RIOK2 is a typical kinase implicated in multiple human cancers. The right open reading frame (RIO) kinases belong to the atypical kinases family. RIO kinases contain a C-terminal RIO domain that is structurally homologous to typical protein kinases. However, RIOKs lack the key motifs which can convert the enzyme from an inactive to an active state. Additionally, there are four members: RIOK1 and RIOK2 (conserved kinases). Whereas multicellular eukaryotes, including humans, have a third RIOK, RIOK3. It's worth noting that RioB only exists in some archaea and eubacteria.

CQ211 is a potent and selective RIOK2 inhibitor.

This compound displays a high binding affinity (K_d=6.1 nM). And it shows excellent selectivity to RIOK2 in both enzymatic and cellular studies. As a RIOK2-Specific Inhibitor, CQ211 exhibits excellent selectivity to RIOK2. And there demonstrates no interaction between CQ211 and any of the other wild-type kinases. What’s more, CQ211 exhibits binding interactions only with three FLT3 mutants, FLT3-ITDD835V, FLT3-ITD-F691L, and FLT3-D835V with percentage. CQ211 significantly suppresses the ATPase activity of recombinant RIOK2 with an IC₅₀ value of 0.139±0.046 μM. CQ211 exhibits effective anti-proliferation activity. Additionally, it obviously suppresses the proliferation of MKN-1 and HT-29 cells with IC₅₀ values of 0.61±0.18 and 0.38±0.01 μM, respectively. Furthermore, it also decreases the mTOR phosphorylation level with a dose of CQ211 >0.60 μM in MKN-1 and HT-29 cells. In the MKN-1 xenografts model, CQ211 exhibits potent-antitumor efficacy after an intraperitoneal injection dosage 25 mg/kg. And CQ211 has a poor oral bioavailability (3.06%) and low C_max (13±5 ng/mL). In summary, we introduce a highly potent and selective RIOK2 inhibitor in vitro and in vivo. And it is a potent chemical probe to accelerate future research into the biological functions of RIOK2.