Coumarin-transition metal complexes with biological activity: current trends and perspectives

Coumarin (2H-1-benzopyran-2-one) presents the fundamental structure of an enormous class of biologically active compounds of natural, semi-synthetic, and synthetic origin. Extensive efforts are continually being put into the research and development of coumarin derivatives with medicinal properties by the broad scientific community. Transition metal coordination compounds with potential biological activity are a "hot topic" in the modern search for novel drugs. Complexation with transition metals can enhance the physiological effect of a molecule, modify its safety profile, and even imbue it with novel attributes of interest in the fields of medicine and pharmacy. The present review aims to inform the reader of the latest developments in the search for coumarin transition metal complexes with biological activity, their potential applications, and structure-activity relationships, where such can be elucidated. Each section of the present review addresses a certain kind of biological activity (antiproliferative, antioxidant, antimicrobial, etc.), explores the most recent discoveries in the field, and, at the same time, tries to offer useful perspectives for potential future investigations.

Understanding the role of solvents in bottom-up synthesis of multi-element hydroxides

Here we report a comparative study on the bottom-up synthesis of multi-element hydroxides composed of Mg, Al, Fe and Zn cations to understand the role of solvents. Two common solvents, water and ethylene glycol, a typical polyol, are used. The polyol-derived MgAlFeZn-OH are nanosheets with homogeneous elemental distribution, while the hydrothermal-derived MgAlFeZn-OH are mixtures of plate-like hydroxide layers and rod-like spinel oxides. The coordinating properties and the high viscosity of the ethylene glycol provide the possibility to mediate the hydrolysis rates and to control the particle growth. The high specific surface area of the polyol-derived multi-element hydroxide nanosheets (352.4 m2 g-1) guarantees them as excellent adsorbents for adsorbing anionic dyes in aqueous solution.

Research Progress of Metal Anticancer Drugs

Cancer treatments, including traditional chemotherapy, have failed to cure human malignancies. The main reasons for the failure of these treatments are the inevitable drug resistance and serious side effects. In clinical treatment, only 5 percent of the 50 percent of cancer patients who are able to receive conventional chemotherapy survive. Because of these factors, being able to develop a drug and treatment that can target only cancer cells without affecting normal cells remains a big challenge. Since the special properties of cisplatin in the treatment of malignant tumors were accidentally discovered in the last century, metal anticancer drugs have become a research hotspot. Metal anticancer drugs have unique pharmaceutical properties, such as ruthenium metal drugs with their high selectivity, low toxicity, easy absorption by tumor tissue, excretion, and so on. In recent years, efficient and low-toxicity metal antitumor complexes have been synthesized. In this paper, the scientific literature on platinum (Pt), ruthenium (Ru), iridium (Ir), gold (Au), and other anticancer complexes was reviewed by referring to a large amount of relevant literature at home and abroad.

DksA is a conserved master regulator of stress response in Acinetobacter baumannii

Coordination of bacterial stress response mechanisms is critical for long-term survival in harsh environments for successful host infection. The general and specific stress responses of well-studied Gram-negative pathogens like Escherichia coli are controlled by alternative sigma factors, archetypically RpoS. The deadly hospital pathogen Acinetobacter baumannii is notoriously resistant to environmental stresses, yet it lacks RpoS, and the molecular mechanisms driving this incredible stress tolerance remain poorly defined. Here, using functional genomics, we identified the transcriptional regulator DksA as a master regulator for broad stress protection and virulence in A. baumannii. Transcriptomics, phenomics and in vivo animal studies revealed that DksA controls ribosomal protein expression, metabolism, mutation rates, desiccation, antibiotic resistance, and host colonization in a niche-specific manner. Phylogenetically, DksA was highly conserved and well-distributed across Gammaproteobacteria, with 96.6% containing DksA, spanning 88 families. This study lays the groundwork for understanding DksA as a major regulator of general stress response and virulence in this important pathogen.

Recent Trends in the Development of Novel Metal-Based Antineoplastic Drugs

Since the accidental discovery of the anticancer properties of cisplatin more than half a century ago, significant efforts by the broad scientific community have been and are currently being invested into the search for metal complexes with antitumor activity. Coordination compounds of transition metals such as platinum (Pt), ruthenium (Ru) and gold (Au) have proven their effectiveness as diagnostic and/or antiproliferative agents. In recent years, experimental work on the potential applications of elements including lanthanum (La) and the post-transition metal gallium (Ga) in the field of oncology has been gaining traction. The authors of the present review article aim to help the reader "catch up" with some of the latest developments in the vast subject of coordination compounds in oncology. Herewith is offered a review of the published scientific literature on anticancer coordination compounds of Pt, Ru, Au, Ga and La that has been released over the past three years with the hope readers find the following article informative and helpful.

Kinetics of Phenol Biodegradation by Heavy Metal Tolerant Rhizobacteria Glutamicibacter nicotianae MSSRFPD35 From Distillery Effluent Contaminated Soils

Biodegradation of phenol using bacteria is recognized as an efficient, environmentally friendly and cost-effective approach for reducing phenol pollutants compared to the current conventional physicochemical processes adopted. A potential phenol degrading bacterial strain Glutamicibacter nicotianae MSSRFPD35 was isolated and identified from Canna indica rhizosphere grown in distillery effluent contaminated sites. It showed high phenol degrading efficiency up to 1117 mg L^–1 within 60 h by the secretion of catechol 1,2-dioxygenase via ortho intradial pathway. The strain MSSRFPD35 possess both the catechol 1,2 dioxygenase and catechol 2,3 dioxygenase coding genes that drive the ortho and meta pathways, but the enzymatic assay revealed that the strain cleaves catechol via ortho pathway. Haldane’s kinetic method was well fit to exponential growth data and the following kinetic parameter was obtained: μ^∗ = 0.574 h^–1, K_i = 268.1, K_s = 20.29 mg L^–1. The true μ_max and S_m were calculated as 0.37 h^–1 and 73.76 mg L^–1, respectively. The Haldane’s constant values were similar to earlier studies and healthy fitness depicted in correlation coefficient value R² of 0.98. Phenol degrading kinetic’s was predicted using Haldane’s model as q_max 0.983, K_i′ 517.5 and K_s′ 9.152. Further, MSSRFPD35 was capable of utilizing different monocyclic and polycyclic aromatic hydrocarbons and to degrade phenol in the presence of different heavy metals. This study for the first time reports high phenol degrading efficiency of G. nicotianae MSSRFPD35 in the presence of toxic heavy metals. Thus, the strain G. nicotianae MSSRFPD35 can be exploited for the bioremediation of phenol and its derivatives polluted environments, co-contaminated with heavy metals.

Copper as an alternative antimicrobial coating for implants - An in vitro study

AIM

To investigate osteoconductive and antimicrobial properties of a titanium-copper-nitride (TiCuN) film and an additional BONIT^® coating on titanium substrates.

METHODS

For micro-structuring, the surface of titanium test samples was modified by titanium plasma spray (TPS). On the TPS-coated samples, the TiCuN layer was deposited by physical vapor deposition. The BONIT^® layer was coated electrochemically. The concentration of copper ions released from TiCuN films was measured by atomic absorption spectrometry. MG-63 osteoblasts on TiCuN and BONIT^® were analyzed for cell adhesion, viability and spreading. In parallel, Staphylococcus epidermidis (S. epidermidis) were cultivated on the samples and planktonic and biofilm-bound bacteria were quantified by counting of the colony-forming units.

RESULTS

Field emission scanning electron microscopy (FESEM) revealed rough surfaces for TPS and TiCuN and a special crystalline surface structure on TiCuN + BONIT^®. TiCuN released high amounts of copper quickly within 24 h. These release dynamics were accompanied by complete growth inhibition of bacteria and after 2 d, no planktonic or adherent S. epidermidis were found on these samples. On the other hand viability of MG-63 cells was impaired during direct cultivation on the samples within 24 h. However, high cell colonization could be found after a 24 h pre-incubation step in cell culture medium simulating the in vivo dynamics closer. On pre-incubated TiCuN, the osteoblasts span the ridges and demonstrate a flattened, well-spread phenotype. The additional BONIT^®coating reduced the copper release of the TiCuN layer significantly and showed a positive effect on the initial cell adhesion.

CONCLUSION

The TiCuNcoating inhibits the formation of bacterial biofilms on orthopedic implants by influencing the “race for the surface” to the advantage of osteoblasts.

Investigation of roles of divalent cations in Shewanella oneidensis pellicle formation reveals unique impacts of insoluble iron

BACKGROUND

Bacteria adopt a variety of lifestyles in their natural habitats and can alternate among different lifestyles in response to environmental changes. At high cell densities, bacteria can form extracellular matrix encased cell population on submerged tangible surfaces (biofilms), or at the air-liquid interface (pellicles). Compared to biofilm, pellicle lifestyle allows for better oxygen access, but is metabolically more costly to maintain. Further understanding of pellicle formation and environmental cues that influence cellular choices between these lifestyles will definitely improve our appreciation of bacterial interaction with their environments.

METHODS

Shewanella oneidensis cells were cultured in 24-well plates with supplementation of varied divalent cations, and pellicles formed under such conditions were evaluated. Mutants defective in respiration of divalent cations were used to further characterize and confirm unique impacts of iron.

RESULTS AND CONCLUSIONS

Small amount of Fe(2+) was essential for pellicle formation, but presence of over-abundant iron (0.3mM Fe(2+) or Fe(3+)) led to pellicle disassociation without impairing growth. Such impacts were found due to S. oneidensis-mediated formation of insoluble alternative electron acceptors (i.e., Fe3O4) under physiologically relevant conditions. Furthermore, we demonstrated that cells preferred a lifestyle of forming biofilm and respiring on such insoluble electron acceptors under tested conditions, even to living in pellicles.

GENERAL SIGNIFICANCE

Our finding suggests that bacterial lifestyle choice involves balanced evaluation of multiple aspects of environmental conditions, and yet-to-be-characterized signaling mechanism is very likely underlying such processes.

Identification of a metagenomic gene cluster containing a new class A beta-lactamase and toxin-antitoxin systems

Several reports mention the presence of antibiotic resistance genes in natural and polluted environments, but many studies are based on their detection via polymerase chain reaction (PCR amplification of known genes and not on an activity screening. We constructed a metagenomic fosmid bank from DNA isolated from a polluted river in Brussels, Belgium, the Zenne. A total of 120,000 clones were pooled and plated directly on solid media containing different antibiotics. Several clones were isolated which could grow in the presence of ampicillin. The DNA from several clones was extracted and subjected to restriction analysis and, based on their restriction pattern, two different clones were found. One of the clones was selected for further study as it showed a higher level of resistance to different β-lactams antibiotics (ticarcilline and ceftazidime). To find out which gene is responsible for the resistance, an in vitro transposon mutagenesis was performed and clones having lost the resistance phenotype were analyzed via inverse PCR amplification. Several clones had an insert in a gene encoding a new type of β-lactamase. The amplified fosmid DNA was fully sequenced revealing an insert of 41 kb containing 39 open reading frames (ORFs). Transposon insertions inactivating the resistance to β-lactams were also found in the ORF upstream of the blaA gene, encoding an aminotransferase, suggesting a polar effect on the transcription of the gene downstream. In addition, other genes were found such as histidine biosynthesis genes, which were found to be scattered on the insert, a relA/spoT gene, and genes belonging to type II toxin–antitoxin system. This predicted system was experimentally validated in Escherichia coli using an inducible expression system.

Effect of the metals iron, copper and silver on fluorobenzene biodegradation by Labrys portucalensis

Organic and metallic pollutants are ubiquitous in the environment. Many metals are reported to be toxic to microorganisms and to inhibit biodegradation. The effect of the metals iron, copper and silver on the metabolism of Labrys portucalensis F11 and on fluorobenzene (FB) biodegradation was examined. The results indicate that the addition of 1 mM of Fe(2+) to the culture medium has a positive effect on bacterial growth and has no impact in the biodegradation of 1 and 2 mM of FB. The presence of 1 mM of Cu(2+) was found to strongly inhibit the growth of F11 cultures and to reduce the biodegradation of 1 and 2 mM of FB to ca. 50 %, with 80 % of stoichiometrically expected fluoride released. In the experiments with resting cells, the FB degraded (from 2 mM supplied) was reduced ca. 20 % whereas the fluoride released was reduced to 45 % of that stoichiometrically expected. Ag(+) was the most potent inhibitor of FB degradation. In experiments with growing cells, the addition of 1 mM of Ag(+) to the culture medium containing 1 and 2 mM of FB resulted in no fluoride release, whereas FB degradation was only one third of that observed in control cultures. In the experiments with resting cells, the addition of Ag(+) resulted in 25 % reduction in substrate degradation and fluoride release was only 20 % of that stoichiometrically expected. The accumulation of catechol and 4-fluorocatechol in cultures supplemented with Cu(2+) or Ag(+) suggest inhibition of the key enzyme of FB metabolism-catechol 1,2-dioxygenase.

Regulation of Cu(I)/Ag(I) efflux genes in Escherichia coli by the sensor kinase CusS

Two-component systems are widely used by bacteria to mediate adaptive responses to a variety of environmental stimuli. The CusR/CusS two-component system in Escherichia coli induces expression of genes involved in metal efflux under conditions of elevated Cu(I) and Ag(I) concentrations. As seen in most prototypical two-component systems, signal recognition and transmission is expected to occur by ligand binding in the periplasmic sensor domain of the histidine kinase CusS. Although discussed in the extant literature, little experimental evidence is available to establish the role of CusS in metal homeostasis. In this study, we show that the cusS gene is required for Cu(I) and Ag(I) resistance in E. coli and that CusS is linked to the expression of the cusCFBA genes. These results show a metal-dependent mechanism of CusS activation and suggest an absolute requirement for CusS in Cu(I)- and Ag(I)-dependent upregulation of cusCFBA expression in E. coli.