Design, synthesis, and biological evaluation of novel benzimidazole derivatives as sphingosine kinase 1 inhibitor.

Sphingosine kinase 1 (SphK1) has emerged as an attractive drug target for different diseases. Recently, discovered SphK1 inhibitors have been recommended in cancer therapeutics; however, selectivity and potency are great challenges. In this study, a novel series of benzimidazoles was synthesized and evaluated as SphK1 inhibitors. Our design strategy is twofold: It aimed first to study the effect of replacing the 5-position of the benzimidazole ring with a polar carboxylic acid group on the SphK1-inhibitory activity and cytotoxicity. Our second aim was to optimize the structures of the benzimidazoles through the elongation of the chain. The enzyme inhibition potentials against all the synthesized compounds toward SphK1 were evaluated, and the results revealed that most of the studied compounds inhibited SphK1 effectively. The binding affinity of the benzimidazole derivatives toward SphK1 was measured by fluorescence binding and molecular docking. Compounds 33, 37, 39, 41, 42, 43, and 45 showed an appreciable binding affinity. Therefore, the SphK1-inhibitory potentials of compounds 33, 37, 39, 41, 42, 43, and 45 were studied and IC50 values were determined, to reveal high potency. The study showed that these compounds inhibited SphK1 with effective IC50 values. Among the studied compounds, compound 41 was the most effective one with the lowest IC50 value and a high cytotoxicity on a wide spectrum of cell lines. Molecular docking revealed that most of these compounds fit well into the ATP-binding site of SphK1 and form hydrogen bond interactions with catalytically important residues. Overall, the findings suggest the therapeutic potential of benzimidazoles in the clinical management of SphK1-associated diseases.

New thiopyrimidine-benzenesulfonamide conjugates as selective carbonic anhydrase II inhibitors: synthesis, in vitro biological evaluation, and molecular docking studies.

In the present work, a new series of thiopyrimidine-benzenesulfonamide conjugates was designed, synthesized and tested as carbonic anhydrase (CA, EC 4.2.1.1) inhibitors. Our design strategy was based on the molecular hybridization of the benzenesulfonamide moiety as a zinc binding group (ZBG), an alkylated thiopyrimidine moiety as a spacer and (un)substituted phenyl moieties with various electronic and hydrophobic environments as a tail. The designed and synthesized compounds were evaluated against four human (h) CA isoforms hCA I, hCA II, hCA IX and hCA XII. Series 6 showed promising activity and selectivity toward the cytosolic isoforms hCA I and hCA II versus the membrane bound isoforms hCA IX and hCA XII. Compounds 6e and 6f showed Ki of 0.04 µM against hCA II with a selectivity of 15.8- to 980-fold towards hCA II over hCA I, hCA IX, hCA XII isoforms. Molecular docking in the hCA II active site attributed the promising inhibitory activity of series 6 to the interaction of their sulfonamide moiety with the active site Zn2+ ion as well as its hydrogen bonding with the key amino acids Thr199 and Thr200. Through hydrophobic interaction, the benzenesulfonamide and the thiopyrimidine moieties interact with the hydrophobic side chains of the amino acids Val121/Leu198 and Ile91/Phe131, respectively. These results indicated that the designed and synthesized series is an interesting scaffold that can be further optimized for the development of selective antiglaucoma drugs.

Potent Dual Inhibitors of Steroid Sulfatase and 17ß-Hydroxysteroid Dehydrogenase Type 1 with a Suitable Pharmacokinetic Profile for In Vivo Proof-of-Principle Studies in an Endometriosis Mouse Model.

Treating estrogen-dependent diseases like endometriosis with drugs suppressing local estrogen activation may be superior to existing endocrine therapies. Steroid sulfatase (STS) and 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) are key enzymes of local estrogen activation. We describe the rational design, synthesis, and biological profilation of furan-based compounds as a novel class of dual STS/17ß-HSD1 inhibitors (DSHIs). In T47D cells, compound 5 showed irreversible inhibition of STS and potent, reversible inhibition of 17ß-HSD1. It was selective over 17ß-HSD2 and displayed high metabolic stabilities in human and mouse liver S9 fractions. No effect on cell viability was detected up to 31 µM (HEK293) and 23 µM (HepG2), respectively, and there was no activation of the aryl hydrocarbon receptor (AhR) up to 3.16 µM. Single daily application to mice revealed steady-state plasma levels high enough to make this compound eligible for an in vivo proof-of-principle study in a mouse endometriosis model.

Towards Translation of PqsR Inverse Agonists: From In Vitro Efficacy Optimization to In Vivo Proof-of-Principle.

Pseudomonas aeruginosa (PA) is an opportunistic human pathogen, which is involved in a wide range of dangerous infections. It develops alarming resistances toward antibiotic treatment. Therefore, alternative strategies, which suppress pathogenicity or synergize with antibiotic treatments are in great need to combat these infections more effectively. One promising approach is to disarm the bacteria by interfering with their quorum sensing (QS) system, which regulates the release of various virulence factors as well as biofilm formation. Herein, this work reports the rational design, optimization, and in-depth profiling of a new class of Pseudomonas quinolone signaling receptor (PqsR) inverse agonists. The resulting frontrunner compound features a pyrimidine-based scaffold, high in vitro and in vivo efficacy, favorable pharmacokinetics as well as clean safety pharmacology characteristics, which provide the basis for potential pulmonary as well as systemic routes of administration. An X-ray crystal structure in complex with PqsR facilitated further structure-guided lead optimization. The compound demonstrates potent pyocyanin suppression, synergizes with aminoglycoside antibiotic tobramycin against PA biofilms, and is active against a panel of clinical isolates from bronchiectasis patients. Importantly, this in vitro effect translated into in vivo efficacy in a neutropenic thigh infection model in mice providing a proof-of-principle for adjunctive treatment scenarios.

Inhibitors of the Elastase LasB for the Treatment of Pseudomonas aeruginosa Lung Infections.

Infections caused by the Gram-negative pathogen Pseudomonas aeruginosa are emerging worldwide as a major threat to human health. Conventional antibiotic monotherapy suffers from rapid resistance development, underlining urgent need for novel treatment concepts. Here, we report on a nontraditional approach to combat P. aeruginosa-derived infections by targeting its main virulence factor, the elastase LasB. We discovered a new chemical class of phosphonates with an outstanding in vitro ADMET and PK profile, auspicious activity both in vitro and in vivo. We established the mode of action through a cocrystal structure of our lead compound with LasB and in several in vitro and ex vivo models. The proof of concept of a combination of our pathoblocker with levofloxacin in a murine neutropenic lung infection model and the reduction of LasB protein levels in blood as a proof of target engagement demonstrate the great potential for use as an adjunctive treatment of lung infections in humans.

Dual Targeting of Steroid Sulfatase and 17ß-Hydroxysteroid Dehydrogenase Type 1 by a Novel Drug-Prodrug Approach: A Potential Therapeutic Option for the Treatment of Endometriosis.

A novel approach for the dual inhibition of steroid sulfatase (STS) and 17ß-hydroxysteroid dehydrogenase type 1(17ß HSD1) by a single drug was explored, starting from in-house 17ß HSD1 inhibitors via masking their phenolic OH group with a sulfamate ester. The sulfamates were intentionally designed as drugs for the inhibition of STS and, at the same time, prodrugs for 17ß-HSD1 inhibition ("drug-prodrug approach"). The most promising sulfamates 13, 16, 18-20, 22-24, 36, and 37 showed nanomolar IC50 values for STS inhibition in a cellular assay and their corresponding phenols displayed potent 17ß-HSD1 inhibition in cell-free and cellular assays, high selectivity over 17ß-HSD2, reasonable metabolic stability, and low estrogen receptor α affinity. A close relationship was found between the liberation of the phenolic compound by sulfamate hydrolysis and 17ß-HSD1 inactivation. These results showed that the envisaged drug-prodrug concept was successfully implemented. The novel compounds constitute a promising class of therapeutics for the treatment of endometriosis and other estrogen-dependent diseases.

Discovery and Characterization of Synthesized and FDA-Approved Inhibitors of Clostridial and Bacillary Collagenases.

In view of the worldwide antimicrobial resistance (AMR) threat, new bacterial targets and anti-infective agents are needed. Since important roles in bacterial pathogenesis have been demonstrated for the collagenase H and G (ColH and ColG) from Clostridium histolyticum, collagenase Q1 and A (ColQ1 and ColA) from Bacillus cereus represent attractive antivirulence targets. Furthermore, repurposing FDA-approved drugs may assist to tackle the AMR crisis and was addressed in this work. Here, we report on the discovery of two potent and chemically stable bacterial collagenase inhibitors: synthesized and FDA-approved diphosphonates and hydroxamates. Both classes showed high in vitro activity against the clostridial and bacillary collagenases. The potent diphosphonates reduced B. cereus-mediated detachment and death of cells and Galleria mellonella larvae. The hydroxamates were also tested in a similar manner; they did not have an effect in infection models. This might be due to their fast binding kinetics to bacterial collagenases.

Divergent synthesis and biological evaluation of 2-(trifluoromethyl)pyridines as virulence-attenuating inverse agonists targeting PqsR.

A short and divergent route towards new derivatives of 2-(trifluoromethyl)pyridines as potent inverse agonists of the bacterial target PqsR against Pseudomonas aeruginosa (PA) infections is described. This Gram-negative pathogen causes severe nosocomial infections and common antibiotic treatment options are rendered ineffective due to resistance issues. Based on an earlier identified optimized hit, we conducted derivatization and rigidification attempts employing two central building blocks. The western part of the molecule is built up via a 2-(trifluoromethyl)pyridine head group equipped with a terminal alkyne. The eastern section is then introduced through aryliode motifs exploiting Sonogashira as well as Suzuki-type chemistry. Subsequent modification provided quick access to an array of compounds, allowed for deep SAR insights, and enabled to optimize the hit scaffold into a lead structure of nanomolar potency combined with favorable in vitro ADME/T features.

17ß-Hydroxysteroid Dehydrogenase Type 1 Inhibition: A Potential Treatment Option for Non-Small Cell Lung Cancer.

In the face of the clinical challenge posed by non-small cell lung cancer (NSCLC), the present need for new therapeutic approaches is genuine. Up to now, no proof existed that 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) is a viable target for treating this disease. Synthesis of a rationally designed library of 2,5-disubstituted furan derivatives followed by biological screening led to the discovery of 17ß-HSD1 inhibitor 1, capable of fully inhibiting human NSCLC Calu-1 cell proliferation. Its pharmacological profile renders it eligible for further in vivo studies. The very high selectivity of 1 over 17ß-HSD2 was investigated, revealing a rational approach for the design of selective inhibitors. 17ß-HSD1 and 1 hold promise in fighting NSCLC.

Inhibitors of 17ß-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 17ß-hydroxysteroid dehydrogenase types 1 and 2 (17ß-HSD1 and 17ß-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 17ß-HSD1 and steroid sulfatase (STS) as well as the first inhibitors of 17ß-HSD14 are covered.

Effects of 17ß-HSD2 inhibition in bones on osteoporosis based on an animal rat model.

Hormone replacement therapy is a viable option to protect bone from postmenopausal osteoporosis. Systemically elevated estrogen levels, however, are disadvantageous because of the risk of harmful side effects in other organs. The rationale of the study presented here is to target a key enzyme in estradiol (E2) and testosterone (T) metabolism to increase E2 levels in an organ-specific manner, thereby avoiding the disadvantages of systemically increased E2 levels. The 17ß-hydroxysteroid dehydrogenase (17ß-HSD2), which is e.g. expressed in bone, catalyzes the oxidation of E2 and T into estrone (E1) and androstenedione. We postulate that inhibiting 17ß-HSD2 should lead to elevated E2 and T levels in organs expressing the enzyme. Therefore, we can use the benefits of E2 directly, or those of T following aromatization into E2, in the bone without affecting systemic levels. We tested for the first time, the novel and potent 17ß-HSD2 inhibitor, compound 24 (C24), to explore the therapeutic potential of a 17ß-HSD2 inhibition in an ovariectomy (ovx)-induced rat model of bone loss. We tested the inhibitor alone and, together with low dose estrogen supplementation to model estrogen levels in the postmenopausal situation. Female mature Wistar-Hannover rats were treated for 8 weeks with doses of 2, 10, 50 mg C24 per kg body weight per day alone or in the presence of estradiol benzoate (E2B) supplementation to alleviate ovx-induced bone loss. Ovx placebo and sham operated animals served as negative and positive controls. The experiment was evaluated regarding aspects of efficacy and safety: Bone was analyzed to evaluate bone protective effects, and uterus for potential, unwanted E2-mediated side effects. We observed a good bioavailability of C24 as very high plasma concentrations were measured, up to a group mean of 15,412 nM for the ovx C24-high group. Histomorphometrical analyses and in vivo &ex vivo µCT revealed significant bone protective effects for the lowest inhibitor concentration used. Irrespective of the plasma concentration, no proliferative effects in the uterus could be observed. These results support our approach of intracellular targeting key enzymes of E2 and T metabolism to increase E2 and T levels in an organ specific manner.

Development of potential preclinical candidates with promising in vitro ADME profile for the inhibition of type 1 and type 2 17ß-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. 17ß-Hydroxysteroid dehydrogenase type 1 (17ß-HSD1) catalyzes the biosynthesis of E2 by reduction of E1 while the type 2 enzyme catalyzes the reverse reaction. Thus, 17ß-HSD1 and 17ß-HSD2 are attractive targets for treatment of estrogen-dependent diseases. Recently, we reported the first proof-of-principle study of a 17ß-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 17ß-HSD1 and 17ß-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 17ß-HSD1 and 17ß-HSD2.

Design, Synthesis, and Biological Characterization of Orally Active 17ß-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 17ß-hydroxysteroid dehydrogenase type 2 (17ß-HSD2), may be more efficacious in the treatment of osteoporosis. Blockade of 17ß-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 17ß-HSD2 inhibitor (compound 24). Compound 24 is a nanomolar potent inhibitor of human 17ß-HSD2 (IC50 of 6.1 nM) and rodent 17ß-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.

Targeted Endocrine Therapy: Design, Synthesis, and Proof-of-Principle of 17ß-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 17ß-hydroxysteroid dehydrogenase type 2 (17ß-HSD2) inhibitor (compound 15) and successful targeted intracrine therapy in a mouse bone fracture model. Blockade of 17ß-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 17ß-HSD2 inhibition thus enables targeted intracrine therapy.

Highly Potent 17ß-HSD2 Inhibitors with a Promising Pharmacokinetic Profile for Targeted Osteoporosis Therapy.

Intracellular elevation of E2 levels in bone by inhibition of 17ß hydroxysteroid dehydrogenase type 2 (17ß-HSD2) without affecting systemic E2 levels is an attractive approach for a targeted therapy against osteoporosis, a disease which is characterized by loss of bone mineral density. Previously identified inhibitor A shows high potency on human and mouse 17ß-HSD2, but poor pharmacokinetic properties when applied perorally in mice. A combinatorial chemistry approach was utilized to synthesize truncated derivatives of A, leading to highly potent compounds with activities in the low nanomolar to picomolar range. Compound 33, comparable to A in terms of inhibitor potency against both human and mouse enzymes, displays high in vitro metabolic stability in human and mouse liver S9 fraction as well as low toxicity and moderate hepatic CYP inhibition. Thus, compound 33 showed a highly improved peroral pharmacokinetic profile in comparison to A, making 33 a promising candidate for further development.

First Dual Inhibitors of Steroid Sulfatase (STS) and 17ß-Hydroxysteroid Dehydrogenase Type 1 (17ß-HSD1): Designed Multiple Ligands as Novel Potential Therapeutics for Estrogen-Dependent Diseases.

STS and 17ß-HSD1 are attractive targets for the treatment of estrogen-dependent diseases like endometriosis and breast cancer. The simultaneous inhibition of both enzymes appears more promising than blockage of either protein alone. We describe a designed multiple ligand approach resulting in highly potent dual inhibitors. The most interesting compound 9 showed nanomolar IC50 values for both proteins, membrane permeability, and no interference with estrogen receptors. It efficiently reversed E1S- and E1-induced T47D cell proliferation.

Treatment of estrogen-dependent diseases: Design, synthesis and profiling of a selective 17ß-HSD1 inhibitor with sub-nanomolar IC50 for a proof-of-principle study.

Current endocrine therapeutics for the estrogen-dependent disease endometriosis often lead to considerable side-effects as they act by reducing estrogen action systemically. A more recent approach takes advantage of the fact that the weak estrogen estrone (E1) which is abundant in the plasma, is activated in the target cell to the highly estrogenic estradiol (E2) by 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1). 17ß-HSD1 is overexpressed in endometriosis and thus a promising target for the treatment of this disease, with the prospect of less target-associated side-effects. Potent inhibitors from the class of bicyclic substituted hydroxyphenylmethanones with sulfonamide moiety recently described by us suffered from high molecular weight and low selectivity over 17ßHSD2, the physiological adversary of 17ß-HSD1. We describe the structural optimizations leading to the discovery of (5-(3,5-dichloro-4-methoxyphenyl)thiophen-2-yl)(2,6-difluoro-3-hydroxyphenyl)methanone 20, which displayed a sub-nanomolar IC50 towards 17ß-HSD1 as well as high selectivity over the type 2 enzyme, the estrogen receptors α and ß and a range of hepatic CYP enzymes. The compound did neither show cellular toxicity, nor PXR activation nor mutagenicity in the AMES II assay. Additional favourable pharmacokinetic properties (rat) make 20 a suitable candidate for proof-of-principle studies using xenotransplanted immunodeficient rats.

Part I: Design, synthesis and biological evaluation of novel pyrazole-benzimidazole conjugates as checkpoint kinase 2 (Chk2) inhibitors with studying their activities alone and in combination with genotoxic drugs.

Activated checkpoint kinase 2 (Chk2) is a tumor suppressor as one of the main enzymes that affect the cell cycle. 2-Biarylbenzimidazoles are potent selective class of Chk2 inhibitors; the structure-based design was applied to synthesize a new series of this class with replacing the lateral aryl group by substituted pyrazoles. Ten pyrazole-benzimidazole conjugates from the best fifty candidates according to docking programs have been subjected to chemical synthesis in this study. The activities of the conjugates 5-14 as checkpoint kinase inhibitors and as antitumor alone and in combination with genotoxic drugs were evaluated. The effect of compounds 7 and 12 on cell-cycle phases was analyzed by flow cytometry analysis. Antitumor activity of compounds 7 and 12 as single-agents and in combinations with doxorubicin was assessed in breast cancer bearing animals induced by MNU. The Results indicated that compounds 5-14 inhibited Chk2 activity with high potency (IC50 52.8 nM-5.5 nM). The cytotoxicity of both cisplatin and doxorubicin were significantly potentiated by the most of the conjugates against MCF-7 cell lines. Compounds 7 and 12 and their combinations with doxorubicin induced the cell cycle arrest in MCF-7 cells. Moreover, compound 7 exhibited marked higher antitumor activity as a single agent in animals than it's combination with doxorubicin or doxorubicin alone. The combination of compound 12 with doxorubicin was greatly effective on animal than their single-dose treatment. In conclusion, pyrazole-benzimidazole conjugates are highly active Chk2 inhibitors that have anticancer activity and potentiate activity of genotoxic anticancer therapies and deserve further evaluations.

First Structure-Activity Relationship of 17ß-Hydroxysteroid Dehydrogenase Type 14 Nonsteroidal Inhibitors and Crystal Structures in Complex with the Enzyme.

17ß-HSD14 belongs to the SDR family and oxidizes the hydroxyl group at position 17 of estradiol and 5-androstenediol using NAD+ as cofactor. The goal of this study was to identify and optimize 17ß-HSD14 nonsteroidal inhibitors as well as to disclose their structure-activity relationship. In a first screen, a library of 17ß-HSD1 and 17ß-HSD2 inhibitors, selected with respect to scaffold diversity, was tested for 17ß-HSD14 inhibition. The most interesting hit was taken as starting point for chemical modification applying a ligand-based approach. The designed compounds were synthesized and tested for 17ß-HSD14 inhibitory activity. The two best inhibitors identified in this study have a very high affinity to the enzyme with a Ki equal to 7 nM. The strong affinity of these inhibitors to the enzyme active site could be explained by crystallographic structure analysis, which highlighted the role of an extended H-bonding network in the stabilization process. The selectivity of the most potent compounds with respect to 17ß-HSD1 and 17ß-HSD2 is also addressed.

Towards the evaluation in an animal disease model: Fluorinated 17ß-HSD1 inhibitors showing strong activity towards both the human and the rat enzyme.

17ß-Estradiol (E2), the most potent human estrogen, is known to be involved in the etiology of estrogen-dependent diseases (EDD) like breast cancer and endometriosis. 17ß-Hydroxysteroid dehydrogenase type 1 (17ß-HSD1) catalyses the last step of E2 biosynthesis and is thus a promising target for the treatment of EDD. The previously described bicyclic substituted hydroxyphenylmethanones (BSHs) display high inhibitory potency towards human 17ß-HSD1, but marginal activity towards rodent 17ß-HSD1, precluding a proof of principle study in an animal endometriosis model. The aim of this work was to perform structural optimizations in the BSHs class to enhance inhibitory activity against rodent (mouse and rat) 17ß-HSD1 while maintaining activity against the human enzyme. The introduction of fluorine atoms on the benzoyl moiety resulted in compounds with the desired properties. Molecular docking and homology modeling were applied to elucidate the binding mode and interspecies differences in activity. Compound 33 is the most potent inhibitor of both human and rat 17ß-HSD1 up to date (IC50 = 2 nM and 97 nM, respectively).