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

Real-time quantification of radioligand binding to cells under in vivo-like conditions improves evaluation of clinical potential. 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 ¹²⁵I-trastuzumab solution. The time-dependent cell binding was measured using a NaI detector, and the binding parameters were derived by computational analysis. The detection efficiency of ¹²⁵I 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 × 10⁴ M^-1 s^-1 and k_off was 0.11-4.2 × 10^-5 s^-1. Radioligands can be rapidly evaluated by binding to living cells for selection and optimization of radioconjugates for diagnostic and therapeutic purposes.