Photoinduced anticancer activity studies of iridium(III) complexes targeting mitochondria and tubules

Induction of ferroptosis of iridium(III) complexes localizing at the mitochondria and lysosome by photodynamic therapy

In this study, [Ir(ppy)2(DMHBT)](PF6) (ppy = deprotonated 1-phenylpyridine, DMHBT = 10,12-dimethylpteridino[6,7-f][1,10]phenanthroline-11,13-(10,12H)-dione, 8a), [Ir(bzq)2(DMHBT)](PF6) (bzq = deprotonated benzo[h]quinoline, 8b) and [Ir(piq)2(DMHBT)](PF6) (piq = deprotonated 1-phenylisoquinoline, 8c) were synthesized and characterized by HRMS, 13C NMR and 1H NMR. In vitro cytotoxicity experiments showed that 8a, 8b, 8c show moderate cytotoxicity against B16 cells, while the cytotoxicity of the complexes 8a, 8b and 8c toward B16 cells was greatly improved upon light irradiation, which can be used as photosensitizers to exert anticancer efficacy in photodynamic therapy (PDT). After being taken up by cells, 8a, 8b, 8c were localized in the mitochondria, resulting in a large amount of Ca2+ in-flux, a burst release of ROS, a sustained opening of mitochondrial permeability transition pore, and a decrease of the mitochondrial membrane potential, which led to mitochondrial dysfunction and further activation of caspase 3 and Bcl-2 family proteins to induce apoptosis. Overloaded ROS reacted with polyunsaturated fatty acids on the cell membrane, and initiated lipid peroxidation, inhibited the xc--system-glutathione (GSH)-glutathione peroxidase 4 (GPX4) antioxidant defense system, and upregulated the expression of the damage-associated molecules, HMGB1, CRT, and HSP70. The presence of Fer-1 was effective on increasing the cell survival, which demonstrates that the complexes possess the potential to induce ferroptosis and immunogenic cell death. In addition, 8a, 8b and 8c induced autophagy by inhibiting the AKT/PI3K/mTOR signaling pathway, downregulating p62 and promoting Beclin-1 expression upon light irradiation.

White light increases anticancer effectiveness of iridium(III) complexes toward lung cancer A549 cells

Anticancer activity has been extensively studies. In this article, three ligands 2-(6-bromobenzo[d][1,3]dioxol-5-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (BDIP), 2-(7-methoxybenzo[d][1,3]dioxol-5-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (MDIP), 2-(6-nitrobenzo[d][1,3]dioxol-5-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (NDIP) and their iridium(III) complexes: [Ir(ppy)2(BDIP)](PF6) (ppy = deprotonated 2-phenylpyridine, 3a), [Ir(ppy)2(MDIP)](PF6) (3b) and [Ir(ppy)2(NDIP)](PF6) (3c) were synthesized. The cytotoxicity of 3a, 3b, 3c against Huh7, A549, BEL-7402, HepG2, HeLa, and non-cancer NIH3T3 was tested using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method. The results obtained from the MTT test stated clearly that these complexes demonstrated moderate or non-cytotoxicity toward Huh7, BEL-7402, HepG2 and HeLa except A549 cells. To improve the anticancer efficacy, we used white light to irradiate the mixture of cells and complexes for 30 min, the anticancer activity of the complexes was greatly enhanced. Particularly, 3a and 3b exhibited heightened capability to inhibit A549 cells proliferation with IC50 (half maximal inhibitory concentration) values of 0.7 ± 0.3 μM and 1.8 ± 0.1 μM, respectively. Cellular uptake has shown that 3a and 3b can be accumulated in the cytoplasm. Wound healing and colony forming showed that 3a and 3b significantly hinder the cell migration and growth in the S phase. The complexes open mitochondrial permeability transition pore (MPTP) channel and cause the decrease of membrane potential, release of cytochrome C, activation of caspase 3, and finally lead to apoptosis. In addition, 3a and 3b cause autophagy, increase the lipid peroxidation and lead to ferroptosis. Also, 3a and 3b increase the expression of calreticulin (CRT), high mobility group box 1 (HMGB1), heat shock protein 70 (HSP70), thereby inducing immunogenic cell death.

A Semi-Automated, High-Throughput Approach for the Synthesis and Identification of Highly Photo-Cytotoxic Iridium Complexes

The discovery of new compounds with pharmacological properties is usually a lengthy, laborious and expensive process. Thus, there is increasing interest in developing workflows that allow for the rapid synthesis and evaluation of libraries of compounds with the aim of identifying leads for further drug development. Herein, we apply combinatorial synthesis to build a library of 90 iridium(III) complexes (81 of which are new) over two synthesise-and-test cycles, with the aim of identifying potential agents for photodynamic therapy. We demonstrate the power of this approach by identifying highly active complexes that are well-tolerated in the dark but display very low nM phototoxicity against cancer cells. To build a detailed structure-activity relationship for this class of compounds we have used density functional theory (DFT) calculations to determine some key electronic parameters and study correlations with the experimental data. Finally, we present an optimised semi-automated synthesise-and-test protocol to obtain multiplex data within 72 hours.

Synthesis and anticancer mechanisms of four novel platinum(II) 4'-substituted-2,2':6',2''-terpyridine complexes

Mitophagy, a selective autophagic process, has emerged as a pathway involved in degrading dysfunctional mitochondria. Herein, new platinum(II)-based chemotherapeutics with mitophagy-targeting properties are proposed. Four novel binuclear anticancer Pt(II) complexes with 4'-substituted-2,2':6',2''-terpyridine derivatives (tpy1-tpy4), i.e., [Pt2(tpy1)(DMSO)2Cl4]·CH3OH (tpy1Pt), [Pt(tpy2)Cl][Pt(DMSO)Cl3]·CH3COCH3 (tpy2Pt), [Pt(tpy3)Cl][Pt(DMSO)Cl3] (tpy3Pt), and [Pt(tpy4)Cl]Cl·CH3OH (tpy4Pt), were designed and prepared. Moreover, their potential antitumor mechanism was studied. Tpy1Pt-tpy4Pt exhibited more selective cytotoxicity against cisplatin-resistant SK-OV-3/DDP (SKO3cisR) cancer cells compared with those against ovarian SK-OV-3 (SKO3) cancer cells and normal HL-7702 liver (H702) cells. This selective cytotoxicity of Tpy1Pt-tpy4Pt was better than that of its ligands (i.e., tpy1-tpy4), the clinical drug cisplatin, and cis-Pt(DMSO)2Cl2. The results of various experiments indicated that tpy1Pt and tpy2Pt kill SKO3cisR cancer cells via a mitophagy pathway, which involves the disruption of the mitophagy-related protein expression, dissipation of the mitochondrial membrane potential, elevation of the [Ca2+] and reactive oxygen species levels, promotion of mitochondrial DNA damage, and reduction in the adenosine triphosphate and mitochondrial respiratory chain levels. Furthermore, in vivo experiments indicated that the dinuclear anticancer Pt(II) coordination compound (tpy1Pt) has remarkable therapeutic efficiency (ca. 52.4%) and almost no toxicity. Therefore, the new 4'-substituted-2,2':6',2''-terpyridine Pt(II) coordination compound (tpy1Pt) is a potential candidate for next-generation mitophagy-targeting dinuclear Pt(II)-based anticancer drugs.

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.

Exploring the Potential of Metal-Based Candidate Drugs as Modulators of the Cytoskeleton

During recent years, accumulating evidence suggested that metal-based candidate drugs are promising modulators of cytoskeletal and cytoskeleton-associated proteins. This was substantiated by the identification and validation of actin, vimentin and plectin as targets of distinct ruthenium(II)- and platinum(II)-based modulators. Despite this, structural information about molecular interaction is scarcely available. Here, we compile the scattered reports about metal-based candidate molecules that influence the cytoskeleton, its associated proteins and explore their potential to interfere in cancer-related processes, including proliferation, invasion and the epithelial-to-mesenchymal transition. Advances in this field depend crucially on determining binding sites and on gaining comprehensive insight into molecular drug-target interactions. These are key steps towards establishing yet elusive structure-activity relationships.

Exploration of Remarkably Potential Multitarget-Directed N-Alkylated-2-(substituted phenyl)-1H-benzimidazole Derivatives as Antiproliferative, Antifungal, and Antibacterial Agents

Improving lipophilicity for drugs to penetrate the lipid membrane and decreasing bacterial and fungal coinfections for patients with cancer pose challenges in the drug development process. Here, a series of new N-alkylated-2-(substituted phenyl)-1H-benzimidazole derivatives were synthesized and characterized by 1H and 13C NMR, FTIR, and HRMS spectrum analyses to address these difficulties. All the compounds were evaluated for their antiproliferative, antibacterial, and antifungal activities. Results indicated that compound 2g exhibited the best antiproliferative activity against the MDA-MB-231 cell line and also displayed significant inhibition at minimal inhibitory concentration (MIC) values of 8, 4, and 4 μg mL-1 against Streptococcus faecalis, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus compared with amikacin. The antifungal data of compounds 1b, 1c, 2e, and 2g revealed their moderate activities toward Candida albicans and Aspergillus niger, with MIC values of 64 μg mL-1 for both strains. Finally, the molecular docking study found that 2g interacted with crucial amino acids in the binding site of complex dihydrofolate reductase with nicotinamide adenine dinucleotide phosphate.

Disparities in Cisplatin-Induced Cytotoxicity-A Meta-Analysis of Selected Cancer Cell Lines

Cisplatin is a classic anticancer drug widely used as a reference drug to test new metal complex drug candidates. We found an unexpected diversity in cisplatin-related cytotoxicity values, expressed as IC50 (the half-maximal inhibitory concentration) in tumour cell lines, such as MCF-7, HepG2 and HeLa. We reviewed the data published from 2018 to 2022. A total of 41 articles based on 56 in vitro experiments met our eligibility criteria. Using a meta-analysis based on a random effect model, we evaluated the cytotoxicity of cisplatin (IC50) after 48- or 72-h cell exposure. We found large differences between studies using a particular cell line. According to the random effect model, the 95% confidence intervals for IC50 were extremely wide. The heterogeneity of cisplatin IC50, as measured by the I2 index for all cancer cell lines, was over 99.7% at culture times of 48 or 72 h. Therefore, the variability between studies is due to experimental heterogeneity rather than chance. Despite the higher IC50 values after 48 h than after 72 h, the heterogeneity between the two culture periods did not differ significantly. This indicates that the duration of cultivation is not the main cause of heterogeneity. Therefore, the available data is diverse and not useful as a reference. We discuss possible reasons for the IC50 heterogeneity and advise researchers to conduct preliminary testing before starting experiments and not to solely rely on the published data. We hope that this systematic meta-analysis will provide valuable information for researchers searching for new cancer drugs using cisplatin as a reference drug.

Mitochondrial targeting half-sandwich iridium(III) and ruthenium(II) dppf complexes and in vitro anticancer assay

Considering the potential application of half-sandwich and ferrocenyl-containing organometallic complexes in the area of anticancer, four half-sandwich iridium(III) (Ir^III) and ruthenium(II) (Ru^II) diphenylphosphino ferrocene (dppf) complexes were prepared in this study. Complexes showed favorable anti-proliferation activity towards A549 cell lines compared to cisplatin, meanwhile, which could effectively inhibit cell migration. These complexes followed an energy dependence uptake mechanism, effectively accumulated in mitochondria with a Pearson's Colocalization Coefficient (PCC) of 0.77, decreased the mitochondrial membrane potential, induced a surge of reactive oxygen species, disturbed cell cycle, and eventually led to apoptosis. Western blot assay further confirmed that these complexes induced apoptosis following a mitochondrial pathway. Above all, half-sandwich Ir^III and Ru^II dppf complexes show the prospect of becoming a new multifunctional therapeutic platform for mitochondrial targeted imaging and anticancer drugs.

Light activation of iridium(III) complexes driving ROS production and DNA damage enhances anticancer activity in A549 cells

The work aimed to synthesize and characterize two iridium(III) complexes [Ir(ppy)₂(IPPH)](PF₆) (Ir1, IPPH = (2S,3R,5S,6R)-2-(2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenoxy)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol, ppy = 2-phenylpyridine), [Ir(piq)₂(IPPH)](PF₆) (Ir2, piq = 1-phenylisoquinoline). The cytotoxicity of the complexes against BEL-7402, A549, HCT-116, B16 cancer cells and normal LO2 was evaluated through 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) method. The complexes show no cytotoxic activity (IC₅₀ > 100 μM) against these cancer cells, while their cytotoxicity can significantly be elevated upon illumination. The IC₅₀ values range from 0.2 ± 0.05 to 35.5 ± 3.5 μM. The cellular uptake, endoplasmic reticulum and mitochondria localization, reactive oxygen species, the change of mitochondrial membrane potential, γ-H2AX levels, cycle arrest, apoptosis and the expression of B-cell lymphoma-2 were investigated. The calreticulin (CRT), heat shock protein 70 (HSP70), high mobility group box 1 (HMGB1) were explored. This study demonstrates that photoactivatable complexes induce cell death in A549 through ROS-mediated endoplasmic reticulum stress-mitochondrial pathway, DNA damage pathways, immunogenic cell death (ICD), activation of PI3K/AKT signaling pathway and inhibit the cell growth at S phase.

Novel glycosylation zinc(II)-cryptolepine complexes perturb mitophagy pathways and trigger cancer cell apoptosis and autophagy in SK-OV-3/DDP cells

With the aim of shedding some light on the mechanism of action of zinc(II) complexes in antiproliferative processes and molecular signaling pathways, three novel glycosylated zinc(II)-cryptolepine complexes, i.e., [Zn(QA1)Cl₂] (Zn(QA1)), [Zn(QA2)Cl₂] (Zn(QA2)), and [Zn(QA3)Cl₂] (Zn(QA3)), were prepared by conjugating a glucose moiety with cryptolepine, followed by complexation of the resulting glycosylated cryptolepine compounds N-((1-(2-morpholinoethyl)-1H-1,2,3-triazol-4-yl)methyl)-benzofuro[3,2-b]quinolin-11-amine (QA1), 2-(4-((benzofuro[3,2-b]quinolin-11-ylamino)methyl)-1H-1,2,3-triazol-1-yl)ethan-1-ol (QA2), and (2S,3S,4R,5R,6S)-2-(4-((benzofuro[3,2-b]quinolin-11-ylamino)-methyl)-1H-1,2,3-triazol-1-yl)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol (QA3) with zinc(II), and their anticancer activity was evaluated. In MTT assays, Zn(QA1)-Zn(QA3) were more active against cisplatin-resistant ovarian SK-OV-3/DDP cancer cells (SK-OV-3cis) than ZnCl₂ and the QA1-QA3 ligands, with IC₅₀ values of 1.81 ± 0.50, 2.92 ± 0.32, and 1.01 ± 0.11 μM, respectively. Complexation of glycosylated cryptolepine QA3 with zinc(II) increased the antiproliferative activity of the ligand, suggesting that Zn(QA3) could act as a chaperone to deliver the active ligand intracellularly, in contrast with other cryptolepine metal complexes previously reported. In vivo and in vitro investigations suggested that Zn(QA3) exhibited enhanced anticancer activity with treatment effects comparable to those of the clinical drug cisplatin. Furthermore, Zn(QA1)-Zn(QA3) triggered SK-OV-3cis cell apoptosis through mitophagy pathways in the order Zn(QA1) > Zn(QA1) > Zn(QA2). These results demonstrate the potential of glycosylated zinc(II)-cryptolepine complexes for the development of chemotherapy drugs against cisplatin-resistant SK-OV-3cis cells.

An N-heterocyclic carbene iridium(III) complex as a potent anti-cancer stem cell therapeutic

Cancer stem cells (CSCs) represent a difficult to treat cellular niche within tumours due to their unique characteristics, which give them a high propensity for resistance to classical anti-cancer treatments and the ability to repopulate the tumour mass. An attribute that may be implicated in the high rates of recurrence of certain tumours. However, other characteristics specific to these cells, such as their high dependence on mitochondria, may be exploited for the development of new therapeutic agents that are effective against the niche. As such, a previously described phosphorescent N-heterocyclic carbene iridium(III) compound which showed a high level of cytotoxicity against classical tumour cell lines with mitochondria-specific effects was studied for its potential against CSCs. The results showed a significantly higher level of activity against several CSC lines compared to non-CSCs. Mitochondrial localisation and superoxide production were confirmed. Although the cell death involved caspase activation, their role in cell death was not definitive, with a potential implication of other, non-apoptotic pathways shown. A cytostatic effect of the compound was also displayed at low mortality doses. This study thus provides important insights into the mechanisms and the potential for this class of molecule in the domain of anti-CSC therapeutics.

Iridium Complex-Loaded Sorafenib Nanocomposites for Synergistic Chemo-photodynamic Therapy of Hepatocellular Carcinoma

Although sorafenib, a multi-kinase inhibitor, has provided noteworthy benefits in patients with hepatocellular carcinoma (HCC), the inevitable side effects, narrow therapeutic window, and low bioavailability seriously affect its clinical application. To be clinically distinctive, innovative drugs must meet the needs of reaching tumor tissues and cause limited side effects to normal organs and tissues. Recently, photodynamic therapy, utilizing a combination of a photosensitizer and light irradiation, was selectively accumulated at the tumor site and taken up effectively via inducing apoptosis or necrosis of cancer cells. In this study, a nano-chemo-phototherapy drug was fabricated to compose an iridium-based photosensitizer combined with sorafenib (IPS) via a self-assembly process. Compared to the free iridium photosensitizer or sorafenib, the IPS exhibited significantly improved therapeutic efficacy against tumor cells because of the increased cellular uptake and the subsequent simultaneous release of sorafenib and generation of reactive oxygen species production upon 532 nm laser irradiation. To evaluate the effect of synergistic treatment, cytotoxicity detection, live/dead staining, cell proliferative and apoptotic assay, and Western blot were performed. The IPS exhibited sufficient biocompatibility by hemolysis and serum biochemical tests. Also, the results suggested that IPS significantly inhibited HCC cell proliferation and promoted cell apoptosis. More importantly, marked anti-tumor growth effects via inhibiting cell proliferation and promoting tumor cell death were observed in an orthotopic xenograft HCC model. Therefore, our newly proposed nanotheranostic agent for combined chemotherapeutic and photodynamic therapy notably improves the therapeutic effect of sorafenib and has the potential to be a new alternative option for HCC treatment.

The strong in vitro and vivo cytotoxicity of three new cobalt(II) complexes with 8-methoxyquinoline

Three new cobalt(II) complexes, [Co(MQL)₂Cl₂] (CoCl), [Co(MQL)₂Br₂] (CoBr), and [Co(MQL)₂I₂] (CoI), bearing 8-methoxyquinoline (MQL) have been designed for the first time. MTT assays showed that CoCl, CoBr, and CoI exhibit much better antiproliferative activities than cisplatin toward cisplatin-resistant SK-OV-3/DDP and SK-OV-3 ovarian cancer cells, with IC₅₀ values of as low as 0.32-5.49 μM. Further, CoCl and CoI can regulate autophagy-related proteins in SK-OV-3/DDP cells and, therefore, they can induce primarily autophagy-mediated cell apoptosis in the following order: CoCl > CoI. The different antiproliferative activities of the MQL complexes CoCl, CoBr, and CoI could be correlated with the lengths of their Co-X bonds, which adopted the following order: CoI > CoBr > CoCl. The 8-HOMQ complexes CoCl (ca. 60.1%) and CoI (ca. 48.8%) also showed potent in vivo anticancer effects after 15 days of treatment. In summary, the MQL ligand highly enhances the antiproliferative activities of cobalt(II) complexes in comparison to other previously reported 8-hydroxyquinoline metal complexes.

Dipyridophenazine iridium(III) complex as a phototoxic cancer stem cell selective, mitochondria targeting agent

In this work, the mechanism underlying the anticancer activity of a photoactivatable Ir(III) compound of the type [Ir(CˆN)₂(dppz)][PF₆] where CˆN = 1-methyl-2-(2'-thienyl)benzimidazole (complex 1) was investigated. Complex 1 photoactivated by visible light shows potent activity against highly aggressive and poorly treatable Rhabdomyosarcoma (RD) cells, the most frequent soft tissue sarcomas of children. This remarkable activity of 1 was observed not only in RD cells cultured in 2D monolayers but, more importantly, also in 3D spheroids, which resemble in many aspects solid tumors and serve as a promising model to mimic the in vivo situation. Importantly, photoactivated 1 kills not only differentiated RD cells but also even more effectively cancer stem cells (CSCs) of RD. One of the factors responsible for the activity of irradiated 1 in RD CSCs is its ability to produce ROS in these cells more effectively than in differentiated RD cells. Moreover, photoactivated 1 caused in RD differentiated cells and CSCs a significant decrease of mitochondrial membrane potential and promotes opening mitochondrial permeability transition pores in these cells, a mechanism that has never been demonstrated for any other metal-based anticancer complex. The results of this work give evidence that 1 has a potential for further evaluation using in vivo models as a promising chemotherapeutic agent for photodynamic therapy of hardly treatable human Rhabdomyosarcoma, particularly for its activity in both stem and differentiated cancer cells.

Complexes of Zn(II) with a mixed tryptanthrin derivative and curcumin chelating ligands as new promising anticancer agents

In this study, two novel curcumin (H-Cur)-tryptanthrin metal compounds-[Zn(TA)Cl₂], i.e., Zn(TA), and [Zn(TA)(Cur)]Cl, i.e., Zn(TAC)-were synthesized and investigated using 5-(bis-pyridin-2-ylmethyl-amino)-pentanoic acid (6,12-dioxo-6,12-dihydro-indolo[2,1-b]quinazolin-8-yl)-amide (TA) and H-Cur as the targeting and high-activity anticancer chemotherapeutic moieties, respectively. They were then compared with the di-(2-picolyl)amine (PA) Zn(II) complex [Zn(PA)Cl₂], i.e., Zn(PA). When compared with Zn(PA) and cisplatin, the IC₅₀ values of Zn(TA) and Zn(TAC) indicated that the compounds had high cytotoxicity against A549/DDP cancer cells, implying that the H-Cur-tryptanthrin Zn(II) compounds have the potential for use as anticancer drugs. We propose the use of synthesized theragnostic H-Cur-tryptanthrin Zn(II) complexes with nuclear-targeting and DNA-damaging capabilities as a simple therapeutic strategy against tumors. The Zn(TA) and Zn(TAC) complexes could be traced via red fluorescence and were found to accumulate in the cell nuclei and induce DNA damage, cell cycle arrest, mitochondrial dysfunction, and cell apoptosis both in vitro and in vivo. In addition, Zn(TAC) exhibited a higher antiproliferative effect on A549/DDP than Zn(TA) and Zn(PA), which was undoubtedly associated with the key roles of the novel tryptanthrin derivative TA and H-Cur in the Zn(TAC) complex.

Benzothiazole-decorated iridium-based nanophotosensitizers for photodynamic therapy of cancer cells

Photodynamic therapy (PDT) is an effective non-invasive treatment for tumors. The structure of a photosensitizer has an important influence on light utilization and efficiency of singlet-oxygen generation. In this study, we synthesized three π-type iridium(III) complexes and modified the C^N and N^N ligands with benzothiazole (BTZ) to regulate their light-absorption capacity and efficiency of singlet-oxygen generation. We assembled the nano-photosensitizers by wrapping them with an amphiphilic polyethylene glycol polymer with folic acid-targeting function to improve their targeting ability and biocompatibility. Modification of the BTZ group on the C^N ligand enhanced the ability of the photosensitizer to generate singlet oxygen and improved the cell uptake and PDT efficacy of the corresponding nanophotosensitizer. We believe that this type of photosensitizer provides the basis for the design of new photosensitizers based on the structure of iridium(III) complexes.

A new class of nickel(II) oxyquinoline-bipyridine complexes as potent anticancer agents induces apoptosis and autophagy in A549/DDP tumor cells through mitophagy pathways

A new class of nickel(II) oxyquinoline-bipyridine complexes, namely, [Ni(La1)2(Lb6)] (Ni1), [Ni(La1)2(Lb2)] CH3OH (Ni2), [Ni(La7)2(Lb11)]2H2O (Ni3), [Ni(La1)2(Lb9)] (Ni4), [Ni(La1)2(Lb8)] (Ni5), [Ni(La2)2(Lb1)] (Ni6), [Ni(La2)2(Lb6)]CH3OH (Ni7), [Ni(La2)2(Lb11)]CH3OH (Ni8), [Ni(La2)2(Lb3)] (Ni9), [Ni(La2)2(Lb2)]CH3OH (Ni10), [Ni(La2)2(Lb5)]CH3OH...

Synthesis and biological evaluation of mixed-ligand cyclometalated iridium(III)-quinoline complexes

With the aim of gaining new insight into the underlying apoptosis mechanisms and in vivo efficacy of cyclometalated Ir(III) complexes as metalodrugs, six new cyclometalated Ir(III)-quinoline complexes, [Ir(1a)(2pq)2] (2a), [Ir(1b)(2pq)2] (2b), [Ir(1c)(2pq)2] (2c), [Ir(1d)(2pq)2] (2d), [Ir(1e)(2pq)2] (2e), and [Ir(1f)(2pq)2] (2f) (2pq = 2-phenylisoquinoline), have been synthesized using 5,7-dihalo-8-hydroxylquinoline ligands (1a-1f) and [Ir(2pq)2Cl]2 precursors and characterized. Complexes 2a-2f have shown potent anticancer activity against cisplatin-resistant SK-OV-3/DDP and A549/DDP cells (IC50 = 0.11-1.83 μM), following the order 2e > 2f > 2b > 2c > 2d > 2a. Confocal microscopy images suggest that 2e and 2b could act as red-color probes for specific cell imaging and efficiently initiate apoptosis and autophagy in the mitochondria, cell cytosol, and nucleus. Overexpression of beclin1, caspase-9, cytochrome c, LC3II, and apaf-1; inhibition of p62, cyclin D1, cyclin A2, and CDK2; and a substantial rapid accumulation suggest a paraptotic mode of cell death induced by autophagy, DNA damage, and mitochondrial stress. In addition, the inhibitory rate of 2e on A549/DDP tumor growth was 64.1% at a concentration of 10.0 mg kg-1, which is clearly higher than that of cisplatin. According to the biological assay, the cyclometalated Ir(III)-quinoline complex 2e exhibited a higher anticancer effect than 2b, which may be associated with the electronic effect of the methyl group of the 1e ligand of 2e playing a key role in the mechanism.

Polymeric Nanoparticles for Mitochondria Targeting Mediated Robust Cancer Therapy

Despite all sorts of innovations in medical researches over the past decades, cancer remains a major threat to human health. Mitochondria are essential organelles in eukaryotic cells, and their dysfunctions contribute to numerous diseases including cancers. Mitochondria-targeted cancer therapy, which specifically delivers drugs into the mitochondria, is a promising strategy for enhancing anticancer treatment efficiency. However, owing to their special double-layered membrane system and highly negative potentials, mitochondria remain a challenging target for therapeutic agents to reach and access. Polymeric nanoparticles exceed in cancer therapy ascribed to their unique features including ideal biocompatibility, readily design and synthesis, as well as flexible ligand decoration. Significant efforts have been put forward to develop mitochondria-targeted polymeric nanoparticles. In this review, we focused on the smart design of polymeric nanosystems for mitochondria targeting and summarized the current applications in improving cancer therapy.

Smart Stimuli-Responsive and Mitochondria Targeting Delivery in Cancer Therapy

Dysfunction in the mitochondria (Mc) contributes to tumor progression. It is a major challenge to deliver therapeutic agents specifically to the Mc for precise treatment. Smart drug delivery systems are based on stimuli-responsiveness and active targeting. Here, we give a whole list of documented pathways to achieve smart stimuli-responsive (St-) and Mc-targeted DDSs (St-Mc-DDSs) by combining St and Mc targeting strategies. We present the formulations, targeting characteristics of St-Mc-DDSs and clarify their anti-cancer mechanisms as well as improvement in efficacy and safety. St-Mc-DDSs usually not only have Mc-targeting groups, molecules (lipophilic cations, peptides, and aptamers) or materials but also sense the surrounding environment and correspondingly respond to internal biostimulators such as pH, redox changes, enzyme and glucose, and/or externally applied triggers such as light, magnet, temperature and ultrasound. St-Mc-DDSs exquisitely control the action site, increase therapeutic efficacy and decrease side effects of the drug. We summarize the clinical research progress and propose suggestions for follow-up research. St-Mc-DDSs may be an innovative and sensitive precision medicine for cancer treatment.

High anticancer activity and apoptosis- and autophagy-inducing properties of novel lanthanide(III) complexes bearing 8-hydroxyquinoline-N-oxide and 1,10-phenanthroline

In the quest for rare earth metal complexes with enhanced cancer chemotherapeutic properties, the discovery of seven lanthanide(iii) complexes bearing 8-hydroxyquinoline-N-oxide (NQ) and 1,10-phenanthroline (phen) ligands, i.e., [SmIII(NQ)(phen)(H2O)Cl2] (Ln1), [EuII(NQ)(phen)(H2O)Cl2] (Ln2), [GdIII(NQ)(phen)(H2O)Cl2] (Ln3), [DyIII(NQ)(phen)(H2O)Cl2] (Ln4), [HoIII(NQ)(phen)(H2O)Cl2] (Ln5), [ErIII(NQ)(phen)(H2O)Cl2] (Ln6), and [YbIII(NQ)(phen)(H2O)Cl2] (Ln7), as potential anticancer drugs is described. Complexes Ln1-Ln7 exhibit high antiproliferative activity against cisplatin-resistant A549/DDP cells (IC50 = 0.025-0.097 μM) and low toxicity to normal HL-7702 cells. Moreover, complex Ln1, and to a lesser extent Ln7, can upregulate the expression of LC3 and Beclin1 and downregulate p62 to induce apoptosis in cisplatin-resistant A549/DDP cell lines, which is related to the cell autophagy-inducing properties of Ln1 and Ln7. Furthermore, in vivo assays suggest that Ln1 significantly inhibits A549/DDP xenograft tumor growth (56.5%). These results indicate that lanthanide(iii) complex Ln1 is a promising candidate as an anticancer drug against cisplatin-resistant A549/DDP cells.

Mitochondria-localizing curcumin-cryptolepine Zn(II) complexes and their antitumor activity

Many metal complexes are potent candidates as mitochondrial-targeting agents. In this study, four novel Zn(II) complexes, [Zn(BPQA)Cl₂] (Zn1), [Zn(BPQA)(Curc)]Cl (Zn2), [Zn(PQA)Cl₂] (Zn3), and [Zn(PQA)(Curc)]Cl (Zn4), containing N,N-bis(pyridin-2-ylmethyl)benzofuro[3,2-b]quinolin-11-amine (BPQA), N-(pyridin-2-ylmethyl)benzofuro[3,2-b]quinolin-11-amine (PQA), and curcumin (H-Curc) were synthesized. An MTT assay showed that Zn1-Zn4 had strong anticancer activities against SK-OV-3/DDP and T-24 tumor cells with IC₅₀ values of 0.03-6.19 μM. Importantly, Zn1 and Zn2 displayed low toxicities against normal HL-7702 cells. Mechanism experiments demonstrated that probe Zn2 showed appreciable fluorescence in the red region of the spectrum, and substantial accumulation of Zn2 occurred in the mitochondria after treatment, indicating increases in Ca²⁺ and reactive oxygen species levels, loss of the mitochondrial membrane potential, and consequent induction of mitochondrial dysfunction at low concentrations. In addition, the probe Zn2 effectively (50.7%) inhibited the growth of T-24 bladder tumor cells in vivo. The probe Zn2 shows potential for use in cancer therapy while retaining the H-Curc as an imaging probe.

Dual-light triggered metabolizable nano-micelles for selective tumor-targeted photodynamic/hyperthermia therapy

Phototherapy, including photodynamic and photothermal therapies, is a non-invasive photo-triggered tumor treatment. Combination therapy and new synergistic therapeutic reagents may hold promise for improving these treatments. Herein, we report an amphiphilic iridium-based photosensitizer (C14-IP2000) loaded with a hydrophobic photo-thermal drug (ZnPc) to form nano-micelles (ZNPs) for dual-light triggered tumor phototherapy. The C14-IP2000 was contained within ZNPs consisting of an iridium complex core decorated with hydrophilic polyethylene glycol chains to extend the time in blood circulation, and two hydrophobic carbon chains to enhance the loading capacity and the hydrophobic interaction with the loaded reagent. The designed ZNPs showed effective blood circulation, passive tumor targeting ability, remarkable photodynamic conversion ability, and good photothermal conversion capability, and therefore may be used for combined tumor ablation. Our results demonstrated that the amphipathic bionic structure of ZNPs not only enables self-assembled reagent fabrication with prolonged circulation time and favorable metabolic characteristics for tumor combination therapy, but also provides a nanostructure strategy for the modification of functionalized reagents.

Novel Papaverine Metal Complexes with Potential Anticancer Activities

Cancer is one of the leading causes of death worldwide. Although several potential therapeutic agents have been developed to efficiently treat cancer, some side effects can occur simultaneously. Papaverine, a non-narcotic opium alkaloid, is a potential anticancer drug that showed selective antitumor activity in various tumor cells. Recent studies have demonstrated that metal complexes improve the biological activity of the parent bioactive ligands. Based on those facts, herein we describe the synthesis of novel papaverine–vanadium(III), ruthenium(III) and gold(III) metal complexes aiming at enhancing the biological activity of papaverine drug. The structures of the synthesized complexes were characterized by various spectroscopic methods (IR, UV–Vis, NMR, TGA, XRD, SEM). The anticancer activity of synthesized metal complexes was evaluated in vitro against two types of cancer cell lines: human breast cancer MCF-7 cells and hepatocellular carcinoma HepG-2 cells. The results revealed that papaverine-Au(III) complex, among the synthesized complexes, possess potential antimicrobial and anticancer activities. Interestingly, the anticancer activity of papaverine–Au(III) complex against the examined cancer cell lines was higher than that of the papaverine alone, which indicates that Au-metal complexation improved the anticancer activity of the parent drug. Additionally, the Au complex showed anticancer activity against the breast cancer MCF-7 cells better than that of cisplatin. The biocompatibility experiments showed that Au complex is less toxic than the papaverine drug alone with IC₅₀ ≈ 111µg/mL. These results indicate that papaverine–Au(III) complex is a promising anticancer complex-drug which would make it a suitable candidate for further in vivo investigations.

Synthesis, Characterisation and In Vitro Anticancer Activity of Catalytically Active Indole-Based Half-Sandwich Complexes

The synthesis, characterisation and evaluation of the in vitro cytotoxicity of four indole-based half-sandwich metal complexes towards two ovarian cancer cell lines (A2780 and A2780cisR) and one normal prostate cell line (PNT2) are presented herein. Although capable of inducing catalytic oxidation of NADH and able to reduce NAD+ with high turnover frequencies, in cells and in the presence of sodium formate, these complexes also strongly interact with biomolecules such as glutathione. This work highlights that efficient out-of-cells catalytic activity might lead to higher reactivity towards biomolecules, thus inhibiting the in-cells catalytic processes.

Is the Way to Fight Cancer Paved with Gold? Metal-Based Carbene Complexes with Multiple and Fascinating Biological Features

Herein, we report the synthesis and the multiple anti-tumor properties of new gold and silver carbene complexes. The chemical modifications, grounded on our previous studies, led us to identify a good lead complex, gold-based, whose biological features are very exciting and promising in the anti-cancer research and could be further developed. Indeed, the bis-[4,5-dichloro-(N-methyl-N’(2-hydroxy-2-phenyl)ethyl-imidazole-2-ylidene)gold(I)]⁺[dichloro-gold]⁻ (AuL7) complex possesses the ability to interfere with at least three important and different intracellular targets, namely the human topoisomerases I and II and tubulin, which are able to modulate metabolic processes not directly correlated each other. We proved that the modifications of the ligands structure in AuL7, with respect to another already published complex, i.e., bis-[4,5-dichloro-(N-methyl-N’(cyclopentane-2ol)-imidazole-2-ylidine)gold(I)]⁺[dichloro-gold]⁻ (AuL4), produce a different behavior toward tubulin-polymerization process, since AuL7 is a tubulin-polymerization inhibitor and AuL4 a stabilizer, with the final same result of hampering the tumor growth. Taken together, our outcomes designate AuL7 as a promising compound for the development of multi-targeted anti-cancer therapies.

X-ray tomography of cryopreserved human prostate cancer cells: mitochondrial targeting by an organoiridium photosensitiser

Abstract

The organoiridium complex Ir[(C,N)₂(O,O)] (1) where C, N = 1-phenylisoquinoline and O,O = 2,2,6,6-tetramethyl-3,5-heptanedionate is a promising photosensitiser for Photo-Dynamic Therapy (PDT). 1 is not toxic to cells in the dark. However, irradiation of the compound with one-photon blue or two-photon red light generates high levels of singlet oxygen (¹O₂) (in Zhang et al. Angew Chem Int Ed Engl 56 (47):14898-14902 10.1002/anie.201709082,2017), both within cell monolayers and in tumour models. Moreover, photo-excited 1 oxidises key proteins, causing metabolic alterations in cancer cells with potent antiproliferative activity. Here, the tomograms obtained by cryo-Soft X-ray Tomography (cryo-SXT) of human PC3 prostate cancer cells treated with 1, irradiated with blue light, and cryopreserved to maintain them in their native state, reveal that irradiation causes extensive and specific alterations to mitochondria, but not other cellular components. Such new insights into the effect of ¹O₂ generation during PDT using iridium photosensitisers on cells contribute to a detailed understanding of their cellular mode of action.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s00775-020-01761-8) contains supplementary material, which is available to authorized users.

Identification of two mitochondrial-targeting cyclometalated iridium(III) complexes as potent anti-glioma stem cells agents

Glioma stem cells (GSCs) are thought to be responsible for the recurrence and invasion of glioblastoma multiform (GBM), which have been evaluated and exploited as the therapeutic target for GBM. Cyclometalated iridium(III) complexes have been demonstrated as the potential anticancer agents, however, their antitumor efficacies against GSCs are still unknown. Herein, we investigated the antitumor activity of two cyclometalated iridium(III) complexes [Ir(ppy)₂L](PF₆) (Ir1) and [Ir(thpy)₂L](PF₆) (Ir2) (ppy = 2-phenylpyridine, thpy = 2-(2-thienyl)pyridine and L = 4,4'-Bis(hydroxymethyl)-2,2'-bipyridine) against GSCs. The results clearly indicate that Ir1 and Ir2 kill GSCs selectively with IC₅₀ values ranging from 5.26-9.05 μM. Further mechanism research display that Ir1 and Ir2 can suppress the proliferation of GSCs, penetrate into GSCs efficiently, localize to mitochondria, and induce mitochondria-mediated apoptosis, including the loss of mitochondrial membrane (MMP), elevation of intracellular reactive oxygen species (ROS) and caspases activation. Moreover, Ir1 and Ir2 can destroy the GSCs self-renewal and unlimited proliferation capacity by affecting the GSCs colony formation. According our knowledge, this is the first study to investigate the anti-GSCs properties of cyclometalated iridium(III) complexes.

Design and synthesis of new ruthenium polypyridyl complexes with potent antitumor activity in vitro

We herein report the synthesis, characterization and anticancer activity of BTPIP (2-(4-(benzo[b]thiophen-2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its four ruthenium(II) polypyridyl complexes [Ru(NN)₂(BTPIP)](ClO₄)₂ (N-N = bpy = 2,2'-bipyridine, Ru(II)-1; phen = 1,10-phenanthroline, Ru(II)-2; dmb = 4,4'-dimethyl-2,2'-bipyridine, Ru(II)-3; dmp = 2,9-dimethyl-1,10-phenanthroline, Ru(II)-4). The DNA binding behaviors reveal that the complexes bind to calf thymus DNA by intercalation. Cytotoxicity of the complexes against A549, HepG-2, SGC-7901 and Hela cells were evaluated in vitro. Complexes Ru(II)-1, Ru(II)-2, Ru(II)-3, Ru(II)-4 show moderate activity on the cell proliferation in A549 cells with IC₅₀ values of 9.3 ± 1.2, 12.1 ± 1.6, 10.3 ± 1.6, 8.9 ± 1.2 μM, respectively. Apoptosis assessment, intracellular mitochondrial membrane potential (MMP), location in mitochondria, reactive oxygen species (ROS), cell invasion assay and cell cycle arrest were also performed to explore the mechanism of this action. When the concentration of the ruthenium(II) complexes is increased, the amount of reactive oxygen species increases obviously and the mitochondrial membrane potential decreases dramatically in A549 cells. Most importantly, the ruthenium(II) polypyridyl complexes could arrive the cytoplasm through the cell membrane and accumulate in the mitochondria. These results showed that the ruthenium(II) complexes could induce apoptosis in A549 cells through an ROS-mediated mitochondrial dysfunction pathway.

Evaluation of anticancer activity in vitro and in vivo of iridium(iii) polypyridyl complexes

Three new iridium(iii) polypyridyl complexes were synthesized. The cytotoxic activity in vitro and in vivo, apoptosis, cell cycle arrest, mitochondrial membrane potential, ROS and the expression of Bcl-2 family proteins were investigated.

Anticancer and antibacterial activity in vitro evaluation of iridium(III) polypyridyl complexes

Three iridium(III) polypyridyl complexes [Ir(ppy)₂(PYTA)](PF₆) (1) (ppy = 2-phenylpyridine), [Ir(bzq)₂(PYTA)](PF₆) (2) (bzq = benzo[h]quinolone) and [Ir(piq)₂(PYTA)](PF₆) (3) (piq = 1-phenylisoquinoline, PYTA = 2,4-diamino-6-(2'-pyridyl)-1,3,5-triazine) were synthesized and characterized by elemental analysis, IR, ¹H NMR and ¹³C NMR. The cytotoxic activity of the complexes toward cancer SGC-7901, Eca-109, A549, HeLa, HepG2, BEL-7402 and normal LO2 cell lines was investigated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Complex 3 shows the most effective on inhibiting the above cell growth among these complexes. The complexes locate at the lysosomes and mitochondria. AO/EB, Annex V and PI and comet assays indicate that the complexes can induce apoptosis in SGC-7901 cells. Intracellular ROS and mitochondrial membrane potential were examined under fluorescence microscopy. The results demonstrate that the complexes increase the intracellular ROS levels and induce a decrease in the mitochondrial membrane potential. The complexes can enhance intracellular Ca²⁺ concentration and cause a release of cytochrome c. The autophagy was studied using MDC staining and western blot. Complexes 1-3 can effectively inhibit the cell invasion with a concentration-dependent manner. Additionally, the complexes target tubules and inhibit the polymerization of tubules. The antimicrobial activity of the complexes against S. aureus, E. coli, Salmonella and L. monocytogenes was explored. The mechanism shows that the complexes induce apoptosis in SGC-7901 cells through ROS-mediated lysosomal-mitochondrial, targeting tubules and damage DNA pathways. Three iridium(III) complexes [Ir(N-C)₂(PYTA)](PF₆) (N-C = ppy, 1; bzq, 2; piq, 3) were synthesized and characterized. The anticancer activity of the complexes against SGC-7901 cells was studied by apoptosis, comet assay, autophagy, ROS, mitochondrial membrane potential, intracellular Ca²⁺ levels, release of cytochrome c, tubules and western blot analysis. The antibacterial activity in vitro was also assayed.