Objective: The purpose of this study was to develop an imaging technique to
measure and monitor tumor cells undergoing programmed death caused by radi
ation and chemotherapy using Tc-99m-EC-annexin V. Annexin V has been used t
o measure programmed cell death both in vitro and in vivo. Assessment of ap
optosis would be useful to evaluate the efficacy and mechanisms of therapy
and disease progression or regression. Methods: Ethylenedicysteine (EC) was
conjugated to annexin V using sulfo-N-hydroxysuccinimide and 1-ethyl-3-(3-
dimethylaminopropyl) carbodiimide-HCl as coupling agents. The yield of EC-a
nnexin V was 100%. In vitro cellular uptake, pre- and post-radiation (10-30
Gy) and paclitaxel treatment, was quantified using Tc-99m-EC-annexin V. Ti
ssue distribution and planar imaging of Tc-99m-EC-annexin V were determined
in breast tumor-bearing mts at 0.5, 2, and 4 hrs. To demonstrate in vivo c
ell apoptosis that occurred during chemotherapy, a group of mts was treated
with paclitaxel and planar imaging studies were conducted at 0.5-4 hrs. Co
mputer outlined region of interest (ROI) was used to quantify tumor uptake
on day 3 and clay 5 post-treatment. Results: In vitro cellular uptake showe
d that there was significantly increased uptake of Tc-99m-EC-annexin V afte
r irradiation (10-30 Gy) and paclitaxel treatment In vivo biodistribution o
f Tc-99m-EC-annexin in breast tumor-bearing rats showed increased tumor-to-
blood, tumor-to-lung and tumor-to-muscle count density ratios as a function
of time. Conversely, tumor-to-blood count density ratios showed a time-dep
endent decrease with Tc-99m-EC in the same time period Planar images confir
med that the tumors could be visualized clearly with 99mTc-EC-annexin. Ther
e was a significant difference of ROI ratios between pre- and post-paclitax
el treatment groups at 2 and 4 hrs post injection. Conclusion: The results
indicate that apoptosis can be quantified using Tc-99m-EC-annexin and that
it is feasible to use Tc-99m-EC-annexin to image tumor apoptosis.