A Gallium(III) Complex that Engages Protein Disulfide Isomerase A3 (PDIA3) as an Anticancer Target

Identification of Cellular Protein Targets of a Half-Sandwich Iridium(III) Complex Reveals Its Dual Mechanism of Action via Both Electrophilic and Oxidative Stresses

Identification of intracellular targets of anticancer drug candidates provides key information on their mechanism of action. Exploiting the ability of the anticancer (C∧N)-chelated half-sandwich iridium(III) complexes to covalently bind proteins, click chemistry with a bioorthogonal azido probe was used to localize a phenyloxazoline-chelated iridium complex within cells and profile its interactome at the proteome-wide scale. Proteins involved in protein folding and actin cytoskeleton regulation were identified as high-affinity targets. Upon iridium complex treatment, the folding activity of Heat Shock Protein HSP90 was inhibited in vitro and major cytoskeleton disorganization was observed. A wide array of imaging and biochemical methods validated selected targets and provided a multiscale overview of the effects of this complex on live human cells. We demonstrate that it behaves as a dual agent, inducing both electrophilic and oxidative stresses in cells that account for its cytotoxicity. The proposed methodological workflow can open innovative avenues in metallodrug discovery.

Schiff bases and their metal complexes to target and overcome (multidrug) resistance in cancer

Overcoming multidrug resistance (MDR) is one of the major challenges in cancer therapy. In this respect, Schiff base-related compounds (bearing a R1R2CNR3 bond) gained high interest during the past decades. Schiff bases are considered privileged ligands for various reasons, including the easiness of their preparation and the possibility to form complexes with almost all transition metal ions. Schiff bases and their metal complexes exhibit many types of biological activities and are used for the treatment and diagnosis of various diseases. Until now, 13 Schiff bases have been investigated in clinical trials for cancer treatment and hypoxia imaging. This review represents the first collection of Schiff bases and their complexes which demonstrated MDR-reversal activity. The areas of drug resistance covered in this article involve: 1) Modulation of ABC transporter function, 2) Targeting lysosomal ABCB1 overexpression, 3) Circumvention of ABC transporter-mediated drug efflux by alternative routes of drug uptake, 4) Selective activity against MDR cancer models (collateral sensitivity), 5) Targeting GSH-detoxifying systems, 6) Overcoming apoptosis resistance by inducing necrosis and paraptosis, 7) Reactivation of mutated p53, 8) Restoration of sensitivity to DNA-damaging anticancer therapy, and 9) Overcoming drug resistance through modulation of the immune system. Through this approach, we would like to draw attention to Schiff bases and their metal complexes representing highly interesting anticancer drug candidates with the ability to overcome MDR.

Synthesis, characterization and in vitro cytotoxicity of gallium(III)-dithiocarbamate complexes

A library of homoleptic mononuclear Ga(III) complexes of the general formula [Ga(DTC)3], where DTC is an alicyclic or a linear dithiocarbamate chelator, is reported. The complexes were prepared in high yields starting from Ga(NO3)3·6H2O and fully characterized by elemental analysis and IR and NMR spectroscopy. Crystals of five of these complexes were obtained. The antitumor activity of the newly synthesized compounds against a panel of human cancer cell lines was evaluated. The chemical nature of the DTC does not have a marked impact on the structural features of the final compound. X-ray crystal structure analyses revealed that all these complexes have a trigonal prismatic geometry with three identical chelating DTCs coordinating the Ga(III) ion. It is noteworthy that in complex 22, [Ga(NHEt)3] (NHEt = N-ethyldithiocarbamate), the asymmetric unit is formed by two independent and structurally different molecules. Cellular studies showed that all the synthesized Ga-DTC complexes exhibit marked cytotoxic activity, even against human colon cancer cells that are less sensitive to cisplatin. Among the tested compounds, 6 ([Ga(CEPipDTC)3], CEPipDTC = (ethoxycarbonyl)-piperidinedithiocarbamate) and 21 ([Ga(Pr-13)3], PR13 = 4 and N-(2-ethoxy-2-oxoethyl)-N-methyldithiocarbamate) are very promising derivatives, but they have no selectivity towards cancer cells. Nevertheless, the obtained data provide a foundation for developing gallium-dithiocarbamate complexes as anticancer agents.

New Stable Gallium(III) and Indium(III) Complexes with Thiosemicarbazone Ligands: A Biological Evaluation

The aim of this work is to explore a new library of coordination compounds for medicinal applications. Gallium is known for its various applications in this field. Presently, indium is not particularly important in medicine, but it shares a lot of chemical traits with its above-mentioned lighter companion, gallium, and is also used in radio imaging. These metals are combined with thiosemicarbazones, ligating compounds increasingly known for their biological and pharmaceutical applications. In particular, the few ligands chosen to interact with these hard metal ions share the ideal affinity for a high charge density. Therefore, in this work we describe the synthesis and the characterization of the resulting coordination compounds. The yields of the reactions vary from a minimum of 21% to a maximum of 82%, using a fast and easy procedure. Nuclear Magnetic Resonance (NMR) and Infra Red (IR) spectroscopy, mass spectrometry, elemental analysis, and X-ray Diffraction (XRD) confirm the formation of stable compounds in all cases and a ligand-to-metal 2:1 stoichiometry with both cations. In addition, we further investigated their chemical and biological characteristics, via UV-visible titrations, stability tests, and cytotoxicity and antibiotic assays. The results confirm a strong stability in all explored conditions, which suggests that these compounds are more suitable for radio imaging applications rather than for antitumoral or antimicrobic ones.

Highly emissive 4-carbazole-appended salen-indium complex: the effect of strong donor-acceptor interaction

Herein, we report our findings on 4-carbazole (CBZ)-appended salen-based indium complexes, CBZIn1 and CBZIn2, which feature diimine bridges exhibiting different electron-accepting properties. Notably, CBZIn2 exhibited a significantly higher photoluminescence quantum efficiency (PLQY, ΦPL) in toluene than CBZIn1, with a value over 15 times greater (ΦPL = 57.7% for CBZIn2; ΦPL = 3.7% for CBZIn1). In particular, in the rigid state of THF at 77 K, CBZIn2 exhibited a near-unity PLQY of 98.2%. Even in the PMMA film, CBZIn2 maintained a high level of PLQY (ΦPL = 70.2%). These results can be attributed to the highly efficient radiative decay process based on intramolecular charge-transfer (ICT) transition between the moderately twisted CBZ, characterized by its conformational rigidity and the 1,2-dicyanoethylene-bridged salen, which exhibits a strong electron-accepting ability. Furthermore, these findings are supported by theoretical calculations.

Hot-Electron Dynamics Mediated Medical Diagnosis and Therapy

Surface plasmon resonance excitation significantly enhances the absorption of light and increases the generation of "hot" electrons, i.e., conducting electrons that are raised from their steady states to excited states. These excited electrons rapidly decay and equilibrate via radiative and nonradiative damping over several hundred femtoseconds. During the hot-electron dynamics, from their generation to the ultimate nonradiative decay, the electromagnetic field enhancement, hot electron density increase, and local heating effect are sequentially induced. Over the past decade, these physical phenomena have attracted considerable attention in the biomedical field, e.g., the rapid and accurate identification of biomolecules, precise synthesis and release of drugs, and elimination of tumors. This review highlights the recent developments in the application of hot-electron dynamics in medical diagnosis and therapy, particularly fully integrated device techniques with good application prospects. In addition, we discuss the latest experimental and theoretical studies of underlying mechanisms. From a practical standpoint, the pioneering modeling analyses and quantitative measurements in the extreme near field are summarized to illustrate the quantification of hot-electron dynamics. Finally, the prospects and remaining challenges associated with biomedical engineering based on hot-electron dynamics are presented.

Gallium Triggers Ferroptosis through a Synergistic Mechanism

The gallium ion (Ga3+ ) has long been believed to disrupt ferric homeostasis in the body by competing with iron cofactors in metalloproteins, ultimately leading to cell death. This study revealed that through an indirect pathway, gallium can trigger ferroptosis, a type of non-apoptotic cell death regulated by iron. This is exemplified by the gallium complex of the salen ligand (Ga-1); we found that Ga-1 acts as an effective anion transporter that can affect the pH gradient and change membrane permeability, leading to mitochondrial dysfunction and the release of ferrous iron from the electron transfer chain (ETC). In addition, Ga-1 also targeted protein disulfide isomerases (PDIs) located in the endoplasmic reticulum (ER) membrane, preventing the repair of the antioxidant glutathione (GSH) system and thus enforcing ferroptosis. Finally, a combination treatment of Ga-1 and dietary polyunsaturated fatty acids (PUFAs), which enhances lipid peroxidation during ferroptosis, showed a synergistic therapeutic effect both in vitro and in vivo. This study provided us with a strategy to synergistically induce Ferroptosis in tumor cells, thereby enhancing the anti-neoplastic effect.

Methods to identify protein targets of metal-based drugs

Metal-based anticancer agents occupy a distinct chemical space due to their particular coordination geometry and reactivity. Despite the initial DNA-targeting paradigm for this class of compounds, it is now clear that they can also be tuned to target proteins in cells, depending on the metal and ligand scaffold. Since metallodrug discovery is dominated by phenotypic screenings, tailored proteomics strategies were crucial to identify and validate protein targets of several investigative and clinically advanced metal-based drugs. Here, such experimental approaches are discussed, which showed that metallodrugs based on ruthenium, gold, rhenium and even platinum, can selectively and specifically target proteins with clear-cut down-stream effects. Target identification strategies are expected to support significantly the mechanism-driven clinical translation of metal-based drugs.

Recent Trends in the Development of Novel Metal-Based Antineoplastic Drugs

Since the accidental discovery of the anticancer properties of cisplatin more than half a century ago, significant efforts by the broad scientific community have been and are currently being invested into the search for metal complexes with antitumor activity. Coordination compounds of transition metals such as platinum (Pt), ruthenium (Ru) and gold (Au) have proven their effectiveness as diagnostic and/or antiproliferative agents. In recent years, experimental work on the potential applications of elements including lanthanum (La) and the post-transition metal gallium (Ga) in the field of oncology has been gaining traction. The authors of the present review article aim to help the reader "catch up" with some of the latest developments in the vast subject of coordination compounds in oncology. Herewith is offered a review of the published scientific literature on anticancer coordination compounds of Pt, Ru, Au, Ga and La that has been released over the past three years with the hope readers find the following article informative and helpful.

Developing a Gallium(III) Agent Based on the Properties of the Tumor Microenvironment and Lactoferrin: Achieving Two-Agent Co-delivery and Multi-targeted Combination Therapy of Cancer

To develop a next-generation anticancer metal-based drug, realize the multi-targeted combination therapy of protein drug and metal-based drug for cancer, solve their co-delivery challenges, and improve their in vivo targeting ability, we proposed to develop a multi-targeted anticancer metal-based agent exploiting the properties of the tumor microenvironment (TME) and of lactoferrin (LF). To this end, we optimized a series of gallium (Ga, III) isopropyl-2-pyridyl-ketone thiosemicarbazone compounds to obtain a Ga compound (C4) with remarkable cytotoxicity and then constructed a new LF-C4 nanoparticle (LF-C4 NP) delivery system. In vivo studies showed that LF-C4 NPs not only had a greater capacity for inhibiting tumor growth than LF or C4 alone but also solved the co-delivery problems of LF and C4 and improved their targeting ability. Furthermore, free C4 and LF-C4 NPs inhibited tumor growth through multiple synergistic actions on the TME: killing cancer cell, inhibiting tumor angiogenesis, and activating immune system.

Breaking the Iron Homeostasis: A "Trojan Horse" Self-Assembled Nanodrug Sensitizes Homologous Recombination Proficient Ovarian Cancer Cells to PARP Inhibition

Poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors are used in ovarian cancer treatment and have greatly improved the survival rates for homologous recombination repair (HRR)-deficient patients. However, their therapeutic efficacy is limited in HRR-proficient ovarian cancer. Thus, sensitizing HRR-proficient ovarian cancer cells to PARP inhibitors is important in clinical practice. Here, a nanodrug, olaparib-Ga, was designed using self-assembly of the PARP inhibitor olaparib into bovine serum albumin through gallic acid gallium(III) coordination via a convenient and green synthetic method. Compared with olaparib, olaparib-Ga featured an ultrasmall size of 7 nm and led to increased suppression of cell viability, induction of DNA damage, and enhanced cell apoptosis in the SKOV3 and OVCAR3 HRR-proficient ovarian cancer cells in vitro. Further experiments indicated that the olaparib-Ga nanodrug could suppress RRM2 expression, activate the Fe²⁺/ROS/MAPK pathway and HMOX1 signaling, inhibit the PI3K/AKT signaling pathway, and enhance the expression of cleaved-caspase 3 and BAX protein. This, in turn, led to increased cell apoptosis in HRR-proficient ovarian cancer cells. Moreover, olaparib-Ga effectively restrained SKOV3 and OVCAR3 tumor growth and exhibited negligible toxicity in vivo. In conclusion, we propose that olaparib-Ga can act as a promising nanodrug for the treatment of HRR-proficient ovarian cancer.

Gallium Nanodroplets are Anti-Inflammatory without Interfering with Iron Homeostasis

Gallium (Ga) compounds, as the source of Ga ions (Ga³⁺), have been historically used as anti-inflammatories. Currently, the widely accepted mechanisms of the anti-inflammatory effects for Ga³⁺ are rationalized on the basis of their similarities to ferric ions (Fe³⁺), which permits Ga³⁺ to bind with Fe-binding proteins and subsequently disturbs the Fe homeostasis in the immune cells. Here in contrast to the classic views, our study presents the mechanisms of Ga as anti-inflammatory by delivering Ga nanodroplets (GNDs) into lipopolysaccharide-induced macrophages and exploring the processes. The GNDs show a selective inhibition of nitric oxide (NO) production without affecting the accumulation of pro-inflammatory mediators. This is explained by GNDs disrupting the synthesis of inducible NO synthase in the activated macrophages by upregulating the levels of eIF2α phosphorylation, without interfering with the Fe homeostasis. The Fe³⁺ transferrin receptor-independent endocytosis of GNDs by the cells prompts a fundamentally different mechanism as anti-inflammatories in comparison to that imparted by Ga³⁺. This study reveals the fundamental molecular basis of GND-macrophage interactions, which may provide additional avenues for the use of Ga for anti-inflammatory and future biomedical and pharmaceutical applications.

L-Selenocysteine induced HepG-2 cells apoptosis through reactive oxygen species-mediated signaling pathway

BACKGROUND

Currently, Liver cancer is the fifth most common tumor and the second most important reason for cancer-related death in the world. However, there are still many limitations of the clinical treatment of liver cancer, and new treatment options are clearly needed. Fortunately, studies have shown that L-Selenocysteine has a certain effect on cancer. This study was to investigate the effects of L-Selenocysteine on the inhibition of cell proliferation and the promotion of apoptosis of HepG-2 cells through ROS mediated fine signaling pathway.

MATERIALS AND METHODS

CCK-8 assay was applied to evaluating the cytotoxic effect of L-Selenocysteine on HepG-2 cells. Electron microscopy, flow cytometry and Western Blot was utilization in further researching cells signaling pathways.

RESULTS

The growth of HepG-2 cells was inhibited by L-selenocysteine ​​treatment in a dose-dependent manner. The cell viability decreased to 52.20%, 43.20% and 30.83% under the treatment of 4, 8, 16 µM L-selenocysteine, respectively. L-Selenocysteine had higher cytotoxicity towards HepG-2 cells than normal cells. L-Selenocysteine can induce the apoptosis of HepG-2 cells by increasing the DNA fragmentation, and activating the Caspase-3. In addition, it was found that the mechanism of the induction to HepG-2 cell apoptosis by L-Selenocysteine was closely related to the overproduction of ROS and promoted apoptosis through the Bcl-2 signaling pathway.

CONCLUSIONS

Our data suggest that L-selenocysteine ​​may cause mitochondrial damage and subsequently stimulate ROS production. ROS can damage cellular DNA and mediate the production of Casapase-8, Bid, Bcl-2 and other proteins, affecting downstream signaling pathways, and ultimately induced apoptosis.

Gallium(III) Complex with Cloxyquin Ligands Induces Ferroptosis in Cancer Cells and Is a Potent Agent against Both Differentiated and Tumorigenic Cancer Stem Rhabdomyosarcoma Cells

In this work, gallium(III) complex with cloxyquin (5-chloro-8-quinolinol, HClQ) ligands is shown to effectively inhibit proliferation of rhabdomyosarcoma cells, the frequent, aggressive, and poorly treatable cancer of children. It offers striking selectivity to cancer cells compared to noncancerous human fibroblasts. The data reveal that the complex induces ferroptosis in rhabdomyosarcoma cells, likely due to interfering with iron metabolism. Importantly, it can kill both bulk and stem rhabdomyosarcoma cells. To the best of our knowledge, this is the first compound based on metal other than Fe capable of inducing ferroptosis in cancer cells.

Metallodrugs in cancer nanomedicine

Metal complexes are extensively used for cancer therapy. The multiple variables available for tuning (metal, ligand, and metal-ligand interaction) offer unique opportunities for drug design, and have led to a vast portfolio of metallodrugs that can display a higher diversity of functions and mechanisms of action with respect to pure organic structures. Clinically approved metallodrugs, such as cisplatin, carboplatin and oxaliplatin, are used to treat many types of cancer and play prominent roles in combination regimens, including with immunotherapy. However, metallodrugs generally suffer from poor pharmacokinetics, low levels of target site accumulation, metal-mediated off-target reactivity and development of drug resistance, which can all limit their efficacy and clinical translation. Nanomedicine has arisen as a powerful tool to help overcome these shortcomings. Several nanoformulations have already significantly improved the efficacy and reduced the toxicity of (chemo-)therapeutic drugs, including some promising metallodrug-containing nanomedicines currently in clinical trials. In this critical review, we analyse the opportunities and clinical challenges of metallodrugs, and we assess the advantages and limitations of metallodrug delivery, both from a nanocarrier and from a metal-nano interaction perspective. We describe the latest and most relevant nanomedicine formulations developed for metal complexes, and we discuss how the rational combination of coordination chemistry with nanomedicine technology can assist in promoting the clinical translation of metallodrugs.

Osmium(VI) nitride triggers mitochondria-induced oncosis and apoptosis

We report a new osmium(VI) nitrido complex bearing a nonplanar tetradentate ligand with potent anticancer activity. This complex causes mitochondrial damage, which induces liver cancer cell death via oncosis and apoptosis. This is the first osmium-based anticancer candidate that induces oncosis.

Roles of Protein Disulfide Isomerase in Breast Cancer

Protein disulfide isomerase (PDI) is the endoplasmic reticulum (ER)'s most abundant and essential enzyme and serves as the primary catalyst for protein folding. Due to its apparent role in supporting the rapid proliferation of cancer cells, the selective blockade of PDI results in apoptosis through sustained activation of UPR pathways. The functions of PDI, especially in cancers, have been extensively studied over a decade, and recent research has explored the use of PDI inhibitors in the treatment of cancers but with focus areas of other cancers, such as brain or ovarian cancer. In this review, we discuss the roles of PDI members in breast cancer and PDI inhibitors used in breast cancer research. Additionally, a few PDI members may be suggested as potential molecular targets for highly metastatic breast cancers, such as TNBC, that require more attention in future research.

Highly red-emissive salen–indium complexes: impact of 4-amino-substitution on the photophysical properties

4-NR2-appended salen–indium complexes were prepared via a one-pot synthetic pathway. The complexes exhibited narrow-bandwidth red emissions with high photoluminescence quantum yields that are the highest among the reported salen-based luminophores.

Identification of dihydrotanshinone I as an ERp57 inhibitor with anti-breast cancer properties via the UPR pathway

Salvia miltiorrhiza (Danshen) is a well-known traditional Chinese medicine for treating various diseases, such as breast cancer. However, knowledge regarding its mechanisms is scant. Herein, the active ingredient dihydrotanshinone I (DHT) in Salvia miltiorrhiza extract (SME), which binds ERp57 was identified and verified by an enzymatic solid-phase method combined with LC-MS/MS. DHT potentially inhibited ERp57 activity and suppressed ERp57 expression at both the RNA and protein levels. Molecular docking simulation indicated that DHT could form a hydrogen bond with catalytic site of ERp57. Moreover, ERp57 overexpression decreased DHT-induced cytotoxicity in MDA-MB-231 cells. Thereafter, the signaling pathway downstream of ERp57 was investigated by Western blot analysis. The mechanistic study revealed that DHT treatment resulted in activation of endoplasmic reticulum (ER) stress, the unfolded protein response (UPR), and cellular apoptosis. In conclusion, our data implied that DHT targeted ERp57 for inhibition and induced ER stress and UPR activation, which in turn triggered breast cancer cell apoptosis.

Bioactive metal-containing nanomaterials for ferroptotic cancer therapy

The clinical performance of the current cancer therapies is still far from satisfactory. The emerging ferroptosis-driven therapy strategies reignite the hope of chemotherapy in tumor treatment due to their incredible tumor suppression. Among ferroptosis-based cancer therapies, metal elements have attracted remarkable attention due to their inherent physicochemical properties in inducing ferroptosis of tumor cells quickly and strongly without complex cellular signal transduction. Although the discovery and applications of ferroptosis for tumor treatment have been discussed in many reviews, the unique advantages of metal-containing nanomaterials interfering ferroptotic cancer therapies (MIFCT) have seldom been mentioned. Here, we outline the latest advances of MIFCT comprehensively. Firstly, the functions of different kinds of metal elements or their ions are introduced to illustrate their advantages in MIFCT. Secondly, the emerging metal-containing nanomaterials that are designed to achieve ferroptosis-driven therapy are overviewed, including their ability to boost the Fenton or Fenton-like reaction for reactive oxygen species generation, act as hydrogen peroxide self-providers, damage the reducing system, and disturb cellular communication. Moreover, metal-containing nanomaterials with external energy conversion features for MIFCT are discussed. Finally, the future expectations and challenges of MIFCT for clinical cancer therapy are spotlighted.

A cytotoxic nitrido-osmium(VI) complex induces caspase-mediated apoptosis in HepG2 cancer cells

The osmium(vi) nitrido complex [OsVI(N)(sap)(py)Cl] is a potential anti-cancer drug with promising in vitro antiproliferative activities toward a panel of cancer cell lines, including cisplatin-resistant cells (IC50 values of 2.8-13.8 μM). This drug targets DNA and changes its conformation via covalent binding and insertion. In vitro studies indicate that the drug induces HepG2 cells G2/M phase arrest, disrupts the mitochondrial membrane potential and causes caspase-mediated apoptosis. Further in vivo studies using HepG2-bearing nude mice reveal that this drug not only shows good antitumor efficacy of inhibiting tumor growth, but also does not show the side effect of weight loss.