Design, synthesis, and antitumor mechanism investigation of iridium(III) complexes conjugated with ibuprofen

The design and synthesis of a series of metal complexes formed by non-steroidal anti-inflammatory drugs (NSAIDs) ibuprofen (IBP) and iridium(III), with the molecular formula [Ir(C^N)2bpy(4-CH2OIBP-4'-CH2OIBP)](PF6) (Ir-IBP-1, Ir-IBP-2) (C^N = 2-phenylpyridine (ppy, Ir-IBP-1), 2-(2-thienyl)pyridine (thpy, Ir-IBP-2)) was introduced in this article. Firstly, it was found that the anti-proliferative activity of these complexes was more effective than that of cisplatin. Further research showed that Ir-IBP-1 and Ir-IBP-2 can accumulate in intracellular mitochondria, thereby disrupting mitochondrial membrane potential (MMP), increasing intracellular reactive oxygen species (ROS), blocking the G2/M phase of the cell cycle, and inducing cell apoptosis. In terms of protein expression, the expression of COX-2, MMP-9, NLRP3 and Caspase-1 proteins can be downregulated, indicating their ability to anti-inflammatory and overcome immune evasion. Furthermore, Ir-IBP-1 and Ir-IBP-2 can induce immunogenic cell death (ICD) by triggering the release of cell surface calreticulin (CRT), high mobility group box 1 (HMGB1) and adenosine triphosphate (ATP). Overall, iridium(III)-IBP conjugates exhibit various anti-tumor mechanisms, including mitochondrial damage, cell cycle arrest, inflammatory suppression, and induction of ICD.

Ir(III) Half-Sandwich Photosensitizers with a π-Expansive Ligand for Efficient Anticancer Photodynamic Therapy

One approach to reduce the side effects of chemotherapy in cancer treatment is photodynamic therapy (PDT), which allows spatiotemporal control of the cytotoxicity. We have used the strategy of coordinating π-expansive ligands to increase the excited state lifetimes of Ir(III) half-sandwich complexes in order to facilitate the generation of 1O2. We have obtained derivatives of formulas [Cp*Ir(C∧N)Cl] and [Cp*Ir(C∧N)L]BF4 with different degrees of π-expansion in the C∧N ligands. Complexes with the more π-expansive ligand are very effective photosensitizers with phototoxic indexes PI > 2000. Furthermore, PI values of 63 were achieved with red light. Time-dependent density functional theory (TD-DFT) calculations nicely explain the effect of the π-expansion. The complexes produce reactive oxygen species (ROS) at the cellular level, causing mitochondrial membrane depolarization, cleavage of DNA, nicotinamide adenine dinucleotide (NADH) oxidation, as well as lysosomal damage. Consequently, cell death by apoptosis and secondary necrosis is activated. Thus, we describe the first class of half-sandwich iridium cyclometalated complexes active in PDT.

Cyclometalated iridium(III) complexes as anti-breast cancer and anti-metastasis agents via STAT3 inhibition

Breast cancer is the most commonly diagnosed cancer and second‑leading cause of cancer deaths in women. Signal transducer and activator of transcription 3 (STAT3) plays a critical role in promoting breast cancer cell proliferation, invasion, angiogenesis, and metastasis, and the high expression of STAT3 is related to the occurrence and poor chemotherapy sensitivity of breast cancer. Iridium(III) complexes Ir-PTS-1- 4 containing a pterostilbene-derived ligand were synthesized to inhibit the STAT3 pathway in breast cancer. Ir-PTS-4 inhibited the proliferation of breast cancer cells by suppressing the expression of phosphorylated STAT3 and STAT3-related cyclin D1, arresting cell cycle in the S-phase, inducing DNA damage and reactive oxygen species (ROS) generation, eventually leading to autophagic cell death. The cell metastasis and invasion were also inhibited after Ir-PTS-4 treatment. Besides, Ir-PTS-4 exhibited excellent anti-proliferation activity in 3D multicellular tumor spheroids, showing potential for the treatment of solid tumors. This work presents the rational design of metal-based anticancer agents to block the STAT3 pathway for simultaneously inhibiting breast cancer proliferation and metastasis.

Recent Advancement in the Synthesis of Ir-Based Complexes

Cancer is a devastating disease with over 100 types, including lung and breast cancer. Cisplatin and metal-based drugs are limited due to their drug resistance and side effects. Iridium-based compounds have emerged as promising candidates due to their unique chemical properties and resemblance to platinum compounds. The objective of this study is to investigate the synthesis and categorization of iridium complexes, with a particular emphasis on their potential use as anticancer agents. The major focus of this research is to examine the synthesis of these complexes and their relevance to the field of cancer treatment. The negligible side effects and flexibility of cyclometalated iridium(III) complexes have garnered significant interest. Organometallic half-sandwich Ir(III) complexes have notable benefits in cancer research and treatment. The review places significant emphasis on categorizing iridium complexes according to their ligand environment, afterward considering the ligand density and coordination number. This study primarily focuses on several methods for synthesizing cyclometalated and half-sandwich Ir complexes, divided into subgroups based on ligand denticity. The coordination number of iridium complexes determines the number of ligands coordinated to the central iridium atom, which impacts their stability and reactivity. Understanding these complexes is crucial for designing compounds with desired properties and investigating their potential as anticancer agents. Cyclometalated iridium(III) complexes, which contain a meta-cycle with the E-M-C order σ bond, were synthesized in 1999. These complexes have high quantum yields, significant stock shifts, luminescence qualities, cell permeability, and strong photostability. They have been promising in biosensing, bioimaging, and phosphorescence of heavy metal complexes.

3D-Shaped Binders of Unfolded Proteins Inducing Cancer Cell-Specific Endoplasmic Reticulum Stress In Vitro and In Vivo

The amount of unfolded proteins is increased in cancer cells, leading to endoplasmic reticulum (ER) stress. Therefore, cancer cells are sensitive to drugs capable of further enhancing ER stress. Examples of such drugs include the clinically approved proteosome inhibitors bortezomib and carfilzomib. Unfortunately, the known ER stress inducers exhibit dose-limiting side effects that justify the search for better, more cancer-specific drugs of this type. Herein, we report on FeC 2, which binds to unfolded proteins prevents their further processing, thereby leading to ER stress and ROS increase in cancer cells, but not in normal cells. FeC 2 exhibits low micromolar toxicity toward human acute promyelocytic leukemia HL-60, Burkitt's lymphoma BL-2, T-cell leukemia Jurkat, ovarian carcinoma A2780, lung cancer SK-MES-1, and murine lung cancer LLC1 cells. Due to the cancer-specific mode of action, 2 is not toxic in vivo up to the dose of 147 mg/kg, does not affect normal blood and bone marrow cells at the therapeutically active dose, but strongly suppresses both primary tumor growth (confirmed in Nemeth-Kellner lymphoma and LLC1 lung cancer models of murine tumor) and spreading of metastases (LLC1).

Tailoring the π-system of benzimidazole ligands towards stable light-harvesting cyclometalated iridium(III) complexes

The synthesis, structure, optical and redox properties as well as photovoltaic studies of iridium(III) complexes with cyclometalated 2-arylbenzimidazoles decorated with various polyaromatic fragments and an ancillary aromatic β-diketone are reported. Despite the strong preference of the iridium(III) ion to form bis- or tris-cyclometalated complexes in which the metal participates in five-membered metallacycles, the cyclometalation of the benzimidazole ligands containing rigid π-extended systems yields dimeric complexes containing strained five- or six-membered metallacycles and allows for generating an extremely rare monocyclometalated complex. X-ray crystallography shows that the steric strain observed in the dimers is retained in heteroleptic diketonate complexes which is also corroborated by gas-phase DFT calculations. While emission maxima and redox potentials of the heteroleptic complexes exhibit just a moderate variation upon the change of the cyclometalated ligands, the extension of the π-system of the benzimidazole ligands give the complexes remarkable light absorption in the visible spectral range, which meets the requirements for application in dye-sensitized solar cells. At the titania photoanodes, these iridium dyes retain their optical properties and exhibit power conversion efficiencies under standard AM 1.5 G conditions comparable to those of other iridium-based sensitizers. These results demonstrate that the size and position of the π-extended fragment in cyclometalated ligands can modulate not only the electronic structure of the corresponding iridium(III) complexes, but also affect their composition, structure and reactivity that may find implications in future design of emerging iridium dyes, emitters and catalysts.

Synthesis and anticancer mechanisms of zinc(II)-8-hydroxyquinoline complexes with 1,10-phenanthroline ancillary ligands

Twenty new zinc(II) complexes with 8-hydroxyquinoline (H-Q1-H-Q6) in the presence of 1,10-phenanthroline derivatives (D1-D10) were synthesized and formulated as [Zn(Q1)₂(D1)] (DQ1), [Zn(Q2)₂(D2)]·CH₃OH (DQ2), [Zn(Q1)₂(D3)] (DQ3), [Zn(Q1)₂(D4)] (DQ4), [Zn(Q3)₂(D5)] (DQ5), [Zn(Q3)₂(D4)] (DQ6), [Zn(Q4)₂(D5)]·CH₃OH (DQ7), [Zn(Q4)₂(D6)] (DQ8), [Zn(Q4)₂(D3)]·CH₃OH (DQ9), [Zn(Q4)₂(D1)]·H₂O (DQ10), [Zn(Q5)₂(D4)] (DQ11), [Zn(Q6)₂(D6)]·CH₃OH (DQ12), [Zn(Q5)₂(D2)]·5CH₃OH·H₂O (DQ13), [Zn(Q5)₂(D7)]·CH₃OH (DQ14), [Zn(Q5)₂(D8)]·CH₂Cl₂ (DQ15), [Zn(Q5)₂(D9)] (DQ16), [Zn(Q5)₂(D1)] (DQ17), [Zn(Q5)₂(D5)] (DQ18), [Zn(Q5)₂(D10)]·CH₂Cl₂ (DQ19) and [Zn(Q5)₂(D3)] (DQ20). They were characterized using multiple techniques. The cytotoxicity of DQ1-DQ20 was screened using human cisplatin-resistant SK-OV-3/DDP ovarian cancer (SK-OV-3CR) cells and normal hepatocyte (HL-7702) cells. Complex DQ6 showed low IC₅₀ values (2.25 ± 0.13 μM) on SK-OV-3CR cells, more than 3.0-8.0 times more cytotoxic than DQ1-DQ5 and DQ7-DQ20 (≥6.78 μM), and even 22.2 times more cytotoxic than the standard cisplatin, the corresponding free H-Q1-H-Q6 and D1-D10 alone (>50 μM). As a comparison, DQ1-DQ20 displayed nontoxic rates against healthy HL-7702 cells. Furthermore, DQ6 and DQ11 induced significant apoptosis via mitophagy pathways. DQ6 also significantly inhibited tumor growth in an in vivo SK-OV-3-xenograft model (ca. 49.7%). Thus, DQ6 may serve as a lead complex for the discovery of new antitumor agents.

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.

N-Heterocyclic Carbene-Iridium Complexes as Photosensitizers for In Vitro Photodynamic Therapy to Trigger Non-Apoptotic Cell Death in Cancer Cells

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, namely PC-3 (prostate cancer), T24 (bladder cancer), MCF7 (breast cancer), A549 (lung cancer) and HeLa (cervix cancer), and two non-cancerous cell models (NIH-3T3 fibroblasts and MC3T3 osteoblasts). After irradiation at 458 nm, all tested complexes showed a strong selectivity against cancer cells, with a selectivity index (SI) ranging from 8 to 34 compared with non-cancerous cells. The cytotoxic effect of all these complexes was found to be independent of the anti-apoptotic protein Bcl-xL. The compound exhibiting the best selectivity, complex 4a, was selected for further investigations. Complex 4a was mainly localized in the mitochondria. We found that the loss of cell viability and the decrease in ATP and GSH content induced by complex 4a were independent of both Bcl-xL and caspase activation, leading to a non-apoptotic cell death. By counteracting the intrinsic or acquired resistance to apoptosis associated with cancer, complex 4a could be an interesting therapeutic alternative to be studied in preclinical models.

Carrier free nanomedicine to reverse anti-apoptosis and elevate endoplasmic reticulum stress for enhanced photodynamic therapy

As a first studied and generally accepted programmed cell death regulator, Bcl-2 has been identified to overexpress in many types of cancer promoting tumor proliferation and progression. Herein, inspired by drug self-delivery systems, a self-assembled nanomedicine (designated as GosCe) was designed based on the hydrophobic interaction between chlorin e6 (Ce6) and gossypol (Gos). Without extra carriers, GosCe exhibited high drug loading rates, favorable size distribution, and a long-term stability at aqueous phase. More importantly, GosCe could be internalized by tumor cells more effectively than free Ce6, which brought about its multiple toxicity. Upon intravenous injection, GosCe preferred to accumulate in tumor site through enhanced permeability and retention (EPR) effect. After cellular internalization, Gos contributed to increasing the lethality of Ce6-guided photodynamic therapy (PDT) by down-regulating Bcl-2 protein expression and inducing endoplasmic reticulum (ER) stress. Both in vitro and in vivo investigations indicated that the Gos-assisted PDT greatly inhibit cell proliferation and tumor growth. This study might shed light on developing carrier free nanomedicine for PDT-based synergistic tumor therapy. STATEMENT OF SIGNIFICANCE: Metabolic abnormalities of tumor cells create defensive microenvironments which induce a therapeutic resistance against photodynamic therapy (PDT). Among which, the upregulated B-cell lymphoma (Bcl-2) in tumors could inhibit the PDT-induced cell apoptosis. In this work, a self-delivery nanomedicine (GosCe) was developed based on a Bcl-2 inhibitor and photosensitizer through intermolecular interactions, which had favorable size distribution, high drug contents and improved drug delivery efficiency. Importantly, GosCe increased the PDT efficacy by Bcl-2 inhibition and endoplasmic reticulum stress elevation. Thus, GosCe greatly inhibited the tumor growth while caused a reduced side effect in vivo. This carrier free nanomedicine with tumor microenvironment regulation would advance the development of photodynamic nanoplatform in tumor treatment.

Current status of iridium-based complexes against lung cancer

Lung cancer is one of the most common malignant tumors, with the highest mortality rate in the world, and its incidence is second only to breast cancer. It has posed a serious threat to human health. Cisplatin, a metal-based drug, is one of the most widely used chemotherapeutic agents for the treatment of various cancers. However, its clinical efficacy is seriously limited by numerous side effects and drug resistance. This has led to the exploration and development of other transition metal complexes for the treatment of malignant tumors. In recent years, iridium-based complexes have attracted extensive attention due to their potent anticancer activities, limited side effects, unique antitumor mechanisms, and rich optical properties, and are expected to be potential antitumor drugs. In this review, we summarize the recent progress of iridium complexes against lung cancer and introduce their anti-tumor mechanisms, including apoptosis, cycle arrest, inhibition of lung cancer cell migration, induction of immunogenic cell death, etc.

Subcellular delivery of lipid nanoparticles to endoplasmic reticulum and mitochondria

Primarily responsible for the biogenesis and metabolism of biomolecules, endoplasmic reticulum (ER) and mitochondria are gradually becoming the targets of therapeutic modulation, whose physiological activities and pathological manifestations determine the functional capacity and even the survival of cells. Drug delivery systems with specific physicochemical properties (passive targeting), or modified by small molecular compounds, polypeptides, and biomembranes demonstrating tropism for ER and mitochondria (active targeting) are able to reduce the nonselective accumulation of drugs, enhancing efficacy while reducing side effects. Lipid nanoparticles feature high biocompatibility, diverse cargo loading, and flexible structure modification, which are frequently used for subcellular organelle-targeted delivery of therapeutics. However, there is still a lack of systematic understanding of lipid nanoparticle-based ER and mitochondria targeting. Herein, we review the pathological significance of drug selectively delivered to the ER and mitochondria. We also summarize the molecular basis and application prospects of lipid nanoparticle-based ER and mitochondria targeting strategies, which may provide guidance for the prevention and treatment of associated diseases and disorders. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Pancreatic Cancer: Challenges and Opportunities in Locoregional Therapies

Simple Summary

Pancreatic cancer is a serious ongoing global health burden, with an overall 5-year survival rate of less than 5%. One major hurdle in the treatment of this disease is the predominantly elderly patient population, leading to their ineligibility for curative surgery and a low rate of successful outcomes. Systemic administration introduces chemo-agents throughout the body via the blood, attacking not only tumours but also healthy organs. When localised interventions are employed, chemo-agents are retained specifically at tumour site, minimizing unwanted toxicity. As a result, there is a growing interest in finding novel localised interventions as alternatives to systemic therapy. Here, we present a detailed review of current locoregional therapies used in pancreatic cancer therapy. This work aims to present a thorough guide for researchers and clinicians intended to employ established and novel localised interventions in the treatment of pancreatic cancer. Furthermore, we present our insights and opinions on the potential ideals to improve these tools.

Abstract

Pancreatic cancer (PC) remains the seventh leading cause of cancer-related deaths worldwide and the third in the United States, making it one of the most lethal solid malignancies. Unfortunately, the symptoms of this disease are not very apparent despite an increasing incidence rate. Therefore, at the time of diagnosis, 45% of patients have already developed metastatic tumours. Due to the aggressive nature of the pancreatic tumours, local interventions are required in addition to first-line treatments. Locoregional interventions affect a specific area of the pancreas to minimize local tumour recurrence and reduce the side effects on surrounding healthy tissues. However, compared to the number of new studies on systemic therapy, very little research has been conducted on localised interventions for PC. To address this unbalanced focus and to shed light on the tremendous potentials of locoregional therapies, this work will provide a detailed discussion of various localised treatment strategies. Most importantly, to the best of our knowledge, the aspect of localised drug delivery systems used in PC was unprecedentedly discussed in this work. This review is meant for researchers and clinicians considering utilizing local therapy for the effective treatment of PC, providing a thorough guide on recent advancements in research and clinical trials toward locoregional interventions, together with the authors’ insight into their potential improvements.

Recent advances in noble metal complex based photodynamic therapy

Photodynamic therapy (PDT) utilizes light-activated photosensitizers (PSs) to generate toxic species for therapeutics. It has become an emerging solution for cancer treatment because of its specific spatiotemporal selectivity and minimal invasiveness. Noble metal (Ru, Ir and Pt) complexes are of increasing interest as photosensitizers for their excellent photophysical, photochemical, and photobiological properties. In this review, we highlight recent advancements in the development of noble metal complex photosensitizers for PDT during the last 5 years. We will summarize the design strategies of noble metal complexes for efficient and precise PDT, including increasing the light penetration depth, reducing the oxygen-dependent nature and improving target ability. Finally, we summarize recent efforts for the development of noble-based PSs and discuss the limitations of such PSs in clinical application and future perspectives in this field, such as the combination of PDT with other treatment modalities.

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.

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 two-photon fluorescence probe with endoplasmic reticulum targeting ability for turn-on sensing photosensitized singlet oxygen in living cells and brain tissues

Endoplasmic reticulum (ER) is an indispensable organelle responsible for protein synthesis, transportation, and maintenance of Ca²⁺ homeostasis in eukaryotic cells. Recent studies highlighted that ER-targeted photosensitizers with high yield of singlet oxygen (¹O₂) are effective in selectively disrupting ER function and are promising candidates for anticancer therapy. Unfortunately, no ER targetable fluorescent probes for determining ¹O₂ photosensitized in this photodynamic therapy process is available. In this work, we synthesized an ER-targetable, two-photon fluorescence probe, ER-¹O₂, for fluorescence turn-on sensing of ¹O₂. ER-¹O₂ demonstrated high sensitivity to ¹O₂ sensing with a wide detection range (0-2.75 μM) and a low detection limit (0.11 μM). ER-¹O₂ also displayed excellent selectivity toward ¹O₂ out of other ROS and metal ions. Notably, ER-¹O₂ exhibited low cytotoxicity but with specific ER targetable capability. On account of these advantageous features, fluctuations of ¹O₂ in living cells and brain tissues were effectively visualized by ER-¹O₂.

Luminescent Iridium(III) Dipyrrinato Complexes: Synthesis, X-ray Structures, DFT and Photocytotoxicity Studies of Glycosylated Derivatives

A series of luminescent Ir(III) dipyrrinato complexes were synthesized having various aromatic chromophores on the C-5 position of dipyrrin ligand. The presence of different chromophores on the Ir(III) dipyrrinato complexes...

Photosensitized Oxidation of Intracellular Targets: Understanding the Mechanisms to Improve the Efficiency of Photodynamic Therapy

The development of improved photosensitizers is a key aspect in the establishment of photodynamic therapy (PDT) as a reliable treatment modality. In this chapter, we discuss how molecular design can lead to photosensitizers with higher selectivity and better efficiency, with focus on the importance of specific intracellular targeting in determining the cell death mechanism and, consequently, the PDT outcome.

Photodynamic Therapy-Mediated Immune Responses in Three-Dimensional Tumor Models

Photodynamic therapy (PDT) is a promising non-invasive phototherapeutic approach for cancer therapy that can eliminate local tumor cells and produce systemic antitumor immune responses. In recent years, significant efforts have been made in developing strategies to further investigate the immune mechanisms triggered by PDT. The majority of in vitro experimental models still rely on the two-dimensional (2D) cell cultures that do not mimic a three-dimensional (3D) cellular environment in the human body, such as cellular heterogeneity, nutrient gradient, growth mechanisms, and the interaction between cells as well as the extracellular matrix (ECM) and therapeutic resistance to anticancer treatments. In addition, in vivo animal studies are highly expensive and time consuming, which may also show physiological discrepancies between animals and humans. In this sense, there is growing interest in the utilization of 3D tumor models, since they precisely mimic different features of solid tumors. This review summarizes the characteristics and techniques for 3D tumor model generation. Furthermore, we provide an overview of innate and adaptive immune responses induced by PDT in several in vitro and in vivo tumor models. Future perspectives are highlighted for further enhancing PDT immune responses as well as ideal experimental models for antitumor immune response studies.

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.

Innovative strategies for enhanced tumor photodynamic therapy

Photodynamic therapy (PDT) is an approved and promising treatment approach that utilizes a photosensitizer (PS) to produce cytotoxic reactive oxygen species (ROS) through irradiation to achieve tumor noninvasive therapy. However, the limited singlet oxygen generation, the nonspecific uptake of PS in normal cells, and tumor hypoxia have become major challenges in conventional PDT, impeding its development and further clinical application. This review summarizes an overview of recent advances for the enhanced PDT. The development of PDT with innovative strategies, including molecular engineering and heavy atom-free photosensitizers is presented and future directions in this promising field are also provided. This review aims to highlight the recent advances in PDT and discuss the potential strategies that show promise in overcoming the challenges of PDT.

Mitochondria-targeted artesunate conjugated cyclometalated iridium(iii) complexes as potent anti-HepG2 hepatocellular carcinoma agents

Hepatocellular carcinoma (HCC) poses a serious threat to people's health worldwide. Artesunate (ART), one of the classical antimalarial drugs, has recently been shown to exert significant cytotoxicity in various cancers, but its bioavailability is low. Cyclometalated iridium(iii) complexes have emerged as a promising class of anticancer therapeutic agents. Herein, through conjugation of two of them, three novel Ir(iii)-ART conjugates, [Ir(C-N)2(bpy-ART)](PF6) (bpy = 2,2'-bipyridine, C-N = 2-phenylpyridine (ppy, Ir-ART-1), 2-(2-thienyl)pyridine (thpy, Ir-ART-2), and 2-(2,4-difluorophenyl)pyridine (dfppy, Ir-ART-3)) have been synthesized, and their potential as anti-HCC agents was evaluated. We demonstrate that Ir-ART-1-3 display higher cytotoxicity against HCC cell lines than normal liver cells, and they can especially locate to mitochondria of HepG2 cells and induce a series of mitochondria-mediated apoptosis events. Moreover, Ir-ART-1-3 can regulate the cell cycle and inhibit metastasis of HepG2 cells. Finally, in vivo antitumor evaluation also demonstrates the inhibitory activity of Ir-ART-1 on tumor growth. Taken together, these Ir(iii)-ART conjugates have the potential to become drug candidates for future anti-HCC treatments.

Photodynamic Therapy of Inorganic Complexes for the Treatment of Cancer†

Photodynamic therapy (PDT) is a medicinal tool that uses a photosensitizer and a light source to treat several conditions, including cancer. PDT uses reactive oxygen species such as cytotoxic singlet oxygen (¹ O₂ ) to induce cell death in cancer cells. Chemotherapy has historically utilized the cytotoxic effects of many metals, especially transition metal complexes. However, chemotherapy is a systemic treatment so all cells in a patient's body are exposed to the same cytotoxic effects. Transition metal complexes have also shown high cytotoxicity as PDT agents. PDT is a potential localized method for treating several cancer types by using inorganic complexes as photosensitizing agents. This review covers several in vitro and in vivo studies, as well as clinical trials that reported on the anticancer properties of inorganic pharmaceuticals used in PDT against different types of cancer.

Red-Light-Responsive Ru Complex Photosensitizer for Lysosome Localization Photodynamic Therapy

Photoresponsive ruthenium (Ru) complexes have been extensively studied in the photodynamic therapy (PDT) of cancer. The metal-to-ligand charge transfer (MLCT) absorption maximum of most Ru complexes is located in the short-wavelength visible region, which is well suited for superficial tumors but shows inefficient therapeutic effects for more deep-seated ones. Moreover, Ru complexes are primarily located in the mitochondria or nucleus, always resulting in high levels of dark toxicity and DNA mutation. Herein, we reported a new ruthenium complex (Ru-I) for red-light-triggered PDT. The activation wavelength of Ru-I is successfully extended to 660 nm. Importantly, the complex photosensitizer can be quickly taken up by cancer cells and selectively accumulated in the lysosome, an ideal localization for PDT purposes. Intratumoral injection of Ru-I into tumor-bearing mice achieved excellent therapeutic effects and thus holds great promise for applications in lysosome localization photodynamic therapy.

Mitochondria and Endoplastic Reticulum Targeting Strategy for Enhanced Phototherapy

To ensure improved efficacy and minimized toxicity of therapeutic molecules, it is generally accepted that specifically delivering them to the subcellular site of their action will be attractive. Phototherapy has received considerable attention because of its noninvasiveness, high temporal-spatial resolution, and minimal drug resistance. As important functional organelles in cells, mitochondria and endoplasmic reticulum (ER) participate in fundamental cellular processes, which make them much more sensitive to reactive oxygen species (ROS) and hyperthermia. Thus, mitochondria- or ER-targeted phototherapy will be rational strategies for synergetic cancer therapy. In this review, we focus on the latest advances in molecules and nanomaterials currently used for mitochondria- and ER-targeted phototherapy.

Cyclometalated Iridium(III) Complexes as Mitochondria-targeting Photosensitizers against Cisplatin-resistant Cells†

Four iridium (III) complexes Ir1-Ir4 were synthesized and characterized. Possessing high singlet oxygen production ability and specific mitochondria-localization, Ir1 was developed as a mitochondria-targeting photosensitizer. Ir1 exhibited strong phototoxicity against cancer cell line A549 and its corresponding cisplatin-resistant one A549R. In contrast, Ir1 showed low cytotoxicity toward normal cell HLF. This selectivity resulted from the different uptake amount. With 405 nm irradiation, Ir1 induced mitochondria-mediated cell death in A549R cells, achieving the overcome of drug-resistant.

Sterically hindered phenanthroimidazole ligands drive the structural flexibility and facile ligand exchange in cyclometalated iridium(III) complexes

A series of bis-cyclometalated iridium(iii) complexes with 2-arylphenanthroimidazole "antenna" ligands containing electron-donor or withdrawing substituents and a more flexible ancillary aromatic β-diketone bearing the "anchoring" carboxymethyl function has been prepared. Thorough X-ray study of the complexes revealed significant structural strains caused by bulky cyclometalated 2-arylphenanthroimidazoles resulting in dramatic distortions of the iridium octahedron and even in twist of the phenanthrene fragment. The crystal data were corroborated by gas-phase DFT calculations whereby the geometry of the complexes was distorted in the same way. While redox potentials, absorption and emission maxima of the complexes displayed expected change upon the variation of the electron-donating ability of the cyclometalated ligands, the complexes readily exchanged the bidentate ancillary ligand in the presence of a negligible amount of protons that was inspected in solution by UV-Vis spectroscopy. Moreover, after hydrolysis of the carboxymethyl group the resulting complexes readily react with the surface of titanium dioxide giving unique binuclear structures in which the deprotonated carboxy group of the coordinated β-diketonate binds the second bis-cyclometalated unit by forming a four-membered metallacycle. Though the enhanced reactivity of the complexes is contrary to the common idea of the high inertness of iridium(iii) compounds it can be seen as a consequence of the interplay between the steric hindrance induced by the ligands and the strong preference of the iridium(iii) ion for octahedral geometry. This study demonstrates that the use of bulky ligands provides access to light-harvesting iridium(iii) complexes with required extent of lability which may be promising as photocatalysts and biologically active molecules.

Cellular compartments challenged by membrane photo-oxidation

The lipid composition impacts directly on the structure and function of the cytoplasmic as well as organelle membranes. Depending on the type of membrane, specific lipids are required to accommodate, intercalate, or pack membrane proteins to the proper functioning of the cells/organelles. Rather than being only a physical barrier that separates the inner from the outer spaces, membranes are responsible for many biochemical events such as cell-to-cell communication, protein-lipid interaction, intracellular signaling, and energy storage. Photochemical reactions occur naturally in many biological membranes and are responsible for diverse processes such as photosynthesis and vision/phototaxis. However, excessive exposure to light in the presence of absorbing molecules produces excited states and other oxidant species that may cause cell aging/death, mutations and innumerable diseases including cancer. At the same time, targeting key compartments of diseased cells with light can be a promising strategy to treat many diseases in a clinical procedure called Photodynamic Therapy. Here we analyze the relationships between membrane alterations induced by photo-oxidation and the biochemical responses in mammalian cells. We specifically address the impact of photosensitization reactions in membranes of different organelles such as mitochondria, lysosome, endoplasmic reticulum, and plasma membrane, and the subsequent responses of eukaryotic cells.

Enhancing the ROS generation ability of a rhodamine-decorated iridium(iii) complex by ligand regulation for endoplasmic reticulum-targeted photodynamic therapy

The endoplasmic reticulum (ER) is a very important organelle responsible for crucial biosynthetic, sensing, and signalling functions in eukaryotic cells. In this work, we established a strategy of ligand regulation to enhance the singlet oxygen generation capacity and subcellular organelle localization ability of a rhodamine-decorated iridium(iii) complex by variation of the cyclometallating ligand. The resulting metal complex showed outstanding reactive oxygen species generation efficiency (1.6-fold higher than that of rose bengal in CH₃CN) and highly specific ER localization ability, which demonstrated the promise of the metal-based photo-theranostic agent by simultaneously tuning the photochemical/physical and biological properties. Additionally, low dark cytotoxicity, high photostability and selective tumour cell uptake were featured by this complex to demonstrate it as a promising candidate in photodynamic therapy (PDT) applications. In vivo near infrared fluorescence (NIRF) imaging and tumour PDT were investigated and showed preferential accumulation at the tumour site and remarkable tumour growth suppression, respectively.

Cyclometalated Iridium(III) Complexes as High-Sensitivity Two-Photon Excited Mitochondria Dyes and Near-Infrared Photodynamic Therapy Agents

Photodynamic therapy (PDT) using two-photon near-infrared light excitation is a very effective way to avoid the use of short-wavelength ultraviolet or visible light which cannot efficiently penetrate into the biological tissues and is harmful to the healthy cells. Herein, a series of cyclometalated Ir(III) complexes with a structurally simple diimine ligand were designed and the synthetic route and preparation procedure were optimized, so that the complexes could be obtained in apparently higher yield, productivity, and efficiency in comparison to the traditional methods. Their ground state and excited singlet and triplet state properties were studied by spectroscopy and quantum chemistry theoretical calculations to investigate the effect of substituent groups on the photophysical properties of the complexes. The Ir(III) complexes, especially Ir1 and Ir3, showed very low dark toxicities and high phototoxicities under both one-photon and two-photon excitation, indicating their great potential as PDT agents. They were also found to be highly sensitive two-photon mitochondria dyes.

Exploring the In Vivo and In Vitro Anticancer Activity of Rhenium Isonitrile Complexes

The established platinum-based drugs form covalent DNA adducts to elicit their cytotoxic response. Although they are widely employed, these agents cause toxic side-effects and are susceptible to cancer-resistance mechanisms. To overcome these limitations, alternative metal complexes containing the rhenium(I) tricarbonyl core have been explored as anticancer agents. Based on a previous study ( Chem. Eur. J. 2019, 25, 9206), a series of highly active tricarbonyl rhenium isonitrile polypyridyl (TRIP) complexes of the general formula fac-[Re(CO)3(NN)(ICN)]+, where NN is a chelating diimine and ICN is an isonitrile ligand, that induce endoplasmic reticulum (ER) stress via activation of the unfolded protein response (UPR) pathway are investigated. A total of 11 of these TRIP complexes were synthesized, modifying both the equatorial polypyridyl and axial isonitrile ligands. Complexes with more electron-donating equatorial ligands were found to have greater anticancer activity, whereas the axial ICN ligands had a smaller effect on their overall potency. All 11 TRIP derivatives trigger a similar phenotype that is characterized by their abilities to induce ER stress and activate the UPR. Lastly, we explored the in vivo efficacy of one of the most potent complexes, fac-[Re(CO)3(dmphen)(ptolICN)]+ (TRIP-1a), where dmphen = 2,9-dimethyl-1,10-phenanthroline and ptolICN = para-tolyl isonitrile, in mice. The 99mTc congener of TRIP-1a was synthesized, and its biodistribution in BALB/c mice was investigated in comparison to the parent Re complex. The results illustrate that both complexes have similar biodistribution patterns, suggesting that 99mTc analogues of these TRIP complexes can be used as diagnostic partner agents. The in vivo antitumor activity of TRIP-1a was then investigated in NSG mice bearing A2780 ovarian cancer xenografts. When administered at a dose of 20 mg/kg twice weekly, this complex was able to inhibit tumor growth and prolong mouse survival by 150% compared to the vehicle control cohort.

Photodynamic therapy of pancreatic cancer: Where have we come from and where are we going?

Photodynamic therapy (PDT) is a potential adjuvant therapy in pancreatic cancer with several advantages. Mechanistically, pancreatic cancer PDT can induce apoptosis and necrosis of pancreatic cancer cells and lead to vascular damage and enhance anti-tumor immune response in tumor tissues. However, limitations of current photosensitizers such as limited penetration depth, poor targeted therapy and inadequate reactive oxygen species (ROS) generation still exist. Recently, several novel photosensitizers have been reported to break through limits in pancreatic cancer PDT. Methods combined with biomedical engineering, materialogy and chemical engineering have been employed to overcome the difficulties and to realize targeted therapy. Preclinical and clinical trials also preliminarily confirmed the technical feasibility and safety of pancreatic cancer PDT. Therefore, PDT may be potential to be used as an effective adjuvant therapy in pancreatic cancer multimodality therapy. This review will give an overview about pancreatic cancer PDT from basic experimental studies, preclinical and clinical application to future direction of pancreatic cancer PDT.

Dual-Targeted Phototherapeutic Agents as Magic Bullets for Cancer

Imagine the ideal cancer drug that only kills cancer cells and does not affect nearby noncancerous cells. In the words of Paul Ehrlich, the drug acts like a magic bullet. This Topical Review summarizes an emerging new strategy to achieve this audacious goal. The central concept is a dual-targeted phototherapeutic agent for photodynamic or photothermal therapy. The dual-targeted phototherapeutic agent promotes cancer cell specificity by leveraging three levels of selectivity. Cell death will only occur in the anatomical location that is illuminated with light (Selectivity Level 1) and in cancer cells within the illumination area that have selectively accumulated the agent (Selectivity Level 2). The cancer cell killing effect is highly localized if the agent accumulates in hypersensitive intracellular organelles (Selectivity Level 3). The common targeting units for cancer cells and organelles are described, along with recent examples of dual-targeted phototherapeutic agents that incorporate these two classes of targeting units.