Challenges in nanomedicine clinical translation.

New nanomedicine formulations and novel applications of nanomedicinal drugs are reported on an almost daily basis. While academic progress and societal promise continue to shoot for the stars, industrial acceptance and clinical translation are being looked at increasingly critically. We here discuss five key challenges that need to be considered when aiming to promote the clinical translation of nanomedicines. We take the perspective of the end-stage users and consequently address the developmental path in a top-down manner. We start off by addressing central and more general issues related to practical and clinical feasibility, followed by more specific preclinical, clinical, and pharmaceutical aspects that nanomedicinal product development entails. We believe that being more aware of the end user's perspective already early on in the nanomedicine development path will help to better oversee the efforts and investments needed, and to take optimally informed decisions with regard to market opportunities, target disease indication, clinical trial design, therapeutic endpoints, preclinical models, and formulation specifications. Critical reflections on and careful route planning in nanomedicine translation will help to promote the success of nanomedicinal drugs. Graphical abstract.