Drug discovery is extremely difficult. There are many unanticipated scientific, medical and business challenges to every drug discovery programme. It is important to increase our understanding of the fundamental properties of effective drugs so that we can anticipate potential problems in developing new agents. This article addresses potential drug discovery and development risks associated with the biochemical mechanism of drug action, and proposes simple rules to minimize these risks.

Biochemical mechanisms of drug action: what does it take for success?

Although many studies implicate sex steroids in the process of sexual differentiation, the exact role played by these substances in lower vertebrates, especially teleost fish, is not clear, since it is not conclusively known whether sex steroids are the cause or an early consequence of sex differentiation. By hormonal manipulation and specific crossings, it is possible to produce all-female stocks of the otherwise gonochoristic chinook salmon (Oncorhynchus tshawytscha). These all-female stocks are an excellent model to study the effects of steroids on sexual differentiation since the genetic sex is known before the actual differentiation of the embryonic gonads takes place. In the present study, we show that treatment with a nonsteroidal inhibitor of aromatase, the enzyme that catalyzes the conversion from androgens to estrogens, for only 2 hours when the gonads were bipotent, caused genetic females to develop into normal males. Furthermore, these males had testes which were indistinguishable both in size and in structure from those of genetic males, and completed all the stages of spermatogenesis. At 2 years of age, these males produced viable sperm capable of inducing normal embryonic development when used to fertilize eggs, with a resulting all-female progeny. These results provide strong support for Yamamoto's theory (Yamamoto, '69) that androgens and estrogens are natural sex inducers in gonochoristic fish, and suggest that aromatase plays a pivotal role in the sex differentiation of salmon. Thus, by brief treatment with an aromatase inhibitor at a specific time in development, an organism was induced to develop a funtional, phenotypic sex different from its genetic sex. © 1994 Wiley-Liss, Inc.

Brief treatment with an aromatase inhibitor during sex differentiation causes chromosomally female salmon to develop as normal, functional males

https://www.hormonebalance.org/images/documents/Pasqualini%2004%20SERMs%20BC%20review%20BBActa.pdf

The selective estrogen enzyme modulators in breast cancer: a review.

We have developed an estrogen bioassay using the Ishikawa human endometrial adenocarcinoma cell line growing in 96-well microtiter plates Alkaline phosphatase enzyme activity (AlkP) in these cells is markedly stimulated by estrogens, and this enzyme can be easily quantified in situ using a chromogenic substrate These cells are very sensitive to estrogens; estradiol induces AlkP at levels as low as 10-12 M Antiestrogens completely block the action of estradiol Various estrogens stimulate AlkP with potencies comparable to those achieved in vivo The induction of AlkP is specific for estrogens; no other type of steroid, including androgens, progestins, mineralocorticoids, or glucocorticoids produce this effect The stimulation of AlkP in Ishikawa cells is specific for estrogens, is highly reproducible and sensitive, and permits large numbers of samples to be assayed with ease We have used this assay to investigate the estrogenic action of the adrenal Δ5-3β-hydroxysteroids While pregnenolone is inactive

A Simple and Sensitive Microtiter Plate Estrogen Bioassay Based on Stimulation of Alkaline Phosphatase in Ishikawa Cells: Estrogenic Action of Δ5 Adrenal Steroids*

L.-Y. Wing

Papers

Aromatase inhibitors and the treatment of breast cancer.