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What is a porphysome?

A porphysome is a spherical nanovesicle that is formed from self-assembled porphyrin (an organic compound that is found in naturally occurring compounds like hemogloblin and chlorophyll) bilayers with a diameter of 100 nm. Porphysomes were listed as one of the top 10 cancer breakthroughs of 2011 by the Canadian Cancer Society.

How were they discovered?

Dr. Gang Zheng and his team at the Ontario Cancer Institute at the University Health Network were interested in attaching an optically active porphyrin group to a liposome, an artificial vesicle that is used as a vehicle for drug delivery. They discovered that the stability of the molecule increased when the tail of the liposome lipid was replaced with a porphyrin group. Eventually, all of the natural phospholipids were removed and a new molecule–the porphysome—was born.

What can they do?

Porphysomes are special because they are fully organic and naturally multifunctional, with capabilities to treat, image, and deliver different drugs to specific disease sites.

Porphysomes are a phototherapy agent, able to destroy diseased tissue by releasing heat due to their ability to absorb light in the near infrared region. The thermal expansion of the tissue during heating generates a photoacoustic signal which can then be converted to an image. Porphysomes can also be used as a drug delivery system—they can be directly labeled with radioisotopes to allow for real-time noninvasive imaging tracking. Porphysomes are also fluorescent upon dissociation of the molecule and can be imaged optically to confirm the drug release. A physician can potentially inject drug-loaded porphysomes into a patient, confirm the arrival of the drug to the appropriate target, know exactly when the drug is released, and thus determine a drug’s efficacy. All this is done with a simple and elegant molecular structure that is completely biocompatible and non-toxic.

For more information regarding porphysomes, please refer to the following articles:

1. Porphysome nanovesicles generated by porphyrin bilayers for use as multimodal biophotonic contrast agents,
Jonathan F. Lovell, Cheng S. Jin, Elizabeth Huynh, Honglin Jin, Chulhong Kim, John L. Rubinstein, Warren C. W. Chan, Weiguo Cao, Lihong V. Wang, Gang Zheng,
Nature Mat. 2011 (highlighted on Nat Methods. 2011 8:370-1)

2. Enzymatic Regioselection for the Synthesis and Biodegradation of Porphysome Nanovesicles.
Jonathan F. Lovell, Cheng S. Jin, Elizabeth Huynh, Thomas D. MacDonald, Weiguo Cao, Gang Zheng,
Angewandte Chemie. 2012