Rapid, high-resolution procedure for assessment of estrogen receptor heterogeneity in clinical samples

Approximately two-third of the women with breast cancer may benefit from hormone therapies if the lesion contains estrogen receptor in reasonable levels (greater than 10 fmol/mg cytosol protein). Our lab and others have suggested that not only the concentration, but the various molecular form(s) of the receptor may be an important factor in predicting patient responsiveness. Until now, this heterogeneity has been determined by analysis on sucrose density gradients requiring 16 h of centrifugation. Other methodologies which can disclose the profile of receptor isoforms are compromised by irreproducibility, poor recovery, or the length of time required to perform the analysis. We believe that high-performance liquid chromatography (HPLC) in the anion-exchange and chromatofocusing modes may be able to supply more insight into receptor structure than currently available by any other method. Utilizing the high activity ligand [16 alpha-125I]iodoestradiol-17 beta (2200 Ci/mmol) and flow-through equipment to monitor conductivity, pH, and radioactivity, we are able to describe the distribution of ionic isoforms in crude cytosolic preparations of breast cancer and uterus. This "on-line" technology is rapid (chromatogram is complete within 120 min), sensitive (receptor isoforms equivalent to 1 fmol are apparent), efficient (columns typically return greater than 90% of applied radio-labeled receptor) and reproducible (due to the sophistication of modern HPLC equipment). It is clear these techniques may be used in the clinical setting to better describe the profile of estrogen receptor isoforms and should be explored as a method of correlating receptor structure with hormone function in responsive tissues.