A Novel Method for Real-Time Quantification of Radioligand Binding to Living Tumor Cells In Vitro .

Background: Real-time quantification of radioligand binding to cells under in vivo -like conditions improves evaluation of clinical potential. Materials and Methods: SKOV-3 tumor cells were grown in a monolayer on a thin glass plate placed in a sealable shallow chamber with a continuous flow of 125 I-trastuzumab solution. The time-dependent cell binding was measured using a NaI detector, and the binding parameters were derived by computational analysis. Results: The detection efficiency of 125 I was 65 cps/kBq for radioligand bound to the cells. Experiments were analyzed to find the values of k on and k off . The resulting k on was 3.2-7.9 × 10 4 M -1 s -1 and k off was 0.11-4.2 × 10 -5 s -1 . Conclusions: Radioligands can be rapidly evaluated by binding to living cells for selection and optimization of radioconjugates for diagnostic and therapeutic purposes.