title: Response to histone deacetylase inhibition of novel PML/RARalpha mutants detected in retinoic acid-resistant APL cells.
abstract: Resistance to all-trans retinoic acid (ATRA) remains a clinical problem in the treatment of acute promyelocytic leukemia (APL) and provides a model for the development of novel therapies. Molecular alterations in the ligand-binding domain (LBD) of the PML/RARalpha fusion gene that characterizes APL constitute one mechanism of acquired resistance to ATRA. We identified missense mutations in PML/RARalpha from an additional ATRA-resistant patient at relapse and in a novel ATRA-resistant cell line, NB4-MRA1. These cause altered binding to ligand and transcriptional coregulators, leading to a dominant-negative block of transcription. These mutations are in regions of the LBD that appear to be mutational hot spots occurring repeatedly in ATRA-resistant APL patient cells. We evaluated whether histone deacetylase (HDAC) inhibition could overcome the effects of these mutations on ATRA-induced gene expression. Cotreatment with ATRA and TSA restored RARbeta gene expression in NB4-MRA1 cells, whose PML/RARalpha mutation is in helix 12 of the LBD, but not in an APL cell line harboring the patient-derived PML/RARalpha mutation, which was between helix 5 and 6. Furthermore, ATRA combined with TSA increases histone 4 acetylation on the RARbeta promoter only in NB4-MRA1 cells. Consistent with these results, the combined treatment induces differentiation of NB4-MRA1 only. Thus, the ability of an HDAC inhibitor to restore ATRA sensitivity in resistant cells may depend on their specific molecular defects. The variety of PML/RARalpha mutations arising in ATRA-resistant patients begins to explain how APL patients in relapse may differ in response to transcription therapy with HDAC inhibitors.
authors.affiliation: Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital and McGill University Department of Oncology and Medicine, Montreal, Quebec, Canada.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Côté
authors.forename: Angelika
authors.initials: A
authors.lastname: Rosenauer
authors.forename: Andrea
authors.initials: A
authors.lastname: Bianchini
authors.forename: Karen
authors.initials: K
authors.lastname: Seiter
authors.forename: Jonathan
authors.initials: J
authors.lastname: Vandewiele
authors.forename: Clara
authors.initials: C
authors.lastname: Nervi
authors.forename: Wilson H
authors.initials: WH
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000970:Antineoplastic Agents / Q000633:toxicity; D001483:Base Sequence; D002454:Cell Differentiation; D002843:Chromatin / Q000235:genetics / Q000648:ultrastructure; D017931:DNA Primers; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000235:genetics / Q000473:pathology*; D009154:Mutation; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics*; D015514:Oncogene Proteins, Fusion / Q000037:antagonists & inhibitors / Q000235:genetics*; D016133:Polymerase Chain Reaction; D017384:Sequence Deletion; D014212:Tretinoin / Q000633:toxicity*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D002843:Chromatin; D017931:DNA Primers; D009363:Neoplasm Proteins; D015514:Oncogene Proteins, Fusion; C093476:promyelocytic leukemia-retinoic acid receptor alpha fusion oncoprotein; D014212:Tretinoin; D006655:Histone Deacetylases