Copper-nuclease efficiency correlates with cytotoxicity for the 4-methoxypyrrolic natural products

Transition metal complexes as self-activating chemical nucleases: proficient DNA cleavage without any exogenous redox agents

Chemical nucleases have found potential applications in the research fields of chemistry, biotechnology and medicine. A variety of metal complexes have been explored as good to outstanding therapeutic agents for DNA cleavage activity most likely via hydrolytic, oxidative or photoinduced cleavage pathways. However, most of these DNA cleaving agents lack their utility in in vivo applications due to their dependence on exogenous oxidants or reductants to achieve successful DNA damage. In view of addressing these issues, the development of metal complexes/organic molecules serving as self-activating chemical nucleases has received growing attention from researchers. In only the last decade, this field has dramatically expanded for the usage of chemical nucleases as therapeutic agents for DNA damage. The present study provides an overview of the opportunities and challenges in the design and development of self-activating chemical nucleases as improved DNA therapeutic candidates in the absence of an external redox agent. The reports on DNA nuclease activity via self-activation, especially with copper, zinc and iron complexes, and their mechanistic investigation have been discussed in this review article.

Investigating Alkylated Prodigiosenes and Their Cu(II)-Dependent Biological Activity: Interactions with DNA, Antimicrobial and Photoinduced Anticancer Activity

Prodigiosenes are a family of red pigments with versatile biological activity. Their tripyrrolic core structure has been modified many times in order to manipulate the spectrum of activity. We have been looking systematically at prodigiosenes substituted at the C ring with alkyl chains of different lengths, in order to assess the relevance of this substituent in a context that has not been investigated before for these derivatives: Cu(II) complexation, DNA binding, self‐activated DNA cleavage, photoinduced cytotoxicity and antimicrobial activity. Our results indicate that the hydrophobic substituent has a clear influence on the different aspects of their biological activity. The cytotoxicity study of the Cu(II) complexes of these prodigiosenes shows that they exhibit a strong cytotoxic effect towards the tested tumor cell lines. The Cu(II) complex of a prodigiosene lacking any alkyl chain excelled in its photoinduced anticancer activity, thus demonstrating the potential of prodigiosenes and their metal complexes for an application in photodynamic therapy (PDT). Two derivatives along with their Cu(II) complexes showed also antimicrobial activity against Staphylococcus aureus strains.

Bioactive Compounds from Marine Heterobranchs

The natural products of heterobranch molluscs display a huge variability both in structure and in their bioactivity. Despite the considerable lack of information, it can be observed from the recent literature that this group of animals possesses an astonishing arsenal of molecules from different origins that provide the molluscs with potent chemicals that are ecologically and pharmacologically relevant. In this review, we analyze the bioactivity of more than 450 compounds from ca. 400 species of heterobranch molluscs that are useful for the snails to protect themselves in different ways and/or that may be useful to us because of their pharmacological activities. Their ecological activities include predator avoidance, toxicity, antimicrobials, antifouling, trail-following and alarm pheromones, sunscreens and UV protection, tissue regeneration, and others. The most studied ecological activity is predation avoidance, followed by toxicity. Their pharmacological activities consist of cytotoxicity and antitumoral activity; antibiotic, antiparasitic, antiviral, and anti-inflammatory activity; and activity against neurodegenerative diseases and others. The most studied pharmacological activities are cytotoxicity and anticancer activities, followed by antibiotic activity. Overall, it can be observed that heterobranch molluscs are extremely interesting in regard to the study of marine natural products in terms of both chemical ecology and biotechnology studies, providing many leads for further detailed research in these fields in the near future.

The Effects of the Alkaloid Tambjamine J on Mice Implanted with Sarcoma 180 Tumor Cells

The tambjamines are a small group of bipyrrolic alkaloids that, collectively, display a significant range of biological activities including antitumor, antimicrobial and immunosuppressive properties. The key objective of the present study was to undertake preclinical assessments of tambjamine J (T-J) so as to determine its in vivo antitumor effects. To that end, sarcoma 180 cells were transplanted in mice and the impacts of the title compound then evaluated using a range of protocols including hematological, biochemical, histopathological, genotoxic and clastogenic assays. As a result it was established that this alkaloid has a significant therapeutic window and effectively reduces tumor growth (by 40 % and 79 % at doses of 10 and 20 mg/kg/day, respectively). In this regard it displays similar antitumor activity to the anticancer agent cyclophosphamide and alters animal weight in an analogous manner.

Dinuclear copper(II) complexes with derivative triazine ligands as biomimetic models for catechol oxidases and nucleases

The research reported herein focuses on the synthesis of two new Cu(II) complexes {[Cu₂(2-X-4,6-bis(di-2-picolylamino)-1,3,5-triazine], with X = butane-1,4-diamine (2) or N-methylpyrenylbutane-1,4-diamine (3)}, the latter with a pyrene group as a possible DNA intercalating agent. The structure of complex (3) was determined by X-ray crystallography and shows the dinuclear {Cu^II(μ-OCH₃)₂Cu^II} unit in which the Cu^II···Cu^II distance of 3.040 Å is similar to that of 2.97 Å previously found for 1, which contains a {Cu^II(μ-OH)₂Cu^II} structural unit. Complexes (2) and (3) were also characterized in spectroscopic and electrochemical studies, and catecholase-like activity were performed for both complexes. The kinetic parameters obtained for the oxidation of the model substrate 3,5-di-tert-butylcatechol revealed that the insertion of the spacer butane-1,4-diamine and the pyrene group strongly contributes to increasing the catalytic efficiency of these systems. In fact, K_ass becomes significantly higher, indicating that these groups influence the interaction between the complex and the substrate. These complexes also show DNA cleavage under mild conditions with moderate reaction times. The rate of cleavage (k_cat) indicated that the presence of butane-1,4-diamine and pyrene increased the activity of both complexes. The reaction mechanism seems to have oxidative and hydrolytic features and the effect of DNA groove binding compounds and circular dichroism indicate that all complexes interact with plasmid DNA through the minor groove. High-resolution DNA cleavage assays provide information on the interaction mechanism and for complex (2) a specificity for the unpaired hairpin region containing thymine bases was observed, in contrast to (3).

The carbon chain-selective adenylation enzyme TamA: the missing link between fatty acid and pyrrole natural product biosynthesis

TamA is the adenylating enzyme that selects and activates fatty acids for tambjamine biosynthesis.

The marine bacterium Pseudoalteromonas tunicata produces the bipyrrole antibiotic tambjamine YP1. This natural product is built from common amino acid and fatty acid building blocks in a biosynthetic pathway that is encoded in the tam operon which contains 19 genes. The exact role that each of these Tam proteins plays in tambjamine biosynthesis is not known. Here, we provide evidence that TamA initiates the synthesis and controls the chain length of the essential tambjamine fatty amine tail. Sequence analysis suggests the unusual TamA is comprised of an N-terminal adenylation (ANL) domain fused to a C-terminal acyl carrier protein (ACP). Mass spectrometry analysis of recombinant TamA revealed the surprising presence of bound C11 and C12 acyl-adenylate intermediates. Acylation of the ACP domain was observed upon attachment of the phosphopantetheine (4′-PP) arm to the ACP. We also show that TamA can transfer fatty acids ranging in chain length from C6–C13 to an isolated ACP domain. Thus TamA bridges the gap between primary and secondary metabolism by linking fatty acid and pyrrole biosynthetic pathways.

Synthesis of N-acyl amide natural products using a versatile adenylating biocatalyst

TamA is the enzyme that controls the acyl chain length of the tambjamine natural products. Here we show that the catalytic ANL domain of TamA can be used to prepare a range of N-acyl amides.

Natural products are secondary metabolites produced by many different organisms such as bacteria, fungi and plants. These biologically active molecules have been widely exploited for clinical application. Here we investigate TamA, a key enzyme from the biosynthetic pathway of tambjamine YP1, an acylated bipyrrole that is produced by the marine microorganism Pseudoalteromonas tunicata. TamA is a didomain enzyme composed of a catalytic adenylation (ANL) and an acyl carrier protein (ACP) domain that together control the fatty acid chain length of the YP1. Here we show that the TamA ANL domain alone can be used to generate a range of acyl adenylates that can be captured by a number of amines thus leading to the production of a series of fatty N-acyl amides. We exploit this biocatalytic promiscuity to produce the recently discovered class of N-acyl histidine amide natural products from Legionella pneumophila.

Isolation and characterization of tambjamine MYP1, a macrocyclic tambjamine analogue from marine bacterium Pseudoalteromonas citrea

Tambjamines are natural products that consist of a conserved bipyrrole core functionalized with different imines giving rise to many derivatives. The core structure of tambjamines allows ion coordination through the nitrogen atoms, which is a key aspect in many of their observed antimicrobial, anticancer, and antimalarial bioactivities. Minor variances in the compound structure have a considerable impact on the potency of these activities, so identifying new analogues is valuable for maximizing tambjamine biological potential. In this work, we describe the isolation and structure elucidation of the first naturally occurring macrocyclized tambjamine, tambjamine MYP1, from the marine microbe Pseudoalteromonas citrea. We also compare the apparent pK _a of cyclic and linear tambjamine analogues and discuss how structural strain may effect the compound's ion coordination abilities.

Copper(II) complexes of N3O tripodal ligands appended with pyrene and polyamine groups: Anti-proliferative and nuclease activities

A series of tripodal ligands based on the 2-tert-butyl-4-R-6-phenol was synthesized, where R=aldehyde (HL¹), R=putrescine-pyrene (HL²) and R=putrescine (HL³). A dinucleating ligand wherein a putrescine group connects two tripodal moieties was also prepared (H₂L⁴). The corresponding copper complexes (1, 2, 3, and 4, respectively) were prepared and characterized. We determined the phenol's pKas in the range 2.47-3.93. The DNA binding constants were determined at 6×10⁶, 5.5×10⁵ and 2.7×10⁶ for 2, 3 and 4, respectively. The complexes display a metal-centered reduction wave at E_p^c,red=-0.45 to -0.5V vs. saturated calomel electrode, as well as a ligand-centered oxidation wave above 0.57V at pH7. In the presence of ascorbate they promote an efficient cleavage of DNA, with for example a concentration required to cleave 50% of supercoiled DNA of 1.7μM for 2. The nuclease activity is affected by the nature of the R group: putrescine-pyrene≈bis-ligating>putrescine>aldehyde. The species responsible for strand scission is the hydroxyl radical. The cytotoxicity of the complexes was evaluated on bladder cancer cell lines sensitive or resistant to cis-platin. The IC₅₀ of complexes 2 and 4 span over a short range (1.3-2μM) for the two cell lines. They are lower than those of the other complexes (3.1-9.7μM) and cis-platin. The most active compounds block the cell cycle at the G0/1 phase and promote apoptosis.

Marine Mollusk-Derived Agents with Antiproliferative Activity as Promising Anticancer Agents to Overcome Chemotherapy Resistance

The chemical investigation of marine mollusks has led to the isolation of a wide variety of bioactive metabolites, which evolved in marine organisms as favorable adaptations to survive in different environments. Most of them are derived from food sources, but they can be also biosynthesized de novo by the mollusks themselves, or produced by symbionts. Consequently, the isolated compounds cannot be strictly considered as "chemotaxonomic markers" for the different molluscan species. However, the chemical investigation of this phylum has provided many compounds of interest as potential anticancer drugs that assume particular importance in the light of the growing literature on cancer biology and chemotherapy. The current review highlights the diversity of chemical structures, mechanisms of action, and, most importantly, the potential of mollusk-derived metabolites as anticancer agents, including those biosynthesized by mollusks and those of dietary origin. After the discussion of dolastatins and kahalalides, compounds previously studied in clinical trials, the review covers potentially promising anticancer agents, which are grouped based on their structural type and include terpenes, steroids, peptides, polyketides and nitrogen-containing compounds. The "promise" of a mollusk-derived natural product as an anticancer agent is evaluated on the basis of its ability to target biological characteristics of cancer cells responsible for poor treatment outcomes. These characteristics include high antiproliferative potency against cancer cells in vitro, preferential inhibition of the proliferation of cancer cells over normal ones, mechanism of action via nonapoptotic signaling pathways, circumvention of multidrug resistance phenotype, and high activity in vivo, among others. The review also includes sections on the targeted delivery of mollusk-derived anticancer agents and solutions to their procurement in quantity.

Synthesis and characterization of FeIII(μ-OH)ZnII complexes: effects of a second coordination sphere and increase in the chelate ring size on the hydrolysis of a phosphate diester and DNA

Effects of a second coordination sphere and of the chelate ring size in Fe^III(μ-OH)Zn^II complexes properties and catalysis.

Synthesis and anticancer activity of prodigiosenes bearing C-ring esters and amides

Ten novel prodigiosenes with anticancer activity.

Targeting survivin with prodigiosin isolated from cell wall of Serratia marcescens induces apoptosis in hepatocellular carcinoma cells

BACKGROUND

Abnormal activation of the Wnt/β-catenin signaling pathway increases survivin expression that is involved in hepatocarcinogenesis. Therefore, downregulation of survivin may provide an attractive strategy for treatment of hepatocellular carcinoma. In this regard, little is known about the anticancer effects of prodigiosin isolated from cell wall of Serratia marcescens on the survivin expression and induction of apoptosis in hepatocellular carcinoma cells.

METHODS

Human hepatocellular carcinoma (HepG2) cells were treated with 100-, 200-, 400-, and 600-nM prodigiosin after which morphology of cells, cell number, growth inhibition, survivin expression, caspase-3 activation, and apoptotic rate were evaluated by inverted microscope, hemocytometer, MTT assay, RT-PCR, fluorometric immunosorbent enzyme assay, and flow cytometric analysis, respectively.

RESULTS

Prodigiosin changed morphology of cells to apoptotic forms and disrupted cell connections. This compound significantly increased growth inhibition rate and decreased metabolic activity of HepG2 cells in a dose- and time-dependent manner. After 24-, 48-, and 72-h treatments with prodigiosin at concentrations ranging from 100 nM to 600 nM, growth inhibition rates were measured to be 1.5-10%, 24-47.5%, and 55.5-72.5%, respectively, compared to untreated cells. At the same conditions, metabolic activities were measured to be 91-83%, 74-53%, and 47-31% for indicated concentrations of prodigiosin, respectively, compared to untreated cells. We also found that treatment of HepG2 cells for 48 h decreased significantly cell number and survivin expression and increased caspase-3 activation in a dose-dependent manner. Specifically, treatment with 600-nM prodigiosin resulted in 77% decrease in cell number, 88.5% decrease in survivin messenger RNA level, and 330% increase in caspase-3 activation level compared to untreated cells. An increase in the number of apoptotic cells (late apoptosis) ranging from 36.9% to 97.4% was observed with increasing prodigiosin concentrations.

CONCLUSION

From our data, prodigiosin is an attractive compound that turns the profile of high-level survivin expression in hepatocellular carcinoma cells into that of normal cells and may provide a novel approach to the hepatocellular carcinoma-targeted therapy.

Copper-obatoclax derivative complexes mediate DNA cleavage and exhibit anti-cancer effects in hepatocellular carcinoma

Obatoclax is an indole-pyrrole compound that induces cancer cell apoptosis through targeting the anti-apoptotic Bcl-2 protein family. Previously, we developed a series of obatoclax derivatives and studied their STAT3 inhibition-dependent activity against cancer cell lines. The obatoclax analog, prodigiosin, has been reported to mediate DNA cleavage in cancer cells by coordinating with copper complexes. To gain an understanding of copper-obatoclax complex activity, we applied obatoclax derivatives to examine their copper-mediated nuclease activity as a means to establish a basis for structure activity relationship. Replacement of the indole ring of obatoclax with furanyl, thiophenyl or Boc-indolyl rings reduced the DNA cleavage ability. The same effect was achieved through the replacement of the obatoclax pyrrolyl ring with thiazolidinedione and thioacetal. Among the compounds tested, we demonstrated that the complex of obatoclax or compound 7 with copper exhibited potent DNA strand scission which correlated with HCC cell growth inhibition.

Prodigiosin analogue designed for metal coordination: stable zinc and copper pyrrolyldipyrrins

The pyrrolyldipyrrin motif is found in several naturally occurring prodigiosin pigments. The potential roles of the interactions of prodigiosins with transition metals and the properties of metal-bound pyrrolyldipyrrins, however, have been difficult to assess because of the very limited number of well-characterized stable complexes. Here, we show that the introduction of a meso-aryl substituent and an ethyl ester group during the sequential assembly of the three heterocycles affords a pyrrolyldipyrrin of enhanced coordinating abilities when compared to that of natural prodigiosins. UV-visible absorption studies indicate that this ligand promptly binds Zn(II) ions with 2:1 ligand-to-metal stoichiometry and Cu(II) ions with 1:1 stoichiometry. Notably, no addition of base is required for the formation of the resulting stable complexes. The crystal structures reveal that whereas the tetrahedral zinc center engages two nitrogen donors on each ligand, the pseudosquare planar copper complex features coordination of all three pyrrolic nitrogen atoms and employs the ester group as a neutral ligand. This first example of coordination of a redox-active transition metal within a fully conjugated pyrrolyldipyrrin framework was investigated spectroscopically by electron paramagnetic resonance to show that the 1:1 metal-to-ligand ratio found in the crystal structure is also maintained in solution.

Investigations regarding the utility of prodigiosenes to treat leukemia

Prodigiosenes, possessing a 4-methoxypyrrolyldipyrrin skeleton, are known for their anti-cancer activity. Structural modification of the C-ring resulted in a series of prodigiosenes that displayed promising activity against leukemia cell lines during in vitro analysis against the NCI 60 cancer cell line panel. Further in vivo studies of these compounds using the zebrafish model showed persistence of anti-leukemia properties in human K562 chronic myelogenous leukemia cells.

Pyrroles, dipyrrins and prodigiosenes: one, two and three

The Thompson group aims to further the chemistry of pyrroles, dipyrrins and prodigiosenes. This micro-review discusses each of these research areas in turn, focussing on our achievements thus far.

Apoptosis of human lung adenocarcinoma A549 cells induced by prodigiosin analogue obtained from an entomopathogenic bacterium Serratia marcescens

An entomopathogenic bacterial strain SCQ1 was isolated from silkworm (Bombyx mori) and identified as Serratia marcescens via 16S rRNA gene analysis. This strain produces a red pigment that causes acute septicemia of silkworm. The red pigment of strain SCQ1 was identified as prodigiosin analogue (PGA) with various reported biological activities. In this study, we found that low concentration of PGA showed significant anticancer activity in human lung adenocarcinoma A549 cells, but has little effect in human bone marrow stem cells, in vitro. By exposure to different concentrations of PGA for 24 h, morphological changes and the MTT assay showed that A549 cell line was very sensitive to PGA, with IC(50) value about 2.2 mg/L. Early stage of apoptosis was detected by flow cytometry while A549 cells were treated with PGA for 4 and 12 h, respectively. The proportion of dead cells was increased with treatment time or the concentrations of PGA, but it was inversely proportional to that of apoptotic cells. These results indicate that PGA obtained from strain SCQ1 induces apoptosis in A549 cells, but the molecular mechanisms of cell death are complicated, and the S. marcescens strain SCQ1 may serve as a source of the anticancer compound, PGA.

Diverse DNA-cleaving capacities of the jadomycins through precursor-directed biosynthesis

Gel mobility assays were used to establish that some members of the jadomycin family of natural products act as DNA cleaving agents. Moreover, it was found that subtle structural changes generated through the use of precursor-directed biosynthesis lead to marked effects on the DNA-damaging properties of these glycosylated polyketide-derived natural products.

Anticancer and immunosuppressive properties of bacterial prodiginines

Bacterial prodiginines are a family of red-pigmented, tripyrrolic compounds that display numerous biological activities, including antibacterial, antifungal, antiprotozoal, antimalarial, immunosuppressive and anticancer properties. Recently, significant progress has been made in understanding the biosynthesis and regulation of bacterial prodiginines. An understanding of the biosynthesis of prodiginines will allow engineering of bacterial strains capable of synthesizing novel prodiginines through rational design and mutasynthesis experiments. Bacterial prodiginines and synthetic derivatives are effective proapoptotic agents with multiple cellular targets, and they are active against numerous cancer cell lines, including multidrug-resistant cells, with little or no toxicity towards normal cell lines. A synthetic derivative, GX15-070 (Obatoclax), developed through structure-activity relationship studies of the pyrrolic ring A of GX15, is in multiple Phase I and II clinical trials in both single and dual-agent studies to treat different types of cancer. Therefore, prodiginines have real therapeutic potential in the clinic.

The anticancer agent prodigiosin induces p21WAF1/CIP1 expression via transforming growth factor-beta receptor pathway

The anticancer agent prodigiosin has been shown to act as an efficient immunosuppressant, eliciting cell cycle arrest at non-cytotoxic concentrations, and potent proapoptotic and antimetastatic effects at higher concentrations. Gene expression profiling of MCF-7 cells after treatment with a non-cytotoxic concentration of prodigiosin showed that expression of the p21WAF1/CIP1 gene, a negative cell cycle regulator was induced. In this study, we show that prodigiosin induces p21 expression leading to cell cycle blockade. Subsequently, we attempted to elucidate the molecular mechanisms involved in prodigiosin-mediated p21 gene expression. We demonstrate that prodigiosin induces p21 in a p53-independent manner as prodigiosin induced p21 in cells with both mutated and dominant negative p53. Conversely, the transforming growth factor-beta (TGF-beta) pathway has been found to be necessary for p21 induction. Prodigiosin-mediated p21 expression was blocked by SB431542, a TGF-beta receptor inhibitor. Nevertheless, this pathway alone is not enough to induce p21 expression. The TGF-beta family member (nonsteroidal anti-inflammatory drug)-activated gene 1/growth differentiation factor 15 (NAG-1) may activate this pathway, as it has previously been suggested to signal through the TGF-beta pathway and is overexpressed in response to prodigiosin treatment. We show that NAG-1 colocalizes with TGF-beta receptor type I, suggesting a possible interaction between them. Taken together, these results suggest the TGF-beta pathway is required for induction of p21 expression after prodigiosin treatment of MCF-7 cells.

Tautomeric equilibria in phenolic A-ring derivatives of prodigiosin natural products

The prodigiosin natural products contain a common 4-methoxy-pyrromethene chromophore that is attached to a pyrrole A-ring that has its lone-pair nitrogen electrons in conjugation with the pyrromethene entity. This feature is known to play a key role in the biological activities (anticancer, antimicrobial, and immunosuppressive) of the prodigiosins. In an attempt to alter or improve upon the therapeutic potential of the prodigiosins, we have synthesized two new isomeric analogues that contain phenolic A-ring systems (a para (p)-phenol; an ortho (o)-phenol with respect to the pyrromethene) with lone-pair oxygen electrons in conjugation with the pyrromethene chromophore of the natural product. Herein, we report on the optical properties of the phenolic prodigiosin analogues that have been measured using absorbance and steady-state emission spectroscopy. For both analogues absorption measurements in aprotic solvents show that the neutral (L) ligands exist as the enol tautomers with lambda(max) ~ 460 nm, as noted for the parent prodigiosin natural product. However, in polar protic solvents the phenolic derivatives undergo ground-state prototropic tautomerization to generate keto tautomers with lambda(max) ~ 530 nm. This unique feature for a prodigiosin analogue involves proton transfer from the phenolic OH to the pyrromethene N1 proton acceptor atom. Tautomeric equilibrium constants (KT) of 1.4 in 1:4 MeCN/H2O (v/v) have been determined from examination of the absorption spectra. Titration of the o-phenolic derivative with Zn(II) in methanol yielded a 40-fold increase in fluorescence intensity (lambda(max) 542 nm) and generated a new 1:1 complex with Zn(II) with a log K of 5.29, suggesting the potential utility of this analogue to act as a fluorescence probe in a biological matrix to monitor Zn(II) concentrations. Our results demonstrate that phenolic A-ring derivatives of prodigiosins possess some unique properties that may act to enhance the biological properties of the prodigiosin natural products.

Mechanisms of prodigiosin cytotoxicity in human neuroblastoma cell lines

Prodigiosin is a bacterial red pigment with cytotoxic properties and potential antitumor activity that has been tested against different cancerous cells. In this study we report the effect and mechanisms of action of prodigiosin against different human neuroblastoma cell lines: SH-SY5Y, LAN-1, IMR-32 (N-type) and SK-N-AS (S-type). We compare the anticancerous effect of prodigiosin with that of cisplatin at different concentrations during 24 h of exposure. Prodigiosin is more potent, with IC50 values lower than 1.5 microM in N-type neuroblastoma cells and around 7 microM in the S-type neuroblastoma cell line. We describe prodigiosin as a proton sequestering agent that destroys the intracellular pH gradient, and propose that its main cytotoxic effect could be related to its action on mitochondria, where it exerts an uncoupling effect on the electronic chain transport of protons to mitochondrial ATP synthase. As a result of this action, ATP production is reduced but without decreasing in oxygen consumption. This mechanism of action differs from those induced by conventional chemotherapeutic drugs, suggesting a possible role for prodigiosin to enhance the effect of antitumor agents in the treatment of neuroblastoma.

The use of functional genomics for the identification of a gene cluster encoding for the biosynthesis of an antifungal tambjamine in the marine bacterium Pseudoalteromonas tunicata

A large insert library was created in Escherichia coli from the DNA of the surface-associated marine bacterium Pseudoalteromonas tunicata. Screening of the library for antifungal activity resulted in the detection and identification of a large gene cluster encoding for the biosynthesis of an antifungal tambjamine. A biosynthetic pathway has been proposed based on analysis and annotation of the gene cluster.

The action of the bacterial toxin, microcin B17, on DNA gyrase

Microcin B17 (MccB17) is a peptide-based bacterial toxin that targets DNA gyrase, the bacterial enzyme that introduces supercoils into DNA. The site and mode of action of MccB17 on gyrase are unclear. We review what is currently known about MccB17-gyrase interactions and summarise approaches to understanding its mode of action that involve modification of the toxin. We describe experiments in which treatment of the toxin at high pH leads to the deamidation of two asparagine residues to aspartates. The modified toxin was found to be inactive in vivo and in vitro, suggesting that the Asn residues are essential for activity. Following on from these studies we have used molecular modelling to suggest a 3D structure for microcin B17. We discuss the implications of this model for MccB17 action and investigate the possibility that it binds metal ions.

Prodigiosin induces the proapoptotic gene NAG-1 via glycogen synthase kinase-3beta activity in human breast cancer cells

Prodigiosin (2-methyl-3-pentyl-6-methoxyprodigiosene) is a bacterial metabolite that has anticancer and antimetastatic properties. However, the molecular mechanisms responsible for these abilities are not fully understood. Gene expression profiling of the human breast cancer cell line MCF-7 treated with prodigiosin was analyzed by cDNA array technology. The majority of the significantly modified genes were related to apoptosis, cell cycle, cellular adhesion, or transcription regulation. The dramatic increase of the nonsteroidal anti-inflammatory drug-activated gene 1 (NAG-1) made this gene an interesting candidate regarding the possible mechanism by which prodigiosin induces cytotoxicity in MCF-7 cells. Our results show that prodigiosin triggers accumulation of the DNA-damage response tumor-suppressor protein p53 but that NAG-1 induction was independent of p53 accumulation. Moreover, prodigiosin caused AKT dephosphorylation and glycogen synthase kinase-3beta (GSK-3beta) activation, which correlated with NAG-1 expression. Prodigiosin-induced apoptosis was recovered by inhibiting GSK-3beta, which might be due, at least in part, to the blockade of the GSK-3beta-dependent up-regulation of death receptors 4 and 5 expression. These findings suggest that prodigiosin-mediated GSK-3beta activation is a key event in regulating the molecular pathways that trigger the apoptosis induced by this anticancer agent.

Synthesis and Anti-Cancer Activity of C-Ring-Functionalized Prodigiosin Analogues

Prodigiosin is the parent member of the 4-methoxypyrrolyldipyrromethene family of natural products and is known for its anti-cancer activity. A new series of analogues was synthesized, incorporating pendent functional esters and beta-carbonyl substituents on the C-ring. The beta-carbonyl group allowed for the facile isolation of the prodigiosenes, and the pendent esters allow for further derivatization. The novel prodigiosenes generally retain the anti-cancer activity of prodigiosin in 60 human cell lines derived from nine cancer cell types, with neither the conjugated beta-carbonyl group, as either ketone or ester, nor the pendent ester significantly reducing the anti-cancer activity of the core skeleton.

Total Synthesis, Molecular Editing and Evaluation of a Tripyrrolic Natural Product: The Case of “Butylcycloheptylprodigiosin”

Conflicting reports are found in the literature on whether the ortho-pyrrolophane derivative 6, which has been named "butylcycloheptylprodigiosin" even though it is a cyclononane derivative, is a natural product or merely a mis-assigned structure. This dispute has now been resolved by an unambiguous total synthesis of this complex alkaloid which confirms the initial structure assignment. The chosen approach is largely catalysis-based, featuring the first application of a "Narasaka-Heck" reaction in natural product chemistry. This palladium-catalyzed transformation allows the unsaturated oxime ester 26 to be converted into the bicyclic dihydropyrrole 27. Other notable reactions of the reported approach to 6 are a regioselective Tsuji-Trost reaction of the doubly allylic acetate 21 with methyl acetoacetate, a base-induced aromatization of 27 to the corresponding pyrrole 28, a chemoselective oxidation of the benzylic methyl group in 33 with cerium ammonium nitrate in a biphasic reaction medium that does not affect the labile pyrrole nucleus, and a Suzuki cross-coupling for the completion of the heterocyclic domain. Diversification in the latter step leads to a set of analogues that differ from the natural product in the terminal (hetero)arene ring. This structural modification results in complete loss of the very pronounced ability of the parent compound 6 to induce oxidative cleavage in double stranded DNA in the presence of Cu(II). Several cyclononane-, cyclononene- and cyclononadiene derivatives prepared en route to 6 have been characterized by crystal structure analysis, allowing the conformational behavior of nine-membered carbocycles to be studied.

Chloride anion transport and copper-mediated DNA cleavage by C-ring functionalized prodigiosenes

A new class of prodigiosenes with stability-enhancing functionalities appended to the C-ring were found to transport chloride anions through liposomal membranes, as well as to induce copper-mediated DNA cleavage.

Photoinduced Cytotoxicity and Thioadduct Formation by a Prodigiosin Analogue

[reaction: see text] The prodigiosin alkaloid 1 and the synthetic analogue 2 show photoinduced cytotoxicity against HL-60 cancer cells. Photoirradiation of 1 and 2 causes photofading, photooxidation, and thioadduct formation. These results provide a model for the redox properties of prodigiosins that play a role in their biological activity and provide a new way to functionalize their pyrromethene entity with water-soluble thiol groups.

Proteomic analysis of prodigiosin-induced apoptosis in a breast cancer mitoxantrone-resistant (MCF-7 MR) cell line

Prodigiosin (PG) is a bacterial, red-pigmented antibiotic with immunosuppressive and apoptotic activities. To better understand its mechanisms of action, we tried to identify proteins associated with apoptosis induced by PG. For this purpose, the variation of protein expression on exposure to apoptotic concentrations of PG was examined, by high-resolution two-dimensional gel electrophoresis (2D-E), in the MCF-7 cancer cell line resistant to mitoxantrone (MCF-7-MR). Six PG apoptosis-associated protein spots were further characterized by complementary peptide mass fingerprinting and tandem mass spectrometry data obtained on a matrix-assisted laser desorption ionization-time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometer. The proteins identified were involved in various cellular functions, including cell defence, DNA repair and cellular organization. Our data provide novel information on cell response to PG, a new apoptotic drug with interesting anticancer activity.