Endocrine Abstracts

Small cell lung cancer (SCLC) is an aggressive neuro-endocrine tumour with an abysmal prognosis. These cancers are characteristically resistant to glucocorticoid (Gc) action, and display glucocorticoid receptor (GR) abnormalities. We therefore selected model cell lines displaying reduced GR expression and Gc insensitivity as tractable in vitro systems in which to discover the effects of restored GR expression. GR fused to the yellow fluorescent protein, eYFP, was over-expressed in these cells using a retroviral delivery system and the outcomes measured by flow cytometry, confocal microscopy, reporter gene studies and quantitative PCR. Retroviral infection resulted in increased GR expression. This caused a decrease in cell proliferation and an upregulation of the endogenous Gc target gene, GILZ, in response to Gc exposure, indicating that restored GR expression confers Gc sensitivity to the cells. Interestingly, over-expression of GR in the cells resulted in an increase in cell death which could be partially blocked by the addition of a GR agonist. Flow cytometry using propidium iodide, a marker of cell death, and Annexin V, a marker of early stage apoptosis, revealed that the mode of cell death was by apoptosis. In addition, confocal microscopy revealed a significant increase in the number of fragmenting, apoptotic nuclei after GR over-expression. As restoration of GR expression in vitro results in apoptotic cell death of SCLC cells, our next objective was to determine whether GR expression can induce apoptosis in vivo. To this end, SCLC xenografts were created, the pathology of which is similar to that of human SCLC. Our aim is to inject the tumours with adenovirus expressing GR-eYFP to determine whether apoptosis is induced in infected cells and/or whether tumour growth is inhibited.