Recent advances in ruthenium(II) and iridium(III) complexes containing nanosystems for cancer treatment and bioimaging

Facile one-pot synthesis of Ir(III) Bodipy polymeric gemini nanoparticles for tumor selective NIR photoactivated anticancer therapy

Over the last decades, a variety of metal complexes have been developed as chemotherapeutic agents. Despite the promising therapeutic prospects, the vast majority of these compounds suffer from low solubility, poor pharmacological properties, and most importantly poor tumor accumulation. To circumvent these limitations, herein, the incorporation of cytotoxic Ir(III) complexes and a variety of photosensitizers into polymeric gemini nanoparticles that selectively accumulate in the tumorous tissue and could be activated by near-infrared (NIR) light to exert an anticancer effect is reported. Upon exposure to light, the photosensitizer is able to generate singlet oxygen, triggering the rapid dissociation of the nanostructure and the activation of the Ir prodrug, thereby initiating a cascade of mitochondrial targeting and damage that ultimately leads to cell apoptosis. While selectively accumulating into tumorous tissue, the nanoparticles achieve almost complete eradication of the cisplatin-resistant cervical carcinoma tumor in vivo upon exposure to NIR irradiation.

Ferrocene-modified half-sandwich iridium(III) and ruthenium(II) propionylhydrazone complexes and anticancer application

Ferrocene, ruthenium(II) and iridium(III) organometallic complexes, potential substitutes for platinum-based drugs, have shown good application prospects in the field of cancer therapy. Therefore, in this paper, six ferrocene-modified half-sandwich ruthenium(II) and iridium(III) propionylhydrazone complexes were prepared, and the anticancer potential was evaluated and compared with cisplatin. These complexes showed potential in-vitro anti-proliferative activity against A549 cancer cells, especially for Ir-based complexes, and showing favorable synergistic anticancer effect. Meanwhile, these complexes showed little cytotoxicity and effective anti-migration activity. Ir3, the most active complex (ferrocene-appended iridium(III) complex), could accumulate in the intracellular mitochondria, disturb the cell cycle (S-phase), induce the accumulation of reactive oxygen species, and eventually cause the apoptosis of A549 cells. Then, the design of these complexes provides a good structural basis for the multi-active non‑platinum organometallic anticancer complexes.

Mitochondria-targeted ruthenium complexes can be generated in vitro and in living cells to target triple-negative breast cancer cells by autophagy inhibition

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer, which owned severe resistance to platinum-based anticancer agents. Herein, we report a new metal-arene complex, Ru-TPE-PPh3, which can be synthesized in vitro and in living cells with copper catalyzed the cycloaddition reaction of Ru-azide and alkynyl (CuAAC). The complex Ru-TPE-PPh3 exhibited superior inhibition of the proliferation of TNBC MDA-MB-231 cells with an IC50 value of 4.0 μM. Ru-TPE-PPh3 could induce the over production of reactive oxygen species (ROS) to initiate the oxidative stress, and further damage the mitochondria both functionally and morphologically, as loss of mitochondrial membrane potential (MMP) and cutting the supply of adenosine triphosphate (ATP), the disappearance of cristae structure. Moreover, the damaged mitochondria evoked the occurrence of mitophagy with the autophagic flux blockage and cell death. The complex Ru-TPE-PPh3 also demonstrated excellent anti-proliferative activity in 3D MDA-MB-231 multicellular tumor spheroids (MCTSs), indicating the potential to inhibit solid tumors in living cells. This study not only provided a potent agent for the TNBC treatment, but also demonstrated the universality of the bioorthogonally catalyzed lethality (BCL) strategy through CuAAC reation.

Towards efficient Ir(III) anticancer photodynamic therapy agents by extending π-conjugation on N^N ligands

In this work we disclose a new family of biscyclometallated Ir(III) complexes of the general formula [Ir(C^N)2(N^N)]Cl (IrL1-IrL5), where HC^N is 1-phenyl-β-carboline and N^N ligands (L1-L5) are different diimine ligands that differ from each other in the number of aromatic rings fused to the bipyridine scaffold. The photophysical properties of IrL1-IrL5 were thoroughly studied, and theoretical calculations were performed for a deeper comprehension of the respective variations along the series. All complexes exhibited high photostability under blue light irradiation. An increase in the number of aromatic rings led to a reduction in the HOMO-LUMO band gap causing a red-shift in the absorbance bands. Although all the complexes generated singlet oxygen (1O2) in aerated aqueous solutions through a photocatalytic process, IrL5 was by far the most efficient photosensitizer. Consequently, IrL5 was highly active in the photocatalytic oxidation of NADH. The formation of aggregates in DMSO at a high concentration (25 mM) was confirmed using different techniques, but was proved to be negligible in the concentration range of biological experiments. Moreover, ICP-MS studies proved that the cellular uptake of IrL2 and IrL3 is much better relative to that of IrL1, IrL4 and IrL5. The antiproliferative activity of IrL1-IrL5 was investigated in the dark and under blue light irradiation against different cancer cell lines. Complexes IrL1-IrL4 were found to be cytotoxic under dark conditions, while IrL5 turned out to be weakly cytotoxic. Despite the low cellular uptake of IrL5, this derivative exhibited a high increase of cytotoxicity upon blue light irradiation resulting in photocytotoxicity indexes (PI) up to 38. IrL1-IrL4 showed lower photocytotoxicity indexes ranging from 1.3 to 17.0. Haemolytic experiments corroborated the compatibility of our complexes with red blood cells. Confocal microscopy studies proved their accumulation in mitochondria, leading to mitochondrial membrane depolarization, and ruled out their localization in lysosomes. Overall, the mitochondria-targeted activity of IrL5, which inhibits considerably the viability of cancer cells upon blue light irradiation, allows us to outline this PS as a new alternative to traditional chemotherapeutic agents.

Neutral 2-phenylbenzimidazole-based iridium(III) complexes with picolinate ancillary ligand: tuning the emission properties by manipulating the substituent on the benzimidazole ring

We report the synthesis and characterization of ten neutral bisheteroleptic iridium(III) complexes with 2-phenylbenzimidazole cyclometallating ligand and picolinate as ancillary ligand. The 2-phenylbenzimidazole has been modified by selected substituents introduced on the cyclometallating ring and/or on the benzimidazole moiety. The integrity of the complexes has been assessed by NMR spectroscopy, by high-resolution mass spectrometry and by elemental analysis. The complexes are demonstrated to be highly phosphorescent at room temperature and a luminescence study with comprehensive ab initio calculations allow us to determine the lowest emitting excited state which depends on the substituent nature and its position on the cyclometallating ligand.

Two-photon absorption properties of simple neutral Ir(III) complexes

A series of neutral Ir(2-phenylpyridine)3 derivatives substituted on the para-position of the pyridyl ligands with a π-conjugated substituent possessing different donor abilities has been prepared. Their two-photon absorption properties have been determined using the Z-scan technique. Such simple iridium(III) neutral complexes, which are easy to synthesize, show good two-photon absorption activity, with relevant TPA cross sections (the best is 750 GM), giving rise to multifunctional chromophores, since they present also high second-order NLO properties.

Hybrid nanospheres of silica covalently containing yellow-emitting cationic iridium(III) complex: preparation and application in white light-emitting diodes

A yellow-emitting cationic iridium(III) complex [(dfppy)2Ir(TBD)]PF6 (TBD: N4,N4'-bis(3-(triethoxysilyl)propyl)-[2,2'-bipyridine]-4,4'-dicarboxamide; dfppy: 2-(2,4-difluorophenyl)pyridine) containing hydrolysable alkoxysilanes was synthesized. Then, a series of silica-based hybrid nanospheres with diameters of around 400 nm was prepared via the hydrolysis of this complex together with tetraethyl orthosilicate (TEOS, a silica source). When the amount of the complex used was 5.0 wt%, hybrid nanospheres showed the best photoluminescence (PL) properties, relative to the PL quantum yield of pure solid [(dfppy)2Ir(TBD)]PF6 (12.7%), that of hybrid nanospheres increased to 26.2%. Moreover, the thermal decomposition temperature (Td) of pure solid [(dfppy)2Ir(TBD)]PF6 was 331 °C, the Td of the complex in hybrid nanospheres increased to 447 °C. However, the yellow light emission was almost unchanged and was still located at 500-750 nm with a maximum wavelength (λem,max) of 577 nm. Under the excitation of blue-emitting chips (λem,max ≈ 455 nm), cold/neutral/warm white light-emitting diodes (WLEDs) with good luminous quality can all be fabricated using these hybrid nanospheres as phosphors in epoxy resin at different blending concentrations. Compared with two or three iridium(III) complexes being contained in silica-based particles as phosphors as described in literatures, in this study, silica-based hybrid nanospheres covalently containing only one yellow-emitting cationic iridium(III) complex as phosphors provide a more effective and simpler method for preparation high-performance WLEDs.

Novel 2-(5-Arylthiophen-2-yl)-benzoazole Cyclometalated Iridium(III) dppz Complexes Exhibit Selective Phototoxicity in Cancer Cells by Lysosomal Damage and Oncosis

A second-generation series of biscyclometalated 2-(5-aryl-thienyl)-benzimidazole and -benzothiazole Ir(III) dppz complexes [Ir(C^N)2(dppz)]+, Ir1-Ir4, were rationally designed and synthesized, where the aryl group attached to the thienyl ring was p-CF3C6H4 or p-Me2NC6H4. These new Ir(III) complexes were assessed as photosensitizers to explore the structure-activity correlations for their potential use in biocompatible anticancer photodynamic therapy. When irradiated with blue light, the complexes exhibited high selective potency across several cancer cell lines predisposed to photodynamic therapy; the benzothiazole derivatives (Ir1 and Ir2) were the best performers, Ir2 being also activatable with green or red light. Notably, when irradiated, the complexes induced leakage of lysosomal content into the cytoplasm of HeLa cancer cells and induced oncosis-like cell death. The capability of the new Ir complexes to photoinduce cell death in 3D HeLa spheroids has also been demonstrated. The investigated Ir complexes can also catalytically photo-oxidate NADH and photogenerate 1O2 and/or •OH in cell-free media.

FRET Luminescent Probe for the Ratiometric Imaging of Peroxynitrite in Rat Brain Models of Epilepsy-Based on Organic Dye-Conjugated Iridium(III) Complex

Epilepsy is a chronic neurological disorder characterized by recurrent seizures globally, imposing a substantial burden on patients and their families. The pathological role of peroxynitrite (ONOO-), which can trigger oxidative stress, inflammation, and neuronal hyperexcitability, is critical in epilepsy. However, the development of reliable, in situ, and real-time optical imaging tools to detect ONOO- in the brain encounters some challenges related to the depth of tissue penetration, background interference, optical bleaching, and spectral overlapping. To address these limitations, we present Ir-CBM, a new one-photon and two-photon excitable and long-lived ratiometric luminescent probe designed specifically for precise detection of ONOO- in epilepsy-based on the Förster resonance energy transfer mechanism by combining an iridium(III) complex with an organic fluorophore. Ir-CBM possesses the advantages of rapid response, one-/two-photon excitation, and ratiometric luminescent imaging for monitoring the cellular levels of ONOO- and evaluating the effects of different therapeutic drugs on ONOO- in the brain of an epilepsy model rat. The development and utilization of Ir-CBM offer valuable insights into the design of ratiometric luminescent probes. Furthermore, Ir-CBM serves as a rapid imaging and screening tool for antiepileptic drugs, thereby accelerating the exploration of novel antiepileptic drug screening and improving preventive and therapeutic strategies in epilepsy research.

Configurationally regulated half-sandwich iridium(III)-ferrocene heteronuclear metal complexes: Potential anticancer agents

Half-sandwich iridium(III) (IrIII) complexes and ferrocenyl (Fc) derivatives are becoming the research hotspot in the field of anticancer because of their good bioactivity and unique anticancer mechanism different from platinum-based drugs. Then, a series of half-sandwich IrIII-Fc pyridine complexes have been prepared through the structural regulation in this study. The incorporation of half-sandwich IrIII complex with Fc unit successfully improves their anticancer activity, and the optimal performance (IrFc5) is almost 3-fold higher than that of cisplatin against A549 cells, meanwhile, which also shows better anti-proliferative activity against A549/DDP cells. Complexes can aggregate in the intracellular lysosome of A549 cells and induce lysosomal damage, disrupt the cell cycle, increase the level of intracellular reactive oxygen species, and eventually lead to cell apoptosis. Half-sandwich IrIII-Fc heteronuclear metal complexes possess a different anticancer mechanism from cisplatin, which can serve as a potential alternative to platinum-based drugs and show a good application prospect.

A cell-impermeable luminogenic probe for near-infrared imaging of prostate-specific membrane antigen in prostate cancer microenvironments

Prostate-specific membrane antigen (PSMA) imaging probes are a promising tool for the diagnosis and image-guided surgery of prostate cancer (PCa). However, PSMA-specific luminescence probes for PCa detection and heterogeneity studies with high imaging contrast are lacking. Here, we report the first near-infrared (NIR) iridium(III) complex for the wash-free and specific imaging of PSMA in PCa cells and spheroids. The conjugation of a PSMA inhibitor, Lys-urea-Glu, to an iridium(III) complex synergizes the PSMA-specific affinity and biocompatibility of the inhibitor with the desirable photophysical properties of the iridium(III) complex, including NIR emission (670 nm), high photostability and a large Stokes shift. The cellular impermeability of the probe along with its strong binding affinity to PSMA enhances its specificity for PSMA, enabling the washing-free luminescent imaging of membrane PSMA with lower cytotoxicity. The probe was successfully applied for selectively visualizing PSMA-expressing cells and for the imaging of PSMA in a multicellular PCa model with good imaging penetration, indicating its potential use in complicated and heterogeneous tumor microenvironments. Furthermore, the probe showed good imaging performance in the PCa-bearing tumor mice via targeting PSMA in vivo. This work provides a novel strategy for the development of highly sensitive and specific NIR probes for PSMA in biological systems in vitro, which is of great significance for the precise diagnosis of PCa and for elucidating PCa heterogeneity.

Diruthenium(II-III)-ibuprofen-loaded chitosan-based microparticles and nanoparticles systems: encapsulation, characterisation, anticancer activity of the nanoformulations against U87MG human glioma cells

The aim of this work was to investigate novel formulations containing diruthenium(II-III)-ibuprofen (RuIbp) metallodrug encapsulated into the chitosan (CT) biopolymer. Microparticles (RuIbp/CT MPs, ∼ 1 µm) were prepared by spray-drying, and RuIbp/CT-crosslinked nanoparticles (NPs) by ionic gelation (RuIbp/CT-TPP, TPP = tripolyphosphate (1), RuIbp/CT-TPP-PEG, PEG = poly(ethyleneglycol (2)) or pre-gel/polyelectrolyte complex method (RuIbp/CT-ALG, ALG = alginate (3)). Ru analysis was conducted by energy dispersive x-ray fluorescence or inductively coupled plasma atomic emission spectroscopy, and physicochemical characterisation by powder x-ray diffraction, electronic absorption and FTIR spectroscopies, electrospray ionisation mass spectrometry, thermal analysis, scanning electron, transition electron and atomic force microscopies, and dynamic light scattering. The RuIbp-loaded nanosystems exhibited encapsulation efficiency ∼ 20-37%, drug loading∼ 10-20% (w/w), hydrodynamic diameter (nm): 103.2 ± 7.9 (1), 91.7 ± 12.6 (2), 270.2 ± 58.4 (3), zeta potential (mV): +(47.7 ± 2.8) (1), +(49.2 ± 3.6) (2), -(28.2 ± 2.0) (3). Nanoformulation (1) showed the highest cytotoxicity with increased efficacy in relation to the RuIbp free metallodrug against U87MG human glioma cells.

Configurationally Nonselective Aquation of a Mononuclear Ru(II) Chloro Complex to Aquo Complex Isomers with Distinctive Aspects in Photoisomerization, Redox, and Catalytic Water Oxidation

distal-[Ru(EtOtpy)(pynp)Cl]+ (d-EtO1Cl) (EtOtpy = 4'-ethoxy-2,2':6',2″-terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine), and distal/proximal-[Ru(EtOtpy)(pynp)OH2]2+ (d/p-EtO1H2O) complexes were newly synthesized to investigate the synergistic influence of the geometric configuration coupled with substituent introduction of an ethoxy (EtO) group on the physicochemical properties and reactions of the Ru(II) complexes. Configurationally nonselective aquation of d-EtO1Cl was uniquely observed to form d/p-EtO1H2O isomers in water, in contrast to configurationally selective aquation of distal-[Ru(tpy)(pynp)Cl]+ (d-1Cl, tpy = 2,2':6',2″-terpyridine) without the EtO group [Yamazaki, H. . J. Am. Chem. Soc. 2011, 133, 8846-8849].The kinetic profiles of the aquation reactions of d-EtO1Cl were well analyzed using a sequential reversible reaction model assuming the reversible interconversion between d/p-EtO1H2O isomers via d-EtO1Cl. The observed equilibrium constant (Kiso) of isomerization between p/d-EtO1H2O was calculated from the kinetic analysis as Kiso = 0.45, which is consistent with the final concentration ratio (1:0.43) of p/d-EtO1H2O generated in the aquation reaction of d-EtO1Cl. The irreversible photoisomerization from d-EtO1H2O to p-EtO1H2O was observed in water with an internal quantum yield (Φ) of 0.44% at 520 nm. Electrochemical measurements showed that d-EtO1H2O undergoes a 2-step oxidation reaction of 1H+-coupled 1e- processes of RuII-OH2/RuIII-OH and RuIII-OH/RuIV═O at pH 1.3-9.7, whereas p-EtO1H2O undergoes a 1-step oxidation reaction of a 2H+-coupled 2e- process of RuII-OH2/RuIV═O in the pH range of 1.8-11.5. Any redox potential of d/p-EtO1H2O isomers was decreased by the electro-donating EtO substitution, compared with distal/proximal-[Ru(tpy)(pynp)OH2]2+ (d/p-1H2O). The turnover frequency (kO2 = 1.7 × 10-2 s-1) of d-EtO1H2O for water oxidation catalysis is higher than that (3.5 × 10-4 s-1) of p-EtO1H2O by a factor of 48.6. The kO2 value (1.7 × 10-2 s-1) for d-EtO1H2O is 4.5-fold higher than those of d-1H2O (3.8 × 10-3 s-1). The higher kO2 value of d-EtO1H2O compared with d-1H2O could be explained by the fast oxidation rate from RuIV═O to RuV═O involved in the rate-determining step due to the electron-donating EtO group.

Anticancer Potential of Dendritic Poly(aryl ether)-Substituted Polypyridyl Ligand-Based Ruthenium(II) Coordination Entities

This paper studies the anticancer potency of dendritic poly(aryl ether)-substituted polypyridyl ligand-based ruthenium(II) coordination entities. The dendritic coordination entities were successfully designed, synthesized, and characterized by different spectral methods such as Fourier transform infrared (FTIR), 1H and 13C- NMR, and mass spectrometry. Further, to understand the structure and solvation behavior of the coordination entities, we performed all-atom molecular dynamics (MD) simulations. The behavior, configuration, and size of the coordination entities in DMSO and water were studied by calculating the radius of gyration (Rg) and solvent-accessible surface area (SASA). The MTT assay was used to assess the in vitro cytotoxicity of all of the coordination entities against cancerous A549 (lung cancer cells), MDA MB 231 (breast cancer cells), and HepG2 (liver cancer cells) and was found to be good with comparable IC50 values with respect to the standard drug cisplatin. The coordination entities exhibited dose dependence, and the highest activity was shown against HepG2 cell lines in comparison to the other cancer cell lines. In addition, fluorescence staining studies, such as AO/EB, DAPI, and cell death analysis by PI staining, were performed on the coordination entities to understand the apoptosis mechanism. Furthermore, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) assays confirmed apoptosis in cancer cells via the mitochondrial pathway. The DNA fragmentation assay was done followed by molecular docking analysis with DNA executed to strengthen and support the experimental observations.

Ruthenium(II) polypyridyl complexes with visible light-enhanced anticancer activity and multimodal cell imaging

Ruthenium(II) polypyridyl complexes have drawn growing attention due to their photophysical properties and anticancer activity. Herein we report four ruthenium(II) polypyridyl complexes [(N^N)2RuII(L)]2+ (1-4, L = 4-anilinoquinazoline derivatives, N^N = bidentate ligands with bis-nitrogen donors) as multi-functional anticancer agents. The epidermal growth factor receptor (EGFR) is overexpressed in a broad range of cancer cells and related to many kinds of malignance. EGFR inhibitors, such as gefitinib and erlotinib, have been approved as clinical anticancer drugs. The EGFR-inhibiting 4-anilinoquinazoline ligands greatly enhanced the in vitro anticancer activity of these ruthenium(II) polypyridyl complexes against a series of human cancer cell lines compared to [Ru(bpy)2(phen)], but interestingly, these complexes were actually not potent EGFR inhibitors. Further mechanism studies revealed that upon irradiation with visible light, complexes 3 and 4 generated a high level of singlet oxygen (1O2), and their in vitro anticancer activities against human non-small-cell lung (A549), cervical (HeLa) and squamous (A431) cancer cells were significantly improved. Specifically, complex 3 displayed potent phototoxicity upon irradiation with blue light, of which the photo-toxicity indexes (PIs) against HeLa and A431 cells were 11 and 8.3, respectively. These complexes exhibited strong fluorescence emission at ca. 600 nm upon excitation at about 450 nm. A subcellular distribution study by fluorescence microscopy imaging and secondary ion mass spectrometry imaging (ToF-SIMS) demonstrated that complex 3 mainly localized at the cytoplasm and complex 4 mainly localized in the nuclei of cells. Competitive binding with ctDNA showed that complex 4 was more favorable to bind to the DNA minor groove than complex 3. These differences support that complex 3 possibly exerts its anticancer activities majorly by photo-induced 1O2 generation and complex 4 by binding to DNA.

Silica-Based Materials Containing Inorganic Red/NIR Emitters and Their Application in Biomedicine

The low absorption of biological substances and living tissues in the red/near-infrared region (therapeutic window) makes luminophores emitting in the range of ~650-1350 nm favorable for in vitro and in vivo imaging. In contrast to commonly used organic dyes, inorganic red/NIR emitters, including ruthenium complexes, quantum dots, lanthanide compounds, and octahedral cluster complexes of molybdenum and tungsten, not only exhibit excellent emission in the desired region but also possess additional functional properties, such as photosensitization of the singlet oxygen generation process, upconversion luminescence, photoactivated effects, and so on. However, despite their outstanding functional applicability, they share the same drawback-instability in aqueous media under physiological conditions, especially without additional modifications. One of the most effective and thus widely used types of modification is incorporation into silica, which is (1) easy to obtain, (2) biocompatible, and (3) non-toxic. In addition, the variety of morphological characteristics, along with simple surface modification, provides room for creativity in the development of various multifunctional diagnostic/therapeutic platforms. In this review, we have highlighted biomedical applications of silica-based materials containing red/NIR-emitting compounds.

Metal-Based Photosensitizers as Inducers of Regulated Cell Death Mechanisms

Over the last few decades, various forms of regulated cell death (RCD) have been discovered and were found to improve cancer treatment. Although there are several reviews on RCD induced by photodynamic therapy (PDT), a comprehensive summary covering metal-based photosensitizers (PSs) as RCD inducers has not yet been presented. In this review, we systematically summarize the works on metal-based PSs that induce different types of RCD, including ferroptosis, immunogenic cell death (ICD), and pyroptosis. The characteristics and mechanisms of each RCD are explained. At the end of each section, a summary of the reported commonalities between different metal-based PSs inducing the same RCD is emphasized, and future perspectives on metal-based PSs inducing novel forms of RCD are discussed at the end of the review. Considering the essential roles of metal-based PSs and RCD in cancer therapy, we hope that this review will provide the stage for future advances in metal-based PSs as RCD inducers.

Unprecedented hetero-coordinated Ir(C^N)2tmd complexes containing both five- and six-membered Ir-(C^N) rings based on phenanthrylpyridine ligands: syntheses, crystal structures and photophysical properties

By using 2-(9-phenanthryl)pyridine (phpyr) and its derivatives as cyclometalated ligands, we synthesized a set of isomeric red-emitting complexes Ir(phpyr-R)2tmd (R = -H, -CF3, -F and -CH3, tmd = 2,2,6,6-tetramethylheptane-3,5-dione) with different coordinated modes, including bis-five-membered and five- + six-membered Ir-(C^N) ring chelating modes. The latter are the first examples of hetero-coordinated Ir(C^N)2(L^X)-type complexes containing both five- and six-membered Ir-(C^N) metallocycles. Their coordination geometries were distinctly determined using X-ray crystallographic analysis. Compared to typical bis-five-membered ring-chelated complexes, these novel hetero-coordinated isomers show bathochromic emission and lower quantum yields. On careful analysis of their electrochemical behavior and DFT calculations, it has been found that the regulatory effects of the solitary six-membered metallocycles in Ir(phpyr-R)2tmd could not only stabilize the LUMO but also destabilize the HOMO, leading to a narrower energy gap. More importantly, DFT calculations of the relative energies of these isomeric complexes demonstrated that bis-five-membered and five- + six-membered chelating modes are more stable compared to bis-six-membered rings, consistent with experiments. This work provides guidance for the structural design of Ir(C^N)2(L^X)-type complexes.

Transferrin-targeted iridium nanoagglomerates with multi-enzyme activities for cerebral ischemia-reperfusion injury therapy

Cerebral ischemia-reperfusion injury (CIRI) is a complex pathological condition with high mortality. In particular, reperfusion can stimulate overproduction of reactive oxygen species (ROS) and activation of inflammation, causing severe secondary injuries to the brain. Despite tremendous efforts, it remains urgent to rationally design antioxidative agents with straightforward and efficient ROS scavenging capability. Herein, a potent antioxidative agent was explored based on iridium oxide nano-agglomerates (Tf-IrO2 NAs) via the facile transferrin (Tf)-templated biomineralization approach, and innovatively applied to treat CIRI. Containing some small-size IrO2 aggregates, these NAs possess intrinsic hydroxyl radicals (•OH)-scavenging ability and multifarious enzyme activities, such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx). Moreover, they also showed improved blood-brain barrier (BBB) penetration and enhanced accumulation in the ischemic brain via Tf receptor-mediated transcytosis. Therefore, Tf-IrO2 NAs achieved robust in vitro anti-inflammatory and cytoprotection effects against oxidative stress. Importantly, mice were effectively protected against CIRI by enhanced ROS scavenging activity in vivo, and the therapeutic mechanism was systematically verified. These findings broaden the idea of expanding Ir-based NAs as potent antioxidative agents to treat CIRI and other ROS-mediated diseases. STATEMENT OF SIGNIFICANCE: (1) The ROS-scavenging activities of IrO2 are demonstrated comprehensively, which enriched the family of nano-antioxidants. (2) The engineering Tf-IrO2 nano-agglomerates present unique multifarious enzyme activities and simultaneous transferrin targeting and BBB crossing ability for cerebral ischemia-reperfusion injury therapy. (3) This work may open an avenue to enable the use of IrO2 to alleviate ROS-mediated inflammatory and brain injury diseases.

Half-sandwich Ru(II) N-heterocyclic carbene complexes in anticancer drug design

The ruthenium arene fragment is a rich source for the design of anticancer drugs; in this design, the co-ligand is a critical factor for obtaining effective anticancer complexes. In comparison with other types of ligands, N-heterocyclic carbenes (NHCs) have been less explored, despite the versatility in structural modifications and the marked stabilization of metal ions, being these characteristics important for the design of metal drugs. However, notable advances have been made in the development of NHC Ruthenium arene as anticancer agents. These advances include high antitumor activities, proven both in in vitro and in in vivo models and, in some cases, with marked selectivity against tumorigenic cells. The versatility of the structure has played a fundamental role, since they have allowed a selective interaction with their molecular targets through, for example, bio-conjugation with known anticancer molecules. For this reason, the structure-activity relationship of the imidazole, benzimidazole, and abnormal NHC ruthenium (II) η6-arene complexes have been studied. Taking into account this study, several synthetic aspects are provided to contribute to the next generations of this kind of complexes. Moreover, in recent years nanotechnology has provided innovative nanomedicines, where half-sandwich Ruthenium(II) complexes are paving their way. In this review, the recent developments in nanomaterials functionalized with Ruthenium complexes for targeted drug delivery to tumors will also be highlighted.

Recent progress in metal complexes functionalized nanomaterials for photodynamic therapy

Metal complexes have shown promise as photosensitizers for cancer diagnosis and therapeutics. However, the vast majority of metal photosensitizers are not ideal and associated with several limitations including pharmacokinetic limitations, off-target toxicity, fast systemic clearance, poor membrane permeability, and hypoxic tumour microenvironments. Metal complex functionalized nanomaterials have the potential to construct multifunctional systems, which not only overcome the above defects of metal complexes but are also conducive to modulating the tumour microenvironment (TME) and employing combination therapies to boost photodynamic therapy (PDT) efficacy. In this review, we first introduce the current challenges of photodynamic therapy and summarize the recent research strategies (such as metal coordination bonds, self-assembly, π-π stacking, physisorption, and so on) used for preparing metal complexes functionalized nanomaterials in the application of PDT.

Design, synthesis and biological evaluation of liposome entrapped iridium(III) complexes toward SGC-7901 cells

In this study, two new iridium(III) polypyridyl complexes [Ir(bzq)₂(DIPH)](PF₆) (bzq = deprotonated benzo[h]quinoline, DIPH = 4-(2,5-dibromo-4-(1H-imidazo[4,5-f][1,10]phenanthrolim-2-yl)-4-hydroxybutan-2-one) (Ir1) and [Ir(piq)₂(DIPH)](PF₆) (piq = deprotonated 1-phenylisoquinoline) (Ir2) were synthesized and characterized by elemental analysis, HRMS, ¹H and ¹³C NMR. The cytotoxic activity of Ir1, Ir2, Ir1lipo and Ir2lipo against cancer cells SGC-7901, HepG2, A549, HeLa, B16 and normal NIH3T3 cells in vitro was evaluated using 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) method. Ir1 and Ir2 showed no cytotoxic activity, but their liposome-entrapped Ir1 (Ir1lipo) and Ir2 (Ir2lipo) showed significant cellular activity, especially sensitive to SGC-7901 with IC₅₀ values of 4.7 ± 0.2 and 12.4 ± 0.5 μM, respectively. The cellular uptake, endoplasmic reticulum (ER) localization, autophagy, tubulin polymerization, glutathione (GSH), malondialdehyde (MDA) and release of cytochrome c were investigated to explore the mechanisms of apoptosis. The calreticulin (CRT), heat shock protein 70 (HSP70), high mobility group box 1 (HMGB1) were also explored. Western blotting showed that Ir1lipo and Ir2lipo inhibited PI3K (phosphoinositide-3 kinase), AKT (protein kinase B), p-AKT and activated Bcl-2 (B-cell lymphoma-2) protein and apoptosis-regulated factor caspase 3 (cysteinyl aspartate specific proteinase-3) and cleaving PARP (poly ADP-ribose polymerase). The results demonstrated that Ir1lipo and Ir2lipo induce cell apoptosis through targeting the endoplasmic reticulum (ER), cause oxidative stress damage, inhibiting PI3K/AKT signaling pathway, immunogenic cell death (ICD) and inhibit the cell growth at G2/M phase.

Isolation, Detection and Analysis of Circulating Tumour Cells: A Nanotechnological Bioscope

Cancer is one of the dreaded diseases to which a sizeable proportion of the population succumbs every year. Despite the tremendous growth of the health sector, spanning diagnostics to treatment, early diagnosis is still in its infancy. In this regard, circulating tumour cells (CTCs) have of late grabbed the attention of researchers in the detection of metastasis and there has been a huge surge in the surrounding research activities. Acting as a biomarker, CTCs prove beneficial in a variety of aspects. Nanomaterial-based strategies have been devised to have a tremendous impact on the early and rapid examination of tumor cells. This review provides a panoramic overview of the different nanotechnological methodologies employed along with the pharmaceutical purview of cancer. Initiating from fundamentals, the recent nanotechnological developments toward the detection, isolation, and analysis of CTCs are comprehensively delineated. The review also includes state-of-the-art implementations of nanotechnological advances in the enumeration of CTCs, along with future challenges and recommendations thereof.

Unlocking the potential of iridium and ruthenium arene complexes as anti-tumor and anti-metastasis chemotherapeutic agents

It is a major challenge to design novel multifunctional metal-based chemotherapeutic agents for anti-tumor and anti-metastasis applications. Two complexes (OA-Ir and OA-Ru) were synthesized via CuAAC (copper-catalyzed azide-alkyne cycloaddition) reaction from nontoxic Ir-N₃ or Ru-N₃ species and low toxic alkynyl precursor OA-Alkyne, and exhibited satisfactory anti-tumor and anti-metastasis pharmacological effects. Conjugation of Oleanolic acid (OA) and metal-arene species significantly enhanced the cytotoxicity in A2780 cells compared to the precursors through mitochondrial-induced autophagy pathway. Moreover, the two complexes could inhibit the cell metastasis and invasion through damage of actin dynamics and down-regulation of MMP2/MMP9 proteins. Combination of two precursors improved the lipophilicity and biocompatibility, simultaneously enhanced the cell uptake and the mitochondrial accumulation of metal-arene complexes, which caused mitochondrial membrane potential damage, oxidative phosphorylation, ATP depletion and autophagy. Besides, OA-Ir and OA-Ru displayed excellent activity to disintegrate the 3D multicellular tumor spheroids, showing potential for the treatment of solid tumors. This work provides a new way for developing novel metal-based complexes via CuAAC reaction for simultaneously inhibiting tumor proliferation and metastasis.

Norbornene-Substituted Cationic Iridium(III) Complex and Water-Soluble Luminescent Polymers Based on It: Synthesis, Photophysical and Cytotoxic Properties

Abstract

A norbornene-substituted cationic iridium(III) complex containing 1-phenylisoquinoline cyclometalating ligands and an additional phenylimidazophenanthroline ligand was synthesized. On the base of this complex, water-soluble polymers were obtained by ring-opening metathesis polymerization (ROMP). The resulting polymers showed oxygen-dependent phosphorescence in the orange spectral region and high cytotoxicity against HCT116 cancer cells.

Ir(III) Complexes with AIE Characteristics for Biological Applications

Both biological process detection and disease diagnosis on the basis of luminescence technology can provide comprehensive insights into the mechanisms of life and disease pathogenesis and also accurately guide therapeutics. As a family of prominent luminescent materials, Ir(III) complexes with aggregation-induced emission (AIE) tendency have been recently explored at a tremendous pace for biological applications, by virtue of their various distinct advantages, such as great stability in biological media, excellent fluorescence properties and distinctive photosensitizing features. Significant breakthroughs of AIE-active Ir(III) complexes have been achieved in the past few years and great progress has been witnessed in the construction of novel AIE-active Ir(III) complexes and their applications in organelle-specific targeting imaging, multiphoton imaging, biomarker-responsive bioimaging, as well as theranostics. This review systematically summarizes the basic concepts, seminal studies, recent trends and perspectives in this area.

Ruthenium-based antitumor drugs and delivery systems from monotherapy to combination therapy

Ruthenium complex is an important compound group for antitumor drug research and development. NAMI-A, KP1019, TLD1433 and other ruthenium complexes have entered clinical research. In recent years, the research on ruthenium antitumor drugs has not been limited to single chemotherapy drugs; other applications of ruthenium complexes have emerged such as in combination therapy. During the development of ruthenium complexes, drug delivery forms of ruthenium antitumor drugs have also evolved from single-molecule drugs to nanodrug delivery systems. The review summarizes the following aspects: (1) ruthenium complexes from monotherapy to combination therapy, including the development of single-molecule compounds, carrier nanomedicine, and self-assembly of carrier-free nanomedicine; (2) ruthenium complexes in the process of ADME in terms of absorption, distribution, metabolism and excretion; (3) the applications of ruthenium complexes in combination therapy, including photodynamic therapy (PDT), photothermal therapy (PTT), photoactivated chemotherapy (PACT), immunotherapy, and their combined application; (4) the future prospects of ruthenium-based antitumor drugs.

Bioactive Iridium Nanoclusters with Glutathione Depletion Ability for Enhanced Sonodynamic-Triggered Ferroptosis-Like Cancer Cell Death

Ferroptosis is a regulated form of necrotic cell death that involves the accumulation of lipid peroxide (LPO) species in an iron- and reactive oxygen species (ROS)-dependent manner. Previous investigations have reported that ferroptosis-based cancer therapy can overcome the limitations of traditional therapeutics targeting the apoptosis pathway. However, it is still challenging to enhance the antitumor efficacy of ferroptosis due to intrinsic cellular regulation. In this study, a ferroptosis-inducing agent, i.e., chlorin e6 (Ce6)-conjugated human serum albumin-iridium oxide (HSA-Ce6-IrO₂ , HCIr) nanoclusters, is developed to achieve sonodynamic therapy (SDT)-triggered ferroptosis-like cancer cell death. The sonosensitizing role of both Ce6 and IrO₂ within the HCIr nanoclusters exhibits highly efficient ¹ O₂ generation capacity upon ultrasound stimulation, which promotes the accumulation of LPO and subsequently induces ferroptosis. Meanwhile, the HCIr can deplete glutathione (GSH) by accelerating Ir (IV)-Ir (III) transition, which further suppresses the activity of glutathione peroxidase 4 (GPX4) to enhance the ferroptosis efficacy. Through in vitro and in vivo experiments, it is demonstrated that HCIr possesses tremendous capacity to reduce the intracellular GSH content, which enhances SDT-triggered ferroptosis-like cancer cell death. Thus, an iridium-nanoclusters-based ferroptosis-inducing agent is developed, providing a promising strategy for inducing ferroptosis-like cancer cell death.

Synthesis and Characterization of New Ruthenium (II) Complexes of Stoichiometry [Ru(p-Cymene)Cl2L] and Their Cytotoxicity against HeLa-Type Cancer Cells

When the [Ru(p-cymene)(μ-Cl)Cl]2 complex is made to react, in dichloromethane, with the following ligands: 2-aminobenzonitrile (2abn), 4-aminobenzonitrile (4abn), 2-aminopyridine (2ampy) and 4-aminopyridine (4ampy), after addition of hexane, the following compounds are obtained: [Ru(p-cymene)Cl2(2abn)] (I), [Ru(p-cymene)Cl2(4abn)] (II), [Ru(p-cymene)Cl2(2ampy] (III) and [Ru(p-cymene)Cl2(μ-(4ampy)] (IV). All the compounds are characterized by elemental analysis of carbon, hydrogen and nitrogen, proton nuclear magnetic resonance, COSY 1H-1H, high-resolution mass spectrometry (ESI), thermogravimetry and single-crystal X-ray diffraction (the crystal structure of III is reported and compared with the closely related literature of II). The cytotoxicity effects of complexes were described for cervical cancer HeLa cells via 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) assay. The results demonstrate a low in vitro anticancer potential of the complexes.

Deep-Red/Near-Infrared to Blue-Green Phosphorescent Iridium(III) Complexes Featuring Three Differently Charged (0, -1, and -2) Ligands: Structures, Photophysics, and Organic Light-Emitting Diode Application

We have designed and synthesized a new family of neutral phosphorescent iridium(III) complexes (Ir1-Ir6) featuring three differently charged (0, -1, and -2) ligands, in which biphenyl (bp) is used as a dianionic (-2) ligand, 4,6-difluorophenylpyridine (dfppy) or 1-phenylisoquinoline (piq) is used as a monoanionic (-1) ligand, and 2,2'-bipyridyl (bpy), 1,10-phenanthroline (phen), 1,2-bis(diphenylphosphanyl)benzene (dppb), or 1,2-bis(diphenylphosphanyl)ethane (dppe) is used as a neutral (0) ligand. The X-ray structures confirm that three coordination carbon atoms of all complexes assume a facial geometry, which can be beneficial to the stability of the structure. More importantly, the emitting color of the complexes can be tuned from deep red/near-infrared (NIR) (680-710 nm) to blue-green (466-496 nm) with different monoanionic (-1) ligands and neutral (0) ligands. Interestingly, the complex Ir5 shows a significant aggregation-induced phosphorescent emission effect, while Ir6 with a similar structure shows an opposite aggregation-caused quenching effect, mainly due to slight differences in the neutral (0) ligand structure. Notably, all deep red/NIR-emitting complexes (Ir1-Ir4) exhibit a distinct charge transfer (CT) excited state from the dianionic (-2) ligand to the neutral (0) ligand according to density functional theory calculations, whereas the excited state of blue-green-emitting complexes (Ir5-Ir6) displays the CT from the dianionic (-2) ligand to the monoanionic (-1) ligand. Considering better stability and optical performance, the deep red-emitting complexes (Ir2 and Ir4) with a simple structure are used as emitting layers of organic light-emitting diode devices and achieved good maximum external quantum efficiency (4.9 and 5.8%) peaking at 676 and 655 nm, respectively, with a very low turn-on voltage (2.5 V). This research provides a good strategy for the design of phosphorescent iridium complexes based on three differently charged (0, -1, and -2) ligands and their optoelectric applications.

Interference Reduction Biosensing Strategy for Highly Sensitive microRNA Detection

MicroRNAs are potential biomarkers for human cancers and other diseases due to their roles as post-transcriptional regulators for gene expression. However, the detection of miRNAs by conventional methods such as RT-qPCR, in situ hybridization, northern blot-based platforms, and next-generation sequencing is complicated by short length, low abundance, high sequence homology, and susceptibility to degradation of miRNAs. In this study, we developed a nicking endonuclease-mediated interference reduction rolling circle amplification (NEM-IR-RCA) strategy for the ultrasensitive and highly specific detection of miRNA-21. This method exploits the advantages of the optical properties of long-lived iridium(III) probes, in conjunction with time-resolved emission spectroscopy (TRES) and exponential rolling circle amplification (E-RCA). Under the NEM-IR-RCA-based signal enhancement processes, the limit of detection of miRNA-21 was down to 0.0095 fM with a linear range from 0.05 to 100 fM, which is comparable with the conventional RT-qPCR. Unlike RT-qPCR, the strategy was performed at a lower and constant temperature without heating/cooling cycles and reverse transcription. The strategy could clearly discriminate between matched and mismatched targets, demonstrating high specificity. Moreover, the potential application of this method was demonstrated in cancer cells and mouse serum samples, showing good agreement with RT-qPCR results. Apart from miRNA-21 detection, this platform could be also adapted for detecting other miRNAs, such as let-7a and miRNA-22, indicating its excellent potential for biomedical research and clinical diagnostics.

Photodecaging of a Mitochondria-Localized Iridium(III) Endoperoxide Complex for Two-Photon Photoactivated Therapy under Hypoxia

Despite the clinical success of photodynamic therapy (PDT), the application of this medical technique is intrinsically limited by the low oxygen concentrations found in cancer tumors, hampering the production of therapeutically necessary singlet oxygen (¹O₂). To overcome this limitation, we report on a novel mitochondria-localized iridium(III) endoperoxide prodrug (2-O-IrAn), which, upon two-photon irradiation in NIR, synergistically releases a highly cytotoxic iridium(III) complex (2-IrAn), singlet oxygen, and an alkoxy radical. 2-O-IrAn was found to be highly (photo-)toxic in hypoxic tumor cells and multicellular tumor spheroids (MCTS) in the nanomolar range. To provide cancer selectivity and improve the pharmacological properties of 2-O-IrAn, it was encapsulated into a biotin-functionalized polymer. The generated nanoparticles were found to nearly fully eradicate the tumor inside a mouse model within a single treatment. This study presents, to the best of our knowledge, the first example of an iridium(III)-based endoperoxide prodrug for synergistic photodynamic therapy/photoactivated chemotherapy, opening up new avenues for the treatment of hypoxic tumors.

Development of a ruthenium–aquo complex for utilization in synthesis and catalysis for selective hydration of nitriles and alkynes

A ruthenium(ii)–aquo complex serves as a precursor for the synthesis of new ternary complexes and also as an efficient catalyst for selective hydration of aryl nitriles to aryl amides and aryl alkynes to aryl aldehydes.

pH-Responsive Iridium(III) Two-Photon Photosensitizers Loaded CaCO3 Nanoplatform for Combined Ca2+ Overload and Photodynamic Therapy

Intracellular calcium levels are closely related to cell survival. The disruption of the calcium buffering capacity or an overload of the calcium levels enhances the susceptibility of cells towards external...

Heterostructures Made of Upconversion Nanoparticles and Metal-Organic Frameworks for Biomedical Applications

Heterostructure nanoparticles (NPs), constructed by two single-component NPs with distinct nature and multifunctional properties, have attracted intensive interest in the past few years. Among them, heterostructures made of upconversion NPs (UCNPs) and metal-organic frameworks (MOFs) can not only integrate the advantageous characteristics (e.g., porosity, structural regularity) of MOFs with unique upconverted optical features of UCNPs, but also induce cooperative properties not observed either for single component due to their special optical or electronic communications. Recently, diverse UCNP-MOF heterostructures are designed and synthesized via different strategies and have demonstrated appealing potential for applications in biosensing and imaging, drug delivery, and photodynamic therapy (PDT). In this review, the synthesis strategies of UCNP-MOF heterostructures are first summarized, then the authors focus mainly on discussion of their biomedical applications, particularly as PDT agents for cancer treatment. Finally, the authors briefly outlook the current challenges and future perspectives of UCNP-MOF hybrid nanocomposites. The authors believe that this review will provide comprehensive understanding and inspirations toward recent advances of UCNP-MOF heterostructures.

Recent progress in metal-based molecular probes for optical bioimaging and biosensing

Biological imaging and biosensing from subcellular/cellular level to whole body have enabled non-invasive visualisation of molecular events during various biological and pathological processes, giving great contributions to the rapid and impressive advances in chemical biology, drug discovery, disease diagnosis and prognosis. Optical imaging features a series of merits, including convenience, high resolution, good sensitivity, low cost and the absence of ionizing radiation. Among different luminescent probes, metal-based molecules offer unique promise in optical bioimaging and biosensing in vitro and in vivo, arising from their small sizes, strong luminescence, large Stokes shifts, long lifetimes, high photostability and tunable toxicity. In this review, we aim to highlight the design of metal-based molecular probes from the standpoint of synthetic chemistry in the last 2 years for optical imaging, covering d-block transition metal and lanthanide complexes and multimodal imaging agents.

In Vitro Anticancer Activity of Nanoformulated Mono- and Di-nuclear Pt Compounds

Nanoformulations of mononuclear Pt complexes cis-PtCl₂ (PPh₃ )₂ (1), [Pt(PPh₃ )₂ (L-Cys)] ⋅ H₂ O (3, L-Cys=L-cysteinate), trans-PtCl₂ (PPh₂ PhNMe₂ )₂ (4; PPh₂ PhNMe₂ =4-(dimethylamine)triphenylphosphine), trans-PtI₂ (PPh₂ PhNMe₂ )₂ (5) and dinuclear Pt cluster Pt₂ (μ-S)₂ (PPh₃ )₄ (2) have comparable cytotoxicity to cisplatin against murine melanoma cell line B16F10. Masking of these discrete molecular entities within the hydrophobic core of Pluronic® F-127 significantly boosted their solubility and stability, ensuring efficient cellular uptake, giving in vitro IC₅₀ values in the range of 0.87-11.23 μM. These results highlight the potential therapeutic value of Pt complexes featuring stable Pt-P bonds in nanocomposite formulations with biocompatible amphiphilic polymers.