The first small molecule to be reported bearing the pyridopyrimidine core was PD0166285 [87] Although it showed a potent Wee1 inhibition activity (IC50 = 24 nM) in various cancer cell lines and xenografts [67,87,136,137,138], its clinical application is limited because of its non-selective Wee1 inhibition. Here, WEE1 is linked to cancer.