Structure-activity relationships of natural quinone vegfrecine analogs with potent activity against VEGFR-1 and -2 tyrosine kinases.

A series of analogs of vegfrecine, a natural quinone vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor, was synthesized via oxidative amination of 2,5-dihydroxybenzamide with functionalized arylamine followed by ammonolysis and substitution of the quinone ring. The inhibitory activities of the analogs against the VEGFR-1 and -2 tyrosine kinases were assayed in vitro with the aim to identify a compound suitable to treat cancer and inflammatory diseases. Alterations of the functionality of the phenyl group, substitution of the quinone ring, and oxidative cyclization of the 1-carboxamide-2-aminoquinone moiety to form an isoxazole quinone ring were examined. Introduction of halo- and alkyl-substituents at the 5'-position of the phenyl ring resulted in potent inhibition of the VEGFR-1 and -2 tyrosine kinases. In particular, structural modification at C-5' on the phenyl ring was shown to significantly affect the selectivity of the inhibition between the VEGFR-1 and -2 tyrosine kinases. Compound 8, 5'-methyl-vegfrecine, showed superior selectivity toward the VEGFR-2 tyrosine kinase over the VEGFR-1 tyrosine kinase.

Corrigendum: Microbial metabolites and derivatives targeted at inflammation and bone diseases therapy: chemistry, biological activity and pharmacology.

This corrects the article DOI: 10.1038/ja.2017.138.

Microbial metabolites and derivatives targeted at inflammation and bone diseases therapy: chemistry, biological activity and pharmacology.

Microbial metabolites have attracted increasing interest as a source of therapeutics and as probes for biological mechanisms. New microbial metabolites and derivatives targeted at inflammation and bone disease therapy have been identified by focusing on prostaglandin release, osteoblast differentiation and immune cell functions. These modulators of inflammatory processes and bone disease contribute to our understanding of biological mechanisms and support identification of the therapeutic potential of drug lead candidates. The present review describes recent advances in the chemistry and analysis of inhibitors of prostaglandin release or other functional molecules of immune cells, as well as inducers of osteoblast differentiation, including biological and pharmacological activities.The Journal of Antibiotics advance online publication, 1 November 2017; doi:10.1038/ja.2017.138.

Sacchathridine A, a prostaglandin release inhibitor from Saccharothrix sp.

Sacchathridine A (1) was isolated from the fermentation broth of strain Saccharothrix sp. MI559-46F5. The structure was determined as a new naphthoquinone derivative with an acetylhydrazino moiety by a combination of NMR, MS spectral analyses, and chemical degradation. Compound 1 showed inhibitory activity of prostaglandin E2 release in a concentration-dependent manner from human synovial sarcoma cells, SW982, with an IC50 value of 1.0 µM, but had no effect on cell growth up to 30 µM.

NAD(P)H quinone oxidoreductase 1 (NQO1)-bioactivated pronqodine A regulates prostaglandin release from human synovial sarcoma cells.

Natural products have contributed to the elucidation of biological mechanisms as well as drug discovery research. Even now, the expectation for natural products is undiminished. We screened prostaglandin release inhibitors that had no effect on in vitro cyclooxygenase activity derived from natural product sources and discovered pronqodine A. Using spectral analysis and total synthesis, the structure of pronqodine A was shown to be a benzo[d]isothiazole-4,7-dione analogue. Evaluation of the biological activity of pronqodine A revealed that the NAD(P)H dehydrogenase quinone 1 (NQO1) converted pronqodine A into a two-electron reductive form. The reductive form underwent autoxidation and reversed to its native form immediately with the generation of reactive oxygen species. Further investigations proved that pronqodine A inhibited cyclooxygenase enzyme activity only in the presence of NQO1. Pronqodine A acts as a potential bioreductive compound, inhibiting prostaglandin release in selectively activated NQO1-expressing cells.

Vegfrecine, an inhibitor of VEGF receptor tyrosine kinases isolated from the culture broth of Streptomyces sp.

A new inhibitor of VEGF receptor tyrosine kinases, vegfrecine (1), was isolated from the culture broth of Streptomyces sp. MK931-CF8. The molecular structure of 1 was determined by NMR and MS analysis combined with synthesis. Compound 1 showed potent inhibitory activity against vascular endothelial growth factor receptor (VEGFR) tyrosine kinases in in vitro enzyme assays, but platelet-derived growth factor receptors (PDGFRs), fibroblast growth factor receptor (FGFR), and epidermal growth factor receptor (EGFR) responded only weakly. Compound 1 is a promising new selective VEGFR inhibitor for investigating new treatments of cancer and inflammatory diseases.

Decalpenic acid, a novel small molecule from Penicillium verruculosum CR37010, induces early osteoblastic markers in pluripotent mesenchymal cells.

Osteoblasts are the cells responsible for bone formation during embryonic development and adult life. Small compounds that could induce osteoblast differentiation might be promising sources of therapies for bone diseases such as osteoporosis. During screening for inducers of osteoblast differentiation of mouse pluripotent mesenchymal C3H10T1/2 cells, we isolated a small compound from the fermentation broth of Penicillium verruculosum CR37010. This compound, named decalpenic acid, bears a decalin moiety with a tetraenoic acid side chain. Treatment of C3H10T1/2 cells with decalpenic acid alone induced the expression of early osteoblast markers, such as alkaline phosphatase activity and osteopontin mRNA, but did not induce the late osteoblast marker osteocalcin mRNA or adipocyte markers under our experimental conditions.

Identification of the toxic trigger in mushroom poisoning.

We have isolated the small, highly strained carboxylic acid cycloprop-2-ene carboxylic acid from the Asian toxic mushroom Russula subnigricans. This compound is responsible for fatal rhabdomyolysis, a new type of mushroom poisoning that is indicated by an increase in serum creatine phosphokinase activity in mice. We found that polymerization of the compound at high concentrations via ene reaction abolishes its toxicity.

A new teleocidin analog from Streptomyces sp. MM216-87F4 induces substance P release from rat dorsal root ganglion neurons.

A new teleocidin analog was isolated from the fermentation medium of Streptomyces sp. MM216-87F4 and its structure was elucidated as 14-O-(N-acetylglucosaminyl) teleocidin A (GlcNAc-TA). GlcNAc-TA induces the translocation of protein kinases Calpha and theta fused with enhanced green fluorescent protein (PKCalpha-EGFP and PKCtheta-EGFP) to the plasma membrane in stable transfectants, and reduces intracellular calcium mobilization induced by agonists of G-protein coupled receptors in various cell lines without causing irritation of the mouse ear. Further, GlcNAc-TA sensitizes the release of excitatory neuropeptides substance P induced by capsaicin from primary-cultured dorsal root ganglion (DRG) neurons of the rat and GlcNAc-TA alone also triggers substance P release in a dose-dependent manner. This study provides the first observation that a teleocidin analog without a free hydroxyl group at C-14 acts as a PKC activator and directly induces the release of excitatory neuropeptide.

Migrastatin acts as a muscarinic acetylcholine receptor antagonist.

Migrastatin and its analogs have various biological activities such as inhibition of cell migration and anchorage-independent growth of cancer cells. Although its biosynthesis and chemical synthesis have been under investigation, little is known about the biological target of migrastatin. Here, we found that migrastatin inhibited intracellular calcium mobilization induced by carbachol in neuroblastoma SK-N-SH cells without affecting Ca2+ mobilization and cAMP accumulation induced by ligands of other receptors. The binding of [3H] N-methylscopolamine, an antagonist for muscarinic receptor was also inhibited by migrastain. Functionally, migrastatin inhibited Ca2+ mobilization induced by carbachol in primary cultures of smooth muscle cells of rat bladder. This study reveals that migrastatin acts as a muscarinic acetylcholine receptor antagonist.

Chemistry and biology of moverastins, inhibitors of cancer cell migration, produced by Aspergillus.

Cancer cell migration is a required step in cancer metastasis. We screened for inhibitors of cancer cell migration of microbial origin, and obtained moverastin, a member of the cylindrol family, from Aspergillus sp. F7720. However, the results of an NMR spectroscopic analysis raised the possibility that moverastin is a mixture of two diastereomers. Separation of the C-10 epimers of synthetic moverastin and a bioassay revealed that both diastereomers (moverastins A and B) had inhibitory effects on cell migration. Furthermore, we demonstrated that moverastins A and B inhibited FTase in vitro, and they also inhibited both the membrane localization of H-Ras and the activation of the PI3K/Akt pathway in EC17 cells. Thus, moverastins inhibited the migration of tumor cells by inhibiting the farnesylation of H-Ras, and subsequent H-Ras-dependent activation of the PI3K/Akt pathway.

A prostacyclin receptor antagonist inhibits the sensitized release of substance P from rat sensory neurons.

Prostacyclin, one of the cyclooxygenase metabolites, causes various biological effects, including vasodilation and antithrombogenicity, and is also involved in several pathophysiological effects, such as inflammatory pain and bladder disorders. The prostacyclin receptor (IP receptor) agonists iloprost, cicaprost, and carbacyclin have been useful for clarifying the role of the IP receptor signaling, since the endogenous ligand, prostacyclin, is very unstable. On the other hand, only a few IP receptor antagonists have been reported to date. Here, we characterized the biological activities of 2-[4-(1H-indol-4-yloxymethyl)-benzyloxycarbonylamino]-3-phenyl-propionic acid (compound A) in various in vitro systems. Compound A inhibited the accumulation of the second messenger cyclic AMP in the UMR-108 rat osteosarcoma cell line and primary cultured rat dorsal root ganglion (DRG) neurons in a concentration-dependent manner up to 10 microM, without affecting other eicosanoid receptors. Functionally, the IP receptor plays an important role in DRG neuron sensitization, which is measured by release of the neurotransmitter substance P. Although the effects of iloprost or Lys-bradykinin, an inflammatory peptide, alone on substance P release were limited, stimulation of the neurons with both these ligands induced substantial amounts of substance P release. This synergistic effect was suppressed by compound A. Collectively, these results suggest that compound A is a highly selective IP receptor antagonist that inhibits iloprost-induced sensitization of sensory neurons. Furthermore, these findings suggest that IP receptor antagonist administration may be effective for abnormal neural activities of unmyelinated sensory afferents. Compound A should prove useful for further investigations of the IP receptor in various biological processes.

Functional role of prostacyclin receptor in rat dorsal root ganglion neurons.

Recent studies on prostanoids showed that some of prostanoid receptors are expressed in rat dorsal root ganglion (DRG) neurons. These facts suggest that prostanoid receptors might be involved in the excitation mechanism of DRG neurons. In the present study, PCR experiments revealed that one of prostanoid receptor, prostacyclin receptor (IP receptor) was expressed in L6 and S1 rat DRG neurons and that the expression of IP receptor was not changed in DRG neurons obtained from the cyclophosphamide (CYP)-induced cystitis rat. We examined the functional role of IP receptor agonist and other prostanoids by measuring cyclic AMP (cAMP) accumulation and substance P (SP) release in primary cultured DRG neurons. The pretreatment of DRG neurons with prostanoid agonists such as iloprost (IP), butaprost (EP(2)), misoprostol (EP(2-4)), PGE(2) (EP(1-4)) or PGD(2) (DP and CRTH2) sensitized the DRG neurons and hence potentiated the lys-bradykinin-induced SP release. The increase of SP release by lys-BK plus prostanoid agonists was proportion to cAMP accumulation. Iloprost was the most potent agonist to induce cAMP accumulation and SP release among prostanoid agonists evaluated in this study and its effect is mediated by IP receptor. Moreover, capsaicin-, ATP- and KCl-induced SP release was also enhanced by iloprost although iloprost did not change intracellular Ca(2+) and membrane depolarization induced by these chemical stimuli. These results strongly indicate that IP receptor play an important role in the sensitization of rat sensory neuron.