Phase Ib study of BET inhibitor RO6870810 with venetoclax and rituximab in patients with diffuse large B-cell lymphoma.

Overview

abstract

Bromodomain and extra-terminal (BET) proteins are transcriptional activators for multiple oncogenic processes in diffuse large B-cell lymphoma (DLBCL), including MYC, BCL2, E2F and toll-like receptor signaling. We report results of a phase 1b dose-escalation study of the novel, subcutaneous BET inhibitor RO6870810 (RO) combined with the BCL-2 inhibitor venetoclax, and rituximab, in recurrent/refractory DLBCL (NCT03255096). RO was delivered for 14 days of a 21-day cycle, while venetoclax was delivered continuously. A 3 + 3 escalation design was used to determine the safety of the RO + venetoclax doublet, rituximab was added in later cohorts. Thirty-nine patients were treated with a median of 2.8 cycles (range, 1-11). Dose-limiting toxicities included grade 3 febrile neutropenia, grade 4 diarrhea and hypomagnesemia for the doublet; and grade 3 hyperbilirubinemia and grade 4 diarrhea when rituximab was added. The doublet maximum tolerated dose (MTD) was determined to be 0.65 mg/kg RO + 600 mg venetoclax; for RO + venetoclax + rituximab the MTDs were 0.45 mg/kg, 600 mg and 375 mg/m2, respectively. The most frequent grade 3/4 adverse events were neutropenia (28%), anemia and thrombocytopenia (23% each). Responses were seen in all cohorts and molecular subtypes. Sustained decreases in CD11b on monocytes indicated pharmacodynamic activity of RO. Overall response rate according to modified Lugano criteria was 38.5%, 48% of responses lasted for ≥180 days. Complete response was observed in 8 patients (20.5%). Optimization of the treatment schedule and a better understanding of predictors of response would be needed to support broader clinical use.