MCL1 and plasma cell myeloma: The apoptotic action of ATO has been shown to involve downregulation of the anti-apoptotic protein Mcl-1 in several cell systems, including myeloma [36] and myeloid leukemia cells [37] and, in many cases, upregulation of the pro-apoptotic proteins Bax and/or Bim [36], [38], [39].