25 Years of Nanoparticles: A Look Forward

The term "nanoparticle" encompasses a variety of structures with sizes of 1–100 nm that have found utility as carriers for either highly toxic payloads, such as chemotherapeutics, or very fragile payloads, such as proteins or nucleic acids. Panayiotis P. Constantinides, PhD, founder and principal of Biopharmaceutical and Drug Delivery Consulting, spoke to BioPharm International about what to expect in the future development of this technology.

BioPharm: What advances do you expect to see in the future that will improve selectivity or efficacy of nanoparticles?

Constantinides: Within the broader definition of a nanoparticle are also submicron particles with sizes between 100 and 1000 nm, such as those in the marketed oral and parenteral nanoparticulate drug products. Nanoparticle selectivity and efficacy are particularly important in parenteral drug delivery and targeting for cancer and other diseases. Linked to nanoparticle selectivity and efficacy is their potential toxicity. Further advances in cell and tissue imaging techniques and other in vitro and in vivo characterization methods of nanomaterials and nanoparticles are necessary to better understand and predict toxicity. To this end, further development and clinical application of multifunctional nanoparticles which combine disease diagnosis with therapy (nanotheranostics) could prove to be very useful. These systems consist of a core which can be magnetic for MRI or quantum dot for optimal imaging, a lipidic and/or polymeric shell for intracellular targeting and an outer layer incorporating a surfactant or polymeric stabilizer and a targeting moiety (e.g., antibody, aptamer, or ligand). The drug, small molecule or biologic, can be encapsulated in the core and/or the shell of the particle.

Advances in image-guided drug delivery will offer several advantageous features and enable scientists and clinicians to monitor and quantify drug release, non-invasively assess drug site accumulation, visualize biodistribution in real time, analyze drug distribution at the target site, predict drug response and evaluate drug efficacy and toxicity. Ultimately and perhaps not in the distant future, these features could be incorporated into microchips and personalized medicines.

Most nanoparticles accumulate in the liver but depending on their size and charge can also accumulate in the kidney and other tissues. All classes of nanomaterials have extensive tissue retention, particularly carbon nanotubes and quantum dots, and this has toxicological implications. The state of nanomaterials once deposited in the tissue is largely unknown. Furthermore, comparison between and across complex nanoparticles is difficult.

In reference to nanoparticle toxicity, limited number of nanomaterials have been evaluated to date, and mechanisms for nanomaterial toxicity are actively being pursued. Specific properties of nanometerials, particularly their surface characteristics, contribute to their toxicity. There is a need for nanotoxicity guidelines, and no specific regulations are available at the present time. However, assessing nanomaterial risks should be proactively pursued to identify and analyze potential hazards, assess potential exposure scenarios and evaluate toxicity and analyze and communicate potential risks and uncertainties.

From a formulation and process development perspective, we need to critically assess what lessons learned from the marketed nanoparticulate drug products can be applied to 1–100 nm particles and what is truly new science and knowledge. For example, new processing and characterization methods are needed along with the establishment of meaningful controls, specifications, and standards for 1–100 nm particles. Further advances in manufacturing methods are required in order to scale up and reproducibly produce complex multifunctional nanoparticles with an acceptable shelf-life.

Drivers for future growth and commercialization of drug delivery nanoparticles include, availability of funding, patent landscape, increased understanding of the pathophysiology of disease, and need for novel drugs and safe therapies.

Panayiotis P. Constantinides can be reached at ppconstantinides@bpddc.com