Transfer of copper from a chelated 67Cu-antibody conjugate to ceruloplasmin in lymphoma patients

Abstract

The Lym-1 monoclonal antibody was conjugated with the bifunctional chelating agent 6-[ p-(bromoacetamido)benzyl]-1,4,8,11-tetraazacyclotetradecane- N,N′,N″,N‴-tetraacetic acid (BAT), using 2IT as a linker, and radiolabeled with 67Cu to make the radiopharmaceutical, 67Cu-2IT-BAT-Lym-1. Ten patients received a total of 18 doses of 67Cu-2IT-BAT-Lym-1 as targeted, systemic radiotherapy. The beta phase of blood clearance, when corrected for 67Cu decay, was positive or flat, a phenomenon not observed in similar patients treated with 131I-Lym-1. The flat beta phase of blood clearance suggested recycling of 67Cu from 67Cu-2IT-BAT-Lym-1 to another plasma protein. Therefore, the amount of 67Cu transferred from the radiopharmaceutical to CP, Alb, and TF was measured using affinity-purified polyclonal antibodies. The fraction of plasma 67Cu precipitated by anti-human CP increased daily; most blood radioactivity was 67Cu-CP after a median of 4 days (range 2–7 days). The transfer of 67Cu to CP was observed in all patients and was consistent from dose to dose within the same patient. An average of 2.8 ± 1.5% (range 0.8–7.8%) of the 67Cu dose (%ID) was transferred to CP. The release rate of 67Cu-CP from the liver into the blood was 0.9 ± 0.4 %ID/day for the first 3 days. The 67Cu-CP effective clearance half-life was 3.7 ± 0.7 days. Subtraction of the 67Cu-CP activity from the total blood radioactivity yielded a biphasic blood clearance similar to that obtained for patients given 131I-Lym-1. Cu-67-CP increased the AUC for whole blood by 24 ± 10%. The %ID of 67Cu recycled correlated with GGT, ALT, and alkaline phosphatase levels; r = 0.958 ( p < 0.001), 0.857 ( p < 0.01), and 0.822 ( p < 0.01), respectively. Albumin levels correlated negatively with recycled copper ( r = −0.745, p < 0.05). The data suggest that the liver metabolizes 67Cu-2IT-BAT-Lym-1 and recycles a small fraction of the 67Cu, transferring it to CP.