In vivo imaging of integrin [alpha][nu][beta]3 expression using fluorescence-mediated tomography

Purpose Optical imaging would be desirable for cancer diagnostics since it can potentially resolve relevant oncological target structures in vivo. We therefore synthesised an alphavBeta3 targeted fluorochrome and imaged tumour xenografts with different alphavBeta3 expression levels using both planar and tomographic optical imaging methods. Methods An alphavBeta3-targeted RGD peptide was labelled with a cyanine dye (Cy 5.5). Binding of the optical tracer was tested on M21 melanoma (n=5), HT-1080 fibrosarcoma (n=6) and MCF-7 adenocarcinoma (n=5) cells and their tumour xenografts. All optical imaging studies were performed using two-dimensional planar fluorescence reflectance imaging (FRI) technology and three-dimensional fluorescence-mediated tomography (FMT). Results In vitro, the peptide-dye conjugate showed a clear binding affinity to alphavBeta3-positive M21 and HT-1080 cells while alphavBeta3-negative MCF-7 cells and pre-dosing with the free RGD peptide revealed little to no fluorescence. In vivo, tumour xenografts were clearly visualised by FRI and FMT up to 24 h post injection. FMT allowed quantification of the fluorochrome distribution in deeper tissue sections showing an average fluorochrome concentration of 417.61 +/- 105.82 nM Cy 5.5 (M21), 353.68 +/- 54.02 nM Cy 5.5 (HT-1080) and 262.83 +/- 155.36 nM Cy 5.5 (MCF-7) in the target tissue 60 min after tracer administration. Competition with the free RGD peptide resulted in a reduction in the fluorochrome concentration in M21 tumour tissue (294.35 +/- 84.27 nM). Conclusion RGD-Cy 5.5 combined with novel tomographic optical imaging methods allows non-invasive imaging of tumour-associated alphavBeta3 expression and may thus be a promising strategy for sensitive evaluation of tumour target expression. [PUBLICATION ABSTRACT]