Phase 1b and Pharmacokinetic Study of Idelalisib in Japanese Patients with Relapsed or Refractory (R/R) Indolent B-Cell Non-Hodgkin Lymphoma (iNHL) or Chronic Lymphocytic Leukemia (CLL)

Background: Increased phosphatidylinositol-3-kinase delta (PI3Kd) activity drives proliferation and survival of malignant B-cells and mediates trafficking to lymphoid tissues. Idelalisib, a first-in-class, selective, oral inhibitor of PI3Kd, is approved in combination with rituximab for patients with relapsed CLL and as monotherapy in patients with relapsed/refractory (R/R) follicular lymphoma (FL) in North America and the EU.

Methods: Six Japanese patients were enrolled between October 2014 and November 2014. This is an open-label 6+6 study design for continuous dosing of idelalisib 150mg BID in patients with R/R CLL and iNHL until PD or intolerable toxicity. The primary objective was to evaluate the 28-day safety, tolerability and pharmacokinetics of idelalisib and its metabolite GS-563117. The primary endpoint was the incidence of dose-limiting toxicity (DLT) defined as grade 4 hematological toxicities persisting for >14 days, grade ≥3 non-hematological toxicities, grade >3 laboratory abnormalities, red cell transfusion, and a therapeutic platelet transfusion. Key inclusion criteria were: age ≥20 yrs, patient of Japanese ancestry. Key exclusion criteria were known histological transformation to an aggressive histology, history of iNHL or CLL with CNS involvement. Response assessments as per modified Hallek 2008 and Cheson criteria 2007 were performed using CT scans at pre-determined time points by investigators.

Results: Baseline characteristics included 3 patients each with CLL (2/3 refractory, 1/3 relapsed) or FL (3/3 refractory), and median age was 64 years (range 49-74). Median number of prior Rx regimens was 3.5 (range 1-6). Prior therapies included bendamustine plus rituximab (67%), R-CHOP (67%), and R-CVP (33%). No Japanese patients experienced a DLT within the 28-day window. The PK of idelalisib and GS-563117 were comparable between Japanese and non-Japanese patients; non-Japanese PK data predicted from preceding Phase 2 and Phase 3 studies. The most common treatment-emergent any grade/≥ grade 3 AEs in increasing frequency were gastritis (33%/0%), pyrexia (33%/0%), transaminases increased (33%/33%), chest pain (17%/0%), decreased appetite (17%/17%), diarrhea (17%/17%), neutrophil count decreased (17%/17%) and common laboratory abnormalities were decreased WBC (50%/17%), decreased neutrophil count (50%/17%), increased ALT (33%/17%), and increased AST (17%/17%). At the time of this analysis, a total of 3 patients experienced serious AEs (50%); decreased appetite, diarrhea, and increased transaminases. Investigator response assessments were 5/6 (83%) patients achieving partial response (PR) and 1/6 (17%) stable disease.

Conclusions: Continuous dosing of idelalisib demonstrated a manageable safety profile with promising efficacy in Japanese patients with R/R CLL and FL. The PK of idelalisib and GS-563117 were comparable between Japanese and non-Japanese patients. The study was registered at ClincalTrials.gov (NCT02242045).