Extending the Scope of the C-Functionalization of Cyclam via Copper(I)-Catalyzed Alkyne-Azide Cycloaddition to Bifunctional Chelators of Interest.

Cyclam, known for its potent chelation properties, is explored for diverse applications through selective N-functionalization, offering versatile ligands for catalysis, medical research, and materials science. The challenges arising from N-alkylation, which could decrease the coordination properties, are addressed by introducing a robust C-functionalization method. The facile two-step synthesis proposed here involves the click chemistry-based C-functionalization of a hydroxyethyl cyclam derivative using Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC). Boc-protecting groups prevent undesired copper coordination, resulting in compounds with a wide range of functionalities. The optimized synthesis conditions enable C-functional cyclams to be obtained easily and advantageously, with high application potential in the previously cited fields. The methodology has been extended to trehalose-based Siamese twin amphiphiles, enabling efficient gene delivery applications.

Selective synthesis of an elusive C-functional bis-cyclam and study of its inhibition of the CXCR4 chemokine receptor.

This article presents the controlled synthesis of a rare example of C,C'-linked bis-cyclam architecture in mild conditions through the "bis-aminal" route previously used for the advantageous synthesis of cyclam, N- and C-functional cyclams and N,N'-bis-cyclams. Two synthetic pathways were explored with the smart design of α,ß-unsaturated ketones or alkyl halides bis-cyclizing agents. The first led to the isolation of a key intermediate for the future design of N-functionalized bis-cyclams, whereas the second allowed the preparation of the targeted C,C'-xylylene-bis-cyclam under mild conditions with decent yield. This compound was then studied as a CXCR4 receptor inhibitor, one of the main applications known for bis-macrocyclic compounds, in particular in the context of HIV (human immunodeficiency virus) infection. Although results demonstrated that its potency is lower (i.e. 137-fold higher IC50) than the gold standard AMD3100 against HIV infection, clear evidence of CXCR4 inhibition is presented, confirming the potential of this novel architecture and related compounds in this research field.

Trehalose-polyamine/DNA nanocomplexes: impact of vector architecture on cell and organ transfection selectivity.

A novel family of precision-engineered gene vectors with well-defined structures built on trehalose and trehalose-based macrocycles (cyclotrehalans) comprising linear or cyclic polyamine heads have been synthesized through procedures that exploit click chemistry reactions. The strategy was conceived to enable systematic structural variations and, at the same time, ensuring that enantiomerically pure vectors are obtained. Notably, changes in the molecular architecture translated into topological differences at the nanoscale upon co-assembly with plasmid DNA, especially regarding the presence of regions with short- or long-range internal order as observed by TEM. In vitro and in vivo experiments further evidenced a significant impact on cell and organ transfection selectivity. Altogether, the results highlight the potential of trehalose-polyamine/pDNA nanocomplex monoformulations to achieve targeting transfection without the need for any additional cell- or organ-sorting component.

Exploring the Limits of Ligand Rigidification in Transition Metal Complexes with Mono-N-Functionalized Pyclen Derivatives.

We report the synthesis of a new family of side-bridged pyclen ligands. The incorporation of an ethylene bridge between two adjacent nitrogen atoms was reached from the pyclen-oxalate precursor described previously. Three new side-bridged pyclen macrocycles, Hsb-3-pc1a, sb-3-pc1py, and Hsb-3-pc1pa, were obtained with the aim to assess their coordination properties toward Cu2+ and Zn2+ ions. We also prepared their nonreinforced analogues H3-pc1a, 3-pc1py, and H3-pc1pa as comparative benchmarks. The two series of ligands were characterized and their coordination properties were investigated in detail. The Zn2+ and Cu2+ complexes with the nonside-bridged series H3-pc1a, 3-pc1py, and H3-pc1pa were successfully isolated and their structures were assessed by X-ray diffraction studies. In the case of the side-bridged family, the synthesis of the complexes was far more difficult and, in some cases, unsuccessful. The results of our studies demonstrate that this difficulty is related to the extreme stiffening and basicity of such side-bridged pyclens.

Multistep synthesis of a novel copper complex with potential for Alzheimer's disease diagnosis.

Positron emission tomography (PET) imaging of Aß plaques, is recognized as a tool for the diagnosis of Alzheimer's disease. As a contribution to the development of new strategies for early diagnosis of the disease, using PET medical imaging technique, a new copper complex, the [Cu(TE1PA-ONO)]+ was synthesized in ten steps. The key step of our strategy is the coupling of a monopicolinate-N-alkylated cyclam-based ligand with a moiety capable of recognizing Aß plaques via a successful and challenging Buchwald-Hartwig coupling reaction. To our knowledge, it is the first time that such a strategy is used to functionalize polyazamacrocyclic derivatives. The thermodynamic stability constants determined in MeOH/H2O solvent indicate that the attachment of this moiety does not weaken the chelating properties of TE1PA-ONO ligand in relation to parent HTE1PA. The novel complex described here is able to recognize amyloid plaques in brain sections from Alzheimer's disease patients and shows low toxicity to human neuronal cells.

Synthesis and Photophysical Properties of Lanthanide Pyridinylphosphonic Tacn and Pyclen Derivatives: From Mononuclear Complexes to Supramolecular Heteronuclear Assemblies.

Synthetic methodologies were developed to achieve the preparation of ligands L1 and L2 consisting of tacn- and pyclen-based chelators decorated with pyridinylphosphonic pendant arms combined with ethylpicolinamide or acetate coordinating functions, respectively. Phosphonate functions have been selected for their high affinity toward Ln3+ ions compared to their carboxylated counterparts and for their steric hindrance that favors the formation of less-hydrated complexes. Thanks to regiospecific N-functionalization of the macrocyclic backbones, the two ligands were isolated with good yields and implicated in a comprehensive photophysical study for the complexation of Eu3+, Tb3+, and Yb3+. The coordination behavior of L1 and L2 with these cations has been first investigated by means of a combination of UV-vis absorption spectroscopy, steady-state and time-resolved luminescence spectroscopy, and 1H and 31P NMR titration experiments. Structural characterization in solution was assessed by NMR spectroscopy, corroborated by theoretical calculations. Spectroscopic characterization of the Ln3+ complexes of L1 and L2 was done in water and D2O and showed the effective sensitization of the lanthanide metal-centered emission spectra, each exhibiting typical lanthanide emission bands. The results obtained for the phosphonated ligands were compared with those reported previously for the corresponding carboxylated analogues.

H3nota Derivatives Possessing Picolyl and Picolinate Pendants for Ga3+ Coordination and 67Ga3+ Radiolabeling.

We synthesized, thanks to the regiospecific N-functionalization using an orthoamide intermediate, two 1,4,7-triazacyclononane derivatives containing an acetate arm and either a methylpyridine or a picolinic acid group, respectively, Hnoapy and H2noapa, as new Ga3+ chelators for potential use in nuclear medicine. The corresponding Ga3+ complexes were synthesized and structurally characterized in solution by 1H and 13C NMR. The [Ga(noapy)]2+ complex appears to exist in solution as two diasteroisomeric pairs of enantiomers, as confirmed by density functional theory (DFT) calculations, while for [Ga(noapa)]+, a single species is present in solution. Solid-state investigations were possible for the [Ga(noapa)]+ complex, which crystallized from water as a pair of enantiomers. The average length of the N-Ga bonds of 2.090 Å is identical with that found for the [Ga(nota)] complex, showing that the presence of the picolinate arm does not hinder the coordination of the ligand to the metal ion. Protonation constants of noapy- and noapa2- were determined by potentiometric titrations, providing an overall basicity ∑log KiH (i = 1-4) that increases in the order noapy- < noapa2- < nota3- with increases in the negative charge of the ligand. Stability constants determined by pH-potentiometric titrations supplemented with 71Ga NMR data show that the stabilities of [Ga(noapy)]2+ and [Ga(noapa)]+ are lower compared to that of [Ga(nota)] but higher than those of other standards such as [Ga(aazta)]-. 67Ga radiolabeling studies were performed in order to demonstrate the potential of these chelators for 67/68Ga-based radiopharmaceuticals. The labelings of Hnoapy and H2noapa were nearly identical, outperforming H3nota. Stability studies were conducted in phosphate-buffered saline and in the presence of human serum transferrin, revealing no significant decomplexation of [67Ga][Ga(noapy)]2+ and [67Ga][Ga(noapa)]+ compared to [67Ga][Ga(nota)]. Finally, all complexes were found to be highly hydrophilic, with calculated log D7.4 values of -3.42 ± 0.05, -3.34 ± 0.04, and -3.00 ± 0.23 for Hnoapy, H2noapa, and H3nota, respectively, correlating with the charge of each complex and the electrostatic potentials obtained with DFT.

Preclinical Evaluation of a 64Cu-Based Theranostic Approach in a Murine Model of Multiple Myeloma.

Although the concept of theranostics is neither new nor exclusive to nuclear medicine, it is a particularly promising approach for the future of nuclear oncology. This approach is based on the use of molecules targeting specific biomarkers in the tumour or its microenvironment, associated with optimal radionuclides which, depending on their emission properties, allow the combination of diagnosis by molecular imaging and targeted radionuclide therapy (TRT). Copper-64 has suitable decay properties (both ß+ and ß- decays) for PET imaging and potentially for TRT, making it both an imaging and therapy agent. We developed and evaluated a theranostic approach using a copper-64 radiolabelled anti-CD138 antibody, [64Cu]Cu-TE1PA-9E7.4 in a MOPC315.BM mouse model of multiple myeloma. PET imaging using [64Cu]Cu-TE1PA-9E7.4 allows for high-resolution PET images. Dosimetric estimation from ex vivo biodistribution data revealed acceptable delivered doses to healthy organs and tissues, and a very encouraging tumour absorbed dose for TRT applications. Therapeutic efficacy resulting in delayed tumour growth and increased survival without inducing major or irreversible toxicity has been observed with 2 doses of 35 MBq administered at a 2-week interval. Repeated injections of [64Cu]Cu-TE1PA-9E7.4 are safe and can be effective for TRT application in this syngeneic preclinical model of MM.

Design of Bifunctional Pyclen-Based Lanthanide Luminescent Bioprobes for Targeted Two-Photon Imaging.

In the past, Lanthanide Luminescent Bioprobes (LLBs) based on pyclen-bearing π-extended picolinate antennas were synthesized and demonstrated well-adapted optical properties for biphotonic microscopy. The objective of this work is to develop a strategy to design bifunctional analogues of the previously studied LLBs presenting an additional reactive chemical group to allow their coupling to biological vectors to reach deep in vivo targeted two-photon bioimaging. Herein, we elaborated a synthetic scheme allowing the introduction of a primary amine on the para position of the macrocyclic pyridine unit. The photophysical and bioimaging studies demonstrate that the introduction of the reactive function does not alter the luminescent properties of the LLBs paving the way for further applications.

A Phosphine Oxide-Functionalized Cyclam as a Specific Copper(II) Chelator.

Although cyclam-based ligands are among the strongest copper(II) chelators available, they also usually present good affinity for other divalent cations [Zn(II), Ni(II), and Co(II)], with no copper(II)-specific cyclam ligands having been described so far. As such a property is highly desirable in a wide range of applications, we present herein two novel phosphine oxide-appended cyclam ligands that could be efficiently synthesized through Kabachnik-Fields type reactions on protected cyclam precursors. Their copper(II) coordination properties were closely studied by different physicochemical techniques [electron paramagnetic resonance (EPR) and ultraviolet-visible (UV-vis) spectroscopies, X-ray diffraction, and potentiometry]. The mono(diphenylphosphine oxide)-functionalized ligand demonstrated a copper(II)-specific behavior, unprecedented within the cyclam family of ligands. This was evidenced by UV-vis complexation and competition studies with the parent divalent cations. Density functional theory calculations also confirmed that the particular ligand geometry in the complexes strongly favors copper(II) coordination over that of competing divalent cations, rationalizing the specificity observed experimentally.

Highly inert Cu(II) complexes of C-aryl bifunctional cyclam-picolinates with remarkable 64Cu-labelling and biodistribution.

Cyclam-picolinate chelators were functionalized via click chemistry with an additional carboxyl group for subsequent bioconjugation to antibodies or for the modification of the overall charge of the corresponding 64Cu-radiocomplexes. The C-aryl functionalization strategy developed here preserves the chemical properties of the radiocomplexes whilst deeply enhancing their applications within nuclear medicine.

On the dissociation pathways of copper complexes relevant as PET imaging agents.

Several bifunctional chelators have been synthesized in the last years for the development of new 64Cu-based PET agents for in vivo imaging. When designing a metal-based PET probe, it is important to achieve high stability and kinetic inertness once the radioisotope is coordinated. Different competitive assays are commonly used to evaluate the possible dissociation mechanisms that may induce Cu(II) release in the body. Among them, acid-assisted dissociation tests or transchelation challenges employing EDTA or SOD are frequently used to evaluate both solution thermodynamics and the kinetic behavior of potential metal-based systems. Despite of this, the Cu(II)/Cu(I) bioreduction pathway that could be promoted by the presence of bioreductants still remains little explored. To fill this gap we present here a detailed spectroscopic study of the kinetic behavior of different macrocyclic Cu(II) complexes. The complexes investigated include the cross-bridge cyclam derivative [Cu(CB-TE1A)]+, whose structure was determined using single-crystal X-ray diffraction. The acid-assisted dissociation mechanism was investigated using HClO4 and HCl to analyse the effect of the counterion on the rate constants. The complexes were selected so that the effects of complex charge and coordination polyhedron could be assessed. Cyclic voltammetry experiments were conducted to investigate whether the reduction to Cu(I) falls within the window of common bioreducing agents. The most striking behavior concerns the [Cu(NO2Th)]2+ complex, a 1,4,7-triazacyclononane derivative containing two methylthiazolyl pendant arms. This complex is extremely inert with respect to dissociation following the acid-catalyzed mechanism, but dissociates rather quickly in the presence of a bioreductant like ascorbic acid.

["Imaging of diagnostic and therapeutic biomarkers in oncology" XIIIth edition of the workshop organised by the « Vectorisation, Imagerie, Radiothérapies ¼ network of the Cancéropôle Grand-Ouest, September 25-28, 2019, Le Bono, France]. / "Imaging of diagnostic and therapeutic biomarkers in oncology" XIIIe édition du workshop organisé par le réseau « Vectorisation, Imagerie, Radiothérapies ¼ du Cancéropôle Grand-Ouest, 25­28 septembre 2019, Le Bono, France.

The thirteenth edition of the workshop focused on the last developments on oncologic imaging techniques. Our goal was purposely large, consisting in bringing together chemists, biologists, physicists, pharmacists and physicians to discuss these imaging developments. The meeting focused in four main topics: i) the evolution of imaging modalities such as photoacoustic or the latest PET (positrons emission tomography) imaging progress; ii) the improvements in imaging process; iii) the numerous contributions of chemistry towards medical imaging and iv) novel approaches of nuclear medicine in therapeutic monitoring strategies and theranostic aspects.

Bioconjugated chelates based on (methylpyridinyl)tacn: synthesis, 64Cu labeling and in vitro evaluation for prostate cancer targeting.

Three new bifunctional copper chelators based on the 1,4,7-triazacyclononane (tacn) platform have been synthesized and conjugated to peptides. The first one is constituted of the tacn with two methylpyridinyl and one methylthiazolyl carboxylic acid pendant arms, while, in the second and third ones, the macrocycle is functionalized by three methylpyridinyl groups, with an additional hexynoic acid chain on a carbon of one or two pyridine rings. These three bifunctional chelators have been conjugated to the antagonist DPhe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 peptide for targeting the gastrin-releasing peptide receptor, which is overexpressed in prostate cancer. The resulting monomeric bioconjugates have shown their efficiency to be radiolabeled with ß+ emitter 64Cu, and the hydrophilicity and PC-3 cell internalization properties of these radiolabeled conjugates have been studied. PC-3 cell binding affinity of mono- and dimeric metal-free and natCu metallated conjugates have been evaluated by IC50 measurements. The results demonstrate the potential of these methylpyridinyl tacn derivatives for radiopharmaceutical applications.

New Triazacycloalkane Derivatives as Cytotoxic Agents for CLL Treatment: From Proof of Concept to the Targeting Biomolecule.

The 1,4,7-tris-(2-pyridinylmethyl)-1,4,7-triazacyclononane ligand (no3py) and its bifunctional analogue no3pyCOOK were synthesized to investigate their action toward zinc(II) depletion related to the apoptosis phenomenon in chronic lymphocytic leukemia (CLL) cells. no3py was used as the "free" ligand, while its "graftable" derivative was conjugated on a newly synthesized bifunctional sialoglycan, 6'-SL-NH2, selected to specifically bind CD22 biomarker expressed on the B-CLL cell surface. Both compounds were produced with good yields thanks to a Sonogashira coupling reaction and an orthoester function, respectively, for the chelator and the targeting moiety. The newly reported bioconjugate 6'-SL-no3py was then obtained through a peptidic coupling reaction. Biological in vitro studies of no3py and 6'-SL-no3py consisting of real-time detection of cell health (cytotoxicity and proliferation) and caspases 3/7 activation (crucial enzymes whose activation triggers cell death signaling pathways) have been investigated. First, Ramos, Daudi, and Raji B-cell lines, which present different sensitivity to zinc(II) content variation, were incubated with no3py and 6'-SL-no3py. Then, a videomicroscope allowed the real-time monitoring of the morphological changes leading to cell death from the detection of the cytotoxicity, the antiproliferative effect, and the caspasic activity. In terms of mechanism, the Zn2+ chelator cytotoxic effect of no3py has been evidenced by a culture medium ion supplementation study and by the decrease of intracellular fluorescence of Zn-specific fluorophore zinquin in the presence of no3py and 6'-SL-no3py chelators. Finally, flow cytometry analysis with classical Annexin V staining was conducted to detect no3py- and 6'-SL-no3py-induced apoptotic cell death in B-CLL cells. Time-course analysis, using the Incucyte Live-Cell Analysis System, demonstrated that no3py induced cell death in a time- and dose-dependent manner with variability across cell lines. 6'-SL-no3py exhibited the same dose-dependent trend as no3py, showing the efficiency of the targeting moiety. In both cases, the chelators depicted proliferation curves that were inversely correlated with kinetic death. Morphological changes specific to apoptosis and caspase 3/7 activation were observed for the three cell lines treated with no3py and 6'-SL-no3py, highlighting their role as apoptotic agents. A higher concentration of 6'-SL-no3py is needed to reach 50% of the B-CLL mortality, confirming a targeting of the chelator to the cell membrane. Overall, our results proved that the biological properties of the triazamacrocyclic chelator still remain even after addition of the targeting moiety. The free chelator as well as the bioconjugate constitute promising cytotoxic agents for CLL therapy through apoptosis induction.

Relevance of Palladium to Radiopharmaceutical Development Considering Enhanced Coordination Properties of TE1PA.

Invited for the cover of this issue are the group of Raphaël Tripier and Nathalie Le Bris at the University of Brest (UMR CNRS 6521 CEMCA; France), Cathryn H. S. Driver from the South African Nuclear Energy Corporation in Pretoria (South Africa), and their collaborators. The image depicts the beginning of a new area of research into palladium and complexation of its radioisotopes for applications in nuclear medicine. Read the full text of the article at 10.1002/chem.202200942.

Relevance of Palladium to Radiopharmaceutical Development Considering Enhanced Coordination Properties of TE1PA.

The limited use of palladium-103 and -109 radionuclides for molecular radiotherapy is surely due to the lack of appropriate ligands capable of fulfilling all criteria required for application in nuclear medicine. Furthermore, the thermodynamic properties of these complexes in solution remain difficult to establish. The challenge is compounded when considering that radiolabeling of compounds for translation to clinical trials requires fast complexation. Thus, the coordination of Pd(II) and 103/109 Pd-nuclides is a huge challenge in terms of molecular design and physicochemical characterization. Herein, we report a comprehensive study highlighting TE1PA, a monopicolinate cyclam - already established in nuclear imaging with 64 Cu-PET (positron emission tomography) imaging tracers - as a highly relevant chelator for natural Pd and subsequently 109 Pd-nuclide. The structural, thermodynamic, kinetic and radiolabeling studies of Pd(II) with TE1PA, as well as the comparison of this complex with three structurally related derivatives, support palladium-TE1PA radiopharmaceuticals as leading candidates for targeted nuclear medicine.

Radiopharmaceutical Labelling for Lung Ventilation/Perfusion PET/CT Imaging: A Review of Production and Optimization Processes for Clinical Use.

Lung ventilation/perfusion (V/Q) positron emission tomography-computed tomography (PET/CT) is a promising imaging modality for regional lung function assessment. The same carrier molecules as a conventional V/Q scan (i.e., carbon nanoparticles for ventilation and macro aggregated albumin particles for perfusion) are used, but they are labeled with gallium-68 (68Ga) instead of technetium-99m (99mTc). For both radiopharmaceuticals, various production processes have been proposed. This article discusses the challenges associated with the transition from 99mTc- to 68Ga-labelled radiopharmaceuticals. The various production and optimization processes for both radiopharmaceuticals are reviewed and discussed for optimal clinical use.