Effetti dell'inibizione di HDAC6 sul pathway di NOTCH3 nel carcinoma dell'ovario e nel tumore della mammella triplo negativo.

Histone deacetylases (HDACs) are enzymes involved in the remodeling of chromatin. In the last years, HDACs inhibition has emerged as a potential strategy to reverse aberrant epigenetic changes associated with cancer. In fact, HDAC inhibitors (HDACi) promote apoptosis, induce cell cycle arrest and differentiation of tumor cells. Anyway, pan HDACs inhibitors are often linked to several side effects, therefore selective HDAC inhibition, such as HDAC6 inhibition, would be preferred. High Grade Serous Ovarian Cancer (HGSOC) and Triple Negative Breast Cancer (TNBC) represent common female tumors which are known for their poor prognosis and lack of targeted therapies. Among the main signaling pathways altered in these malignancies, we focused on aberrant activation of NOTCH3, found in a subset of these tumors and associated with chemoresistance and poor therapeutic options. We analyzed NOTCH3 pathway activation in a set of HGSOC patients, PDX and cell lines (OC and TNBC). At variance with previous studies, we did not find NOTCH3 substantial genomic amplification in HGSOC samples, nor any correlation between NOTCH3 copy number and NOTCH3 expression levels. Moreover, controversial results about NOTCH3 functions were obtained in MDAMB468 and OVCAR3 cells. Based on our previous studies in T-ALL indicating that HDAC6 inhibition reduced NOTCH3 protein level and pathway activation, we tested the effects of ACY-1215, a selective HDAC6 inhibitor used in clinical trials, in HGSOC and TNBC specimens with high NOTCH3 protein levels. Results showed that although ACY-1215 treatment reduced NOTCH3 protein level in different cell models, NOTCH3 pathway activation was not affected. Furthermore, transcriptomic analyses unveiled that ACY-1215 mediated multiple, pleiotropic and unexpectedly unselective effects in these cancer cells. Down-modulation of pre-NOTCH expression and processing was observed in MDAMB468 cells, but considering the plenty of modifications induced by ACY-1215, we concluded that NOTCH pathway only played a marginal role. We next uncovered that antiproliferative and proapoptotic effects mediated by ACY-1215 were strongly boosted by the co-administration of the proteasome inhibitor Bortezomib in several OC and TNBC cell lines. Omics techniques highlighted a strong stress response induced by the drugs combination as compared to ACY-1215 single agent and proteomic analysis of MDAMB468 cells clearly uncovered activation of the Unfolded Protein Response (UPR).