Correction for ‘The impact of albumin conjugation on the cytotoxic properties of cisplatin, oxaliplatin and auranofin in cancer cells’ by Valentina Vitali et al. , Inorg. Chem. Front. , 2026, 13 , 106–111, https://doi.org/10.1039/D5QI01487E.

Crystalline nanocellulose (CNC) is a readily available nanostructured form of cellulose, characterized by a high biocompatibility and easily functionalized to produce materials with new properties and applications. In this study, CNC was modified to act as a drug delivery system for the auranofin pharmacophore-specifically, the gold(I)-containing [Et3PAu]+ moiety. For this purpose, commercial CNC was first derivatized with propargyl groups and subsequently with lipoic acid. These two different functionalizations were then used to insert a simple glucose moiety (as a selector for tumor cells) using a CuAAC reaction with the propargyl end. Meanwhile the lipoic acid S-S bond was reduced with dithiothreitol to react with two equivalents of the gold complex Et3PAuCl, an analogue of auranofin. The modification of CNC afforded a nanohybrid characterized by a loading of 113.2 mg of Au and 0,41 mmol of selector per g of CNC and by a mean diameter of 290 nm and a Zeta Potential with a value of -51 +/- 5 mV. This work opens the possibility of future studies on the use of Auranofin analogues supported on drug delivery systems for biomedical applications. future studies on the use of Auranofin analogues supported on drug delivery systems for biomedical applications.

In recent years, gold(I) complexes have attracted increasing interest as an alternative to conventional metallo-chemotherapeutic agents. Their mode of action differs significantly from that of traditional platinum-based drugs. However, the identification of their intracellular targets and the elucidation of their mechanisms of action remain major challenges, largely due to the lack of suitable molecular tools for tracking these compounds in biological systems. To address these issues, three novel gold(I) complexes bearing two different fluorescent labels were synthesized and characterized. These complexes include an N-heterocyclic monocarbene gold(I) complex 3 and the corresponding biscarbene 4, both of which are functionalized with an anthracenyl moiety, as well as an NHC gold(I) monocarbene complex bearing a BODIPY label 5. The specific aim of this study was to generate trackable metallodrug models for mechanistic and metallomics-oriented research. These compounds were characterized using 1H and 13C NMR spectroscopy and elemental analysis. The crystallographic structure of the anthracenyl gold monocarbene was also determined. Interaction studies with human serum albumin (HSA) using UV-vis absorption spectroscopy and ESI-MS provided clear evidence of metallodrug-protein interactions. The uptake of the complexes in A2780 ovarian cancer cells was measured using fluorescence-activated cell sorting (FACS) cytofluorimetry, which indicated strong cellular uptake for the anthracenyl-labeled compounds 3 and 4. A cell fractionation approach was used for the quantitative analysis of subcellular drug disposition. These approaches collectively enabled a direct visualization of the intracellular fate of the gold complexes, providing a framework for correlating cellular distribution with biological activity. Finally, the gold complexes bearing the anthracenyl probe were evaluated for their cytotoxic activity in cisplatin-sensitive and -resistant A2780 cancer cells; the BODIPY complex could not be evaluated due to its insolubility. Overall, this study provides solid evidence that gold complexes bearing the anthracenyl probe retain significant cytotoxic properties and enable monitoring the uptake and fate of these gold species inside cancer cells, thus providing a proof-of-concept that fluorescently labeled gold complexes can serve as powerful tools for mechanistic investigations, including metallomics and proteomics-oriented studies aimed at identifying molecular targets and affected pathways.

Organopalladium compounds are a new class of metal-based drugs with significant yet largely unexplored therapeutic potential. Previous studies have suggested that these compounds act as prodrugs that can strongly interact with protein targets. However, the underlying protein metalation processes have scarcely been investigated to date. To gain a deeper insight into this issue, we analyzed the interactions of two representative organopalladium compounds with the model protein RNase A using a strategy that combined electrospray ionization mass spectrometry (ESI MS) and X-ray crystallography. Time-course and titration ESI-MS studies revealed that the two palladium compounds readily react with RNase A to form stable adducts with distinct structural characteristics. The crystal structures of two organopalladium/RNase A adducts were then determined. These structures revealed that the palladium-containing fragments bind to histidine and methionine side chains. Interestingly, one of the two complexes interacts with the catalytically important residues His12 and His119, causing significant inhibition of the protein's enzymatic activity. Overall, these results provide detailed insights into the main features of protein metalation reactions promoted by organopalladium compounds as well as the nature of protein-bound palladium fragments.

Cryptosporidium spp. cause cryptosporidiosis, a severe diarrheal disease, particularly in young children and immunocompromised individuals. Treatment options are limited, and the only approved drug, nitazoxanide, is poorly effective in the most susceptible populations. Cryptosporidium relies exclusively on the thioredoxin reductase/thioredoxin (TrxR/Trx) system for redox homeostasis as Cryptosporidium lacks a glutathione reductase gene. Consistent with this vulnerability, TrxR ablation blocks parasite proliferation and sexual development, identifying TrxR as an essential drug target. C. parvum TrxR (CpTrxR) contains two redox-active cysteine motifs: a conserved N-terminal site and an apicomplexan-specific C-terminal site absent in human TrxRs. Here, by employing six structurally diverse gold-containing compounds, including clinically used agents, we probed the reactivity of CpTrxR toward these pharmacologically relevant chemotypes. Through a combination of X-ray crystallography, mass spectrometry, and functional studies, we discovered that enzyme inhibition arises from the distinct chemical properties of these compounds, which enable them to target either the N-terminal or the apicomplexan-specific C-terminal redox sites. These findings reinforce the potential of CpTrxR as a chemically tractable and parasite-selective target and establish gold-based scaffolds as a promising foundation for developing novel anti-Cryptosporidium therapeutics.

Human H-type ferritin is an attractive protein candidate for the targeted delivery of anticancer metallodrugs. In this study, we report on the formation of ferritin conjugates with oxaliplatin via a direct reaction in solution. This process typically results in the decoration of the protein surface with metallofragments of the type ((R,R)-trans-1,2-diaminocyclohexane)platinum(II) (DACH)Pt. A series of oxaliplatin/ferritin conjugates were obtained and systematically characterized by ESI-MS and ICP measurements. The ESI-MS profiles obtained demonstrate that adduct formation is both time- and concentration-dependent. The nature, stoichiometry and likely anchoring sites of the ferritin-bound platinum fragments were elucidated by ESI-MS analysis coupled with trypsinization experiments. We then evaluated the biological effects of the oxaliplatin-ferritin cage bioconjugate (preprared at 120:1 metal to protein ratio) in comparison to the free drug on A2780 human ovarian cancer cells. We observed that conjugation of oxaliplatin to ferritin resulted in similar platinum uptake by the cells compared to the free drug. However, the anticancer activity of the drug was unexpectedly lost. We critically discuss the implications of these results for the design and preparation of new anticancer platinum-ferritin bioconjugates.

Gold compounds are a promising class of experimental anticancer metallodrugs. Unlike platinum-based drugs, their antiproliferative effects are thought to result mainly from modulation of cancer cell metabolism rather than direct interaction with DNA. Previous NMR studies have shown that four cytotoxic gold compounds - auranofin, aurothiomalate and two gold N-heterocyclic carbenes - induce distinct metabolic changes in A2780 ovarian cancer cells, suggesting the occurrence of different mechanisms of action. To better understand these effects, we constructed a genome-scale metabolic model (GEM) of A2780 cells to analyze the NMR-detected metabolomic changes. The model successfully predicts the diverse metabolic responses induced by each gold compound and identifies common metabolic changes. These results confirm the potential of GEMs as a powerful tool for interpreting and predicting cellular responses to gold-based drugs, providing insights into their mechanisms of action and potential therapeutic applications.

A combination of pathway enrichment and metabolite clustering analysis is used to interpret untargeted 1H NMR metabolomics data, enabling a biochemically informative comparison of the effects induced by a panel of known cytotoxic gold(I) and gold(III) compounds in A2780 ovarian cancer cells. The identification of the most dysregulated pathways for the major classes of compounds highlights specific chemical features that lead to common biological effects. The proposed approach may have broader applicability to the screening of metal-based drug candidate libraries, which is always complicated by their multitarget nature, and support the comprehensive interpretation of their metabolic actions.

Here we investigated cytotoxicity and DNA and protein binding of an iodido analog of picoplatin, the cis-ammine-diiodido(2-methylpyridine)platinum(II) complex (I-picoplatin). I-picoplatin (IC50 = 3.7-12.4 μM) outperforms picoplatin (IC50 = 11.8-22.6 μM) in the human cancer cell lines used and shows a greater ability to overcome the cisplatin resistance of A2780 ovarian cancer cells than does picoplatin. I-picoplatin also induces different cell cycle changes (reduced S-phase fraction and an increase in the G2/M phase arrest) in HeLa cervical carcinoma cells compared to both picoplatin and cisplatin. Binding of the metal compound to DNA model systems was investigated by ethidium bromide displacement assay and circular dichroism. Its reactivity with lysozyme (HEWL) and pancreatic RNase A was studied by X-ray diffraction and mass spectrometry experiments. I-picoplatin binds the DNA double helix and is able to retain the 2-methylpyridine ligand and at least one of the two iodido ligands when bound to the two proteins. Various Pt-containing moieties, including one based on the isomerized structure of I-picoplatin, coordinate the His and Met residues. A low-resolution structure of the I-picoplatin/human serum albumin (HSA) adduct has also been solved. The side chains of His146, Met289, and Met329 are the primary binding sites of the I-picoplatin moieties on HSA.

The role of human serum albumin (HSA) in the delivery of anticancer metallodrugs remains unclear and requires further investigation. To this end, bioconjugates of HSA with the metallodrugs cisplatin (CIS), oxaliplatin (OXA) and auranofin (AF) were prepared, characterised by ESI-MS and ICP, and tested for their cytotoxic properties in A2780 and HCT116 cancer cells. Significant differences in the biological activities of the two Pt bioconjugates compared to that of the Au bioconjugate emerged, and they are interpreted and discussed in the context of the available literature.

A series of ruthenium(II) arene complexes of the general formula [(η6-pCymene)Ru(L)Cl]PF6 (hereafter RACs) have been designed, synthesized, and characterized with a view to their possible use as antimicrobial agents. We specifically report on five structurally related RAC complexes, i.e., Ru-pCy1-5, incorporating bidentate polypyridyl ligands of different nature (L1 = benzo[i]dipyrido[3,2-a: 2',3'-c]phenazine, L2 = 4,7-diphenyl-1,10-phenanthroline, L3 = 2,2'-biquinoline, L4 = 2,2'-bipyridine-4,4'-diylbis(morpholinomethanone), L5 = (2,2'-bipyridine-4,4'-diylbis(morpholinomethylene)). The complexes Ru-pCy1-5, which showed substantial inertness when dissolved in aqueous media, were investigated by ESI-MS for their ability to interact with two representative model proteins, i.e., SOD and RNase A. Interestingly, these complexes, with the sole exception of Ru-pCy3, tend to form stable adducts with the two proteins upon release of the chloride ligand, in agreement with previous observations on similar Ru compounds. The antimicrobial properties of these compounds were then tested against Gram-positive bacterium Bacillus subtilis and Gram-negative bacterium Burkholderia cenocepacia. The observed antibacterial effects were then tentatively correlated with the structural features of each complex.

Solution interactions of three organomercury compounds, i.e., methylmercury chloride, thimerosal and phenylmercury acetate, with a group of biochemically relevant proteins, namely cytochrome c (Cyt c), ribonuclease A (RNase A), carbonic anhydrase I (hCA I), superoxide dismutase (SOD), and serum albumin (HSA), were investigated using an established ESI MS approach. Temporal analysis of sample aliquots provided insight into the binding kinetics, while comparative analysis of the obtained mass spectra disclosed adduct formation of each mercurial with the tested proteins and the relative abundance of the species. The three organomercurials bind, exclusively and tightly, to free cysteine residues as no binding was observed in the case of proteins lacking such groups. hCA I, SOD and HSA formed distinct mercury adducts, preserving the Hg bound alkyl/aryl ligands; yet, the three organomercurials displayed significant differences in reactivity in relation to their chemical structure. The investigation was then extended to analyze the reactions with the C-terminal dodecapeptide of the enzyme human thioredoxin reductase, which contains a characteristic selenol-thiol moiety: tight Hg binding was observed. Notably, this peptide was able to remove effectively and completely the alkyl/aryl ligands of the three tested organomercurials; this behavior may be relevant to the detoxification mechanism of organomercurials in mammals. Finally, a competition experiment was carried out to establish whether protein bound mercury centers may be displaced by other competing metals. Interestingly, and quite unexpectedly, we observed that a protein bound mercury fragment may be partially displaced from its coordination site in hCA I by the medicinal gold compound auranofin.

The charge of paddlewheel diruthenium complexes has a major role in defining their interaction with proteins: negatively charged complexes bind proteins noncovalently, while cationic complexes form adducts where the Ru2 core binds to Asp side chains at the equatorial sites, or to the main chain carbonyl groups or the side chains of His, Arg or Lys residues at the axial sites. Here we study the interactions of the neutral compound [Ru2(D-p-FPhF)(O2CCH3)2(O2CO)]& sdot;3H2O (D-p- FPhF- = N , N '- bis (4-fluorophenyl)formamidinate), a very rare example of a paddlewheel diruthenium compound with three different equatorial ligands, with the model protein bovine pancreatic ribonuclease (RNase A) by means of UV-visible absorption spectroscopy, circular dichroism (CD), electrospray ionization mass spectrometry (ESI-MS) and X-ray crystallography. It is the first attempt to investigate the binding of a neutral diruthenium compound to a protein. ESI-MS data indicate that, in solution, under the investigated experimental conditions, the diruthenium compound binds the protein upon the loss of an acetate ligand. The crystallographic results indicate the replacement of an acetate by two water molecules and the coordination of the [Ru2(D-p-FPhF)(O2CCH3)2(O2CO)(OH2)2]+ ion, that is expected to be a highly reactive species in the absence of the protein, to the imidazole ring of His105 at the axial site. The side chains of Glu9 and His119 are also identified as possible diruthenium binding sites. The binding significantly affects the protein ability to form dimers and higher-order oligomers, without significantly altering its secondary structure content and thermal stability. These data show that: i) Glu side chain has to be considered as a possible alternative binding site for diruthenium compounds, ii) diruthenium containing fragments that would be unstable in solution can be formed upon reaction of diruthenium compounds with a protein, iii) diruthenium compounds could be used as modulators of protein aggregation.

Crystallographic and spectrometric studies of AP-1, cisplatin and transplatin binding to a B-DNA double helix dodecamer are reported.

Aurothiomalate (AuTM) is an FDA-approved antiarthritic gold drug with unique anticancer properties. To enhance its anticancer activity, we prepared a bioconjugate with human apoferritin (HuHf) by attaching some AuTM moieties to surface protein residues. The reaction of apoferritin with excess AuTM yielded a single adduct, that was characterized by ESI MS and ICP-OES analysis, using three mutant ferritins and trypsinization experiments. The adduct contains ~3 gold atoms per ferritin subunit, arranged in a small cluster bound to Cys90 and Cys102. MD simulations provided a plausible structural model for the cluster. The adduct was evaluated for its pharmacological properties and was found to be significantly more cytotoxic than free AuTM against A2780 cancer cells mainly due to higher gold uptake. NMR-metabolomics showed that AuTM bound to HuHf and free AuTM induced qualitatively similar changes in treated cancer cells, indicating that the effects on cell metabolism are approximately the same, in agreement with independent biochemical experiments. In conclusion, we have demonstrated here that a molecularly precise bioconjugate formed between AuTM and HuHf exhibits anticancer properties far superior to the free drug, while retaining its key mechanistic features. Evidence is provided that human ferritin can serve as an excellent carrier for this metallodrug.

INTRODUCTION:Auranofin (AF) is a well-established, FDA-approved, antiarthritic gold drug that is currently being reevaluated for a variety of therapeutic indications through drug repurposing. AF has shown great promise as a potential anticancer agent and has been approved for a few clinical trials in cancer. The renewed interest in AF has led to extensive research into the design, preparation and biological evaluation of auranofin analogs, which may have an even better pharmacological profile than the parent drug. AREAS COVERED:This article reviews the strategies for chemical modification of the AF scaffold. Several auranofin analogs have been prepared and characterized for medical application in the field of cancer treatment over the last 20 years. Some emerging structure-function relationships are proposed and discussed. EXPERT OPINION:The chemical modification of the AF scaffold has been the subject of intense activity in recent years and this strategy has led to the preparation and evaluation of several AF analogs. The case of iodauranofin is a particularly promising example. The availability of homogeneous biological data for a group of AF derivatives allows some initial structure-function relationships to be proposed, which may inspire the design and synthesis of new and better AF analogs for cancer treatment.

Many efforts have been made in the last few decades to selectively transport antitumor agents to their potential target sites with the aim to improve efficacy and selectivity. Indeed, this aspect could greatly improve the beneficial effects of a specific anticancer agent especially in the case of orphan tumors like the triple negative breast cancer. A possible strategy relies on utilizing a protective leaving group like alizarin as the Pt(II) ligand to reduce the deactivation processes of the pharmacophore enacted by Pt resistant cancer cells. In this study a new series of neutral mixed-ligand Pt(II) complexes bearing alizarin and a variety of diamine ligands were synthesized and spectroscopically characterized by FT-IR, NMR and UV-Vis analyses. Three Pt(II) compounds, i.e., 2b, 6b and 7b, emerging as different both in terms of structural properties and cytotoxic effects (not effective, 10.49 ± 1.21 μM and 24.5 ± 1.5 μM, respectively), were chosen for a deeper investigation of the ability of alizarin to work as a selective carrier. The study comprises the in vitro cytotoxicity evaluation against triple negative breast cancer cell lines and ESI-MS interaction studies relative to the reaction of the selected Pt(II) complexes with model proteins and DNA fragments, mimicking potential biological targets. The results allow us to suggest the use of complex 6b as a prospective anticancer agent worthy of further investigations.

The reactivity of the anticancer drug picoplatin (cis-amminedichlorido(2-methylpyridine)platinum(ii) complex) with the model proteins hen egg white lysozyme (HEWL) and bovine pancreatic ribonuclease (RNase A) was investigated by electrospray ionisation mass spectrometry (ESI MS) and X-ray crystallography. The data were compared with those previously obtained for the adducts of these proteins with cisplatin, carboplatin and oxaliplatin under the same experimental conditions. ESI-MS data show binding of Pt to both proteins, with fragments retaining the 2-methylpyridine ligand and, possibly, a chloride ion. X-ray crystallography identifies different binding sites on the two proteins, highlighting a different behaviour of picoplatin in the absence or presence of dimethyl sulfoxide (DMSO). Metal-containing fragments bind to HEWL close to the side chains of His15, Asp18, Asp119 and both Lys1 and Glu7, whereas they bind to RNase A on the side chain of His12, Met29, His48, Asp53, Met79, His105 and His119. The data suggest that the presence of DMSO favours the loss of 2-methylpyridine and alters the ability of the Pt compound to bind to the two proteins. With both proteins, picoplatin appears to behave similarly to cisplatin and carboplatin when dissolved in DMSO, whereas it behaves more like oxaliplatin in the absence of the coordinating solvent. This study provides important insights into the pharmacological profile of picoplatin and supports the conclusion that coordinating solvents should not be used to evaluate the biological activities of Pt-based drugs. The reactivity of the anticancer drug picoplatin with the model proteins hen egg white lysozyme and bovine pancreatic ribonuclease was investigated by electrospray ionisation mass spectrometry and X-ray crystallography.

The possibility of using selectively incorporated 19 F nuclei for NMR spectroscopic studies has retrieved increasing interest in recent years. The high gyromagnetic ratio of 19 F and its absence in native biomolecular systems make this nucleus an interesting alternative to standard 1 H NMR spectroscopy. Here we show how we can attach a label, carrying a 19 F atom, to protein tyrosines, through the use of a specific three component Mannich-type reaction. To validate the efficacy and the specificity of the approach, we tested it on two selected systems with the aid of ESI MS measurements.