Table I. Cellular characterization of rilzabrutinib confirms selectivity and limited off-target effects
TargetCell Type and AssayIC50 ± SD, nM
On-target activity
 BCRB cell: human proliferation5 ± 2
 BTKB cell: Ramos occupancy8 ± 2
 FcγRMonocyte: IgG activation56 ± 45
 BCRB cell: human whole blood activation123 ± 38
 FcεRBasophil: IgE activation in human whole blood490 ± 130
Off-target activity
 TCRT cell: Jurkat receptor signaling>5,000
 IL-4/STAT6B cell: Ramos IL-4–induced STAT6>5,000
 EGFRCellular reporter assay>5,000
 CytotoxicityHCT116 cells>16,000
  • Cells were selected based on the presence or absence of BTK, BCR, FcR, and non-BTK–related functions to determine rilzabrutinib selectivity. Following treatment with rilzabrutinib, cell-based assays examined the on-target and off-target activity (measured by IC50 levels) of rilzabrutinib on B cell activation, Fc-receptor signaling, T cells, and other non-BTK–dependent cellular pathways.