Shinya Fujii

Boron Cluster-based Development of Potent Nonsecosteroidal Vitamin D Receptor Ligands: Direct Observation of Hydrophobic Interaction between Protein Surface and Carborane

We report here the design and synthesis of a novel vitamin D receptor (VDR) agonist whose hydrophobic core structure is p-carborane (1,12-dicarba-closo-dodecaborane, an icosahedral carbon-containing boron cluster having remarkable thermal and chemical stability and a characteristically hydrophobic B-H surface). This carborane-based VDR ligand exhibited moderate vitamin D activity, comparable to that of the natural hormone, despite its simple and flexible structure. X-ray structure analysis provided direct evidence that the carborane cage binds to the hydrophobic surface of the ligand-binding pocket of the receptor, promoting transition to the active conformation. These results indicate that the spherical B-H surface of carborane can function efficiently as a hydrophobic anchor in binding to the receptor surface, thereby allowing induced fitting of the three essential hydroxyl groups on the alkyl chains to the appropriate positions for interaction with the VDR binding site, despite the entropic disadvantage of the flexible structure. We suggest that carborane structure is a promising option in the design of novel drug candidates.

Chemical library screening for WNK signalling inhibitors using fluorescence correlation spectroscopy.

WNKs (with-no-lysine kinases) are the causative genes of a hereditary hypertensive disease, PHAII (pseudohypoaldosteronism typexa0II), and form a signal cascade with OSR1 (oxidative stress-responsive 1)/SPAK (STE20/SPS1-related proline/alanine-rich protein kinase) and Slc12a (solute carrier family 12) transporters. We have shown that this signal cascade regulates blood pressure by controlling vascular tone as well as renal NaCl excretion. Therefore agents that inhibit this signal cascade could be a new class of antihypertensive drugs. Since the binding of WNK to OSR1/SPAK kinases was postulated to be important for signal transduction, we sought to discover inhibitors of WNK/SPAK binding by screening chemical compounds that disrupt the binding. For this purpose, we developed a high-throughput screening method using fluorescent correlation spectroscopy. As a result of screening 17000 compounds, we discovered two novel compounds that reproducibly disrupted the binding of WNK to SPAK. Both compounds mediated dose-dependent inhibition of hypotonicity-induced activation of WNK, namely the phosphorylation of SPAK and its downstream transporters NKCC1 (Na/K/Cl cotransporter 1) and NCC (NaCl cotransporter) in cultured cell lines. The two compounds could be the promising seeds of new typesxa0of antihypertensive drugs, and the method that we developed could be applied as a general screening method to identify compounds that disrupt the binding of two molecules.

Acidic heterocycles as novel hydrophilic pharmacophore of androgen receptor ligands with a carborane core structure.

A novel series of androgen receptor (AR) ligands bearing an acidic heterocycle with hydrogen-bonding ability as the terminal polar group was developed. Since most non-steroidal AR ligands so far known are structurally limited to nitro- or cyanobenzanilide as the polar pharmacophore, development of alternative hydrogen-bonding components is required to obtain novel AR ligands. Various acidic heterocycles were introduced into a hydrophobic phenylcarborane (1-phenyl-1,12-dicarba-closo-dodecaborane) core structure to provide a moiety that could interact effectively with the critical basic arginine residue of the AR ligand binding domain. The most potent compounds, 1,2,4-oxadiazole-5-thione derivatives 21a and 21b, exhibited higher affinity for hAR than did the well-known anti-androgen hydroxyflutamide. The results suggest that this heterocyclic functionality is potential bioisoster of the nitro and cyano groups forming the polar pharmacophores of known non-steroidal AR ligands.

Discovery of Novel SPAK Inhibitors That Block WNK Kinase Signaling to Cation Chloride Transporters

Upon activation by with-no-lysine kinases, STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) phosphorylates and activates SLC12A transporters such as the Na(+)-Cl(-) cotransporter (NCC) and Na(+)-K(+)-2Cl(-) cotransporter type 1 (NKCC1) and type 2 (NKCC2); these transporters have important roles in regulating BP through NaCl reabsorption and vasoconstriction. SPAK knockout mice are viable and display hypotension with decreased activity (phosphorylation) of NCC and NKCC1 in the kidneys and aorta, respectively. Therefore, agents that inhibit SPAK activity could be a new class of antihypertensive drugs with dual actions (i.e., NaCl diuresis and vasodilation). In this study, we developed a new ELISA-based screening system to find novel SPAK inhibitors and screened >20,000 small-molecule compounds. Furthermore, we used a drug repositioning strategy to identify existing drugs that inhibit SPAK activity. As a result, we discovered one small-molecule compound (Stock 1S-14279) and an antiparasitic agent (Closantel) that inhibited SPAK-regulated phosphorylation and activation of NCC and NKCC1 in vitro and in mice. Notably, these compounds had structural similarity and inhibited SPAK in an ATP-insensitive manner. We propose that the two compounds found in this study may have great potential as novel antihypertensive drugs.Upon activation by with-no-lysine kinases, STE20/SPS1-related proline–alanine-rich protein kinase (SPAK) phosphorylates and activates SLC12A transporters such as the Na + -Cl − cotransporter (NCC) and Na + -K + -2Cl − cotransporter type 1 (NKCC1) and type 2 (NKCC2); these transporters have important roles in regulating BP through NaCl reabsorption and vasoconstriction. SPAK knockout mice are viable and display hypotension with decreased activity (phosphorylation) of NCC and NKCC1 in the kidneys and aorta, respectively. Therefore, agents that inhibit SPAK activity could be a new class of antihypertensive drugs with dual actions ( i.e., NaCl diuresis and vasodilation). In this study, we developed a new ELISA-based screening system to find novel SPAK inhibitors and screened >20,000 small-molecule compounds. Furthermore, we used a drug repositioning strategy to identify existing drugs that inhibit SPAK activity. As a result, we discovered one small-molecule compound (Stock 1S-14279) and an antiparasitic agent (Closantel) that inhibited SPAK-regulated phosphorylation and activation of NCC and NKCC1 in vitro and in mice. Notably, these compounds had structural similarity and inhibited SPAK in an ATP-insensitive manner. We propose that the two compounds found in this study may have great potential as novel antihypertensive drugs.

Crystal structure, docking study and structure-activity relationship of carborane-containing androgen receptor antagonist 3-(12-hydroxymethyl-1,12-dicarba-closo-dodecaboran-1-yl)benzonitrile.

A potent androgen receptor (AR) antagonist, 3-(12-hydroxymethyl-1,12 dicarba-closo-dodecaboran-1-yl)benzonitrile (3a, BA341), contains a p-carborane cage as a hydrophobic pharmacophore. We elucidated the structural properties of 3a by means of single-crystal X-ray diffraction analysis and conducted a docking study of 3a with hAR LBD. The cyano group of 3a formed hydrogen bonds with Gln711 and Arg752 and the hydroxymethyl group did so with Asn705 and Thr877 in hAR LBD. The bulky p-carborane cage was accommodated in the hydrophobic pocket of hAR LBD. To understand the structure-activity relationship around the hydroxymethyl group of 3a, we designed, synthesized, and evaluated the biological activities of various novel AR ligands. Since the biological activities of carbonyl compounds 8a, 8b, and 8c were similar to or weaker than those of the parent hydroxyl compounds 3a, 7a, and 7b, it seems to be necessary to have not only a hydrogen bonding acceptor, but also a hydrogen bonding donor adjacent to the hydroxymethyl group of 3a for efficient interaction with hAR LBD.

p-Carborane-based androgen antagonists active in LNCaP cells with a mutated androgen receptor

Development of antagonists for a mutated androgen receptor (AR) is important for treatment of anti-androgen-refractory prostate cancers. We describe here application of the p-carborane cage as a hydrophobic core structure for novel anti-androgens active toward LNCaP human prostate cancer cells with mutated AR. These compounds are expected to be versatile lead compounds not only for development of AR pan-antagonists, but also for discovery of mutant-selective anti-androgens.

Design and synthesis of nonsteroidal progesterone receptor antagonists based on C,C'-diphenylcarborane scaffold as a hydrophobic pharmacophore.

The progesterone receptor (PR) plays important roles in multiple physiological processes, including female reproduction. Here, we report the synthesis of nonsteroidal PR antagonists containing a boron cluster as the hydrophobic core. We found that 1,7-diphenyl-meta-carborane was the preferred substructure among the three carborane isomers. Compound 39 was the most potent PR antagonist (IC50: 29 nM). Compound 41 also exhibited potent activity (IC50: 93 nM), and did not bind to androgen receptor, glucocorticoid receptor or mineralocorticoid receptor. These compounds may be useful for investigating potential clinical applications of PR modulators.

Copper‐Mediated CC Cross‐Coupling Reaction of Monocarba‐closo‐dodecaborate Anion for the Synthesis of Functional Molecules

a counterion for the isolation of reactive cations, and for activation of catalysts in organic synthesis. Its unique electronic and molecular structures render 1 as an attractive starting material for the construction of various functional molecules and bioactive/pharmaceutical building blocks. However, progress in the synthesis of such materials is hindered by the lack of methods for the functionalization of 1. In particular, no efficient general methods are available for introduction of aryl and sp/sp-hybridized carbon centers at the carbon vertex of C1-carborane. A cross-coupling reaction is an obvious method for the introduction of aryl groups and sp/sp-hybridized carbon centers at the carbon vertex of C1-carborane derivatives, but has not yet been successful. 10] The intrinsic difficulty appears to be associated mainly with the sterically hindered and hypervalent nature of the vertex carbon atom in 1. We report herein a general and efficient copper-mediated C C cross-coupling reaction of 1 under palladium catalysis that yields a variety of C-functionalized C1-carborane derivatives and provides a basic architecture for pharmacophores and functional materials. The reaction is demonstrated not only for the parent C1-carborane but also its B-halogenated derivatives. To demonstrate utility of the method and the resulting new class of compounds, we describe the synthesis of multivalent anions and disclose preliminary results of the biological activity and liquid crystal behavior of selected derivatives. We commenced our studies by screening for a suitable metal species at the C1-carborane carbon vertex for crosscoupling reaction with aryl iodide 2a under palladium catalysis (Table 1). Reactions of various zinc carborate derivatives 1a (i.e. Negishi-type reaction), including zincate complexes, were unsuccessful (Table 1, entry 1). The Suzuki–Miyaura-type cross-coupling with pinacol borate 1b was also examined under a variety of conditions, but failed to give the desired product, affording only halogenated C1carboranes, with most of the pinacol borate moiety remaining intact (Table 1, entry 2). These results imply that the nature of the vertex carbon atom with respect to transmetalation is quite different from that of typical aryl or alkyl carbon atoms. After extensive screening of other systems, we found that a combination of copper(I) carborate 1c and a palladium catalyst promoted the coupling reaction with 2a at room temperature to give the desired product 3a (Table 1, Scheme 1. C1-carborane (1).

Design and Synthesis of 4-(4-Benzoylaminophenoxy)phenol Derivatives As Androgen Receptor Antagonists

We report the design and synthesis of novel 4-(4-benzoylaminophenoxy)phenol derivatives that bind to the androgen receptor (AR) ligand-binding domain and exhibit potent androgen-antagonistic activity. Compound 22 is one of the most potent of these derivatives, inhibiting the dihydrotestosterone-promoted growth of SC-3 cell line bearing wild-type AR (IC50 0.75 μM), LNCaP cell line bearing T877A-mutated AR (IC50 0.043 μM), and 22Rv1 cell line bearing H874Y-mutated AR (IC50 0.22 μM). Structure-activity relationship studies confirmed that the pharmacophore of these novel AR antagonists is distinct from the nitro- or cyano-substituted anilide substructure of other nonsteroidal AR antagonists. This novel pharmacophore is expected to provide a basis for designing new antiprostate cancer agents.

Design and synthesis of tetraol derivatives of 1,12-dicarba-closo-dodecaborane as non-secosteroidal vitamin D analogs

Vitamin D receptor (VDR), a nuclear receptor for 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3, 1), is a promising target for multiple clinical applications. We recently developed non-secosteroidal VDR ligands based on a carbon-containing boron cluster, 1,12-dicarba-closo-dodecaborane (p-carborane), and examined the binding of one of them to VDR by means of crystallographic analysis. Here, we utilized that X-ray structure to design novel p-carborane-based tetraol-type vitamin D analogs, and we examined the biological activities of the synthesized compounds. Structure-activity relationship study revealed that introduction of an ω-hydroxyalkoxy functionality enhanced the biological activity, and the configuration of the substituent significantly influenced the potency. Among the synthesized compounds, 4-hydroxybutoxy derivative 9a exhibited the most potent activity, which was equal to that of the secosteroidal vitamin D analog, 19-nor-1α,25-dihydroxyvitamin D3 (2).