4958.2:
Nanocrystal-mediated functional imaging of cellular and vascular targets for early detection of age related macular degeneration, cancer and other diseases, as well as improving therapy and drug screening
Abstract
Since fluorescence-based and magnetic resonance techniques are particularly sensitive and simple to apply, they have had a strong impact on biomedical science, covering topics from basic research to clinical applications. The field suffers from two main drawbacks: 1) lack of target specificity of the fluorophores or contrast agent, and 2) non-optimal optical properties of the organic dye molecules used. Here we propose solutions to these two drawbacks and describe effective preclinical tests of these solutions. Our approach is based on the creation of a single molecular structure, which consists of a targeting unit with high specificity combined with an optimised fluorescence or contrast enhancing unit. Neovascularisation associated with age-related macular degeneration (AMD) is taken as an example of functional imaging. Several small peptides have been shown to specifically address receptors like the v3 and v5 integrins, overexpressed in hyperproliferative blood vessels. A significant increase in binding avidity to such cellular targets can be obtained using a multivalent structure like a synthetic ”comb” (collaboration with Keith Rose, Geneva) or a proteinlike ”peptabody" (collaboration with J.-P. Mach, Lausanne) as carrier for such specific peptide sequences. A single molecule or structure undergoes much stronger binding to the neovascular endothelial cells by multiple peptide-integrin links. This multifunctional structure is then covalently attached to a 1-10 nm sized quantum dot, consisting for instance of a surface derivatised CdSe, InP or InAs particle. Such nanoparticles show high fluorescence yields, can be excited over a wide range of wavelengths, while fluorescing specifically in narrow bands. Since their emission depends on the particle size, crosstalk is avoided in the case of multiple drug-use which can be particularly useful in multidrug screening. Fluorescence lifetimes of about 100 ns enable reduction of background tissue autofluorescence, while photobleaching is negligible. In a similar way, superparamagnetic nanoparticles can be attached to polyfunctional peptide structures for detection by MRI of early stage and metastatic cancer. We will test the target-selective tags in neovessels induced in the fertilised chicken-egg CAM model, in Ryan's AMD model and in 7,12 DMBA induced early squamous cell cancer in the cheeckpouch of the Chinese hamster. Finally, the same multifunctional targeting structures will be used for more selective therapy.