API-1

API-1 is a specific small molecule inhibitor of the peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1). It functions by targeting the Pin1 peptidyl-prolyl isomerase (PPIase) domain, thereby blocking its cis-trans isomerizing activity. In the context of hepatocellular carcinoma (HCC), Pin1 is frequently overexpressed and contributes to tumor progression by passivating phosphorylated exportin-5 (XPO5), which impairs the nuclear-to-cytoplasmic export of precursor microRNAs (miRNAs). API-1 treatment prevents this passivation, maintaining XPO5 in its active conformation and restoring miRNA biogenesis. This reactivation of tumor-suppressive miRNA pathways leads to the suppression of HCC cell proliferation, migration, and tumor growth in xenograft models. Note that the code name API-1 is also commonly used in scientific literature to refer to an unrelated Akt pathway inhibitor, Triciribine.