A Phase I Study Of The Oral Btk Inhibitor ONO-4059 In Patients With Relapsed/Refractory and High Risk Chronic Lymphocytic Leukaemia (CLL)

The B-cell receptor (BCR) pathway plays a central role in signal transduction pathways that regulate survival, activation, proliferation and differentiation of B-lineage lymphoid cells. Bruton’s tyrosine kinase (Btk) is a critical kinase in BCR signal transduction and recent studies support that targeting Btk is effective in the treatment of B-cell malignancies. ONO-4059 is a highly potent and selective oral Btk inhibitor with an IC50 in the sub-nmol/L range that has demonstrated anti-tumour activity in several pre-clinical models (Yasuhiro T et al, AACR 2013).

This Phase I study was initiated to determine the safety, tolerability, dose-limiting toxicity (DLT), pharmacokinetics and pharmacodynamics of ONO-4059 given as monotherapy to patients with relapsed/refractory, high risk CLL for whom no therapy of higher priority was available. In this safety-driven, dose-escalating 3+3 design, ONO-4059 was administered as an oral, daily dose (flat dose) given continuously initially for up to 6 months, with the option of additional dosing up to 2 years. We present the safety and efficacy data on 16 evaluable patients, median age 67 yrs (range 40-77), with high risk cytogenetics (17p [38% (6/16)] or 11q [19% (3/16)], 12/16 displaying unmutated IgVH status, 8/16 displaying TP53 mutation), median baseline tumour burden 4,534mm² [461-14,492 mm²]. Patients had received a median of 3 prior therapies [2-7], including fludarabine (16/16) and rituximab-containing therapy (13/16). Baseline median haematology parameters included hemoglobin 11.3 g/dL [8.5 -15.2], WBC 56.02 x 10⁹/L [2.06-394.74], platelets 95.5 x 10⁹/L [23-173], lymphocytes 50.6 x 10⁹/L [0.5-390], neutrophils 2.46 x 10⁹/L [0.5-11.1]. Patients were treated with ONO-4059 at doses ranging from 20mg-320mg (cohorts 1-5) and the study is currently ongoing with additional dose escalation cohorts to be completed.

ONO-4059 was found to be well tolerated, with no dose limiting toxicities (DLTs). A total of 15 ONO-4059-related Grade 1 (n=10) and 2 (n=5) adverse events were reported in 8 out of 16 patients, including one event of diarrhea (G2) and two events of rash (G1, G2). ONO-4059-related G3 or G4 haematological toxicities were infrequent and independent of dose; neutropenia (n=3 [G4 x1, G3 x 2]), febrile neutropenia (n=1 [G3]) occurring in 2 patients at the 20mg dose level only. Only one Grade 3 ONO-4059-related non-haematological event (pyrexia) was reported. Infection rate was low with only one event of bronchitis reported (G2, related). Three ONO-4059-related SAEs were reported in two patients (febrile neutropenia [G3] and pyrexia [G3] in one patient [20 mg]; rash [G2] in another [80 mg]). The pharmacokinetics of ONO-4059 reflects rapid absorption and elimination, a half-life of ∼6 hours, a dose dependent increase in exposure with no accumulation of ONO-4059 exposure and low inter- or intra-patient variability; with Btk occupancy in peripheral blood (as measured by phosphorylated Btk) being maintained for at least 24 hours across all dose levels.

Responses have occurred across all dose levels. All patients experienced rapid reductions in lymphadenopathy observed early in treatment, between D1-D28 of the first cycle, accompanied by an increase in absolute lymphocyte count in some, but not all patients. Best overall response rate according to IWCLL criteria (including modified PR with lymphocytosis) was 70% [based on CT-scan and P/E for 7/10 evaluable patients]; with 2 PR, 5 PR with lymphocytosis (For 7 responding patients, median reduction of lymph nodes was 67% [Range 61%-79%]), 2 SD, 1 patient PD (possible Richter’s). All patients showed an improvement in haematological parameters after ≥3 months on treatment. Patients (ONO-4059 20mg [1pt] and 40mg [1pt] respectively) who had grade 3 thrombocytopenia at study baseline had a significant improvement in platelet count (>100 x 10⁹/L) with ONO-4059 treatment. To date, 15 of 16 patients remain on treatment with a median progression-free survival of 99 days [Range 8-268].

In conclusion, ONO-4059 is a highly potent and selective oral Btk inhibitor with a favourable safety profile along with promising efficacy in this heavily pre-treated population, with responses observed in relapsed, refractory and 17p deleted patients.

Salles:Janssen: Honoraria; Gilead: Honoraria; Celgene: Honoraria. Karlin:Janssen: Honoraria; Celgene: Honoraria. Morschhauser:ONO Pharma: Honoraria; Roche: Honoraria; Celgene: Honoraria; Mundipharma: Honoraria. Dyer:ONO Pharma: Honoraria, Research Funding. Hutchinson:ONO Pharma: Research Funding. Fegan:ONO Pharma: Honoraria. Cartron:ONO Pharma: Honoraria. Knurowski:ONO Pharma: Consultancy. Saunders:ONO Pharma: Consultancy; Pharmacyclics: Consultancy. Wright:ONO Pharma: Consultancy. Honda:ONO Pharma: Employment. Mazur:ONO Pharma: Consultancy. Yoshizawa:Ono Pharma: Employment. Kawabata:Ono Pharmaceutical Co., Ltd.: Employment. Birkett:Ono Pharma UK: Employment.