Super-Enhancer Analysis Defines Novel Epigenomic Subtypes of Non-APL AML Including an RAR{alpha} Dependency Targetable by SY-1425, a Potent and Selective RAR{alpha} Agonist [Research Articles]

We characterized the enhancer landscape of 66 AML patients, identifying 6 novel subgroups and their associated regulatory loci. These subgroups are defined by their super-enhancer (SE) maps, orthogonal to somatic mutations, and are associated with distinct leukemic cell states. Examination of transcriptional drivers for these epigenomic subtypes uncovers a subset of patients with a particularly strong super-enhancer at the retinoic acid receptor alpha (RARA) gene locus. Presence of a RARA SE and concomitant high levels of RARA mRNA predisposes cell lines and ex vivo models to exquisite sensitivity to a selective agonist of RARα, SY-1425 (tamibarotene). Furthermore, only AML patient-derived xenograft (PDX) models with high RARA mRNA were found to respond to SY-1425. Mechanistically, we show that the response to SY-1425 in RARA-high AML cells is similar to that of APL treated with retinoids, characterized by the induction of known retinoic acid response genes, increased differentiation, and loss of proliferation.

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