Structure of Abiraterone

Here is the chemical structure of Abiraterone (Zytiga). Note the 4 rings of the steroidal skeleton that are joined at the 17 position to a 3-pyridyl ring. The blue colour shows the nitrogen of the 3 pyridyl group that is responsible for its pharmacological action by binding to the iron atom at the centre of the CYP17 enzyme. The red colour shows the oxygen atom at the front end of the molecule. This mimics the oxygen of the natural substrate pregnenolone so Abiraterone fits the enyme active sit as precisely as the natural substrate but acts as an inhibitor through coordination of the central iron atom. In this way Abiraterone makes a precise fit into the CYP17 enzyme and inhibits it completely preventing it from making any androgens so the plasma androgen levels fall to zero when taking zytiga.