Preparation, biodistribution and dosimetry of copper-64-labeled anti-colorectal carcinoma monoclonal antibody fragments 1A3-F(ab')2.
Antibody fragments labeled with a radiometal using bifunctional chelates generally undergo renal clearance followed by trapping of the metabolites, leading to high radiation doses to the kidneys. Copper-64-labeled BAT-2IT-1A3-F(ab')2 was recently reported to accumulate in colorectal tumors in an animal model, however, kidney uptake was also high. In this study, the preparation of 64Cu-BAT-2IT-1A3-F(ab')2 was optimized to reduce the renal uptake.


METHODS
The bifunctional chelate 6-bromoacetamidobenzyl-1,4,8,11-tetraazacyclotetradecane-N,N ',N",N'"-tetraacetic acid (BAT) was conjugated to 1A3-F(ab')2 using the linking agent 2-iminothiolane (2IT). The conjugation reaction produced 20% of a lower molecular weight (molecular wieght) impurity found to be TETA-1A3-Fab'. The conjugation procedure was optimized to include FPLC purification of the BAT-2IT-1A3-F(ab')2 from TETA-1A3-Fab' after conjugation prior to labeling with 64Cu. The biodistribution of 64Cu-labeled FPLC-purified and unpurified conjugates was determined in normal Sprague-Dawley rats and tumor bearing Golden Syrian hamsters. Human absorbed doses were calculated from rat biodistribution data and PET imaging of a baboon.


RESULTS
Upon FPLC purification of the BAT-2IT-1A3-F(ab')2, the immunoreactivity of 64Cu-labeled 1A3-F(ab')2 was significantly improved over that of non-FPLC-purified 64Cu-BAT-2IT-1A3-F(ab')2, and the kidney uptake was decreased in normal rats. The biodistribution in hamsters showed some improvement in both tumor uptake and kidney clearance with FPLC-purified 64Cu-BAT-2IT-1A3-F(ab')2.


CONCLUSIONS
The improved dosimetry of 64Cu-labeled FPLC purified BAT-2IT-1A3-F(ab')2 should more readily allow this agent to be investigated clinically to image colorectal cancer using PET.
Anderson
C J
CJ
Mallinckrodt Institute of Radiology, St Louis, MO 63110, USA.
Schwarz
S W
SW
Connett
J M
JM
Cutler
P D
PD
Guo
L W
LW
Germain
C J
CJ
Philpott
G W
GW
Zinn
K R
KR
Greiner
D P
DP
Meares
C F
CF
D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging / Q000276:immunology*; D003301:Copper Radioisotopes / Q000493:pharmacokinetics; D006224:Cricetinae; D007128:Immunoglobulin Fragments; D008647:Mesocricetus; D010215:Papio; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
D000911:Antibodies, Monoclonal; D003301:Copper Radioisotopes; D007128:Immunoglobulin Fragments