Rational discovery of novel type-III FTF antagonists to competitively suppress TIF-2 coactivation in liver cancer

The α-fetoprotein transcription factor (FTF) is a member of the nuclear receptor NR5A subfamily, which is involved in the pathogenesis of liver Cancer and some other gastrointestinal cancers. The protein's transcriptional activity is regulated by binding TIF-2 coactivator at its coactivator-interacting site (CIS); suppression of the transcriptional activity has been recognized as a potential therapeutic strategy against Cancer. Previously, small-molecule antagonists have been developed to target the ligand-binding site (LBS) of FTF ligand-binding domain, which simply occupy the site to exclusively block natural ligand entry (type-I antagonists) or destabilize the agonist conformation of activation helix 12 of the domain (type-II antagonists). Here, we describe the use of small-molecule competitors (type-III antagonists) to directly disrupt FTF-TIF-2 interaction by competitively targeting FTF CIS site. High-throughput virtual screening is performed against a structurally diverse, commercially available compound library to identify FTF CIS binders as competitor candidates, from which 12 hits are manually selected and their competitive potency with TIF-2 core binding sequence for FTF CIS site is tested with CC₅₀ values up to 2.5 μM. Structural modeling analysis revealed that the competitive ligands can form a complicated network of noncovalent interactions to specifically or nonspecifically pack against FTF CIS site, thus preventing TIF-2 from binding to the site.