Development and Evaluation of a Novel 99mTc-Labeled Annexin A5 for Early Detection of Response to Chemotherapy
ABSTRACT
99mTc-HYNIC-annexin A5 can be considered as a benchmark in the field of apoptosis imaging. However, 99mTc-HYNICannexin A5 has characteristics of high uptake and long retention
in non-target tissues such as kidney and liver. To minimize this problem,
we developed a novel 99mTc-labeled annexin A5 using a bis(hydroxamamide) derivative [C3(BHam)2] as a bifunctional chelating agent, and evaluated its usefulness as an
imaging agent for detecting apoptosis. The amino group of C3(BHam)2 was converted to a maleimide group, and was coupled to thiol groups of annexin A5 pretreated with 2-iminothiolane. 99mTc labeling was performed by a ligand exchange reaction with 99mTc-glucoheptonate. Biodistributionexperiments for both 99mTc-C3(BHam)2-annexin A5 and 99mTc-HYNIC-annexin A5 were performed in normal mice. In addition, in tumor-bearing
mice, the relationship between the therapeutic effects of chemotherapy
(5-FU) and the tumor accumulation of 99mTc-C3(BHam)2-annexin A5 just after the first treatment of 5-FU was evaluated. 99mTc-C3(BHam)2-annexin A5 was prepared with a radiochemical purity of over 95%. In biodistribution
experiments, 99mTc-C3(BHam)2-annexin A5 hada much lower kidney accumulation of radioactivity than 99mTc-HYNIC-annexin A5. In the organs for metabolism, such as liver and kidney,
radioactivity after the injection of 99mTc-HYNIC-annexin A5 was residual for a long time. On the other hand, radioactivity after the injection of 99mTc-C3(BHam)2-annexin A5 gradually decreased. In therapeutic experiments, tumor growth
in the mice treated with 5-FU was significantly inhibited. Accumulation
of 99mTc-C3(BHam)2-annexin A5 in tumors significantly increased after 5-FU treatment. The accumulation of radioactivity in tumor correlated positively with the counts of TUNEL-positive cells. These findings suggest that 99mTc-C3(BHam)2-annexin A5 may contribute to the efficient detection of apoptotic tumor
response after chemotherapy.