Clinical Responsiveness to All-trans Retinoic Acid Is Potentiated by LSD1 Inhibition and Associated with a Quiescent Transcriptome in Myeloid Malignancies.

In preclinical studies, the lysine-specific histone demethylase 1A (LSD1) inhibitor tranylcypromine (TCP) combined with all-trans retinoic acid (ATRA) induces differentiation and impairs survival of myeloid blasts in non-acute promyelocytic leukemia acute myeloid leukemia (AML). We conducted a phase I clinical trial (NCT02273102) to evaluate the safety and activity of ATRA plus TCP in patients with relapsed/refractory AML and myelodysplasia (MDS). Seventeen patients were treated with ATRA and TCP (three dose levels: 10 mg twice daily, 20 mg twice daily, and 30 mg twice daily). ATRA-TCP had an acceptable safety profile. The MTD of TCP was 20 mg twice daily. Best responses included one morphologic leukemia-free state, one marrow complete remission with hematologic improvement, two stable disease with hematologic improvement, and two stable disease. By intention to treat, the overall response rate was 23.5% and clinical benefit rate was 35.3%. Gene expression profiling of patient blasts showed that responding patients had a more quiescent CD34+ cell phenotype at baseline, including decreased MYC and RARA expression, compared with nonresponders that exhibited a more proliferative CD34+ phenotype, with gene expression enrichment for cell growth signaling. Upon ATRA-TCP treatment, we observed significant induction of retinoic acid-target genes in responders but not nonresponders. We corroborated this in AML cell lines, showing that ATRA-TCP synergistically increased differentiation capacity and cell death by regulating the expression of key gene sets that segregate patients by their clinical response. These data indicate that LSD1 inhibition sensitizes AML cells to ATRA and may restore ATRA responsiveness in subsets of patients with MDS and AML.