In vivo imaging of tumour angiogenesis in mice with the αvβ3 integrin-targeted tracer 99mTc-RAFT-RGD

Purpose The molecular imaging of tumour neoangiogenesis currently represents a major field of research for the diagnostic and treatment strategy of solid tumours. Endothelial cells from tumour neovessels overexpress the alpha(v)beta(3) integrin, which selectively binds to Arg-Gly-Asp (RGD)-containing peptides. We evaluated the potential of the novel radiotracer Tc-99m-RAFT-RGD for the non-invasive molecular imaging of alpha(v)beta(3) integrin expression in mice models of tumour development. Methods Tc-99m-RAFT-RGD, Tc-99m-cRGD (specific control) and Tc-99m-RAFT-RAD (non-specific control) were injected intravenously to mice bearing B16F0 or TS/A-pc tumours. In vivo whole-body tomographic imaging and post-mortem biodistribution studies were performed 60 min following tracer injection. Adjacent tumour slices were used to compare the localisation of neovessels from immunostaining and the pattern of Tc-99m-RAFT-RGD uptake from autoradiographic ex vivo imaging. Results Biodistribution studies indicated that Tc-99m-RAFT-RGD tumour uptake was significantly higher than that of Tc-99m-RAFT-RAD in B16F0 (2.4 +/- 0.5 vs 1.0 +/- 0.1%ID/g, respectively) and in TS/A-pc tumours (2.7 +/- 0.8 vs 0.7 +/- 0.1%ID/g, respectively). Immunohistochemical and autoradiographic studies indicated that Tc-99m-RAFT-RGD intratumoural uptake preferentially occurred in angiogenic areas. Tomographic imaging allowed tumour visualisation following injection of Tc-99m-RAFT-RGD and Tc-99m-cRGD with similar tumour-to-contralateral muscle (T/CM) ratios in B16F0 and in TS/A-pc tumours whereas Tc-99m-RAFT-RAD T/CM ratios did not allow tumour imaging. In accordance with the higher level of alpha(v)beta(3) integrin expression on TS/A-pc tumours than on B16F0 tumours as determined from western blot and immunoprecipitation analyses, the Tc-99m-RAFT-RGD T/CM ratio was significantly higher in TS/A-pc than in B16F0 tumours. Conclusion Tc-99m-RAFT-RGD allowed the in vivo imaging of alpha(v)beta(3) integrin tumour expression.