The inhibition of AGTR1 and Aromatase as a new potential therapeutic strategy for Glioblastoma treatment.

Abstract

IntroductionGlioblastoma multiforme (GBM) is the most malignant form of glioma causing 3–4% of all cancer‐related deaths. Specific cancer treatment for GBM includes surgery, radiotherapy and chemotherapy with temozolomide. Despite the continuous development of new clinical therapies, the prognosis and survival of GBM patients remain dismal. Thus, the deregulated growth, the migratory and invasive capabilities of glioma cells remain the most important obstacles to the development of effective GBM treatments. Angiotensin II (Ang II)/Ang II receptor 1 (AGTR1) axis is expressed in normal and tumoral tissues, including human GBM. It has been reported in different experimental models that Ang II is able to stimulate aromatase expression through the AGTR1 activation. Different studies have demonstrated that aromatase enzyme is expressed in GBM cells and local estrogen production may act as an autocrine or paracrine factor in enhancing glioblastoma growth and progression. In the present study, we investigated if Ang II/AGTR1 signalling may modulate aromatase expression and consequently local estrogen production, thus influencing glioblastoma survival and growth.MethodsThe Aromatase expression role under treatment with Ang II has been assessed by RT‐PCR, Western blotting, Aromatase activity assay, Transient transfection assays, ELISA assay, cell proliferation assay (Thymidine incorporation), Boyden chamber migration and invasion assays, in the GBM cell line U‐87 MG.ResultsWe identified in U‐87 MG cells that the Ang II up‐regulates the aromatase expression in terms of mRNA, protein levels, and its enzymatic activity. In order to evaluate if Ang II may activate aromatase at transcriptional level we transiently transfected U‐87 MG cells with a vector containing human aromatase promoter I.4, broadly distributed around the brain and widely expressed in glioblastoma cells. Ang II treatment induces an increased aromatase promoter transcriptional activity. Mutagenesis studies and chromatin immunoprecipitation analysis reveal that the integrity of specificity protein 1 (SP1) and interferon‐gamma activation site (GAS) binding sites, within the aromatase promoter is required for Ang II modulation of human aromatase I.4 promoter activity in U87‐MG cells. The enhanced aromatase activity was paralleled by an higher estradiol production concomitant with an increase in cell proliferation, migration and invasion in U‐87 MG cells. These effects are reversed by treatment with an AGTR1 antagonist and/or an aromatase inhibitor, such as Losartan and Anastrozole respectively.ConclusionsAng II/AGTR1 signalling through Aromatase enhances local estrogen production which in turn promotes tumor growth and invasiveness. Therefore, their combined inhibitory targeting may prospectively provide a novel therapeutic strategy for Glioblastoma treatment.