Synthesis of metal-carbonyl-dendrimer-antibody immunoconjugates: towards a new format for carbonyl metallo immunoassay

Biocompatible Size-Defined Dendrimer-Albumin Binding Protein Hybrid Materials as a Versatile Platform for Biomedical Applications

For the design of a biohybrid structure as a ligand-tailored drug delivery system (DDS), it is highly sophisticated to fabricate a DDS based on smoothly controllable conjugation steps. This article reports on the synthesis and the characterization of biohybrid conjugates based on noncovalent conjugation between a multivalent biotinylated and PEGylated poly(amido amine) (PAMAM) dendrimer and a tetrameric streptavidin-small protein binding scaffold. This protein binding scaffold (SA-ABDwt) possesses nM affinity toward human serum albumin (HSA). Thus, well-defined biohybrid structures, finalized by binding of one or two HSA molecules, are available at each conjugation step in a controlled molar ratio. Overall, these biohybrid assemblies can be used for (i) a controlled modification of dendrimers with the HSA molecules to increase their blood-circulation half-life and passive accumulation in tumor; (ii) rendering dendrimers a specific affinity to various ligands based on mutated ABD domain, thus replacing tedious dendrimer-antibody covalent coupling and purification procedures.

Vibrational spectroscopy of metal carbonyls for bio-imaging and -sensing

Transition metal carbonyls exhibit strong CO absorptions in the 2200–1800 cm⁻¹ region, which is free of interference from other functional groups. This feature has led to their applications in bio-imaging and -sensing, in particular through mid-IR, Raman and more recently, surface-enhanced Raman spectroscopy (SERS).

Towards the Preparation of Novel Re/99mTc Tricarbonyl-Containing Peptide Nucleic Acid Bioconjugates

A novel azido derivative of the di-(2-picolyl)amide (Dpam) ligand, namely 3-azido-N,N-bis-pyridin-2-ylmethyl-propionamide (3), was prepared from 3-bromo-N,N-bis(pyridin-2-ylmethyl)propanamide (2) with an excess of sodium azide in DMSO. 3 was then reacted, by CuI-catalyzed [3 + 2] cycloaddition (often referred to as ‘Click Chemistry’), with the previously reported alkyne-containing peptide nucleic acid (PNA) monomer Fmoc-1-OtBu to give the Dpam-containing PNA monomer (Fmoc-4-OtBu) in 44% yield. It was also demonstrated that 3 could be reacted by Click Chemistry, on the solid phase, to an alkyne-containing PNA oligomer (Alkyne-PNA) to yield Dpam-PNA. Our attempts to complex Dpam-PNA with [NEt4]2[ReBr3(CO)3] and [99mTc(CO)3(H2O)3]+ are also discussed in detail.

Synthesis of metallocarbonyl substituted 1,2,3-triazole complexes via copper(I)-catalyzed azide–alkyne cycloaddition

(η5-C5H5)M(CO)x(η1-N-maleimidato) (M = Fe, x = 2; M = W, x = 3) complexes react with propargylamine and propargyl alcohol giving products from the Michael addition to the η1-N-maleimidato ligand. Metallocarbonyl compounds bearing a terminal alkyne group were reacted with organic azides affording corresponding 1,2,3-triazoles in high yields. One of these metallocarbonyl 1,2,3-triazoles (M = Fe, x = 2) was characterized by X-ray diffraction.

Site-specific conjugation of metal carbonyl dendrimer to antibody and its use as detection reagent in immunoassay

We describe here the conjugation of polyclonal goat anti-rabbit antibody to generation 4 polyamidoamine (G4-PAMAM) dendrimers carrying (i) (η(5)-cyclopentadienyl) iron dicarbonyl succinimidato complexes as infrared (IR) probes, (ii) nitroaniline entities as nuclear magnetic resonance (NMR) probes, (iii) acetamide groups for surface neutralization, and (iv) hydrazide-terminated spacer arms for the reaction with aldehyde. To preserve a high binding affinity, the conjugation was performed on the carbohydrate moieties located on the Fc fragment. The resulting conjugates were characterized by Fourier transform-IR, ultraviolet (UV), and high-mass matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. On the basis of relative concentration ratios of IR probes and antibody, an average labeling of 30 IR probes per antibody was reached (i.e., more than twice the value obtained with our previous strategy that generated no spacer arm). Immunoassays revealed that the antibody-dendrimer conjugates retained 55.1% of immunoreactivity on average with respect to underivatized antibody. Finally, the conjugates were used to quantify their antigen by solid-phase carbonyl metallo immunoassay (CMIA). Results showed a significant enhancement of the IR signal, demonstrating the efficiency of the new conjugation strategy and the potential of the new antibody-dendrimer conjugates as universal immunoanalytical reagents.

Pro-oxidant properties of AZT and other thymidine analogues in macrophages: implication of the azido moiety in oxidative stress

Zidovudine (azidothymidine, AZT) was the first drug approved for human immunodeficiency virus (HIV) treatment. Unfortunately, AZT is known to lead to severe side effects, many of which are generally thought to result from increased reactive oxygen species (ROS) production. In this work, the pro-oxidative properties of AZT and other thymidine analogues were investigated electrochemically at microelectrodes. Macrophages pre-incubated with AZT were found to release significant amounts of reactive species, including H(2)O(2), ONOO(-), NO(*) and NO(2) (-). Interestingly, the total amounts of released species were the greatest when cells were incubated with azido-containing analogues. The pro-oxidative effect of these compounds decreased significantly when the free azide terminal group was modified by reaction with a triosmium cluster. As expected, thymidine incubation did not lead to any increase in overall ROS levels. This work implicates the azido moiety in AZT-induced oxidative stress.

Multifunctional Dendrimer-templated Antibody Presentation on Biosensor Surfaces for Improved Biomarker Detection

Dendrimers, with their well-defined globular shape and a high density of functional groups, are ideal nanoscale materials for templating sensor surfaces. This work exploits dendrimers as a versatile platform for capturing biomarkers with improved sensitivity and specificity. Synthesis, characterization, fabrication, and functional validation of the dendrimer-based assay platform are described. Bifunctional hydroxyl/thiol functionalized G4-polyamidoamine (PAMAM) dendrimer is synthesized and immobilized on to the polyethylene-glycol (PEG)-functionalized assay plate by coupling PEG-maleimide and dendrimer thiol groups. Simultaneously, part of the dendrimer thiol groups are converted to hydrazide functionalities. The resulting dendrimer-modified surface is coupled to the capture antibody in the Fc region of the oxidized antibody. This preserves the orientation flexibility of the antigen binding region (Fv) of the antibody. To validate the approach, the fabricated plates are further used as a solid phase for developing a sandwich type ELISA to detect IL-6 and IL-1β, important biomarkers for early stages of chorioamnionitis. The dendrimer-modified plate provides assays with significantly enhanced sensitivity, lower nonspecific adsorption, and a detection limit of 0.13 pg ml-1 for IL-6 luminol detection and 1.15 pg ml-1 for IL-1β TMB detection, which are significantly better than those for the traditional ELISA. The assays were validated in human serum samples from normal (non-pregnant) woman and pregnant women with pyelonephritis. The specificity and the improved sensitivity of the dendrimer-based capture strategy could have significant implications for the detection of a wide range of cytokines and biomarkers since the capture strategy could be applied to multiplex microbead assays, conductometric immunosensors and field effect biosensors.