Medical Physics Seminar – Monday, September 29, 2014
Porphysome Nanotechnology and Beyond: Explore New Frontiers of Cancer Imaging & Therapy
Gang Zheng, PhD (guest of Dr. Weibo Cai)
Professor, Department of Medical Biophysics, University of Toronto & Princess Margaret Cancer Center, Ontario - CANADA -
We recently discovered ‘porphysomes’, the first all-organic nanoparticles with intrinsic multimodal photonic properties. They are self-assembled from porphyrin-lipid building blocks to form liposome-like bilayer vesicle (~100 nm diameter). The very high porphyrin packing density (>80,000 per particle) results in both ‘super’-absorption and structure-dependent ‘super’-quenching, which, in turn, converts light energy to heat with extremely high efficiency, giving them ideal photothermal and photoacoustic properties that are unprecedented for organic nanoparticles. Upon porphysome nanostructure dissociation, fluorescence of free porphyrins is restored to enable low background fluorescence imaging. In addition, metal ions (e.g., radioactive copper-64 or paramagnetic Mn) can be directly incorporated into the porphyrin building blocks of the preformed porphysomes thus unlocking their potential for PET, MRI and radiation therapy. As a result of their organic nature, porphysomes were biodegradable in vivo and induced minimal acute toxicity in mice with high intravenous doses. In a similar manner to liposomes, porphysomes can be easily scaled up via commercial extrusion techniques and the large aqueous core of porphysomes could be passively or actively loaded with drugs, opening up a new avenue for image-guided drug delivery. By changing the way porphyrin-lipid assembles, we developed ultra small high-density lipoprotein (HDL)-like porphyrin nanoparticles (<20nm), trimodal (US/photoacoustic/fluorescence) porphyrin shell microbubbles (~2um), versatile porphyrin microreactors (~100um) and hybrid porphyrin-gold nanoparticles, expanding the purview of porphyrin nanophotonics. Compared with classical “all-in-one†nanoparticles containing many functional modules, the simple yet “one-for-all†nature of porphysomes represents a novel approach to the design of multifunctional nanoparticle and confers high potential for clinical translation.