Department of Chemistry
University of Toronto
Abstract: One of the goals of modern bioanalytical chemistry is the simultaneous (multiplexed) detection of multiple biomarkers in individual cells. A biomarker can be broadly defined as a characteristic protein, gene, or small molecule that can be objectively measured and evaluated as an indicator of normal biological or pathogenic processes. The classical approach to high throughput biomarker detection employs flow cytometry, in which antibodies (Abs) are labeled with fluorescent dyes. Here spectral overlap limits the number of dyes that can be detected simultaneously and restricts the number of biomarkers per cell that can be detected.
Mass cytometry (MC) is a much newer technique in which various Abs are labeled with different heavy metal isotopes. Cells are injected into the plasma torch of an inductively coupled plasma mass spectrometer with time of flight detection. Here signal intensity increases linearly with the number of copies of an isotope carried by each Ab. Our contribution to this technique is the synthesis of metal-chelating polymers (MCPs) with 20 to 50 chelators for carrying a metal ion and functionality at one end for covalent attachment to the Ab. In this way, each Ab can carry up to 200 copies of an isotope, and with these reagents, detection and quantification at high throughput of 40 to 45 biomarkers per cell is now routine. There is a need to increase the sensitivity of MC by one to two orders of magnitude, so that one can detect as few as 100 molecules per cell. To address this problem, we synthesize heavy metal nanoparticles such as 12 nm NaHoF4 NPs that contain on the order of 15000 Ho atoms. The two main challenges are passivating the NP surface to prevent non-specific interactions with cells and introducing functionality for attachment of Abs.
We are also part of a team led by my colleague R. M. Reilly in our Faculty of Pharmacy to develop MCPs as radioimmunotherapeutic agents for imaging tumors and treating pancreatic cancer. Our MCPs are attached to therapeutic antibodies or antibody fragments. The conjugates are labeled with 111In for µSPECT imaging or 64Cu for PET imaging. Electrons emitted by the radiometals enhance the cytotoxicity of the antibodies. 111In undergoes Auger decay, emitting electrons that are highly destructive to cells but travel only short distances (up to 1 µm). For effective use in therapy, we need to develop polymer conjugates that not only target tumor cells, but are transported to the cell nucleus, to ensure localized destruction of nuclear DNA. For studies in animal models and for eventual clinical applications, the polymers also have to be designed to maximize blood circulation time and to minimize uptake in the body by healthy tissues like the liver and spleen. In my talk I will summarize our progress in trying to meet these challenging goals.
Mitch Winnik is Professor of Chemistry at the University of Toronto, specializing in fundamental and applied aspects of polymer science. His research group provided new scientific knowledge that helped the coatings industry develop the environmentally friendly paints that are now sold commercially. In parallel, he collaborated with Ian Manners to pioneer the study of crystallization-driven self-assembly of block copolymer micelles in solution. In 2005, he joined a team of scientists who were developing mass cytometry for rapid multiparameter cell-by-cell analysis of biomarker expression. He and his students created polymer reagents for this technique. More recently, he has become involved in a collaboration to develop metal-chelating polymers into targeted reagents for radioimmunotherapy treatment of breast cancer and pancreatic cancer. He is an ISI “Most cited author” in chemistry, with 730+ publications and 20,000+ citations. His contributions have been recognized by an Alexander von Humboldt Senior Scientist Award (Germany), the 2013 national award in Applied Polymer Science of the American Chemical Society, the 2004 CIC Medal, and the 2011 LeSueur Memorial Award, Society of the Chemical Industry, Canada. He is a Fellow of the Royal Society of Canada, and in 1998 he was named University Professor, the University of Toronto’s highest recognition for scholarly achievement.