Phospholipids have a polar head (red) and two tails. When one tail is replaces with a porphyrin molecule (blue hexagon), the new phospholipid derivatives can form a construct known as a porphysome (right).
By Tyler Irving
Posted June 2011
A nanoparticle that delivers drugs, provides photothermal therapy, acts as a fluorescent tracer and is non-toxic seems too good to be true. But a research team at the University of Toronto’s Institute of Biomaterials and Biomedical Engineering has created a nanoparticle, called a porphysome, which does all this and more.
Porphysomes were developed while trying to examine porphyrin properties in liposomes, an artificial cell membrane made of a phospholipid bilayer. “Phospholipids have a polar head and two tails,” explains Gang Zheng, who heads the U of T team. Zheng’s team replaced one tail with a porphyrin. Since the porphyrin group — derived from chlorophyll — is optically active, incorporating the porphyrin-phospholipid into the liposome should have allowed it to react with light. Surprisingly, adding these new molecules didn’t destabilize the liposome, but rather increased stability as additional molecules were added. “By the end, we completely got rid of the natural phospholipids,” says Zheng. This meant that the spherical structure was no longer a liposome, but something entirely new — a porphysome.
The porphysome is similar to cell membranes in the human body, which makes it non-toxic. However, it becomes a multi-functional weapon once it reaches a tumour. It absorbs laser light, heating up enough to destroy cancer cells. It can be filled with cancer-fighting drugs like doxorubicin, which are released when the porphysome degrades. At the same time, the porphyrins become fluorescent, allowing researchers to see exactly when and where the drugs were released. As they travel through the body, the porphysomes can also be tracked in real time using photoacoustic imaging.
The beauty of the porphysome is its simplicity. “The fact that it’s intrinsically multifunctional, multi-modal and such a simple structure — that’s very satisfying,” says Zheng. Having demonstrated these functions in rats and mice, the team is trying to find additional uses, as well as collecting the safety data that will allow the porphysome to be tested in humans.
Photo Credit: Jon Lovell
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