Theranostics: are we there yet?

The U.S. National Institutes of Health through the National Cancer Institute (NCI) have been charged with the goal of eliminating death and suffering from cancer by the year 2015. In order to achieve this very ambitious goal, the development of novel nanotechnology-based devices and therapeutics that are capable of one or more clinically important functions is envisioned. There is great hope and expectation in the development of theranostic nanocarriers, which combine diagnostic and therapeutic agents in one entity. Main delivery approaches include prodrugs, liposomes, polymersomes, and polymeric micelles and nanoparticles. Diagnostic and therapeutic agents are physically entrapped or conjugated to the nanocarriers, or they are conjugated to carefully designed polymers which subsequently form nanocarriers. This focus discusses pros and cons of the different theranostic approaches and tries to answer the question which approach has the highest probability to translate into the clinic and benefit patients. Carefully designed polymers, conjugated with diagnostic and therapeutic agents, that either self-assemble or can be processed to form nanocarriers offer clear advantages over random physical entrapment or conjugation of these agents to existing nanocarriers. These polymers can optionally be fitted with terminal stabilizing or anchoring functionalities and a targeting ligand. However, the need for nanocarriers that are subjected to the enhanced permeability and retention (EPR) effect to carry ligands for active targeting still needs to be demonstrated. Thirty-seven of the 41 nanocarrier-based formulations that are on the market or are under investigation at different levels of clinical development rely on passive targeting. The answer to the title question, not surprisingly, can only be no, but very promising approaches are being developed that have the potential to translate into the clinic and meet regulatory requirements.