Terbium fluorescence studies of cisplatin binding to GH3/B6 pituitary tumor cells

Terbium (Tb3+) fluorescence was used to investigate the interaction of cisplatin with GH3/B6 pituitary tumor cells. The binding of cisplatin to GH3/B6 cells quenched the fluorescence intensity of bound Tb3+. The IC50 for cisplatin inhibition of Tb3+-GH3/B6 fluorescence was determined to be 190 microM. Cisplatin was found to non-competitively inhibit the cellular binding of Tb3+, causing a dramatic decrease in the maximum number of high-affinity Tb3+ binding sites (by 33%), without markedly affecting their binding affinity. The half-life for the cellular binding of cisplatin was calculated to be 2.7 min. It was suggested that the plasma membrane of GH3/B6 cells contain a specific protein receptor for binding cisplatin.