A leptomycin B resistance gene of Schizosaccharomyces pombe encodes a protein similar to the mammalian P-glycoproteins

Screening for leptomycin B (LMB)-resistant transformants in a gene library constructed in Schizosaccharomyces pombe with the chromosomal DNA of an LMB-resistant mutant of S. pombe and with multicopy plasmid pDB248' as the vector led to the isolation of a gene, named pmd1+, encoding a 1362-amino-acid protein. This protein showed great similarity in amino acid sequence to the mammalian P-glycoprotein encoded by the multidrug resistance gene, mdr, and the Saccharomyces cerevisiae a-factor transporter encoded by STE6. In addition, computer analyses predicted that the protein encoded by pmd1+ formed an intramolecular duplicated structure and each of the halves contained six transmembrane regions as well as two ATP-binding domains, as observed with the P-glycoproteins and the STE6 product. Consistent with this was that S. pombe cells containing the pmd1+ gene on a multicopy plasmid showed resistance not only to LMB but also to several cytotoxic agents. The pmd1 null mutants derived by gene disruption were viable and hypersensitive to these agents. All these data suggest that the pmd1+ gene encodes a protein that is a structural and functional counterpart of mammalian mdr proteins.     

Syntheses of benzophenone-xanthone hybrid polyketides and their antibacterial activities

Muchimangins are benzophenone-xanthone hybrid polyketides produced by Securidaca longepedunculata. However, their biological activities have not been fully investigated, since they are minor constituents in this plant. To evaluate the possibility of muchimangins as antibacterial agent candidates, five muchimangin analogs were synthesized from 2,4,5-trimethoxydiphenyl methanol and the corresponding xanthones, by utilizing p-toluenesulfonic acid monohydrate for the Brønsted acid-catalysis. The antibacterial assays against Gram-positive bacteria, Staphylococcus aureus and Bacillus subtilis, and Gram-negative bacteria, Klebsiella pneumoniae and Escherichia coli, revealed that the muchimangin analogs (±)-1,3,6,8-tetrahydroxy-4-(phenyl-(2′,4′,5′-trimethoxyphenyl)methyl)-xanthone (1), (±)-1,3,6-trihydroxy-4-(phenyl-(2′,4′,5′-trimethoxyphenyl)methyl)-xanthone (2), and (±)-1,3-dihydroxy-4-(phenyl-(2′,4′,5′-trimethoxyphenyl)methyl)-xanthone (3) showed significant activities against S. aureus, with MIC values of 10.0, 10.0, and 25.0 μM, respectively. Analogs (±)-1 and (±)-2 also exhibited antibacterial activities against B. subtilis, with MIC values of 50.0 and 12.5 μM, respectively. Furthermore, (+)-3 enhanced the antibacterial activity against S. aureus, with a MIC value of 10 μM.     

Probing biosynthesis of plant polyketides with synthetic N-acetylcysteamine thioesters

Recombinant chalcone synthase (CHS) from Scutellaria baicalensis accepted cinnamoyl diketide-NAC and cinnamoyl-NAC as a substrate, and carried out sequential condensations with malonyl-CoA to produce 2',4',6'-trihydroxychalcone. Steady-state kinetic analysis revealed that the CHS accepted the diketide-NAC with less efficiency, while cinnamoyl-NAC primed the enzyme reaction almost as efficiently as cinnamoyl-CoA. On the other hand, it was for the first time demonstrated that the diketide-NAC was also a substrate for recombinant polyketide reductase (PKR) from Glycyrrhiza echinata, and converted to the corresponding beta-ketohemithioester. Furthermore, by co-action of the CHS and the PKR, the NAC-thioesters were converted to 6'-deoxychalcone in the presence of NADPH and malonyl-CoA.     

Effects of leptomycin B on the cell cycle of fibroblasts and fission yeast cells

An antifungal antibiotic, leptomycin B (LMB), which induced cell elongation of fission yeast, Schizosaccharomyces pombe, was found to be a unique inhibitor of the cell cycle of mammalian and fission yeast cells. Proliferation of rat 3Y1 fibroblasts was reversibly blocked by LMB in both the G1 and G2 phases and the treated cells were presumably introduced into the resting state (GO). After removal of LMB, proliferative tetraploid cells were produced from the cells which had been arrested by LMB at the G2 phase, as a result of DNA replication without passage through the M phase. LMB also inhibited the proliferation of S. pombe in both the G1 and G2 phases. These results suggest that the molecular target of LMB is one of the components necessary for progression of both G1 and G2 in the eukaryotic cell cycle.     

Phomoxins B and C: polyketides from an endophytic fungus of the genus Eupenicillium

Chemical investigations of the culture broth from an endophytic fungus Eupenicillium sp. have afforded two natural products phomoxins B (1) and C (2) as well as the previously reported fungal metabolite eupenoxide (3). Compounds 1 and 2 both contain a cyclic carbonate moiety that is rare among natural products. This paper reports the full spectroscopic characterisation of phomoxins B (1) and C (2) by NMR, UV, IR and MS data. All compounds were inactive against a panel of nosocomial microbes.     

Participation of the beta-hydroxyketone part for potent cytotoxicity of callystatin A, a spongean polyketide

The participation of the beta-hydroxyketone part of callystatin A in the potent cytotoxicity was analyzed through the analogue-syntheses and the assessment of their biological potencies. The ketonic carbonyl, the 19-hydroxyl, and the three asymmetric methyl groups located in the beta-hydroxyketone part of callystatin A were revealed to contribute to the cytotoxic potency, respectively. Moreover, the alpha,beta-unsaturated delta-lactone portion was shown to serve as a conclusive functional group for the cytotoxic activity.     

Ratjadone and leptomycin B block CRM1-dependent nuclear export by identical mechanisms

Research on the export of proteins and nucleic acids from the nucleus to the cytoplasm has greatly gained from the discovery that the actinobacterial toxin leptomycin B (LMB) specifically inactivates the export receptor chromosomal region maintenance 1 (CRM1). Recently, it was shown that myxobacterial cytotoxins, named ratjadones (RATs), also bind to CRM1 and inhibit nuclear export. However, the reaction mechanism of RATs was not resolved. Here, we show that LMB and RAT A employ the same molecular mechanism to inactivate CRM1. Alkylation of residue Cys528 of CRM1 determines both LMB and RAT sensitivity and prevents nuclear export of CRM1 cargo proteins.     

Assay of hybrid ribonuclease using a membrane filter-immobilized synthetic hybrid: application to the human leukemic cell

A method for assaying hybrid ribonuclease has been devised which utilizes as substrate the synthetic hybrid [3H]polyriboadenylic acid [poly(rA)]:polydeoxythymidylic acid [poly(dT)] immobilized on the solid matrix of nitrocellulose filters. The hybridization on filter of [3H]poly(rA) to poly(dT) has been explored in terms of efficacy of the process and the response of the product to RNase H. A pulse of uv irradiation of poly(dT) while in dry state on the filter increased its firm binding to the filter in a concentration-dependent manner, resulting in a concomitant increase of the yield of hybrid formation. The filter-immobilized hybrid was 95% resistant to RNase A but sensitive to RNase H. When stored in toluene in the cold the hybrid maintained its stability for over 6 months, as judged by its resistance to RNase A. The method offers a number of advantages over assays that use solution hybrids as substrates and was readily applicable in the screening of leukemic patients, in the leukocytes of which it has demonstrated increased RNase H levels.     

Participation of the conjugated diene part for potent cytotoxicity of callystatin A, a spongean polyketide

5-epi, 10-epi, 8-Deethyl, and 10-demethyl analogues of callystatin A, a potent cytotoxic spongean polyketide, were synthesized to elucidate structure-requirement for cytotoxic potency. Inversion of the asymmetric center at C-10 in callystatin A minimally affected the activity, while lack of the 10-methyl group in callystatin A decreased cytotoxicity. In addition, the C-5 epimer and the 8-deethyl analogue of callystatin A showed weaker cytotoxicity.     

Antibiotic properties of novel synthetic temporin A analogs and a cecropin A-temporin A hybrid peptide

Temporin A, 18 analogs, and a cecropin A-temporin A hybrid peptide were tested with antibiotic sensitive and resistant bacteria, fungi, human erythrocytes, and in clotting assays. Several peptides were active in these assays, and some analogs (D-TA, W1-TA, and Con-L4,G10) may be useful lead compounds for further antibiotics development. The activity of temporin A was found to be dependent upon several of its structural features, including amino acid composition and sequence, chirality, helicity, and positive charge.     

A hybrid synthetic pathway for butanol production by a hyperthermophilic microbe

Biologically produced alcohols are of great current interest for renewable solvents and liquid transportation fuels. While bioethanol is now produced on a massive scale, butanol has superior fuel characteristics and an additional value as a solvent and chemical feedstock. Butanol production has been demonstrated at ambient temperatures in metabolically-engineered mesophilic organisms, but the ability to engineer a microbe for in vivo high-temperature production of commodity chemicals has several distinct advantages. These include reduced contamination risk, facilitated removal of volatile products, and a wide temperature range to modulate and balance both the engineered pathway and the host׳s metabolism. We describe a synthetic metabolic pathway assembled from genes obtained from three different sources for conversion of acetyl-CoA to 1-butanol, and 1-butanol generation from glucose was demonstrated near 70 °C in a microorganism that grows optimally near 100 °C. The module could also be used in thermophiles capable of degrading plant biomass.     

Chemotherapeutic sensitization of leptomycin B resistant lung cancer cells by pretreatment with doxorubicin

The development of novel targeted therapies has become an important research focus for lung cancer treatment. Our previous study has shown leptomycin B (LMB) significantly inhibited proliferation of lung cancer cells; however, p53 wild type lung cancer cells were resistant to LMB. Therefore, the objective of this study was to develop and evaluate a novel therapeutic strategy to sensitize LMB-resistant lung cancer cells by combining LMB and doxorubicin (DOX). Among the different treatment regimens, pretreatment with DOX (pre-DOX) and subsequent treatment with LMB to A549 cells significantly decreased the 50% inhibitory concentration (IC50) as compared to that of LMB alone (4.4 nM vs. 10.6 nM, P<0.05). Analysis of cell cycle and apoptosis by flow cytometry further confirmed the cytotoxic data. To investigate molecular mechanisms for this drug combination effects, p53 pathways were analyzed by Western blot, and nuclear proteome was evaluated by two dimensional-difference gel electrophoresis (2D-DIGE) and mass spectrometry. In comparison with control groups, the levels of p53, phospho-p53 (ser15), and p21 proteins were significantly increased while phospho-p53 (Thr55) and survivin were significantly decreased after treatments of pre-DOX and LMB (P<0.05). The 2D-DIGE/MS analysis identified that sequestosome 1 (SQSTM1/p62) had a significant increase in pre-DOX and LMB-treated cells (P<0.05). In conclusion, our results suggest that drug-resistant lung cancer cells with p53 wild type could be sensitized to cell death by scheduled combination treatment of DOX and LMB through activating and restoring p53 as well as potentially other signaling pathway(s) involving sequestosome 1.     

A cyclic carbonate and related polyketides from a marine-derived fungus of the genus Phoma

Two metabolites, phomoxin and phomoxide, as well as the previously synthesized antibiotic eupenoxide, have been isolated from the fermentation broth of a marine-derived fungus of the genus Phoma (strain CNC-651). The new compounds are highly oxygenated polyketides of a new structural class. Phomoxin contains an unusual cyclic carbonate functionality that is rare among natural products. The structures of the new metabolites were assigned by spectroscopic methods that relied heavily on 2D NMR spectroscopic analysis.     

Natural abenquines and synthetic analogues: Preliminary exploration of their cytotoxic activity

In this study, we explore the cytotoxic activity of four natural abenquines (2a–d) and fourteen synthetic analogues (2e–j and 3a–h) against a panel of six human cancer cell lines using a SRB assay. It was found that most of the compounds revealed higher levels of cytotoxic activities than naturally occurring abenquines. The analogues carrying ethylpyrrolidinyl and ethylpyrimidinyl with either an acetyl group (2 h–i) or a benzoyl group (3f–g), were the most potent against all human cancer cell lines and displayed EC₅₀ between a range of 0.6–3.4 μM. Notably, of the compounds tested, compound 2i proved the most cytotoxic against both ovarian (A2780) and breast (MCF7) cells, showing EC₅₀ = 0.6 and 0.8 μM respectively. Likewise, the analogues 2i, 3f and 3 g showed strong activity against cell HT29 with EC₅₀ = 0.9 μM for these compounds.     

Anthracobic acids A and B, two polyketides, produced by an endophytic fungus Anthracobia sp

Two new polyketides, anthracobic acids A and B (1 and 2, resp.), were isolated from a cultured endophytic fungus, Anthracobia sp. The NMR study revealed that both anthracobic acids contain a carboxylic acid conjugated tetraene attached to an octahydronaphthalene moiety. Both compounds showed antimicrobial activity.     

Heterologous expression of the naphthocyclinone hydroxylase gene from Streptomyces arenae for production of novel hybrid polyketides

Streptomyces arenae produces at least four different isochromanequinone antibiotics, the naphthocyclinones, of which the - and -form are active against Gram-positive bacteria. The naphthocyclinone biosynthesis gene cluster was isolated from Streptomyces arenae DSM 40737 and by sequence analysis the minimal polyketide synthase genes and several genes encoding tailoring enzymes were identified. Southern blot analysis of the naphthocyclinone gene cluster indicated that a 3.5 kb BamHI fragment located approximately 9 kb downstream of the minimal PKS genes hybridizes to the schC hydroxylase DNA probe isolated from S. halstedii. Two complete and one incomplete open reading frames were identified on this fragment. Sequence analysis revealed strong homology to the genes of the actVA region of S. coelicolor, to several (suggested) hydroxylases and a putative FMN-dependent monooxygenase. The proposed hydroxylase, encoded by ncnH, could hydroxylate aloesaponarin II, a molecule that is produced by the actinorhodin minimal polyketide synthase in combination with the actinorhodin ketoreductase, aromatase and cyclase. Furthermore, this enzyme is capable of accepting additional polyketide core structures that contain a 5-hydroxy-1,4-naphthoquinone moiety as substrates which makes it an interesting tailoring enzyme for the modification of polyketide structures.     

Asitrilobins A and B: cytotoxic mono-THF annonaceous acetogenins from the seeds of Asimina triloba.

The seeds of Asimina triloba have yielded two novel cytotoxic mono-tetrahydrofuran (THF) Annonaceous acetogenins, asitrilobins A (1) and B (2). In addition, annonacin, asimin and asiminacin, which are known, and annomontacin and xylomaticin, which are known but are new in this species, were obtained. Compounds 1 and 2 have a relative stereochemical relationship of erythro/cis/threo across the mono-THF ring with its two flanking hydroxyls and they, thus, represent a new type of acetogenin. Their structures were established on the basis of chemical and spectral evidence. 1 and 2 showed potent bioactivities in the brine shrimp lethality test (BST) and among six human solid tumor cell lines with notable selectivity for the pancreatic cell line (MIA PaCa-2) at ten to one-hundred times the potency of adriamycin.     

The enzymatic activity of human cytotoxic T-lymphocyte granzyme A and cytolysis mediated by cytotoxic T-lymphocytes are potently inhibited by a synthetic antiprotease, FUT-175

The synthetic antiprotease, FUT-175 (6-amidino-2-naphthyl-4-guanidinobenzoate), was found to be an extraordinarily potent and rapid inhibitor of human Q31 cytotoxic T-lymphocyte granzyme A. The granzyme A was inhibited in a time-dependent manner with kobs/i = 430,000 +/- 80,000 M-1 s-1. Four other FUT-175 analogs were also found to be potent, rapid Q31 granzyme A inhibitors. All five compounds inhibited Q31 cytotoxic T-lymphocyte-mediated cytolysis of human JY lymphoma cells, but at concentrations far in excess of those needed for granzyme A inhibition. The data presented suggest that postmarketing surveillance of FUT-175 should include a review of possible immunosuppressive side-effects, such as increased susceptibility to viral infections and to neoplastic transformations.     

A synthetic entry to pladienolide B and FD-895

Presented within are syntheses of the pladienolide B and FD-895 side-chains, as well as models of the essential ring-closing metathesis and Stille coupling that will be used to complete their total syntheses. Several analogs of the pladienolide B side-chain were also prepared in order to evaluate the scope of the methodology and to create a library of structures that could be used for stereochemical and SAR analyses.