Cell-permeable. A potent and highly specific inhibitor for the BET (bromodomain and extra-terminal) family of bromodomains. (+)-JQ1 binds to BRD4 bromodomains 1 and 2 with Kd values of ~ 50 and 90 nM, respectively. The binding is competitive with acetyl lysine. (+)-JQ1 can be a useful chemical probe to investigate the role of BET bromodomains in the transcriptional regulation of oncogenesis.