Imaging taxane-induced tumor apoptosis using PEGylated, 111In-labeled annexin V.
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%).


CONCLUSIONS
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.
Ke
Shi
S
Division of Diagnostic Imaging, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Wen
Xiaoxia
X
Wu
Qing-Ping
QP
Wallace
Sidney
S
Charnsangavej
Chusilp
C
Stachowiak
Anne M
AM
Stephens
Clifton L
CL
Abbruzzese
James L
JL
Podoloff
Donald A
DA
Li
Chun
C
D000818:Animals; D017304:Annexin A5 / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D000970:Antineoplastic Agents / Q000008:administration & dosage; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D001952:Bridged-Ring Compounds / Q000008:administration & dosage*; D005260:Female; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009942:Organometallic Compounds / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D043823:Taxoids / Q000008:administration & dosage*; D016896:Treatment Outcome
C483471:(111)indium-DTPA-PEG-annexin V; D017304:Annexin A5; D000970:Antineoplastic Agents; D001952:Bridged-Ring Compounds; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D043823:Taxoids; C080625:taxane