Radio-labeled annexin V for imaging apoptosis in radiated human follicular thyroid carcinomas

Objectives Induction of apoptosis is a widely used strategy for cancer therapy, but it is still a problem to evaluate the success of this therapy. In order to see whether radio-labeled annexin V could be a suitable substance for the non-invasive in vivo detection of apoptosis in thyroid tissue, we investigated two poorly differentiated thyroid carcinoma cell lines (ML-1, FTC-133).

Methods Apoptosis was evaluated before, 2d and 4d after in vitro irradiation with 30 Gy X-rays (p.r.). Binding of FITC- and of 125-I-labeled annexin V was measured in comparison to other apoptosis markers (Bax, caspase-3 Fas) determined by flow cytometry and western blot analysis.

Results ML-1 and FTC-133 cells showed a significant increase in annexin V binding 2d p.r.. 4d p.r., annexin V absorption capability of ML-1 cells was still maximal, while the living fraction of FTC increased significantly. The amount of caspase-3 and Bax were clearly increased at 4d p.r., and had normalized after 4d in both cell lines. Fas protein concentrations remained unchanged in ML-1 cells, but significantly enhanced in FTC-133 cells.

Conclusions The binding of FITC- and 125-I-labeled annexin V showed a significant accordance. A reliable evaluation of apoptosis induced by radiotherapy in thyroid tumors was possible 4d p.r., when binding of radio-labeled annexin V is most significantly enhanced. Allthough using two poorly differentiated cell lines of thyroid carcinoma, the cells showed a completely contrary response. An individualized study protocol for each type of tumor and probably within each type is necessary.