BackgroundBETd-260 is a potent BET degrader based on PROTAC technology, with an IC50 of 30 pM against BRD4 protein in RS4;11 leukemia cell line.BETd-260 is a potent BET degrader based on PROTAC technology, with an IC50 of 30 pM for BRD4 protein in RS4;11 leukemia cell line. BETd-260 (ZBC260; Compound 23) shows inhibitory activity against the growth of RS4;11 leukemia cells and MOLM-13 cells with IC50s of 51 pM and 2.2 nM, respectively, and induces apoptosis in both RS4;11 and MOLM-13 cell lines at 3-10 nM.BETd-260 (5 mg/kg, i.v., every other day, thrice a week for 3 weeks) causes rapid tumor regression with a maximum of >90% regression in mice bearing RS4;11 xenograft tumors, and with no body weight loss or other signs of toxicity in mice. BETd-260 (5 mg/kg, i.v.) degrades the BRD2, BRD3, and BRD4 proteins for more than 24 h, with robust cleavage of PARP and caspase-3, and strong down-regulation of c-Myc protein in RS4;11 xenograft mice model.