The novel triterpenoid CDDO induces apoptosis and differentiation of humanosteosarcoma cells by a caspase-8 dependent mechanism

The oleanane triterpenoid 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDD O) is a multifunctional molecule that induces monocytic differentiation of human myeloid leukemia cells and inhibits proliferation of diverse human tu mor cell lines. The present studies on human osteosarcoma cells demonstrate that CDDO induces mitochondrial cytochrome c release, caspase-3 activation , and internucleosomal DNA fragmentation. Overexpression of the caspase-8 i nhibitor CrmA blocked CDDO-induced cytochrome c release and apoptosis. By c ontrast, overexpression of the antiapoptotic Bcl-x(L) protein blocked CDDO- induced cytochrome c release, but only partly inhibited caspase-3 activatio n and apoptosis. In concert with these findings, we demonstrate that CDDO: 1) activates caspase-8 and thereby caspase-3 by a cytochrome c-independent mechanism and 2) induces cytochrome c release by caspase-8-dependent cleava ge of Bid. The results also demonstrate that treatment of osteosarcoma cell s with CDDO induces differentiation, as assessed by alkaline phosphatase ac tivity and osteocalcin production, and that this response is abrogated in c ells that overexpress CrmA. These findings demonstrate that CDDO induces bo th osteoblastic differentiation and apoptosis by caspase-8-dependent mechan isms.