Lung Cancer: A Classic Example of Tumor Escape and Progression While Providing Opportunities for Immunological Intervention
Elevated tumor cyclooxygenase 2 (COX-2) expression is associated with increased angiogenesis, tumor invasion, and promotion of tumor cell resistance to apoptosis. In our previous studies using non-small cell lung cancer (NSCLC) cell lines constitutively expressing COX-2 cDNA in sense and antisense orientations, we demonstrated that constitutive overexpression of COX-2 leads to stabilization of the inhibitor of apoptosis protein survivin resulting in the elevated apoptosis resistance of COX-2-overexpressing cells. Genetic or pharmacologic suppression of COX-2 activity increased proteasomal degradation of survivin and cellular response to apoptosis induction. Our data show that expression of survivin in non-small cell lung cancer cells can be significantly down-regulated by RNA interference. Whereas COX-2-overexpressing NSCLC cells have significantly higher apoptosis resistance than the parental cells, inhibition of survivin expression by small interfering RNA decreases apoptosis resistance to the level of the parental non-small cell lung cancer. We conclude that COX-2-dependent expression of survivin is critical for apoptosis resistance in non-small cell lung cancer.