1B). In fact, paracrine-induced histone modifications resulted in enhanced expression of Bmi-1, a transcriptional kinase inhibitors repressor upregulated in a variety of cancers and associated with tumor aggressiveness, and poor survival along with the expression of vimentin, a canonical marker of EMT (Figure ​(Figure1B1B)[192-199]. Similar to our in vitro findings, human HNSCC samples presented coexpression of acetylated histone 3 and vimentin in the proximity of normal endothelial cells (Figure ​(Figure1C-white1C-white dashed line) next to the tumor invasion front in human HNSSC samples (Figure ​(Figure1C-yellow1C-yellow dashed line). Therefore, acetylation of tumor histones are associated to changes in cellular

behavior, phenotype and associated to increased invasion. In fact, malignant tumors derived from epithelial cells (carcinomas) are known to undergo EMT that precedes local invasion and metastasis of cancer cells[200-204]. EMT is characterized by the loss of cell adhesion, increased motility, aggressive behavior, acquisition of an elongated fibroblastoid morphology and expression of vimentin[200,205,206], similar to what we observe with pharmacological inhibition of HDAC in HNSCC cell lines (Figure ​(Figure2-HN62-HN6 and HN13 cells).

Interestingly, cellular morphology is not altered and vimentin is not induced in normal epithelial cells (NOK-SI) treated with HDAC inhibitors, suggesting that hyperacetylation of chromatin differentially modulates normal and neoplastic cells (Figure ​(Figure2).2). However, changes in the acetylation of HNSCC chromatin also triggered an unexpected phenotype, which was the loss of CSCs. HNSCC treated with Trichostatin A, a histone deacetylase

inhibitor, lose the ability to generate and maintain tumor spheres and experience rapid reduction in the enzymatic activity of ALDH1 (Figure ​(Figure33)[151]. It has been suggested that epigenetic signals play a major role in stem cell control through deacetylation of histones, which promotes chromatin condensation and reactivation of stem cell-like transcription programs[34]. Cilengitide These striking findings suggest that chromatin acetylation selectively disrupts the physiological requirements for maintenance of CSC. Indeed, chromatin acetylation has long been known to induce cellular differentiation and restrict cellular transformation of normal cells[34,207,208]. Figure 1 Data represents acetylation status of histone 3 in Head and Neck Squamous Cell Carcinoma by Giudice et al[151]. A: Tumor cells present hypoacetylation of histone 3 (ac.H3) in a panel of Head and Neck Squamous Cell Carcinoma (HNSCC) compared to control … Figure 2 Figure from Giudice et al[151] depicting chemically-induced chromatin acetylation leading to activation of the epithelial-mesenchymal transition phenotype. Inhibition of HDAC induces vimentin expression in HNSCC cells and EMT.