PFI-1 is a potent and selective inhibitor of the BET (bromodomain and extra-terminal) family of proteins, particularly targeting BRD4. Its primary application lies in epigenetic research, where it is used to study gene regulation mechanisms mediated by bromodomain-containing proteins. By blocking the acetyl-lysine binding sites on BET proteins, PFI-1 disrupts their interaction with chromatin, leading to downregulation of key oncogenes such as MYC. This makes it a valuable tool compound in cancer research, especially in models of leukemia, lymphoma, and other MYC-driven cancers. In addition to oncology, PFI-1 has been used to investigate inflammatory diseases and viral latency, as BET proteins play a role in the transcriptional control of inflammatory mediators and HIV reactivation. Due to its cell permeability and relatively favorable pharmacokinetic profile, PFI-1 is widely used in cellular assays and in vivo studies to validate BET inhibition as a therapeutic strategy. It serves as a lead compound for the development of more advanced BET inhibitors with clinical potential.