GE3, a novel hexadepsipeptide antitumor antibiotic, produced by Streptomyces sp. I. Taxonomy, production, isolation, physico-chemical properties, and biological activities

Pharmacological Targeting of Vacuolar H+-ATPase via Subunit V1G Combats Multidrug-Resistant Cancer

Multidrug resistance (MDR) in cancer remains a major challenge for the success of chemotherapy. Natural products have been a rich source for the discovery of drugs against MDR cancers. Here, we applied high-throughput cytotoxicity screening of an in-house natural product library against MDR SGC7901/VCR cells and identified that the cyclodepsipeptide verucopeptin demonstrated notable antitumor potency. Cytological profiling combined with click chemistry-based proteomics revealed that ATP6V1G directly interacted with verucopeptin. ATP6V1G, a subunit of the vacuolar H⁺-ATPase (v-ATPase) that has not been previously targeted, was essential for SGC7901/VCR cell growth. Verucopeptin exhibited strong inhibition of both v-ATPase activity and mTORC1 signaling, leading to substantial pharmacological efficacy against SGC7901/VCR cell proliferation and tumor growth in vivo. Our results demonstrate that targeting v-ATPase via its V1G subunit constitutes a unique approach for modulating v-ATPase and mTORC1 signaling with great potential for the development of therapeutics against MDR cancers.

Piperazic acid-containing natural products: structures and biosynthesis

Piperazic acid is a cyclic hydrazine and a non-proteinogenic amino acid found in diverse non-ribosomal peptide (NRP) and hybrid NRP–polyketide (PK) structures.

Characterization of the aurantimycin biosynthetic gene cluster and enhancing its production by manipulating two pathway-specific activators in Streptomyces aurantiacus JA 4570

Background

Aurantimycin (ATM), produced by Streptomyces aurantiacus JA 4570, is a potent antimicrobial and antitumor antibiotic. Although the chemical structure of ATM is highly distinctive and features a cyclohexadepsipeptide scaffold attached with a C₁₄ acyl side chain, little is known about its biosynthetic pathway and regulatory mechanism.

Results

In this work, we report the identification and characterization of the ATM biosynthetic gene cluster from S. aurantiacus JA 4570. Targeted inactivation of artG, coding for a NRPS enzyme, completely abolished ATM production, thereof demonstrating the target gene cluster (art) is responsible for ATM biosynthesis. Moreover, four NRPS adenylation (A) domains including a freestanding enzyme ArtC have been characterized in vitro, whose substrate specificities are consistent with in silico analysis. Further genetic analysis of the two regulatory genes artB and artX unambiguously suggested both of them play positive roles in ATM biosynthesis, and ATM-A production was thus rationally enhanced to about 2.5 fold via tandem overexpression of artB and artX in S. aurantiacus JA 4570.

Conclusions

These results will provide the basis for the understanding of precise mechanisms for ATM biosynthesis, and open the way for both rational construction of high-production ATM producer and orient-directed generation of designer ATM derivatives via synthetic biology strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0559-7) contains supplementary material, which is available to authorized users.

Identification and characterization of the biosynthetic gene cluster of polyoxypeptin A, a potent apoptosis inducer

BACKGROUND

Polyoxypeptin A was isolated from a culture broth of Streptomyces sp. MK498-98 F14, which has a potent apoptosis-inducing activity towards human pancreatic carcinoma AsPC-1 cells. Structurally, polyoxypeptin A is composed of a C₁₅ acyl side chain and a nineteen-membered cyclodepsipeptide core that consists of six unusual nonproteinogenic amino acid residues (N-hydroxyvaline, 3-hydroxy-3-methylproline, 5-hydroxypiperazic acid, N-hydroxyalanine, piperazic acid, and 3-hydroxyleucine) at high oxidation states.

RESULTS

A gene cluster containing 37 open reading frames (ORFs) has been sequenced and analyzed for the biosynthesis of polyoxypeptin A. We constructed 12 specific gene inactivation mutants, most of which abolished the production of polyoxypeptin A and only ΔplyM mutant accumulated a dehydroxylated analogue polyoxypeptin B. Based on bioinformatics analysis and genetic data, we proposed the biosynthetic pathway of polyoxypeptin A and biosynthetic models of six unusual amino acid building blocks and a PKS extender unit.

CONCLUSIONS

The identified gene cluster and proposed pathway for the biosynthesis of polyoxypeptin A will pave a way to understand the biosynthetic mechanism of the azinothricin family natural products and provide opportunities to apply combinatorial biosynthesis strategy to create more useful compounds.

Synthesis and biological evaluation of delavayin-C

The synthesis of a cyclic heptapeptide, delavayin-C, cyclo(gly-tyr-tyr-tyr-pro-val-pro) is described. The structure of this compound was established on the basis of analytical IR, ¹H NMR and FAB mass spectral data. The antibacterial and antifungal activities of this peptide are also described.

Biosynthetic chlorination of the piperazate residue in kutzneride biosynthesis by KthP

Kutznerides 2 and 8 of the cyclic hexadepsipeptide family of antifungal natural products from the soil actinomycete Kutzneria sp. 744 contain two sets of chlorinated residues, a 6,7-dichlorohexahydropyrroloindole moiety derived from dichlorotryptophan and a 5-chloropiperazate moiety, as well as a methylcyclopropylglycine residue that may arise from isoleucine via a cryptic chlorination pathway. Previous studies identified KtzD, KtzQ, and KtzR as three halogenases in the kutzneride pathway but left no candidate for installing the C5 chlorine on piperazate. On the basis of analysis of the complete genome sequence of Kutzneria, we now identify a fourth halogenase in the pathway whose gene is separated from the defined kutzneride cluster by 12 open reading frames. KthP (kutzneride halogenase for piperazate) is a mononuclear nonheme iron halogenase that acts on the piperazyl ring tethered by a thioester linkage to the holo forms of thiolation domains. MS analysis of the protein-bound product confirmed chlorination of the piperazate framework from the (3S)- but not the (3R)-piperazyl-S-pantetheinyl thiolation proteins. After thioesterase-mediated release, nuclear magnetic resonance was used to assign the free imino acid as (3S,5S)-5-chloropiperazate, distinct from the 3S,5R stereoisomer reported in the mature kutznerides. These results demonstrate that a fourth halogenase, KthP, is active in the kutzneride biosynthetic pathway and suggest further processing of the (3S,5S)-5-chloropiperazate during subsequent incorporation into the kutzneride depsipeptide frameworks.

Total synthesis of (+)-A83586C, (+)-kettapeptin and (+)-azinothricin: powerful new inhibitors of beta-catenin/TCF4- and E2F-mediated gene transcription

Herein we describe our asymmetric total syntheses of (+)-A83586C, (+)-kettapeptin and (+)-azinothricin. We also demonstrate that molecules of this class powerfully inhibit beta-catenin/TCF4- and E2F-mediated gene transcription within malignant human colon cancer cells at low drug concentrations.

Total synthesis of (+)-azinothricin and (+)-kettapeptin

Asymmetric total syntheses of (+)-azinothricin and (+)-kettapeptin have been completed through a common new pathway that exploits a highly chemoselective coupling reaction between the fully elaborated cyclodepsipeptide 5 and the glycal activated esters 3 and 4 at the final stages of both respective syntheses.

Synthesis and inhibitory effect on fat accumulation of (-)-ternatin derivatives modified in the beta-OH-D-Leu(7) moiety

An efficient synthesis of (-)-ternatin derivatives directed toward their SAR at the beta-OH-D-Leu(7) moiety and their biological activities against 3T3-L1 murine adipocytes are described.

Kettapeptin: Isolation, Structure Elucidation and Activity of a New Hexadepsipeptide Antibiotic from a Terrestrial Streptomyces sp

The ethyl acetate extract of the Streptomyces sp. isolate GW99/1572 exhibited significant biological activity against Gram-positive bacteria and delivered kettapeptin (1), a new hexadepsipeptide antibiotic of the azinothricin type. The structure was elucidated by various 1D and 2D NMR techniques, mass spectrometry and by comparison of the NMR data with those of closely related antibiotics. The absolute configuration of the compound was derived by crystal structure analysis and by comparison with the optical rotation data of related compounds.

Lipase TL-mediated kinetic tesolution of 5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol at low temperature: concise asymmetric synthesis of both enantiomers of a piperazic acid derivative

Lipase TL-mediated kinetic resolution of (+/-)-5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol (5) at low temperature proceeded to give the corresponding (S)-alcohol 5 and (R)-acetate 6 in quantitative yields with high enantiomeric purity. The addition of bases such as pyridine, DMAP, 2,4- and 2,6-lutidines, or triethylamine considerably enhanced the rate of kinetic resolution. The alcohol (S)-5 and the acetate (R)-6 were converted to piperazic acid derivatives (R)- and (S)-3, respectively, via the intramolecular Mitsunobu reaction as a key step.

Synthetic route to the GE3 cyclodepsipeptide

[reaction: see text] A reasonably efficient [2 + 2 + 2] fragment condensation strategy has been developed for assembling the cyclodepsipeptide sector of GE3 that involves 5-7. A Carpino HATU-mediated macrolactamization was used to close the 19-membered cyclodepsipeptide ring.

A synthetic strategy for the cyclodepsipeptide core of the antitumor antibiotic verucopeptin

[reaction: see text]. An efficient [2 + 2 + 2]-fragment condensation strategy is described for obtaining the cyclodepsipeptide core of verucopeptin. The 19-membered macrocycle was established through a Carpino HATU mediated macrolactamization, which proceeded in good yield under high-dilution conditions.

Anticancer activity of hydrophobic peptides from soy proteins

An anticancer peptide from soy protein was purified and isolated. Defatted soy protein was hydrolyzed with thermoase and hydrophobic peptides were extracted with ethanol. The peptide extract was fractionated by XAD-2 hydrophobic, gel filtration chromatography, and different C18 HPLCs. Anticancer activity of each fraction was assayed by measuring in vitro cytotoxicity on P388D1, a mouse monocyte macrophage cell line. IC50 value of a peptide fraction from Sephadex G-25 chromatography was 0.16 mg/ml. This peptide fraction at 1 mg/ml significantly affected cell cycle progression by arresting P388D1 at G2/M phases. Finally purified peptide from analytical C18 HPLC was nonapeptide of which molecular weight was 1157 Da and the sequence was X-Met-Leu-Pro-Ser-Tye-Ser-Pro-Tyr.