Kyangwi Patrick Malikidogo

L’Imagerie par Résonance Magnétique (IRM) est classiquement utilisée pour l’obtention d’images anatomiques et fonctionnelles. L’émergence de l’imagerie moléculaire, qui cherche à visualiser des modifications biochimiques apparaissant de manière plus précoces que les changements morphologiques, nécessite l’utilisation de sondes spécifiques du processus à détecter. Cela a conduit à la conception de nouveaux agents de contraste IRM « intelligents » à base de Gd(III). La détection du Zn(II) reste un enjeu important du fait de son rôle dans les processus physiologiques et son implication dans diverses pathologies. Un des problèmes majeurs à surmonter est sa quantification. Dans cette perspective, nous avons développé des sondes bimodales variant uniquement par la nature du Ln(III) : Gd(III) pour l’IRM (technique responsive) et 165Er(III) pour la tomographie par émission monophotonique(technique quantitative). Ces sondes sont composées d’un complexe de Ln(III) à base de pyridine relié à un motif DPA (dipicolylamide) ou DPA modifié pour la complexation du Zn(II) via un espaceur.Nous nous sommes d’abord attachés à optimiser la réponse des complexes de Gd(III) au Zn(II). Nous avons augmenté la stabilité thermodynamique des complexes de Ln(III) par ajout d’une fonction carboxylate sur le ligand. Cette famille de complexes répond au Zn(II) en présence de HSA (Albumine sérique humaine) par modification du temps de corrélation rotationnel. Nous avons ensuite réalisé une étude structurale afin de rationaliser les paramètres importants pour optimiser la réponse au Zn(II) en présence de HSA et/ou la sélectivité, en particulier vis-à-vis du Cu(II). Nous avons également développé une famille de molécules répondant à la présence de Zn(II) par variation modeste du nombre d’hydratation q.Finalement nous avons pu valider l’utilisation de l’165Er(III) pour la détection quantitative in vitro de Zn(II).

An anisolyl-picolinate antenna grafted onto different macrocyclic ligands such as tacn, pyclen, or cyclen renders the resulting terbium(III) complexes highly sensitive to oxygen in aqueous solutions, enabling the design of ratiometric or lifetime-based molecular sensors. The underlying sensitization mechanism was investigated using analogous gadolinium(III) complexes, and the oxygen sensitivity was studied using transient absorption spectroscopy. The antenna-based triplet lifetime increased by up to 900-fold upon degassing, underscoring the role of the ligand excited states in designing highly sensitive oxygen probes.

An anisolyl-picolinate antenna grafted onto different macrocyclic ligands such as tacn, pyclen or cyclen renders the resulting terbium (III) complexes highly sensitive towards oxygen in aqueous solutions, enabling the design of ratiometric or lifetime-based molecular sensors. The underlying sensitization mechanism was investigated on analogous Gd(III) complexes and the oxygen sensitivity was studied using transient absorption spectroscopy. The antenna-based triplet lifetime increased up to 900-fold upon degassing, underscoring the role of the ligand excited states in designing highly sensitive oxygen probes.

Lanthanide(III) (Ln³⁺) complexes have desirable photophysical properties for optical bioimaging. However, despite their advantages over organic dyes, their use for microscopy imaging is limited by the high-energy UV excitation they require and their poor ability to cross the cell membrane and reach the cytosol. Here we describe a novel family of lanthanide-based luminescent probes, termed dTAT[Ln·L], based on (i) a DOTA-like chelator with a picolinate moiety, (ii) a two-photon absorbing antenna to shift the excitation to the near infrared and (ii) a dimeric TAT cell-penetrating peptide for cytosolic delivery. Several Tb³⁺ and Eu³⁺ probes were prepared and characterized. Two-photon microscopy of live cells was attempted using a commercial microscope with the three probes showing the highest quantum yields (>0.15). A diffuse Ln³⁺ emission was detected in most cells, which is characteristic of cytosolic delivery of the Ln³⁺ complex. The cytotoxicity of these three probes was evaluated and the IC₅₀ ranged from 7 μM to >50 μM. The addition of a single positive or negative charge to the antenna of the most cytotoxic compound was sufficient to lower significantly or suppress its toxicity under the conditions used for two-photon microscopy. Therefore, the design reported here provides excellent lanthanide-based probes for two-photon microscopy of living cells.

Zn²⁺-responsive magnetic resonance imaging (MRI) contrast agents are typically composed of a Gd chelate conjugated to a Zn²⁺-binding moiety via a linker. They allow for Zn²⁺ detection in the presence of human serum albumin (HSA). In order to decipher the key parameters that drive their Zn²⁺-dependent MRI response, we designed a pyridine-based ligand, PyAmC2mDPA, and compared the properties of GdPyAmC2mDPA to those of analogue complexes with varying Gd core, Zn-binding moiety, or linker sizes. The stability constants determined by pH potentiometry showed the good selectivity of PyAmC2mDPA for Gd³⁺ (log K_Gd = 16.27) versus Zn²⁺ (log K_Zn = 13.58), proving that our modified Zn²⁺-binding DPA moiety prevents the formation of previously observed dimeric species. Paramagnetic relaxation enhancement measurements indicated at least three sites that are available for GdPyAmC2mDPA binding on HSA, as well as a 2-fold affinity increase when Zn²⁺ is present (K_D = 170 μM versus K_DZn = 60 μM). Fluorescence competition experiments provided evidence of the higher affinity for site II vs site I, as well as the importance of both the Zn-binding part and the Gd core in generating enhanced HSA affinity in the presence of Zn²⁺. Finally, an analysis of nuclear magnetic relaxation dispersion (NMRD) data suggested a significantly increased rigidity for the Zn²⁺-bound system, which is responsible for the Zn²⁺-dependent relaxivity response.

We present the contradictory in vitro and in vivo behaviour of a Gd ³⁺ -based contrast agent that respond to Zn ²⁺ upon interaction with Human Serum Albumin.

The MRI efficacy of the zinc finger peptide is greatly increased upon zinc binding thanks to a combination of reversible binding of phosphoserine to Gd³⁺ and increased rigidity. This versatile system is highly sensitive to small amino acid changes.

Alzheimer's disease (AD) is an incurable neurodegenerative disease that leads to the progressive and irreversible loss of mental functions. The amyloid beta (Aβ) peptide involved in the disease is responsible for the production of damaging reactive oxygen species (ROS) when bound to Cu ions. A therapeutic approach that consists of removing Cu ions from Aβ to alter this deleterious interaction is currently being developed. In this context, we report the ability of five different 12‐membered thiaazacyclen ligands to capture Cu from Aβ and to redox silence it. We propose that the presence of a sole sulfur atom in the ligand increases the rate of Cu capture and removal from Aβ, while the kinetic aspect of the chelation was an issue encountered with the 4N parent ligand. The best ligand for removing Cu from Aβ and inhibiting the associated ROS production is the 1‐thia‐4,7,10‐triazacyclododecane [3N1S]. Indeed the replacement of more N by S atoms makes the corresponding Cu complexes easier to reduce and thus able to produce ROS on their own. In addition, the ligand with three sulfur atoms has a weaker affinity for Cu^II than Aβ, and is thus unable to remove Cu from CuAβ.

Amino-terminal Cu^II and Ni^II (ATCUN) binding sequences are widespread in the biological world. Here, we report on the study of eight ATCUN peptides aimed at targeting copper ions and stopping the associated formation of reactive oxygen species (ROS). This study was actually more focused on Cu(Aβ)-induced ROS production in which the Aβ peptide is the “villain” linked to Alzheimer’s disease. The full characterization of Cu^II binding to the ATCUN peptides, the Cu^II extraction from Cu^II(Aβ), and the ability of the peptides to prevent and/or stop ROS formation are described in the relevant biological conditions. We highlighted in this research that all the ATCUN motifs studied formed the same thermodynamic complex but that the addition of a second histidine in position 1 or 2 allowed for an improvement in the Cu^II uptake kinetics. This kinetic rate was directly related to the ability of the peptide to stop the Cu^II(Aβ)-induced production of ROS, with the most efficient motifs being HWHG and HGHW.