Monoclonal antibodies for progesterone receptor assays and polymorphism studies in breast cancer. Comparison with radioligand assays.
Progesterone receptors (PR) from human breast tumors were assayed by a new method using monoclonal antibodies immobilized on beads (PR-EIA, Abbott Laboratories). EIA results were compared to those obtained with the dextran-coated charcoal method using a tritiated ligand (ORG 2058). The precision and reproducibility of the EIA method were studied over a 3-month period: intra-assay coefficients of variation were less than 6% for the range of the assay (between 5-250 fmol/ml), and inter-assay coefficients of variation calculated on 13 consecutive standard curves were less than 10%, except for standard 0 (33%). PR assays performed on 78 tumors both by EIA and radioligand (RLA) were compared. The linear regression obtained was: PR-EIA = 0.81 RLA+1 fmol/mg protein (r = 0.88). For reproducibility studies, cytosols were assayed twice during a period ranging from 1 week-3 months, both by EIA and RLA. The linear regression obtained between the second assay (B) and the first assay (A) was: B = 0.98 A + 11 fmol/mg protein for RLA (r = 0.98), and B = 0.99 A-7 fmol/mg protein for EIA (r = 0.98). To study the effect of KCl on PR-EIA, 26 tumors were homogenized in 0.4 M KCl Tris buffer and assayed both by EIA and RLA. A good correlation was obtained between the 2 methods, but higher values were obtained with PR-EIA (P = 1.6) in comparison with RLA. The addition of KCl to the cytosol showed that KCl had no effect on EIA results, but significantly lowered RLA results. To study the effect of KCl on progesterone receptor isoforms, cytosols were analyzed by chromatography on TSK G3000 SW columns, and the presence of PR was detected in each fraction by both EIA and RLA. In the absence of KCl, only the oligomeric form of PR was observed; however with both techniques, detection of this form different from tumor to tumor, emphasizing the inter-tumoral molecular heterogeneity of PR. After PR isoform dissociation by KCl (0.4 M) and chromatographic analysis of the forms obtained, monoclonal antibodies detected PR molecular forms different from those observed by radioligand; furthermore, chromatographic patterns obtained were different from one tumor to another and confirmed the inter-tumoral molecular heterogeneity of the progesterone receptor.
D000911:Antibodies, Monoclonal; D001943:Breast Neoplasms / Q000032:analysis*; D002850:Chromatography, Gel; D003600:Cytosol / Q000032:analysis; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D011189:Potassium Chloride / Q000494:pharmacology; D011869:Radioligand Assay; D011980:Receptors, Progesterone / Q000032:analysis*
D000911:Antibodies, Monoclonal; D011980:Receptors, Progesterone; D011189:Potassium Chloride