99mTc-Annexin-V and 99mTc-Sestamibi uptake as indicators of chemotherapy induced apoptosis.

Objectives ^99mTc-Annexin-V can be employed to monitor apoptosis in vivo.^99mTc-Sestamibi has been shown to be inversely correlated with levels of Bcl-2: reduction of ^99mTc-Sestamibi uptake in response to an antiblastic agent would reflect resistance to apoptosis.We evaluated ^99mTc-Annexin V and ^99mTc-Sestamibi uptake in a virus-induced model of mouse breast cancer .

Methods Biodistribution was evaluated in tumor-bearing mice in baseline conditions and 1, 3, 6 and 24 hr after 0.02 mg/g bw Paclitaxel given iv.Biodistribution was assessed 1 hr after injection of ^99mTc-Annexin V and 20 min after ^99mTc-Sestamibi.Tumour samples were also processed by WB and IF to identify apoptotic cells (TUNEL) and expression of Caspase-3, Caspase-8 and Bcl-2.

Results A highly significant correlation between ^99mTc-Annexin V and ^99mTc-Sestamibi with a peak 3-hr uptake was found,suggesting that they both may be used as indicators of apoptosis.TUNEL was significantly correlated with uptake of both ^99mTc-Annexin V (p<0.0001) and ^99mTc-Sestamibi (p=0.0122).Caspase-3 and -8 expression was prevalent in baseline condition and 6-24 hr after treatment, while Bcl-2 was high in baseline condition, reached a nadir at 3 hr and subsequent recovered.

Conclusions These observations confirm the anti-apoptotic role of Bcl-2 and suggest the co-existence of two apoptotic cell populations: an early apoptotic response probably mediated by Caspase-10 and a later, minor apoptotic event mediated by Caspase-3.