Abstract
Herceptin, the common anti-breast cancer medicine prevailed in recent years, contains mainly trastuzumab. Trastuzumab, the DNA recombinated humanized monoclonal antibody (mAb), can recognize specifically Human Epidermal Growth Factor Receptor 2 protein (HER2) on cell membrane. HER2 is a 185 kDa transmembrane receptor tyrosine kinase which is overexpressed in 25-30% of breast cancers. As HER2 is blocked by trastuzumab mAb, the growth factor will greatly reduce its binding with the receptor leading to lower the cell proliferation. Moreover, trastuzumab mAb will induce natural killer cells and macrophage to kill the cancer cells to cure breast cancer. The study is to develop a novel 99m Tc labeled trastuzumab construct and via the high affinity of trastuzumab toward HER2 to adopt as an imaging agent for HER2 overexpressed breast cancer. For the radiolabeling, the tricarbonyl techenium compound, [99mTc(CO)3(OH2)3]+, was synthesized and utilized as the precursor to conjugate rapidly with the monoclonal antibody, trastuzumab, by coordinating with N, O and S donors. The labeled mAb, 99mTc(I)-trastuzumab, was characterized by high performance liquid chromatography (HPLC) and size-exclusion chromatography (SEC) for its labeling yield and radiochemical purity. In addition, immunoreactivity assay and animal model experiment were undertaken to confirm its in vitro and in vivo stability, immunoreactivity and specific affinity with HER2 overexpressed cells. In conclusion, 99mTc(I)-trastuzumab is stable in serum and retains the inherent property and immunoreactivity of trastuzumab. The result of biodistribution also reveals that 99mTc(I)-trastuzumab is of high affinity with HER2-positive BT-474 cells and related animal tumor, in constrast with much lower affinity with HER2-negative MCF-7 models.