A rapid and efficient microtechnique for the analysis of functional transferrin receptors on tumor cells

A simple and efficient method for the analysis of the affinity and number of functional transferrin receptors (TFR) on human tumor cells is described. The technique is designed to utilize microtitration equipment; and is suitable for easy comparison of up to 8 different cell preparations per assay. Using this technique, 5 established cell lines were evaluated for functional TFR expression. The control erythroleukemic cell line K562 possessed 3.28 X 10(5) functional TFR per cell (+/- 3.69 X 10(4), SEM) Kd = 9.0 X 10(-9) X M-1. Trypsin and heat-pretreated cells were compared to control erythroleukemic K562 cells from the same culture to determine both the effects of receptor removal and cell viability on the assay. Trypsin and heat pretreatment of these K562 cells severely decreased receptor function as indicated by Scatchard analysis as well as by time course and cold competition analysis respectively. Whereas the affinity of trypsin-treated receptors on cells was similar to control values, heat-killed cells displayed an altered cellular affinity for 125I-transferrin underscoring the importance of utilizing cells of high viability in receptor assays.