DESCRIPTION: (adapted from application) Towards developing an efficient and relevant in vitro method to screen estrogenic chemicals, the PI has finished his objectives of the Phase I STTR and optimized the MCF-7 focus formation assay. In this Phase II application, the PI proposes to validate the MCF-7 focus assay using a group of known estrogen modulators and characterize the mechanistic basis of estrogen modulators of focus formation in regard to ER binding or regulation of metabolic alterations. PROPOSED COMMERCIAL APPLICATION: The MCF-7 focus assay will be applied commercially for the detection and characterization of estrogen modulators in environmentally relevant samples. In addition, it will be marketed to the pharmaceutical industry as a physiological screen for leads with regard to estrogenic and anti estrogenic activity, either as targeted endpoints or as deleterious side effects. These applications of the focus assay will bridge the gap between non-physiological high-through-put assays and more costly animal studies. The end point of estrogen dependent postconfluent cell proliferation and tissue restructuring, resulting in the development of multicelluar foci, has physiological relevance since it is based on an in vitro analogue of the in vivo estrogenic response, using specific clones of the human breast tissue-derived estrogen-responsive MCF-7 cell line.