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 37°C, 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.