HDAC9 and gastric adenocarcinoma: Takahashi and colleagues showed that diverse HDAC inhibitors reduce ACE2 expression in gastric adenocarcinoma cell lines, and do not modulate the transmembrane serine protease 2 (TMPRSS2) (49), therefore, we investigated the possible effect of the HDACi on their expression in epithelial cells of the upper and lower respiratory tract.