Umbralisib Plus Ublituximab (U2) Is Superior to Obinutuzumab Plus Chlorambucil (O+Chl) in Patients with Treatment Naïve (TN) and Relapsed/Refractory (R/R) Chronic Lymphocytic Leukemia (CLL): Results from the Phase 3 Unity-CLL Study

Background: Umbralisib is an oral, once-daily, novel, dual inhibitor of phosphatidylinositol-3-kinase-delta (PI3Kδ) and casein kinase-1ε (CK1ε) that exhibits improved selectivity for the delta isoform of PI3K. Ublituximab is a novel anti-CD20 monoclonal antibody glycoengineered for enhanced antibody-dependent cellular cytotoxicity that targets a unique epitope on CD20. U2 has been well-tolerated and demonstrated promising activity in heavily pre-treated CLL patients. Herein, results are presented for the randomized, multicenter, Phase 3 UNITY-CLL trial (NCT02612311), which evaluated U2 vs O+Chl in patients with TN and R/R CLL.

Methods: Patients ≥18 years of age with treatment-naïve (TN) or relapsed/refractory (R/R) CLL requiring treatment per iwCLL criteria with adequate organ function and ECOG PS ≤2 were eligible. Stratification factors included treatment status (TN vs R/R) and del(17p) status. Patients were initially randomized 1:1:1:1 to receive U2, O+Chl, umbralisib monotherapy, or ublituximab monotherapy. Following establishment of contribution comparing U2 to the single agents, patients were randomized 1:1 to U2 or O+Chl.

Umbralisib was given orally at 800 mg once-daily until progression or removal from treatment for other reasons. Ublituximab was administered intravenously at 900 mg on Days 1/2 [split 150/750 mg], 8, and 15 of Cycle 1, Day 1 of Cycles 2 – 6, and on Day 1 every 3 cycles after Cycle 6. O was given intravenously at 1000 mg on Days 1/2 [split 100/900], 8, and 15 of Cycle 1, and Day 1 of Cycles 2 – 6. Chl was given orally at 0.5 mg/kg on Day 1 and 15 of Cycles 1 – 6. Each cycle was 28 days.

The primary endpoint was independent review committee (IRC)-assessed progression-free survival (PFS) of U2 vs O+Chl. Key secondary endpoints included IRC-assessed overall response rate (ORR), complete response (CR), undetectable minimal residual disease (uMRD), duration of response (DOR), and safety (assessed from the first dose until 30 days after the last dose of study medication in each arm) as well as contribution of umbralisib and ublituximab to the U2 combination.

Results: From Feb 2016 – Oct 2017, 421 pts were randomized to the U2 (n=210) or O+Chl (n=211) arms. The median age was 67 y (range, 36-91); 57% of patients (n=240) were treatment-naïve; 43% (n=181) had R/R CLL (median number of prior treatments = 1); 10% had del(17p), 20% del(11q), and 56% were IgHV unmutated. 66% were male. Demographics were well-balanced between treatment arms.

At a median follow-up of 36.2 mos, U2 significantly prolonged PFS vs O+Chl (median 31.9 mos vs 17.9 mos; HR 0.546, 95% CI 0.413-0.720, P<0.0001; Figure 1). Estimated 24-mo PFS rates with U2 and O+Chl were 60.8% and 40.4%, respectively. PFS improvement with U2 vs O+Chl was consistent across all subgroups examined including treatment naïve patients (median 38.5 mos vs 26.1 mos; HR [95% CI]; 0.482 [0.316-0.736]); and relapsed/refractory patients (median 19.5 mos vs 12.9 mos; HR [95% CI]; 0.601 [0.415-0.869]). IRC-assessed ORR was higher with U2 (83.3%; 95% CI, 78.1%-88.6%) vs O+Chl (68.7%; 95% CI, 62.2%-75.2%; P<0.001). Among previously treated subjects, twenty-six (6%) received prior ibrutinib (14 on U2, 12 on O+Chl), with an ORR of 57% observed for U2 compared to 25% for O+Chl in this population. MRD data is currently being analyzed.

The median treatment duration was 23 mos for U2 (range, 0.1 - 49 mos) and 5 mos (range, 0.1 – 7 mos) for O+Chl. G3/4 AEs of interest regardless of causality (U2 vs O+Chl) included neutropenia (30.6% vs 34.7%), thrombocytopenia (3.4% vs 13.1%), diarrhea (12.1% vs 2.5%), infusion related reaction (1.9% vs 3.5%), elevated AST/ALTs (8.3% vs 2%), colitis (3.4% vs 0%) and pneumonitis (2.9% vs 0%). AEs led to treatment discontinuation in 34 patients (16.5%) on U2 and 16 patients (7.6%) on O+Chl.

Conclusions: UNITY-CLL is the first randomized Phase 3 study in CLL of a PI3Ki vs. chemoimmunotherapy, and the first randomized study of a PI3Ki in treatment-naive CLL. U2 exhibited a well-tolerated safety profile, and significantly improved PFS vs. standard of care chemoimmunotherapy in patients with treatment-naive and relapsed/refractory CLL.