Preliminary biological evaluation of 125I-labeled anti-carbonic anhydrase IX monoclonal antibody in the mice bearing HT-29 tumors
Objective To evaluate 125I-labeled anti-carbonic anhydrase IX monoclonal antibody (125I-MAb) as a novel single-photon emission computed tomography tracer for imaging carbonic anhydrase IX in the mice bearing HT-29 tumors. Methods Anti-carbonic anhydrase IX monoclonal antibody was labeled with iodine-125 by the iodogen method. The radiochemical purity of 125I-MAb was measured by radio-thin-layer chromatography. The in-vitro stability of 125I-MAb was determined in PBS (0.05 mol/l, pH 7.4) or new-born calf serum at 378C, and analyzed by radio-thin-layer chromatography. A biodistribution study and planar imaging were carried out in the mice bearing HT-29 tumors. The expression of CA IX in HT-29 tumors was analyzed by immunohistochemistry. Results 125I-MAb was obtained with a radiolabeling efficiency of 98%, and showed high stability in PBS and new-born calf serum. Furthermore, the biodistribution study showed specific tumor uptake in the mice bearing HT-29 tumors, and planar imaging with 125I-MAb 48 h post injection showed a high concentration of radioactivity in tumors and a much decreased concentration in tumors in the blocking group. An immunohistochemical analysis showed the expression of CA IX in HT-29 tumors. Conclusion The preliminary biodistribution study and results from planar imaging showed the potential of 125I-MAb as an agent for tumor diagnosis and encouraged further investigation.