WEE1-IN-5 is a potent WEE1 inhibitor with an IC50 value of 0.8 nM. WEE1-IN-5 inhibits phospho-CDC2. WEE1-IN-5 abrogates the G2 check point, increasing sensitivity to DNA damaging agents in cancer cells. WEE1-IN-5 can be used for researching anticancer.