Feasibility of ^99mTc-annexin V for repetitive detection of apoptotic tumor response to chemotherapy: An experimental study using a rat tumor model

Annexin V (annexin A5), a human protein with a high affinity for phosphatidylserine, labeled with ^99mTc can detect apoptosis in vivo. In the repetitive detection of apoptosis with ^99mTc-annexin V, however, the specific binding of annexin V to phosphatidylserine might affect the subsequent detection of apoptosis with this compound. To determine whether there is interference with repetitive doses of annexin V, we evaluated the effects of previous administration of cold annexin V on accumulation of ^99mTc-annexin V in tumors in an experimental tumor model. Methods: Rats bearing hepatoma received cyclophosphamide (150 mg/kg, intraperitoneally) 11 d after the tumor inoculation. Cold annexin V (20 μg/kg, intravenously) was administered 24 h before or after the cyclophosphamide treatment (n = 7/group). ^99mTc-Annexin V was injected intravenously (radioactive dose, 5-23 MBq/kg; mass dose, 20 μg/kg), and radioactivity in tissues was determined 6 h later. Results: Accumulation of ^99mT-cannexin V in tumors was not significantly affected by previous treatment with cold annexin V before or after chemotherapy. Conclusion: These results demonstrate the feasibility of ^99mT-cannexin V imaging for repetitive detection of apoptosis, which is highly required in the clinical setting.