Towards a RIOK2 chemical probe: cellular potency improvement of a selective 2-(acylamino)pyridine series

Exploration of tricyclic heterocycles as core structures for RIOK2 inhibitors

Right open reading frame kinase 2 (RIOK2) is an atypical kinase and has been proved to be involved in multiple human cancers including non-small cell lung cancer (NSCLC), acute myeloid leukemia (AML), glioblastoma and anemia. Although tremendous efforts have been devoted to the studies of RIOK2, its biological functions remain poorly understood. It is highly important to develop potent and selective RIOK2 inhibitors as potential research tools to elucidate its functions and as drug candidates for further therapies. We have previously identified a highly potent and selective RIOK2 inhibitor (CQ211). To confirm the importance of the "V-shaped" structure of CQ211 for binding with RIOK2, a variety of tricyclic compounds with different core structures instead of the [1,2,3]triazolo[4,5-c]quinolin-4-one core of CQ211 were designed, synthesized, and the binding affinities of these tricyclic heterocycles with RIOK2 were also evaluated.

Discovery of 8-(6-Methoxypyridin-3-yl)-1-(4-(piperazin-1-yl)-3-(trifluoromethyl)phenyl)-1,5-dihydro-4H-[1,2,3]triazolo[4,5-c]quinolin-4-one (CQ211) as a Highly Potent and Selective RIOK2 Inhibitor

RIOK2 is an atypical kinase implicated in multiple human cancers. Although recent studies establish the role of RIOK2 in ribosome maturation and cell cycle progression, its biological functions remain poorly elucidated, hindering the potential to explore RIOK2 as a therapeutic target. Here, we report the discovery of CQ211, the most potent and selective RIOK2 inhibitor reported so far. CQ211 displays a high binding affinity (K_d = 6.1 nM) and shows excellent selectivity to RIOK2 in both enzymatic and cellular studies. It also exhibits potent proliferation inhibition activity against multiple cancer cell lines and demonstrates promising in vivo efficacy in mouse xenograft models. The crystal structure of RIOK2-CQ211 sheds light on the molecular mechanism of inhibition and informs the subsequent optimization. The study provides a cell-active chemical probe for verifying RIOK2 functions, which may also serve as a leading molecule in the development of therapeutic RIOK2 inhibitors.