Phase 2 Trial of Entospletinib (GS-9973), a Selective Syk Inhibitor, in Chronic Lymphocytic Leukemia (CLL) and Small Lymphocytic Lymphoma (SLL)
Authors: Sharman Jeff P. , Klein Leonard M. , Boxer Michael , Kolibaba Kathryn S. , Abella Steve , Di Paolo Julie , Eng Clarence , Hu Jing , He Jing , Reddy Anita , Yasenchak Christopher A. 
Published: October 2019

Abstract
Background: Spleen tyrosine kinase (Syk) is a mediator of B-cell receptor signaling in normal and transformed B-cells. GS-9973 is an orally bioavailable, selective inhibitor of Syk.
Methods: This Phase 2 trial enrolled 41 patients with CLL and 15 patients with SLL treated with GS-9973 800 mg BID. Tumor imaging occurred at weeks 8, 16, 24 and then every 12. Response was independently evaluated according to Hallek 2008 as modified by Cheson 2012 for patients with CLL and Cheson 2007 for patients with SLL. Primary endpoint for the study was PFS at 24 weeks.
Results: The median ages of CLL and SLL patients were 73 (range 51-89) and 70 (range 57-84), respectively. 68% of CLL subjects and 60% of SLL subjects were male. Ten patients had 17p deletions/TP53 mutations and 17 had SF3B1 or NOTCH1 mutation, or 11q22.3 deletion. The median number of prior regimens for CLL was 2 (range 1-8) and for SLL was 2 (range 1-10). Prior therapies included anti-CD20 antibodies (98%), alkylating agents (86%, [bendamustine 63%]) and fludarabine (66%). 12 CLL and 6 SLL patients are still on treatment; the median duration of treatment for all CLL and SLL patients was 36 weeks
The most common treatment emergent AEs (any Grade/≥Gr 3, independent of causality) were fatigue (70%/7%), nausea (54%/2%), diarrhea(48%/0%), cough(34%/0%), dizziness (32%/2%), headache (29%/0%), pyrexia (29%/0%), decreased appetite (27%/2%), upper respiratory tract infection(27%/0%), constipation (23%/0%). Common laboratory abnormalities were increased AST (30%/5%), increased ALT (43%/4%), increased total bilirubin (41%/16%), anemia (50%/7%) and neutropenia (54%/29%).
Forty-nine patients were treated for at least 8 weeks and 54 patients had ≥ 1 efficacy assessment, two patients discontinued prior to the first response assessment, one due to AE and one withdrew consent. Per investigator assessment, 51 out of 52 (98%) patients evaluable for SPD experienced reduced tumor bulk; 38 (73%) achieved a decrease of ≥ 50%. The ORR was 62.5% (95% CI: 48.6%, 75.1%), with 35 patients achieving a PR and no subject achieving a CR. Thirteen patients (23.2%) had stable disease.
The primary end point of 24 weeks PFS was 72.3% (95% CI: 57.1%, 83.0%). Median PFS was 20.5 months (95% CI: 7.7 months, not reached). There were 24 patients (42.9%) with events, 22 (39%) with disease progression and two deaths (4%) attributed to septic pneumonia and pseudomonal infection which was unrelated to entospletinib by investigator assessment. Among the 35 responding patients, median DOR was 21.3 months (95% CI: 13.2 months, not reached). Results of an independent response assessment are pending and will be presented.
Entospletinib was well tolerated and demonstrated substantial activity in patients with CLL, and SLL including those with poor prognostic features. Entospletinib activity seems comparable to that reported by other approved BCR pathway inhibitors with the median PFS reported for Idela of 15.8 months (Blood. 2014;123(22):3390-3397) and Ibrutinib reported 42.6% overall response rate and a PFS of 70-80% @ 12 months (ibrutinib PI) Current studies plans include studying Entospletinib in combination therapy.
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Disclosures
Sharman: Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Roche: Research Funding; Calistoga: Honoraria; Pharmacyclics: Consultancy, Honoraria, Research Funding; Celgene Corporation: Consultancy, Research Funding; TG Therapeutics, Inc.: Research Funding; Janssen: Research Funding. Kolibaba:Janssen: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; TG Therapeutics: Research Funding; GSK: Research Funding; Celgene: Research Funding; Acerta: Research Funding; Seattle Genetics, Inc.: Research Funding; Takeda Pharmaceuticals International Co.: Research Funding; Gilead: Consultancy, Research Funding. Abella:Gilead: Employment. Di Paolo:Gilead Sciences: Employment, Equity Ownership. Eng:Gilead: Employment. Hu:gilead: Employment. He:Gilead Sciences: Employment. Reddy:gilead: Employment. Yasenchak:Seattle Genetics, Inc.: Research Funding.