Inhibition of 17β-HSD1: SAR of bicyclic substituted hydroxyphenylmethanones and discovery of new potent inhibitors with thioether linker

Isolation and purification of sinensetin, and in silico screening of phytochemicals from Orthosiphon aristatus (Blume) Miq. for anti-breast cancer activity

Orthosiphon aristatus (Blume) Miq. (O. aristatus), a traditional herbal medicine, exhibits a wide range of biological activities but its anti-breast cancer effect is not fully established. In this study, sinensetin was isolated and purified through a multistep process, beginning with liquid-liquid partitioning using dichloromethane, followed by classic column chromatography using gradient elution. Preparative high-performance liquid chromatography with acetonitrile-water (41:59, v/v) mobile phase successfully isolated sinensetin to 95% purity. In silico screening of O. aristatus-derived bioactive compounds revealed that flavonoids (including sinensetin), polyphenols (i.e. 2,3-O-dicaffeoyltartaric acid, rosmarinic acid), diterpenoid (i.e. trans-ozic acid), triterpenoids and dipeptide (i.e. aurantiamide acetate) have good binding affinities with 17β-HSD1, ErbB2/HER2 and PI3K-PKB/Akt proteins. These findings suggest that O. arsistatus could be a rich natural source of inhibitors targeting molecular pathways involved in breast cancer, offering promising therapeutic benefits.

Development of potential preclinical candidates with promising in vitro ADME profile for the inhibition of type 1 and type 2 17β-Hydroxysteroid dehydrogenases: Design, synthesis, and biological evaluation

Estrogens are the major female sex steroid hormones, estradiol (E2) being the most potent form in humans. Disturbing the balance between E2 and its weakly active oxidized form estrone (E1) leads to diverse types of estrogen-dependent diseases such as endometriosis or osteoporosis. 17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) catalyzes the biosynthesis of E2 by reduction of E1 while the type 2 enzyme catalyzes the reverse reaction. Thus, 17β-HSD1 and 17β-HSD2 are attractive targets for treatment of estrogen-dependent diseases. Recently, we reported the first proof-of-principle study of a 17β-HSD2 inhibitor in a bone fracture mouse model, using subcutaneous administration. In the present study, our aim was to improve the in vitro ADME profile of the most potent 17β-HSD1 and 17β-HSD2 inhibitors described so far. The optimized compounds show strong and selective inhibition of both the human enzymes and their murine orthologs. In addition, they display good metabolic stability in human liver microsomes (S9 fraction), low in vitro cytotoxicity as well as better aqueous solubility and physicochemical properties compared to the lead compounds. These achievements make the compounds eligible for testing in preclinical in vivo animal model studies on the effects of inhibition of 17β-HSD1 and 17β-HSD2.

Design, Synthesis, and Biological Characterization of Orally Active 17β-Hydroxysteroid Dehydrogenase Type 2 Inhibitors Targeting the Prevention of Osteoporosis

Osteoporosis is predominantly treated with drugs that inhibit further bone resorption due to estrogen deficiency. Yet, osteoporosis drugs that not only inhibit bone resorption but also stimulate bone formation, such as potentially inhibitors of 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2), may be more efficacious in the treatment of osteoporosis. Blockade of 17β-HSD2 is thought to increase intracellular estradiol and testosterone in bone, thereby inhibiting bone resorption by osteoclasts and stimulating bone formation by osteoblasts, respectively. We here describe the design, synthesis, and biological characterization of a novel bicyclic-substituted hydroxyphenylmethanone 17β-HSD2 inhibitor (compound 24). Compound 24 is a nanomolar potent inhibitor of human 17β-HSD2 (IC₅₀ of 6.1 nM) and rodent 17β-HSD2 with low in vitro cellular toxicity, devoid of detectable estrogen receptor α affinity, displays high aqueous solubility and in vitro metabolic stability, and has an excellent oral pharmacokinetic profile for testing in a rat osteoporosis model. Administration of 24 in a rat osteoporosis model demonstrates its bone-sparing efficacy.

Inhibitors of 17β-hydroxysteroid dehydrogenase type 1, 2 and 14: Structures, biological activities and future challenges

During the past 25 years, the modulation of estrogen action by inhibition of 17β-hydroxysteroid dehydrogenase types 1 and 2 (17β-HSD1 and 17β-HSD2), respectively, has been pursued intensively. In the search for novel treatment options for estrogen-dependent diseases (EDD) and in order to explore estrogenic signaling pathways, a large number of steroidal and nonsteroidal inhibitors of these enzymes has been described in the literature. The present review gives a survey on the development of inhibitor classes as well as the structural formulas and biological properties of their most interesting representatives. In addition, rationally designed dual inhibitors of both 17β-HSD1 and steroid sulfatase (STS) as well as the first inhibitors of 17β-HSD14 are covered.

Thioether-based 2-aminobenzamide derivatives: Novel HDAC inhibitors with potent in vitro and in vivo antitumor activity

Previously, we focused on a series of 2-aminobenzamide-based histone deacetylase (HDAC) inhibitors, compound 9 of which displayed potent HDAC inhibitory activity against HDAC1 and HDAC2, and moderate anti-proliferative activity against several cancer cell lines. In the current study, we have designed and synthesized a series of novel HDAC inhibitors based on thioether moiety with 9 as a lead compound. Representative compounds12 g and 12 h showed apparently potent anti-proliferative activities against five solid cancer cell lines: A549, HCT116, Hela, A375 and SMMC7721, and low cytotoxicity against NIH 3T3 normal cells. Especially, 12 g and 12 h also revealed potent HDAC inhibitory activity against HDAC1, 2 and 3. In addition, the two compounds could arrest cell cycle in G2/M phase and promote cell apoptosis. Moreover, they showed extended inhibition of colony formation and effectively blocked cell migration towards A549 cancer cells. Furthermore, 12 g and 12 h possessed better pharmacokinetic properties than the lead compound 9. Benefiting from these results, we also explored 12 g and 12 h in the A549 xenografts model for in vivo antitumor activity. The in vivo experiment indicated that 12 g and 12 h could evidently augment antitumor activity (TGI = 56.9% and 62.7% respectively).

Targeted Endocrine Therapy: Design, Synthesis, and Proof-of-Principle of 17β-Hydroxysteroid Dehydrogenase Type 2 Inhibitors in Bone Fracture Healing

Current therapies of steroid hormone-dependent diseases predominantly alter steroid hormone concentrations (or their actions) in plasma, in target and nontarget tissues alike, rather than in target organs only. Targeted therapy through the inhibition of steroidogenic enzymes may pose an attractive alternative with much less side effects. Here, we describe the design of a nanomolar potent 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2) inhibitor (compound 15) and successful targeted intracrine therapy in a mouse bone fracture model. Blockade of 17β-HSD2 in bone is thought to increase intracellular estradiol (E2) and testosterone (T), which thereby inhibits bone resorption by osteoclasts and stimulates bone formation by osteoblasts, respectively. Administration of compound 15 in the mouse fracture model strongly increases the mechanical stability of the healing fractured bone because of a larger periosteal callus with newly formed bone without changing the plasma E2 and T concentrations. Steroidogenic 17β-HSD2 inhibition thus enables targeted intracrine therapy.

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.