Multimodality molecular imaging of tumor angiogenesis using quantum dots

W. J. Mulder, G. J. Strijkers, C. de Mello Donegá, R. J. Brandwijk, P. T. Chin, R. Koole, K. Castermans, G. Storm, A. W. Griffioen, K. Nicolay Biomedical NMR, Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, Condensed Matter and Interfaces, Utrecht University, Utrecht, Netherlands, Department of Pathology, Maastricht University, Maastricht, Netherlands, Molecular Materials and Nanoscience, Eindhoven University of Technology, Eindhoven, Netherlands, Department of Pharmaceutics, Utrecht University, Utrecht, Netherlands Introduction Quantum dots, semiconductor nanocrystals in a size range of 2 to 6 nm have gained much interest the last few years for biological imaging purposes, especially because of their bright fluorescence, their photo-stability, and their narrow and tunable emission spectrum. In this study we developed quantum dots (QDs) with a pegylated and paramagnetic coating (Figure 1A) to make them detectable by both MR and optical imaging. Angiogenesis, the formation of new blood vessels, is involved in many pathological processes, including cancer In the angiogenic cascade different cell surface receptors, including the αvβ3-integrin, are expressed at the activated tumor endothelium. The non-invasive in vivo detection of this integrin would thus allow one to monitor angiogenesis and to follow the effect of anti-angiogenic therapies. To that aim multiple αvβ3-specific RGD-peptides were conjugated to the paramagnetically coated quantum dots (RGD-pQDs). Next, the RGD-pQDs were assessed for their specificity on endothelial cells (HUVEC) in vitro. Cells that were incubated with bare pQDs and cells that were incubated without contrast agent were used as controls. On the cells both fluorescence microscopy and MRI was performed. Upon injection of this contrast agent activated endothelial cells were visualized in tumor bearing mice with intravital microscopy (IVM) and MRI in vivo. The assessment of the tumors with IVM allowed the investigation of angiogenesis at subcellular level with a small scanning window and limited penetration depth. On the other hand, MRI allowed the investigation of angiogenesis on anatomical level with a large scanning window.