Abstract 148: Glucocorticoid receptor-mediated cell survival following androgen receptor blockade in castrate-resistant prostate cancer

Abstract

Abstract Introduction: Sustained androgen receptor (AR) signaling is required for the development of castrate resistant prostate cancer (CRPC). We have shown that following androgen deprivation therapy for prostate cancer, tumor glucocorticoid receptor (GR) expression is increased (The Prostate, 2011). The GR and AR are known to share similar DNA binding sequences and to regulate several common target genes, including the anti-apoptotic protein serum/glucocorticoid regulated kinase 1 (SGK1). We hypothesized that increased GR expression might compensate for diminished AR signaling, thereby facilitating resistance to potent inhibitors of the AR through sustained expression of apoptosis inhibitor. Methods: CWR-22RV1 (22RV1) and LAPC4 prostate cancer cell lines were grown in vitro with various combinations of the AR antagonist MDV3100 (10μM), synthetic androgen R1881 (10nM), GR agonist dexamethasone (Dex, 1μM) or the SGK1 kinase inhibitor GSK650394 (1μM). SGK1-FLAG or vector was stably expressed and cellular viability, secreted PSA, and protein lysates were collected. Results: Following MDV3100 treatment, GR expression increased in both CWR-22RV1 and LAPC4 cell lines. Although proliferation rates of both SGK1 and vector expressing cell lines were slower following Dex, there was a relative protection from MDV3100-associated cell death. For LAPC4 cells, cell survival compared to R1881 control was improved with Dex (66% vs. 47%, p<0.05). For 22RV1, Dex treatment also increased cell survival despite MDV3100 (151% vs. 51% without Dex). Dex treatment also led to increased PSA secretion despite MDV3100 treatment. For LAPC4 cells, secreted PSA levels (ng/nL) were 22.7 (R1881), 1.4 (MDV3100), and 31.5 (MDV3100+Dex). For the CWR-22RV1's there was similar antagonism of MDV3100 activity following Dex treatment: 10.9, 4.4, and 41.9 for R1881, MDV3100 and MDV3100+Dex respectively. Expression of SGK1 was reduced with MDV3100, but increased with the addition of Dex. To test if SGK1 was required for GR-mediated protection from cell death following AR inhibition, the cell lines were grown with or without GSK650394. Cell survival with both cell lines was impaired following treatment with the SGK1 inhibitor. For LAPC4, relative to R1881+Dex control, % survival was 58% with MDV3100+Dex and only 19% with the addition of GSK650394 (p<0.05). Results with the 22RV1 cells were similar. SGK1-Flag over-expressing LAPC4 cells were protected from MDV3100 treatment compared to vector controls-61% vs. 24% survival (p<0.05). Conclusions: These data suggest that increased GR expression and activity antagonizes AR inhibition and sustains tumor cell survival. Furthermore, SGK1 appears to be a downstream mediator of this effect. Further in vitro and in vivo studies are underway to test this hypothesis. If supported, GR or SGK1 inhibition may be a useful adjunct to blocking AR activity in CRPC treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 148. doi:1538-7445.AM2012-148