Aim: To investigate the role of the glucocorticoid receptor in human small cell lung cancer

Small cell lung cancers (SCLC) are aggressive neuro-endocrine tumours with an abysmal prognosis. Their ectopic secretion of the neuro-peptide, ACTH, is characteristically resistant to the normal negative feedback of circulating glucocorticoids (Gc). We identified dramatically reduced expression of the glucocorticoid receptor (GR) in a panel of SCLC cell lines compared to a non-SCLC cell line. In addition, while the non-SCLC cells were sensitive to Gc-mediated inhibition of proliferation, the SCLC cells were unresponsive to Gc action. Over-expression of the GR by retroviral infection in the SCLC cells decreased ACTH secretion and inhibited proliferation suggesting that a threshold level of GR is required in SCLC cells to facilitate Gc action. Restored GR expression in SCLC cells resulted in a significant increase in cell death quantitated by PI staining and flow cytometric analysis. Cell death was prevented when SCLC cells were exposed to the GR antagonist, RU486, inferring that cell death was due directly to over-expression of the GR. Cells over-expressing GR were shown to have significantly more fragmenting nuclei when compared to control cells. This, coupled with Annexin V flow cytometric results, suggested that over-expression of GR results in SCLC cell death by apoptosis. Apoptotic cell death as a result of over-expression of GR was not seen in the equally Gc insensitive cell line, HEK cells. Microarray studies were performed to identify downstream targets of the GR in SCLC cells. These studies showed that GR upregulated the pro-apoptotic genes, BAD and BAX. We have shown that restoring GR expression in SCLC cells causes cell death by apoptosis by induction of the apoptotic cascade and, therefore, that the loss of GR expression in these cells confers a survival advantage to SCLC cells. The apoptosis and array studies were performed in the absence of GR ligand suggesting that SCLC cells are exquisitely sensitive to apoptotic induction by the GR and this may explain low levels of GR in SCLC cell lines.Understanding how the GR acts to induce apoptotic cell death of SCLC cells may uncover new therapeutic strategies.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA