PIN1 inhibitor API-1 is primarily used in cancer research due to its ability to block the activity of the peptidyl-prolyl cis/trans isomerase Pin1 enzyme. This enzyme plays a critical role in regulating cell cycle progression and is often overexpressed in various cancers, including breast, prostate, and lung cancers. By inhibiting Pin1, API-1 disrupts oncogenic signaling pathways, leading to suppression of tumor cell proliferation and induction of apoptosis.

It has shown potential in enhancing the effectiveness of other anticancer agents, particularly in hormone-resistant cancers, by modulating key signaling molecules such as cyclin D1 and c-Myc. Additionally, API-1 is used as a research tool to study Pin1-dependent cellular processes, including transcription regulation and stress response. Its application supports the development of targeted therapies aimed at disrupting protein-protein interactions involved in cancer progression.