MS‐1020 is a novel small molecule that selectively inhibits JAK3 activity

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Abstract
Summary: In order to identify Janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling inhibitors, a cell‐based high throughput screening was performed using a plant extract library that identified Nb‐(α‐hydroxynaphthoyl)serotonin called MS‐1020 as a novel JAK3 inhibitor. MS‐1020 potently inhibited persistently‐active STAT3 in a cell type‐specific manner. Further examination showed that MS‐1020 selectively blocked constitutively‐active JAK3 and consistently suppressed interleukin‐2‐induced JAK3/STAT5 signalling but not prolactin‐induced JAK2/STAT5 signalling. Furthermore, MS‐1020 affected cell viability only in cancer cells harbouring persistently‐active JAK3/STATs, and in vitro kinase assays showed MS‐1020 binds directly with JAK3, blocking its catalytic activity. Therefore, the present study suggested that this reagent selectively inhibits JAK3 and subsequently leads to a block in STAT signalling. Finally, MS‐1020 decreased cell survival by inducing apoptosis via down‐regulation of anti‐apoptotic gene expression. These results suggest that MS‐1020 may have therapeutic potential in the treatment of cancers harbouring aberrant JAK3 signalling.

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