Improving the Properties of Techentium-99m Labeled Angiogenesis Antagonist Polypeptide for the Detection of Breast Cancer by External Imaging

摘要

The polypeptide RGD-4C has been shown to localize preferentially on integrins at sites of tumor angiogeneisis. The terminal amines of both RGD-4C and RGE-4C peptides were conjugated with NHS-HYNIC end radiolabeled with (sup 99m)T(sub c) using tricine. Primarily in the first year, studies in tissue culture were conducted with human umbilical vein endothelial cells (HUVE). Successful radiolabeling of both the RGD-4C and RGE-4C was confirmed by RP and SE HPLC at specific radioactivity of 18 - 20 Ci/micromol. Both (sup 99m)T(sub c) complexes were stable. At 1 hr, 4 deg C and at nM concentrations, the cell accumulation of (sup 99m)T(sub c) RGD-4C peptide was as much as 16 times greater than the control. As a check, unlabeled RGD-4C blocked 50% of the binding of (sup 99m)T(sub c) labeled RGD-4C. The binding of (sup 99m)T(sub c) labeled RGD- 4C to purified alpha(sub v)beta 3 integrin protein was 6.8 fold higher than that of (sup 99m)T(sub c) labeled RGE-4C. Thus in the first year of funding, we have shown that a (sup 99m)T(sub c)-labeled cyclic RGD-4C peptide shows high selectivity for alpha(sub v)beta 3 integrin-expressing cells in vitro. In the second year, animalimaging studies were performed with the radiolabeled peptides with poor tumor accumulations. Careful cell binding studies confirmed that one likely reason for the negative results is a low binding affinity of the peptides to the integrin and, especially, a limited number of integrins per cell. Finally, novel alternative labeling methods were investigated to confirm the latter conclusion.