S2157

Lysine‐specific demethylase 1 (LSD1) is a flavin adenine dinucleotide (FAD)‐dependent enzyme that catalyzes the demethylation of histone H3 and regulates gene expression. Because it is implicated in the regulation of diseases such as acute myeloid leukemia, potent LSD1‐specific inhibitors have been pursued. Trans‐2‐phenylcyclopropylamine (2‐PCPA)‐based inhibitors featuring substitutions on the amino group have emerged, with sub‐micromolar affinities toward LSD1 and high selectivities over monoamine oxidases (MAOs). We synthesized two N‐alkylated 2‐PCPA‐based LSD1 inhibitors, S2116 and S2157, based on the previously developed S2101. S2116 and S2157 exhibited enhanced potency for LSD1 by 2.0‐ to 2.6‐fold, as compared with S2101. In addition, they exhibited improved selectivity over MAOs. Structural analyses of LSD1 co‐crystallized with S2101, S2116, S2157, or another N‐alkylated inhibitor (FCPA‐MPE) confirmed that the N‐substituents enhance the potency of a 2‐PCPA‐based inhibitor of LSD1, without constituting the adduct formed with FAD.

Lysine-specific demethylase 1 (LSD1) regulates several biological processes via the bifunctional modulation of enhancer functions. Recently, we reported that LSD1 overexpression is a founder abnormality of T-cell leukemogenesis and is maintained in fully transformed T-cell acute lymphoblastic leukemia (T-ALL) cells. On the basis of this finding, we attempted to develop novel LSD1 inhibitors effective for T-ALL with central nervous system (CNS) involvement.

We chemically modified the prototype LSD inhibitor tranylcypromine (TCP) and screened for cytotoxicity against TCP-resistant T-ALL cell lines. In vivo efficacy of novel LSD1 inhibitors was examined in immunodeficient mice transplanted with luciferase-expressing T-ALL cell lines, which faithfully reproduce human T-ALL with CNS involvement.

We found robust cytotoxicity against T-ALL cells, but not normal bone marrow progenitors, for two N-alkylated TCP derivatives, S2116 and S2157. The two compounds induced apoptosis in TCP-resistant T-ALL cells in vitro and in vivo by repressing transcription of the NOTCH3 and TAL1 genes through increased H3K9 methylation and reciprocal H3K27 deacetylation at superenhancer regions. Both S2116 and S2157 significantly retarded the growth of T-ALL cells in xenotransplanted mice and prolonged the survival of recipients as monotherapy and in combination with dexamethasone. Notably, S2157 could almost completely eradicate CNS leukemia because of its ability to efficiently pass through the blood–brain barrier.

These findings provide a molecular basis and rationale for the inclusion of a brain-permeable LSD1 inhibitor, S2157, in treatment strategies for T-ALL with CNS involvement.