Clotilde Policar

In the objective of exploiting the MnII/III redox couple combined with the bispidine scaffold for the development of redox-responsive magnetic resonance imaging (MRI) probes, we have designed and synthesized H3L1 ligand, featuring a phenol pendant arm. This novel ligand is hypothesized to lower the MnII/III redox potential relative to previously reported derivatives, while retaining the high kinetic inertness and good relaxivity properties characteristic of MnII bispidine complexes. The [MnIIL1(H2O)]- complex exhibits high thermodynamic stability (log KMnIIL1 = 14.2), notable kinetic inertness (dissociation half-life, t1/2 = 20.4 h at pH 6 in the presence of 50 equiv of ZnII), and high relaxivity (r1 = 3.91 mM–1s–1 at 60 MHz, 25 °C, pH 7), highlighting the suitability of the MnII complex as a platform for MRI probe development. Electrochemical studies revealed a significantly lower oxidation potential (E1/2 = 306 mV vs SCE) compared to other Mn-bispidine chelates, enabling successful synthesis of the oxidized [MnIIIL1] form in methanol. Although the aqueous stability of the +III oxidation state remains limited and highly dependent on water content, these results demonstrate that the incorporation of a phenolate donor effectively tunes the MnII/III redox properties of the bispidine scaffold.

The therapeutic effectiveness of metallodrugs is heavily influenced by their propensity to release metal ions within biological systems. This is particularly relevant in the case of labile first series transition metal ions, the release leading to loss in complex-based activity. While thermodynamic parameters governing the stability and efficacy of metallodrugs can be analyzed using established analytical techniques, assessing live-cell integrity of a metallodrug remains a significant challenge. Determination of in-cell integrity is essential for optimizing the design and therapeutic potential of metallodrugs. Importantly, the study should be performed in living cells because biological environments can significantly impact the stability and lability. Currently, no experimental approach directly visualizes metal ions released by metallodrugs and determines their in-cell-integrity. To address this gap, we propose a novel assay to monitor the extent of release of metal ions from metallodrugs using binding-based, reversible fluorescent metal ion sensors in live cells. We tested the relevance of the assay on a series of manganese antioxidants (Mn superoxide dismutase (SOD) mimics) utilizing Mn(II) selective reversible fluorescent sensors. The results showed that the SOD mimic Mn1 , with the lowest intrinsic K _d from the series of antioxidants tested, exhibited the highest amount of Mn-release, while Mn1CP , with the highest K _d , demonstrated lower Mn-release. Interestingly, the level of metal-release correlates with the intrinsic lability of metallodrugs and not with their intrinsic thermodynamic stability. The study demonstrates the importance of assessing in-cell metal ion release for optimizing the therapeutic outcome of metallodrugs. The novel fluorescence assay developed here offers a valuable tool for the evaluation of metallodrug behavior in cellular environments. Overall, this work shows that in-cell metal ion release from these manganese metallodrugs appears to correlate with intrinsic lability and thus is under kinetic control.

(Text in French) Bioinorganic chemistry and inorganic chemical biology: metal complexes in a cellular context. History, issues and example of manganese antioxidant complexes, from design to study in a biological environment Bioinorganic chemistry focuses on metallic systems in biological environments, with the dual aim of better understanding these natural systems and exploiting the solutions developed during evolution to design new industrial or therapeutic applications. Closely related to metallomics, it lays down the fundamental principles for studying metal systems in living organisms, raising complex questions that provide a fruitful perspective. Indeed, biological systems can be a source of inspiration: to design antioxidant molecules, low molecular weight complexes reproducing the activity of superoxide dismutases (SOD), commonly called “SOD mimics”, can be designed. To test them in a cellular context, the cells must be disrupted enough to record an effect, but not too much to allow a return to normal in the presence of these mimics. Intestinal epithelial cells can be challenged using lipopolysaccharide (LPS)-induced inflammation, which is mediated by oxidative stress, shown to occur in the short term (15 minutes). Co-incubation of SOD mimics with LPS limits both the effects of short-term oxidative stress and changes in the proteome over longer periods (6 hours). These considerations aim to illustrate the scope of inorganic chemobiology, from fundamental concepts to potential applications.

As FDA‐approved platinum (Pt) anticancer drugs (e.g. cisplatin, oxaliplatin and carboplatin) grapple with clinical challenges including chemoresistance and systemic side‐effects, Pt(IV) prodrugs have emerged as potent alternative chemotherapies. In this work, a novel bimetallic dual‐action Pt(IV) prodrug bearing a manganese (Mn) superoxide dismutase mimic (SODm) is presented, demonstrating high stability in solution. The prodrug displays intrinsic antisuperoxide properties and in vitro comparable cytotoxic activities to that of oxaliplatin in 2‐ and 3D colorectal cancer cellular models, as well as an increase in intracellular reactive oxygen species (ROS) production. The prodrug is further evaluated in an in vivo mice model for colorectal cancer, demonstrating a similar performance to that of oxaliplatin. Additionally, a total tumor remission is reached with a PEGylated micellar encapsulation of the prodrug. This novel formulation increases the lifetime of the prodrug and therefore its tumoral uptake and plasma content with respect to the unencapsulated drug. This enhanced activity suggests the therapeutic potential of said formulation.

Bioinorganic chemistry is a multidisciplinary field that bridges the apparent divide between inorganic chemistry and biology. The very name “bioinorganic” is an intriguing oxymoron, as “inorganic” chemistry traditionally refers to the study of the inanimate world, while the “bio” prefix refers to living systems. Bioinorganic chemistry focuses on metallic systems within biological environments, with the dual aims of better understanding these natural systems and leveraging the solutions developed through evolution to design new industrial or therapeutic applications. As a close cousin of the field of metallomics, bioinorganic chemistry shares the fundamental principles that underpin metallomics’ systemic analyses of metal-containing biomolecules. In this article, we trace the historical development of bioinorganic chemistry, highlighting its recent advancements and outlining future research challenges in this dynamic interdisciplinary area. Graphical abstract

Metal complexes are increasingly used as metallo-probes or metallo-drugs. Their characterization in cellular or biological environments poses specific challenges related to possible decoordination, metal exchange, fixation of additional ligands, or precipitation. These phenomena can hardly be foreseen and it is important to integrate the design of these complexes with their study in cells, from characterization in cells (quantification, speciation, integrity of the complex in cells, location) to bioactivity. Redox homeostasis and oxidative stress are strongly associated with biochemistry of metal ions. Metalloenzymes protecting against oxidative stress have evolved such as catalase or superoxide dismutase. Bioactive antioxidant metal complexes can be designed as catalysts bioinspired from these natural antioxidant enzymes protecting the cell against oxidative stress. To characterize their activity, it is important to develop dedicated cellular models to evaluate their ability to restore normal cell life from a situation compromised by oxidative stress. This article describes cellular models and assays that have been developed in that context as well as approaches to interrogate the complexes’ nature in cells.

Overproduction of reactive oxygen species and antioxidant superoxide dismutases (SOD1, SOD2) dysregulation contribute to chronic inflammation such as generated in inflammatory bowel diseases (IBD). A kinetic redox shotgun proteomic strategy (OcSILAC for Oxidized cysteine Stable Isotope Labelling by Amino acids in Cell culture) was used to explore the lipopolysaccharide (LPS) effects including LPS‐induced oxidation and inflammation cascades on a dedicated intestinal epithelial cell line (HT29‐MD2) together with the potential mitigating role of a Mn‐based SOD‐mimic Mn1 . While LPS induced transient oxidative damages at early times (15 min), cells incubated with Mn1 showed, in this time frame, a significantly reduced cysteine oxidation, highlighting Mn1 antioxidant properties. Over time, cysteine oxidation of LPS‐treated cells was counteracted by an overexpression of antioxidant proteins (SOD1, NQO1) and a late (6 h) preponderant increase in SOD2 level. Mn1 , when co‐incubated with LPS, attenuated the level of most LPS‐modified proteins, that is, proteins involved in the inflammatory response. Our results highlight Mn1 as a potentially effective antioxidant and anti‐inflammatory agent to consider in the treatment of IBD, as well as a useful tool for exploring the interconnection between oxidative stress and inflammation.

Overproduction of reactive oxygen species and antioxidant superoxide dismutases (SOD1, SOD2) dysregulation contribute to chronic inflammation such as generated in inflammatory bowel diseases (IBD). A kinetic redox shotgun proteomic strategy (OcSILAC for Oxidized cysteine Stable Isotope Labelling by Amino acids in Cell culture) was used to explore the lipopolysaccharide (LPS) effects including LPS‐induced oxidation and inflammation cascades on a dedicated intestinal epithelial cell line (HT29‐MD2) together with the potential mitigating role of a Mn‐based SOD‐mimic Mn1 . While LPS induced transient oxidative damages at early times (15 min), cells incubated with Mn1 showed, in this time frame, a significantly reduced cysteine oxidation, highlighting Mn1 antioxidant properties. Over time, cysteine oxidation of LPS‐treated cells was counteracted by an overexpression of antioxidant proteins (SOD1, NQO1) and a late (6 h) preponderant increase in SOD2 level. Mn1 , when co‐incubated with LPS, attenuated the level of most LPS‐modified proteins, that is, proteins involved in the inflammatory response. Our results highlight Mn1 as a potentially effective antioxidant and anti‐inflammatory agent to consider in the treatment of IBD, as well as a useful tool for exploring the interconnection between oxidative stress and inflammation.

Bioinorganic chemistry and inorganic chemical biology are multidisciplinary fields dealing with metal ions in biological systems. In this article we will describe a research journey in these fields. This journey will take us from chemical design of inorganic metal complexes with a biological activity (catalytic antioxidants) or a biological interest (metal-based probes) and their characterization out of cellular context, typical of bioinorganic chemistry, to their studies in cells, typical of chemical biology. First, we will focus on the description of a bio-inspired strategy to design metal-based catalytic antioxidants. Starting from the description of the main features of an antioxidant cell-protecting metalloenzyme, the superoxide dismutase (SOD), we will delineate the main parameters to be controlled to design low-molecular weight (LMW) metal complexes meant to mimic its activity: choice of the metal cation, tuning of the redox potential, and modulation of the charge. The effect of the hydration level and inertness with regard to metal ion release have also been explored. Methods to quantify the SOD-like activity, out of cellular context and in cells, and analysis of the integrity of the metal-based antioxidant in cells (through ion mobility coupled with mass spectrometry) will be described. Strategies to develop peptide-based metal complexes through conjugation of a LMW complex with peptides aimed at targeting specific organelle will be presented. Peptides can also be used to coordinate the metal ion: a combinatorial approach, with an activity-based screening, or and a rationale design using three-stranded coil-coiled, will also be presented. The cellular activity of a molecule is strongly dependent on its sub-cellular location. A second focus of this article will be X-ray fluorescence imaging and infra-red microscopy, as techniques to image metal cations and metal-carbonyls in cells using the metallic core (M and M(CO) _x ). After a brief overview, we will describe how metal-based probes can be developed, as trackers of organelles or tags, with application to mitochondria tracking and to the imaging of the Mn-based SOD mimics previously described. Overall, we hope this this story will provide an insight of what are bioinorganic chemistry and inorganic chemical biology, showing how artificial metal-based systems can be chemically designed, associated with their direct study in cells.