Recoding the Cancer Epigenome by Intervening in Metabolism and Iron Homeostasis with Mitochondria-Targeted Rhenium(I) Complexes

Theranostic Rhenium(I)-Based ER-Phagy Retardant Promotes Immunogenic Cell Death

ER-phagy is a double-edged sword in the occurrence, development, and treatment of cancer; especially, its functions in immunotherapy are still unknown. In this work, we designed a theranostic Re complex (Re1) containing a BODIPY-derived ligand and a β-carboline ligand to target the endoplasmic reticulum (ER) and block ER-phagy at the late stages. Interestingly, as validated both in vitro and in vivo, ER-phagy blockage greatly enhances the capability of Re1 to induce immunogenic cell death (ICD). In summary, we dexterously fused two molecular modules for ER targeting and ER-phagy blockage into a coordination complex to afford a highly effective ICD inducer, which provides clues for designing new cancer immunotherapeutics.

Ruthenium(II) Lipid-Mimics Drive Lipid Phase Separation to Arouse Autophagy-Ferroptosis Cascade for Photoimmunotherapy

Lipid-mediated phase separation is crucial for the formation of lipophilic spontaneous domain to regulate lipid metabolism and homeostasis, furtherly contributing to multiple cell death pathways. Herein, a series of Ru(II) lipid-mimics based on short chains or midchain lipids are developed. Among them, Ru-LipM with two dodecyl chains significantly induces natural lipid phase separation via hydrocarbon chain-melting phase transitions. Accompanied by the aggregation of Ru-LipM-labeled lipophilic membrane-less compartments, most polyunsaturated lipids are increased and the autophagic flux is retarded with the adaptor protein sequestosome 1 (p62). Upon low-dose irradiation, Ru-LipM further drives ferritinophagy, providing an additional source of labile iron and rendering cells more sensitive to ferroptosis. Meanwhile, the peroxidation of polyunsaturated lipids occurs due to the deactivation of glutathione peroxidase 4 (GPX4) and the overexpression of acyl-CoA synthetase long-chain family member 4 (ACSL4), leading to the immunogenic ferroptosis. Ultimately, both innate and adaptive immunity are invigorated, indicating the tremendous antitumor capability of Ru-LipM in vivo. This study presents an unprecedented discovery of small molecules capable of inducing and monitoring lipid phase separation, thereby eliciting robust immune responses in living cells. It provides a biosimulation strategy for constructing efficient metal-based immune activators.

Rational Design of a Hetero-multinuclear Gadolinium(III)-Copper(II) Complex: Integrating Magnetic Resonance Imaging, Photoacoustic Imaging, Mild Photothermal Therapy, Chemotherapy and Immunotherapy of Cancer

For more accurate diagnosis and effective treatment of cancer, we proposed to develop a hetero-multinuclear metal complex based on the property of apoferritin (AFt) for targeting tumor theranostics by integrating dual-modality imaging diagnosis and multimodality therapy. To this end, we rational designed and synthesized a trinuclear Gd(III)-Cu(II) thiosemicarbazone complex (Gd-2Cu) and then constructed a Gd-2Cu@AFt nanoparticle (NP) delivery system. Gd-2Cu/Gd-2Cu@AFt NPs not only had significant T1-weighted magnetic resonance imaging and photoacoustic imaging of the tumor but also effectively inhibited tumor growth through a combination of mild photothermal therapy, chemotherapy, and immunotherapy. Gd-2Cu@AFt NPs optimized the behavior of imaging diagnosis and therapy of Gd-2Cu, improved its targeting ability, and reduced the side effects in vivo. Besides, we revealed and clarified the anticancer mechanism of Gd-2Cu: interrupting energy metabolism of the tumor cell, inducing apoptosis of the tumor cell, and activating a systemic immune response by inducing immunogenic cell death of cancer cells.

Zinc peroxide-based nanotheranostic platform with endogenous hydrogen peroxide/oxygen generation for enhanced photodynamic-chemo therapy of tumors

Nanotheranostic platforms, which can respond to tumor microenvironments (TME, such as low pH and hypoxia), are immensely appealing for photodynamic therapy (PDT). However, hypoxia in solid tumors harms the treatment outcome of PDT which depends on oxygen molecules to generate cytotoxic singlet oxygen (1O2). Herein, we report the design of TME-responsive smart nanotheranostic platform (DOX/ZnO2@Zr-Ce6/Pt/PEG) which can generate endogenously hydrogen peroxide (H2O2) and oxygen (O2) to alleviate hypoxia for improving photodynamic-chemo combination therapy of tumors. DOX/ZnO2@Zr-Ce6/Pt/PEG nanocomposite was prepared by the synthesis of ZnO2 nanoparticles, in-situ assembly of Zr-Ce6 as typical metal-organic framework (MOF) on ZnO2 surface, in-situ reduction of Pt nanozymes, amphiphilic lipids surface coating and then doxorubicin (DOX) loading. DOX/ZnO2@Zr-Ce6/Pt/PEG nanocomposite exhibits average sizes of ∼78 nm and possesses a good loading capacity (48.8 %) for DOX. When DOX/ZnO2@Zr-Ce6/Pt/PEG dispersions are intratumorally injected into mice, the weak acidic TEM induces the decomposition of ZnO2 core to generate endogenously H2O2, then Pt nanozymes catalyze H2O2 to produce O2 for alleviating tumor hypoxia. Upon laser (630 nm) irradiation, the Zr-Ce6 component in DOX/ZnO2@Zr-Ce6/Pt/PEG can produce cytotoxic 1O2, and 1O2 generation rate can be enhanced by 2.94 times due to the cascaded generation of endogenous H2O2/O2. Furthermore, the generated O2 can suppress the expression of hypoxia-inducible factor α, and further enable tumor cells to become more sensitive to chemotherapy, thereby leading to an increased effectiveness of chemotherapy treatment. The photodynamic-chemo combination therapy from DOX/ZnO2@Zr-Ce6/Pt/PEG nanoplatform exhibits remarkable tumor growth inhibition compared to chemotherapy or PDT. Thus, the present study is a good demonstration of a TME-responsive nanoplatform in a multimodal approach for cancer therapy.

Triazoles in Medicinal Chemistry: Physicochemical Properties, Bioisosterism, and Application

Triazole demonstrates distinctive physicochemical properties, characterized by weak basicity, various dipole moments, and significant dual hydrogen bond acceptor and donor capabilities. These features are poised to play a pivotal role in drug-target interactions. The inherent polarity of triazole contributes to its lower logP, suggesting the potential improvement in water solubility. The metabolic stability of triazole adds additional value to drug discovery. Moreover, the metal-binding capacity of the nitrogen atom lone pair electrons of triazole has broad applications in the development of metal chelators and antifungal agents. This Perspective aims to underscore the unique physicochemical attributes of triazole and its application. A comparative analysis involving triazole isomers and other heterocycles provides guiding insights for the subsequent design of triazoles, with the hope of offering valuable considerations for designing other heterocycles in medicinal chemistry.

Novel Re(I) Complexes as Potential Selective Theranostic Agents in Cancer Cells and In Vivo in Caenorhabditis elegans Tumoral Strains

A series of rhenium(I) complexes of the type fac-[Re(CO)3(N^N)L]0/+, Re1-Re9, was synthesized, where N^N = benzimidazole-derived bidentate ligand with an ester functionality and L = chloride or pyridine-type ligand. The new compounds demonstrated potent activity toward ovarian A2780 cancer cells. The most active complexes, Re7-Re9, incorporating 4-NMe2py, exhibited remarkable activity in 3D HeLa spheroids. The emission in the red region of Re9, which contains an electron-deficient benzothiazole moiety, allowed its operability as a bioimaging tool for in vitro and in vivo visualization. Re9 effectivity was tested in two different C. elegans tumoral strains, JK1466 and MT2124, to broaden the oncogenic pathways studied. The results showed that Re9 was able to reduce the tumor growth in both strains by increasing the ROS production inside the cells. Moreover, the selectivity of the compound toward cancerous cells was remarkable as it did not affect neither the development nor the progeny of the nematodes.

Quantitative Determination of Endoplasmic Reticulum Viscosity during Immunogenic Cell Death by a Theranostic Rhenium Complex

The endoplasmic reticulum (ER) is an important targeting organelle for metal-based immunogenic cell death (ICD) inducers. Metal complexes can induce ER stress by causing protein misfolding, which can be reflected by alternations in microenvironmental parameters, including viscosity. We present here a theranostic Re(I) complex (Re1) that shows viscosity-dependent emission intensity and lifetime. Re1 can trigger immunogenic cell death (ICD) in MDA-MB-231 cells by localizing in the ER and causing ER stress. We demonstrate that Re1 can simultaneously induce and monitor the gradual increase in the ER viscosity quantitatively.

Improving In Vivo Tumor Accumulation and Efficacy of Platinum Antitumor Agents by Electronic Tuning of the Kinetic Lability

The impact of kinetic lability or reactivity on in vitro cytotoxicity, stability in plasma, in vivo tumor and tissue accumulation, and antitumor efficacy of functional platinum(II) (Pt) anticancer agents containing a O˄O β-diketonate leaving ligand remain largely unexplored. To investigate this, we synthesized Pt complexes [(NH3 )2 Pt(L1-H)]NO3 and [(DACH)Pt(L1-H)]NO3 (L1=4,4,4-trifluoro-1-ferrocenylbutane-1,3-dione, DACH=1R,2R-cyclohexane-1,2-diamine) containing an electron deficient [L1-H]- O˄O leaving ligand and [(NH3 )2 Pt(L2-H)]NO3 and [(DACH)Pt(L2-H)]NO3 (L2=1-ferrocenylbutane-1,3-dione) containing an electron-rich [L2-H]- O˄O leaving ligand. While all four complexes have comparable lipophilicity, the presence of the electron-withdrawing CF3 group was found to dramatically enhance the reactivity of these complexes toward nucleophilic biomolecules. In vitro cellular assays revealed that the more reactive complexes have higher cellular uptake and higher anticancer potency as compared to their less reactive analogs. But the scenario is opposite in vivo, where the less reactive complex showed improved tissue and tumor accumulation and better anticancer efficacy in mice bearing ovarian xenograft when compared to its more reactive analog. Finally, in addition to demonstrating the profound but contrasting impact of kinetic lability on in vitro and in vivo antitumor potencies, we also described the impact of kinetic lability on the mechanism of action of this class of promising antitumor agents.

Necrosis-Inducing High-Valent Oxo-Rhenium(V) Complexes with Potent Antitumor Activity: Synthesis, Aquation Chemistry, Cisplatin Cross-Resistance Profile, and Mechanism of Action

Chemotherapy with the cytotoxic platinum (Pt) drugs cisplatin, carboplatin, and oxaliplatin is the mainstay of anticancer therapy in the clinic. The antitumor activity of Pt drugs originates from their ability to induce apoptosis via covalent adduct formation with nuclear DNA. While the phenomenal clinical success is highly encouraging, resistance and adverse toxic side effects limit the wider applicability of Pt drugs. To circumvent these limitations, we embarked on an effort to explore the antitumor potential of a new class of oxo-rhenium(V) complexes of the type [(N∧N)(EG)Re(O)Cl] (where EG = ethylene glycolate and N∧N = bipyridine, Bpy (1); phenanthroline, Phen (2); 3,4,7,8-tetramethyl-phenanthroline, Me4Phen (3)). Investigation of speciation chemistry in aqueous media revealed the formation of [(N∧N)Re(O)(OH)3] as the biologically active species. Complex 3 was found to be the most potent among the three, with IC50 values ranging from 0.1 to 0.4 μM against a panel of cancer cells, which is 5-70-fold lower when compared with cisplatin. The higher potency of 3 is attributed to its higher lipophilicity, which enhanced cellular uptake. Importantly, complex 3 efficiently overcomes cisplatin resistance in ovarian, lung, and prostate cancer cells. In addition to reporting the aquation chemistry and identifying the active species in aqueous media, we performed in-depth in vitro mechanistic studies, which revealed that complex 3 preferentially accumulates in mitochondria, depletes mitochondrial membrane potential, and upregulates intracellular reactive oxygen species (ROS), leading to ER stress-mediated necrosis-mediated cancer cell death.

Mitochondria-targeted cyclometalated iridium (III) complexes: Dual induction of A549 cells apoptosis and autophagy

In this study, we synthesized 4 cyclometalated iridium complexes using N-(1,10-phenanthrolin-5-yl)picolinamide (PPA) as the main ligand, denoted as [Ir(ppy)2PPA]PF6 (ppy = 2-phenylpyridine, Ir1), [Ir(bzq)2PPA]PF6 (bzq = benzo[h]quinoline, Ir2), [Ir(dfppy)2PPA]PF6 (dfppy = 2-(3,5-difluorophenyl)pyridine, Ir3), and [Ir(thpy)2PPA]PF6 (thpy = 2-(thiophene-2-yl)pyridine, Ir4). Compared to cisplatin and oxaliplatin, all four complexes exhibited significant anti-tumor activity. Among them, Ir2 demonstrated higher cytotoxicity against A549 cells, with an IC50 value of 1.6 ± 0.2 μM. The experimental results indicated that Ir2 primarily localized in the mitochondria, inducing a large amount of reactive oxygen species (ROS) generation, that decreased in mitochondrial membrane potential (MMP), reduced ATP production, and further impaired mitochondrial function, leading to cytochrome c release. Additionally, Ir2 caused cell cycle arrest at the S phase and induced apoptosis through the AKT-mediated signaling pathway. Further investigations revealed that Ir2 could simultaneously induce both apoptosis and autophagy in A549 cells, with the latter acting as a non-protective mechanism that promoted cell death. More importantly, Ir2 exhibited low toxicity to both normal LO2 cells in vitro and zebrafish embryos in vivo. Consequently, these newly developed Ir(III) complexes show great potential in the development of novel and low-toxicity anticancer agents.

Neuroprotective Bioorthogonal Catalysis in Mitochondria Using Protein-Integrated Hydrogen-Bonded Organic Frameworks

Mitochondria-targeted bioorthogonal catalysis holds promise for controlling cell function precisely, yet achieving selective and efficient chemical reactions within organelles is challenging. In this study, we introduce a new strategy using protein-integrated hydrogen-bonded organic frameworks (HOFs) to enable synergistic bioorthogonal chemical catalysis and enzymatic catalysis within mitochondria. Utilizing catalytically active tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) to self-assemble with [1,1'-biphenyl]-4,4'-biscarboximidamide, we synthesized nanoscale RuB-HOFs that exhibit high photocatalytic reduction activity. Notably, RuB-HOFs efficiently enter cells and preferentially localize to mitochondria, where they facilitate bioorthogonal photoreduction reactions. Moreover, we show that RuB-HOFs encapsulating catalase can produce hydrogen sulfide (H2 S) in mitochondria through photocatalytic reduction of pro-H2 S and degrade hydrogen peroxide through enzymatic catalysis simultaneously, offering a significant neuroprotective effect against oxidative stress. Our findings not only introduce a versatile chemical toolset for mitochondria-targeted bioorthogonal catalysis for prodrug activation but also pave the way for potential therapeutic applications in treating diseases related to cellular oxidative stress.

The Power of Kinetic Inertness in Improving Platinum Anticancer Therapy by Circumventing Resistance and Ameliorating Nephrotoxicity

Even in the modern era of precision medicine and immunotherapy, chemotherapy with platinum (Pt) drugs remains among the most commonly prescribed medications against a variety of cancers. Unfortunately, the broad applicability of these blockbuster Pt drugs is severely limited by intrinsic and/or acquired resistance, and high systemic toxicity. Considering the strong interconnection between kinetic lability and undesired shortcomings of clinical Pt drugs, we rationally designed kinetically inert organometallic Pt based anticancer agents with a novel mechanism of action. Using a combination of in vitro and in vivo assays, we demonstrated that the development of a remarkably efficacious but kinetically inert Pt anticancer agent is feasible. Along with exerting promising antitumor efficacy in Pt-sensitive as well as Pt-resistant tumors in vivo, our best candidate has the ability to mitigate the nephrotoxicity issue associated with cisplatin. In addition to demonstrating, for the first time, the power of kinetic inertness in improving the therapeutic benefits of Pt based anticancer therapy, we describe the detailed mechanism of action of our best kinetically inert antitumor agent. This study will certainly pave the way for designing the next generation of anticancer drugs for effective treatment of various cancers.

Promotion of ICD via Nanotechnology

Immunotherapy represents the most promising treatment strategy for cancer, but suffers from compromised therapeutic efficiency due to low immune activity of tumor cells and an immunosuppressive microenvironment, which significantly hampers the clinical translations of this treatment strategy. To promote immunotherapy with desired therapeutic efficiency, immunogenic cell death (ICD), a particular type of death capable of reshaping body's antitumor immune activity, has drawn considerable attention due to the potential to stimulate a potent immune response. Still, the potential of ICD effect remains unsatisfactory because of the intricate tumor microenvironment and multiple drawbacks of the used inducing agents. ICD has been thoroughly reviewed so far with a general classification of ICD as a kind of immunotherapy strategy and repeated discussion of the related mechanism. However, there are no published reviews, to the authors' knowledge, providing a systematic summarization on the enhancement of ICD via nanotechnology. For this purpose, this review first discusses the four stages of ICD according to the development mechanisms, followed by a comprehensive description on the use of nanotechnology to enhance ICD in the corresponding four stages. The challenges of ICD inducers and possible solutions are finally summarized for future ICD-based enhanced immunotherapy.

Potent Zinc(II)-Based Immunogenic Cell Death Inducer Triggered by ROS-Mediated ERS and Mitochondrial Ca2+ Overload

Zn1 and Zn2 are Zn-based complexes that activate the immunogenic cell death (ICD) effect by Ca2+-mediated endoplasmic reticulum stress (ERS) and mitochondrial dysfunction. Compared with Zn1, Zn2 effectively caused reactive oxidative species (ROS) overproduction in the early phase, leading to ERS response. Severe ERS caused the release of Ca2+ from ER to cytoplasm and further to mitochondria. Excessive Ca2+ in mitochondria triggered mitochondrial dysfunction. The damage-associated molecular patterns (DAMPs) of CRT, HMGB1, and ATP occurred in T-24 cells exposed to Zn1 and Zn2. The vaccination assay demonstrated that Zn1 and Zn2 efficiently suppressed the growth of distant tumors. The elevated CD8+ cytotoxic T cells and decreased Foxp3+ cells in vaccinated mice supported our conclusion. Moreover, Zn1 and Zn2 improved the survival rate of mice compared with oxaliplatin. Collectively, our findings provided a new design strategy for a zinc-based ICD inducer via ROS-induced ERS and mitochondrial Ca2+ overload.

Activation of the cGAS-STING pathway by a mitochondrial DNA-targeted emissive rhodium(iii) metallointercalator

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon (STING) pathway is a key mediator of innate immunity involved in cancer development and treatment. The roles of mitochondrial DNA (mtDNA) in cancer immunotherapy have gradually emerged. Herein, we report a highly emissive rhodium(iii) complex (Rh-Mito) as the mtDNA intercalator. Rh-Mito can specifically bind to mtDNA to cause the cytoplasmic release of mtDNA fragments to activate the cGAS-STING pathway. Moreover, Rh-Mito activates the mitochondrial retrograde signaling by disturbing the key metabolites involved in epigenetic modifications, which alters the nuclear genome methylation landscape to influence the expression of genes related to immune signaling pathways. Finally, we demonstrate that ferritin-encapsulated Rh-Mito elicits potent anticancer activities and evokes intense immune responses in vivo by intravenous injection. Overall, we report for the first time that small molecules targeting mtDNA can activate the cGAS-STING pathway, which gives insights into the development of biomacromolecule-targeted immunotherapeutic agents.

Targeting iron to contrast cancer progression

An altered metabolism of iron fuels cancer growth, invasion, metastasis, and recurrence. Ongoing research in cancer biology is delineating a complex iron-trafficking program involving both malignant cells and their support network of cancer stem cells, immune cells, and other stromal components in the tumor microenvironment. Iron-binding strategies in anticancer drug discovery are being pursued in clinical trials and in multiple programs at various levels of development. Polypharmacological mechanisms of action, combined with emerging iron-associated biomarkers and companion diagnostics, are poised to offer new therapeutic options. By targeting a fundamental player in cancer progression, iron-binding drug candidates (either alone or in combination therapy) have the potential to impact a broad range of cancer types and to address the major clinical problems of recurrence and resistance to therapy.

Kinetic aspects of iron(III)-chelation therapy with deferasirox (DFX) revealed by the solvolytic dissociation rate of the Fe(III)-DFX complex estimated with capillary electrophoretic reactor

Capillary electrophoresis was used to estimate the solvolytic dissociation rate (k_d) of metal complexes of deferasirox (DFX, H₃L), a drug used to treat iron overload. Inert Co^IIIL₂^3- did not dissociate. The estimated k_d value for Fe^IIIL₂^3- was (2.7 ± 0.3) × 10^-4 s^-1 (298 K, pH 7.4). The k_d values of other complexes (Al^IIIL₂^3-, Ni^IIL₂^4-, and Mn^IIL^-) were in the range 10^-3-10^-4 s^-1. In contrast, Zn^IIL^- and Cu^IIL^- were too labile to allow k_d estimation. The fact that the half-life of Fe^IIIL₂^3- (43.3 min) is shorter than the blood half-life of DFX (8-16 h) implies that the blood concentration of DFX should be high enough to prevent dissociation of Fe^IIIL₂^3-. The possibility of a safer iron-chelation therapy that avoids excretion of other essential metal ions such as Zn^II is discussed, highlighting the importance of selectivity in terms of kinetic stability.

Mitochondria as a target of third row transition metal-based anticancer complexes

In pursuit of better treatment options for malignant tumors, metal-based complexes continue to show promise as attractive chemotherapeutics due to tunability, novel mechanisms, and potency exemplified by platinum agents. The metabolic character of tumors renders the mitochondria and other metabolism pathways fruitful targets for medicinal inorganic chemistry. Cumulative understanding of the role of mitochondria in tumorigenesis has ignited research in mitochondrial targeting metal-based complexes to overcome resistance and inhibit tumor growth with high potency and selectivity. Here, we discuss recent progress made in third row transition metal-based mitochondrial targeting agents with the goal of stimulating an active field of research toward new clinical anticancer agents and the elucidation of novel mechanisms of action.

Near-infrared AIE-active phosphorescent iridium(III) complex for mitochondria-targeted photodynamic therapy

Mitochondria-targeted photodynamic therapy (PDT) has recently been recognized as a promising strategy for effective cancer treatment. In this work, a mitochondria-targeted near-infrared (NIR) aggregation-induced emission (AIE)-active phosphorescent Ir(III) complex (Ir1) is reported with highly favourable mitochondria-targeted bioimaging and cancer PDT properties. Complex Ir1 has strong absorption in the visible light region (∼500 nm) and can effectively produce singlet oxygen (¹O₂) under green light (525 nm) irradiation. It preferentially accumulates in the mitochondria of human breast cancer MDA-MB-231 cells as revealed by colocalization analysis. Complex Ir1 displays high phototoxicity toward human breast cancer MDA-MB-231 cells and mouse breast cancer 4T1 cells. Complex Ir1 induces reactive oxygen species (ROS) production, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress in MDA-MB-231 cells upon photoirradiation, leading to apoptotic cell death. The favorable PDT performance of Ir1in vivo has been further demonstrated in tumour-bearing mice. Together, the results suggest that Ir1 is a promising photosensitizer for mitochondria-targeted imaging and cancer phototherapy.

Synthesis, structural characterization and study of antioxidant and anti-PrPSc properties of flavonoids and their rhenium(I)-tricarbonyl complexes

This study aims at the synthesis and initial biological evaluation of novel rhenium-tricarbonyl complexes of 3,3',4',5,7-pentahydroxyflavone (quercetin), 3,7,4΄-trihydroxyflavone (resokaempferol), 5,7-dihydroxyflavone (chrysin) and 4΄,5,7-trihydroxyflavonone (naringenin) as neuroprotective and anti-PrP agents. Resokaempferol was synthesized from 2,2΄,4-trihydroxychalcone by H₂O₂/NaOH. The rhenium-tricarbonyl complexes of the type fac-[Re(CO)₃(Fl)(sol)] were synthesized by reacting the precursor fac-[Re(CO)₃(sol)₃]⁺ with an equimolar amount of the flavonoids (Fl) quercetin, resokaempferol, chrysin and naringenin and the solvent (sol) was methanol or water. The respective Re-flavonoid complexes were purified by semi-preparative HPLC and characterized by spectroscopic methods. Furthermore, the structure of Re-chrysin was elucidated by X-ray crystallography. Initial screening of the neuroprotective properties of these compounds included the in vitro assessment of the antioxidant properties by the DPPH assay as well as the anti-lipid peroxidation of linoleic acid in the presence of AAPH and their ability to inhibit soybean lipoxygenase. From the above studies, it was concluded that the complexes' properties are mainly correlated with the structural characteristics and the presence of the flavonoids. The flavonoids and their respective Re-complexes were also tested in vitro for their ability to inhibit the formation and aggregation of the amyloid-like abnormal prion protein, PrP^Sc, by employing the real-time quaking-induced conversion assay with recombinant PrP seeded with cerebrospinal fluid from patients with Creutzfeldt-Jakob disease. All the compounds blocked de novo abnormal PrP formation and aggregation.

Potent Ruthenium-Ferrocene Bimetallic Antitumor Antiangiogenic Agent That Circumvents Platinum Resistance: From Synthesis and Mechanistic Studies to In Vivo Evaluation in Zebrafish

Emergence of resistance in cancer cells and dose-limiting side effects severely limit the widespread use of platinum (Pt) anticancer drugs. Multi-action hybrid anticancer agents that are constructed by merging two or more pharmacophores offer the prospect of circumventing issues of Pt drugs. Herein, we report the design, synthesis, and in-depth biological evaluation of a ruthenium-ferrocene (Ru-Fc) bimetallic agent [(η6-p-cymene)Ru(1,1,1-trifluoro-4-oxo-4-ferrocenyl-but-2-en-2-olate)Cl] and its five analogues. Along with aquation/anation chemistry, we evaluated the in vitro antitumor potency, Pt cross-resistance profile, and in vivo antiangiogenic properties. A structure activity analysis was performed to understand the impact of Fc, CF3, and p-cymene groups on the anticancer potency of the Ru-Fc hybrid. Finally, in addition to assessing cellular uptake and intracellular distribution, we demonstrated that the Ru-Fc hybrid binds to nucleophilic biomolecules and produces reactive oxygen species, which causes mitochondrial dysfunction and induces ER stress, leading to poly(ADP-ribose) polymerase-mediated necroptotic cell death.

Emerging Potential Mechanism and Therapeutic Target of Ferroptosis in PDAC: A Promising Future

Pancreatic cancer (PC) is a devastating malignant tumor of gastrointestinal (GI) tumors characterized by late diagnosis, low treatment success and poor prognosis. The most common pathological type of PC is pancreatic ductal adenocarcinoma (PDAC), which accounts for approximately 95% of PC. PDAC is primarily driven by the Kirsten rat sarcoma virus (KRAS) oncogene. Ferroptosis was originally described as ras-dependent cell death but is now defined as a regulated cell death caused by iron accumulation and lipid peroxidation. Recent studies have revealed that ferroptosis plays an important role in the development and therapeutic response of tumors, especially PDAC. As the non-apoptotic cell death, ferroptosis may minimize the emergence of drug resistance for clinical trials of PDAC. This article reviews what has been learned in recent years about the mechanisms of ferroptosis in PDAC, introduces the association between ferroptosis and the KRAS target, and summarizes several potential strategies that are capable of triggering ferroptosis to suppress PDAC progression.

Photoinduced Processes in Rhenium(I) Terpyridine Complexes Bearing Remote Amine Groups: New Insights from Transient Absorption Spectroscopy

Photophysical properties of two Re(I) complexes [ReCl(CO)3(R-C6H4-terpy-κ2N)] with remote amine groups, N-methyl-piperazinyl (1) and (2-cyanoethyl)methylamine (2), were investigated. The complexes show strong absorption in the visible region corresponding to metal-to-ligand charge transfer (1MLCT) and intraligand-charge-transfer (1ILCT) transitions. The energy levels of 3MLCT and 3ILCT excited-states, and thus photoluminescence properties of 1 and 2, were found to be strongly affected by the solvent polarity. Compared to the parent chromophore [ReCl(CO)3(C6H5-terpy-κ2N)] (3), both designed complexes show significantly prolonged (by 1–2 orders of magnitude) phosphorescence lifetimes in acetonitrile and dimethylformamide, contrary to their lifetimes in less polar chloroform and tetrahydrofuran, which are comparable to those for 3. The femtosecond transient absorption (fsTA) measurements confirmed the interconversion between the 3MLCT and 3ILCT excited-states in polar solvents. In contrast, the emissive state of 1 and 2 in less polar environments is of predominant 3MLCT nature.

Controlling of Photophysical Behavior of Rhenium(I) Complexes with 2,6-Di(thiazol-2-yl)pyridine-Based Ligands by Pendant π-Conjugated Aryl Groups

The structure-property correlations and control of electronic excited states in transition metal complexes (TMCs) are of high significance for TMC-based functional material development. Within these studies, a series of Re(I) carbonyl complexes with aryl-substituted 2,6-di(thiazol-2-yl)pyridines (Arn-dtpy) was synthesized, and their ground- and excited-state properties were investigated. A number of condensed aromatic rings, which function as the linking mode of the aryl substituent, play a fundamental role in controlling photophysics of the resulting [ReCl(CO)3(Arn-dtpy-κ2N)]. Photoexcitation of [ReCl(CO)3(Arn-dtpy-κ2N)] with 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl leads to the population of 3MLCT. The lowest triplet state of Re(I) chromophores bearing 9-anthryl, 2-anthryl, 1-pyrenyl groups is ligand localized. The rhenium(I) complex with appended 1-pyrenyl group features long-lived room temperature emission attributed to the equilibrium between 3MLCT and 3IL/3ILCT. The excited-state dynamics in complexes [ReCl(CO)3(9-anthryl-dtpy-κ2N)] and [ReCl(CO)3(2-anthryl-dtpy-κ2N)] is strongly dependent on the electronic coupling between anthracene and {ReCl(CO)3(dtpy-κ2N)}. Less steric hindrance between the chromophores in [ReCl(CO)3(2-anthryl-dtpy-κ2N)] is responsible for the faster formation of 3IL/3ILCT and larger contribution of 3ILCTanthracene→dtpy in relation to the isomeric complex [ReCl(CO)3(9-anthryl-dtpy-κ2N)]. In agreement with stronger electronic communication between the aryl and Re(I) coordination centre, [ReCl(CO)3(2-anthryl-dtpy-κ2N)] displays room-temperature emission contributed to by 3MLCT and 3ILanthracene/3ILCTanthracene→dtpy phosphorescence. The latter presents rarely observed phenomena in luminescent metal complexes.

Synthesis, Characterization and Antitumor Mechanism Investigation of Heterometallic Ru(Ⅱ)-Re(Ⅰ) Complexes

The development of heteronuclear metal complexes as potent anticancer agents has received increasing attention in recent years. In this study, two new heteronuclear Ru(Ⅱ)-Re(Ⅰ) metal complexes, [Ru(bpy)₂LRe(CO)₃(DIP)](PF₆)₃ and [Ru(phen)₂LRe(CO)₃(DIP)](PF₆)₃ [RuRe-1 and RuRe-2, L = 2-(4-pyridinyl)imidazolio[4,5-f][1,10]phenanthroline, bpy = 2,2′-bipyridine, DIP = 4,7-diphenyl-1,10-phenanthroline, phen = 1,10-phenanthroline], were synthesized and characterized. Cytotoxicity assay shows that RuRe-1 and RuRe-2 exhibit higher anticancer activity than cisplatin, and exist certain selectivity toward human cancer cells over normal cells. The anticancer mechanistic studies reveal that RuRe-1 and RuRe-2 can induce apoptosis through the regulation of cell cycle, depolarization of mitochondrial membrane potential (MMP), elevation of intracellular reactive oxygen species (ROS), and caspase cascade. Moreover, RuRe-1 and RuRe-2 can effectively inhibit cell migration and colony formation. Taken together, heteronuclear Ru(Ⅱ)-Re(Ⅰ) metal complexes possess the prospect of developing new anticancer agents with high efficacy.

Anticancer and Antibiotic Rhenium Tri- and Dicarbonyl Complexes: Current Research and Future Perspectives

Organometallic compounds are increasingly recognized as promising anticancer and antibiotic drug candidates. Among the transition metal ions investigated for these purposes, rhenium occupies a special role. Its tri- and dicarbonyl complexes, in particular, attract continuous attention due to their relative ease of preparation, stability and unique photophysical and luminescent properties that allow the combination of diagnostic and therapeutic purposes, thereby permitting, e.g., molecules to be tracked within cells. In this review, we discuss the anticancer and antibiotic properties of rhenium tri- and dicarbonyl complexes described in the last seven years, mainly in terms of their structural variations and in vitro efficacy. Given the abundant literature available, the focus is initially directed on tricarbonyl complexes of rhenium. Dicarbonyl species of the metal ion, which are slowly gaining momentum, are discussed in the second part in terms of future perspective for the possible developments in the field.

Anticancer Properties of Rhenium(I) Tricarbonyl Complexes of N-Heterocyclic Carbene Ligands

A family of eight rhenium(I) tricarbonyl complexes bearing pyridyl-imidazolylidene or bis-imidazolylidene ligand in combination with a series of N-acetyl amino acids ligands (glycine, isoleucine, proline) and acetate have been synthesised...

V, Kar B, Das U, Paira P. Target-specific mononuclear and binuclear rhenium(i) tricarbonyl complexes as upcoming anticancer drugs

Metal complexes have gradually been attracting interest from researchers worldwide as potential cancer therapeutics. Driven by the many side effects of the popular platinum-based anticancer drug cisplatin, the tireless endeavours of researchers have afforded strategies for the design of appropriate metal complexes with minimal side effects compared to cisplatin and its congeners to limit the unrestricted propagation of cancer. In this regard, transition metal complexes, especially rhenium-based complexes are being identified and highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body. This is attributed the amazing photophysical properties of rhenium complexes together with their ability to selectively attack different organelles in cancer cells. Therefore, this review presents the properties of different rhenium-based complexes to highlight their recent advances as anticancer agents based on their cytotoxicity results.

In this review, rhenium-based complexes are highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body.

Current understanding of ferroptosis in the progression and treatment of pancreatic cancer

Pancreatic cancer is a highly malignant tumour of the digestive tract. Despite advances in treatment, its 5-year survival rate remains low, and its prognosis is the worst among all cancers; innovative therapeutic methods are needed. Ferroptosis is a form of regulatory cell death driven by iron accumulation and lipid peroxidation. Recent studies have found that ferroptosis plays an important role in the development and treatment response of tumours, particularly pancreatic cancer. This article reviews the current understanding of the mechanism of ferroptosis and ferroptosis-related treatment in pancreatic cancer.

A highly potent ruthenium(II)-sonosensitizer and sonocatalyst for in vivo sonotherapy

As a basic structure of most polypyridinal metal complexes, [Ru(bpy)₃]²⁺, has the advantages of simple structure, facile synthesis and high yield, which has great potential for scientific research and application. However, sonodynamic therapy (SDT) performance of [Ru(bpy)₃]²⁺ has not been investigated so far. SDT can overcome the tissue-penetration and phototoxicity problems compared to photodynamic therapy. Here, we report that [Ru(bpy)₃]²⁺ is a highly potent sonosensitizer and sonocatalyst for sonotherapy in vitro and in vivo. [Ru(bpy)₃]²⁺ can produce singlet oxygen (¹O₂) and sono-oxidize endogenous 1,4-dihydronicotinamide adenine dinucleotide (NADH) under ultrasound (US) stimulation in cancer cells. Furthermore, [Ru(bpy)₃]²⁺ enables effective destruction of mice tumors, and the therapeutic effect can reach deep tissues over 10 cm under US irradiation. This work paves a way for polypyridinal metal complexes to be applied to the noninvasive precise sonotherapy of cancer.

Sonodynamic therapy has therapeutic promise due to its safety and good tissue penetration, but is currently bottlenecked due to a lack of efficient and safe sonosensitizers. Here the authors show that [Ru(bpy)₃]²⁺ can produce singlet oxygen and sonooxidize NADH in deep tissue, and destroy mouse tumors effectively.

Self-stabilized Pt(IV) amphiphiles by precise regulation of branch length for enhanced chemotherapy

A surge of platinum(IV) compounds are utilized or investigated in cancer treatment but their therapeutic outcomes have been greatly compromised by remaining adverse effects and limited antitumor performance, attributable to nonspecific distribution and insufficient activation in tumor site. Herein, we designed a series of disulfide bond introduced Pt(IV)-lipid prodrugs with different branch length, all of which are able to self-stabilize into nanomedicine and be activated by high intracellular glutathione (GSH) level. The impact of precise modification of these prodrugs on their assembly stability, pharmacokinetics and cytotoxicity was probed to establish a connection between chemical structure and antiproliferation efficiency. With optimal assembly manner and delivery efficacy, the longest axial branched Pt(IV) prodrug CSS18 exhibited the most impressive therapeutic outcome, providing a potential path to more efficient nanocarriers for chemotherapeutic agents by chemical modulation and, giving insights into the rational design of reduction responsive platinum delivery system.

Phosphorescent rhenium(I) complexes conjugated with artesunate: Mitochondrial targeting and apoptosis-ferroptosis dual induction

Cell death is essential for cancer, which can be induced through multiple mechanisms. Ferroptosis, a newly emerging form of non-apoptotic cell death, involves the generation of iron-dependent reactive oxygen species (ROS). In this study, we designed and synthesized two artesunate (ART) conjugated phosphorescent rhenium(I) complexes (Re(I)-ART conjugates), [Re(N^N)(CO)₃(PyCH₂OART)](PF₆) (Re-ART-1 and Re-ART-2) (Py = pyridine, N^N = 1,10-phenanthroline (phen, in Re-ART-1) and 4,7-diphenyl-1,10-phenanthroline (DIP, in Re-ART-2)) that can specifically locate in the mitochondria of human cervical carcinoma (HeLa). Mechanism studies show that Re-ART-1 and Re-ART-2 exhibit high cytotoxicity against cancer cells lines and can induce both apoptosis and ferroptosis in HeLa cells through mitochondrial damage, caspase cascade, glutathione (GSH) depletion, glutathione peroxidase 4 (GPX4) inactivation and lipid peroxidation accumulation. As a result, this work presents the rational design of Re(I)-ART conjugates as a promising strategy to induce both apoptosis and ferroptosis and improve therapeutic efficiency of cancer treatment.

Developing a Novel Anticancer Gold(III) Agent to Integrate Chemotherapy and Immunotherapy

To effectively treat gastric cancer, we innovatively attempted to develop a metal agent to integrate immunotherapy and chemotherapy by dual targeting the cellular components in the tumor microenvironment (TME) based on the specific residue of human serum albumin (HSA) nanoparticles (NPs). We synthesized a series of Au(III) α-N-heterocyclic thiosemicarbazone compounds and obtained a Au agent (5b) with remarkable cytotoxicity to gastric cancer cells; moreover, we successfully constructed a novel HSA-5b complex NP delivery system. Importantly, the in vivo results showed that 5b/HSA-5b NPs effectively inhibited gastric tumor growth and HSA-5b NPs enhanced the therapeutic efficiency, bioavailability, and targeting ability compared with those of 5b alone. Furthermore, the in vitro/in vivo results revealed that 5b/HSA-5b NPs could integrate chemotherapy and immunotherapy by synergistically attacking two different cellular components in TME at the same time, namely, polarizing the tumor-associated macrophages and inducing apoptosis of gastric cancer cells.

Tumor Microenvironment-Responsive Theranostic Nanoplatform for Guided Molecular Dynamic/Photodynamic Synergistic Therapy

The integration of reactive oxygen species (ROS)-involved molecular dynamic therapy (MDT) and photodynamic therapy (PDT) holds great promise for enhanced anticancer effects. Herein, we report a biodegradable tumor microenvironment-responsive nanoplatform composed of sinoporphyrin sodium (SPS) photosensitizer-loaded zinc peroxide nanoparticles (SPS@ZnO₂ NPs), which can enhance the action of ROS through the production of hydrogen peroxide (H₂O₂) and singlet oxygen (¹O₂) for MDT and PDT, respectively, and the depletion of glutathione (GSH). Under these conditions, SPS@ZnO₂ NPs show excellent MDT/PDT synergistic therapeutic effects. We demonstrate that the SPS@ZnO₂ NPs quickly degrade to H₂O₂ and endogenous Zn²⁺ in an acidic tumor environment and produce toxic ¹O₂ with 630 nm laser irradiation both in vitro and in vivo. Anticancer mechanistic studies show that excessive production of ROS damages lysosomes and mitochondria and induces cellular apoptosis. We show that SPS@ZnO₂ NPs increase the uptake and penetration depth of photosensitizers in cells. In addition, the fluorescence of SPS is a powerful diagnostic tool for the treatment of tumors. The depletion of intracellular GSH through H₂O₂ production and the release of cathepsin B enhance the effectiveness of PDT. This theranostic nanoplatform provides a new avenue for tumor microenvironment-responsive and ROS-involved therapeutic strategies with synergistic enhancement of antitumor activity.

Anti-metastasis and anti-proliferation effect of mitochondria-accumulating ruthenium(II) complexes via redox homeostasis disturbance and energy depletion

The antiproliferative activity of three cyclometalated Ru(II) complexes with the formula [Ru(bpy)₂L]PF₆, where bpy = 2,2'-bipyridine, Ru1: L1 = phenanthro[4,5-fgh]quinoxaline; Ru2: L2 = benzo[f]naphtho[2,1-h]quinoxaline; and Ru3: L3 = phenanthro[9,10-b]pyrazine, have been synthesized and characterized. The lipophilicity of the three Ru(II) complexes was modulated by the alteration of the planarity in the ligands of the complexes. With appropriate lipophilicity, Ru1-Ru3 exhibited mitochondrial accumulating property and cytotoxic activity against a spectrum of cancer cell lines. The underlying mechanism study indicated that these Ru(II) complexes can selectively accumulate in mitochondria and disrupt physiological processes, including the redox balance and energy generation in cancer cells. Elevation of iron content in triple-negative breast cancer (MDA-MB-231 cells) was observed after treatment with Ru(II) complexes, which may contribute to the production of reactive oxygen species (ROS) via Fenton reaction chemistry. Besides, the Ru(II) complexes decreased the intracellular glutathione (GSH) in cancer cells, leading to the failure in the cells to combat oxidative damage. Both of the mentioned processes contribute to the high oxidative stress and eventually lead to cancer cell death. On the other hand, Ru1-Ru3 significantly induced the depletion of adenosine triphosphate (ATP), causing disturbance of energy generation. Moreover, the results of wound-healing assay and transwell invasion assay, as well as the tube formation assay indicated the anti-migration and anti-angiogenesis properties of Ru1-Ru3. Our study demonstrated that these Ru(II) complexes are promising chemotherapeutic agents with oxidative stress induction and energy generation disturbance.

Phosphorescent metal complexes as theranostic anticancer agents: combining imaging and therapy in a single molecule

Phosphorescent metal complexes are a new kind of multifunctional antitumor compounds that can integrate imaging and antitumor functions in a single molecule. In this minireview, we summarize the recent research progress in this field, concentrating on the theranostic applications of phosphorescent iridium(iii), ruthenium(ii) and rhenium(i) complexes. The molecular design that affords these complexes with tumour- or subcellular organelle-targeting properties is elucidated. The potential of these complexes to induce and monitor the dynamic behavior of subcellular organelles and the changes in microenvironment during the process of therapy is demonstrated. Moreover, the potential and advantages of applying new technologies, such as super-resolution imaging and phosphorescence lifetime imaging, are also described. Finally, the challenges faced in the development of novel theranostic metallo-anticancer complexes for possible clinical translation are proposed.

Sulfur-Coordinated Organoiridium(III) Complexes Exert Breast Anticancer Activity via Inhibition of Wnt/β-Catenin Signaling

The sulfur-coordinated organoiridium(III) complexes pbtIrSS and ppyIrSS, which contain C,N and S,S (dithione) chelating ligands, were found to inhibit breast cancer tumorigenesis and metastasis by targeting Wnt/β-catenin signaling for the first time. Treatment with pbtIrSS and ppyIrSS induces the degradation of LRP6, thereby decreasing the protein levels of DVL2, β-catenin and activated β-catenin, resulting in downregulation of Wnt target genes CD44 and survivin. Additionally, pbtIrSS and ppyIrSS can suppress cell migration and invasion of breast cancer cells. Furthermore, both complexes show the ability to inhibit sphere formation and mediate the stemness properties of breast cancer cells. Importantly, pbtIrSS exerts potent anti-tumor and anti-metastasis effects in mouse xenograft models through the blockage of Wnt/β-catenin signaling. Taken together, our results indicate that pbtIrSS has great potential to be developed as a breast cancer therapeutic agent with a novel mechanism.