Near-infrared absorbing Ru(ii) complexes act as immunoprotective photodynamic therapy (PDT) agents against aggressive melanoma

Intrinsic 77 K Phosphorescence Characteristics and Computational Modeling of Ru(II)-(Bidentate Cyclometalated-Aromatic Ligand) Chromophores: Their Relatively Low Nonradiative Rate Constants Originating from Low Spin-Orbit Coupling Driven Vibronic Coupling Amplitudes between Emitting and Ground States

We investigated the photoinduced relaxation of Kasha-type emitting ruthenium-(bidentate cyclometalated aromatic ligand), Ru-CM, chromophores of [Ru(pzpy)2(CM)]+ ions (CM = 1-phenylisoquinoline, 2,3-diphenylpyrazine, and 1,4-diazatriphenylene and pzpy = 2-pyrazol-1-yl-pyridine). This is the first report of the phosphorescence behavior of pure Ru-(bidentate CM) chromophores. The 77 K photoinduced relaxation characteristics of phosphorescence chromophores showed emission quantum yields higher than those of reference Ru-bpy (bpy = 2,2'-bipyridine) chromophores in the emission region of 670-900 nm. This phenomenon of the Ru-CM chromophores could be attributed to their unusually low magnitudes for 77 K nonradiative rate constants (kNRD), although their radiative rate-constants (kRAD) are not remarkable. In order to examine the 77 K photoinduced behavioral relaxation difference between Ru-CM and Ru-bpy chromophores, we used computational simulation, applying the fundamental formalism of kRAD and temperature-independent kNRD equations, which included calculated spin-orbit coupling values.

Leveraging the Photofunctions of Transition Metal Complexes for the Design of Innovative Phototherapeutics

Despite the advent of various medical interventions for cancer treatment, the disease continues to pose a formidable global health challenge, necessitating the development of new therapeutic approaches for more effective treatment outcomes. Photodynamic therapy (PDT), which utilizes light to activate a photosensitizer to produce cytotoxic reactive oxygen species (ROS) for eradicating cancer cells, has emerged as a promising approach for cancer treatment due to its high spatiotemporal precision and minimal invasiveness. However, the widespread clinical use of PDT faces several challenges, including the inefficient production of ROS in the hypoxic tumor microenvironment, the limited penetration depth of light in biological tissues, and the inadequate accumulation of photosensitizers at the tumor site. Over the past decade, there has been increasing interest in the utilization of photofunctional transition metal complexes as photosensitizers for PDT applications due to their intriguing photophysical and photochemical properties. This review provides an overview of the current design strategies used in the development of transition metal complexes as innovative phototherapeutics, aiming to address the limitations associated with PDT and achieve more effective treatment outcomes. The current challenges and future perspectives on the clinical translation of transition metal complexes are also discussed.

Light enhanced cytotoxicity and antitumoral effect of a ruthenium-based photosensitizer inspired from natural alkaloids

In this work, we report on the synthesis and properties of a new sensitizer for photodynamic therapy applications, constituted by a ruthenium(ii) complex (1) featuring a ligand inspired from natural isoquinoline alkaloids. The spectroscopic analysis revealed that 1 is characterized by an intense red emission (λ em = 620 nm, Φ = 0.17) when excited at 550 nm, a low energy radiation warranting for a safe therapeutic approach. The phototoxicity of 1 on human breast cancer (Hs578T) and melanoma (A375) cell lines was assessed after irradiation using a LED lamp (525 nm, total fluence 10 J cm-2). In vitro biological assays indicated that the cytotoxicity of 1 was significantly enhanced by light reaching IC50 values below the micromolar threshold. The cell damage induced by 1 proved to be strictly connected with the overproduction of reactive oxygen species (ROS) responsible for mitochondrial dysfunction leading to the activation of caspases and then to apoptosis, and for DNA photocleavage leading to cell cycle arrest.

Ruthenium complexes bearing nile red chromophore and one of its derivative: Theoretical evaluation of PDT-related properties

The outcomes of DFT-based calculations are here reported to assess the applicability of two synthesized polypyridyl Ru(II) complexes, bearing ethynyl nile red (NR) on a bpy ligand, and two analogues, bearing modified-NR, in photodynamic therapy. The absorption spectra, together with the non-radiative rate constants for the S1 - Tn intersystem crossing transitions, have been computed for this purpose. Calculations evidence that the structural modification on the chromophore destabilizes the HOMO of the complexes thus reducing the H-L gap and, consequently, red shifting the maximum absorption wavelength within the therapeutic window, up to 620 nm. Moreover, the favored ISC process from the bright state involves the triplet state closest in energy, which is also characterized by the highest SOC value and by the involvement of the whole bpy ligand bearing the chromophore in delocalising the unpaired electrons. These outcomes show that the photophysical behavior of the complexes is dominated by the chromophore.

Dinuclear Tridentate Ru(II) Complex with Strong Near-Infrared Light-Triggered Anticancer Activity

The design of the dinuclear Ru(II) complex (Ru2) with strong near-infrared (NIR) absorption properties has been reported for efficient anticancer phototherapy. Under 700 nm LED light excitation, Ru2 exhibited remarkable synergistic type I/II photosensitization ability and photocatalytic activity toward intracellular biomolecules. Ru2 showed impressive 700 nm light-triggered anticancer activity under normoxia and hypoxia compared with the clinically used photosensitizer Chlorin e6. The mechanistic studies showed that Ru2 induced intracellular redox imbalance and perturbed the energy metabolism and biosynthesis in A549 cancer cells. Overall, this work provides a new strategy for developing efficient metal-based complexes for anticancer phototherapy under NIR light.

The copper (II) complex of salicylate phenanthroline induces immunogenic cell death of colorectal cancer cells through inducing endoplasmic reticulum stress

BACKGROUND

In our previous study, Cu(sal)phen was found to have anti-tumor effects, yet its precise mechanism remains unknown. Research has shown that dying tumor cells release damage-associated molecular patterns (DAMPs) to promote anti-tumor immune response. Therefore, we have further explored the effects and potential molecular mechanisms of Cu(sal)phen-induced immunogenic cell death (ICD) in colorectal cancer (CRC).

METHODS

ELISA and flow cytometry were used to detect the effects of Cu(sal)phen treatment on ICD markers. The molecular mechanisms of Cu(sal)phen-induced ICD were investigated through the detection of endoplasmic reticulum stress (ERS) and reactive oxygen species (ROS) in vitro using Western blot and flow cytometry. Additionally, a mouse model was constructed to study the effects of Cu(sal)phen on immune cells and anti-tumor-related cytokines in vivo.

RESULTS

Cu(sal)phen induced the release of calreticulin (CRT), adenosine triphosphate (ATP) and high mobility group box 1 (HMGB1), the main molecular markers of ICD, by promoting the accumulation of ROS and inducing ERS. Furthermore, Cu(sal)phen promoted the maturation of dendritic cells (DCs) and activation of CD8+T cells, as well as the secretion of interleukin-12 (IL-12) and interferon-γ (IFN-γ), while downregulating transforming growth factor-β (TGF-β) levels, thereby activating the anti-tumor immune response.

CONCLUSION

Cu(sal)phen has the potential to induce ICD in tumors and activate the adaptive immune response to achieve anti-tumor effects. This makes Cu(sal)phen a promising candidate for the treatment of CRC.

Green Light-Triggered Photocatalytic Anticancer Activity of Terpyridine-Based Ru(II) Photocatalysts

The relentless increase in drug resistance of platinum-based chemotherapeutics has opened the scope for other new cancer therapies with novel mechanisms of action (MoA). Recently, photocatalytic cancer therapy, an intrusive catalytic treatment, is receiving significant interest due to its multitargeting cell death mechanism with high selectivity. Here, we report the synthesis and characterization of three photoresponsive Ru(II) complexes, viz., [Ru(ph-tpy)(bpy)Cl]PF6 (Ru1), [Ru(ph-tpy)(phen)Cl]PF6 (Ru2), and [Ru(ph-tpy)(aip)Cl]PF6 (Ru3), where, ph-tpy = 4'-phenyl-2,2':6',2″-terpyridine, bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and aip = 2-(anthracen-9-yl)-1H-imidazo[4,5-f][1,10] phenanthroline, showing photocatalytic anticancer activity. The X-ray crystal structures of Ru1 and Ru2 revealed a distorted octahedral geometry with a RuN5Cl core. The complexes showed an intense absorption band in the 440-600 nm range corresponding to the metal-to-ligand charge transfer (MLCT) that was further used to achieve the green light-induced photocatalytic anticancer effect. The mitochondria-targeting photostable complex Ru3 induced phototoxicity with IC50 and PI values of ca. 0.7 μM and 88, respectively, under white light irradiation and ca. 1.9 μM and 35 under green light irradiation against HeLa cells. The complexes (Ru1-Ru3) showed negligible dark cytotoxicity toward normal splenocytes (IC50s > 50 μM). The cell death mechanistic study revealed that Ru3 induced ROS-mediated apoptosis in HeLa cells via mitochondrial depolarization under white or green light exposure. Interestingly, Ru3 also acted as a highly potent catalyst for NADH photo-oxidation under green light. This NADH photo-oxidation process also contributed to the photocytotoxicity of the complexes. Overall, Ru3 presented multitargeting synergistic type I and type II photochemotherapeutic effects.

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.

Metal-based nanoparticles in cancer therapy: Exploring photodynamic therapy and its interplay with regulated cell death pathways

Photodynamic therapy (PDT) represents a non-invasive treatment strategy currently utilized in the clinical management of selected cancers and infections. This technique is predicated on the administration of a photosensitizer (PS) and subsequent irradiation with light of specific wavelengths, thereby generating reactive oxygen species (ROS) within targeted cells. The cellular effects of PDT are dependent on both the localization of the PS and the severity of ROS challenge, potentially leading to the stimulation of various cell death modalities. For many years, the concept of regulated cell death (RCD) triggered by photodynamic reactions predominantly encompassed apoptosis, necrosis, and autophagy. However, in recent decades, further explorations have unveiled additional cell death modalities, such as necroptosis, ferroptosis, cuproptosis, pyroptosis, parthanatos, and immunogenic cell death (ICD), which helps to achieve tumor cell elimination. Recently, nanoparticles (NPs) have demonstrated substantial advantages over traditional PSs and become important components of PDT, due to their improved physicochemical properties, such as enhanced solubility and superior specificity for targeted cells. This review aims to summarize recent advancements in the applications of different metal-based NPs as PSs or delivery systems for optimized PDT in cancer treatment. Furthermore, it mechanistically highlights the contribution of RCD pathways during PDT with metal NPs and how these forms of cell death can improve specific PDT regimens in cancer therapy.

Ru(II) Phenanthroline-Based Oligothienyl Complexes as Phototherapy Agents

Ru(II) polypyridyl complexes have gained widespread attention as photosensitizers for photodynamic therapy (PDT). Herein, we systematically investigate a series of the type [Ru(phen)2(IP-nT)]2+, featuring 1,10-phenanthroline (phen) coligands and imidazo[4,5-f][1,10]phenanthroline ligands tethered to n = 0-4 thiophene rings (IP-nT). The complexes were characterized and investigated for their electrochemical, spectroscopic, and (photo)biological properties. The electrochemical oxidation of the nT unit shifted by -350 mV as n = 1 → 4 (+920 mV for Ru-1T, +570 mV for Ru-4T); nT reductions were observed in complexes Ru-3T (-2530 mV) and Ru-4T (-2300 mV). Singlet oxygen quantum yields ranged from 0.53 to 0.88, with Ru-3T and Ru-4T being equally efficient (∼0.88). Time-resolved absorption spectra of Ru-0T-1T were dominated by metal-to-ligand charge-transfer (3MLCT) states (τTA = 0.40-0.85 μs), but long-lived intraligand charge-transfer (3ILCT) states were observed in Ru-2T-4T (τTA = 25-148 μs). The 3ILCT energies of Ru-3T and Ru-4T were computed to be 1.6 and 1.4 eV, respectively. The phototherapeutic efficacy against melanoma cells (SK-MEL-28) under broad-band visible light (400-700 nm) increases as n = 0 → 4: Ru-0T was inactive up to 300 μM, Ru-1T-2T were moderately active (EC50 ∼ 600 nM, PI = 200), and Ru-3T (EC50 = 57 nM, PI > 1100) and Ru-4T (EC50 = 740 pM, PI = 114,000) were the most phototoxic. The activity diminishes with longer wavelengths of light and is completely suppressed for all complexes except Ru-3T and Ru-4T in hypoxia. Ru-4T is the more potent and robust PS in 1% O2 over seven biological replicates (avg EC50 = 1.3 μM, avg PI = 985). Ru-3T exhibited hypoxic activity in five of seven replicates, underscoring the need for biological replicates in compound evaluation. Singlet oxygen sensitization is likely responsible for phototoxic effects of the compounds in normoxia, but the presence of redox-active excited states may facilitate additional photoactive pathways for complexes with three or more thienyl groups. The 3ILCT state with its extended lifetime (30-40× longer than the 3MLCT state for Ru-3T and Ru-4T) implicates its predominant role in photocytotoxicity.

Light dose effect of photodynamic therapy on growth inhibition and apoptosis induction in non-small cell lung cancer: A study in nude mouse model

BACKGROUND

Photodynamic therapy (PDT) is receiving increasing attention in treating non-small cell lung cancer (NSCLC) worldwide, but in clinical practice, the relationship between treatment effect and PDT light dose in NSCLC remains unclear. Therefore, we aimed to determine the optimal light dose for PDT by exploring molecular biomarkers and evaluating tumor growth data.

METHODS

We applied bioinformatics to identify promising genes and pathways in NSCLC and PDT. Then, the human lung adenocarcinoma cell line A549-bearing BALB/c nude mice were treated with hematoporphyrin derivative (HPD, 3 mg/kg) that is currently used widely for lung cancer treatment in the world even with photosensitization issues. After 48 h, tumor-bearing mice were irradiated superficially at doses of 100, 200, 300, 400, and 500 J/cm2. The tumor growth data and apoptotic molecules were assessed and calculated.

RESULTS

Bioinformatics results indicated that the apoptosis pathway was significantly enriched and caspase 3 was the most promising biomarker on prognosis in NSCLC-PDT. Compared to the untreated group, there was no difference in the relative tumor volume (RTV) of the 100 J/cm2 group, while the RTV of the other treatment groups (200-500 J/cm2) was significantly lower. In the 100 J/cm2 group, there were significant differences in the complete remission (CR, 0 %) and the percentage of tumor growth inhibition rate (TGI%) over 75 % (20 %) compared with the other treatment groups, especially the 300 and 400 J/cm2 groups (CR 70 %; TGI% 90 %). In the 300 and 400 J/cm2 groups, the expression of caspase 3, cleaved-caspase 3, PARP1, and Bax was increased significantly, while Bcl-2 expression was significantly lower.

CONCLUSIONS

Moderate doses of PDT (300 or 400 J/cm2) are more effective than low (100 or 200 J/cm2) or high doses (500 J/cm2) in the A549 tumor-bearing mice model. Since the A549 tumor is more akin to human tumors in pathological behavior, these experimental data may contribute to improving HPD-PDT illumination protocols for favorable clinical outcomes.

Ruthenium(II) Polypyridyl-Based Photocages for an Anticancer Phytochemical Diallyl Sulfide: Comparative Dark and Photoreactivity Studies of Caged and Precursor Uncaged Complexes

The spatiotemporal control over the drug's action offered by ruthenium(II) polypyridyl complexes by the selective activation of the prodrug inside the tumor has beaconed toward much-desired selectivity issues in cancer chemotherapy. The photocaging of anticancer bioactive ligands attached synergistically with cytotoxic Ru(II) polypyridyl cores and selective release thereof in cancer cells are a promising modality for more effective drug action. Diallyl sulfide (DAS) naturally found in garlic has anticancer, antioxidant, and anti-inflammatory activities. Herein, we designed two Ru(II) polypyridyl complexes to cage DAS having a thioether-based donor site. For in-depth photocaging studies, we compared the reactivity of the DAS-caged compounds with the uncaged Ru(II)-complexes with the general formula [Ru(ttp)(NN)(L)]+/2+. Here, in the first series, ttp = p-tolyl terpyridine, NN = phen (1,10-phenanthroline), and L = Cl- (1-Cl) and H2O (1-H2O), while for the second series, NN = dpq (pyrazino[2,3-f][1,10]phenanthroline), and L = Cl- (2-Cl) and H2O (2-H2O). The reaction of DAS with 1-H2O and 2-H2O yielded the caged complexes [Ru(ttp)(NN)(DAS)](PF6)2, i.e., 1-DAS and 2-DAS, respectively. The complexes were structurally characterized by X-ray crystallography, and the solution-state characterization was done by 1H NMR and ESI-MS studies. Photoinduced release of DAS from the Ru(II) core was monitored by 1H NMR and UV-vis spectroscopy. When irradiated with a 470 nm blue LED in DMSO, the photosubstitution quantum yields (Φ) of 0.035 and 0.057 were observed for 1-DAS and 2-DAS, respectively. Intriguing solution-state speciation and kinetic behaviors of the uncaged and caged Ru(II)-complexes emerged from 1H NMR studies in the dark, and they are depicted in this work. The caged 1-DAS and 2-DAS complexes remained mostly structurally intact for a reasonably long period in DMSO. The uncaged 1-Cl and 2-Cl complexes, although did not undergo substitution in only DMSO but in the 10% DMSO/H2O mixture, completely converted to the corresponding DMSO-adduct within 16 h. Toward gaining insights into the reactivity with the biological targets, we observed that 1-Cl upon hydrolysis formed an adduct with 5'-GMP, while a small amount of GSSG-adduct was observed when 1-Cl was reacted with GSH in H2O at 323 K. 1-Cl after hydrolysis reacted with l-methionine, although the rate was slightly slower compared with that with DMSO, suggesting varying reaction kinetics with different sulfur-based linkages. Although 1-H2O reacted with sulfoxide and thioether ligands at room temperature, the rate was much faster at higher temperatures obviously, and thiol-based systems needed higher thermal energy for conjugation. Overall, these studies provide insight for thoughtful design of new generation Ru(II) polypyridyl complexes for caging suitable bioactive organic molecules.

Ru(II)-Cyanine Complexes as Promising Photodynamic Photosensitizers for the Treatment of Hypoxic Tumours with Highly Penetrating 770 nm Near-Infrared Light

Light-activated treatments, such as photodynamic therapy (PDT), provide temporal and spatial control over a specific cytotoxic response by exploiting toxicity differences between irradiated and dark conditions. In this work, a novel strategy for developing near infrared (NIR)-activatable Ru(II) polypyridyl-based photosensitizers (PSs) was successfully developed through the incorporation of symmetric heptamethine cyanine dyes in the metal complex via a phenanthrimidazole ligand. Owing to their strong absorption in the NIR region, the PSs could be efficiently photoactivated with highly penetrating NIR light (770 nm), leading to high photocytotoxicities towards several cancer cell lines under both normoxic and hypoxic conditions. Notably, our lead PS (Ru-Cyn-1), which accumulated in the mitochondria, exhibited a good photocytotoxic activity under challenging low-oxygen concentration (2 % O2 ) upon NIR light irradiation conditions (770 nm), owing to a combination of type I and II PDT mechanisms. The fact that the PS Protoporphyrin IX (PpIX), the metabolite of the clinically approved 5-ALA PS, was found inactive under the same challenging conditions positions Ru-Cyn-1 complex as a promising PDT agent for the treatment of deep-seated hypoxic tumours.

Ru(ii)/Os(ii)-based carbonic anhydrase inhibitors as photodynamic therapy photosensitizers for the treatment of hypoxic tumours

Photodynamic therapy (PDT) is a medical technique for the treatment of cancer. It is based on the use of non-toxic molecules, called photosensitizers (PSs), that become toxic when irradiated with light and produce reactive oxygen specious (ROS) such as singlet oxygen (1O2). This light-induced toxicity is rather selective since the physician only targets a specific area of the body, leading to minimal side effects. Yet, a strategy to improve further the selectivity of this medical technique is to confine the delivery of the PS to cancer cells only instead of spreading it randomly throughout the body prior to light irradiation. To address this problem, we present here novel sulfonamide-based monopodal and dipodal ruthenium and osmium polypyridyl complexes capable of targeting carbonic anhydrases (CAs) that are a major target in cancer therapy. CAs are overexpressed in the membrane or cytoplasm of various cancer cells. We therefore anticipated that the accumulation of our complexes in or outside the cell prior to irradiation would improve the selectivity of the PDT treatment. We show that our complexes have a high affinity for CAs, accumulate in cancer cells overexpressing CA cells and importantly kill cancer cells under both normoxic and hypoxic conditions upon irradiation at 540 nm. More importantly, Os(ii) compounds still exhibit some phototoxicity under 740 nm irradiation under normoxic conditions. To our knowledge, this is the first description of ruthenium/osmium-based PDT PSs that are CA inhibitors for the selective treatment of cancers.

Imidazolium-Based Heavy-Atom-Free Photosensitizer for Nucleus-Targeted Fluorescence Bioimaging and Photodynamic Therapy

The development of heavy-atom-free photosensitizers (PSs) for photodynamic therapy (PDT) has encountered significant challenges in achieving simultaneous high fluorescence emission and reactive oxygen species (ROS) generation. Moreover, the limited water solubility of these PSs imposes further limitations on their biomedical applications. To overcome these obstacles, this study presents a molecular design strategy employing hydrophilic heavy-atom-free PSs based on imidazolium salts. The photophysical properties of these PSs were comprehensively investigated through a combination of experimental and theoretical analyses. Notably, among the synthesized PSs, the ethylcarbazole-naphthoimidazolium (NI-Cz) conjugate exhibited efficient fluorescence emission (ΦF = 0.22) and generation of singlet oxygen (ΦΔ = 0.49), even in highly aqueous environments. The performance of NI-Cz was validated through its application in fluorescence bioimaging and PDT treatment in HeLa cells. Furthermore, NI-Cz holds promise for two-photon excitation and type I ROS generation, nucleus localization, and selective activity against Gram-positive bacteria, thereby expanding its scope for the design of heavy-atom-free PSs and phototheranostic applications.

Study on antitumor activity of three ruthenium arene complexes in vitro

Three ruthenium arene complexes, namely {[(η6-p-cymene)Ru(Cl)]2(dpb)}(PF6)2 (1), [(η6-p-cymene)Ru(dpb)Cl](PF6) (2) and [(η6-p-cymene) Ru(dpb)py](PF6) (3) (dpb = 2,3-bis(2-pyridyl)benzo-quinoxaline, py = pyridine), were synthesized and their antitumor properties were introduced. Complexes 1-3 were characterized by 1H NMR, MS, and elemental analysis. As a binuclear ruthenium structure, the absorption of metal ligand electron transfer (MLCT) of 1 extended to 700 nm. Complex 1 was significantly hydrolyzed under dark conditions. The cytotoxicity in vitro study showed that complexes 1 and 2 are more toxic to human lung cancer cells (A549) and human cervial cancer cells (Hela) than cisplatin. Moreover, there was almost no cross-resistance between complex 1-2 and cisplatin. Under the irradiation at 478 nm, complexes 1-3 all produced singlet oxygen (1O2), and the 1O2 quantum yield of complex 1 in PBS is the highest among complexes 1-3. Complex 1 also produced 1O2 under 600 nm light irradiation. DNA gel electrophoresis showed that 1 caused the photocleavage of plasmid DNA. The hydrolysis rate of complex 1 was accelerated under light (λ > 600 nm). And the phototoxicity of complex 1 to Hela cells under light (λ > 600 nm) was much greater than its dark toxicity, which may be due to its generation of 1O2 and the promotion of its hydrolysis under long-wave light irradiation.

Synthesis, characterization, molecular docking, RNA-sequence and anticancer efficacy evaluation in vitro of ruthenium(II) complexes on B16 cells

In recent years, the studies of the ruthenium(II) complexes on anticancer activity have been paid great attention, many Ru(II) complexes possess high anticancer efficiency. In this paper, three ligands CPIP (2-(4-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), DCPIP (2-(3,4-dichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), TCPIP (2-(2,3,5-trichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and their three ruthenium (II) complexes [Ru(dip)2(CPIP)](PF6)2 (1, dip = 4,7-diphenyl-1,10-phenanthroline), [Ru(dip)2(DCPIP)](PF6)2 (2) and [Ru(dip)2(TCPIP)](PF6)2 (3) were synthesized and characterized. 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) assay was used to investigate in vitro cytotoxicity of complexes against various cancer cells. The results showed that complexes 1-3 exhibited pronounced cytotoxic effect on B16 cells with low IC50 values of 7.2 ± 0.1, 11.7 ± 0.6 and 1.2 ± 0.2 μM, respectively. The 3D model demonstrated that the complexes can validly prevent the cell proliferation. Apoptosis determined using Annexin V-FITC/PI double staining revealed that complexes 1-3 can effectively induce apoptosis in B16 cells. The intracellular localization of 1-3 in the mitochondria, the levels of intracellular reactive oxygen species (ROS), the opening of mitochondrial permeability transition pore as well as the decline of mitochondrial membrane potential were investigated, which demonstrated that the complexes 1-3 led to apoptosis via a ROS-mediated mitochondrial dysfunction pathway. The RNA-sequence indicated that the complexes upregulate the expression of 74 genes and downregulate the expression of 81 genes. The molecular docking showed that the complexes interact with the proteins through hydrogen bond, π-cation and π-π interaction. The results show that ruthenium(II) complexes 1, 2 and 3 can block tumor cell growth and induce cell death through autophagy and ROS-mediated mitochondrial dysfunction pathways.

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

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

Metal-Based Photosensitizers as Inducers of Regulated Cell Death Mechanisms

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

A Half-Sandwich Ruthenium(II) (N^N) Complex: Inducing Immunogenic Melanoma Cell Death in Vitro and in Vivo

Efficacy of clinical chemotherapeutic agents depends not only on direct cytostatic and cytotoxic effects but also involves in eliciting (re)activation of tumour immune effects. One way to provoke long-lasting antitumour immunity is coined as immunogenic cell death (ICD), exploiting the host immune system against tumour cells as a "second hit". Although metal-based antitumour complexes hold promise as potential chemotherapeutic agents, ruthenium (Ru)-based ICD inducers remain sparse. Herein, we report a half-sandwich complex Ru(II) bearing aryl-bis(imino) acenaphthene chelating ligand with ICD inducing properties for melanoma in vitro and in vivo. Complex Ru(II) displays strong anti-proliferative potency and potential cell migration inhibition against melanoma cell lines. Importantly, complex Ru(II) drives the multiple biochemical hallmarks of ICD in melanoma cells, i. e., the elevated expression of calreticulin (CRT), high mobility group box 1 (HMGB1), Hsp70 and secretion of ATP, followed by the decreased expression of phosphorylation of Stat3. In vivo the inhibition of tumour growth in prophylactic tumour vaccination model further confirms that mice with complex Ru(II)-treated dying cells lead to activate adaptive immune responses and anti-tumour immunity by the activation of ICD in melanoma cells. Mechanisms of action studies show that complex Ru(II)-induced ICD could be associated with mitochondrial damage, ER stress and impairment of metabolic status in melanoma cells. We believe that the half-sandwich complex Ru(II) as an ICD inducer in this work will help to design new half-sandwich Ru-based organometallic complexes with immunomodulatory response in melanoma treatments.

Near-infrared metal agents assisting precision medicine: from strategic design to bioimaging and therapeutic applications

Metal agents have made incredible strides in preclinical research and clinical applications in recent years, but their short emission/absorption wavelengths continue to be a barrier to their distribution, therapeutic action, visual tracking, and efficacy evaluation. Nowadays, the near-infrared window (NIR, 650-1700 nm) provides a more accurate imaging and treatment option. Thus, there has been ongoing research focusing on developing multifunctional NIR metal agents for imaging and therapy that have deeper tissue penetration. The design, characteristics, bioimaging, and therapy of NIR metal agents are covered in this overview of papers and reports published to date. To start with, we focus on describing the structure, design strategies, and photophysical properties of metal agents from the NIR-I (650-1000 nm) to NIR-II (1000-1700 nm) region, in order of molecular metal complexes (MMCs), metal-organic complexes (MOCs), and metal-organic frameworks (MOFs). Next, the biomedical applications brought by these superior photophysical and chemical properties for more accurate imaging and therapy are discussed. Finally, we explore the challenges and prospects of each type of NIR metal agent for future biomedical research and clinical translation.

Computational Assessment of a Dual-Action Ru(II)-Based Complex: Photosensitizer in Photodynamic Therapy and Intercalating Agent for Inducing DNA Damage

A combined quantum-mechanical and classical molecular dynamics study of a recent Ru(II) complex with potential dual anticancer action is reported here. The main basis for the multiple action relies on the merocyanine ligand, whose electronic structure allows the drug to be able to absorb within the therapeutic window and in turn efficiently generate ¹O₂ for photodynamic therapy application and to intercalate within two nucleobases couples establishing reversible electrostatic interactions with DNA. TDDFT outcomes, which include the absorption spectrum, triplet states energy, and spin-orbit matrix elements, evidence that the photosensitizing activity is ensured by an MLCT state at around 660 nm, involving the merocyanine-based ligand, and by an efficient ISC from such state to triplet states with different characters. On the other hand, the MD exploration of all the possible intercalation sites within the dodecamer B-DNA evidences the ability of the complex to establish several electrostatic interactions with the nucleobases, thus potentially inducing DNA damage, though the simulation of the absorption spectra for models extracted by each MD trajectory shows that the photosensitizing properties of the complex remain unaltered. The computational results support that the anti-tumor effect may be related to multiple mechanisms of action.

Recent Progress in Photodynamic Immunotherapy with Metal-Based Photosensitizers

Cancer ranks as a leading cause of death. There is an urgent need to develop minimally invasive methods to eradicate tumors and prevent their recurrence. As a light-driven modality, photodynamic therapy takes advantage of high tumor selectivity and low normal tissue damage. However, it shows poor potential for preventing tumor recurrence. Immunotherapy is currently being used as an alternative treatment for the control of malignant diseases. Although immunotherapy can establish long-time immune memory and efficiently protects treated patients from cancer relapse, its clinical efficacy is limited by the minority of patients' responding rate. Recently, photodynamic immunotherapy, which utilizes photosensitizers as an immunotherapy trigger to exert synergistic effects of photodynamic therapy and tumor immunotherapy, has attracted considerable interest. Like all the newly proposed treatments, there is still room for improvement. In this mini review, the progress in photodynamic immunotherapy with metal-based photosensitizers is summarized. It is hoped that this review can give a broad update on photodynamic immunotherapy and inspire readers.

Synthesis, RNA-sequence and evaluation of anticancer efficacy of ruthenium(II) polypyridyl complexes toward HepG2 cells

In this article, four new Ru(II) complexes [Ru(dmbpy)₂(TFBIP)](PF₆)₂ (dmbpy = 4,4'-dimethyl-2,2'-bipyridine, TFPIP = 2-(4'-trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) (Ru1), [Ru(bpy)₂(TFBIP)](PF₆)₂ (bpy = 2,2'-bipyridine) (Ru2), [Ru(phen)₂(TFBIP)](PF₆)₂ (phen = 1,10-phenanthroline) (Ru3) and [Ru(dmp)₂(TFBIP)](PF₆)₂ (dmp = 2,9-dimethyl-1,10-phenanthroline) (Ru4) were synthesized and characterized by elemental analysis, HRMS, IR, ¹H NMR, ¹³C NMR and ¹⁹F NMR. The in vitro anticancer effect of the complexes on HepG2, A549, B16, HeLa, BEL-7402 and non-cancer LO2 cells was screened using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method. The results illustrate that the complexes display moderate anticancer activity. Apoptotic assay with Annexin V/PI double staining method indicated that complexes induce apoptosis in HepG2 cells. Also, the complexes interfere with the mitochondrial functions, accompanied by the production of intracellular ROS as well as a reduction of mitochondrial membrane potential. The results obtained from the western blot demonstrated that the complexes upregulate pro-apoptotic Bax and downregulate anti-apoptotic Bcl-2, which further activates caspase 3 and promotes the cleavage of PARP. RNA-sequence showed that the complexes upregulate the expression of 40 genes and downregulate 66 genes. Antitumour in vivo demonstrated that Ru1 inhibits the tumor growth with a high inhibitory rate of 51.19%. Taken together, these results revealed that complexes Ru1, Ru2, Ru3 and Ru4 induce cell death in HepG2 cells via autophagy and a ROS-mediated mitochondrial apoptotic pathway.

Low-Temperature Observation of the Excited-State Decay of Ruthenium-(Mono-2,2':6',2″-Terpyridine) Ions with Innocent Ligands: DFT Modeling of an 3MLCT-3MC Intersystem Crossing Pathway

The synthesis, electrochemistry, and photophysical characterization of five 2,2':6',2″-terpyridine ruthenium complexes (Ru-tpy complexes) is reported. The electrochemical and photophysical behavior varied depending on the ligands, i.e., amine (NH₃), acetonitrile (AN), and bis(pyrazolyl)methane (bpm), for this series of Ru-tpy complexes. The target [Ru(tpy)(AN)₃]²⁺ and [Ru(tpy)(bpm)(AN)]²⁺ complexes were found to have low-emission quantum yields in low-temperature observations. To better understand this phenomenon, density functional theory (DFT) calculations were performed to simulate the singlet ground state (S₀), T_e, and metal-centered excited states (³MC) of these complexes. The calculated energy barriers between T_e and the low-lying ³MC state for [Ru(tpy)(AN)₃]²⁺ and [Ru(tpy)(bpm)(AN)]²⁺ provided clear evidence in support of their emitting state decay behavior. Developing a knowledge of the underlying photophysics of these Ru-tpy complexes will allow new complexes to be designed for use in photophysical and photochemical applications in the future.

Anticancer Screening of Ru(II) Photoredox Catalysts at Single Cancer Cell Level

The rapid efflux of Pt-based chemotherapeutics by cancer cells is one of the major causes of drug resistance in clinically available drugs. Therefore, both the high cellular uptake as well as adequate retention efficiency of an anticancer agent are important factors to overcome drug resistance. Unfortunately, rapid and efficient quantification of metallic drug concentration in individual cancer cells still remains a tricky problem. Herein, with the help of newly developed single cell inductively coupled plasma mass spectrometry (SC-ICP-MS), we have found that the well-known Ru(II)-based complex, Ru3, displayed remarkable intracellular uptake and retention efficiency in every single cancer cell with high photocatalytic therapeutic activity to overcome cisplatin resistance. Moreover, Ru3 has shown sensational photocatalytic anticancer properties with excellent in-vitro and in-vivo biocompatibility under light exposure.

Heteronuclear Ru(II)-Re(I) complexes as potential photodynamic anticancer agents with anti-metastatic and anti-angiogenic activities

Herein, three heterometallic Ru(II)-Re(I) complexes, [Ru(NN)₂(tpphz)Re(CO)₃Cl](PF₆)₂ (N-N = 2,2'-bipyridine (bpy, in RuRe1), 1,10-phenanthroline (phen, in RuRe2), 4,7-diphenyl-1,10-phenanthroline (DIP, in RuRe3), tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2″',3″'-j]phenazine), using tpphz as a bridging ligand to connect Ru(II) polypyridyl moiety and Re(I) tricarbonyl moiety were designed and synthesized. Cytotoxicity tests revealed that RuRe1-3 exhibited high phototoxicities against several cancer cell lines tested, with IC₅₀ values ranging from 0.8 to 6.8 μM. Notably, RuRe2 exhibited the most significant increase in cytotoxicity against human prostate cancer (PC3) cells under light (450 nm) irradiation, with phototoxicity index (PI) value increasing by >112.3-fold. Further mechanistic studies of RuRe2 revealed that RuRe2-mediated PDT could induce tumor cell apoptosis through the mitochondrial pathway. Moreover, RuRe2-mediated PDT could inhibit PC3 cell scratch healing and reduce the expression levels of matrix metalloproteinases 2 (MMP-2), matrix metalloproteinases 9 (MMP-9) and vascular endothelial growth factor receptor VEGFR2. Finally, angiogenic activity assays performed in human umbilical vein endothelial cells (HUVECs) showed that RuRe2 exerted an anti-angiogenesis effect. Our study demonstrated that RuRe1-3 were promising PDT antitumor agents with potential anti-metastatic and anti-angiogenic activities.

Establishing a Robust and Reliable Response from a Potent Osmium-Based Photosensitizer Via Lipid Nanoformulation†

Osmium (Os) based photosensitizers (PSs) are a unique class of nontetrapyrrolic metal-containing PSs that absorb red light. We recently reported a highly potent Os(II) PS, rac-[Os(phen)2 (IP-4T)](Cl)2 , referred to as ML18J03 herein, with light EC50 values as low as 20 pm. ML18J03 also exhibits low dark toxicity and submicromolar light EC50 values in hypoxia in some cell lines. However, owing to its longer oligothiophene chain, ML18J03 is not completely water soluble and forms 1-2 μm sized aggregates in PBS containing 1% DMSO. This aggregation causes variability in PDT efficacy between assays and thus unreliable and irreproducible reports of in vitro activity. To that end, we utilized PEG-modified DPPC liposomes (138 nm diameter) and DSPE-mPEG2000 micelles (10.2 nm diameter) as lipid nanoformulation vehicles to mitigate aggregation of ML18J03 and found that the spectroscopic properties important to biological activity were maintained or improved. Importantly, the lipid formulations decreased the interassay variance between the EC50 values by almost 20-fold, with respect to the unformulated ML18J03 when using broadband visible light excitation (P = 0.0276). Herein, lipid formulations are presented as reliable platforms for more accurate in vitro photocytotoxicity quantification for PSs prone to aggregation (such as ML18J03) and will be useful for assessing their in vivo PDT effects.

Immunogenic Cell Death Inducing Metal Complexes for Cancer Therapy

Cancer is one of the deadliest diseases worldwide. Recent statistics have shown that metastases and tumor relapse are the leading causes of cancer-associated deaths. While traditional treatments are able to efficiently remove the primary tumor, secondary tumors remain poorly accessible. Capitalizing on this there is an urgent need for novel treatment modalities. Among the most promising approaches, increasing research interest has been devoted to immunogenic cell death inducing agents that are able to trigger localized cell death of the cancer cells as well as induce an immune response inside the whole organism. Preliminary studies have shown that immunogenic cell death inducing compounds could be able to overcome metastatic and relapsing tumors. Herein, the application of metal complexes as immunogenic cell death inducing compounds is systematically reviewed.

Towards Selective Delivery of a Ruthenium(II) Polypyridyl Complex-Containing Bombesin Conjugate into Cancer Cells

An increasing number of novel Ru(II) polypyridyl complexes have been successfully applied as photosensitizers (PSs) for photodynamic therapy (PDT). Despite recent advances in optimized PSs with refined photophysical properties, the lack of tumoral selectivity is often a major hurdle for their clinical development. Here, classical maleimide and versatile NHS-activated acrylamide strategies were employed to site-selectively conjugate a promising Ru(II) polypyridyl complex to the N-terminally Cys-modified Bombesin (BBN) targeting unit. Surprisingly, the decreased cell uptake of these novel Ru-BBN conjugates in cancer cells did not hamper the high phototoxic activity of the Ru-containing bioconjugates and even decreased the toxicity of the constructs in the absence of light irradiation. Overall, although deceiving in terms of selectivity, our new bioconjugates could still be useful for advanced cancer treatment due to their nontoxicity in the dark.

A mitochondria-localized iridium(iii) photosensitizer for two-photon photodynamic immunotherapy against melanoma

Conventional photodynamic therapy mainly causes a therapeutic effect on the primary tumor through the localized generation of reactive oxygen species, while metastatic tumors remain poorly affected. Complementary immunotherapy is effective in eliminating small, non-localized tumors distributed across multiple organs. Here, we report the Ir(iii) complex Ir-pbt-Bpa as a highly potent immunogenic cell death inducing photosensitizer for two-photon photodynamic immunotherapy against melanoma. Ir-pbt-Bpa can produce singlet oxygen and superoxide anion radicals upon light irradiation, causing cell death by a combination of ferroptosis and immunogenic cell death. In a mouse model with two physically separated melanoma tumors, although only one of the primary tumors was irradiated, a strong tumor reduction of both tumors was observed. Upon irradiation, Ir-pbt-Bpa not only induced the immune response of CD8+ T cells and the depletion of regulatory T cells, but also caused an increase in the number of the effector memory T cells to achieve long-term anti-tumor immunity.

Quaternary Ru(II) complexes of terpyridines, saccharin and 1,2-azoles: effect of substituents on molecular structure, speciation, photoactivity, and photocytotoxicity

Six photoactive ruthenium quaternary complexes (a four-component system consisting of three different N-donor ligands and Ru(II)): trans-[Ru(R-tpy)(pyz/ind)(sac)₂] (1-6) containing substituted terpyridine (R-tpy), saccharin (sac), and monodentate N-donor heterocycles were designed. Here, R-tpy = 4'-(2-furyl (1, 2); thienyl (3, 4); pyridyl (5, 6))-2,2':6',2'' terpyridines, pyz = 1H-pyrazole for 1, 3 and 5 and ind = 1H-indazole for 2, 4 and 6. The azoles are present in a large number of FDA-approved clinical drugs and bioactive molecules. The saccharin acting as a carbonic anhydrase inhibitor (CA-IX) could potentially target aggressive hypoxic tumors that overexpress CA-IX. Such multi-functional ligands bound to a Ru(II)-photocage provide ample scope to tune the electronic structures, photochemistry, and synergistic effect of the photolabile ligands in photoactivated chemotherapy (PACT). The complexes were characterized using various spectroscopic studies, and the molecular structures were determined from X-ray crystallography. They exhibit a distorted octahedral {RuN₆} geometry with equatorial sites coordinated to the tridentate N₃-donor R-tpy and N-donor pyz/ind, while two transoidal axial sites bound to the N-donor saccharinate (sac) ligands. The solvolysis kinetics showed these complexes undergo facile ligand-exchange reactions in equilibrium with varying rates reflecting the possible electronic effect of the R-groups in R-tpy. The photoreactivity of the complexes in green (λ_ex = 530 nm) LED light indicates that the complexes undergo photodissociation of the monodentate N-donors (i.e., sac/pyz/ind) and showed an efficient generation of singlet oxygen (Φ_1O2 = 0.29-0.47), signifying the potential of these complexes in PACT and/or PDT. All the complexes show good binding affinity with CT-DNA with possible intercalation from extended planar polypyridyl ligands with duplex DNA and BSA. The synchronous fluorescence study with BSA suggested preferential interaction at the tryptophan residue in the protein microenvironment. The confocal microscopy studies showed adequate permeability and localization in the cytosol and nucleus of cervical cancer (HeLa) and breast cancer (MCF7) cells. The dose-dependent cytotoxicity of the complexes for both HeLa and MCF7 cells increases upon low-energy (365 nm) photoirradiation. The mechanistic studies revealed that the complexes induce apoptosis and generate reactive oxygen species (ROS) upon green light (λ_ex = 530 nm) irradiation. Overall, these quaternary Ru(II) complexes equipped with three different types of ligands with distinct roles could pave the way for designing multi-targeted chemotherapeutic metallodrugs with synergistic roles for each bioactive ligand.

Ru(II) CONTAINING PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY: A CRITIQUE ON REPORTING AND AN ATTEMPT TO COMPARE EFFICACY

Ruthenium(II)-based coordination complexes have emerged as photosensitizers (PSs) for photodynamic therapy (PDT) in oncology as well as antimicrobial indications and have great potential. Their modular architectures that integrate multiple ligands can be exploited to tune cellular uptake and subcellular targeting, solubility, light absorption, and other photophysical properties. A wide range of Ru(II) containing compounds have been reported as PSs for PDT or as photochemotherapy (PCT) agents. Many studies employ a common scaffold that is subject to systematic variation in one or two ligands to elucidate the impact of these modifications on the photophysical and photobiological performance. Studies that probe the excited state energies and dynamics within these molecules are of fundamental interest and are used to design next-generation systems. However, a comparison of the PDT efficacy between Ru(II) containing PSs and 1st or 2nd generation PSs, already in clinical use or preclinical/clinical studies, is rare. Even comparisons between Ru(II) containing molecular structures are difficult, given the wide range of excitation wavelengths, power densities, and cell lines utilized. Despite this gap, PDT dose metrics quantifying a PS's efficacy are available to perform qualitative comparisons. Such models are independent of excitation wavelength and are based on common outcome parameters, such as the photon density absorbed by the Ru(II) compound to cause 50% cell kill (LD50) based on the previously established threshold model. In this focused photophysical review, we identified all published studies on Ru(II) containing PSs since 2005 that reported the required photophysical, light treatment, and in vitro outcome data to permit the application of the Photodynamic Threshold Model to quantify their potential efficacy. The resulting LD50 values range from less than 1013 to above 1020 [hν cm-3], indicating a wide range in PDT efficacy and required optical energy density for ultimate clinical translation.

Red-Absorbing Ru(II) Polypyridyl Complexes with Biotin Targeting Spontaneously Assemble into Nanoparticles in Biological Media

Four new ruthenium(II) polypyridyl complexes were synthesized to study the effect of poly(ethylene glycol) and/or biotin conjugation on their physical and biological properties, including their hydrophilicity, their cellular uptake, and their phototoxicity. Unexpectedly, these complexes self-assembled into nanoparticles upon dilution in biological media. This behavior leads to their accumulation in lysosomes following their internalization by cells. While a significant increase in cellular uptake was observed for the biotin-conjugated complexes, it did not result in an increase in their phototoxicity. However, their high phototoxicity upon irradiation at long wavelengths (645-670 nm) and their self-assembling behavior make them a promising backbone for the development of new lysosome-targeted photosensitizers for photodynamic therapy.

Minimally invasive nanomedicine: nanotechnology in photo-/ultrasound-/radiation-/magnetism-mediated therapy and imaging

Traditional treatments such as chemotherapy and surgery usually cause severe side effects and excruciating pain. The emergence of nanomedicines and minimally invasive therapies (MITs) has brought hope to patients with malignant diseases. Especially, minimally invasive nanomedicines (MINs), which combine the advantages of nanomedicines and MITs, can effectively target pathological cells/tissues/organs to improve the bioavailability of drugs, minimize side effects and achieve painless treatment with a small incision or no incision, thereby acquiring good therapeutic effects. In this review, we provide a comprehensive review of the research status and challenges of MINs, which generally refers to the medical applications of nanotechnology in photo-/ultrasound-/radiation-/magnetism-mediated therapy and imaging. Additionally, we also discuss their combined application in various fields including cancers, cardiovascular diseases, tissue engineering, neuro-functional diseases, and infectious diseases. The prospects, and potential bench-to-bedside translation of MINs are also presented in this review. We expect that this review can inspire the broad interest for a wide range of readers working in the fields of interdisciplinary subjects including (but not limited to) chemistry, nanomedicine, bioengineering, nanotechnology, materials science, pharmacology, and biomedicine.

An osmium-peroxo complex for photoactive therapy of hypoxic tumors

The limited therapeutic effect on hypoxic and refractory solid tumors has hindered the practical application of photodynamic therapy. Herein, we report our investigation of an osmium-peroxo complex (Os2), which is inactive in the dark, but can release a peroxo ligand O₂^•− upon light irradiation even in the absence of oxygen, and is transformed into a cytotoxic osmium complex (Os1). Os1 is cytotoxic in the presence or absence of irradiation in hypoxic tumors, behaving as a chemotherapeutic drug. At the same time, the light-activated Os2 induces photocatalytic oxidation of endogenous 1,4-dihydronicotinamide adenine dinucleotide in living cancer cells, leading to ferroptosis, which is mediated by glutathione degradation, lipid peroxide accumulation and down-regulation of glutathione peroxidase 4. In vivo studies have confirmed that the Os2 can effectively inhibit the growth of solid hypoxic tumors in mice. A promising strategy is proposed for the treatment of hypoxic tumors with metal-based drugs.

Photodynamic therapy has been a promising technique for the treatment of tumours. In this manuscript, the authors report on the photoactivation of the osmium peroxo complex and its potential use for chemotherapy and photodynamic therapy under blue light irradiation against tumours in their hypoxic environment.

The Current State of Treatment and Future Directions in Cutaneous Malignant Melanoma

Malignant melanoma is the leading cause of death among cutaneous malignancies. While its incidence is increasing, the most recent cancer statistics show a small but clear decrease in mortality rate. This trend reflects the introduction of novel and more effective therapeutic regimens, including the two cornerstones of melanoma therapy: immunotherapies and targeted therapies. Immunotherapies exploit the highly immunogenic nature of melanoma by modulating and priming the patient's own immune system to attack the tumor. Treatments combining immunotherapies with targeted therapies, which disable the carcinogenic products of mutated cancer cells, have further increased treatment efficacy and durability. Toxicity and resistance, however, remain critical challenges to the field. The present review summarizes past treatments and novel therapeutic interventions and discusses current clinical trials and future directions.

Interaction with a Biomolecule Facilitates the Formation of the Function-Determining Long-Lived Triplet State in a Ruthenium Complex for Photodynamic Therapy

TLD1433 is the first ruthenium (Ru)-based photodynamic therapy (PDT) agent to advance to clinical trials and is currently in a phase II study for treating nonmuscle bladder cancer with PDT. Herein, we present a photophysical study of TLD1433 and its derivative TLD1633 using complex, biologically relevant solvents to elucidate the excited-state properties that are key for biological activity. The complexes incorporate an imidazo [4,5-f][1,10]phenanthroline (IP) ligand appended to α-ter- or quaterthiophene, respectively, where TLD1433 = [Ru(4,4'-dmb)₂(IP-3T)]Cl₂ and TLD1633 = [Ru(4,4'-dmb)₂(IP-4T)]Cl₂ (4,4'-dmb = 4,4'-dimethyl-2,2'-bipyridine; 3T = α-terthiophene; 4T = α-quaterthiophene). Time-resolved transient absorption experiments demonstrate that the excited-state dynamics of the complexes change upon interaction with biological macromolecules (e.g., DNA). In this case, the accessibility of the lowest-energy triplet intraligand charge-transfer (³ILCT) state (T₁) is increased at the expense of a higher-lying ³ILCT state. We attribute this behavior to the increased rigidity of the ligand framework upon binding to DNA, which prolongs the lifetime of the T₁ state. This lowest-lying state is primarily responsible for O₂ sensitization and hence photoinduced cytotoxicity. Therefore, to gain a realistic picture of the excited-state kinetics that underlie the photoinduced function of the complexes, it is necessary to interrogate their photophysical dynamics in the presence of biological targets once they are known.

Photodynamic therapy of melanoma with new, structurally similar, NIR-absorbing ruthenium (II) complexes promotes tumor growth control via distinct hallmarks of immunogenic cell death

Cancer therapies that generate T cell-based anti-cancer immune responses are critical for clinical success and are favored over traditional therapies. One way to elicit T cell immune responses and generate long-lasting anti-cancer immunity is through induction of immunogenic cell death (ICD), a form of regulated cell death that promotes antigenicity and adjuvanticity within dying cells. Therefore, research in the last decade has focused on developing cancer therapies which stimulate ICD. Herein, we report novel photodynamic therapy (PDT) compounds with immunomodulatory and ICD inducing properties. PDT is a clinically approved, minimally invasive anti-cancer treatment option and has been extensively investigated for its tumor-destroying properties, lower side effects, and immune activation capabilities. In this study, we explore two structurally related ruthenium compounds, ML19B01 and ML19B02, that can be activated with near infrared light to elicit superior cytotoxic properties. In addition to its direct cell killing abilities, we investigated the effect of our PSs on immunological pathways upon activation. PDT treatment with ML19B01 and ML19B02 induced differential expression of reactive oxygen species, proinflammatory response-mediating genes, and heat shock proteins. Dying melanoma cells induced by ML19B01-PDT and ML19B02-PDT contained ICD hallmarks such as calreticulin, ATP, and HMGB1, initiated activation of antigen presenting cells, and were efficiently phagocytosed by bone marrow-derived dendritic cells. Most importantly, despite the distinct profiles of ICD hallmark inducing capacities, vaccination with both PDT-induced dying cancer cells established anti-tumor immunity that protected mice against subsequent challenge with melanoma cells.

A Sequential Dual-Model Strategy Based on Photoactivatable Metallopolymer for On-Demand Release of Photosensitizers and Anticancer Drugs

The synergistic combination of chemotherapy and photodynamic therapy has attracted considerable attention for its enhanced antitumoral effects; however, it remains challenging to successfully delivery photosensitizers and anticancer drugs while minimizing drug leakage at off-target sites. A red-light-activatable metallopolymer, Poly(Ru/PTX), is synthesized for combined chemo-photodynamic therapy. The polymer has a biodegradable backbone that contains a photosensitizer Ru complex and the anticancer drug paclitaxel (PTX) via a singlet oxygen (1 O2 ) cleavable linker. The polymer self-assembles into nanoparticles, which can efficiently accumulate at the tumor sites during blood circulation. The distribution of the therapeutic agents is synchronized because the Ru complex and PTX are covalently conjugate to the polymer, and off-target toxicity during circulation is also mostly avoided. Red light irradiation at the tumor directly cleaves the Ru complex and produces 1 O2 for photodynamic therapy. Sequentially, the generated 1 O2 triggers the breakage of the linker to release the PTX for chemotherapy. Therefore, this novel sequential dual-model release strategy creates a synergistic chemo-photodynamic therapy while minimizing drug leakage. This study offers a new platform to develop smart delivery systems for the on-demand release of therapeutic agents in vivo.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Antitumor Immune Response Triggered by Metal-Based Photosensitizers for Photodynamic Therapy: Where Are We?

Metal complexes based on transition metals have rich photochemical and photophysical properties that are derived from a variety of excited state electronic configurations triggered by visible and near-infrared light. These properties can be exploited to produce powerful energy and electron transfer processes that can lead to oxygen-(in)dependent photobiological activity. These principles are the basis of photodynamic therapy (PDT), which is a clinically approved treatment that offers a promising, effective, and noninvasive complementary treatment or even an alternative to treat several types of cancers. PDT is based on a reaction involving a photosensitizer (PS), light, and oxygen, which ultimately generates cytotoxic reactive oxygen species (ROS). However, skin photosensitivity, due to the accumulation of PSs in skin cells, has hampered, among other elements, its clinical development and application. Therefore, these is an increasing interest in the use of (metal-based) PSs that are more specific to tumor cells. This may increase efficacy and corollary decrease side-effects. To this end, metal-containing nanoparticles with photosensitizing properties have recently been developed. In addition, several studies have reported that the use of immunogenic/immunomodulatory metal-based nanoparticles increases the antitumor efficacy of immune-checkpoint inhibitor-based immunotherapy mediated by anti-PD-(L)1 or CTLA-4 antibodies. In this review, we discuss the main metal complexes used as PDT PSs. Lastly, we review the preclinical studies associated with metal-based PDT PSs and immunotherapies. This therapeutic association could stimulate PDT.

Mono-/Bimetallic Neutral Iridium(III) Complexes Bearing Diketopyrrolopyrrole-Substituted N-Heterocyclic Carbene Ligands: Synthesis and Photophysics

The synthesis and photophysics (UV-vis absorption, emission, and transient absorption) of four neutral heteroleptic cyclometalated iridium(III) complexes (Ir-1-Ir-4) incorporating thiophene/selenophene-diketopyrrolopyrrole (DPP)-substituted N-heterocyclic carbene (NHC) ancillary ligands are reported. The effects of thiophene versus selenophene substitution on DPP and bis- versus monoiridium(III) complexation on the photophysics of these complexes were systematically investigated via spectroscopic techniques and density functional theory calculations. All complexes exhibited strong vibronically resolved absorption in the regions of 500-700 nm and fluorescence at 600-770 nm, and both are predominantly originated from the DPP-NHC ligand. Complexation induced a pronounced red shift of this low-energy absorption band and the fluorescence band with respect to their corresponding ligands due to the improved planarity and extended π-conjugation in the DPP-NHC ligand. Replacing the thiophene units by selenophenes and/or biscomplexation led to the red-shifted absorption and fluorescence spectra, accompanied by the reduced fluorescence lifetime and quantum yield and enhanced population of the triplet excited states, as reflected by the stronger triplet excited-state absorption and singlet oxygen generation.

Antitumor activity of tridentate pincer and related metal complexes

Pincer complexes featuring tunable tridentate ligand frameworks are one of the most actively studied classes of metal-based complexes. Currently, growing attention is devoted to the cytotoxicity of pincer and related metal complexes. The antiproliferative activity of numerous pincer complexes has been reported. Pincer tridentate ligand scaffolds show different coordination modes and offer multiple options for directed structural modifications. This review summarizes the significant progress in the research studies of the antitumor activity of pincer and related platinum(ii), gold(iii), palladium(ii), copper(ii), iron(iii), ruthenium(ii), nickel(ii) and some other metal complexes, in order to provide a reference for designing novel metal coordination drug candidates with promising antitumor activity.

Photoresponsive metallopolymer nanoparticles for cancer theranostics

Over the past decades, transition metal complexes have been successfully used in anticancer phototherapies. They have shown promising properties in many different areas including photo-induced ligand exchange or release, rich excited state behavior, and versatile biochemical properties. When encorporated into polymeric frameworks and become part of nanostructures, photoresponsive metallopolymer nanoparticles (MPNs) show enhanced water solubility, extended blood circulation and increased tumor-specific accumulation, which greatly improves the tumor therapeutic effects compared to low-molecule-weight metal complexes. In this review, we aim to present the recent development of photoresponsive MPNs as therapeutic nanomedicines. This review will summarize four major areas separately, namely platinum-containing polymers, zinc-containing polymers, iridium-containing polymers and ruthenium-containing polymers. Representative MPNs of each type are discussed in terms of their design strategies, fabrication methods, and working mechanisms. Current challenges and future perspectives in this field are also highlighted.