Dimitri Stanicki

Carboxy-silane coated iron oxide nanoparticles: a convenient platform for cellular and small animal imaging

This study reports the synthesis of stabilized ultrasmall iron oxide nanoparticles (USPIO) as bimodal probes for magnetic resonance and optical imaging. These nanosystems are based on small iron oxide cores surrounded by a thin polysiloxane shell exhibiting carboxylic acid functions. Thanks to these functions, hybrid particles were obtained by conjugating a fluorophore to the superparamagnetic contrastophore. Such modification allowed us to directly follow these USPIO in cellulo, which provided interesting information about their internalization pathway and cellular distribution upon mitosis. Finally, the efficiency of these systems as probes for bimodal imaging was emphasized by the observation of their in vivo behavior in mice using magnetic resonance and optical imaging.

A comparative physicochemical, morphological and magnetic study of silane-functionalized superparamagnetic iron oxide nanoparticles prepared by alkaline coprecipitation.

The characterization of synthetic superparamagnetic iron oxide nanoparticle (SPION) surfaces prior to functionalization is an essential step in the prediction of their successful functionalization, and in uncovering issues that may influence their selection as magnetically targeted drug delivery vehicles (prodrugs). Here, three differently functionalized magnetite (Fe3O4) SPIONs are considered. All were identically prepared by the alkaline coprecipitation of Fe(2+) and Fe(3+) salts. We use X-ray photoelectron spectroscopy, electron microscopy, time-of-flight SIMS, FTIR spectroscopy and magnetic measurements to characterize their chemical, morphological and magnetic properties, in order to aid in determining how their surfaces differ from those prepared by Fe(CO)5 decomposition, which we have already studied, and in assessing their potential use as drug delivery carriers.

New carboxysilane-coated iron oxide nanoparticles for nonspecific cell labelling.

Magnetic resonance imaging (MRI) offers the possibility of tracking cells labelled with a contrast agent and evaluating the progress of cell therapies. This requires efficient cell labelling with contrast agents. A basic incubation of cells with iron oxide nanoparticles (NPs) is a common method. This study reports the synthesis at the gram scale of iron oxide nanoparticles as MRI T₂ contrast agents for cell labelling. These NPs are based on small iron oxide cores coated with a thin polysiloxane shell presenting carboxylic acid functions. The iron oxide cores produced have been characterized by transmission electron microscopy, X-ray diffraction, ζ-potential, infrared, photon correlation spectroscopy, atomic force microscopy, magnetometry and relaxometric measurements. These measurements confirmed the expected surface modification by carboxysilane. Carboxylic groups created electrostatic repulsion between NPs when they are deprotonated. Therefore, highly concentrated aqueous solutions of carboxysilane coated iron oxide NPs can be obtained, up to 70% (w/w). These NPs could be used for cell labelling owing to their aggregation and re-dispersion properties. NPs precipitated in Dulbeccos modified Eagle medium induced a rapid association with 3 T6 fibroblast cells and could easily be re-dispersed in phosphate buffer saline solution to obtain properly labelled cells.

1,4-diarylpiperazines and analogs as anti-tubercular agents: synthesis and biological evaluation.

Despite progress in modern chemotherapy to combat tuberculosis, the causative pathogen Mycobacterium tuberculosis (M.tb.) is far from eradicated. Bacillary resistance to anti-mycobacterial agents, bacillary persistence and human immunodeficiency virus (HIV) co-infection hamper current drug treatment to completely cure the infection, generating a constant demand for novel drug candidates to tackle these problems. A small library of novel heterocyclic compounds was screened in a rapid luminometric in vitro assay against the laboratory M.tb. strain H37Rv. A group of amidines was found to have the highest potency and was further evaluated for acute toxicity against C3A hepatocytes. Next, the most promising compounds were evaluated for activity against a multi-drug resistant clinical isolate. The group of amidines was also tested for their ability to kill intracellular M.tb. residing in mouse J774A.1 macrophages. Finally, we report on a correlation between the structural differences of the compounds and their anti-mycobacterial activity.

1,2-ethane bis-1-amino-4-benzamidine is active against several brain insult and seizure challenges through anti-NMDA mechanisms targeting the 3H-TCP binding site and antioxidant action

Five bis-benzamidines were screened towards murine magnesium deficiency-dependent audiogenic seizures, unravelling two compounds with efficacious doses 50 (ED(50)) less than 10mg/kg. They were also screened against maximal electroshock and subcutaneous pentylenetetrazole-induced seizures, and explored for superoxide -scavenging activity. 1,2-Ethane bis-1-amino-4-benzamidine (EBAB) was selected and evaluated in 6 Hz seizure test (ED(50)=49 mg/kg) and at 4 microg/kg in focal cerebral ibotenate poisoning in pups (sizes of both white and grey matter wounds were halved). EBAB was further tested on NMDA-induced seizures in mice (ED(50)=6 mg/kg) and on (3)H-TC -binding to a rodent cerebral preparation (IC(50)=1.4 microM). Taken as a whole, present data emphasise the suitability of bis-benzamidines as templates for designing brain protective compounds.

Functionalization of the PEG Corona of Nanoparticles by Clip Photochemistry in Water: Application to the Grafting of RGD Ligands on PEGylated USPIO Imaging Agent

The fast development of nanomedicines requires more and more reliable chemical tools in order to accurately design materials and control the surface properties of the nano-objects used in biomedical applications. In this study we describe a smooth and simple photografting technique, i.e., the clip photochemistry, that allows the introduction of molecules of interest in inert polymers or on stealth nanoparticles directly in aqueous solution. First we developed the methodology on polyethylene glycol (PEG) and looked for critical parameters of the process (irradiation times, concentrations, washings) by using several molecular probes and adapted analytical techniques ((19)F qNMR, EA, LSC). We found that the clip photochemistry in water is a robust and efficient method to functionalize PEG. Second we applied it on PEGylated USPIO (USPIO-PEG) magnetic resonance imaging agent and succeeded in introducing RGD peptide and homemade peptidomimetics on their PEG segments. The magnetic abilities of the conjugated nanoparticles were unchanged by the derivatization process as evidenced by their relaxometric properties and their NMRD profile. When tested on Jurkat lymphocyte T Cells, which express αvβ3 integrins, the USPIO conjugated with RGD ligands leads to an increase of the transverse relaxation rate (R2) by a factor 10 to 14 as compared to USPIO-PEG. Consequently, it makes them good candidates for targeted imaging technology in cancer therapy.

Three optimized and validated (using accuracy profiles) LC methods for the determination of pentamidine and new analogs in rat plasma

Three novel LC-UV methods for the determination of pentamidine (PTMD) and two of its new analogs in rat plasma are described. The chromatographic conditions (wavelength, acetonitrile percentage in the mobile phase, internal standard) were optimized to have an efficient selectivity. A pre-step of extraction was simultaneously developed for each compound. For PTMD, a solid phase extraction (SPE) with Oasis(®) HLB cartridges was selected, while for the analogs we used protein precipitation with acetonitrile. SPE for PTMD gave excellent results in terms of extraction yield (99.7 ± 2.8) whereas the recoveries for the analogs were not so high but were reproducible as well (64.6 ± 2.6 and 36.8 ± 1.6 for analog 1 and 2, respectively). By means of a recent strategy based on accuracy profiles (β-expectation tolerance interval), the methods were successfully validated. β was fixed at 95% and the acceptability limits at ± 15% as recommended by the FDA. The method was successfully validated for PTMD (29.6-586.54 ng/mL), analog 1 (74.23-742.3 ng/mL) and analog 2 (178.12-890.6 ng/mL). The first concentration level tested was considered as the LLOQ (lower limit of quantification) for PTMD and analog 1 whereas for analog 2, the LLOQ was not the first level tested and was raised to 178.12 ng/mL.

Relating the Surface Properties of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) to Their Bactericidal Effect towards a Biofilm of Streptococcus mutans

This study was designed to determine the effects of superparamagnetic iron oxide nanoparticles (SPIONs) on the biological activity of a bacterial biofilm (Streptococcus mutans). Our hypothesis was that the diffusion of the SPIONs into biofilms would depend on their surface properties, which in turn would largely be determined by their surface functionality. Bare, positively charged and negatively charged SPIONs, with hydrodynamic diameters of 14.6 ± 1.4 nm, 20.4 ± 1.3 nm and 21.2 ± 1.6 nm were evaluated. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and electrophoretic mobility (EPM) measurements were used to confirm that carboxylic functional groups predominated on the negatively charged SPIONS, whereas amine functional groups predominated on the positively charged particles. Transmission electron microscopy (TEM) showed the morphology and sizes of SPIONs. Scanning electron microscopy (SEM) and EPM measurements indicated that the surfaces of the SPIONs were covered with biomolecules following their incubation with the biofilm. Bare SPIONs killed bacteria less than the positively charged SPIONs at the highest exposure concentrations, but the toxicity of the bare and positively charged SPIONs was the same for lower SPION concentrations. The positively charged SPIONs were more effective in killing bacteria than the negatively charged ones. Nonetheless, electrophoretic mobilities of all three SPIONs (negative, bare and positively charged) became more negative following incubation with the (negatively-charged) biofilm. Therefore, while the surface charge of SPIONS was important in determining their biological activity, the initial surface charge was not constant in the presence of the biofilm, leading eventually to SPIONS with fairly similar surface charges in situ. The study nonetheless suggests that the surface characteristics of the SPIONS is an important parameter controlling the efficiency of antimicrobial agents. The analysis of the CFU/mL values shows that the SPIONs have the same toxicity on bacteria in solution in comparison with that on the biofilm.

Charge effect of superparamagnetic iron oxide nanoparticles on their surface functionalization by photo-initiated chemical vapour deposition

Diverse applications of superparamagnetic iron oxide nanoparticles (SPIONs) in the chemical and biomedical industry depend on their surface properties. In this paper, we investigate the effect of initial surface charge (bare, positively and negatively charged SPIONs) on the resulting physicochemical properties of the particles following treatment through photo-initiated chemical vapour deposition (PICVD). Transmission electron microscopy shows a nanometric polymer coating on the SPIONs and contact angle measurements with water demonstrate that their surface became non-polar following functionalization using PICVD. FTIR and XPS data confirm the change in the chemical composition of the treated SPIONs. Indeed, XPS data reveal an initial charge-dependent increase in the surface oxygen content in the case of treated SPIONs. The O/C percentage ratios of the bare SPIONs increase from 1.7 to 1.9 after PICVD treatment, and decrease from 1.7 to 0.7 in the case of negatively charged SPIONs. The ratio remains unchanged for positively charged SPIONs (1.7). This indicates that bare and negatively charged SPIONs showed opposite preference for the oxygen or carbon attachment to their surface during their surface treatment. These results reveal that both the surface charge and stereochemical effects have determinant roles in the polymeric coating of SPIONs with PICVD. Our findings suggest that this technique is appropriate for the treatment of nanoparticles.Graphical Abstract

Bisbenzamidines as Antifungal Agents. Are Both Amidine Functions Required to Observe an Anti-Pneumocystis carinii Activity?

A library of 19 novel 4-(4-phenylpiperazine-1-yl)benzamidines has been synthesized and evaluated in vitro against Pneumocystis carinii. Among these compounds, N-ethyl- and N-hexyl-4-(4-phenylpiperazine-1-yl)benzamidines emerged as the most promising compounds, with inhibition percentages at 10.0 µg/mL of 87% and 96%, respectively. Those compounds remained active at 0.1 µg/mL.