Synthesis, characterization, in vitro SAR study, and preliminary in vivo toxicity evaluation of naphthylmethyl substituted bis-imidazolium salts

A series of novel bis-imidazolium salts was synthesized, characterized, and evaluated in vitro against a panel of non-small cell lung cancer (NSCLC) cells. Two imidazolium cores were connected with alkyl chains of varying lengths to develop a structure activity relationship (SAR). Increasing the length of the connecting alkyl chain was shown to correlate to an increase in the anti-proliferative activity. The National Cancer Institute's NCI-60 human tumor cell line screen confirmed this trend. The compound containing a decyl linker chain, 10, was chosen for further in vivo toxicity studies with C578BL/6 mice. The compound was well tolerated by the mice and all of the animals survived and gained weight over the course of the study.

Synthesis and Characterization of Cobalt(II) N,N'-Diphenylazodioxide Complexes

Removal of chloride from CoCl₂ with TlPF₆ in acetonitrile, followed by addition of excess nitrosobenzene, yielded the eight-coordinate cobalt(II) complex salt [Co{Ph(O)NN(O)Ph}₄](PF₆)₂, shown by single-crystal X-ray analysis to have a distorted tetragonal geometry. The analogous treatment of the bipyridyl complex Co(bpy)Cl₂ yielded the mixed-ligand cobalt(II) complex salt [Co(bpy){Ph(O)NN(O)Ph}₂](PF₆)₂, whose single-crystal X-ray structure displays a trigonal prismatic geometry, similar to that of the iron(II) cation in the previously known complex salt [Fe{Ph(O)NN(O)Ph}₃](FeCl₄)₂. The use of TlPF₆ to generate solvated metal complex cations from chloride salts or chlorido complexes, followed by the addition of nitrosobenzene, is shown to be a useful synthetic strategy for the preparation of azodioxide complex cations with the noncoordinating, diamagnetic PF₆ ^- counteranion. Coordination number appears to be more important than d electron count in determining the geometry and metal-ligand bond distances of diphenylazodioxide complexes.

Synthesis, characterization, in vitro SAR and in vivo evaluation of N,N'bisnaphthylmethyl 2-alkyl substituted imidazolium salts against NSCLC

Alkyl- and N,N'-bisnaphthyl-substituted imidazolium salts were tested in vitro for their anti-cancer activity against four non-small cell lung cancer cell lines (NCI-H460, NCI-H1975, HCC827, A549). All compounds had potent anticancer activity with 2 having IC50 values in the nanomolar range for three of the four cell lines, a 17-fold increase in activity against NCI-H1975 cells when compared to cisplatin. Compounds 1-4 also showed high anti-cancer activity against nine NSCLC cell lines in the NCI-60 human tumor cell line screen. In vitro studies performed using the Annexin V and JC-1 assays suggested that NCI-H460 cells treated with 2 undergo an apoptotic cell death pathway and that mitochondria could be the cellular target of 2 with the mechanism of action possibly related to a disruption of the mitochondrial membrane potential. The water solubilities of 1-4 was over 4.4mg/mL using 2-hydroxypropyl-β-cyclodextrin as a chemical excipient, thereby providing sufficient solubility for systemic administration.

Synthesis, characterization, and in vitro SAR evaluation of N,N'-bis(arylmethyl)-C2-alkyl substituted imidazolium salts

A series of C2-alkyl substituted N,N'-bis(arylmethyl)imidazolium salts were synthesized, characterized, and tested for their in vitro anti-cancer activity against multiple non-small cell lung cancer cell lines by our group and the National Cancer Institute's-60 human tumor cell line screen to establish a structure-activity relationship. Compounds are related to previously published N,N'-bis(arylmethyl)imidazolium salts but utilize the historical quinoline motif and anion effects to increase the aqueous solubility. Multiple derivatives displayed high anti-cancer activity with IC50 values in the nanomolar to low micromolar range against a panel of non-small cell lung cancer cell lines. Several of these derivatives have high aqueous solubilities with potent anti-proliferative properties and are ideal candidates for future in vivo xenograft studies and have high potential to progress into clinic use.

Synthesis, anti-proliferative activity, SAR study, and preliminary in vivo toxicity study of substituted N,N'-bis(arylmethyl)benzimidazolium salts against a panel of non-small cell lung cancer cell lines

A series of N,N'-bis(arylmethyl)benzimidazolium salts have been synthesized and evaluated for their in vitro anti-cancer activity against select non-small cell lung cancer cell lines to create a structure activity relationship profile. The results indicate that hydrophobic substituents on the salts increase the overall anti-proliferative activity. Our data confirms that naphthylmethyl substituents at the nitrogen atoms (N¹(N³)) and highly lipophilic substituents at the carbon atoms (C² and C⁵(C⁶)) can generate benzimidazolium salts with anti-proliferative activity that is comparable to that of cisplatin. The National Cancer Institute's Developmental Therapeutics Program tested 1, 3-5, 10, 11, 13-18, 20-25, and 28-30 in their 60 human tumor cell line screen. Results were supportive of data observed in our lab. Compounds with hydrophobic substituents have higher anti-cancer activity than compounds with hydrophilic substituents.

An NMR-Guided Screening Method for Selective Fragment Docking and Synthesis of a Warhead Inhibitor

Selective hits for the glutaredoxin ortholog of Brucella melitensis are determined using STD NMR and verified by trNOE and (15)N-HSQC titration. The most promising hit, RK207, was docked into the target molecule using a scoring function to compare simulated poses to experimental data. After elucidating possible poses, the hit was further optimized into the lead compound by extension with an electrophilic acrylamide warhead. We believe that focusing on selectivity in this early stage of drug discovery will limit cross-reactivity that might occur with the human ortholog as the lead compound is optimized. Kinetics studies revealed that lead compound 5 modified with an ester group results in higher reactivity than an acrylamide control; however, after modification this compound shows little selectivity for bacterial protein versus the human ortholog. In contrast, hydrolysis of compound 5 to the acid form results in a decrease in the activity of the compound. Together these results suggest that more optimization is warranted for this simple chemical scaffold, and opens the door for discovery of drugs targeted against glutaredoxin proteins-a heretofore untapped reservoir for antibiotic agents.

Anti-tumor activity of lipophilic imidazolium salts on select NSCLC cell lines

The anti-tumor activity of imidazolium salts is highly dependent upon the substituents on the nitrogen atoms of the imidazolium cation. We have synthesized and characterized a series of naphthalene-substituted imidazolium salts and tested them against a variety of non-smallcell lung cancer cell lines. Several of these complexes displayed anticancer activity comparable to cisplatin. These compounds induced apoptosis in the NCI-H460 cell line as determined by Annexin V staining, caspase-3, and PARP cleavage. These results strongly suggest that this class of compounds can serve as potent chemotherapeutic agents.

Structure and conformation of the medium-sized chlorophosphazene rings

Medium-sized cyclic oligomeric phosphazenes [PCl2N]m (where m = 5-9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N]3 and [PCl2N]4. The medium-sized rings [PCl2N]m have been characterized by electrospray ionization-mass spectroscopy (ESI-MS), their (31)P chemical shifts have been reassigned, and their T1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N]5, and the crystal structures of [PCl2N]6, and [PCl2N]8 are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N]m (m = 3-5, 6, 8). The crystal structures of [P(OPh)2N]7 and [P(OPh)2N]8, which are derivatives of the respective [PCl2N]m, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N]8 and [P(OPh)2N]8 with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.

Synthesis, characterization, and in vivo efficacy of shell cross-linked nanoparticle formulations carrying silver antimicrobials as aerosolized therapeutics

The use of nebulizable, nanoparticle-based antimicrobial delivery systems can improve efficacy and reduce toxicity for treatment of multi-drug-resistant bacteria in the chronically infected lungs of cystic fibrosis patients. Nanoparticle vehicles are particularly useful for applying broad-spectrum silver-based antimicrobials, for instance, to improve the residence time of small-molecule silver carbene complexes (SCCs) within the lung. Therefore, we have synthesized multifunctional, shell cross-linked knedel-like polymeric nanoparticles (SCK NPs) and capitalized on the ability to independently load the shell and core with silver-based antimicrobial agents. We formulated three silver-loaded variants of SCK NPs: shell-loaded with silver cations, core-loaded with SCC10, and combined loading of shell silver cations and core SCC10. All three formulations provided a sustained delivery of silver over the course of at least 2-4 days. The two SCK NP formulations with SCC10 loaded in the core each exhibited excellent antimicrobial activity and efficacy in vivo in a mouse model of Pseudomonas aeruginosa pneumonia. SCK NPs with shell silver cation-load only, while efficacious in vitro, failed to demonstrate efficacy in vivo. However, a single dose of core SCC10-loaded SCK NPs (0.74 ± 0.16 mg Ag) provided a 28% survival advantage over sham treatment, and administration of two doses (0.88 mg Ag) improved survival to 60%. In contrast, a total of 14.5 mg of Ag(+) delivered over 5 doses at 12 h intervals was necessary to achieve a 60% survival advantage with a free-drug (SCC1) formulation. Thus, SCK NPs show promise for clinical impact by greatly reducing antimicrobial dosage and dosing frequency, which could minimize toxicity and improve patient adherence.

Aerosolized antimicrobial agents based on degradable dextran nanoparticles loaded with silver carbene complexes

Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH(2)Cl(2) (organic):PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery.

The Interactions between L-tyrosine based nanoparticles decorated with folic acid and cervical cancer cells under physiological flow

Many anticancer drugs have been established clinically, but their efficacy can be compromised by nonspecific toxicity and an inability to reach the desired cancerous intracellular spaces. In order to address these issues, researchers have explored the use of folic acid as a targeted moiety to increase specificity of chemotherapeutic drugs. To expand upon such research, we have conjugated folic acid to functionalized poly(ethylene glycol) and subsequently decorated the surface of l-tyrosine polyphosphate (LTP) nanoparticles. These nanoparticles possess the appropriate size (100-500 nm) for internalization as shown by scanning electron microscopy and dynamic light scattering. Under simulated physiological flow, LTP nanoparticles decorated with folic acid (targeted nanoparticles) show a 10-fold greater attachment to HeLa, a cervical cancer cell line, compared to control nanoparticles and to human dermal fibroblasts. The attachment of these targeted nanoparticles progresses at a linear rate, and the strength of this nanoparticle attachment is shown to withstand shear stresses of 3.0 dyn/cm(2). These interactions of the targeted nanoparticles to HeLa are likely a result of a receptor-ligand binding, as a competition study with free folic acid inhibits the nanoparticle attachment. Finally, the targeted nanoparticles encapsulated with a silver based drug show increased efficacy in comparison to nondecorated (plain) nanoparticles and drug alone against HeLa cells. Thus, targeted nanoparticles are a promising delivery platform for developing anticancer therapies that overexpress the folate receptors (FRs).

Synthesis, characterization, and antimicrobial activity of silver carbene complexes derived from 4,5,6,7-tetrachlorobenzimidazole against antibiotic resistant bacteria

Silver N-heterocyclic carbene complexes have been shown to have great potential as antimicrobial agents, affecting a wide spectrum of both Gram-positive and Gram-negative bacteria. A new series of three silver carbene complexes (SCCs) based on 4,5,6,7-tetrachlorobenzimidazole has been synthesized, characterized, and tested against a panel of clinical strains of bacteria. The imidazolium salts and their precursors were characterized by elemental analysis, mass spectrometry, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. The silver carbene complexes, SCC32, SCC33, and SCC34 were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. These complexes proved highly efficacious with minimum inhibitory concentrations (MICs) ranging from 0.25 to 6 μg mL(-1). Overall, the complexes were effective against highly resistant bacteria strains, such as methicillin-resistant Staphylococcus aureus (MRSA), weaponizable bacteria, such as Yersinia pestis, and pathogens found within the lungs of cystic fibrosis patients, such as Pseudomonas aeruginosa, Alcaligenes xylosoxidans, and Burkholderia gladioli. SCC33 and SCC34 also showed clinically relevant activity against a silver-resistant strain of Escherichia coli based on MIC testing.

Silver metallation of hen egg white lysozyme: X-ray crystal structure and NMR studies

The X-ray crystal structure, NMR binding studies, and enzyme activity of silver(I) metallated hen egg white lysozyme are presented. Primary bonding of silver is observed through His15 with secondary bonding interactions coming from nearby Arg14 and Asp87. A covalently bound nitrate completes a four coordinate binding pocket.

In vitro antimicrobial studies of silver carbene complexes: activity of free and nanoparticle carbene formulations against clinical isolates of pathogenic bacteria

OBJECTIVES

Silver carbenes may represent novel, broad-spectrum antimicrobial agents that have low toxicity while providing varying chemistry for targeted applications. Here, the bactericidal activity of four silver carbene complexes (SCCs) with different formulations, including nanoparticles (NPs) and micelles, was tested against a panel of clinical strains of bacteria and fungi that are the causative agents of many skin and soft tissue, respiratory, wound, blood, and nosocomial infections.

METHODS

MIC, MBC and multidose experiments were conducted against a broad range of bacteria and fungi. Time-release and cytotoxicity studies of the compounds were also carried out. Free SCCs and SCC NPs were tested against a panel of medically important pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Acinetobacter baumannii (MRAB), Pseudomonas aeruginosa, Burkholderia cepacia and Klebsiella pneumoniae.

RESULTS

All four SCCs demonstrated strong efficacy in concentration ranges of 0.5-90 mg/L. Clinical bacterial isolates with high inherent resistance to purified compounds were more effectively treated either with an NP formulation of these compounds or by repeated dosing. Overall, the compounds were active against highly resistant bacterial strains, such as MRSA and MRAB, and were active against the biodefence pathogens Bacillus anthracis and Yersinia pestis. All of the medically important bacterial strains tested play a role in many different infectious diseases.

CONCLUSIONS

The four SCCs described here, including their development as NP therapies, show great promise for treating a wide variety of bacterial and fungal pathogens that are not easily killed by routine antimicrobial agents.

Poly[[{μ(3)-2-[4-(2-hy-droxy-eth-yl)piperazin-1-yl]ethane-sulfonato}-silver(I)] trihydrate]

Ethane­sulfonic acid-based buffers like 2-[4-(2-hy­droxy­eth­yl)­piperazin-1-yl]ethane­sulfonic acid (HEPES) are commonly used in biological experiments because of their ability to act as non-coordinating ligands towards metal ions. However, recent work has shown that some of these buffers may in fact coordinate metal ions. The title complex, {[Ag(C₈H₁₇N₂O₄S)]·3H₂O}_n, is a metal–organic framework formed from HEPES and a silver(I) ion. In this polymeric complex, each Ag atom is primarily coordinated by two N atoms in a distorted linear geometry. Weaker secondary bonding inter­actions from the hy­droxy and sulfate O atoms of HEPES complete a distorted seesaw geometry. The crystal structure is stabilized by O—H⋯O hydrogen-bonding interactions.

Synthesis and antimicrobial studies of silver N-heterocyclic carbene complexes bearing a methyl benzoate substituent

Due to the properties of silver as an antimicrobial, our research group has synthesized many different silver carbene complexes. Two new silver N-heterocyclic carbene complexes derived from 4,5-dichloroimidazole and theobromine bearing methyl benzoate substituents were synthesized by in situ carbene formation using silver acetate as the base in the reaction. The new compounds were fully characterized by several methods including NMR spectroscopy and X-ray crystallography. Preliminary antimicrobial efficacy studies against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli were conducted. The results of this study demonstrated antimicrobial efficacy of the two complexes comparable to silver nitrate, showing their potential for use in the treatment of bacterial infections.

A theobromine derived silver N-heterocyclic carbene: synthesis, characterization, and antimicrobial efficacy studies on cystic fibrosis relevant pathogens

The increasing incidence of multidrug-resistant (MDR) pulmonary infections in the cystic fibrosis (CF) population has prompted the investigation of innovative silver based therapeutics. The functionalization of the naturally occurring xanthine theobromine at the N(1) nitrogen atom with an ethanol substituent followed by the methylation of the N(9) nitrogen atom gives the N-heterocyclic carbene precursor 1-(2-hydroxyethyl)-3,7,9-trimethylxanthinium iodide. The reaction of this xanthinium salt with silver acetate produces the highly hydrophilic silver carbene complex SCC8. The in vitro antimicrobial efficacy of this newly synthesized complex was evaluated with excellent results on a variety of virulent and MDR pathogens isolated from CF patients. A comparative in vivo study between the known caffeine derived silver carbene SCC1 and SCC8 demonstrated the ability of both complexes to improve the survival rates of mice in a pneumonia model utilizing the clinically isolated infectious strain of Pseudomonas aeruginosa PA M57-15.

Synthesis and in vitro Efficacy Studies of Silver Carbene Complexes on Biosafety Level 3 Bacteria

A series of N-heterocyclic carbene silver complexes have been synthesized and tested against the select group of bio-safety level 3 bacteria Burkholderia pseudomallei, Burkholderia mallei, Bacillus anthracis, methicillin-resistant Staphylococcus aureus and Yersinia pestis. Minimal inhibitory concentrations, minimal bactericidal and killing assays demonstrated the exceptional efficacy of the complexes against these potentially weaponizable pathogens.

The antimicrobial efficacy of sustained release silver-carbene complex-loaded L-tyrosine polyphosphate nanoparticles: characterization, in vitro and in vivo studies

The pressing need to treat multi-drug resistant bacteria in the chronically infected lungs of cystic fibrosis (CF) patients has given rise to novel nebulized antimicrobials. We have synthesized a silver-carbene complex (SCC10) active against a variety of bacterial strains associated with CF and chronic lung infections. Our studies have demonstrated that SCC10-loaded into L-tyrosine polyphosphate nanoparticles (LTP NPs) exhibits excellent antimicrobial activity in vitro and in vivo against the CF relevant bacteria Pseudomonas aeruginosa. Encapsulation of SCC10 in LTP NPs provides sustained release of the antimicrobial over the course of several days translating into efficacious results in vivo with only two administered doses over a 72 h period.

A crystallographically isolated dimeric hydrolyzed chloro-phosphazene dianion

Single crystals of the title compound bis[bis-(1-ethyl-3-methyl-imidazol-2-yl-idene)silver(I)] 1,5,5,7,11,11-hexa-chloro-2,8-di-oxa-4,6,10,12,13,14-hexa-aza-1λ(5),3,5λ(5),7λ(5),9,11λ(5)-hexa-phospha-tricyclo-[7.3.1.1(3,7)]tetra-deca-1(13),4,7(14),10-tetra-ene-6,12-diide 3,9-dioxide, [Ag(C(6)H(10)N(2))(2)](Cl(6)N(6)O(4)P(6))(0.5), were isolated from the reaction of the silver N-heteocyclic carbene complex [Ag(C(6)H(10)N(2))(2)]Cl and hexa-chloro-cyclo-triphos-phazene [NPCl(2)](3 )in the presence of water. The asymmetric unit contains one silver carbene cation with the carbene ligands bound to the Ag(I) in an almost linear arrangement and one half of a hydrolyzed phosphazene dianion. The second cation and additional half of the anion are generated by an inversion center.

Synthesis, stability, and antimicrobial studies of electronically tuned silver acetate N-heterocyclic carbenes

A series of methylated imidazolium salts with varying substituents on the 4 and 5 positions of the imidazole ring were synthesized. These salts were reacted with silver acetate to afford their corresponding silver N-heterocyclic carbene (NHC) complexes. These complexes were then evaluated for their stability in water as well as for their antimicrobial efficacy against a variety of bacterial strains associated with cystic fibrosis and chronic lung infections.

Ovarian cancer activity of cyclic amine and thiaether metal complexes

A thiaether metal complex 1-aza-4,7-dithiacyclononane-RhCl3, 2, and cyclic amine metal complexes tacn-CuBr2, 3, and Me3tacn-RuCl3, 4, have been evaluated for anticancer activity against the ovarian cancer cell line NuTu-19 and for cell toxicity against the noncancerous ovarian tissue cell line OVepi. Specifically, metal complex 2 is active when compared to cisplatin at micromolar concentrations using the MTT and cell invasion assay. The in vitro results reported warrant further evaluation of metal complex 2 in living systems.

Synthesis from caffeine of a mixed N-heterocyclic carbene-silver acetate complex active against resistant respiratory pathogens

The bis(N-heterocyclic carbene) (NHC) silver complex, 3, with a methyl carbonate anion was formed from the reaction of the iodide salt of methylated caffeine, 1, with silver (I) oxide in methanol. Attempts to crystallize this complex from a mixture of common alcohols and ethyl acetate led to the formation of an NHC-silver acetate complex, 4. The more direct synthesis of 4 was accomplished by the in-situ deprotonation of 1 by silver acetate in methanol. Complex 4 demonstrated antimicrobial activity against numerous resistant respiratory pathogens from the lungs of cystic fibrosis (CF) patients including members of the Burkholderia cepacia complex that cause a high rate of mortality in patients with cystic fibrosis (CF). Application of this NHC silver complex to primary cultures of murine respiratory epithelial cells followed by microarray analysis showed minimal gene expression changes at the concentrations effective against respiratory pathogens. Furthermore, methylated caffeine without silver showed some antibacterial and antifungal activity.

Synthesis and characterization of a trigonal bipyramidal supramolecular cage based upon rhodium and platinum metal centers

The reaction of 4-ethynyl-pyridine with tert-butyl lithium followed by its addition to (Me3tacn)RhCl3 affords the facial octahedral complex (Me3tacn)Rh(CCPy)3, condensation of which with the square planar complex cis-(DCPE)Pt(NO3)2 results in a self-assembled trigonal bipyramidal cage with Rh(III) and Pt(II) atoms occupying the vertices.

Lewis Acid Adducts of [PCl2N]3

Reaction of aluminum trichloride or gallium trichloride with the extremely weak base hexachlorotriphosphazene gives adducts in which the group 13 element is bound to a phosphazene nitrogen atom. In solution, the adducts exhibit fluxional behavior. The phosphazene ring of the adducts is distorted into a slight chair conformation.