Epigenetic modifications control loss of adhesion and aggressiveness of cancer stem cells derived from head and neck squamous cell carcinoma with intrinsic resistance to cisplatin.

Objectives: The aims of this study were to investigate the epigenetic mechanisms and biological changes implicated in intrinsic and acquired resistance to cisplatin, a chemotherapy commonly used to treat head and neck squamous cell carcinoma.

Design: Intrinsic resistance (IR) was established in CAL-27 and acquired resistance (AR) in SCC-9 cell lines. Changes in the phenotype were evaluated by immunofluorescence, colony assay, invasion and spheres formation. Epigenetic regulation were assessed by quantitative PCR and western blot.

Results: Changes DNA damage accumulation, and a decrease of reactive oxygen species in cisplatin-resistant cell lines suggest a protection mechanism against cell death. Increases in aggressiveness, observed by clonogenic and invasive potentials, were more pronounced on the CAL-27 IR cell line. Cancer stem cells (CSC) were increased in cisplatin-resistant cells, and the administration of cisplatin increases CSC accumulation in CAL-27 IR. The loss of adhesion was noticed in CSC from IR cells. The upregulation of the genes HDAC2, HDAC9, SIRT1, KAT2B, KAT6A, KAT6B, and BRD4, the HDAC1 nuclear distribution and the decrease of the acetylated proteins H3K9, H3K36, H3K79, and H4K5 indicate that the IR mobilizes epigenetic modifications in acetylation levels, favoring the aggressiveness phenotype. Therefore, the treatment of CSC derived from CAL-27 IR with the histone deacetylase inhibitor, Vorinostat, partially recovered the CSC adhesion ability by up-regulating the levels of FAK, β3 integrin, and Vinculin proteins.

Conclusions: Our findings indicate that intrinsic-resistant cells are regulated by epigenetic modifications, which could be a potential target to treat resistant head and neck squamous cell carcinoma.