Discovery and mechanistic study of thiazole-4-acylsulfonamide derivatives as potent and orally active ChemR23 inhibitors with a long-acting effect in cynomolgus monkeys.

Plasmacytoid dendritic cells (pDCs) are a subset of dendritic cells that can secrete large amounts of type I interferon. ChemR23, a G protein-coupled receptor (GPCR) expressed on the surface of pDCs, contributes to the recruitment of pDCs to inflamed tissues through chemotaxis signaling, and is therefore considered an attractive target for the treatment of autoimmune diseases. We previously reported benzoxazole-based compounds that can inhibit ChemR23 signaling through receptor internalization. Although these compounds showed ChemR23 internalization on pDCs in cynomolgus monkeys after oral administration, further improvement of the pharmacokinetics profile was needed for a clinical candidate and we therefore attempted scaffold-hopping from the benzoxazole core structure leading to novel thiazole derivatives. In this report, the design, synthesis, and biological evaluation of new thiazole-based ChemR23 inhibitors were described. Through sequential structure-activity relationship studies regarding (i) the side chain of the N-acylsulfonamide moiety, (ii) the 5-position of the thiazole ring, and (iii) the 1,2,4-oxadiazol-5-one moiety, we have succeeded in finding a potent thiazole-based ChemR23 inhibitor, 14f (IC80 = 12 nM). In addition, the oral administration of 14f at 30 mg/kg to cynomolgus monkeys demonstrated a sustained pharmacological effect of ChemR23 internalization on pDCs until 8 h after dosing, which was considered a longer effect in comparison to previously reported 2-aminobenzoxazole-based ChemR23 inhibitors. This report also shows the synthesis and evaluation of fluorescein-labeled compound 45c for a mechanistic study, and we could confirm the direct binding of our thiazole derivative to ChemR23. We believe that our research on small molecule ChemR23 inhibitors and chemical probe will contribute to the elucidation and analysis of the functions of ChemR23 as well as identifying novel therapeutics for autoimmune diseases.

The design, synthesis and evaluation of 2-aminobenzoxazole analogues as potent and orally efficacious ChemR23 inhibitors.

We previously reported 2-aminobenzoxazole analogue 1 as a potent ChemR23 inhibitor. The compound showed inhibitory activity against chemerin-induced calcium signaling through ChemR23 internalization in CAL-1 cells, which are cell lines of plasmacytoid dendric cells (pDCs). Furthermore, compound 2 inhibited chemotaxis of CAL-1 triggered by chemerin in vitro. However, we noted a difference in the ChemR23 response to our inhibitor between rodents and non-rodents in a previous study. To address this issue, we performed optimization of ChemR23 inhibitors using CAL-1 cells endogenously expressing human ChemR23 and conducted a pharmacokinetics study in cynomolgus monkeys. Various substituents at the 4-position of the benzoxazole ring exhibited potent in vitro bioactivity, while those at the 6-position were not tolerated. Among substituents, a carboxyl group was identified as key for improving the oral bioavailability in cynomolgus monkeys. Compound 38a with the acidic part changed from a tetrazole group to a 1,2,4-oxadiazol-5-one group to improve bioactivity and pharmacokinetic parameters exhibited inhibitory activity against chemerin-induced chemotaxis in vitro. In addition, we confirmed the ChemR23 internalization of pDCs by compound 38a orally administered to cynomolgus monkeys. These 2-aminobenzoxazole-based ChemR23 inhibitors may be useful as novel immunotherapeutic agents capable of suppressing the migration of pDCs, which are known to be major producers of type I interferons in the lesion area of certain autoimmune diseases, such as systemic lupus erythematosus and psoriasis.

The discovery and optimization of a series of 2-aminobenzoxazole derivatives as ChemR23 inhibitors.

A structural class of 2-aminobenzoxazole derivatives possessing biphenyltetrazole was discovered to be potent human ChemR23 inhibitors. We initially tried to improve the potency of compound 1, which was found through in-house screening using the human plasmacytoid dendritic cell (pDC)-like cell line CAL-1. The introduction of a chiral methyl moiety at a benzylic position in a center of compound 1 showed a large impact on the inhibitory activity against calcium signaling of ChemR23 induced by the natural ligand chemerin. As a result of further investigations at the benzylic position, (R)-isomer 6b was found to show a 30-fold increased potency over desmethyl compound 1. In addition, an extensive structure-activity relationship study on the benzoxazole moiety successfully led to a further increase in the potency. The antagonistic effect of the compounds was based on the induction of ChemR23 internalization. In addition, we observed that compound 31, which contained an amide moiety on benzoxazole, inhibited chemotaxis of CAL-1 cells induced by chemerin in vitro. These results suggest that our ChemR23 inhibitors are attractive compounds for the treatment of pDC-related autoimmune diseases, such as systemic lupus erythematosus and psoriasis.

Total Synthesis and Biological Evaluation of Irciniastatin A (a.k.a. Psymberin) and Irciniastatin B.

Irciniastatin A (a.k.a. psymberin) and irciniastatin B are members of the pederin natural product family, which have potent antitumor activity and structural complexity. Herein, we describe a full account of our total synthesis of (+)-irciniastatin A and (-)-irciniastatin B. Our synthesis features the highly regioselective Eu(OTf)3-catalyzed, DTBMP-assisted epoxide ring opening reaction with MeOH, which enabled a concise synthesis of the C1-C6 fragment, extensive use of AZADO (2-azaadamantane N-oxyl) and its related nitroxyl radical/oxoammonium salt-catalyzed alcohol oxidation throughout the synthesis, and a late-stage assembly of C1-C6, C8-C16, and C17-C25 fragments. In addition, for the synthesis of (-)-irciniastatin B, we achieved the C11-selective control of the oxidation stage via regioselective deprotection and AZADO-catalyzed alcohol oxidation. The synthetic irciniastatins showed high levels of cytotoxic activity against mammalian cells. Furthermore, chemical footprinting experiments using synthetic compounds revealed that the binding site of irciniastatins is the E-site of the ribosome.

Nicotinamide phosphoribosyltransferase is a molecular target of potent anticancer agents identified from phenotype-based drug screening.

Phenotypic screening in drug discovery has been revived with the expectation of providing promising lead compounds and drug targets and improving the success rate of drug approval. However, target identification remains a major bottleneck in phenotype-based drug discovery. We identified the lead compounds K542 and K405 with a selective inhibition of cell viability against sphingosine-1-phosphate lyase 1 (SGPL1)-transduced ES-2 cells by phenotypic screening. We therefore performed an in vivo pharmacological examination and observed the antitumor activity of K542 in an HT-1080 tumor-bearing mouse xenograft model. SGPL1 was expected to be a therapeutic target in some cancers, suggesting that these lead molecules might be promising candidates; however, their mechanisms of action still remain unexplained. We therefore synthesized the affinity probe Ind-tag derived from K542 and identified the proteins binding to Ind-tag via a pull-down experiment. Proteomics and biochemical analyses revealed that the target molecule of these lead compounds was Nicotinamide phosphoribosyltransferase (NAMPT). We established K542-resistant DLD-1 and HT-1080 cells, and genetic analyses of these cells identified a missense mutation in the NAMPT-encoding gene. This enzymatic experiment clearly showed that K393 exerts enzymatic inhibition against NAMPT. These proteomics, genetics and biochemical analyses clarified that compounds K542 and K405 were NAMPT inhibitors.

The synthesis and evaluation of the antiproliferative activity of deacidified GEX1A analogues.

GEX1A/herboxidiene (1) is a natural product isolated from Streptomyces sp. and has been reported to target the pre-mRNA splicing process. Although 1 was shown to have antitumor activity in vivo, weight loss was observed in mice when 1 was consecutively administered. We assumed that the carboxylic acid moiety was one of the causes of this toxicity. In this study, a series of amide, carbamate and urea analogues of 1 were synthesized and their antiproliferative activity was evaluated in vitro. The synthesis of urea analogues featured Curtius rearrangement following amine treatment with the one-pot procedure from 1. Furthermore, a structure-activity relationship study of the urea analogues revealed that the pharmacologically preferable basic side chains were acceptable and that compound 9g was equipotent to parent 1. These basic urea analogues would be promising leads for the development of novel antitumor agents.

Eu(OTf)3-catalyzed highly regioselective nucleophilic ring opening of 2,3-epoxy alcohols: an efficient entry to 3-substituted 1,2-diol derivatives.

In our study of the total synthesis of (+)-irciniastatin A, we found a need to develop a method that enables a C3-selective nucleophilic ring opening of 2,3-epoxy alcohol by MeOH, by which we found that the use of combined catalytic amounts of Eu(OTf)3 and 2,6-di-tert-butyl-4-methylpyridine (DTBMP) enables the intended transformation to obtain 3-methoxy-1,2-diol efficiently. Promising features of a protocol that effects a highly regioselective nucleophilic ring opening of 2,3- and 3,4-epoxy alcohols using various nucleophiles including alcohols, thiols, and unprotected amines are described.

Syntheses and biological evaluation of irciniastatin A and the C1-C2 alkyne analogue.

Syntheses of both natural (+)- and unnatural (-)-irciniastatin A (aka psymberin) as well as a C1-C2 alkyne analogue of (+)-irciniastatin A have been achieved. The key features of the syntheses include a highly regioselective epoxide-opening reaction and a late-stage assembly of C1-C6, C8-C16, and C17-C25 fragments. (+)-Alkymberin retained a high level of cytotoxicity, whereas (-)-irciniastatin A showed almost no activity. These results suggest that (+)-alkymberin could be a useful enantio-differential probe for mode-of-action study.

Irciniastatin A induces JNK activation that is involved in caspase-8-dependent apoptosis via the mitochondrial pathway.

Irciniastatin A (ISA)/psymberin, a pederin-type natural product isolated from marine sponge, exhibits extremely potent and selective cytotoxicity against certain human cancer cell lines, but its molecular target and cytotoxic mechanisms are still unknown. Here we show that ISA is a potent inhibitor of protein translation, and induces apoptosis accompanied with activation of the stress-activated protein kinases via the mitochondrial pathway in human leukemia Jurkat cells. ISA potently inhibited protein translation, and induced a slow but prolonged activation of the stress-activated protein kinases, JNK and p38, at between 1h and 6h after treatment. In Bcl-x(L)-transfected cells, the activation of JNK and p38 by ISA was shortened. The same results were obtained in the cells treated with N-acetyl-L-cysteine, suggesting that the prolonged activation of JNK and p38 by ISA is mediated by reactive oxygen species generated from mitochondria. ISA strongly induced apoptosis, which was partially suppressed by the JNK inhibitor SP600125, but not by the p38 inhibitor SB202190. Apoptosis induction by ISA was partially reduced, but not suppressed by SP600125 in caspase-8-deficient Jurkat cells. These results suggest that ISA activates stress-activated kinases by a mitochondria-mediated mechanism, and that activation of JNK is required for caspase-8-dependent apoptosis.