ARSENIC TRIOXIDE AND MELARSOPROL INDUCE PROGRAMMED CELL-DEATH IN MYELOID-LEUKEMIA CELL-LINES AND FUNCTION IN A PML AND PML-RAR-ALPHA INDEPENDENT MANNER

Inorganic arsenic trioxide (As2O3) and the organic arsenical, melarsop rol, were recently shown to inhibit growth and induce apoptosis in NB4 acute promyelocytic leukemia (APC) and chronic B-cell leukemia cell l ines, respectively. As2O3 has been proposed to principally target PML and PML-RAR alpha proteins in APL cells. We investigated the activity of As2O3 and melarsoprol in a broader context encompassing various mye loid leukemia cell lines, including the APL cell line NB4-306 (a retin oic acid-resistant cell line derived from NB4 that no longer expresses the intact PML-RAR alpha fusion protein), HL60, KG-1, and the myelomo nocytic cell line U937. To examine the role of PML in mediating arseni cal activity, we also tested these agents using murine embryonic fibro blasts (MEFs) and bone marrow (BM) progenitors in which the PML gene h ad been inactivated by homologous recombination. Unexpectedly, we foun d that both compounds inhibited cell growth, induced apoptosis, and do wnregulated bcl-2 protein in all cell lines tested. Melarsoprol was mo re potent than As2O3 at equimolar concentrations ranging from 10(-7) t o 10(-5) mol/L. As2O3 relocalized PML and PML-RAR alpha onto nuclear b odies, which was followed by PML degradation in NB4 as well as in HL60 and U937 cell lines. Although melarsoprol was more potent in inhibiti ng growth and inducing apoptosis, it did not affect PML and/or PML-RAR alpha nuclear localization. Moreover, both As2O3 and melarsoprol comp arably inhibited growth and induced apoptosis of PML+/+ and PML-/- MEF s, and inhibited colony-forming unit erythroid (CFU-E) and CFU granulo cyte-monocyte formation in BM cultures of PML+/+ and PML-/- progenitor s. Together, these results show that As2O3 and melarsoprol inhibit gro wth and induce apoptosis independent of both PML and PML-RAR alpha exp ression in a variety of myeloid leukemia cell lines; and suggest that these agents may be more broadly used for treatment of leukemias other than APL. (C) 1998 by The American Society of Hematology.