Study of antiangiogenic drugs by fluorescence imaging and spectroscopy of a contrast agent in mice

We used two fluorescence techniques based on the Indocyanine Green contrast agent to study the effectiveness of antiangionenic drugs in mice. To this purpose, the volume of the active vasculature in different tumor models implanted in mice was assessed by means of a low noise fluorescence imaging setup and by a photon counting system working in transmittance geometry. Using a first tumor model (carcinoma MDA-MB-435) we observed that mice treated with a Vascular Disrupting Agent (ZD6126) showed a reduction in fluorescence emission of the contrast agent with respect to control mice. This was a clear indication of the vascular shutdown that took place in tumors. The effectiveness of the treatment was also confirmed by histological sections. Then, in a second experiment we considered a second tumor model (carcinoma 1A9-VS I) overexpressing the Vascular Endotelial Growth Factor (VEGF121), which is used by tumor cells to promote angiogenesis. We measured the Indocyanine Green fluorescence in mice treated with an antioangiogenic drug (Avastin™) and in control mice. In tumors of treated mice we observed an ICG emission lower than the one detected in control mice. This demonstrated that VEGF activity was effectively blocked by the treatment with Avastin. In conclusion, ICG fluorescence provides a simple and reliable way to assess the effectiveness of vascular targeting therapies. Measurements of the fluorescence signal can be repeated every 24 hours, thus allowing oncologists to perform longitudinal studies on the same animals.