Assay for estrogen and progesterone receptors of breast cancer cell lines in monolayer culture.

A whole-cell assay for measuring estrogen (ER) and progesterone (PgR) receptors in monolayer culture of human breast cancer cell lines is described. It is based on the measurement of incorporated tritiated ligands during 50 min of incubation (i.e. [3H]estradiol for ER, [3H]ORG-2058 for PgR). The assay fulfills all criteria of specificity as shown by competitive studies and measurements of the dissociation constants of the binding reactions. Moreover, a subcellular fractionation of MCF-7 labeled cells revealed that the majority of incorporated steroids was associated with the nuclear fraction. This finding is consistent with the concept of nuclear location of steroid-receptor complexes. Cultures in the presence of 10(-8) M estradiol indicated that the methodology is adequate for detecting the well-known estrogenic induction of PgR synthesis. The assay proved suitable for the quantitative assessment of the receptor content of various neoplastic (MCF-7; ZR-75-1, Cama-1, Evsa-T) and non-neoplastic (HBL-100) cell lines. The methodology has the other advantages of being simple and rapid, of requiring small amounts of cells and of allowing histological examination of the latter before, during and after biochemical analysis.