Novel macrolactam compound produced by the heterologous expression of a large cryptic biosynthetic gene cluster of Streptomyces rochei IFO12908

In the course of our studies on the heterologous expression of giant biosynthetic genes, we discovered a novel cryptic biosynthetic gene cluster in Streptomyces rochei IFO12908. During our efforts to express biosynthetic genes using the host SUKA strain derived from Streptomyces avermitilis, a novel polyene macrolactam compound designated as JBIR-156 was produced. We report herein the cloning and heterologous expression of the JBIR-156 biosynthetic gene cluster, and the isolation, structure determination, and cytotoxic activity of this novel compound

In vitro Cas9-assisted editing of modular polyketide synthase genes to produce desired natural product derivatives

Several different genetic strategies have been reported for the modification of polyketide synthases but the highly repetitive modular structure makes this difficult. Here the authors report on an adapted Cas9 reaction and Gibson assembly to edit a target region of the polyketide synthases gene in vitro

Synthesis of Spiromamakone A Benzo Analogues via Double Oxa-Michael Addition of 1,8-Dihydroxynaphthalene

Two benzo analogues of cytotoxic spiromamakone A, comprising carbon atoms with the same oxidation state and unsaturation degree as those of the natural products, are synthesized and biologically evaluated. Substitution of α,α′-dioxoketene dithioacetals, derived from 1,3-cyclopentanediones with protected (2-formylphenyl)­magnesium bromide and 1,8-dihydroxynaphthalene, followed by deprotection, generated these analogues via an intramolecular aldol reaction. The cytotoxicity of benzo analogues and synthetic intermediates against cervical carcinoma HeLa cells shows the necessity of the 4-cyclopentene-1,3-dione moiety for biological activity

New azodyrecins identified by a genome mining-directed reactivity-based screening

Only a few azoxy natural products have been identified despite their intriguing biological activities. Azodyrecins D-G, four new analogs of aliphatic azoxides, were identified from two Streptomyces species by a reactivity-based screening that targets azoxy bonds. A biological activity evaluation demonstrated that the double bond in the alkyl side chain is important for the cytotoxicity of azodyrecins. An in vitro assay elucidated the tailoring step of azodyrecin biosynthesis, which is mediated by the S-adenosylmethionine (SAM)-dependent methyltransferase Ady1. This study paves the way for the targeted isolation of aliphatic azoxy natural products through a genome-mining approach and further investigations of their biosynthetic mechanisms

Foxo3a Inhibitors of Microbial Origin, JBIR-141 and JBIR-142

JBIR-141 (<b>1</b>) and JBIR-142 (<b>2</b>) were discovered as potent Foxo3a inhibitors that consist of three quite unique substructures, a 1-((dimethylamino)­ethyl)-5-methyl-4,5-dihydrooxazole-4-carboxylic acid that is originated from Ala-Thr amino acid residues, a 3-acetoxy-4-amino-7-(hydroxy­(nitroso)­amino)-2,2-dimethylheptanoic acid, and an α-acyl tetramic acid fused with a 2-methylpropan-1-ol moiety. Their structures involving absolute configurations were determined by spectroscopic data, chemical degradation, anisotropy methods, and LC–MS analyses of diastereomeric derivatives. Compounds <b>1</b> and <b>2</b> exhibited specific inhibition against Foxo3a transcriptional activity with IC₅₀ values of 23.1 and 166.2 nM, respectively

NK314, a Topoisomerase II Inhibitor That Specifically Targets the α Isoform*

Topoisomerase II (Top2) is a ubiquitous nuclear enzyme that relieves torsional stress in chromosomal DNA during various cellular processes. Agents that target Top2, involving etoposide, doxorubicin, and mitoxantrone, are among the most effective anticancer drugs used in the clinic. Mammalian cells possess two genetically distinct Top2 isoforms, both of which are the target of these agents. Top2α is essential for cell proliferation and is highly expressed in vigorously growing cells, whereas Top2β is nonessential for growth and has recently been implicated in treatment-associated secondary malignancies, highlighting the validity of a Top2α-specific drug for future cancer treatment; however, no such agent has been hitherto reported. Here we show that NK314, a novel synthetic benzo[c]phenanthridine alkaloid, targets Top2α and not Top2β in vivo. Unlike other Top2 inhibitors, NK314 induces Top2-DNA complexes and double-strand breaks (DSBs) in an α isoform-specific manner. Heterozygous disruption of the human TOP2α gene confers increased NK314 resistance, whereas TOP2β homozygous knock-out cells display increased NK314 sensitivity, indicating that the α isoform is the cellular target. We further show that the absence of Top2β does not alleviate NK314 hypersensitivity of cells deficient in non-homologous end-joining, a critical pathway for repairing Top2-mediated DSBs. Our results indicate that NK314 acts as a Top2α-specific poison in mammalian cells, with excellent potential as an efficacious and safe chemotherapeutic agent. We also suggest that a series of human knock-out cell lines are useful in assessing DNA damage and repair induced by potential topoisomerase-targeting agents