Structure-Based Development of Novel Spiro-Piperidine ASH1L Inhibitors

The absent, small, or homeotic-like 1 (ASH1L) protein
is a histone
lysine methyltransferase that plays a crucial role in various cancers,
including leukemia. Despite representing an attractive therapeutic
target, only one class of ASH1L inhibitors was identified to date.
Herein, we report development of advanced ASH1L inhibitors targeting
the catalytic SET domain, which were designed to access previously
unexplored binding pocket on ASH1L. Extensive medicinal chemistry
combined with structure-based design led to identification of 66s (AS-254s), a highly potent and selective
ASH1L inhibitor (IC50 = 94 nM), representing substantially
improved inhibitory activity over previously reported compounds targeting
ASH1L. Furthermore, 66s effectively blocked cell proliferation
and induced apoptosis and differentiation in leukemia cells harboring MLL1 translocations. Overall, this work provides a high-quality
chemical probe targeting the catalytic SET domain of ASH1L with increased
inhibitory activity and cellular efficacy to study biological functions
of ASH1L and potentially to develop novel anticancer therapeutics.