A Convenient Synthetic Method for Alpha-Alkylation of Steroidal 17-Ketone: Preparation of 16β(THPO-Heptyl)-Estradiol

Contribution to the development of inhibitors of 17β-hydroxysteroid dehydrogenase types 1 and 7: key tools for studying and treating estrogen-dependent diseases

17β-Hydroxysteroid dehydrogenases (17β-HSDs) belong to a group of key enzymes involved in the biosynthesis of steroidal hormones by catalyzing the reduction of 17-ketosteroids or the oxidation of 17β-hydroxysteroids. From three members known in the early nineties, the 17β-HSD functional family has grown to 15 members over the last 20 years. This growing number of 17β-HSD isoforms questioned the importance of each member, especially in their implication in estrogen- and androgen-dependent diseases, such as breast and prostate cancers. One of the strategies used to address the physiological importance of 17β-HSDs is to use potent and selective inhibitors. Furthermore, enzyme inhibitors could also be of therapeutic interest by reducing the level of estradiol (E2). Focusing on estrogens, we targeted 17β-HSD types 1 and 7, two enzymes able to transform the weak estrogen estrone (E1) into the potent estrogen E2. The present review article gives a description of different classes of inhibitors of 17β-HSD1 (C6-derivatives of E2, C16-derivatives of E2 as alkylating and dual action compounds, E2-adenosine hybrids, E2-simplified adenosine hybrids, and C16-derivatives of E1 or E2) and of inhibitors of 17β-HSD7, all these inhibitors developed in our laboratory. The chemical structures and inhibitory activity of these steroidal inhibitors, their potential as therapeutic agents, and their use as tools to elucidate the role of these enzymes in particular biological systems will be discussed. Article from the Special issue on Targeted Inhibitors.

Design, synthesis and biological evaluation of estradiol-PEG-linked platinum(II) hybrid molecules: comparative molecular modeling study of three distinct families of hybrids

The synthesis of a series of 17β-estradiol-platinum(II) hybrid molecules is reported. The hybrids are made of a PEG linking chain of various length and a 2-(2'-aminoethyl)pyridine ligand. They are prepared from estrone in only 5 chemical steps with an overall yield of 22%. The length of the PEG chain does not influence the solubility of the compounds as it remains relatively constant throughout the series. MTT assays showed that the derivative with the longest PEG chain showed the best activity against two human breast cancer cell lines (MCF-7 and MDA-MB-231). The novel PEG-hybrids are also compared in terms of activities with two other families of 17β-estradiol-platinum(II) hybrids that we reported in previous studies. Molecular modeling study performed on a representative member of each family of hybrids reveals distinct molecular interactions with the estrogen receptor α which further corroborates their notably contrasting cytocidal activities on breast cancer cell lines. This study also shows that lipophilicity and the orientation of the tether chain between the estrogenic portion and the platinum(II) core contribute markedly to the biological activity of the various families of hybrids. The most active hybrids are those possessing an alkyl tether chain at position 16β of the steroid nucleus. For example, derivative 3 (p=6) is about 16 times more potent on MCF-7 breast cancer cells than the corresponding 16α-PEG-hybrids (2b) made in this study.

Synthesis of 17beta-estradiol-platinum(II) hybrid molecules showing cytotoxic activity on breast cancer cell lines

The synthesis of a series of 17beta-estradiol-platinum(II) hybrid molecules is reported. The hybrids are made of a PEG linking chain of various length and a 2-(2'-aminoethyl)pyridine ligand. They are prepared from estrone in five chemical steps with an overall yield of 22%. The length of the PEG chain does not influence the solubility of the compounds as it remains relatively constant throughout the series. MTT assays showed that the derivative with the longest PEG chain showed the best activity against breast cancer cell lines (MCF-7 and MDA-MB-231). Molecular modeling study rationalized the results.

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.

Synthesis of 17β-estradiol-linked platinum(II) complexes and their cytocidal activity on estrogen-dependent and -independent breast tumor cells

The synthesis of two new highly potent 17beta-estradiol-linked platinum(II) complexes is described. The new molecules are linked at position 16 of the steroid nucleus with an alkyl chain. They are made from estrone in nine chemical steps with an overall yield exceeding 10%. The biological activity of these compounds was evaluated in vitro on estrogen dependent and independent (ER(+) and ER(-)) human breast tumor cell lines: MCF-7 and MDA-MB-231. The novel compounds prove to be highly cytotoxic against breast cancer cell lines. The most cytotoxic derivative shows high affinity for the estrogen receptor alpha.

Synthesis of Simplified Hybrid Inhibitors of Type 1 17β-Hydroxysteroid Dehydrogenase via Cross-Metathesis and Sonogashira Coupling Reactions

[structure: see text] The inhibitor of type 1 17beta-hydroxysteroid dehydrogenase EM-1745 (1) exhibits affinity for both the substrate (estrone or estradiol) and the cofactor (NAD(P)H) binding domains. However, to increase its bioavailability, this compound needs to be simplified. The efficient and convergent synthesis of simplified substrate/cofactor hybrid inhibitors (compounds 2) involving a cross-metathesis and a Sonogashira coupling reaction as key steps is described. Compounds 2a-c were also tested as enzyme inhibitors and compared to EM-1745.

Synthesis of 17β-estradiol platinum(II) complexes: biological evaluation on breast cancer cell lines

The synthesis of a novel series of 17beta-estradiol-linked platinum(II) complexes is described. The new molecules are linked with an alkyl chain at position 16alpha of the steroid nucleus and bear a 16beta-hydroxymethyl side chain. They are made from estrone in five chemical steps with an overall yield exceeding 28%. The biological activity of these compounds was evaluated in vitro on estrogen dependent and independent (ER+ and ER-) human breast cancers. The derivatives incorporating a 2-(2'-aminoethyl)pyridine ligand displayed good activity against the cell lines particularly when the connecting arm is 10 carbon atoms long.

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 stereoselective synthesis of 7 alpha-(3-carboxypropyl) estradiol from a noncontrolled substance

Alkylation of 3,17 beta-bis(2-trimethylsilyl)ethoxymethyl-1,3,5(10) estratriene-6-one (2) with 5-bromo-1-pentene using NaHMDS in THF afforded 3,17 beta-bis(2-trimethylsilyl)ethoxymethyl-7-alpha-(4'pentenyl)-1,3,5(10) estratriene-6-one (3) in excellent stereoselectivity (> 95% epimeric excess). Functionalization of the side chain in compound 3 was accomplished via ozonolysis, oxidation and esterification to give 5 in 72% yield. The reduction of ester (5) using NaBH4 in MeOH afforded the corresponding 6 alpha-hydroxy compound (6) as a single isomer in 72% yield. The hydroxyl group in 6 was removed by converting to the corresponding xanthate (7) followed by reduction using n-Bu3SnH to afford 8 in good yield. Finally, the SEM protective groups in 8 were removed, after which the ester function was hydrolyzed with LiOH to give 7 alpha-(3'-carboxypropyl)estradiol (10), in 10.6% overall yield from 3.

Synthesis of 16-(bromoalkyl)-estradiols having inhibitory effect on human placental estradiol 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD type 1)

The activity of 17 beta-HSD type 1, the enzyme that converts estrone into its more potent metabolite estradiol, has been demonstrated in all classical steroidogenic tissues and almost all peripheral tissues from both rat and human. Since 17 beta-HSD is one of the most important enzymes involved in active steroid hormone formation, its inactivation could be a clinical approach to the treatment of hormono-dependent diseases like breast cancer. Herein we report the synthesis of 16-(bromoalkyl)-estradiols and their potency to inhibit the human placenta cytosolic estradiol 17 beta-HSD (type 1). Synthetic analogues possess various side chain lengths and orientation (alpha or beta) at position 16 of the steroidal D ring. The most potent inhibitory effect was observed when the length of the side chain was 3 or 4 carbons. However, the 16 beta-(bromopropyl)-estradiol easily undergoes cyclization and its effect on 17 beta-HSD is lost. Consequently, 16 alpha-(bromopropyl)-E2, 16 alpha-(bromobutyl)-E2, and 16 beta-(bromobutyl)-E2 were the best inhibitors discussed in this paper.