99mTc-Labeled annexin V has been used for the imaging of tumor apoptosis induced 
by chemotherapy. However, owing to the short half-life of annexin V, multiple 
injections of the radiotracer are necessary to capture the peak apoptotic 
activity. In this study, we evaluated the imaging properties of an 
(111)In-labeled, long-circulating annexin V.
METHODS: Both polyethylene glycol (PEG) and the metal chelator 
diethylenetriaminepentaacetic acid (DTPA) were simultaneously introduced to 
annexin V or ovalbumin through the use of a heterofunctional PEG precursor. 
Imaging studies were performed in mice bearing subcutaneously inoculated human 
mammary MDA-MB-468 tumors. The mice were treated with poly(L-glutamic 
acid)-paclitaxel, monoclonal antibody C225, or a combination of poly(L-glutamic 
acid)-paclitaxel and C225, followed by intravenous injection of 
(111)In-DTPA-PEG-annexin V. Images were acquired 48 h after the injection of the 
radiotracer. Autoradiography and TUNEL (terminal 
deoxynucleotidyltransferase-mediated dUTP nick-end labeling) staining were 
performed on adjacent tumor slices for the localization of apoptotic cells. The 
imaging properties of unPEGylated annexin V and PEGylated ovalbumin were also 
determined to permit assessment of the specificity of (111)In-DTPA-PEG-annexin 
V.
RESULTS: Tumor apoptotic index increased from 1.67% +/- 0.31% at baseline to 
7.60% +/- 0.72% and 11.07% +/- 1.81%, respectively, 4 d after treatment with 
poly(L-glutamic acid)-paclitaxel or combined poly(L-glutamic acid)-paclitaxel 
and C225. Tumor uptake (percentage of injected dose per gram of tumor [%ID/g]) 
of PEGylated (111)In-DTPA-PEG-annexin 4 d after treatment was significantly 
higher in tumors treated with poly(L-glutamic acid)-paclitaxel (10.76 +/- 1.38 
%ID/g; P = 0.001) and with combined poly(L-glutamic acid)-paclitaxel and C225 
(9.84 +/- 2.51 %ID/g; P = 0.029) than in nontreated tumors (6.14 +/- 0.67 
%ID/g), resulting in enhanced visualization of treated tumors. 
(111)In-DTPA-PEG-annexin V distributed into the central zone of tumors, whereas 
(111)In-DTPA-annexin V was largely confined to the tumor periphery. Furthermore, 
uptake of (111)In-DTPA-PEG-annexin V by tumors correlated with apoptotic index 
(r = 0.87, P = 0.02). Increase in tumor uptake of the nonspecific PEGylated 
protein (111)In-DTPA-PEG-ovalbumin was also observed after poly(L-glutamic 
acid)-paclitaxel treatment (55.6%), although this increase was less than that 
observed for (111)In-DTPA-PEG-annexin V (96.7%).
CONCLUSION: Increased uptake of and improved visualization with 
(111)In-DTPA-PEG-annexin V in solid tumors after chemotherapy are mediated 
through both specific binding to apoptotic cells and nonspecific retention of 
macromolecular contrast agents in the tumors. (111)In-Labeled, PEGylated annexin 
V may be used to assess tumor response to chemotherapy.