Preclinical imaging of therapy response using metabolic and apoptosis molecular imaging.

Purpose: Early after therapy, 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) imaging is not always reliable due to the influx of inflammatory cells while apoptosis imaging offers a direct and early measurement of therapy effects. This study uses an improved apoptosis probe ((99m)Tc-hAnxA5) in combination with [(18)F]FDG imaging to evaluate therapy response.

Procedures: Daudi tumor tissue was implanted in the spleen of SCID mice. Treatment was performed with adriamycin and cyclophosphamide. Sequential [(18)F]FDG-positron emission tomography (PET) was acquired over 6 days and (99m)Tc-hAnxA5-SPECT was performed before and 1 day after therapy.

Results: On day 1, therapy induced apoptosis was visualized with (99m)Tc-hAnxA5 without a measurable change in [(18)F]FDG uptake. [(18)F]FDG uptake decreased significantly on day 3 and was even more pronounced on day 6.

Conclusion: In this preclinical model, (99m)Tc-hAnxA5 imaging was able to detect apoptosis before metabolic changes were measured. These results confirm the value of apoptosis imaging for therapy response and give more insight in [(18)F]FDG imaging and its parameters to evaluate response.