenia, thrombocytopenia, diarrhea, rash, leukocytosis, and infusion related reaction. There were no Grade 3/4 adverse events reported in ≥ 10% of patients. Ibrutinib was dose reduced due to an AE in 2 patients (1 diarrhea, 1 rash) and discontinued in 2 patients due to ibrutinib related AE’s (diarrhea and rash). IRR’s were managed with infusion interruptions with no patient requiring an ublituximab dose reduction. As of July 2014, 24/40 patients are evaluable for response. Best response to treatment is as follows:

The one CLL patient who achieved stable disease had a 46% nodal reduction. UTX appears to control ibrutinib related lymphocytosis with more than half of the patients within normal range for ALC by first efficacy assessment.

Conclusions: Data suggests ublituximab, a glycoengineered anti-CD20 mAb, in combination with ibrutinib is both well-tolerated and highly active in patients with relapsed or refractory CLL and MCL. ORR was 94% in patients with CLL (100% in patients with high risk CLL: 17p, 11q del with 1 CR), with responses attained rapidly (median TTR: 8 weeks). In MCL, 83% of patients achieved a response at first efficacy assessment, with 50% of patients achieving a CR by week 20. For most patients, responses improved by the second efficacy assessment. The addition of ublituximab appears to mitigate ibrutinib related lymphocytosis producing earlier clinical responses than historically seen with ibrutinib monotherapy. Efficacy and safety will be updated on all enrolled patients.