Environmental contaminants have been found to produce estrogen-like and androgen-antagonistic effects. It has been hypothesized that environmental estrogens may be playing a role in the decrease of the quantity and quality of human semen, and in the increased incidence of cryptorchidism, and testicular and breast cancer in humans. This hypothesis will require the solution of a series of technical problems before it can be explored. In vitro assays are crucial to accomplish this objective.
The MCF7 cell proliferation assay (E-SCREEN) is the most widely used of the estrogen screens. It is the most sensitive, as it discriminates among agonists and antagonists, and so far, neither false positives nor false negatives have been found among the chemicals screened. Yeast assays do not discriminate among agonists and antagonists. In addition, false negatives have been reported.
The androgen screen (A-SCREEN) assay measures cell proliferation. Alternative assays based on the expression of stable transfected reporter genes are being developed. The only limitation of in vitro/in culture assays is that they cannot detect most prohormones. In order to overcome this limitation, an activation step needs to be developed.