Direct 99mTc labeling of Herceptin (trastuzumab) by 99mTc(I) tricarbonyl ion

By simply incubating Herceptin (trastuzumab) with [99mTc(CO)3(OH2)3]+ ion in saline, a significant yield of 99mTc-labeled trastuzumab was found to be achievable. The effective labeling may be based on that trastuzumab is inherent with endogenous histidine group to which 99mTc(I) tricarbonyl ion can be strongly bound. For practical 99mTc labeling processing, trastuzumab was purified beforehand from the commercial product, Herceptin (Genentech) via size exclusion chromatography to remove the excipient, α-histidine and a high-labeled yield could be obtained by incubating the purified trastuzumab with [99mTc(CO)3(OH2)3]+. Retention of bioactivity of the 99mTc(I)-labeled trastuzumab was validated using a cell binding test.