Elucidating the Mechanism of CDDO, a Promising Chemopreventive Agent <P>

Chemoprevention is the use of natural or synthetic substances to reduce the risk of developing cancer, or to reduce the chance that cancer will recur. The semi-synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) has several biological activities, including the induction of apoptosis in many cancer cell lines, and is currently under evaluation as a possible chemopreventive agent. To begin to elucidate the molecular mechanism of CDDO, immobilized biotinylated-CDDO was used to screen the proteome of a human lymphoma cell line (U937) sensitive to CDDO-induced apoptosis. Tubulin was identified as one of several putative targets. CDDO was shown to selectively bind to tubulin, with a dissociation constant of ~7  M, and to disrupt microtubules. The CDDO-tubulin interaction may involve a hydrophobic site on tubulin and a reversible 1,4-addition with a protein sulfhydryl group. Unlike other known microtubule poisons, CDDO does not result in a temporal increase in the mitotic index. Rather, CDDO appears to initiate apoptosis early in M phase. Thus, it appears that CDDO may function through interactions with several proteins, rather than a single target.