Interaction of a novel fluorescent analog of interferon-gamma with transformed cells.

A fluorescent analog of human recombinant interferon-gamma (IFN-gamma) was prepared for the first time. The recovered pyrene-labeled IFN-gamma (py-IFN-gamma), with an estimated seven pyrene molecules per IFN-gamma, retained over half of its original biological activity. Binding of py-IFN-gamma to human amnion WISH cells showed appreciable enhancement in fluorescence polarization from 0.055 to 0.215 and in fluorescence lifetime from 56 to 80 ns. The ratio of the vibronic peaks did not change, indicating that the pyrene molecules remained in water environment even after binding. Py-IFN-gamma provides a novel tool for unraveling the mechanism of the initial interaction between this antiproliferative lymphokine and its target, cancer cell membrane receptors. Its fluorescence could provide the means to follow receptor recycling when it occurs.