NPM1 and cancer: Nucleophosmin (NPM), a primary target of CDK1 and CDK2/cyclin E-dependent Thr-199 phosphorylation that is overexpressed in cancer cells and helps to promote cell cycle progression,16 was completely inhibited 2 h following roniciclib exposure in HONE-1 and HK-1 cells (Fig. 3c) and by the end of day 1 in the slowly replicating C666-1 cells (Fig. 2a).