Figure 1. Structure of X-370 and its inhibitory activity against lipid kinases.

(A) Chemical structure of X-370. (B) X-370 docked to the crystal structure of PI3Kδ. The model was generated based on the co-crystal structure of PI3Kδ and ZSTK474 (PDB ID: 2WXL). (C) IC₅₀ of X-370 against PI3Kδ increased along with ATP concentration. (D) X-370 displayed high selective activity against PI3Kδ isoforms among representative lipid kinases. Data was obtained from Kinase Profiler Services (Millipore, United Kingdom). Briefly, X-370 was solved in DMSO at a concentration of 10 mM, 10-point kinase inhibitory activity was measured over concentrations in a half-log dilution series started at 1000 nM with ATP at a concentration consistent with Km of each isoform of class I PI3K and IC₅₀s were calculated. Relative kinase activity in the presence of 10 μM X-370 compared to DMSO control was measured for the rest of lipid kinases.