Labeling and biodistribution of the novel radiotracer (¹⁷⁷Lu) Lu-DOTA-trastuzumab

Trastuzumab is an FDA approved humanized monoclonal antibody that targets human epidermal growth factor (HER2) receptors which are known to express 20-30% of invasive breast cancer. Lutetium -177 is a radio lanthanide with beta emission and a half-life of -6.7 days. Lu-177 Trastuzumab kills the cells by immunologic pathway as well as by the emission of high energy beta particles which causes radiation induced death of the targeted cells. The kit contents were reconstituted in 0.5mL of sterile water and were gently shaken till a clear solution was obtained. 30-60mCi of (¹⁷⁷Lu) LuCl₃ with high radioactive concentration was added in the cold kit vial and incubated in a water bath at 37°C for 30-45 minutes. Images were visually analyzed for quality of the image by an expert nuclear medicine physician. The radiochemical purity of (¹⁷⁷Lu) Lu-DOTA-Trastuzumab preparation was found to be >95%. Delayed images show better blood pool clearance that leads to higher tumor to background ratio. 168 hours image showed overall high target to background ratio. Delayed imaging of Lu¹⁷⁷ DOTA Trastuzumab shows better target to background ratio that allows for better visualization of the pathological tracer distribution. Further delayed images can be acquired but the limitation is the physical decay of Lu¹⁷⁷ radioactivity which further affects the overall image quality