Physicochemical characterization of B-hydroxyphenyl phosphine borane derivatives and their evaluation as nuclear estrogen receptor ligands.

Increasing the structural options in medicinal chemistry is a promising approach to develop new drug candidates. In this research, we designed and synthesized a series of B-hydroxyphenyl phosphine borane derivatives and investigated their structure-property and structure-activity relationships. The synthesized B-phenylphosphine borane derivatives exhibited sufficient stability in aqueous media, weaker hydrophobicity than the corresponding alkanes and silanes, and sufficient affinity for lipid membranes to enable permeability. Several B-hydroxyphenyl phosphine borane derivatives exhibited significant estrogen receptor (ER) agonistic activity with superior ligand-lipophilicity efficiency (LLE). The phosphine borane framework appears to be a promising option for structural development in drug discovery studies.

Design, synthesis and structure-activity relationship of 4-(1,1,1,3,3,3-hexafluoro-2-hydroxyisoprop-2-yl)phenylsilane derivatives as liver X receptor agonists.

Liver X receptor (LXR) α and LXRß are nuclear receptors playing key roles in lipid metabolism, and LXR ligands are attractive drug candidates for metabolic disorders. Here we report the structural development of 4-(1,1,1,3,3,3-hexafluoro-2-hydroxyprop-2-yl)phenylsilane derivatives as LXR agonists bearing silyl functionalities as the hydrophobic pharmacophore, based on the structure of the known sulfonamide LXR agonist T0901317. Most of the synthesized compounds exhibit agonistic activity toward LXRs, but the LXR subtype-selectivity differs depending upon the substituents on the silicon atom. Among them, tri(n-propyl) derivative 12 shows potent LXR-agonistic activity with moderate α subtype-selectivity, while dimethylphenylsilyl derivative 19 shows modest ß-selectivity. These results indicate that silanes can serve as an alternative to the sulfonamide moiety of LXR agonists, and are promising structural options for the development of novel subtype-selective LXR agonists.

Image-based screen capturing misfolding status of Niemann-Pick type C1 identifies potential candidates for chaperone drugs.

Niemann-Pick disease type C is a rare, fatal neurodegenerative disorder characterized by massive intracellular accumulation of cholesterol. In most cases, loss-of-function mutations in the NPC1 gene that encodes lysosomal cholesterol transporter NPC1 are responsible for the disease, and more than half of the mutations are considered to interfere with the biogenesis or folding of the protein. We previously identified a series of oxysterol derivatives and phenanthridine-6-one derivatives as pharmacological chaperones, i.e., small molecules that can rescue folding-defective phenotypes of mutated NPC1, opening up an avenue to develop chaperone therapy for Niemann-Pick disease type C. Here, we present an improved image-based screen for NPC1 chaperones and we describe its application for drug-repurposing screening. We identified some azole antifungals, including itraconazole and posaconazole, and a kinase inhibitor, lapatinib, as probable pharmacological chaperones. A photo-crosslinking study confirmed direct binding of itraconazole to a representative folding-defective mutant protein, NPC1-I1061T. Competitive photo-crosslinking experiments suggested that oxysterol-based chaperones and itraconazole share the same or adjacent binding site(s), and the sensitivity of the crosslinking to P691S mutation in the sterol-sensing domain supports the hypothesis that their binding sites are located near this domain. Although the azoles were less effective in reducing cholesterol accumulation than the oxysterol-derived chaperones or an HDAC inhibitor, LBH-589, our findings should offer new starting points for medicinal chemistry efforts to develop better pharmacological chaperones for NPC1.

Structure-activity relationship study of estrogen receptor down-regulators with a diphenylmethane skeleton.

Selective estrogen receptor (ER) down-regulators (SERDs) are pure ER antagonists that also induce ER degradation upon binding to the receptor. Although SERDs have been developed for the treatment of ER-positive breast cancers for nearly a decade, their precise mechanism(s) of action and structure-activity relationship are still unclear. Generally, Western blotting is used to examine the effects of SERDs on ER protein levels, but the methodology is low-throughput and not quantitative. Here, we describe a quantitative, high-throughput, luciferase-based assay for the evaluation of SERDs activity. For this purpose, we established stable recombinant HEK-293 cell lines expressing ERα fused with emerald luciferase. We also designed and synthesized new diphenylmethane derivatives as candidate SERDs, and evaluated their SERDs activity using the developed system in order to examine their structure-activity relationship, taking EC50 as a measure of potency, and Emax as a measure of efficacy.

Design and synthesis of estrogen receptor ligands with a 4-heterocycle-4-phenylheptane skeleton.

The estrogen receptor (ER), a member of the nuclear receptor (NR) family, is involved in the regulation of physiological effects such as reproduction and bone homeostasis. Approximately 70% of human breast cancers are hormone-dependent and ERα-positive, and, thus, ER antagonists are broadly used in breast cancer therapy. We herein designed and synthesized a set of ER antagonists with a 4-heterocycle-4-phenylheptane skeleton.

Phenanthridin-6-one derivatives as the first class of non-steroidal pharmacological chaperones for Niemann-Pick disease type C1 protein.

Niemann-Pick disease type C is a fatal, progressive neurodegenerative disease mostly caused by mutations in Nieamnn-Pick type C1 (NPC1), a late endosomal membrane protein that is essential for intracellular cholesterol transport. The most prevalent mutation, I1061T (Ile to Thr), interferes with the protein folding process. Consequently, mutated but intrinsically functional NPC1 proteins are prematurely degraded via proteasome, leading to loss of NPC1 function. Previously, we reported sterol derivatives as pharmacological chaperones for NPC1, and showed that these derivatives can normalize folding-defective phenotypes of I1061T NPC1 mutant by directly binding to, and stabilizing, the protein. Here, we report a series of compounds containing a phenanthridin-6-one scaffold as the first class of non-steroidal pharmacological chaperones for NPC1. We also examined their structure-activity relationships.

Synthesis and evaluation of novel dual BRD4/HDAC inhibitors.

Epigenetic regulation of gene expression via histone acetylation modulates many cellular processes, including apoptosis, the cell cycle, cell growth and differentiation, and inhibitors are promising drug candidates. We have previously developed inhibitors of BRD4, which recognizes acetylated lysine residue on histones and recruits transcription elongation factor to the transcription start site, while inhibitors of histone deacetylase (HDAC), which catalyzes the removal of acetyl groups on histones, are already in clinical use for cancer treatment. Based on the idea that polypharmacological agents with multiple targets would have a more robust action, we set out to develop dual BRD4/HDAC inhibitors. Here, we describe the design and synthesis of N6-[2-(7-hydroxyamino-7-oxoheptyloxy)benzoyl]adenine (5d) as a BRD4/HDAC dual inhibitor. This compound showed HL-60 cell growth-inhibitory and apoptosis-inducing activity, as well as all-trans retinoic acid (ATRA)-induced HL-60 cell differentiation-enhancing activity, and c-MYC production-inhibitory activity. Interestingly, it also showed growth-inhibitory activity towards BRD4 inhibitor-resistant cells.

Switching subtype-selectivity: Fragment replacement strategy affords novel class of peroxisome proliferator-activated receptor α/δ (PPARα/δ) dual agonists.

Peroxisome proliferator-activated receptors (PPARs) are important drug targets for treatment of dyslipidemia, type 2 diabetes, cardiovascular disease, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and great efforts have been made to develop novel PPAR ligands. However, most existing PPAR ligands contain a carboxylic acid (CA) or thiazolidinedione (TZD) structure (acidic head group) that is essential for activity. We recently discovered non-CA/TZD class PPARα/δ partial agonists, which contain an acetamide moiety and adjacent methyl group, linked to a 1,2,4-oxadiazole ring ("fragment a"). We hypothesized that the acetamide structure might interact with the CA/TZD-binding pocket. To test this idea, we firstly replaced fragment a in one of our compounds with the α-alkoxy-CA structure often found in PPAR agonists. Secondly, we replaced the α-alkoxy-CA head group of several reported PPAR agonists with our acetamide-based fragment a. The agonistic activities of the synthesized hybrid compounds toward PPARs (PPARα, PPARγ and PPARδ) were evaluated by means of cell-based reporter gene assays. All the hybrid molecules showed PPAR-agonistic activities, but replacement of the α-alkoxy-CA head group altered the maximum efficacy and the subtype-specificity. The acetamide-based hybrid molecules showed partial agonism toward PPARα and PPARδ, whereas the α-alkoxy-CA-based molecules were generally selective for PPARα and PPARγ, with relatively high activation efficacies. Thus, the fragment replacement strategy appears promising for the development of novel acetamide-based PPARα/δ dual agonists.

Structure-Activity Relationship Study of N(6)-Benzoyladenine-Type BRD4 Inhibitors and Their Effects on Cell Differentiation and TNF-α Production.

Bromodomains are epigenetic 'readers' of histone acetylation. The first potent bromodomain and extra-terminal domain (BET) inhibitors, (+)-JQ1 and I-BET762 (also known as GSK525762), were reported in 2010. Some BET inhibitors are already under clinical trial for the treatment of cancers, but so far, only a few chemical scaffolds are available. We have reported potent N(6)-benzoyladenine-based inhibitors of BRD4, a BET family member that serves as a key mediator of transcriptional elongation. Here we present an analysis of the structure-activity relationships of these inhibitors. Among the compounds examined, 20, 28 and 29 enhanced all-trans retinoic acid (ATRA)-induced HL-60 cell differentiation and inhibited tumor necrosis factor (TNF)-α production by THP-1 cells.

Discovery of N-(1-(3-(4-phenoxyphenyl)-1,2,4-oxadiazol-5-yl)ethyl)acetamides as novel acetyl-CoA carboxylase 2 (ACC2) inhibitors with peroxisome proliferator-activated receptor α/δ (PPARα/δ) dual agonistic activity.

Acetyl-CoA carboxylases (ACCs) catalyze a critical step in de novo lipogenesis, and are considered as promising targets for treatment of obesity, dyslipidemia and type 2 diabetes mellitus. On the other hand, peroxisome proliferator-activated receptors (PPARs) are well-established therapeutic targets for these metabolic syndrome-related diseases. Therefore, we considered that dual modulators of ACC and PPARs would be promising candidates as therapeutic agents. Here, we designed a series of acetamides based on the molecular similarity between ACC inhibitors and PPAR agonists. Screening of the synthesized compounds identified N-(1-(3-(4-phenoxyphenyl)-1,2,4-oxadiazol-5-yl)ethyl)acetamides as novel ACC2 inhibitors with PPARα/PPARδ dual agonistic activity. Structure-activity relationship studies and further structural elaboration afforded compounds with distinct activity profiles. Our findings should be helpful for the discovery of candidate agents with an appropriate balance of ACC-inhibitory and PPAR-activating activities for therapeutic lipid control.

Structure-activity relationship studies of non-carboxylic acid peroxisome proliferator-activated receptor α/δ (PPARα/δ) dual agonists.

The peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors that contribute to the regulation of lipid, glucose and cholesterol homeostases. They are considered as therapeutic targets for metabolic diseases such as dyslipidemia and type 2 diabetes mellitus. Various PPAR agonists have been developed, but most of them contain a carboxylic acid (CA) or thiazolidinedione (TZD) moiety, which is essential for the activity. However, we recently discovered non-CA/non-TZD class PPARα/δ dual agonists having an acetamide structure. Here, we describe structure-activity relationship (SAR) studies of these novel acetamide-based PPARα/δ dual agonists. The SAR studies revealed that the acetamide functionality and adjacent methyl group contribute greatly to the agonistic activity. Compound (S)-10 was the most potent PPARα/δ dual agonist among the compounds synthesized (PPARα EC50=17nM, PPARδ EC50=23nM).

BET Bromodomain as a Target of Epigenetic Therapy.

Acetylation of histone is a key epigenetic modification, and contributes to many DNA-dependent cellular processes. The bromodomain structure, which consists of approximately 110 amino acid residues, serves as a 'reader' that recognizes acetylated lysine in histones, leading to recruitment of positive transcriptional elongation factor b (P-TEFb), and thereby promoting transcriptional activity and chromatin remodeling. Among bromodomain-containing proteins, members of the bromodomain and extra-terminal domain (BET) family contain tandem N-terminal bromodomains. BET proteins, especially BRD4, have attracted interest as candidate therapeutic targets due to their putative involvement in the pathogenesis of various diseases, including cancer and inflammatory diseases. Several BET inhibitors are under clinical trial for treatment of various cancers. Furthermore, polypharmacological agents such as dual kinase/BET inhibitors and dual histone deacetylase (HDAC)/BET inhibitors have recently been developed, in addition to agents that degrade BET family proteins, such as proteolysis-targeting chimeras (PROTACs). This paper reviews recent progress in epigenetic therapy targeting the BET bromodomain.

Effects of alkyl side chains and terminal hydrophilicity on vitamin D receptor (VDR) agonistic activity based on the diphenylpentane skeleton.

Vitamin D receptor (VDR) is a family of nuclear receptors (NR) that regulates physiological effects such as the immune system, calcium homeostasis, and cell proliferation. We synthesized non-secosteroidal VDR ligands bearing a long alkyl chain based on the diphenylpentane skeleton. The VDR-mediated transcriptional activities of the synthesized compounds were evaluated using a reporter gene assay and HL-60 cell differentiation-inducing assay. We herein described the structure-activity relationship and effects of alkyl-chain length on VDR-mediated transcriptional activity.

Discovery and structure-activity relationship studies of N6-benzoyladenine derivatives as novel BRD4 inhibitors.

Bromodomain and extra-terminal domain (BET) proteins are epigenetic readers that bind to acetylated lysines in histones. Among them, BRD4 is a candidate target molecule of therapeutic agents for diverse diseases, including cancer and inflammatory disease. As a part of our continuing structural development studies of thalidomide to obtain a broad spectrum of biological modifiers based on the 'multi-template' approach, in this work we focused on BRD4-inhibitory activity, and discovered that N6-benzoyladenine derivatives exhibit this activity. Structure-activity relationship studies led to N6-(2,4,5-trimethoxybenzoyl)adenine (29), which exhibits potent BRD4 bromodomain1 inhibitory activity with an IC50 value of 0.427µM. N6-Benzoyladenine appears to be a new chemical scaffold for development of BRD4 inhibitors.

Structure-activity relationships of oxysterol-derived pharmacological chaperones for Niemann-Pick type C1 protein.

Niemann-Pick disease type C is a fatal neurodegenerative disease, and its major cause is mutations in NPC1 gene. This gene encodes NPC1 protein, a late endosomal polytopic membrane protein required for intracellular cholesterol trafficking. One prevalent mutation (I1061T) has been shown to cause a folding defect, which results in failure of endosomal localization of the protein, leading to loss-of-function phenotype. We have previously demonstrated that several oxysterols and their derivatives act as pharmacological chaperones; binding of these compounds to NPC1(I1061T) mutant protein corrects the localization/maturation defect of the mutant protein. Here, we disclose detailed structure-activity relationships of oxysterol derivatives as pharmacological chaperones for NPC1(I1061T) mutant.

Structure-activity relationship of benzodiazepine derivatives as LXXLL peptide mimetics that inhibit the interaction of vitamin D receptor with coactivators.

Suppression of vitamin D receptor (VDR)-mediated transcription is expected to be of therapeutic value in Paget's disease of bone. It is known that interaction between VDR and coactivators is necessary for VDR transactivation, and the interaction occurs when VDR recognizes an LXXLL peptide motif of coactivators. We previously reported that benzodiazepine derivatives designed as LXXLL peptide mimetics inhibited the interaction of VDR and coactivators, and reduced VDR transcription. Here, we investigated the structure-activity relationship of 7- and 8-substituted benzodiazepine derivatives, and established that the amino group at the 8-position is critical for the inhibitory activity.

Small-molecular, non-peptide, non-ATP-competitive polo-like kinase 1 (Plk1) inhibitors with a terphenyl skeleton.

Polo-like kinase (Plk) 1 is a serine-threonine protein kinase that plays a role in cell division, and its overexpression is highly correlated with aggressiveness and prognosis of many cancers. We have designed, synthesized and evaluated a series of terphenyl compounds as inhibitors of the kinase activity of Plk1. Some of them act as non-ATP-competitive Plk1 inhibitors.

Small-molecular inhibitors of Ca²âº-induced mitochondrial permeability transition (MPT) derived from muscle relaxant dantrolene.

A structure consisting of substituted hydantoin linked to a 5-(halophenyl)furan-2-yl group via an amide bond was identified as a promising scaffold for development of low-molecular-weight therapeutic agents to treat vascular dysfunction, including ischemia/reperfusion injury. Among the compounds synthesized, 5-(3,5-dichlorophenyl)-N-{2,4-dioxo-3-[(pyridin-3-yl)methyl]imidazolidin-1-yl}-2-furamide (17) possessed the most potent inhibitory activity against Ca(2+)-induced mitochondrial swelling. The structural development, synthesis and structure-activity relationship of these compounds are described.

Design, synthesis, and biological evaluation of novel transrepression-selective liver X receptor (LXR) ligands with 5,11-dihydro-5-methyl-11-methylene-6H-dibenz[b,e]azepin-6-one skeleton.

To obtain novel transrepression-selective liver X receptor (LXR) ligands, we adopted a strategy of reducing the transactivational agonistic activity of the 5,11-dihydro-5-methyl-11-methylene-6H-dibenz[b,e]azepin-6-one derivative 10, which exhibits LXR-mediated transrepressional and transactivational activity. Structural modification of 10 based on the reported X-ray crystal structure of the LXR ligand-binding domain led to a series of compounds, of which almost all exhibited transrepressional activity at 1 or 10 µM but showed no transactivational activity even at 30 µM. Among the compounds obtained, 18 and 22 were confirmed to have LXR-dependent transrepressional activity by using peritoneal macrophages from wild-type and LXR-null mice. A newly developed fluorescence polarization assay indicated that they bind directly to LXRα. Next, further structural modification was performed with the guidance of docking simulations with LXRα, focusing on enhancing the binding of the ligands with LXRα through the introduction of substituents or heteroatom(s). Among the compounds synthesized, compound 48, bearing a hydroxyl group, showed potent, selective, and dose-dependent transrepressional activity.

Novel selective anti-androgens with a diphenylpentane skeleton.

We have proposed a multi-template approach for drug development, focusing on similar fold structures of proteins, and have effectively generated lead compounds for several drug targets. Modification of these polypharmacological lead compounds is then needed to generate target-selective compounds. In the work presented here, we aimed at separation of the anti-androgen activity and vitamin D activity of previously identified diphenylpentane lead compounds. Based on the determined X-ray crystal structures of androgen receptor and vitamin D receptor, bulky substituents were introduced at the t-butyl group in the lead compounds 2 and 3. As a result of this structural development, we obtained 16c, which exhibits more potent anti-androgen activity (IC(50): 0.13 µM) than clinically used anti-androgen bicalutamide (IC(50): 0.67 µM) with 30-fold selectivity over vitamin D activity. This result indicates that lead compounds obtained via the multi-template approach can indeed be structurally modified to generate target-selective compounds.