Conformation of Pyroglutamated Amyloid ß (3-40) and (11-40) Fibrils - Extended or Hairpin?

Amyloid ß (Aß) is a hallmark protein of Alzheimer's disease. One physiologically important Aß variant is formed by initial N-terminal truncation at a glutamic acid position (either E3 or E11), which is subsequently cyclized to a pyroglutamate (either pE3 or pE11). Both forms have been found in high concentrations in the core of amyloid plaques and are likely of high importance in the pathology of Alzheimer's disease. However, the molecular structure of the fibrils of these variants is not entirely clear. Solid-state NMR spectroscopy studies have reported a molecular contact between Gly25 and Ile31, which would disagree with the conventional hairpin model of wildtype (WT-)Aß1-40 fibrils, most often described in the literature. We investigated the conformation of the monomeric unit of pE3-Aß3-40 and pE11-Aß11-40 (and for comparison also wildtype (WT)-Aß1-40) fibrils to find out whether the hairpin or a newly suggested extended structure dominates the structure of the Aß monomers in these fibrils. To this end, solid-state NMR spectroscopy was applied probing the inter-residual contacts between Phe19/Leu34, Ala21/Leu34, and especially Gly25/Ile31 using suitable isotopic labeling schemes. In the second part, the flexible turn of the Aß40 peptides was replaced by a (3-(3-aminomethyl)phenylazo)phenylacetic acid (AMPP)-based photoswitch, which can predefine the peptide conformation to either an extended (trans) or hairpin (cis) conformation. This enables simultaneous spectroscopic assessment of the conformation of the AMPP-photoswitch, allowing in situ structural investigations during fibrillation in contrast to structural techniques such as NMR spectroscopy or cryo-EM, which can only be applied to stable conformers. Both methods confirm an extended structure for the peptidic monomers in fibrils of all investigated Aß variants. Especially the Gly25/Ile31 contact is a decisive indicator for the extended structure along with the characteristic absorption spectra of trans-AMPP-Aß.

Exploring the potential of tamoxifen-based copper(ii) dichloride in breast cancer therapy.

For decades, tamoxifen-based hormone therapy has effectively addressed oestrogen receptor positive (ER+) luminal A breast cancer. Nonetheless, the emergence of tamoxifen resistance required innovative approaches, leading to hybrid metallodrugs with several therapeutic effects besides the inhibition of oestrogen receptor α (ERα). Drawing inspiration from tamoxifen metabolite structures (4-hydroxytamoxifen and 4,4'-dihyroxytamoxifen), a phenyl ring was replaced by a bidentate 2,2'-bipyridine donor moiety to give 4-[1,1-bis(4-methoxyphenyl)but-1-en-2-yl]-2,2'-bipyridine (L), enabling coordination of bioactive transition metal compounds such as copper(ii) dichloride, yielding [CuCl(µ-Cl)(L-κ2N,N')]2 (1). Notably, copper(ii) complex 1 exhibited remarkable activity within the low micromolar concentration range against ER+ human glioblastoma U251, as well as breast carcinomas MDA-MB-361 and MCF-7, surpassing the efficacy of previously reported palladium(ii) and platinum(ii) dichloride analogs against these cell lines. The pronounced efficacy of complex 1 against triple-negative MDA-MB-231 cells highlights its potential multitherapeutic approach, evident through induction of apoptosis and antioxidant activity. This study evaluates the potential of copper-tamoxifen hybrid complex 1 as a potent therapeutic candidate, highlighting its diverse mechanism of action against challenging breast cancer subtypes.

Correction: Kazimir et al. Metallodrugs against Breast Cancer: Combining the Tamoxifen Vector with Platinum(II) and Palladium(II) Complexes. Pharmaceutics 2023, 15, 682.

In the original publication [...].

Metallodrugs against Breast Cancer: Combining the Tamoxifen Vector with Platinum(II) and Palladium(II) Complexes.

The luminal A-subtype of breast cancer, where the oestrogen receptor α (ERα) is overexpressed, is the most frequent one. The prodrug tamoxifen (1) is the clinically used agent, inhibiting the ERα activity via the formation of several active metabolites, such as 4-hydroxytamoxifen (2) or 4,4'-dihydroxytamoxifen (3). In this study, we present the tamoxifen derivative 4-[1,1-bis(4-methoxyphenyl)but-1-en-2-yl]-2,2'-bipyridine (4), which was combined with platinum or palladium dichloride, the former a well-known scaffold in anticancer treatment, to give [PtCl2(4-κ2N,N')] (5) or [PdCl2(4-κ2N,N'] (6). To prevent fast exchange of weakly coordinating chlorido ligands in aqueous solution, a bulky, highly stable and hydrophobic nido-carborate(-2) ([C2B9H11]2-) was incorporated. The resulting complexes [3-(4-κ2N,N')-3,1,2-PtC2B9H11] (7) and [3-(4-κ2N,N')-3,1,2-PdC2B9H11] (8) exhibit a dramatic change in electronic and biological properties compared to 5 and 6. Thus, 8 is highly selective for triple-negative MDA-MB-231 cells (IC50 = 3.7 µM, MTT test), while 7 is completely inactive against this cell line. The observed cytotoxicity of compounds 4-6 and 8 against this triple-negative cell line suggests off-target mechanisms rather than only ERα inhibition, for which these compounds were originally designed. Spectroscopic properties and electronic structures of the metal complexes were investigated for possible explanations of the biological activities.

Towards Probing Conformational States of Y2 Receptor Using Hyperpolarized 129Xe NMR.

G protein-coupled receptors can adopt many different conformational states, each of them exhibiting different restraints towards downstream signaling pathways. One promising strategy to identify and quantify this conformational landscape is to introduce a cysteine at a receptor site sensitive to different states and label this cysteine with a probe for detection. Here, the application of NMR of hyperpolarized 129Xe for the detection of the conformational states of human neuropeptide Y2 receptor is introduced. The xenon trapping cage molecule cryptophane-A attached to a cysteine in extracellular loop 2 of the receptor facilitates chemical exchange saturation transfer experiments without and in the presence of native ligand neuropeptide Y. High-quality spectra indicative of structural states of the receptor-cage conjugate were obtained. Specifically, five signals could be assigned to the conjugate in the apo form. After the addition of NPY, one additional signal and subtle modifications in the persisting signals could be detected. The correlation of the spectroscopic signals and structural states was achieved with molecular dynamics simulations, suggesting frequent contact between the xenon trapping cage and the receptor surface but a preferred interaction with the bound ligand.

How Single Site Mutations Can Help Understanding Structure Formation of Amyloid ß1-40.

Amyloid fibrils represent the structural endpoint on the energetic (mis)folding landscape of very many proteins. Physiologically, amyloid fibrils are observed as a characteristic hallmark in misfolding diseases often associated with degenerative and neurodegenerative disorders. In the beginning of the scientific discussion, the focus is laid on the fibrillar state, but over the time it becomes increasingly clear that low molecular weight and transient aggregates are of crucial importance for pathological mechanisms. Structural studies find different intra- and intermolecular contacts for the most well-studied peptide amyloid ß (Aß) depending on the stage of fibrillation. In particular, the contact between residues phenylalanine 19 (F19) and leucine 34 (L34) seems to be highly conserved, suggesting that it must be of particular significance for Aß misfolding and possibly the pathological properties of the peptide. This review aims to highlight the rational and the usefulness of point mutations in Aß peptides and their impact on the critical interstrand contact F19-L34 depending on the stage of fibrillation. While the amyloid structure of Aß is very robust against quite a few modifications, the toxicity of mutated Aß molecules highly depends on the F19-L34 contact.

Predicting 2H NMR acyl chain order parameters with graph neural networks.

2H NMR order parameters of the acyl chain of phospholipid membranes are an important indicator of the effects of molecules on membrane order, mobility, and permeability. So far, the evaluation procedures are case-by-case studies for every type of small molecule with certain types of membranes. Rapid screening of the effects of a variety of drugs would be invaluable if it were possible. Unfortunately, to date there is no practical or theoretical approach to this as there is with other experimental parameters, e.g., chemical shifts from 1H and 13C NMR. We aim to remedy this situation by introducing a model based on graph neural networks (GNN) capable of predicting 2H NMR order parameters of lipid membranes in the presence of different molecules based on learned molecular features. Rapid prediction of these parameters would allow fast assessment of potential effects of drugs on lipid membranes, which is important for further drug development and provides insight into potential side effects. We conclude that the graph network-based model presented in this work can predict order parameters with sufficient accuracy, and we are confident that the concepts presented are a suitable basis for future research. We also make our model available to the public as a web application at https://proteinformatics.uni-leipzig.de/g2r/.

Peptide backbone modifications of amyloid ß (1-40) impact fibrillation behavior and neuronal toxicity.

Fibril formation of amyloid ß (Aß) peptides is one of the key molecular events connected to Alzheimer's disease. The pathway of formation and mechanism of action of Aß aggregates in biological systems is still object of very active research. To this end, systematic modifications of the Phe19-Leu34 hydrophobic contact, which has been reported in almost all structural studies of Aß40 fibrils, helps understanding Aß folding pathways and the underlying free energy landscape of the amyloid formation process. In our approach, a series of Aß40 peptide variants with two types of backbone modifications, namely incorporation of (i) a methylene or an ethylene spacer group and (ii) a N-methylation at the amide functional group, of the amino acids at positions 19 or 34 was applied. These mutations are expected to challenge the inter-ß-strand side chain contacts as well as intermolecular backbone ß-sheet hydrogen bridges. Using a multitude of biophysical methods, it is shown that these backbone modifications lead, in most of the cases, to alterations in the fibril formation kinetics, a higher local structural heterogeneity, and a somewhat modified fibril morphology without generally impairing the fibril formation capacity of the peptides. The toxicological profile found for the variants depend on the type and extent of the modification.

Preparing (Metalla)carboranes for Nanomedicine.

"There's plenty of room at the bottom" (Richard Feynman, 1959): an invitation for (metalla)carboranes to enter the (new) field of nanomedicine. For two decades, the number of publications on boron cluster compounds designed for potential applications in medicine has been constantly increasing. Hundreds of compounds have been screened in vitro or in vivo for a variety of biological activities (chemotherapeutics, radiotherapeutics, antiviral, etc.), and some have shown rather promising potential for further development. However, until now, no boron cluster compounds have made it to the clinic, and even clinical trials have been very sparse. This review introduces a new perspective in the field of medicinal boron chemistry, namely that boron-based drugs should be regarded as nanomedicine platforms, due to their peculiar self-assembly behaviour in aqueous solutions, and treated as such. Examples for boron-based 12- and 11-vertex clusters and appropriate comparative studies from medicinal (in)organic chemistry and nanomedicine, highlighting similarities, differences and gaps in physicochemical and biological characterisation methods, are provided to encourage medicinal boron chemists to fill in the gaps between chemistry laboratory and real applications in living systems by employing bioanalytical and biophysical methods for characterising and controlling the aggregation behaviour of the clusters in solution.

2,2'-Bipyridine-Modified Tamoxifen: A Versatile Vector for Molybdacarboranes.

Investigations on the antitumor activity of metallacarboranes are sparse in the literature and limited to a handful of ruthena- and molybdacarboranes. In this study, the molybdacarborane fragment [3-(CO)2 -closo-3,1,2-MoC2 B9 H11 ] was combined with a vector molecule, inspired by the well-known drug tamoxifen or 4,4'-dihydroxytamoxifen (TAM-diOH). The molybdacarborane derivative [3,3-{4-[1,1-bis(4-hydroxyphenyl)but-1-en-2-yl]-2,2'-bipyridine-κ2 N,N'}-3-(CO)2 -closo-3,1,2-MoC2 B9 H11 ] (10), as well as the ligand itself 4-[1,1-bis(4-hydroxyphenyl)but-1-en-2-yl]-2,2'-bipyridine (6) showed cytotoxic activities in the low micromolar range against breast adenocarcinoma (MDA-MB-231, MDA-MB-361 and MCF-7), human glioblastoma (LN-229) and human glioma (U-251) cell lines. In addition, compounds 6 and 10 were found to induce senescence and cytodestructive autophagy, lower ROS/RNS levels, but only the molybdacarborane 10 induced a strong increase of nitric oxide (NO) concentration in the MCF-7 cells.

Spectroscopic and Electronic Properties of Molybdacarborane Complexes with Non-innocently Acting Ligands.

The molybdacarboranes [3-{L-κ2 N,N}-3-(CO)2 -closo-3,1,2-MoC2 B9 H11 ] (L=2,2'-bipyridine (2,2'-bpy, 1 a) or 1,10-phenanthroline (1,10-phen, 1 b)) incorporating well-known potentially non-innocent ligands (CO, 2,2'-bpy, 1,10-phen) and the "non-spectator" nido-carborane ([η5 -C2 B9 H11 ]2- ) ligand were prepared and fully characterised. High-resolution mass spectrometry, single-crystal X-ray diffraction methods, spectroscopy (IR, (resonance) Raman, NMR), cyclic voltammetry and spectroelectrochemistry (electrochemical properties) were supported by theoretical investigations of the electronic structure (DFT, CAS-SCF, TD-DFT).

12-Vertex Zwitterionic Bis-phosphonium-nido-carborates through Ring-Opening Reactions of 1,2-Diphosphetanes.

Carborane-substituted 1,2-diphosphetanes (Ia,b) react with elemental lithium in THF with cleavage of the P-P bond to give a deep red solution from which, in the case of Ia, red crystals of a lithiated intermediate, [{1-Li(THF)PtBu-6-PtBu-4,1,6-closo-Li(THF)C2 B10 H10 }{Li(THF)3 }]2 ⋅2 THF (2 a), are obtained. The compound is dimeric, C2 -symmetric and contains six lithium and four phosphorus atoms. Two lithium atoms cap the six-membered C2 B4 faces, resulting in two 13-vertex closo-clusters (according to Wade's rules) with docosahedral geometry. The addition of methyl iodide resulted in the formation of zwitterionic bis-phosphonium-nido-carborates 7,10-bis(tert-butyldimethylphosphonium)dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1 a) and 7,10-bis(N,N-diisopropylaminodimethylphosphonium)dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1 b) in moderate to good yields. Compounds 1 a and 1 b exhibit short Ccluster -P bonds and large Ccluster ⋅⋅⋅Ccluster distances in the solid state. Further insight into the ring opening and reduction potential of the alkyl halide was obtained from methylation reactions of different 1,2-bis-phosphinocarboranes. The reaction of rac-/meso-1,2-bis(tert-butylmethylphosphino)-1,2-dicarba-closo-dodecaborane(12) (3 a) with two equivalents of methyl iodide also resulted in the formation of 1 a (as shown by NMR spectroscopy), whereas the reaction of 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane(12) with methyl triflate afforded the phosphonium salt 1-methyl-diphenylphosphonium-2-diphenylphosphino-1,2-dicarba-closo-dodecaborane(12) triflate (4) without reduction of the cluster.

Antiproliferative activity of (η6-arene)ruthenacarborane sandwich complexes against HCT116 and MCF7 cell lines.

Three [(η6-arene)RuC2B9H11] complexes (arene = p-cymene (2), biphenyl (3) and 1-Me-4-COOEt-C6H4 (4)) were synthesised according to modified literature procedures and fully characterised. 2-4 were found to be moderately active against two types of tumour cell lines (HCT116 and MCF7), with IC50 values in the low micromolar range. However, viability of normal, healthy cells (MRC-5 cell line, MLEC and mouse macrophages) was not affected by treatment with 2-4, indicating high selectivity of the metallacarborane complexes towards tumour cell lines, compared to the unselective antitumour agent cisplatin and other potential RuII drugs. Moreover, flow cytometric analysis suggested that 4 induces cell death via a caspase-dependent apoptotic mechanism. DFT calculations of the frontier molecular orbitals showed that the HOMO-LUMO gap in 2-4 is smaller than in the corresponding cyclopentadienyl complexes 2-Cp-4-Cp (e.g. 5.47 (2) vs. 6.31 eV (2-Cp)). In order to assess the stability of 2-4, particularly the ruthenium-dicarbollide bond, energy decomposition analysis (EDA) of 2-4, together with the respective cyclopentadienyl analogues 2-Cp-4-Cp, was performed. EDA suggests that the ruthenium(ii)-dicarbollide bond in the three complexes is mostly ionic and far stronger than the ruthenium(ii)-arene bond.

C2-Symmetric P,N Ligands Derived from Carborane-Based Diphosphetanes: Synthesis and Coordination Chemistry.

Racemic carborane-based bisphosphanes were obtained by dismutation reactions between a carborane-based diphosphetane and diaryl dichalogenides. NMR spectroscopic and theoretical studies revealed a two-step mechanism explaining the high stereoselectivity of these reactions. The coordination chemistry of the multidentate P,N ligands 6c and 6d in copper(I) and silver(I) complexes was studied. While 6d acted exclusively as tetradentate ligand, 6c showed either tridentate or tetradentate coordination depending on the metal and the counterion.

Activation of CO by Hydrogenated Magnesium(I) Dimers: Sterically Controlled Formation of Ethenediolate and Cyclopropanetriolate Complexes.

This study details the formal hydrogenation of two magnesium(I) dimers {(Nacnac)Mg}2 (Nacnac = [{(C6H3R2-2,6)NCMe}2CH](-); R = Pr(i) ((Dip)Nacnac), Et ((Dep)Nacnac)) using 1,3-cyclohexadiene. These reactions afford the magnesium(II) hydride complexes, {(Nacnac)Mg(µ-H)}2. Their reactions with excess CO are sterically controlled and lead cleanly to different C-C coupled products, viz. the ethenediolate complex, ((Dip)Nacnac)Mg{κ(1)-O-[((Dip)Nacnac)Mg(κ(2)-O,O-O2C2H2)]}, and the first cyclopropanetriolate complex of any metal, cis-{((Dep)Nacnac)Mg}3{µ-C3(H3)O3}. Computational studies imply the CO activation processes proceed via very similar mechanisms to those previously reported for related reactions involving f-block metal hydride compounds. This work highlights the potential magnesium compounds hold for use in the "Fischer-Tropsch-like" transformation of CO/H2 mixtures to value added oxygenate products.

Two-coordinate hydrido-germylenes.

The first structurally characterised two-coordinate hydrido-germylenes, :Ge(H)L (L = -N(Ar){Si(OBu)}, Ar = C6H2{C(H)Ph2}2R-2,6,4; R = Pr(i) ((tBuO)L(†)), Me ((tBuO)L*)), have been prepared, and their dimerisation shown to be thermodynamically unfavourable, largely due to the extreme steric bulk of their amide ligands.