Phase I study of single-agent CC-292, a highly selective Bruton’s tyrosine kinase inhibitor, in relapsed/refractory chronic lymphocytic leukemia

B-cell receptor (BCR) signaling plays a key role in the pathogenesis of B-cell malignancies, mediating the survival and proliferation of malignant B cells.1,2 Clinical studies have shown that Bruton’s tyrosine kinase (BTK) inhibitors are well tolerated, with promising clinical activity. Ibrutinib has shown 30-month progression-free survival (PFS) of 69% in relapsed chronic lymphocytic leukemia (CLL) patients,3–5 and has substantial activity in mantle cell lymphoma and activated B-cell-type diffuse large B-cell lymphoma.6,7 CC-292 is a highly selective oral small-molecule inhibitor that binds covalently and irreversibly to the same cysteine 481 in BTK as ibrutinib, inhibiting its signaling.8 We report here the results of a phase I study of CC-292 in patients with relapsed/refractory (R/R) CLL/small lymphocytic lymphoma (SLL), B-cell non-Hodgkin lymphoma (B-NHL), and Waldenstrom macroglobulinemia (WM). A total of 113 patients received continuous dosing with CC-292 in 28-day cycles at doses ranging from 125 mg to 1000 mg once daily, and 375 mg and 500 mg twice daily, continuing into dose-expansion cohorts of 750 mg once daily and a preliminary recommended phase II dose (RP2D)-expansion cohort of 500 mg twice daily. Four patients experienced dose-limiting toxicity (DLT) but only one in any treatment cohort. The most frequent grade 3–4 adverse events (AEs) were neutropenia (16%) and thrombocytopenia (8%). The most common non-hematologic treatment-emergent AEs (TEAEs) of any grade were diarrhea (68%) and fatigue (45%). Twice-daily administration of CC-292 was instituted to improve sustained BTK occupancy, and, in fact, did result in more than 90% BTK receptor occupancy at both the 4- and 24-h post-dose time points. Efficacy in the CLL/SLL population (n=84) showed that overall response rate (ORR) in patients receiving twice-daily dosing was 53%; an additional 10% had partial response with lymphocytosis (PR-L). CC-292 was, therefore, well tolerated and achieved high nodal and PR rates in relapsed CLL/SLL patients, but showed less durability than other BTK inhibitors.