The affinity alkylators, 11 alpha-bromoacetoxyprogesterone and estrone 3-bromoacetate, modify a common histidyl residue in the active site of human placental 17 beta,20 alpha-hydroxysteroid dehydrogenase

Estradiol−Adenosine Hybrid Compounds Designed to Inhibit Type 1 17β-Hydroxysteroid Dehydrogenase

The steroidogenic enzyme type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the synthesis of estradiol (E(2)), a hormone well-known to stimulate the growth of estrogen-sensitive tumors. To obtain compounds able to control E(2) formation, two moieties were linked with a methylene side chain: an adenosine moiety for interacting with the cofactor-binding site and an E(2) moiety for interacting with the substrate-binding site. When tested as inhibitors of type 1 17beta-HSD, the hybrid compounds inhibited the reductive activity (E(1) into E(2)) with IC(50) values ranging from 52 to 1,000 nM. The optimal side-chain length was determined to be eight methylene groups for a 16 beta-orientation. The presence of two components (E(2) and adenosine) is essential for good inhibition, since 16 beta-nonyl-E(2) and 5-nonanoyl-O-adenosine, two compounds having only one of the components, did not inhibit the enzyme. Moreover, the 3D-structure analysis of EM-1,745 complexed with type 1 17beta-HSD showed key interactions with both substrate- and cofactor-binding sites.

A concerted, rational design of type 1 17beta-hydroxysteroid dehydrogenase inhibitors: estradiol-adenosine hybrids with high affinity

Human estrogenic 17beta-hydroxysteroid dehydrogenase (17beta-HSD type 1) catalyzes the final step in the synthesis of active estrogens that stimulate the proliferation of breast cancer cells. Based on the initial premise to make use of the binding energies of both the substrate and cofactor sites, and molecular modeling starting from the enzyme structure, several estradiol-adenosine hybrids were designed and synthesized. Among these hybrids, EM-1745 with a linker of 8-CH2 groups is proved to be the best competitive inhibitor with a Ki of 3.0 +/- 0.8 nM. The crystal structure of the EM-1745 enzyme complex at 1.6 A provides evidence at atomic resolution of strong interactions between both the steroid and cofactor moieties and the enzyme molecule, as illustrated by a deltaA-weighted 2Fo-Fc electron density map contoured at 3.0 delta. The substrate entry loop is further stabilized in this complex compared with previous complexes of the enzyme. These results confirm our initial strategy of combining studies of structural biology and enzyme mechanism in the inhibitor design, which may be applied to other steroidogenic enzymes involved in human diseases.

Overview of a rational approach to design type I 17beta-hydroxysteroid dehydrogenase inhibitors without estrogenic activity: chemical synthesis and biological evaluation

Hormone-sensitive diseases such as breast cancer are health problems of major importance in North America and Europe. Endocrine therapies using antiestrogens for the treatment and the prevention of breast cancer are presently under clinical trials. Antiestrogens are drugs that compete with estrogens for the estrogen receptor without activating the transcription of estrogen-sensitive genes. However, an optimal blockade of estrogen action could ideally be achieved by a dual-action compound that would antagonize the estrogen receptor and inhibit the biosynthesis of estradiol. Type I 17beta-hydroxysteroid dehydrogenase (17beta-HSD) was chosen as a key steroidogenic target enzyme to inhibit the formation of estradiol, which is the most potent estrogen. This article describes a rational approach that could lead to the development of compounds that exhibit both actions. The chemical syntheses of estradiol derivatives bearing a bromoalkyl and a bromoalkylamide side chain at the 16alpha-position are summarized. Two parameters were studied for biological evaluation of our synthetic inhibitors: (1) the inhibition of estrone reduction into estradiol by type I 17beta-HSD, and (2) the proliferative/antiproliferative cell assays performed on the estrogen-sensitive ZR-75-1 breast tumor cell line. First, the substitution of the 16alpha-position of estradiol by bromoalkyl side chain led to potent inhibitors of type I 17beta-HSD, but the estrogenic activity remained. Secondly, an alkylamide functionality at the 16alpha- or 7alpha-position of estradiol cannot abolish the estrogenic activity without affecting considerably the inhibitory potency on type I 17beta-HSD. In conclusion, the best dual-action inhibitor synthesized showed an IC50 of 13 +/- 1 microM for type I 17beta-HSD, while displaying antiestrogenic activity at 1.0 microM. Despite the fact that we did not obtain an ideal dual-action blocker, we have optimized several structural parameters providing important structure-activity relationship.

A 6beta-(thiaheptanamide) derivative of estradiol as inhibitor of 17beta-hydroxysteroid dehydrogenase type 1

In an effort to develop potent agents for reducing the levels of the active estrogen, estradiol, we developed a new category of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) type 1 inhibitors. The compounds described possess a butyl methyl alkylamide side chain linked to the C6 position of estradiol by a thioether. With a series of epimeric mixtures, an optimal side-chain length of five methylene groups (between the amide group and steroid part) was first determined. Thereafter, both C6 epimers of optimized mixture were obtained after high-pressure liquid chromatography separation. 1H and 13C NMR experiments were performed to confirm the stereochemistry of each epimer. The 6beta-orientation of the side-chain was found to be crucial for enzymatic inhibition. Indeed, for the optimized side-chain length, the compound with a beta-orientation (5: N-butyl,N-methyl 7-(3',17'beta-dihydroxy-1',3',5'( 10')-estratriene-6'beta-yl)-7-thiaheptanamide) was 70-fold more potent than the 6alpha-analog. Compound 5 did not inactivate 17beta-HSD type 1, suggesting a reversible inhibitor. In addition, it was found to be a more potent inhibitor than the substrate estrone itself or a panel of three known inhibitors.