Investigation of a potential scintigraphic tracer for imaging apoptosis: radioiodinated annexin V-Kunitz protease inhibitor fusion protein.

Radiolabeled annexin V (ANV) has been widely used for imaging cell apoptosis. Recently, a novel ANV-Kunitz-type protease inhibitor fusion protein, ANV-6L15, was found to be a promising probe for improved apoptosis detection based on its higher affinity to phosphatidylserine (PS) compared to native ANV. The present paper investigates the feasibility of apoptosis detection using radioiodinated ANV-6L15. Native ANV and ANV-6L15 were labeled with iodine-123 and iodine-125 using Iodogen method. The binding between the radioiodinated proteins and erythrocyte ghosts or chemical-induced apoptotic cells was examined. ANV-6L15 can be radioiodinated with high yield (40%-60%) and excellent radiochemical purity (>95%). (123)I-ANV-6L15 exhibited a higher binding ratio to erythrocyte ghosts and apoptotic cells compared to (123)I-ANV. The biodistribution of (123)I-ANV-6L15 in mice was also characterized. (123)I-ANV-6L15 was rapidly cleared from the blood. High uptake in the liver and the kidneys may limit the evaluation of apoptosis in abdominal regions. Our data suggest that radiolabeled ANV-6L15 may be a better scintigraphic tracer than native ANV for apoptosis detection.

Monitoring of 2-deoxy-2-[18F]fluoro-D-glucose uptake in tumor-bearing mice using high-sensitivity projection imaging: compared with PET imaging.

OBJECTIVE: To investigate the feasibility of using high-sensitivity projection [F]fluoro-deoxyglucose imaging to monitor chemotherapeutic efficacy in BALB/c mice bearing CT-26 tumor implants. METHODS: A planar positron imaging system (PPIS)-4800 and a microPET R4 were used for projection and tomographic imaging, respectively. Six disks filled with different volumes of F-FDG solution were scanned by PPIS for calibration check. Tumor-bearing mice were treated with saline (control) or cyclophosphamide by intraperitoneal injections. Tumor responses were evaluated by both PPIS and microPET imaging. RESULTS: The disk-activity ratios obtained from PPIS were 1.00: 1.30: 1.98: 2.48: 2.73: 3.53 with corresponding volume ratios of 1.0: 1.5: 2.0: 2.5: 3.0: 3.5. PPIS imaging in tumor-bearing mice showed that the tumor/non-tumor ratios were 1.62, 2.12, 3.03, 4.46, and 3.61 on days 7, 10, 13, 17, and 20, respectively, after tumor inoculation. In addition, PPIS was used to monitor the chemotherapeutic effect of cyclophosphamide on tumor-bearing mice. The correlation coefficients between the tumor sizes and tumor/non-tumor ratios for microPET and PPIS were 0.63 and 0.72, respectively, in the control group, and were 0.98 and 0.81, respectively, in the cyclophosphamide-treated group. CONCLUSION: This study showed that PPIS imaging is a feasible modality for monitoring tumor responses. These results suggest that PPIS, a potential high-throughput screening imaging system, may be used for the preclinical evaluation of tumor response to new anticancer drugs using murine tumor models.