Tricarbonyl 99mTc(I) and Re(I)–thiosemicarbazone complexes: synthesis, characterization and biological evaluation for targeting bacterial infection

Methyl, ethyl and phenyl nitrofuryl thiosemicarbazone ligands (1, 2 and 3 respectively) were radiolabeled with freshly prepared aqueous solution of a fac[99mTc(CO)3(H2O)3]+ precursor. The radiochemical yield was around 98% as determined by thin layer chromatography and HPLC. The complexes exhibited substantial stability. The corresponding Re(I) complexes were prepared from a Re(CO)5Br precursor to understand the coordination behavior of the ligands against a tricarbonyl rhenium(I) precursor. The rhenium(I) complexes were characterized by means of IR, NMR and mass spectroscopic studies as well as by X-ray crystallography, and correlated with the technetium complexes by means of HPLC studies. Electrochemical reduction of monomeric Re(CO)3-complexes of nitrofuryl ethyl thiosemicarbazone was also studied using cyclic voltammetry. Biodistribution studies of 99mTc(CO)3-labeled thiosemicarbazones in rats intramuscularly infected with S. aureus exhibited substantial in vivo stability of the complex and moderate accumulation at the site of focal infectio

Synthesis, Characterization, and Biological Evaluation of 99mTc(CO)3-Labeled Peptides for Potential Use as Tumor Targeted Radiopharmaceuticals

During the past decade, several peptides containing Arg-Gly-Asp sequence have been conjugated with different chelating agents for labeling with various radionuclides for the diagnosis of tumor development. In this study, we report the synthesis of two tetrapeptides (Asp-Gly-Arg-His and Asp-Gly-Arg-Cys) and one hexapeptide [Asp-Gly-Arg-D-Tyr-Lys-His] by changing the amino acid sequence of the Arg-Gly-Asp motif. Peptide synthesis was initiated from aspartic acid. Aspartic acid placed at C-terminal end of the peptide chain can be conjugated with different drug molecules facilitating their transport to the site of action. The peptides were synthesized in excellent yield and labeled using freshly prepared [99mTc(CO)3(H2O)3]+ intermediate. A complexation yield of over 97% was achieved under mild conditions even at low ligand concentrations of 10�2 M. Radiolabeled peptides were characterized by HPLC and were found to be substantially stable in saline, in His solution as well as in rat serum and tissue (kidney, liver) homogenates. Internalization studies using Ehrlich ascites carcinoma cell line showed rapid and significant internalization (30–35% at 30 min of incubation attaining maximum value of about 40–60% after 2–4 h incubation). A good percentage of quick internalization was also observed in avb3-receptor-positive B16F10 mouse melanoma cell line (14–16% after 30 min of incubation and 25–30% after 2–4 h incubation). Imaging and biodistribution studies were performed in Swiss albino mice bearing Ehrlich ascites tumor in right thigh. Radiolabeled peptides exhibited fast blood clearance and rapid elimination through the urinary systems. 99mTc(CO)3-tetra-Pep2 exhibited remarkable localization at tumor site (1.15%, 1.17%, and 1.37% ID/g at 2, 4, and 6 h p.i., respectively) which could be due to slow clearance of the radiolabeled peptide from blood in comparison with the other two radiolabeled peptides. However, 99mTc(CO)3-hexa-Pep exhibited the highest tumor to muscle and tumor to blood ratios among the three. The preliminary results with these amino acid–based peptides are encouraging enough to carry out further experiments for targeting tumor

A Versatile Pd-Catalyzed Alkyne Annulation Process for Benzo[<i>a</i>]carbazoles and their Anticancer Analogues

A Pd-catalyzed, simple, and divergent approach for the direct synthesis of benzo[a]carbazoles from internal alkynes and N-tosyl-iodoindoles has been demonstrated. This methodology highlights the influences of reaction media and temperature for the synthesis of either N-protected or N-deprotected benzo[a]carbazoles. This cascade strategy provides a series of electronically different benzo[a]carbazoles with good yields. The synthesized benzo[a]carbazoles were evaluated for in vitro anticancer activity against human lung cancer A549 cells and human breast cancer MDA-MB-231 cells. Notably, two of the representative analogues displayed potent anticancer activity against both cancer cell lines

99mTc-Labeling of Ciprofloxacin and Nitrofuryl Thiosemicarbazone Using Fac-[99mTc(CO)3(H2O)3] Core: Evaluation of Their Efficacy as Infection Imaging Agents

The aim of this study was to radiolabel ciprofloxacin (Cip) and nitrofuryl thiosemicarbazone (NFT) with the fac-[99mTc(CO)3(H2O)3]+ core and to evaluate the ability of the radiopharmaceuticals as tracers in detecting sites of infection. Cip and NFT were radiolabeled with the fac-[99mTc(CO)3(H2O)3]+ core and characterized by RHPLC. The stabilities of the preparations were evaluated in saline and rat serum. In vitro binding studies of the radiopharmaceuticals with S. aureus were performed. Biodistribution studies were conducted at different time points after injecting (i.v.) the radiopharmaceuticals in rats (intramuscularly infected with S. aureus) as well as in rats with sterile inflammation. To assess the infection targeting capacity of 99mTc-tricarbonyl ciprofloxacin and nitrofuryl thiosemicarbazone, 99mTc(V)O-Cip and 99mTc(V)O-NFT were used as control. Scintigraphic imaging studies of tricarbonyl compounds and 99mTc(V)O-Cip were performed at 4 h after injection. The radiochemical purities of 99mTc(CO)3-Cip and 99mTc(CO)3-NFT were between 97–98% as determined by thin layer chromatography (TLRC) and RHPLC; no further purification is necessary before injection. The radiopharmaceuticals exhibited substantial stability when incubated in isotonic saline and serum up to 24 h. Biodistribution studies showed maximum uptake in the infected rat thigh muscle at 4 h post injection and washing out at slower rate from the infected site than the oxo technetium chelate. The mean ratios of uptake in infected/non–infected thighs were 3.87 : 1, 3.41 : 1 and 3.17 : 1 for 99mTc(CO)3-Cip, 99mTc(CO)3-NFT and 99mTc(V)O-Cip respectively. During scintigraphic studies, infection sites appeared quite distinctly with 99mTc(CO)3-Cip and 99mTc(CO)3-NFT, comparable to the behaviour with 99mTc(V)O-Cip. These results encouraged us for further development of infection imaging radiopharmaceuticals based on the 99mTc-tricarbonyl core

Exploring the Potential of 99mTc(CO)3-Labeled Triazolyl Peptides for Tumor Diagnosis

In recent years the authors have reported on 99mTc(CO)3-labeled peptides that serve as carriers for biomolecules or radiopharmaceuticals to the tumors. In continuation of that work they report the synthesis of a pentapeptide (Met-Phe-Phe-Gly-His; pep-1), a hexapeptide (Met-Phe-Phe-Asp-Gly-His; pep-2), and a tetrapeptide (Asp-Gly- Arg-His; pep-3) and the attachment of 3-amino-1,2,4-triazole to the b carboxylic function of the aspartic acid unit of pep-2 and pep-3. The pharmacophores were radiolabeled in high yields with [99mTc(CO)3(H2O)3]+ metal aqua ion, characterized for their stability in serum and saline, as well as in His solution, and found to be substantially stable. B16F10 cell line binding studies showed favorable uptake and internalization. In vivo behavior of the radiolabeled triazolyl peptides was assessed in mice bearing induced tumor. The 99mTc(CO)3- triazolyl pep-3 demonstrated rapid urinary clearance and comparatively better tumor uptake. Imaging studies showed visualization of the tumor using 99mTc(CO)3-triazolyl pep-3, but due to high abdominal background, low delineation occurred. Based on the results further experiments will be carried out for targeting tumor with triazolyl peptide

Synthesis and Evaluation of Technetium-99m-Labeled Bioreductive Pharmacophores Conjugated with Amino Acids and Peptides for Tumor Imaging

Development of molecular imaging agents to target tumor has become a major trend in nuclear medicine. With the aim to develop new potential 99mTc-radiopharmaceuticals for targeting tumor, we have synthesized 5-nitroimidazolyl amino acids and RGD-coupled 2-nitroimidazoles. Technetium-99m radiolabeling with high radiochemical purity (>90%) was achieved for all the compounds. The radiolabeled complexes exhibited substantial in vitro stability in saline, serum, and histidine solution (10�2M). Cell binding studies in EAC and B16F10 cell lines also revealed rapid and comparatively high cellular internalization. Among all the compounds studied, the binding of 99mTc(CO)3-5 to B16F10 cells was moderately inhibited by the competitive peptide c[RGDfV], suggesting specificity of the radioligand toward avb3 receptor. However, no significant displacement of bound radioligand was observed when the binding of the 99mTc-labeled complexes to above cells was challenged with excess competitive peptide. Fluorescent microscopy study provided direct evidence of intracellular localization of 5(6)-carboxyfluorescein- labeled 2-nitroimidazolyl-RGD-peptide in avb3-positive B16F10 mouse melanoma cell line. The ligands caused only 8–13% of hemolysis toward rat erythrocytes at concentrations as high as 100 lM. Imaging and biodistribution studies were performed in Swiss albino mice bearing induced tumor. 99mTc-1 and 99mTc(CO)3-5 demonstrated a very favorable in vivo profile. Selective uptake and retention in tumor with encouraging tumor/muscle and tumor/blood ratio and significant cellular uptake of fluorescence-labeled-2-nitroimidazolyl RGD indicate the great potentiality of the pharmacophore for further evaluation as potential molecular imaging agent in cancer diagnosis

Evaluation of 99mTc(I)-tricarbonyl complexes of fluoroquinolones for targeting bacterial infection

The aim of this study was to develop 99mTc(CO)3-labeled fluoroquinolones as novel SPECT radiopharmaceuticals for imaging bacterial infection. Fluoroquinolones, e.g., ofloxacin (OFX), levofloxacin (LVX), lomefloxacin (LMX) and norfloxacin (NFX) were labeled with a fac-[99mTc(CO)3(H2O)3]+ precursor. The radiochemical purity of the radiopharmaceuticals exceeded 97% as determined by thin layer chromatography and HPLC. No further purification was necessary before injection. The Re(CO)3 complex of one of the fluoroquinolones (levofloxacin) was synthesized using [Re(CO)3(H2O)3]OTf and Re(CO)5Br precursors in separate experiments and characterized by IR, NMR and mass spectroscopic analysis. These studies revealed the formation of a single species in which the piperazinyl nitrogen and the –COOH group attached to the benzoxazine ring system of quinolone were involved in co-ordination to the Re(CO)3 core. The HPLC elution pattern and retention time of the Re(CO)3-LVX complex were comparable to those of the corresponding 99mTc(CO)3-complex proving their similarity. When incubated in isotonic saline and serum up to 24 h 99mTc(CO)3-labeled fluoroquinolones exhibited good in vitro stability. Biodistribution studies performed at different time points on rats intramuscularly infected with S. aureus as well as on rats with sterile inflammation revealed a higher uptake in the infected area than the turpentine induced inflamed area. The uptake in infected thigh was significant with 99mTc(CO)3-OFX followed by 99mTc(CO)3-LVX. The mean ratios of the uptake in infected/non-infected thighs were 4.75 and 4.27 at 8 h and 24 h, respectively, for 99mTc(CO)3-OFX and 4.42 and 4.18 at 24 h and 8 h, respectively, for 99mTc(CO)3-LVX. The above abscess to muscle ratios were higher than reported for 99mTc-ciprofloxacin and other 99mTc-labeled fluoroquinolones. Scintigraphy studies also showed a significant uptake in the infectious lesions suggesting that 99mTc(CO)3-fluoroquinolones might be useful as diagnostic agents for targeted delivery in bacterial infection

Antibacterial potential of an ethnic probiotic containing food, Akhuni/Axone and its chemical characterization

‘Akhuni/Axone’, a popular traditional fermented soybean food of northeast India, was evaluated for antibacterial activity against Staphylococcus aureus and Escherichia coli along with its mechanism of action and chemical characterization. The effects of “Akhuni/Axone” treatment on these bacteria were assessed using the following methods: zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentrations (MBC), time kill curve analysis, cellular leakage measurement, oxidative stress analysis, EtBr influx/efflux assay and SEM microscopy. Among petroleum ether, ethyl acetate, ethanol and methanol extracts of ‘Akhuni/Axone’, ethyl acetate extract (AKEA) showed significant antibacterial activity against both the pathogens. The MIC of AKEA was found to be 8.09 ± 0.86 mg/ml and 10.79 ± 0.91 mg/ml against S. aureus and E. coli respectively whereas MBC values were 10.79±0.63 mg/ml and 13.45 ± 1.12 mg/ml against S. aureus and E. coli respectively. The time-kill analysis and cellular leakage assay results indicated that AKEA has bactericidal effect in a concentration and time dependent manner towards both the pathogens. Oxidative stress analysis indicated that AKEA treatment led to excessive ROS production and oxidative stress. EtBr influx/efflux assay indicated AKEA as efflux pump inhibitor and SEM microscopy confirmed the morphological changes on the cell wall and cytoplasmic membrane of bacteria. The chemical analysis of AKEA through 1H NMR, 13C NMR and GC-MS showed a high abundance of triglycerides. These findings indicate that ‘Akhuni/Axone’ can inhibit bacteria, S aureus and E coli and results from this study will be helpful in further studies on other antimicrobial compounds and for developing food-based natural preservatives

Tricarbonyltechnetium(I) and tricarbonylrhenium(I) complexes of amino acids: crystal and molecular structure of a novel cyclic dimeric Re(CO)3-amino acid complex comprised of the OON donor atom set of the tridentate ligand

Radiolabeled complexes of monoamino polycarboxylic, polyamino monocarboxylic and thiol containing amino acid ligands were prepared from a fac-[99mTc(CO)3(H2O)3]+ precursor.The overall radiochemical yield was 94–98%. The complexes exhibited substantial in vitro and in vivo stability. The corresponding Re(I) complexes of the ligands DAPA, Asp and CysH were prepared and characterized by means of IR, NMR, and MS spectroscopic studies, as well as X-ray crystallography (for those containing D,L-DAPA and D,L-Asp). The rhenium complexes have been structurally correlated with the technetium complexes by means of HPLC studies. The reaction of Re(CO)5Cl with D,L-Asp in presence of triethylamine led to the formation of a new class of cyclic dimeric complexes formed by the OON donor atom set of the tridentate ligands. The amino carboxylate ligand system formed well defined complexes with a fac-[M(CO)3(H2O)3]+ core and shows good promise in 99mTc(CO)3 tracer developmen