Published papers

Natural products have been utilized for drug discovery. To increase the source diversity, we generated a new chemical library consisting of chemically modified microbial metabolites termed 'Unnatural Natural Products' by chemical conversion of microbial metabolites in crude broth extracts followed by purification of reaction products with the LC-photo diode array-MS system. Using this library, we discovered an XIAP inhibitor, C38OX6, which restored XIAP-suppressed enzymatic activity of caspase-3 in vitro. Furthermore, C38OX6 sensitized cancer cells to anticancer drugs, whereas the unconverted natural product did not. These findings suggest that our library could be a useful source for drug seeds. © 2011 Elsevier Ltd. All rights reserved.

© 2017 Elsevier Inc. 10-Me-aplog-1 is a simplified analog of the tumor-promoting compound debromoaplysiatoxin (DAT) and a unique protein kinase C (PKC) activator with limited tumor-promoting and pro-inflammatory activities. 10-Me-aplog-1 inhibits the growth of several cancer cell lines, but the inhibitory mechanism involving PKC isozymes remains unclear. We quantified the amount of PKC isozymes in nine human cancer cell lines that differ in 10-Me-aplog-1 sensitivity. PKCα and δ were the predominant isozymes expressed in all cell lines, but there was no significant correlation between expression levels and anti-proliferative activity. Knocking down PKCα, and/or PKCδ in the three aplog-sensitive cell lines indicated their involvement in the anti-proliferative and pro-apoptotic activities of 10-Me-aplog-1. This finding suggests that PKCα and/or PKCδ activation could be effective for treating certain cancers. Since the mechanism underlying 10-Me-aplog-1's anti-proliferative activities resembles that of DAT, 10-Me-aplog-1 may be regarded as a special key derived from pleiotropic DAT as a bunch of keys.

Bilirubin, the end product of heme redox metabolism, has cytoprotective properties and is an essential metabolite associated with cardiovascular disease, inflammatory bowel disease, type 2 diabetes, and neurodegenerative diseases including Parkinson's disease (PD). PD is characterized by progressive degeneration of nigral dopaminergic neurons and is associated with elevated oxidative stress due to mitochondrial dysfunction. In this study, using a ratiometric bilirubin probe, we revealed that the mitochondrial inhibitor, rotenone, which is widely used to create a PD model, significantly decreased intracellular bilirubin levels in HepG2 cells. Chemical screening showed that BRUP-1 was a top hit that restored cellular bilirubin levels that were lowered by rotenone. We found that BRUP-1 up-regulated the expression level of heme oxygenase-1 (HO-1), one of the rate-limiting enzyme of bilirubin production via nuclear factor erythroid 2-related factor 2 (Nrf2) activation. In addition, we demonstrated that this Nrf2 activation was due to a direct inhibition of the interaction between Nrf2 and Kelch-like ECH-associated protein 1 (Keap1) by BRUP-1. Both HO-1 up-regulation and bilirubin restoration by BRUP-1 treatment were significantly abrogated by Nrf2 silencing. In neuronal PC12D cells, BRUP-1 also activated the Nrf2-HO-1 axis and increased bilirubin production, resulted in the suppression of neurotoxin-induced cell death, reactive oxygen species production, and protein aggregation, which are hallmarks of PD. Furthermore, BRUP-1 showed neuroprotective activity against rotenone-treated neurons derived from induced pluripotent stem cells. These findings provide a new member of Keap1-Nrf2 direct inhibitors and suggest that chemical modulation of heme metabolism using BRUP-1 may be beneficial for PD treatment.

In actinomycetes, many secondary metabolite biosynthetic genes are not expressed under typical laboratory culture conditions and various efforts have been made to activate these dormant genes. In this study, we focused on high-temperature culture. First, we examined the thermotolerance of 3160 actinomycete strains from our laboratory culture collection and selected 57 thermotolerant actinomycetes that grew well at 45 °C. These 57 thermotolerant actinomycetes were cultured for 5 days in liquid medium at both 30 °C and 45 °C. Culture broths were extracted with 1-butanol, and each extract was subjected to LC/MS analysis. The metabolic profiles of each strain were compared between the 30 °C and 45 °C cultures. We found that almost half of these thermotolerant actinomycetes produced secondary metabolites that were detected only in the 45 °C culture. This result suggests that high-temperature culture induces the production of dormant secondary metabolites. These compounds were named "heat shock metabolites (HSMs)." To examine HSM production in more detail, 18 strains were selected at random from the initial 57 strains and cultivated in six different media at 30 °C and 45 °C; as before, metabolic profiles of each strain in each medium were compared between the 30 °C and 45 °C cultures. From this analysis, we found a total of 131 HSMs. We identified several angucycline-related compounds as HSMs from two thermotolerant Streptomyces species. Furthermore, we discovered a new compound, murecholamide, as an HSM from thermotolerant Streptomyces sp. AY2. We propose that high-temperature culture of actinomycetes is a convenient method for activating dormant secondary metabolite biosynthetic genes.

© 2018 National Academy of Sciences. All rights reserved. The Ciona notochord has emerged as a simple and tractable in vivo model for tubulogenesis. Here, using a chemical genetics approach, we identified UTKO1 as a selective small molecule inhibitor of notochord tubulogenesis. We identified 14-3-3ϵa protein as a direct binding partner of UTKO1 and showed that 14-3-3ϵa knockdown leads to failure of notochord tubulogenesis. We found that UTKO1 prevents 14-3-3ϵa from interacting with ezrin/radixin/moesin (ERM), which is required for notochord tubulogenesis, suggesting that interactions between 14-3-3ϵa and ERM play a key role in regulating the early steps of tubulogenesis. Using live imaging, we found that, as lumens begin to open between neighboring cells, 14-3-3ϵa and ERM are highly colocalized at the basal cortex where they undergo cycles of accumulation and disappearance. Interestingly, the disappearance of 14-3-3ϵa and ERM during each cycle is tightly correlated with a transient flow of 14-3-3ϵa, ERM, myosin II, and other cytoplasmic elements from the basal surface toward the lumen-facing apical domain, which is often accompanied by visible changes in lumen architecture.

© 2017 Japan Antibiotics Research Association All rights reserved. Castration-resistant prostate cancer (CRPC) is the most aggressive form of this disease. CRPC remains dependent on androgen receptor (AR) signaling. Therefore, a novel AR antagonist, enzalutamide, is used clinically for the treatment of men with metastatic CRPC. However, enzalutamide-resistant AR has appeared, and a new type of AR antagonist is desired. Previously, in the course of screening for a new type of AR antagonist, we isolated a series of compounds, designated antarlides A-E, that share a novel 22-membered-ring macrocyclic structure and are produced by Streptomyces sp. BB47. In the present study, we found that this strain also produces antarlides F-H as minor components. Antarlide F is a novel geometric isomer of known antarlides. On the other hand, antarlides G and H are new members of the antarlide family that have a 20-membered-ring macrocyclic structure. Antarlides G and H inhibited the binding of androgen to AR in vitro at concentrations similar to those observed with antarlides A-E. In addition, antarlide G inhibited the transcriptional activity of not only wild-type AR but also enzalutamide-resistant AR, suggesting that antarlides with either 22- or 20-membered rings may serve as potent third-generation AR antagonists capable of overcoming resistance to enzalutamide.

© 2016 Wiley-VCH Verlag GmbH & Co. KGaA. Prostate cancer is treated with androgen receptor (AR) antagonists but most patients experience disease progression after long-term treatment with these compounds. Therefore, new AR antagonists are required for patient follow-up treatment. In the course of screening for a new AR antagonist, we isolated the novel compounds antarlides A-E (1-5) from Streptomyces sp. BB47. Antarlides are mutually isomeric with respect to the double bond and have a 22-membered-ring macrocyclic structure. The full stereostructure of 1 was established by chemical modifications, including methanolysis, the Trost method, acetonide formation, and the PGME method. 1-5 inhibited the binding of androgen to ARs in vitro. In addition, 2 inhibited the transcriptional activity of not only wild-type AR but also mutant ARs, which are seen in patients with acquired resistance to clinically used AR antagonists. Therefore, antarlides are a potent new generation of AR antagonists that overcome resistance.

© 2015 Krajarng et al. Background: Gambogic acid (GA) was extracted from the dried yellow resin of gamboge (Garcinia hanburyi) which is traditionally used as a coloring material for painting and cloth dying. Gamboge has been also used as a folk medicine for an internal purgative and externally infected wound. We focused on the mechanisms of apoptosis induction by GA through the unfold protein response (ER stress) in HeLa cells. Methods: The cytotoxic effect of GA against HeLa cells was determined by trypan blue exclusion assay. Markers of ER stress such as XBP-1, GRP78, CHOP, GADD34 and ERdj4 were analyzed by RT-PCR and Real-time RT-PCR. Cell morphological changes and apoptotic proteins were performed by Hoechst33342 staining and Western blotting technique. Results: Our results indicated a time- and dose-dependent decrease of cell viability by GA. The ER stress induction is determined by the up-regulation of spliced XBP1 mRNA and activated GRP78, CHOP, GADD34 and ERdj4 expression. GA also induced cell morphological changes such as nuclear condensation, membrane blebbing and apoptotic body in Hela cells. Apoptosis cell death detected by increased DR5, caspase-8, -9, and -3 expression as well as increased cleaved-PARP, while decreased Bcl-2 upon GA treatment. In addition, phosphorylated JNK was up-regulated but phosphorylated ERK was down-regulated after exposure to GA. Conclusions: These results suggest that GA induce apoptosis associated with the ER stress response through up-regulation of p-JNK and down-regulation of p-ERK in HeLa cells.

Autophagy is an essential catabolic process that promotes clearance of surplus or damaged intracellular components1. As a recycling process, autophagy is also important for the maintenance of cellular metabolites during periods of starvation2. Loss of autophagy is sufficient to cause cell death in animal models and is likely to contribute to tissue degeneration in a number of human diseases including neurodegenerative and lysosomal storage disorders3–7. However, it remains unclear which of the many cellular functions of autophagy primarily underlies its role in cell survival. Here we have identified a critical role of autophagy in the maintenance of nicotinamide adenine dinucleotide (NAD+/NADH) levels. In respiring cells, loss of autophagy caused NAD(H) depletion resulting in mitochondrial membrane depolarisation and cell death. We also found that maintenance of NAD(H) is an evolutionary conserved function of autophagy from yeast to human cells. Importantly, cell death and reduced viability of autophagy-deficient animal models can be partially reversed by supplementation with an NAD(H) precursor. Our study provides a mechanistic link between autophagy and NAD(H) metabolism and suggests that boosting NAD(H) levels may be an effective intervention strategy to prevent cell death and tissue degeneration in human diseases associated with autophagy dysfunction.

蛍光標識したチロシンホスファターゼの基質を合成し、簡便なチロシンホスファターゼ測定系を提案した。(2ページ)

新規チロシンキナーゼ阻害剤アーブスタチンを発見し、その構造決定を報告した。(2ページ)

Phosphatidylinositol (PI) turnover is considered to be involved in the regulation of cell growth. The enzymes for PI turnover include phospholipase C (PLC), PI4-kinase and PI synthase. We have isolated pholipeptin and fluvirucin B2 from microorganisms and akaterpin from a marine sponge as PLC γ inhibitors. We also isolated echiguanines from Streptomyces as P14-kinase inhibitors. Since echiguanines did not inhibit the enzyme in situ, we synthesized their ribosylated derivatives that were effective in cultured cells. We previously isolated inostamycin from Streptomyces as an inhibitor of PI synthase. We found that inostamycin induced G1 block in cycling NRK cells. Inostamycin inhibited the serum-induced S-phase induction in quiescent NRK cells. Inostamycin was found to decrease serum-induced expression of cyclin D and cyclin E, without inhibiting the activation of MAP kinase. It also inhibited serum-induced activation of CDK2 and phosphorylation of pRB. Thus, PI synthesis was suggested to be involved in regulation of serum- induced S-phase induction by modulating G1 cyclin expression.

Although clinical studies have evaluated several MEK1/2 inhibitors, it is unlikely that MEK1/2 inhibitors will be studied clinically. BRAF mutations have been proposed as a responder marker of MEK1/2 inhibitors in a preclinical study. However, current clinical approaches focusing on BRAF mutations have shown only moderate sensitivity of MEK1/2 inhibitors. This has led to insufficient support for their promoted clinical adoption. Further characterization of tumors sensitive to MEK inhibitors holds great promise for optimizing drug therapy for patients with these tumors. Here, we report that β-catenin mutations accelerate apoptosis induced by MEK1/2 inhibitor. SMK-17, a selective MEK1/2 inhibitor, induced apoptosis in tumor cell lines harboring β-catenin mutations at its effective concentration. To confirm that β-catenin mutations and mutant β-catenin-mediated TCF7L2 (also known as TCF4) transcriptional activity is a predictive marker of MEK inhibitors, we evaluated the effects of dominant-negative TCF7L2 and of active, mutated β-catenin on apoptosis induced by MEK inhibitor. Indeed, dominant-negative TCF7L2 reduced apoptosis induced by MEK inhibitor, whereas active, mutated β-catenin accelerated it. Our findings show that β-catenin mutations are an important responder biomarker for MEK1/2 inhibitors.

Migrastatin (MGS) is a Streptomyces metabolite that inhibits cancer cell migration. In this study, we found that MGS also enhanced the cytotoxicity of vinblastine, vincristine, and taxol in P-glycoprotein-overexpressing VJ-300 cells and P388/VCR cells. Furthermore, MGS increased the intracellular concentration of labeled vinblastine, vincristine, and taxol in both VJ-300 cells and P388/VCR cells. P-glycoprotein was photolabeled with [ 3H]azidopine, but this photolabeling was significantly inhibited in the presence of MGS. These results indicated that MGS directly interacts with and inhibits P-glycoprotein, thereby sensitizing drug-resistant cells to anticancer drugs. © Japan Antibiotics Research Association.

Cell migration of tumor cells is essential for invasion of the extracellular matrix and for cell dissemination. Inhibition of the cell migration involved in the invasion process represents a potential therapeutic approach to the treatment of tumor metastasis; therefore, a novel series of derivatives of moverastins (moverastins A and B), an inhibitor of tumor cell migration, was designed and chemically synthesized. Among these moverastin derivatives, several compounds showed stronger cell migration inhibitory activity than parental moverastins, and UTKO1 was found to have the most potent inhibitory activity against the migration of human esophageal tumor EC17 cells in a chemotaxis cell chamber assay. Interestingly, although moverastins are considered to inhibit tumor cell migration by inhibiting farnesyltransferase (FTase), UTKO1 did not inhibit FTase, indicating that UTKO1 inhibited tumor cell migration by a mechanism other than the inhibition of FTase. © 2011 Published by Elsevier Ltd.