Mature Response Data From a Phase 2 Study Of PI3K-Delta Inhibitor Idelalisib In Patients With Double (Rituximab and Alkylating Agent)-Refractory Indolent B-Cell Non-Hodgkin Lymphoma (iNHL)
Authors: Gopal Ajay , Kahl Brad S. , De Vos Sven , Wagner-Johnston Nina D. , Schuster Stephen J. , Blum Kristie A. , Jurczak Wojciech J. , Flinn Ian W. , Flowers Christopher R. , Martin Peter , Viardot Andreas , Goy Andre , Davies Andrew , Zinzani Pier Luigi , Dreyling Martin H. , Holes Leanne M. , Li Daniel , Dansey Roger , Godfrey Wayne R. , Salles Gilles A. 
Published: October 2019

Abstract

Introduction
Alkylating agent-rituximab combinations are a current standard of care for patients with iNHL. Most iNHL will eventually become refractory to current therapies. Particularly, once iNHL becomes “double-refractory” to rituximab + alkylating agents, there are few data available on beneficial therapeutic options and development of novel therapies is essential for this patient population. PI3K-delta signaling is critical for activation, proliferation and survival of B cells, and is hyperactive in many B-cell malignancies. Idelalisib, a selective oral inhibitor of PI3Kδ, demonstrated considerable activity in recurrent iNHL in a phase 1 trial (Kahl, ICML 2011). We thus evaluated idelalisib in a phase 2 trial for patients with double-refractory iNHL, an area of unmet medical need. We present mature response data and extended follow-up of this study.

Methods
Eligible iNHL patients (pts) included those with measurable disease who were refractory to both rituximab and an alkylating agent. Refractory status was defined as lack of response to, or progression of lymphoma within 6 months of completion of therapy, documented by imaging. Idelalisib 150 mg PO BID was administered continuously until disease progression or intolerance. Responses were evaluated by an independent review committee, using standard criteria (Cheson, 2007). The new data cutoff date for this analysis was June 2013, 8 months after the last patient enrolled.

Results
Enrolled pts (N=125) had a median age of 64 years [range 33-87] and were 64% male. Indolent NHL subtypes included follicular lymphoma (FL) n=72 (58%), small lymphocytic lymphoma (SLL) n=28 (22%), marginal zone lymphoma (MZL) n=15 (12%) and lymphoplasmacytic lymphoma (LPL)/Waldenstrom's macroglobulinemia (WM) n=10 (8%). The median number of prior therapies was 4 [range 2-12], most common regimens included bendamustine/rituximab (BR) (n=60) and rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP) (n=56) and 14 pts (11%) had a prior autologous transplant. 81 pts (65%) had prior bendamustine, of which 61/81 (75%) were refractory. 112 pts (90%) were refractory to their last regimen, and 99 pts (79%) were refractory to ≥2 regimens. Median time since completion of last regimen was 3.9 months. At baseline, pts had elevated LDH (30%), bulky disease >7 cm (26%), anemia ≥grade 1 (51%), neutropenia ≥ grade 1 (24%), and thrombocytopenia ≥grade 1 (34%).
With a median follow up 9.4 months, the overall response rate (ORR) was 57% (95% CI = 47.6, 65.6) with 71 responders, comprising 7 CRs (6%), 63 PRs (50%), and 1 minor response (MR) in a WM pt. There were 42 pts with stable disease (SD) (33%). 90% of pts experienced some decrease in tumor burden (Figure 1). Median time to response was 1.9 months (range 1.6-8.3), median time to CR was 3.7 months (range 1.9-12). ORR for iNHL subtypes was: FL (54%), SLL (61%), LPL/WM (80%), and MZL (47%). ORR for bendamustine refractory pts was 59%. ORR for pts with <4 /≥4 prior therapies was 50%/62%, and for bulky disease <7cm/≥7cm was 57/57%. Among responders, median DOR was 12.5 months. Median PFS for all pts was 11.0 months and median overall survival was 20.4 months.
The most common adverse events were (total%/≥ grade 3%) diarrhea (43/13), fatigue (30/2), nausea (30/2), cough (29/0), pyrexia (28/2), dyspnea (18/3), rash (13/2), and pneumonia (11/7). Based on central laboratory measurements, Grade ≥3 ALT/AST elevations occurred in 16 pts (13%). Drug was held for these pts, and 11/14 pts (79%) were re-treated without recurrence of ALT/AST elevation. Grade ≥3 neutropenia occurred in 27%, thrombocytopenia in 6%, and anemia in 2%. 20% of pts have discontinued therapy due to adverse events.

Conclusions
Idelalisib was well tolerated, had an acceptable safety profile, and was highly effective in this double-refractory iNHL population with an ORR of 57%. The ORR was consistent across all subgroups, regardless of disease histology, number of prior regimens, refractoriness to bendamustine, or tumor bulk. With continued administration of idelalisib, responses were durable beyond one year, substantially exceeding the median DOR for the last prior therapy. Mature response data demonstrate that idelalisib can provide clinical benefit to patients with the unmet medical need of double-refractory iNHL.

Disclosures:
Gopal: Gilead Sciences: Research Funding. Off Label Use: Idelalisib is a PI3K-delta inhibitor currently in phase III trials for multiple hematologic malignancies. Kahl:Gilead Sciences: Advisory Board Other, Research Funding. De Vos:Gilead Sciences: Advisory Board Other, Research Funding. Wagner-Johnston:Gilead Sciences: Research Funding. Schuster:Gilead Sciences: Research Funding. Blum:Gilead Sciences: Research Funding. Jurczak:Gilead Sciences: Research Funding. Flinn:Gilead Sciences: Research Funding. Flowers:Gilead Sciences: Research Funding. Martin:Gilead Sciences: Research Funding. Viardot:Gilead Sciences: Research Funding. Goy:Gilead Sciences: Research Funding. Davies:Gilead Sciences: Research Funding. Zinzani:Gilead Sciences: Research Funding. Dreyling:Gilead Sciences: Research Funding. Holes:Gilead Sciences: Employment. Li:Gilead Sciences: Employment. Dansey:Gilead Sciences: Employment. Godfrey:Gilead Sciences: Employment. Salles:Gilead Sciences: Research Funding.