Active site analysis of 17beta-hydroxysteroid dehydrogenase type 1 enzyme complexes with SPROUT

Current knowledge of the multifunctional 17β-hydroxysteroid dehydrogenase type 1 (HSD17B1)

At the late 1940s, 17β-HSD1 was discovered as the first member of the 17β-HSD family with its gene cloned. The three-dimensional structure of human 17β-HSD1 is the first example of any human steroid converting enzyme. The human enzyme's structure and biological function have thus been studied extensively in the last two decades. In humans, the enzyme is expressed in placenta, ovary, endometrium and breast. The high activity of estrogen activation provides the basis of 17β-HSD1's implication in estrogen-dependent diseases, such as breast cancer, endometriosis and non-small cell lung carcinomas. Its dual function in estrogen activation and androgen inactivation has been revealed in molecular and breast cancer cell levels, significantly stimulating the proliferation of such cells. The enzyme's overexpression in breast cancer was demonstrated by clinical samples. Inhibition of human 17β-HSD1 led to xenograft tumor shrinkage. Unfortunately, through decades of studies, there is still no drug using the enzyme's inhibitors available. This is due to the difficulty to get rid of the estrogenic activity of its inhibitors, which are mostly estrogen analogues. New non-steroid inhibitors for the enzyme provide new hope for non-estrogenic inhibitors of the enzyme.

Hydroxybenzothiazoles as new nonsteroidal inhibitors of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1)

17β-estradiol (E2), the most potent estrogen in humans, known to be involved in the development and progession of estrogen-dependent diseases (EDD) like breast cancer and endometriosis. 17β-HSD1, which catalyses the reduction of the weak estrogen estrone (E1) to E2, is often overexpressed in breast cancer and endometriotic tissues. An inhibition of 17β-HSD1 could selectively reduce the local E2-level thus allowing for a novel, targeted approach in the treatment of EDD. Continuing our search for new nonsteroidal 17β-HSD1 inhibitors, a novel pharmacophore model was derived from crystallographic data and used for the virtual screening of a small library of compounds. Subsequent experimental verification of the virtual hits led to the identification of the moderately active compound 5. Rigidification and further structure modifications resulted in the discovery of a novel class of 17β-HSD1 inhibitors bearing a benzothiazole-scaffold linked to a phenyl ring via keto- or amide-bridge. Their putative binding modes were investigated by correlating their biological data with features of the pharmacophore model. The most active keto-derivative 6 shows IC₅₀-values in the nanomolar range for the transformation of E1 to E2 by 17β-HSD1, reasonable selectivity against 17β-HSD2 but pronounced affinity to the estrogen receptors (ERs). On the other hand, the best amide-derivative 21 shows only medium 17β-HSD1 inhibitory activity at the target enzyme as well as fair selectivity against 17β-HSD2 and ERs. The compounds 6 and 21 can be regarded as first benzothiazole-type 17β-HSD1 inhibitors for the development of potential therapeutics.

17β-Hydroxysteroid dehydrogenases (17β-HSDs) as therapeutic targets: protein structures, functions, and recent progress in inhibitor development

17β-Hydroxysteroid dehydrogenases (17β-HSDs) are oxidoreductases, which play a key role in estrogen and androgen steroid metabolism by catalyzing final steps of the steroid biosynthesis. Up to now, 14 different subtypes have been identified in mammals, which catalyze NAD(P)H or NAD(P)(+) dependent reductions/oxidations at the 17-position of the steroid. Depending on their reductive or oxidative activities, they modulate the intracellular concentration of inactive and active steroids. As the genomic mechanism of steroid action involves binding to a steroid nuclear receptor, 17β-HSDs act like pre-receptor molecular switches. 17β-HSDs are thus key enzymes implicated in the different functions of the reproductive tissues in both males and females. The crucial role of estrogens and androgens in the genesis and development of hormone dependent diseases is well recognized. Considering the pivotal role of 17β-HSDs in steroid hormone modulation and their substrate specificity, these proteins are promising therapeutic targets for diseases like breast cancer, endometriosis, osteoporosis, and prostate cancer. The selective inhibition of the concerned enzymes might provide an effective treatment and a good alternative to the existing endocrine therapies. Herein, we give an overview of functional and structural aspects for the different 17β-HSDs. We focus on steroidal and non-steroidal inhibitors recently published for each subtype and report on existing animal models for the different 17β-HSDs and the respective diseases. Article from the Special issue on Targeted Inhibitors.

Prolactin receptor-associated protein/17beta-hydroxysteroid dehydrogenase type 7 gene (Hsd17b7) plays a crucial role in embryonic development and fetal survival

Our laboratory has previously cloned and purified a protein named PRAP (prolactin receptor-associated protein) that was shown to be a novel 17beta-hydroxysteroid dehydrogenase (HSD) enzyme with dual activity. This enzyme, renamed HSD17B7 or PRAP/17beta-HSD7, converts estrone to estradiol and is also involved in cholesterol biosynthesis. The major site of its expression is the corpus luteum of a great number of species including rodents and humans. To examine the functional significance of HSD17B7 in pregnancy, we generated a knockout mouse model with targeted deletions of exons 1-4 of this gene. We anticipated a mouse with a severe fertility defect due to its inability to regulate estrogen levels during pregnancy. The heterozygous mutant mice are normal in their development and gross anatomy. The females cycle normally, and both male and female are fertile with normal litter size. To our surprise, the breeding of heterozygous mice yielded no viable HSD17B7 null mice. However, we found HSD17B7 null embryo alive in utero on d 8.5 and d 9.5. By d 10.5, the fetuses grow and suffer from severe brain malformation and heart defect. Because the brain depends on in situ cholesterol biosynthesis for its development beginning at d 10, the major cause of fetal death appears to be due to the cholesterol synthetic activity of this enzyme. By ablating HSD17B7 function, we have uncovered, in vivo, an important requirement for this enzyme during fetal development.

A 3D QSAR model of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core applying molecular dynamics simulations and ligand-protein docking

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme plays a crucial role in female hormonal regulation by catalysing the NADPH-dependent reduction of the less potent estrone E1 into the biologically active estradiol E2. Because 17beta-HSD1 is a key enzyme in E2 biosynthesis, it has emerged as an attractive drug target for inhibitor development. Herein we report the plausible binding modes and a 3D QSAR model of 17beta-HSD1 inhibitors based on a (di)cycloalkenothieno[2,3-d]pyrimidin-4(3H)-one core. Two generated enzyme complexes with potent inhibitors were subjected to molecular dynamics simulation to mimic the dynamic process of inhibitor binding. A set of 17beta-HSD1 inhibitors based on the thieno[2,3-d]pyrimidin-4(3H)-one core were docked into the resulting active site, and a CoMFA model employing the most extensive training set to date was generated. The model was validated with an external test set. Active site residues involved in inhibitor binding and CoMFA fields for steric and electrostatic interactions were identified. The model will be used to guide structural modifications of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core in order to improve the biological activity as well as in the design of novel 17beta-HSD1 inhibitors.

Characterization of HSD17B1 sequence variants in breast cancer cases from French Canadian families with high risk of breast and ovarian cancer

A family history of disease and estrogen exposure are risk factors for breast cancer. The HSD17B1 gene encodes a key steroidogenic enzyme that catalyses the final step of estradiol biosynthesis, rendering it a good candidate gene for breast cancer susceptibility. The current study was designed to screen for HSD17B1 germline mutations potentially involved in breast cancer susceptibility. DNA samples from 50 individuals affected with breast cancer from non-BRCA1/2 French Canadian families with a high risk of breast and ovarian cancer were screened for sequence variants in HSD17B1. Our study identified 28 sequence variants, including three non-synonymous variants, p.Ala238Val, p.Arg259His, p.Ser313Gly, one of which (p.Arg259His) was not previously reported. Functional assays failed to show changes in either activity or recombinant proteins levels for all three variants. Thus, our resequencing analysis does not support the existence of deleterious, gain-of-function or transcription mutations in HSD17B1, which could explain the clustering of breast cancer cases in non-BRCA1/2 high-risk French Canadian families. However, a haplotype-based approach was used to establish tSNPs, providing a valuable tool for further searches of common disease-associated variants in this gene, using large cohorts.