A class of drugs, called kinase inhibitors, could stop cancer in its tracks…if only these drugs could reach the tumors, stay for a while, and not be toxic. Hypothesizing that a nanoparticle formulation would solve the inhibitors’ woes, Ashton and colleagues investigated several different compositions of so-called Accurins—polymeric particles that encapsulate charged drugs through ion pairing. An Aurora B kinase, once formulated in Accurins, demonstrated a much-improved therapeutic index and preclinical efficacy compared with its parent molecule, when administered to rats and mice bearing human tumors. The Accurins allowed for sustained release of the drug over days, and did not have the same blood toxicity seen with the parent drug. A phase 1 trial is the next step for this nanomedicine, and additional preclinical studies will reveal whether such nanoformulations can improve the tolerability and efficacy of the broader class of molecularly targeted cancer therapeutics, including cell cycle inhibitors.