In vivo imaging of integrin alpha nu beta(3) expression using fluorescence-mediated tomography

von Wallbrunn A, Holtke C, Zuhlsdorf M, Heindel W, Schafers M, Bremer C

Abstract

Purpose Optical imaging would be desirable for cancer diagnostics since it can potentially resolve relevant oncological target structures in vivo. We therefore synthesised an alpha v beta(3) targeted fluorochrome and imaged tumour xenografts with different alpha v beta(3) expression levels using both planar and tomographic optical imaging methods. Methods An alpha v beta(3)-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). IResults n vitro, the peptide-dye conjugate showed a clear binding affinity to alpha v beta(3)-positive M21 and HT-1080 cells while alpha v beta(3)-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 +/- Ce155.36 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 alpha v beta(3) expression and may thus be a promising strategy for sensitive evaluation of tumour target expression.