222 Dexamethasone Induces Mesenchymal Trans-differentiation and Promotes Hallmarks of Cancer in Glioblastoma

Abstract

Abstract INTRODUCTION Dexamethasone is the most commonly used drug in oncologic patients. In brain cancer and specifically glioblastoma, the drug is used in high doses to treat brain tumor associated vasogenic edema. Besides the rather immediate anti-inflammatory properties of dexamethasone, the longer term molecular effects have not been sufficiently studied. This work uncovers possibly deleterious dexamethasone-mediated effects through mesenchymal trans-differentiation and promotion of cellular hallmarks of cancer in glioblastoma patients. METHODS Three independent glioblastoma stem cell (GSC) lines with tumorigenic potential were used for the experiments. RT-PCR, Western Blot, Immunohistochemistry, invasion assays, whole-genome expression profiling, and pathway analyses were done with dexamethasone-exposed versus control cells both in vitro and in vivo orthotopic mouse xenograft models. GSCs were also co-exposed to dexamethasone, temozolomide, and camptothecin; the latter as a potential neutralizer of dexamethasone-induced deleterious effects. A dexamethasone induced gene signature was interrogated for survival prognostication in two large independent clinico-genomic databases comprising more than 500 patients. RESULTS >Dexamethasone induced the mesenchymal activator CCAAT/enhancer binding protein beta (CEBPB) in a dose dependent manner in vitro and in dexamethasone-treated orthotopic tumors. Significantly altered cellular functions included cell movement, cell survival, apoptosis, and angiogenesis. Dexamethasone-treated GSCs were protected against temozolomide-induced apoptosis and had significant increase of invasion both in vitro and in vivo. Furthermore, dexamethasone exposure resulted in significant elevation of cell proliferation and angiogenesis in vivo. A prognostic dexamethasone induced 33 gene signature was derived from orthotopic tumor expression profile analysis and validated in large clinico-genomic databases (p-value: 0.0007). Camptothecin was validated as potential partial neutralizer of dexamethasone-induced oncogenic effects. CONCLUSION Dexamethasone exposure induces a genetic program and CEBPB expression in GSCs that adversely affects key cellular functions and response to therapeutics. High risk scores associated with these genes have negative prognostic value in patients. Our findings further suggest well tolerated low-dose camptothecin as a potential neutralizer of adverse dexamethasone-mediated effects.