A novel Tc-99m and fluorescence labeled peptide: Multimodal imaging agent for targeting angiogenesis in a murine tumor model

The serine-aspartic acid-valine (SDV) peptide binds specifically to integrin &agr;v&bgr;3. In the present study, we successfully developed both Tc-99m and TAMRA labeled TAMRA-GHEG-ECG-SDV peptide to target the integrin &agr;v&bgr;3 of tumor cells; furthermore, we evaluated the diagnostic performance of Tc-99m TAMRA-GHEG-ECG-SDV as a dual-modality imaging agent for tumor of the murine model. TAMRA-GHEG-ECG-SDV synthesized using Fmoc solid-phase peptide synthesis. Radiolabeling of TAMRA-GHEG-ECG-SDV with Tc-99m was done using ligand exchange methods. Labeling stability and cytotoxicity studies were performed. Gamma camera imaging, biodistribution and ex vivo imaging studies were performed in murine models with HT-1080 and HT-29 tumors. Tumor tissue slide was prepared and analyzed using confocal microscopy. After radiolabeling procedures with Tc-99m, the Tc-99m TAMRA-GHEG-ECG-SDV complexes were prepared in high yield (>99%). Tc-99m TAMRA-GHEG-ECG-SDV was found to be nontoxic to HUVEC and HT-1080 cells at all concentration. On gamma camera imaging study, a substantial uptake of Tc-99m TAMRA-GHEG-ECG-SDV into HT-1080 tumor (integrin &agr;v&bgr;3-positive) and low uptake of Tc-99m TAMRA-GHEG-ECG-SDV in HT-29 tumor (integrin &agr;v&bgr;3-negative) were demonstrated. The HT-1080 tumor-to-normal muscle uptake ratio of Tc-99m TAMRA-GHEG-ECG-SDV reached 6.8 ± 2.3 at 3 h (2.8 ± 0.7, 5.3 ± 1.5 and 6.8 ± 2.3 at 1, 2 and 3 h, respectively). The HT-29 tumor-to-normal muscle uptake ratios of Tc-99m TAMRA-GHEG-ECG-SDV (1.6 ± 0.4, 1.7 ± 0.4 and 2.0 ± 0.5 at 1, 2 and 3 h, respectively) were significantly lower than those of HT-1080 tumor (p < 0.05). Competition study revealed that HT-1080 tumor uptake was effectively blocked by the co-injection of excess concentration SDV. Specific uptake of Tc-99m TAMRA-GHEG-ECG-SDV was confirmed by biodistribution, ex vivo imaging and confocal microscopy studies. Our in vivo and in vitro studies revealed substantial uptake of Tc-99m TAMRA-GHEG-ECG-SDV on the integrin &agr;v&bgr;3-positive tumor. Tc-99m TAMRA-GHEG-ECG-SDV could be a good candidate for dual-modality imaging agent targeting tumor angiogenesis.