Apoptotic cell death was induced by amitriptyline in human multiple myeloma cell lines and primary cells by decreasing histone deacetylase (HDAC) (HDAC-3, 6, 7, 8) expression and inhibiting HDAC activity; furthermore, amitriptyline reduced cyclin D2 expression arresting cells in the G0/G1 phase of the cell cycle [78]. Here, HDAC9 is linked to plasma cell myeloma.