Gains in selectivity and efficacy
PharmTech:
What advances to you expect to see in the future that will improve selectivity or efficacy?
Constantinides:
Nanoparticle selectivity and efficacy is 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 optical 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, noninvasively 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 which 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 the need for novel drugs and safe therapies.
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