Synthesis,radiolabeling and in vitro and in vivo characterization of a technetium‐99m‐labeled alpha‐M2 peptide as a tumor imaging agent

Abstract: In an effort to develop a peptide‐based radiopharmaceutical for the detection of breast cancer, we have prepared an analog of αM2 peptide, modified to incorporate an N₃S chelate system. Mercaptoacetyltriglycine (MAG)₃‐derivatized αM2 peptide was prepared by solid‐phase synthesis and radiolabeled with ^99mTc by an exchange method. In vitro cell‐binding on human breast cancer cell lines, MDA‐MB‐231 and MCF‐7, indicated the affinity and specificity of ^99mTc‐MAG₃‐αM2 toward breast cancer cells. Additionally, the radiolabeled peptide showed rapid internalization into human breast cancer cells. In vivo biodistribution in mice showed that the radiolabeled peptide cleared rapidly from the blood and most non‐target tissues and was excreted significantly via the kidneys. Uptake of ^99mTc‐MAG₃‐αM2 in the tumor was moderate. The radiochemical and in vitro and in vivo characterization indicates that the radiolabeled peptide has certain favorable properties and it might be a useful radiopharmaceutical for the detection of breast cancer in vivo.