SYK Inhibitor Entospletinib in Combination with Obinutuzumab Demonstrates Efficacy in Patients with Relapsed/Refractory Chronic Lymphocytic Leukemia (CLL)

B-cell receptor (BCR) signaling kinases are important targets in therapy of CLL. Resistance of lymphoid niche-resident CLL cells to BCR-signaling inhibition is fostered by the tumor microenvironment. We found that stromal B-cell activation factor (BAFF)-mediated activation of spleen tyrosine kinase (SYK) triggered BCR signaling, thereby contributing to apoptosis resistance in CLL cells (Paiva et al, 2017). The SYK inhibitor entospletinib (ENTO) abrogated BAFF-mediated BCR signaling accompanied by a decrease in pSTAT3 and MCL1 in vitro. We designed a Phase I/II investigator-sponsored trial of ENTO in combination with Obinutuzumab (Obin) in patients (pts) with relapsed/refractory CLL and non-Hodgkin lymphoma (NHL). Eligible pts were aged ≥18 years, had CLL/NHL (Phase I) or CLL (Phase II), relapsed and/or refractory to ≥1 prior therapies (no prior SYK inhibitor), ECOG performance status ≤2 and preserved organ function. The Phase I part of the study followed a standard 3+3 design with two dose levels (DL1: ENTO 200 mg PO BID; DL2 - ENTO 400 mg PO BID). ENTO was given for 7 days (run-in). Subsequently, Obin was given IV concurrently with ENTO on days 1, 2, 8, 15 of Cycle 1 and Day 1 of Cycles 2-6 in standard doses. ENTO was given until disease progression. Primary study objectives were toxicity (Phase I) and efficacy (objective response rate (ORR); Phase II). Correlative analysis of samples was performed at baseline, after run-in phase (7 days of entospletinib single agent) and after 6 cycles of combination therapy. Reverse protein phase array was performed at the RPPA core facility at MD Anderson Cancer Center. T cell populations and cytokine production were analyzed by flow cytometry. At DL1 of Phase I, six pts were enrolled (4 - CLL; 2 - follicular lymphoma). One pt experienced a dose-limiting toxicity (DLT: grade 3 asymptomatic LFT abnormalities which failed to resolve within 72 hours) attributed to ENTO. Other grade 3-4 toxicities included 2 grade 3 infusion reactions and one transient grade 4 neutropenia (attributed to Obin). Two pts remain on therapy after a median follow-up of 15 months. Three pts were enrolled at DL2 without DLTs. In Phase 2, 18 pts with CLL received ENTO 400 mg PO BID (in combination with Obin). One pt was deemed ineligible due to Richter's transformation at study entry. Of the 17 evaluable pts, 71% were men. Median age was 66 years (range 47-76), and 76% were aged >65 years. 94% had ECOG performance status ≤1. Six pts (35%) had a com