Expression and partial characterization of estramustine-binding protein (EMBP) in human breast cancer and malignant...

The expression of the estramustine/estromustine-binding protein (EMBP) in human mammary cancer and malignant melanoma was examined by immunochemical methods and compared with that in endometrial and ovarian cancers. By RIA measurements, EMBP was detected in 6/17 mammary cancers (range 11.3-2,660 ng/g tissue) and 2/3 malignant melanomas (618 and 1,240 ng/g), whereas endometrial (n = 6) and ovarian (n = 3) cancers exhibited non-detectable levels. In breast cancer, EMBP-expressing tumours were all estrogen receptor-negative, suggesting an inverse correlation between EMBP and hormone responsiveness of the tumour. Biochemical characterization revealed properties of EMBP in mammary tumours and melanomas almost identical to those for EMBP purified from rat ventral prostate: i.e. surface-charge distribution by Mono Q/FPLC ion-exchange chromatography, a molecular weight of 50,000 by gel filtration, and a subunit composition by Western blot analysis under denaturing conditions. Finally, the EMBP immunoreactivity was confined to the cytoplasm of malignant cells in breast cancer and melanoma sections by immunohistochemical examination. This is the first study that demonstrates EMBP in mammary cancer and malignant melanoma. Our findings suggest that a mechanism for selective uptake of cytotoxic estramustine and estromustine is prevailing in these malignancies and that monitoring of EMBP in biopsy samples will be of value in defining patients who may benefit from Estracyt treatment.