HDAC9 and plasma cell myeloma: In both patient-derived and immortalized leukemia cell lines, AR42 demonstrated both class 1 and 2 HDACi activity through persistent acetylation of histone H3 (HDAC class 1) and tubulin (HDAC class 2b) as detected by Western blot analysis, while in multiple myeloma cell lines only H3 acetylation has been demonstrated [17,30].