Final results of a phase I study of idelalisib, a selective inhibitor of phosphatidylinositol 3-kinase P110δ (PI3Kδ), in patients with relapsed or refractory mantle cell lymphoma (MCL).

Abstract

8519 Background: PI3K-delta signaling is critical for activation, proliferation and survival of B cells and plays a role in homing and retention in lymphoid tissues. PI3Kδ signaling is hyperactive in many B-cell malignancies. Idelalisib is a first-in-class, selective, oral inhibitor of PI3Kδ. Initial response rate of 42% was previously reported in MCL (Kahl, ICML 2011). Long-term follow-up is now presented. Methods: This phase 1 study evaluated the activity of continuous (48 weeks) idelalisib monotherapy in pts with relapsed or refractory hematologic malignancies. Doses ranged from 50 mg BID to 350 mg BID in 8 cohorts. Response was based on investigator assessments using standard criteria (Cheson et al, 2007). Patients who continued to benefit were able to enroll in an extension study. Results: 40 patients with recurrent MCL enrolled. Patients were 88% male, median age [range] of 69 [52-83] years, 43% with refractory disease. The median [range] number of prior therapies was 4 [1E14]. The median [range] duration of idelalisib treatment was 3.5 [1-26+] months, with 6 (15%) patients continuing on treatment in the extension protocol. Overall response rate (ORR) was 16/40 (40%), with 2/40 CR (5%). The median duration of response (mDOR) was 2.7 months, and median PFS (mPFS) was 3.7 months. The 1-year PFS was 22%. For patients dosed with ≥100 mg BID, ORR was 12/23 (52%), for patients dosed with ≥150 mg BID, ORR was 11/16 (69%) including both CR (12.5%). Most common adverse events included (total%/≥G3%); diarrhea (40/18), nausea (33/5), pyrexia (28/0), fatigue (25/3), rash (25/3), decreased appetite (20/15), URI (20/0), and pneumonia (13/13). Abnormal lab values included (total%/≥G3%) ALT/AST elevations (65/20). 6/40 (15%) patients discontinued therapy due to AEs, potentially treatment related. Conclusions: The oral PI3Kδ inhibitor idelalisib (GSE1101) is active and well tolerated in heavily pre-treated pts with MCL. A proportion of patients have long-term (>1 year) clinical benefit. These data support further clinical evaluation of idelalisib in MCL. Clinical trials with idelalisib in combination with other agents are in progress. Clinical trial information: NCT00710528.