Strategy and validation of a structure-based method for the discovery of selective inhibitors of PAK isoforms and the evaluation of their anti-cancer activity

p21 activated kinase 4 (PAK4), which belongs to the serine/threonine (Ser/Thr) protein kinase family, is a representative member of the PAK family and plays a significant role in multiple processes associated with cancer development. In this study, structure-based virtual screening was performed to discover novel and selective small molecule scaffolds, and a 6-hydroxy-2-mercapto-3-phenylpyrimidin-4(3H)-one-based compound (SPU-106, 14#) was identified as an effective PAK4 inhibitor. By combining both a molecular docking study and molecular dynamics (MD) simulation strategies, the binding mode was determined in the PAK4 site. The SPU-106 compound could efficiently and selectively bind to the PAK4 kinase domain at an IC50 of 21.36 μM according to the kinase analysis. The designed molecular probe demonstrated that SPU-106 binds to the kinase domain in the C-terminus of PAK4. Further investigation revealed that the SPU-106 had a strong inhibitory effect on the invasion of SGC7901 cells but without any cytotoxicity. The western blot analysis indicated that the compound potently inhibited the PAK4/LIMK1/cofilin and PAK4/SCG10 signaling pathways. Thus, our work shows the successful application of computational strategies for the discovery of selective hits, and SPU-106 may be an effective PAK4 inhibitor for further development as an antitumor agent.