ALL-TRANS RETINOIC ACID AND ARSENIC TRIOXIDE INDUCE LASTING DIFFERENTIATION AND DEMETHYLATION OF TARGET GENES IN ACUTE PROMYELOCYTIC LEUKEMIA
Acute promyelocytic leukemia (APL) patients treated with all-trans retinoic acid (ATRA) experience relapse, while patients treated with ATRA and arsenic trioxide (ATO) are often relapse-free. To understand combination therapy, we compared the effects of ATRA, ATO or the combination, on NB4 APL cells during treatment versus 96h post treatment termination. After treatment termination, cells treated with ATRA or ATO reverted to non-differentiated cells, while combination-treated cells remained differentiated. ATRA and combination treatment induced similar levels of target genes during treatment; however, post treatment termination, combination-treated cells retained higher levels of target genes (e.g., transglutaminase 2 and retinoic acid receptor beta). We quantified enrichment of histone modifications by chromatin immunoprecipitation, and CpG methylation by bisulfite-pyrosequencing. While ATRA and combination treatment induced similar histone acetylation enrichment, only combination treatment reduced CpG methylation of target genes. Therefore, DNA methylation changes is associated with lasting differentiation and gene expression changes induced by combination treatment.