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Abstract Background New treatment strategies are emerging to target DNA damage response pathways in ovarian cancer. Our group has previously shown that the class I biased HDAC inhibitor romidepsin (FK228) induces DNA damage response and has potent cytotoxic effects in ovarian cancer cells. Here, we investigated newly discovered HDAC inhibitors, thailandepsin A (TDP-A) and thailandepsin B (TDP-B), to determine the effects on cell viability, apoptosis and DNA damage response in ovarian cancer cells. Methods FK228, TDP-A and TDP-B were tested in five ovarian cancer cell lines. Cellular viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Immunofluorescence assays were used to assess activated caspase 3. Western blots were performed to detect protein expression of PARP cleavage, pH2AX, P-glycoprotein and tubulin acetylation. Results Treatment with TDPs decreased cell viability at nanonomolar concentrations in four of the five ovarian cancer cell lines studied. Similar to FK228, both TDP compounds exerted minimal effects on NCI/ADR-RES ovarian cancer cells. Across the four cell lines sensitive to the TDPs, TDP-B consistently had a greater inhibitory effect than TDP-A on cell viability. TDP-B also had relatively greater effects on promoting cell apoptosis and induction of pH2AX (a mark of DNA damage response), than TDP-A. These antitumor effects of TDP-B were of similar magnitude to those induced by an equal concentration of FK228. Similar to FK228, the nanomolar concentrations of the TDPs had little effect on tubulin acetylation (a mark of class II HDAC6 inhibition). Conclusions The new small molecule HDAC inhibitors TDP-A and TDP-B are FK228 analogues that suppress cell viability and induce apoptosis at nanomolar drug concentrations. TDP-B showed the most similarity to the biological activity of FK228 with greater cytotoxic effects than TDP-A in vitro. Our results indicate that FK228-like small molecule class I HDAC-biased HDAC inhibitors have therapeutic potential for ovarian cancer.

DepR, a LysR-type transcriptional regulator encoded by the last gene of the putative min operon (orf21-20-19-depR) located at the downstream region of the anticancer agent FK228 biosynthetic gene cluster in Chromobacterium violaceum No. 968, positively regulates the biosynthesis of FK228. In this work, the mechanism underlining this positive regulation was probed by multiple approaches. Electrophoretic mobility shift assay (EMSA) and DNase I footprinting assay (DIFA) identified a conserved 35-nt DNA segment in the orf21-orf22 intergenic region where the purified recombinant DepR binds to. Quantitative reverse transcription PCR (RT-qPCR) and green fluorescent protein (GFP) promoter probe assays established that transcription of phasin gene orf22 increases in the depR deletion mutant of C. violaceum (CvΔdepR) compared to the wild-type strain. FK228 production in the orf22-overexpressed strain C. violaceum was reduced compared with the wild-type strain. DepR has two conserved cysteine residues C199 and C208 presumed to form a disulfide bridge upon sensing oxidative stress. C199X point mutations that locked DepR in a reduced conformation decreased the DNA-binding affinity of DepR; T232A or R278A mutation also had a negative impact on DNA binding of DepR. Complementation of CvΔdepR with any of those versions of depR carrying a single codon mutation was not able to restore FK228 production to the level of wild-type strain. All evidences collectively suggested that DepR positively regulates the biosynthesis of FK228 through indirect metabolic networking. [ABSTRACT FROM AUTHOR]

The article presents a comparative analysis of the large conformational change of the pseudomerohedrally twinned monoclinic structure of unfolded free nonactin upon the encapsulation of alkali metal ions. It observes the presence of symmetry-independent half-molecules of nonactin in the asymmetric unit residing on a crystallographic two-fold axis during crystallization. Also observed is the low-temperature high-precision ordered structure of free nonactin possessing an unfolded and more planar geometry but globular when encapsulating a cation.

Abstract: The diverse structures of polyketide natural products are reflected by the equally diverse polyketide biosynthetic enzymes, namely polyketide synthases (PKSs). Three major classes of PKSs are known—noniterative type I PKSs, iterative type II PKSs and acyl carrier protein‐independent type III PKSs, each of which consists of additional variants. One such variant is the noniterative type I PKS in which each PKS module lacks the cognate acyltransferase (AT) domain. The essential AT activity is instead provided by a discrete AT in trans. Termed “AT‐less” type I PKSs, the loading of the malonate extender units by the discrete AT enzyme LnmG to each of the AT‐less PKS modules of LnmI and LnmJ was confirmed experimentally for biosynthesis of the anticancer antibiotic leinamycin (LNM). The LNM PKS has since served as a model for the continuous discovery of numerous additional AT‐less type I PKSs incorporating variable extender units. However, biochemical characterization of AT‐less type I PKSs remains very limited, and the mechanism by which AT‐less type I PKSs accommodate multiple extender units is unknown. This chapter provides the protocols used to establish and characterize the LNM PKS. Application of these methods to other AT‐less type I PKSs should aid the biochemical characterization and hence possible exploitation of these unique PKSs for polyketide natural product structural diversity by combinatorial biosynthetic methods. [Copyright &y& Elsevier]

A 135,638 bp DNA region that encompasses the leinamycin (LNM) biosynthetic gene cluster was sequenced from Streptomyces atroolivaceus S-140. The boundaries of the lnm cluster were defined by systematic inactivation of open reading frames within the sequenced region. The lnm cluster spans 61.3 kb of DNA and consists of 27 genes encoding nonribosomal peptide synthetase (NRPS), polyketide synthase (PKS), hybrid NRPS-PKS, resistance, regulatory, and tailoring enzymes, as well as proteins of unknown function. A model for LNM biosynthesis is proposed, central to which is the LNM hybrid NRPS-PKS megasynthetase consisting of discrete (LnmQ and LnmP) and modular (LnmI) NRPS, acyltransferase-less PKS (LnmG, LnmI, and LnmJ), and PKS modules with unusual domain organization. These studies unveil an unprecedented architectural complexity for the LNM hybrid NRPS-PKS megasynthetase and set the stage to investigate the molecular basis for LNM biosynthesis. [Copyright &y& Elsevier]

In genetic crosses, HC-toxin production in the filamentous fungus Cochliobolus carbonum appears to be controlled by a single locus, TOX2. At the molecular level, TOX2 is composed of at least seven duplicated and coregulated genes involved in HC-toxin biosynthesis, export, and regulation. All copies of four of the TOX2 genes were previously mapped within a 540-kb stretch of DNA in strain SB111. Subsequently, an additional three TOX2 genes, TOXE, TOXF, and TOXG, have been discovered. In this paper we have mapped all copies of the new genes, a total of seven, and show that except for one of the two copies of TOXE, which was previously shown to be on a chromosome of 0.7 Mb in strain SB111, they are all linked to the previously known TOX2 genes within ∼600 kb of each other on a chromosome of 3.5 Mb. We show here that this chromosome also contains at least one non-TOX2 gene, EXG2, which encodes an exo-β1,3-glucanase. EXG2 is still present in strains that have undergone spontaneous deletion of up to ∼1.4 Mb of the 3.5-Mb chromosome. The results contribute to our understanding of the complex organization of the genes involved in HC-toxin biosynthesis and are consistent with the hypothesis that a reciprocal chromosomal translocation accounts for the pattern of distribution of the TOX2 genes in different C. carbonum isolates. [Copyright &y& Elsevier]

Abstract: The bacterial protease ClpP consists of 14 subunits that assemble into two stacked heptameric rings. The central degradation chamber can be accessed via axial pores. In free ClpP, these pores are obstructed by the N-terminal regions of the seven subunits at either end of the barrel. Acyldepsipeptides (ADEPs) are antibacterial compounds that bind in hydrophobic clefts surrounding the pore region, causing the pores to open up. The ensuing uncontrolled degradation of intracellular proteins is responsible for the antibiotic activity of ADEPs. Recently published X-ray structures yielded conflicting models regarding the conformation adopted by the N-terminal regions in the open state. Here, we use hydrogen/deuterium exchange (HDX) mass spectrometry to obtain complementary insights into the ClpP behavior with and without ADEP1. Ligand binding causes rigidification of the equatorial belt, accompanied by destabilization in the vicinity of the binding clefts. The N-terminal regions undergo rapid deuteration with only minor changes after ADEP1 binding, revealing a lack of stable H-bonding. Our data point to a mechanism where the pore opening mechanism is mediated primarily by changes in the packing of N-terminal nonpolar side chains. We propose that a “hydrophobic plug” causes pore blockage in ligand-free ClpP. ADEP1 binding provides new hydrophobic anchor points that nonpolar N-terminal residues can interact with. In this way, ADEP1 triggers the transition to an open conformation, where nonpolar moieties are clustered around the rim of the pore. This proposed mechanism helps reconcile the conflicting models that had been put forward earlier. [Copyright &y& Elsevier]

Histone deacetylase (HDAC) inhibitors are an emerging class of targeted therapy against cancers. Thailandepsin A (TDP-A) is a recently discovered class I HDAC inhibitor with broad anti-proliferative activities. In the present study, we aimed to investigate the potential of TDP-A in the treatment of breast cancer. We demonstrated that TDP-A inhibited cell proliferation and induced apoptosis in breast cancer cells at low nanomolar concentrations. TDP-A activated the intrinsic apoptotic pathway through increase of pro-apoptotic protein Bax, decrease of anti-apoptotic Bcl-2, and cleavage of caspase-3 and poly (ADP-ribose) polymerase (PARP). TDP-A also induced cell cycle arrest at the G2/M phase, and promoted the production of reactive oxygen species (ROS). We have successfully encapsulated TDP-A into our recently developed disulfide cross-linked micelles (DCMs), improving its water solubility and targeted delivery. TDP-A loaded DCMs (TDP-A/DCMs) possess the characteristics of high loading capacity (>20%, w/w), optimal and monodisperse particle size (16 ± 4 nm), outstanding stability with redox stimuli-responsive disintegration, sustained drug release, and preferential uptake in breast tumors. In the MDA-MB-231 breast cancer xenograft model, TDP-A/DCMs were more efficacious than the FDA-approved FK228 at well-tolerated doses. Furthermore, TDP-A/DCMs exhibited synergistic anticancer effects when combined with the proteasome inhibitor bortezomib (BTZ) loaded DCMs (BTZ/DCMs). Our results indicate that TDP-A nanoformulation alone or in combination with BTZ nanoformulation are efficacious against breast cancer. [ABSTRACT FROM AUTHOR]

Abstract: Background: Anaplastic thyroid cancer (ATC) remains refractory to available surgical and medical interventions. Histone deacetylase (HDAC) inhibitors are an emerging targeted therapy with antiproliferative activity in a variety of thyroid cancer cell lines. Thailandepsin A (TDP-A) is a novel class I HDAC inhibitor whose efficacy remains largely unknown in ATC. Therefore, we aimed to characterize the effect of TDP-A on ATC. Methods: Human-derived ATC cells were treated with TDP-A. IC50 was determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) rapid colorimetric assay, and cell proliferation was measured by viable cell count. Molecular mechanisms of cell growth inhibition were investigated by Western blot analysis of canonical apoptosis markers, intrinsic and extrinsic apoptosis regulators, and cell cycle regulatory proteins. Cell cycle staging was determined with propidium iodide flow cytometry. Results: TDP-A dose- and time-dependently reduced cell proliferation. Increased cleavage of the apoptosis markers Caspase-9, Caspase-3, and poly adenosine diphosphate ribose polymerase were observed with TDP-A treatment. Levels of the intrinsic apoptosis pathway proteins BAD, Bcl-XL, and BAX remained unchanged. Importantly, the extrinsic apoptosis activator cleaved Caspase-8 increased dose-dependently, and the antiapoptotic proteins Survivin and Bcl-2 decreased. Among the cell cycle regulatory proteins, levels of CDK inhibitors p21/WAF1 and p27/KIP increased. Flow cytometry showed that ATC cells were arrested in G2/M phase with diminished S phase after TDP-A treatment. Conclusions: TDP-A induces a notable dose- and time-dependent antiproliferative effect on ATC, which is mainly attributed to extrinsic apoptosis with concomitant cell cycle arrest. TDP-A therefore warrants further preclinical and clinical investigations. [Copyright &y& Elsevier]

Summary: ClpP is a cylindrical serine protease whose ability to degrade proteins is regulated by the unfoldase ATP-dependent chaperones. ClpP on its own can only degrade small peptides. Here, we used ClpP as a target in a high-throughput screen for compounds, which activate the protease and allow it to degrade larger proteins, hence, abolishing the specificity arising from the ATP-dependent chaperones. Our screen resulted in five distinct compounds, which we designate as Activators of Self-Compartmentalizing Proteases 1 to 5 (ACP1 to 5). The compounds are found to stabilize the ClpP double-ring structure. The ACP1 chemical structure was considered to have drug-like characteristics and was further optimized to give analogs with bactericidal activity. Hence, the ACPs represent classes of compounds that can activate ClpP and that can be developed as potential novel antibiotics. [ABSTRACT FROM AUTHOR]

Summary: In ClpXP and ClpAP complexes, ClpA and ClpX use the energy of ATP hydrolysis to unfold proteins and translocate them into the self-compartmentalized ClpP protease. ClpP requires the ATPases to degrade folded or unfolded substrates, but binding of acyldepsipeptide antibiotics (ADEPs) to ClpP bypasses this requirement with unfolded proteins. We present the crystal structure of Escherichia coli ClpP bound to ADEP1 and report the structural changes underlying ClpP activation. ADEP1 binds in the hydrophobic groove that serves as the primary docking site for ClpP ATPases. Binding of ADEP1 locks the N-terminal loops of ClpP in a β-hairpin conformation, generating a stable pore through which extended polypeptides can be threaded. This structure serves as a model for ClpP in the holoenzyme ClpAP and ClpXP complexes and provides critical information to further develop this class of antibiotics. [ABSTRACT FROM AUTHOR]

Summary: Disulfide bonds are rare in bacterial natural products, and the mechanism of disulfide bond formation in those products is unknown. Here we characterize a gene and its product critical for a disulfide bond formation in FK228 anticancer depsipeptide in Chromobacterium violaceum. Deletion of depH drastically reduced FK228 production, whereas complementation of the depH-deletion mutant with a copy of depH on a medium copy-number plasmid not only fully restored the FK228 production but also significantly increased the FK228 yield. Purified 6xHis-tagged DepH fusion protein in native form is a homodimer of 71.0 kDa, with each monomer containing one molecule of FAD. DepH efficiently converts an immediate FK228 precursor to FK228 in the presence of NADP+. We conclude that DepH is an FAD-dependent pyridine nucleotide-disulfide oxidoreductase, specifically and efficiently catalyzing a disulfide bond formation in FK228. [Copyright &y& Elsevier]

Presents a study to address the requirement for any pectin-degrading ability in pathogenesis by Cochliobolus carbonum. Methodology used to conduct study; Indication of findings; Discussion on results.

FK228 is an FDA-approved anticancer drug naturally produced by Chromobacterium violaceum No. 968 up to 19 mg/L in a pilot industry-scale batch fermentation. Here we report a genomics-guided discovery of Burkholderia thailandensis MSMB43 as a new and significantly better source of FK228. The genome of B. thailandensis MSMB43 was found to contain a functional biosynthetic gene cluster highly homologous to that of FK228 in C. violaceum No. 968, and the bacterium indeed produces authentic FK228. By simple fermentation in shaking flasks in a preferred M8 medium, B. thailandensis MSMB43 produced FK228 up to 67.7 mg/L; by fed-batch fermentation in a 20-L fermentor in M8 medium, B. thailandensis MSMB43 produced FK228 up to 115.9 mg/L, which is 95 fold higher than that of C. violaceum No. 968 under the same laboratory fermentation conditions. RT-PCR analysis indicated that the high FK228 yield of B. thailandensis MSMB43 was due to high expression of biosynthetic genes, represented by Bth_depA , during the fermentation process. Further genetic manipulation resulted in a recombinant strain, B. thailandensis MSMB43/pBMTL3- tdpR , which harbors a broad host-range vector expressing the thailandepsin biosynthetic pathway regulatory gene tdpR . This engineered strain produced up to 168.5 mg/L of FK228 in fed-batch fermentation in a 20-L fermentor in M8 medium. Therefore, the wild-type B. thailandensis MSMB43 or its engineered derivative could potentially be a good starting point for an industrial process to improve FK228 production for its expanding use in therapy.

The Chromobacterium sp. Panama bacterium has in vivo and in vitro anti-Plasmodium properties. To assess the nature of the Chromobacterium-produced anti-Plasmodium factors, chemical partition was conducted by bioassay-guided fractionation where different fractions were assayed for activity against asexual stages of P. falciparum. The isolated compounds were further partitioned by reversed-phase FPLC followed by size-exclusion chromatography; high resolution UPLC and ESI/MS data were then collected and revealed that the most active fraction contained a cyclic depsipeptide, which was identified as romidepsin. A pure sample of this FDA-approved HDAC inhibitor allowed us to independently verify this finding, and establish that romidepsin also has potent effect against mosquito stages of the parasite's life cycle. Genomic comparisons between C. sp. Panama and multiple species within the Chromobacterium genus further demonstrated a correlation between presence of the gene cluster responsible for romidepsin production and effective antiplasmodial activity. A romidepsin-null Chromobacterium spp. mutant loses its anti-Plasmodium properties by losing the ability to inhibit P. falciparum HDAC activity, and romidepsin is active against resistant parasites to commonly deployed antimalarials. This independent mode of action substantiates exploring a chromobacteria-based approach for malaria transmission-blocking.

Novel therapies for neuroendocrine (NE) cancers are desperately needed as they frequently present as metastatic disease and cause debilitating symptoms by secreting excessive hormones. Induction of Notch isoforms has a tumor suppressive effect in NE cancer cell lines, and we have observed that histone deacetylase inhibitors (HDACi) potently activate Notch. In this study, we describe the potential for Burkholderia thailandensis -derived class I HDACi thailandepsin A (TDP-A) as a Notch activator and therapeutic agent against NE cancer. IC 50 for TDP-A was determined to be 4-6 nM in NE cancer cell lines (BON, MZ-CRC-1, and TT) without cytotoxicity to lung fibroblasts. The binding characteristics of TDP-A to its target HDAC1 was examined using bioluminescence resonance energy transfer (BRET). Western blot and flow cytometry analysis showed that TDP-A induces cell cycle arrest and apoptosis in a dose-dependent manner. TDP-A dose-dependently activated the Notch pathway as measured by increasing functional CBF1-luciferase reporter signal and mRNA and protein expressions of Notch isoforms, which were attenuated by pretreatment with γ-secretase inhibitor DAPT. Furthermore, TDP-A lead to changes in expression level of downstream targets of Notch pathway and reduced expression of NE cancer markers. An in vivo study demonstrated that TDP-A suppressed NE cancer progression. These results show that TDP-A, as a Notch activator, is a promising agent against NE cancers., Competing Interests: CONFLICTS OF INTEREST The authors declare no conflicts of interest.

Purpose: Elevated intraocular pressure (IOP) in primary open-angle glaucoma (POAG) results from glaucomatous damage to the trabecular meshwork (TM). The glaucoma-associated factor TGFβ2 is increased in aqueous humor and TM of POAG patients. We hypothesize that histone acetylation has a role in dysregulated TGFβ2 expression., Methods: Protein acetylation was compared between nonglaucomatous TM (NTM) and glaucomatous TM (GTM) cells using Western immunoblotting (WB). Nonglaucomatous TM cells were treated with 10 nM thailandepsin-A (TDP-A), a potent histone deacetylase inhibitor for 4 days. Total and nuclear proteins, RNA, and nuclear protein-DNA complexes were harvested for WB, quantitative PCR (qPCR), and chromatin immunoprecipitation (ChIP) assays, respectively. Paired bovine eyes were perfused with TDP-A versus DMSO, or TDP-A versus TDP-A plus the TGFβ pathway inhibitor LY364947 for 5 to 9 days. Intraocular pressure, TM, and perfusate proteins were compared., Results: We found increased acetylated histone 3 and total protein acetylation in the GTM cells and TDP-A treated NTM cells. Chromatin immunoprecipitation assays showed that TDP-A induced histone hyperacetylation associated with the TGFβ2 promoter. This change of acetylation significantly increased TGFβ2 mRNA and protein expression in NTM cells. In perfusion-cultured bovine eyes, TDP-A increased TGFβ2 in the perfusate as well as elevated IOP. Histologic and immunofluorescent analyses showed increased extracellular matrix and cytoskeletal proteins in the TM of TDP-A treated bovine eyes. Cotreatment with the TGFβ pathway inhibitor LY364947 blocked TDP-A-induced ocular hypertension., Conclusions: Our results suggest that histone acetylation has an important role in increased expression of the glaucoma-associated factor TGFβ2. Histone hyperacetylation may be the initiator of glaucomatous damage to the TM.

Thailanstatin A (TST-A) is a potent antiproliferative natural product discovered by our group from Burkholderia thailandensis MSMB43 through a genome-guided approach. The limited supply of TST-A, due to its low titer in bacterial fermentation, modest stability and very low recovery rate during purification, has hindered the investigations of TST-A as an anticancer drug candidate. Here we report the significant yield improvement of TST-A and its direct precursor, thailanstatin D (TST-D), through metabolic engineering of the thailanstatin biosynthetic pathway in MSMB43. Deletion of tstP , which encodes a dioxygenase involved in converting TST-A to downstream products including FR901464 (FR), resulted in 58% increase of the TST-A titer to 144.7 ± 2.3 mg/L and 132% increase of the TST-D titer to 14.6 ± 0.5 mg/L in the fermentation broth, respectively. Deletion of tstR , which encodes a cytochrome P450 involved in converting TST-D to TST-A, resulted in more than 7-fold increase of the TST-D titer to 53.2 ± 12.1 mg/L in the fermentation broth. An execution of 90 L pilot-scale fed-batch fermentation of the tstP deletion mutant in a 120-L fermentor led to the preparation of 714 mg of TST-A with greater than 98.5% purity. The half-life of TST-D in a phosphate buffer was found to be at least 202 h, significantly longer than that of TST-A or FR, suggesting superior stability. However, the IC 50 values of TST-D against representative human cancer cell lines were determined to be greater than those of TST-A, indicating weaker antiproliferative activity. This work enabled us to prepare sufficient quantities of TST-A and TST-D for our ongoing translational research.

Tryprostatin A and B are indole alkaloid-based fungal products that inhibit mammalian cell cycle at the G 2 /M phase. They are biosynthetic intermediates of fumitremorgins produced by a complex pathway involving a nonribosomal peptide synthetase (FtmA), a prenyltransferase (FtmB), a cytochrome P450 hydroxylase (FtmC), an O-methyltransferase (FtmD), and several additional enzymes. A partial fumitremorgin biosynthetic gene cluster ( ftmABCD ) from Aspergillus sp. was reconstituted in Escherichia coli BL21(DE3) cells, with or without the co-expression of an Sfp-type phosphopantetheinyltransferase gene ( Cv_sfp ) from Chromobacterium violaceum No. 968. Several recombinant E. coli strains produced tryprostatin B up to 106 mg/l or tryprostatin A up to 76 mg/l in the fermentation broth under aerobic condition, providing an effective way to prepare those pharmaceutically important natural products biologically.

As a ubiquitous second messenger, cyclic dimeric GMP (c-di-GMP) has been studied in numerous bacteria. The oral spirochete Treponema denticola, a periodontal pathogen associated with human periodontitis, has a complex c-di-GMP signaling network. However, its function remains unexplored. In this report, a PilZ-like c-di-GMP binding protein (TDE0214) was studied to investigate the role of c-di-GMP in the spirochete. TDE0214 harbors a PilZ domain with two signature motifs: RXXXR and DXSXXG. Biochemical studies showed that TDE0214 binds c-di-GMP in a specific manner, with a dissociation constant (Kd) value of 1.73 μM, which is in the low range compared to those of other reported c-di-GMP binding proteins. To reveal the role of c-di-GMP in T. denticola, a TDE0214 deletion mutant (TdΔ214) was constructed and analyzed in detail. First, swim plate and single-cell tracking analyses showed that TdΔ214 had abnormal swimming behaviors: the mutant was less motile and reversed more frequently than the wild type. Second, we found that biofilm formation of TdΔ214 was substantially repressed (∼6.0-fold reduction). Finally, in vivo studies using a mouse skin abscess model revealed that the invasiveness and ability to induce skin abscesses and host humoral immune responses were significantly attenuated in TdΔ214, indicative of the impact that TDE0214 has on the virulence of T. denticola. Collectively, the results reported here indicate that TDE0214 plays important roles in motility, biofilm formation, and virulence of the spirochete. This report also paves a way to further unveil the roles of the c-di-GMP signaling network in the biology and pathogenicity of T. denticola.

Purpose: Elevated intraocular pressure (IOP) is a major risk factor in glaucoma. Various changes in the trabecular meshwork (TM) are responsible for elevated IOP. Glucocorticoids (GCs) increase IOP and mediate biochemical changes in the TM, similar to those associated with primary open-angle glaucoma (POAG). There are differences in steroid responsiveness among the population. Approximately 40% of individuals significantly elevate IOP (i.e., responders) upon GC administration, while others do not (i.e., nonresponders). The responders are at higher risk of developing POAG compared to the nonresponders. In addition, almost all POAG patients are steroid responders. GC responsiveness is regulated by the relative levels of the active GC receptor alpha (GRα) and the alternatively spliced dominant negative regulator isoform GRβ. Glaucomatous TM cell strains have a lower GRβ-GRα ratio compared to normal TM cells, making them more sensitive to GCs. Our purpose was to investigate the role of a special class of natural products called thailanstatins (TSTs) in GR alternative splicing and GC response in cultured human TM cells., Methods: Quantitative RT-PCR and Western immunoblotting were used to study the effect of TSTs on GRβ-GRα ratios in human TM cell strains. Effects of TSTs on dexamethasone (DEX) responsiveness were assessed by GRE-luciferase reporter activity assay and fibronectin (FN) induction in TM cells., Results: TSTs increased the GRβ-GRα ratio in TM cells. Increased GRβ-GRα ratios were associated with decreased DEX-mediated FN induction and GRE-luciferase activity., Conclusions: TSTs modulate the GR splicing process to enhance GRβ levels and thereby decrease the GC response in cultured human TM cells. These TSTs, or similar compounds, may potentially be new glaucoma therapeutic agents.

Mining the genome sequence of Burkholderia thailandensis MSMB43 revealed a cryptic biosynthetic gene cluster resembling that of FR901464 (4), a prototype spliceosome inhibitor produced by Pseudomonas sp. No. 2663. Transcriptional analysis revealed a cultivation condition in which a regulatory gene of the cryptic gene cluster is adequately expressed. Consequently, three new compounds, named thailanstatins A (1), B (2), and C (3), were isolated from the fermentation broth of B. thailandensis MSMB43. Thailanstatins are proposed to be biosynthesized by a hybrid polyketide synthase-nonribosomal peptide synthetase pathway. They differ from 4 by lacking an unstable hydroxyl group and by having an extra carboxyl moiety; those differences endow thailanstatins with a significantly greater stability than 4 as tested in phosphate buffer at pH 7.4. In vitro assays showed that thailanstatins inhibit pre-mRNA splicing as potently as 4, with half-maximal inhibitory concentrations in the single to sub-μM range. Cell culture assays indicated that thailanstatins also possess potent antiproliferative activities in representative human cancer cell lines, with half-maximal growth inhibitory concentrations in the single nM range. This work provides new chemical entities for research and development and new structure-activity information for chemical optimization of related spliceosome inhibitors.

THE TITLE COMPOUND [SYSTEMATIC NAME: (3S,8aS)-3-isopropyl-hexa-hydro-pyrrolo-[1,2-a]pyrazine-1,4-dione], C(10)H(16)N(2)O(2),, is a newly isolated cyclic dipeptide from Burkholderia thailandensis MSMB43. There are two independent mol-ecules in the asymmetric unit. Two C atoms and their attached H atoms in the five-membered ring of one of the mol-ecules are disordered over two sets of sites in a 0.715 (5):0.285 (5) ratio. The two independent mol-ecules have the same configuration and the absolute configurations of the chiral centers were determined based on the observation of anomalous dispersion. In the crystal, two types of N-H⋯O hydrogen bonds link pairs of independent mol-ecules.

There is growing interest in discovery of novel bioactive natural products from Burkholderia thailandensis. Here we report a significantly improved genome sequence and reannotation of Burkholderia thailandensis MSMB43, which will facilitate the discovery of new natural products through genome mining and studies of the metabolic versatility of this bacterium.

FK228 [systematic name: (1S,4S,7Z,10S,16E,21R)-7-ethyl-idene-4,21-di(propan-2-yl)-2-oxa-12,13-dithia-5,8,20,23-tetra-za--bicyclo[8.7.6]tricos-16-ene-3,6,9,19,22-pentone], C(24)H(36)N(4)O(6)S(2), also known as FR901228, depsipeptide, NSC 630176, romidepsin, and marketed as Istodax by Celgene Corporation, is crystallized from ethyl acetate in P2(1) as compared to the absolute configuration of FK228, first crystallized from methanol in P2(1)2(1)2(1) [Shigematsu et al. (1994 ▶). J. Anti-biot.47, 311-314]. A slight difference is observed between the absolute configuration of FK228 and the present structure. The molecular structure is stabilized by intramolecular N-H⋯O hydrogen bonds. In the crystal, molecules are linked via N-H⋯O hydrogen bonds.

Three new bicyclic depsipeptides, which are related to the previously reported thailandepsins A ( 1 ), B ( 2 ) and C ( 3 ), were discovered from the culture broth of Burkholderia thailandensis E264 when supplemented with amino acid precursors, and were subsequently named as thailandepsins D ( 4 ), E ( 5 ) and F ( 6 ), respectively. Enzyme assays showed that 1-6 are potent histone deacetylase (HDAC) inhibitors, particularly toward HDAC1 which represents class I human HDACs.

Histone deacetylase (HDAC) inhibitors have emerged as a new class of anticancer drugs, with one synthetic compound, SAHA (vorinostat, Zolinza; 1), and one natural product, FK228 (depsipeptide, romidepsin, Istodax; 2), approved by FDA for clinical use. Our studies of FK228 biosynthesis in Chromobacterium violaceum no. 968 led to the identification of a cryptic biosynthetic gene cluster in the genome of Burkholderia thailandensis E264. Genome mining and genetic manipulation of this gene cluster further led to the discovery of two new products, thailandepsin A (6) and thailandepsin B (7). HDAC inhibition assays showed that thailandepsins have selective inhibition profiles different from that of FK228, with comparable inhibitory activities to those of FK228 toward human HDAC1, HDAC2, HDAC3, HDAC6, HDAC7, and HDAC9 but weaker inhibitory activities than FK228 toward HDAC4 and HDAC8, the latter of which could be beneficial. NCI-60 anticancer screening assays showed that thailandepsins possess broad-spectrum antiproliferative activities with GI50 for over 90% of the tested cell lines at low nanomolar concentrations and potent cytotoxic activities toward certain types of cell lines, particularly for those derived from colon, melanoma, ovarian, and renal cancers. Thailandepsins thus represent new naturally produced HDAC inhibitors that are promising for anticancer drug development.

Functional cross talk between fatty acid biosynthesis and secondary metabolism has been discovered in several cases in microorganisms; none of them, however, involves a modular biosynthetic enzyme. Previously, we reported a hybrid modular nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) pathway for the biosynthesis of FK228 anticancer depsipeptide in Chromobacterium violaceum strain 968. This pathway contains two PKS modules on the DepBC enzymes that lack a functional acyltransferase (AT) domain, and no apparent AT-encoding gene exists within the gene cluster or its vicinity. We report here that, through reconstitution of the FK228 biosynthetic pathway in Escherichia coli cells, two essential genes, fabD1 and fabD2, both encoding a putative malonyl coenzyme A (CoA) acyltransferase component of the fatty acid synthase complex, are positively identified to be involved in FK228 biosynthesis. Either gene product appears sufficient to complement the AT-less PKS modules on DepBC for polyketide chain elongation. Concurrently, a gene (sfp) encoding a putative Sfp-type phosphopantetheinyltransferase was identified to be necessary for FK228 biosynthesis as well. Most interestingly, engineered E. coli strains carrying variable genetic components produced significant levels of FK228 under both aerobic and anaerobic cultivation conditions. Discovery of the trans complementation of modular PKSs by housekeeping ATs reveals natural product biosynthesis diversity. Moreover, demonstration of anaerobic production of FK228 by an engineered facultative bacterial strain validates our effort toward the engineering of novel tumor-targeting bioagents.

The biosynthetic gene cluster of FK228, an FDA-approved anticancer natural product, was identified and sequenced previously. The genetic organization of this gene cluster has now been delineated through systematic gene deletion and transcriptional analysis. As a result, the gene cluster is redefined to contain 12 genes: depA through depJ, depM, and a newly identified pathway regulatory gene, depR.