Towards rational design of multifunctional theranostic nanoparticles: what barriers do we need to overcome?

The quest for early detection and treatment of diseases has led to intense research on theranostics [1]. With diagnosis and therapy combined onto a single platform, theranostics enables real-time monitoring of the status of disease treatment and allows for timely adjustment of type and dose of drugs, paving the way towards personalized medicine. The unique physiochemical properties of nanoparticles (NPs) make them outstanding platforms for the fusion of diagnostic and therapeutic agents [2]. In general, theranostic NPs feature the following characteristics. NPs serve as carriers and sometimes also as imaging and therapeutic agents. Extrinsic imaging and therapeutic agents are attached to surfaces of NPs or encapsulated within NPs. Numerous moieties that enhance targeting are attached to NP surfaces. Lastly, active control of drug release is realized by the use of responsive NPs or molecular valves and propellers attached to the nanoporous NPs [3]. The availability of a broad range of NPs, imaging agents, drugs and moieties has provided immense scope for multifunctional theranostic NPs to enhance the therapeutic efficacy. However, the addition of new functions is also associated with new challenges, including an increased complexity in synthesis and behavioral control of NPs in the body [4]. Despite tremendous progress in theranostic NPs, barriers must be overcome for their success in the clinic to be realized. This editorial will identify major barriers in three basic aspects of applying theranostic NPs: circulation of NPs, targeting of NPs and targeted drug delivery. A discussion of the opportunities for optimization and clinical translation of theranostic NPs will then follow.