@article {Ke108, author = {Shi Ke and Xiaoxia Wen and Qing-Ping Wu and Sidney Wallace and Chusilp Charnsangavej and Anne M. Stachowiak and Clifton L. Stephens and James L. Abbruzzese and Donald A. Podoloff and Chun Li}, title = {Imaging Taxane-Induced Tumor Apoptosis Using PEGylated, 111In-Labeled Annexin V }, volume = {45}, number = {1}, pages = {108--115}, year = {2004}, publisher = {Society of Nuclear Medicine}, abstract = {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 111In-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 111In-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 111In-DTPA-PEG-annexin V. Results: Tumor apoptotic index increased from 1.67\% {\textpm} 0.31\% at baseline to 7.60\% {\textpm} 0.72\% and 11.07\% {\textpm} 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 111In-DTPA-PEG-annexin 4 d after treatment was significantly higher in tumors treated with poly(l-glutamic acid)-paclitaxel (10.76 {\textpm} 1.38 \%ID/g; P = 0.001) and with combined poly(l-glutamic acid)-paclitaxel and C225 (9.84 {\textpm} 2.51 \%ID/g; P = 0.029) than in nontreated tumors (6.14 {\textpm} 0.67 \%ID/g), resulting in enhanced visualization of treated tumors. 111In-DTPA-PEG-annexin V distributed into the central zone of tumors, whereas 111In-DTPA-annexin V was largely confined to the tumor periphery. Furthermore, uptake of 111In-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 111In-DTPA-PEG-ovalbumin was also observed after poly(l-glutamic acid)-paclitaxel treatment (55.6\%), although this increase was less than that observed for 111In-DTPA-PEG-annexin V (96.7\%). Conclusion: Increased uptake of and improved visualization with 111In-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. 111In-Labeled, PEGylated annexin V may be used to assess tumor response to chemotherapy.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/45/1/108}, eprint = {https://jnm.snmjournals.org/content/45/1/108.full.pdf}, journal = {Journal of Nuclear Medicine} }