CDK1 and neoplasm: We observed a direct dose- and time-dependent relationship between RP-6306 plasma concentration and inhibition of CDK1 Thr14 phosphorylation in tumours (Extended Data Fig. 9f, g), with an EC50 of 2.8 nM (95% confidence interval 2.0–3.4 nM), indicating potent on-target activity in vivo.