PFI-1 is a selective BET (bromodomain-containing protein) inhibitor for BRD4 with IC50 of 0.22 μM.

Bromodomains recognize acetylated lysine residues and recruit regulatory complexes to acetylated nucleosomes, thereby controlling chromatin structure and gene expression. The isolated individual or tandem bromodomains of bromodomain-containing protein (BRD) 2 and BRD4 bind acetylated histone tails, which couples histone acetylation marks to the transcriptional regulation of target promoters. Small molecule inhibitors of bromodomain interactions hold promise as useful therapeutics for human disease.PFI-1 is a BET bromodomain inhibitor that exhibits inhibitory activity at BRD2 and BRD4. In an AlphaScreen assay it has been shown to inhibit BRD2 bromodomain 2 and BRD4 bromodomain 1 with IC50 values of 98 nM and 0.22 μM, respectively.