Variation in transcriptional regulation of cyclin dependent kinase inhibitor p21waf1/cip1 among human bronchogenic carcinomas

Aberrant overexpression of antiapoptotic members of the Bcl-2 protein family, including Bcl-2 and Bcl-X(L), contributes to malignant transformation and subsequent resistance to traditional chemotherapeutics. Thus, these proteins represent attractive targets for novel anticancer agents. The small molecule, gossypol, was initially investigated as a contraceptive agent, but subsequently has been shown to possess anticancer properties in vitro and in vivo. Recently gossypol has been found to bind to Bcl-X(L) and, with less affinity, to Bcl-2. Here we investigate the ability of the (-) enantiomer of gossypol, (-)-gossypol, to overcome the apoptosis resistance conferred by Bcl-2 or Bcl-X(L) overexpression in Jurkat T leukemia cells. (-)-Gossypol potently induced cell death in Jurkat cells overexpressing Bcl-2 (IC50, 18.1+/-2.6 micromol/L) or Bcl-X(L) (IC50, 22.9+/-3.7 micromol/L). Vector-transfected control cells were also potently killed by (-)-gossypol (IC50, 7.0+/-2.7 micromol/L). By contrast, the chemotherapy drug etoposide only induced efficient killing of vector-transfected cells (IC50, 9.6+/-2.3 micromol/L). Additionally, (-)-gossypol was more efficient than etoposide at inducing caspase-3 activation and phosphatidylserine externalization in the setting of Bcl-2 or Bcl-X(L) overexpression. (-)-Gossypol-induced apoptosis was associated with Bak activation and release of cytochrome c from mitochondria, suggesting a mitochondrial-mediated apoptotic mechanism. Moreover, (-)-gossypol treatment of isolated mitochondria purified from Bcl-2-overexpressing cells also resulted in cytochrome c release, indicating a possible direct action on Bcl-2 present in the mitochondrial outer membrane. Taken together, these results suggest that (-)-gossypol is a potent and novel therapeutic able to overcome apoptosis resistance by specifically targeting the activity of antiapoptotic Bcl-2 family members. (-)-Gossypol may be a promising new agent to treat malignancies that are resistant to conventional therapies.

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