Fig. 4. Competition labeling experiments using DB008 enables validation of previously reported PARP16 inhibitors. (A) Chemical structures of talazoparib (Tal) and epigallocatechin gallate (EGCG). (B) Tal, but not EGCG, effectively blocks covalent labeling of PARP16 by DB008. In vitro competition assay wherein talazoparib and EGCG were incubated with recombinant PARP16 (40 min) followed by treatment with DB008 (20 min) and clicking to TAMRA-azide for in gel-fluorescence detection of PARP16 labeling; n = 2 biological replicates. (C) Tal, but not EGCG, inhibits PARP16 labeling by DB008 in cells. Cellular competition assay wherein Myc2x-PARP16 expressing HEK 293T cells were dosed with Tal and EGCG for 1 h, then treated with DB008 (0.3 μM) for 30 min, followed by lysis and clicking to TAMRA-azide for in gel-fluorescence detection of PARP16 labeling. (D) Quantification of TAMRA signal from (C); n = 2 biological replicates.