Updated Results from the Phase II Study of Orelabrutinib Monotherapy in Chinese Patients with Relapsed or Refractory Chronic Lymphocytic Leukemia/Small Cell Leukemia

Orelabrutinib (ICP-022) is a novel and highly selective irreversible BTK inhibitor. We previously reported that orelabrutinib had high bioavailability with ~100% BTK occupancy at 24 hours at 150 mg daily dosing regimen and demonstrated excellent safety and efficacy profiles at median follow-up of 8.7 months in a Phase I/II trial of refractory/relapsed (r/r) CLL/SLL (Chronic Lymphocytic Leukemia/Small Cell Leukemia). Here we present an updated analysis of efficacy and safety results from the clinical study of Orelabrutinib in Chinese patients with r/r CLL/SLL following extended treatment. This is an open-label, multicenter, phase II study with objectives to evaluate its safety and efficacy following an oral daily administration. The primary endpoint was objective response rate (ORR). The duration of response (DOR), progression-free survival (PFS) and safety were chosen as secondary endpoints. Response was assessed per 2008 IWCLL criteria with modification for partial remission (PR) with lymphocytosis (PR-L) (Hallek 2012) or the Lugano Classification (Cheson, 2014) for CLL and SLL, respectively.

Results: A total of 80 patients with r/r CLL (n=70)/SLL (n=10) were enrolled. Eligible patients had relapsed after or were refractory to ≥1 prior treatment with median age of 60.0 (range, 36.0-78.0 years). There are 70% of patients for Rai stage 3-4 disease, 22.5% for 17p13.1 deletion [del(17p)] and/or TP53 mutation, 41.3% for unmutated immunoglobulin heavy chain variable region (IGHV) and 23.8% for 11q22.3 deletion [del(11q)]. The median follow-up time was 14.3 months (range, 0.2-21.6 months), and the last patient completed a minimum of 12 cycles of orelabrutinib treatment.

Efficacy: The efficacy results presented here were evaluated by IRC (Independent review committee). Following a minimum of 12 cycles treatment, the ORR (PR-L or above) was 91.3% (95% confidence interval [CI]: 82.80～96.41%) with 10.0% of patients having complete response (CR), 63.8% PR and 17.5% PR-L. Median time for achieving first response was 1.87 months (range, 1.84 - 1.94 months). The median DOR and PFS were not reached. The estimated 12-month DOR was 77.1% (95% CI: 62.50-86.60%), PFS 81.1% (95% CI: 70.53 - 88.13%) and OS 86.3% (95% CI: 76.55 - 92.14%). Patients with Del(17p) and/or TP53 mutation achieved 100% ORR. The ORR is 94.7% for Del(11q)) and 93.9% for unmutated IGHV. Comparing to the first analysis results of which the median follow-up was 8.7 months, the CR rate had increased from 3.8% to 10.0%, and 8 patients with PR-L had converted to a deeper response. So, orelabrutinib showed a significant higher CR rate comparing to other BTK inhibitors at a similar treatment period and we anticipate a further increase of CR rate with longer duration of treatment.

Safety: Most adverse events (AEs) were mild to moderate, similar to the first reported safety profiles at median follow-up of 8.7 months. Extended follow-up analysis did not reveal new safety nor toxicity concerns. The most frequent adverse events (AEs) of any cause/any grade were well characterized as hematological toxicities: thrombocytopenia, neutropenia, and anemia; upper respiratory tract infection, pneumonia and hypokalemia. No case of atrial fibrillation nor secondary malignancy was reported, no patient was observed for ≥3 hypertension and only one patient had ≥3 grade diarrhea. Major hemorrhage was reported in 2 patients, one with intracranial hemorrhage (65-year-old male patient with more than 10 years hypertension) and the other with vitreous hemorrhage which were resulted from posterior vitreous detachment that was assessed as unlikely related to the treatment of orelabrutinib. Once again, it has been further confirmed that orelabrutinib has excellent safety profiles following extended treatment.

Conclusion: This updated and extended study further confirms that orelabrutinib is efficacious in treating r/r CLL patients with a higher CR rate, durable response and improved safety profiles. As a highly selective BTK inhibitor with favorable pharmacokinetic and pharmacodynamic properties, orelabrutinib provides a favorable therapeutic choice for patients with r/r CLL/SLL and a potential best candidate for combination therapy.