Telomeric regions containing G-quadruplex (G4) structures play a pivotal role in the development of cancers. The development of specific binders for G4s is thus of great interest in order to gain a deeper understanding of the role of these structures, and to ultimately develop new anticancer drug candidates. For several years, Ru complexes have been studied as efficient probes for DNA. Interest in these complexes stems mainly from the tunability of their structures and properties, and the possibility of using light excitation as a tool to probe their environment or to selectively trigger their reaction with a biological target. Herein, we report on the synthesis and thorough study of new Ru complexes based on a novel dipyrazino[2,3-a:2',3'-h]phenazine ligand (dph), obtained through a Chichibabin-like reaction. Luminescence experiments, surface plasmon resonance (SPR), and computational studies have demonstrated that these complexes behave as selective probes for G-quadruplex structures.

Rapid antigen tests are currently used for population screening of COVID-19. However, they lack sensitivity and utilize antibodies as receptors, which can only function in narrow temperature and pH ranges. Consequently, molecularly imprinted polymer nanoparticles (nanoMIPs) are synthetized with a fast (2 h) and scalable process using merely a tiny SARS-CoV-2 fragment (∼10 amino acids). The nanoMIPs rival the affinity of SARS-CoV-2 antibodies under standard testing conditions and surpass them at elevated temperatures or in acidic media. Therefore, nanoMIP sensors possess clear advantages over antibody-based assays as they can function in various challenging media. A thermal assay is developed with nanoMIPs electrografted onto screen-printed electrodes to accurately quantify SARS-CoV-2 antigens. Heat transfer-based measurements demonstrate superior detection limits compared to commercial rapid antigen tests and most antigen tests from the literature for both the alpha (∼9.9 fg mL –1 ) and delta (∼6.1 fg mL –1 ) variants of the spike protein. A prototype assay is developed, which can rapidly (∼15 min) validate clinical patient samples with excellent sensitivity and specificity. The straightforward epitope imprinting method and high robustness of nanoMIPs produce a SARS-CoV-2 sensor with significant commercial potential for population screening, in addition to the possibility of measurements in diagnostically challenging environments.

G-rich DNA oligonucleotides derived from the promoter region of the HIV-1 long terminal repeat (LTR) were assembled onto an addressable cyclopeptide platform through sequential oxime ligation, a thiol-iodoacetamide SN2 reaction, and copper-catalyzed azide-alkyne cycloaddition reactions. The resulting conjugate was shown to fold into a highly stable antiparallel G4 architecture as demonstrated by UV, circular dichroism (CD), and NMR spectroscopic analysis. The binding affinities of six state-of-the-art G4-binding ligands toward the HIV-G4 structure were compared to those obtained with a telomeric G4 structure and a hairpin structure. Surface plasmon resonance binding analysis provides new insights into the binding mode of broadly exploited G4 chemical probes and further suggests that potent and selective recognition of viral G4 structures of functional significance might be achieved.

Understanding antigen-antibody interactions is important to many emerging medical and bioanalytical applications. In particular, the levels of antigen expression at the cell surface may determine antibody-mediated cell death. This parameter has a clear effect on outcome in patients undergoing immunotherapy. In this context, CD20 which is expressed in the membrane of B cells has received significant attention as target for immunotherapy of leukemia and lymphoma using the monoclonal antibody rituximab. To systematically study the impact of CD20 density on antibody recognition, we designed self-assembled monolayers that display tunable CD20 epitope densities. For this purpose, we developed in situ click chemistry to functionalize SPR sensor chips. We find that the rituximab binding affinity depends sensitively and non-monotonously on CD20 surface density. Strongest binding, with an equilibrium dissociation constant (KD = 32 nM) close to values previously reported from in vitro analysis with B cells (apparent KD between 5 and 19 nM), was obtained for an average inter-antigen spacing of 2 nm. This distance is required for improving rituximab recognition, and in agreement with the known requirement of CD20 to form clusters to elicit a biological response. More generally, this study offers an interesting outlook in the understanding of the necessity of epitope clusters for effective mAb recognition. Despite the continuous improvement of traditional chemotherapy, the use of monoclonal antibodies (mAbs) as drugs for the treatment of a variety of diseases has been growing steadily for the last two decades. 1 In this context, there is a strong interest in studying mAb recognition of cognate antigens. MAbs are used in oncology for many therapeutic targets including the CD20 antigen, the human epidermal growth factor receptor 2 (HER2), the vascular endothelial growth factor (VEGF), the epidermal growth factor receptor (EGFR) and the programmed cell death protein 1 (PD-1). 2 The hematopoietic differentiation antigens associated with cluster of differentiation (CD) represent the main targets for mAb in oncology. 3 In particular, the CD20 antigen is the target of several therapeutic mAbs and their derivatives (e.g. rituximab, ibritumomab, ofatumumab, obinutuzumab, ocrelizumab) that are successfully used to treat B-cell malignancies, including non-Hodgkin's lymphoma and chronic lymphocytic leukemia, as well as some autoimmune disorders such as rheumatoid arthritis, systemic lupus erythematosus and multiple sclerosis. 4 The antigen-binding activity of mAbs determines their biological efficacy and depends on several factors, including antigen density, association and dissociation rates. Several studies have suggested that the increase of CD20 antigen expression modulates the biological response of mAbs such as complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) that trigger cell death. 5,6,7 As the antigen distribution generally has a direct impact on the clinical efficacies of mAbs, it is of...

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Photosensitizers that gather high photo‐oxidizing power and strong visible‐light absorption are of great interest in the development of new photo‐chemotherapeutics. Indeed, such compounds constitute attractive candidates for the design of type I photosensitizers that are not dependent on the presence of oxygen. In this paper, we report on the synthesis and studies of new ruthenium(II) complexes that display strong visible‐light absorption and can oxidize guanine residues under visible‐light irradiation, as evidenced by nanosecond transient absorption spectroscopy. The reported compounds also tightly bind to G‐quadruplex DNA structures from the human telomeric sequence (TTAGGG repeat). The kinetic and thermodynamic parameters of the interaction of these Ru(II) complexes with G‐quadruplex and duplex DNA were studied thanks to luminescence titrations and bio‐layer interferometry measurements, which revealed higher affinities towards the non‐canonical G‐quadruplex architecture. Docking experiments and non‐covalent ionic analysis allowed us to gain information on the mode and the strength of the interaction of the compounds towards G‐quadruplex and duplex DNA. The different studies emphasize the substantial influence of the position and the number of non‐chelating nitrogen atoms on the interaction with both types of DNA secondary structures.

Antibodies play a major role in clinical diagnostics and biopharmaceutical analysis, but are also a class of drugs that are regularly used to treat numerous diseases. The identification of antibody-epitope binding sites is then of great interest to many emerging medical and bioanalytical applications, particularly to design mAb mimics taking advantage of amino acids residues involved in the binding. Among relevant antibodies, the monoclonal antibody rituximab has received a significant attention as it is exploited to treat several cancers including non-Hodgkin's lymphoma and chronic lymphocytic leukemia, as well as some autoimmune disorders such as rheumatoid arthritis. The binding of rituximab to the targeted cells occurs via the recognition of the CD20 epitope. A crystallography study has shown that the binding area, named paratope, is located at the surface of rituximab. Combining the SPOT method and the complementary surface plasmon resonance technique allowed us to detect an extended recognition domain buried in the pocket of the rituximab Fab formed by four β-sheets. More generally, the present study offers a comprehensive approach to identify antibody-epitope binding sites.Biomolecular recognition is central to many biological processes governing cell fate. In this context, the monoclonal antibodies (mAbs) are able to bind to a specific antigen triggering the death of the targeted cell. 1 To date, mAbs are increasingly used for treatment of a variety of diseases. 2 In particular, rituximab (RTX), first FDA (Food and Drug Administration) approved therapeutic mAb, is routinely used for the treatment of several types of lymphoma as well as some autoimmune disorders. 3 RTX was shown to target a transmembrane protein named CD20 (cluster of differentiation 20), which is highly expressed on most healthy and malignant B cells but not on precursor B cells. 4 The identification of CD20 recognized by Rituximab has raised great interest in recent years especially to better apprehend RTX mechanism and action. Additionally, understanding molecular recognition could pave the way for structure-based design of bioactive molecules. Very recently, it has been shown by using cryo-electron microscopy (cryo-EM) that the native CD20 structure is a compact dimeric form allowing RTX cross-links that can induce complement recruitment. 5,6 This result corroborates other studies indicating that CD20s are not expressed in monomeric form, but organized into supramolecular protein complexes. 7,8 In parallel, our group has studied the effect of CD20 density on the recognition by RTX, which is known to be a critical point for the therapeutic response. 9 An average critical inter-CD20 spacing of nearly 2 nm confers the best conditions for RTX binding. This value is in excellent agreement with cryo-EM structures. 5,6 It is important to note that this finding suggests RTX contacts with two different epitopes. 5 Regarding the identification of the antigen-binding site of the antibody, a pioneer crystal structure of the RTX antigen-binding fra...