Catch and Release Photosensitizers: Combining Dual-Action Ruthenium Complexes with Protease Inactivation for Targeting Invasive Cancers

Photosensitive Ru(II) Complexes as Inhibitors of the Major Human Drug Metabolizing Enzyme CYP3A4

We report the synthesis and photochemical and biological characterization of the first selective and potent metal-based inhibitors of cytochrome P450 3A4 (CYP3A4), the major human drug metabolizing enzyme. Five Ru(II)-based derivatives were prepared from two analogs of the CYP3A4 inhibitor ritonavir, 4 and 6: [Ru(tpy)(L)(6)]Cl₂ (tpy = 2,2':6',2″-terpyridine) with L = 6,6'-dimethyl-2,2'-bipyridine (Me₂bpy; 8), dimethylbenzo[i]dipyrido[3,2-a:2',3'-c]phenazine (Me₂dppn; 10) and 3,6-dimethyl-10,15-diphenylbenzo[i]dipyrido[3,2-a:2',3'-c]phenazine (Me₂Ph₂dppn; 11), [Ru(tpy)(Me₂bpy)(4)]Cl₂ (7) and [Ru(tpy)(Me₂dppn)(4)]Cl₂ (9). Photochemical release of 4 or 6 from 7-11 was demonstrated, and the spectrophotometric evaluation of 7 showed that it behaves similarly to free 4 (type II heme ligation) after irradiation with visible light but not in the dark. Unexpectedly, the intact Ru(II) complexes 7 and 8 were found to inhibit CYP3A4 potently and specifically through direct binding to the active site without heme ligation. Caged inhibitors 9-11 showed dual action properties by combining photoactivated dissociation of 4 or 6 with efficient ¹O₂ production. In prostate adenocarcinoma DU-145 cells, compound 9 had the best synergistic effect with vinblastine, the anticancer drug primarily metabolized by CYP3A4 in vivo. Thus, our study establishes a new paradigm in CYP inhibition using metalated complexes and suggests possible utilization of photoactive CYP3A4 inhibitory compounds in clinical applications, such as enhancement of therapeutic efficacy of anticancer drugs.

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.

Ru(II) Polypyridine Complex-Functionalized Mesoporous Silica Nanoparticles as Photosensitizers for Cancer Targeted Photodynamic Therapy

Cancer is the leading cause of death in the developed world. In the last few decades, photodynamic therapy (PDT) has augmented the number of medical techniques to treat this disease in the clinics. As the pharmacological active species to kill cancer cells are only generated upon light irradiation, PDT is associated with an intrinsic first level of selectivity. However, since PDT agents also accumulate in the surrounding, healthy tissue and since it is practically very challenging to only expose the tumor site to light, some side effects can be observed. Consequently, there is a need for a selective drug delivery system, which would give a second level of selectivity. In this work, a dual tumor targeting approach is presented based on mesoporous silica nanoparticles, which act by the enhanced permeability and retention effect, and the conjugation to folic acid, which acts as a targeting moiety for folate receptor-overexpressed cancer cells. The conjugates were found to be nontoxic in noncancerous human normal lung fibroblast cells while showing a phototoxic effect upon irradiation at 480 or 540 nm in the low nanomolar range in folate receptor overexpressing cancerous human ovarian carcinoma cells, demonstrating their potential for cancer targeted treatment.

Synthesis, DNA-Binding, Anticancer Evaluation, and Molecular Docking Studies of Bishomoleptic and Trisheteroleptic Ru-Diimine Complexes Bearing 2-(2-Pyridyl)-quinoxaline

Herein, we report the synthesis and characterization of a bishomoleptic and a trisheteroleptic ruthenium (II) polypyridyl complex, namely, [Ru(bpy)2(2, 2'-pq)](PF6)2 (1) and [Ru(bpy) (phen) (2, 2'-pq)](PF6)2 (2), respectively, where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and 2, 2'-pq = 2-(2'-pyridyl)-quinoxaline. The complexes were characterized by elemental analysis, TGA, 1H-NMR, FT-IR, UV-Vis, emission spectroscopy, and electrochemistry. Their structures were confirmed by single-crystal X-ray diffraction analysis. Complexes 1 and 2 were crystalized in orthorhombic, Pbca, and monoclinic, P21/n systems, respectively. Various spectroscopic techniques were employed to investigate the interaction of both complexes with calf thymus DNA (CT-DNA). The experimental data were confirmed by molecular docking studies, employing two different DNA sequences. Both complexes, 1 and 2, bind with DNA via a minor groove mode of binding. MTT experiments revealed that both complexes induce apoptosis of MCF-7 (breast cancer) cells in low concentrations. Confocal microscopy indicated that 2 localizes in the nucleus and internalizes more efficiently in MCF-7 than in HEK-293.

Modification of amyloid-beta peptide aggregation via photoactivation of strained Ru(ii) polypyridyl complexes

Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by progressive and irreversible damage to the brain. One of the hallmarks of the disease is the presence of both soluble and insoluble aggregates of the amyloid beta (Aβ) peptide in the brain, and these aggregates are considered central to disease progression. Thus, the development of small molecules capable of modulating Aβ peptide aggregation may provide critical insight into the pathophysiology of AD. In this work we investigate how photoactivation of three distorted Ru(ii) polypyridyl complexes (Ru1-3) alters the aggregation profile of the Aβ peptide. Photoactivation of Ru1-3 results in the loss of a 6,6'-dimethyl-2,2'-bipyridyl (6,6'-dmb) ligand, affording cis-exchangeable coordination sites for binding to the Aβ peptide. Both Ru1 and Ru2 contain an extended planar imidazo[4,5-f][1,10]phenanthroline ligand, as compared to a 2,2'-bipyridine ligand for Ru3, and we show that the presence of the phenanthroline ligand promotes covalent binding to Aβ peptide His residues, and in addition, leads to a pronounced effect on peptide aggregation immediately after photoactivation. Interestingly, all three complexes resulted in a similar aggregate size distribution at 24 h, forming insoluble amorphous aggregates as compared to significant fibril formation for peptide alone. Photoactivation of Ru1-3 in the presence of pre-formed Aβ1-42 fibrils results in a change to amorphous aggregate morphology, with Ru1 and Ru2 forming large amorphous aggregates immediately after activation. Our results show that photoactivation of Ru1-3 in the presence of either monomeric or fibrillar Aβ1-42 results in the formation of large amorphous aggregates as a common endpoint, with Ru complexes incorporating the extended phenanthroline ligand accelerating this process and thereby limiting the formation of oligomeric species in the initial stages of the aggregation process that are reported to show considerable toxicity.

BODIPY-attached zinc(II) complexes of curcumin drug for visible light assisted photo-sensitization, cellular imaging and targeted PDT

Boron-dipyrromethene (BODIPY) based photosensitizers as porphyrinoids and curcumin as natural product possess exciting photophysical features suitable for theranostic applications, namely, imaging and photodynamic therapy (PDT). Limited aqueous solubility and insufficient physiological stability, however, reduce their efficacy significantly. We have designed a novel strategy to deliver these two unusable cytotoxins simultaneously in cancer cells and herein, report the synthesis, characterization and imaging-assisted photocytotoxicity of three zinc(II) complexes containing N³-donor dipicolylamine (dpa) ligands (L^1-3) and O,O-donor curcumin (Hcur) viz. [Zn(L¹)(cur)]Cl (1), [Zn(L²)(cur)]Cl (2) and [Zn(L³)(cur)]Cl (3), where L² and L³ have pendant fluorescent BODIPY and non-emissive di-iodo-BODIPY moieties. Metal chelation imparted remarkable biological stability (pH ∼7.4) to the respective ligands and induces significant aqueous solubility. These ternary complexes could act as replacements of the existing metalloporphyrin-based PDT photosensitizers as their visible-light photosensitizing ability is reinforced by the dual presence of blue light absorbing curcumin and green light harvesting BODIPY units. Complex 2 having emissive BODIPY unit L² and curcumin, showed mitochondria selective localization in HeLa, MCF-7 cancer cells and complex 3, the di-iodinated analogue of complex 2, exhibited type-I/II PDT activity via inducing apoptosis through mitochondrial membrane disruption in cancer cells while being significantly nontoxic in dark and to the healthy cells.

Polymeric Encapsulation of a Ru(II)-Based Photosensitizer for Folate-Targeted Photodynamic Therapy of Drug Resistant Cancers

The currently used photodynamic therapy (PDT) photosensitizers (PSs) are generally associated with a poor cancer cell selectivity, which is responsible for some undesirable side effects. To overcome these problems, there is an urgent need for a selective drug delivery system for PDT PSs. Herein, the encapsulation of a promising Ru(II) polypyridine complex in a polymer with terminal folate groups to form nanoparticles is presented. While the Ru(II) complex itself has a cytotoxic effect in the dark, the encapsulation is able to overcome this drawback. Upon light exposure, the nanoparticles were found to be highly phototoxic in 2D monolayer cells as well as 3D multicellular tumor spheroids upon 480 or 595 nm irradiation. Importantly, the nanoparticles demonstrated a high selectivity for cancerous cells over noncancerous cells and were found to be active in drug resistant cancer cells lines, indicating that they are able to overcome drug resistances.

Targeting drug delivery with light: A highly focused approach

Light is a uniquely powerful tool for controlling molecular events in biology. No other external input (e.g., heat, ultrasound, magnetic field) can be so tightly focused or so highly regulated as a clinical laser. Drug delivery vehicles that can be photonically activated have been developed across many platforms, from the simplest "caging" of therapeutics in a prodrug form, to more complex micelles and circulating liposomes that improve drug uptake and efficacy, to large-scale hydrogel platforms that can be used to protect and deliver macromolecular agents including full-length proteins. In this Review, we discuss recent innovations in photosensitive drug delivery and highlight future opportunities to engineer and exploit such light-responsive technologies in the clinical setting.

Recent progress in photosensitizers for overcoming the challenges of photodynamic therapy: from molecular design to application

Photodynamic therapy (PDT), a therapeutic mode involving light triggering, has been recognized as an attractive oncotherapy treatment. However, nonnegligible challenges remain for its further clinical use, including finite tumor suppression, poor tumor targeting, and limited therapeutic depth. The photosensitizer (PS), being the most important element of PDT, plays a decisive role in PDT treatment. This review summarizes recent progress made in the development of PSs for overcoming the above challenges. This progress has included PSs developed to display enhanced tolerance of the tumor microenvironment, improved tumor-specific selectivity, and feasibility of use in deep tissue. Based on their molecular photophysical properties and design directions, the PSs are classified by parent structures, which are discussed in detail from the molecular design to application. Finally, a brief summary of current strategies for designing PSs and future perspectives are also presented. We expect the information provided in this review to spur the further design of PSs and the clinical development of PDT-mediated cancer treatments.

BODIPY-linked cis-dichlorido zinc(ii) conjugates: the strategic design of organelle-specific next-generation theranostic photosensitizers

Cis-dichlorido Zn(ii)–BODIPY-based smart theranostic photosensitizers, as alternatives to Zn-porphyrins/phthalocyanines, show mitochondrion-targeted and imaging guided type-II photodynamic therapeutic activity.

Novel organo-osmium(ii) proteosynthesis inhibitors active against human ovarian cancer cells reduce gonad tumor growth inCaenorhabditis elegans

Novel Os(ii) arene complexes with a deprotonated ppy or ppy-CHO C^N ligand have been synthesized to selectively act on cancer cells as proteosynthesis inhibitorsin vitroand exert antitumor activityin vivoinC. elegansmodels.

Polymeric Encapsulation of a Ruthenium Polypyridine Complex for Tumor Targeted One- and Two-Photon Photodynamic Therapy

Photodynamic therapy is a medical technique, which is gaining increasing attention to treat various types of cancer. Among the investigated classes of photosensitizers (PSs), the use of Ru(II) polypyridine complexes is gaining momentum. However, the currently investigated compounds generally show poor cancer cell selectivity. As a consequence, high drug doses are needed, which can cause side effects. To overcome this limitation, there is a need for the development of a suitable drug delivery system to increase the amount of PS delivered to the tumor. Herein, we report the encapsulation of a promising Ru(II) polypyridyl complex into polymeric nanoparticles with terminal biotin groups. Thanks to this design, the particles showed much higher selectivity for cancer cells in comparison to noncancerous cells in a 2D monolayer and 3D multicellular tumor spheroid model. As a highlight, upon intravenous injection of an identical amount of the Ru(II) polypyridine complex of the nanoparticle formulation, an improved accumulation inside an adenocarcinomic human alveolar basal epithelial tumor of a mouse up to a factor of 8.7 compared to the Ru complex itself was determined. The nanoparticles were found to have a high phototoxic effect upon one-photon (500 nm) or two-photon (800 nm) excitation with eradication of adenocarcinomic human alveolar basal epithelial tumor inside a mouse model. Overall, this work describes, to the best of our knowledge, the first in vivo study demonstrating the cancer cell selectivity of a very promising Ru(II)-based PDT photosensitizer encapsulated into polymeric nanoparticles with terminal biotin groups.

Intracellular Photophysics of an Osmium Complex bearing an Oligothiophene Extended Ligand

This contribution describes the excited-state properties of an Osmium-complex when taken up into human cells. The complex 1 [Os(bpy)2 (IP-4T)](PF6 )2 with bpy=2,2'-bipyridine and IP-4T=2-{5'-[3',4'-diethyl-(2,2'-bithien-5-yl)]-3,4-diethyl-2,2'-bithiophene}imidazo[4,5-f][1,10]phenanthroline) can be discussed as a candidate for photodynamic therapy in the biological red/NIR window. The complex is taken up by MCF7 cells and localizes rather homogeneously within in the cytoplasm. To detail the sub-ns photophysics of 1, comparative transient absorption measurements were carried out in different solvents to derive a model of the photoinduced processes. Key to rationalize the excited-state relaxation is a long-lived 3 ILCT state associated with the oligothiophene chain. This model was then tested with the complex internalized into MCF7 cells, since the intracellular environment has long been suspected to take big influence on the excited state properties. In our study of 1 in cells, we were able to show that, though the overall model remained the same, the excited-state dynamics are affected strongly by the intracellular environment. Our study represents the first in depth correlation towards ex-vivo and in vivo ultrafast spectroscopy for a possible photodrug.

Photoactivatable Protherapeutic Nanomedicine for Cancer

Therapeutic systems with site-specific pharmaceutical activation hold great promise to enhance therapeutic efficacy while reducing systemic toxicity in cancer therapy. With operational flexibility, noninvasiveness, and high spatiotemporal resolution, photoactivatable nanomedicines have drawn growing attention. Distinct from traditional controlled release systems relying on the difference of biomarker concentrations between disease and healthy tissues, photoactivatable nanomedicines capitalize on the interaction between nanotransducers and light to either trigger photochemical reactions or generate reactive oxygen species (ROS) or heat effect to remotely induce pharmaceutical actions in living subjects. Herein, the recent advances in the development of photoactivatable protherapeutic nanoagents for oncology are summarized. The design strategies and therapeutic applications of these nanoagents are described. Representative examples of each type are discussed in terms of structure, photoactivation mechanism, and preclinical models. Last, potential challenges and perspectives to further develop photoactivatable protherapeutic nanoagents in cancer nanomedicine are discussed.

Intramolecular Hydrogen Bonding: A Key Factor Controlling the Photosubstitution of Ruthenium Complexes

Photosubstitution reactions of ruthenium complexes with pyrazole ligands, cis-[Ru(bpy)₂(pzH)₂]²⁺ (1a), cis-[Ru(bpy)₂(pz)(pzH)]⁺ (1b), and cis-[Ru(bpy)₂(pz)₂]⁰ (1c) (pzH = pyrazole, bpy = 2,2'-bipyridine), were investigated. Dicationic complex 1a was deprotonated to 1b using moderate base (pK_a = 15.2, MeCN), while the second deprotonation to give 1c required more severe conditions (pK_a = 26.9). Monocationic complex 1b possessed an N-H···N-type intramolecular hydrogen bond between the pyrazole and pyrazolate ligands, as corroborated by the solid-state crystal structure. The photosubstitution quantum yield of 1a (Φ = 0.26) was comparable to that of cis-[Ru(bpy)₂(pyridine)₂]²⁺ (Φ = 0.24) in acetonitrile solution. In contrast, the photodissociation of a pzH ligand was strongly suppressed by the deprotonation of a pyrazole ligand N-H group. In the presence of 10 000 equiv of 4,4'-dimethylaminopyridine, the quantum yield dropped to ∼2 × 10^-6 in acetonitrile. The photosubstitution quantum yield of 1b was even smaller than that of neutral complex 1c, although 1c had a smaller HOMO-LUMO energy gap than monocationic complex 1b. The small quantum yield of 1b was attributed to intramolecular hydrogen bonding between pyrazole and pyrazolate ligands. The apparent rate constants for the photosubstitution of 1b were highly solvent-dependent. The photosubstitution of 1b was suppressed in aprotic solvents, while the reaction was accelerated by 2 orders of magnitude in protic solvents with strong proton donor abilities.

DNA photocleavage and melanoma cells cytotoxicity induced by a meso-tetra-ruthenated porphyrin under visible light irradiation

Porphyrins are used as photosensitizing agents in photodynamic therapy (PDT) for several pathologies. Here we demonstrate the DNA photocleavage and cytotoxicity properties of a free-base meso-tetra-ruthenated porphyrin (H₂RuTPyP) in purified DNA samples and in a melanoma cell line, respectively. Cytotoxicity of H₂RuTPyP was investigated by the tetrazolium dye (MTT) colorimetric assay and its genotoxic potential by direct plasmid DNA photocleavage after incubation with specific DNA repair enzymes. H₂RuTPyP porphyrin efficiently induced DNA damage at the lower concentration of 5.0 μM, whereas it induced complete DNA degradation at 15 μM. The addition of different scavengers for reactive oxygen species (ROS) during the visible light exposures did not decrease the DNA damage formation, suggesting a hydrolytic mechanism for the induction of DNA breaks. Also, H₂RuTPyP exhibited a much higher cytotoxicity in melanoma cells in comparison to a keratinocyte cell line. The detection of intracellular reactive oxygen species (ROS) produced by H₂RuTPyP through the DCF-DA assay also suggests that ROS have a minor role in the induction of cytotoxicity. Therefore, H₂RuTPyP seems to be a very effective photosensitizer, representing a promising alternative for the development of new skin cancer treatments using PDT process.

The Self-Assembly of a Cyclometalated Palladium Photosensitizer into Protein-Stabilized Nanorods Triggers Drug Uptake In Vitro and In Vivo

Enhanced passive diffusion is usually considered to be the primary cause of the enhanced cellular uptake of cyclometalated drugs because cyclometalation lowers the charge of a metal complex and increases its lipophilicity. However, in this work, monocationic cyclometalated palladium complexes [1]OAc (N^N^C^N) and [2]OAc (N^N^N^C) were found to self-assemble, in aqueous solutions, into soluble supramolecular nanorods, while their tetrapyridyl bicationic analogue [3](OAc)₂ (N^N^N^N) dissolved as isolated molecules. These nanorods formed via metallophilic Pd···Pd interaction and π–π stacking and were stabilized in the cell medium by serum proteins, in the absence of which the nanorods precipitated. In cell cultures, these protein-stabilized self-assembled nanorods were responsible for the improved cellular uptake of the cyclometalated compounds, which took place via endocytosis (i.e., an active uptake pathway). In addition to triggering self-assembly, cyclometalation in [1]OAc also led to dramatically enhanced photodynamic properties under blue light irradiation. These combined penetration and photodynamic properties were observed in multicellular tumor spheroids and in a mice tumor xenograft, demonstrating that protein-stabilized nanoaggregation of cyclometalated drugs such as [1]OAc also allows efficient cellular uptake in 3D tumor models. Overall, serum proteins appear to be a major element in drug design because they strongly influence the size and bioavailability of supramolecular drug aggregates and hence their efficacy in vitro and in vivo.

Light-activated gold nanorod vesicles with NIR-II fluorescence and photoacoustic imaging performances for cancer theranostics

Fluorescence (FL) and photoacoustic (PA) imaging in the second near infrared window (NIR-II FL and NIR-II PA) hold great promise for biomedical applications because of their non-invasive nature and excellent spatial resolution properties. Methods: We develop a NIR-II PA and NIR-II FL dual-mode imaging gold nanorod vesicles (AuNR Ves) by self-assembly of amphiphilic AuNR coated with light responsive polyprodrug of Ru-complex and PEG, and NIR-II cyanine dye (IR 1061). The AuNR Ves showed strong ligh absorption property and PA imaging performance in the NIR-II windows. Moreover, the NIR-II fluorescence signal of IR 1061 loaded in the AuNR Ve is quenched. Results: The AuNR Ves can release photosensitizer Ru-complex and IR 1061 sequentially triggered by NIR light irradiation, leading to a corresponding NIR-II PA signal decrease and NIR-II FL signal recovery. Meanwhile, Ru-complex can not only serve as a chemotherapeutic drug but also generate singlet oxygen (1O2) under NIR light irradiation. The release of Ru-complex and photodynamic therapy are guided by the responsive variation of NIR-II PA and NIR-II FL signals. Conclusions: The AuNR Ve possessing not only precisely control 1O2/drug release but also the intrinsic ability to monitor therapy process offers a new strategy for the development of smart theranostic nanoplatform.

Photoinduced ligand dissociation follows reverse energy gap law: nitrile photodissociation from low energy 3MLCT excited states

A series of Ru(ii)-terpyridine complexes containing electron-donating bidentate ligands are able to effectively photodissociate nitrile ligands using red light. A spectroscopic investigation of these complexes reveal that they follow anti-energy gap law behavior, providing further evidence that population of ³LF excited states is not necessary for photoinduced nitrile dissociation.

Dual-Action Ru(II) Complexes with Bulky π-Expansive Ligands: Phototoxicity without DNA Intercalation

We report the synthesis and photochemical and biological characterization of Ru(II) complexes containing π-expansive ligands derived from dimethylbenzo[i]dipyrido[3,2-a:2',3'-c]phenazine (Me₂dppn) adorned with flanking aryl substituents. Late-stage Suzuki couplings produced Me₂dppn ligands substituted at the 10 and 15 positions with phenyl (5), 2,4-dimethylphenyl (6), and 2,4-dimethoxyphenyl (7) groups. Complexes of the general formula [Ru(tpy)(L)(py)](PF₆)₂ (8-10), where L = 4-7, were characterized and shown to have dual photochemotherapeutic (PCT) and photodynamic therapy (PDT) behavior. Quantum yields for photodissociation of monodentate pyridines from 8-10 were about 3 times higher than that of parent complex [Ru(tpy)(Me₂dppn)(py)](PF₆)₂ (1), whereas quantum yields for singlet oxygen (¹O₂) production were ∼10% lower than that of 1. Transient absorption spectroscopy indicates that 8-10 possess long excited state lifetimes (τ = 46-50 μs), consistent with efficient ¹O₂ production through population and subsequent decay of ligand-centered ³ππ* excited states. Complexes 8-10 displayed greater lipophilicity relative to 1 and association to DNA but do not intercalate between the duplex base pairs. Complexes 1 and 8-10 showed photoactivated toxicity in breast and prostate cancer cell lines with phototherapeutic indexes, PIs, as high as >56, where the majority of cell death was achieved 4 h after treatment with Ru(II) complexes and light. Flow cytometric data and rescue experiments were consistent with necrotic cell death mediated by the production of reactive oxygen species, especially ¹O₂. Collectively, this study confirms that DNA intercalation by Ru(II) complexes with π-expansive ligands is not required to achieve photoactivated cell death.

Ruthenium-initiated polymerization of lactide: a route to remarkable cellular uptake for photodynamic therapy of cancer

Ruthenium complexes have attracted a lot of attention as potential photosensitizers (PSs) for photodynamic therapy (PDT). However, some of these PSs are unsuitable for PDT applications due to their low cellular uptake, which is possibly the consequence of their relatively low degree of lipophilicity, which prevents them from penetrating into tumor cells. Here, we report the simple one-pot synthesis of ruthenium-containing nanoconjugates from a non-cell-penetrating, non-phototoxic ruthenium(ii) polypyridyl complex (RuOH), by a drug-initiated ring-opening polymerization of lactide through the formation of a zinc initiator. These conjugates were then formulated into nanoparticles by nanoprecipitation and characterized by means of nuclear magnetic resonance spectroscopy (NMR), matrix-assisted laser desorption/ionization – time of flight mass spectrometry (MALDI-TOF MS) and dynamic light scattering (DLS). Finally, their photo-therapeutic activity (λ_exc = 480 nm, 3.21 J cm⁻²) in cancerous human cervical carcinoma (HeLa) and non-cancerous retinal pigment epithelium (RPE-1) cells was tested alongside that of RuOH and their cellular uptake in HeLa cells was assessed by confocal microscopy and inductively coupled plasma – mass spectrometry (ICP-MS). All nanoparticles showed improved photophysical properties including luminescence and singlet oxygen generation, enhanced cellular uptake and, capitalizing on this, an improved photo-toxicity. Overall, this study demonstrates how it is possible to transform a non-phototoxic PDT PS into an active PS using an easy, versatile polymerization technique.

This study shows the transformation of a non-phototoxic PDT photosensitizer into an active photosensitizer using an easy, versatile and generalizable one-pot ruthenium-initiated polymerization technique.

Synthesis, structural characterization, in vitro DNA binding, and antitumor activity properties of Ru(II) compounds containing 2(2,6-dimethoxypyridine-3-yl)-1H-imidazo(4,5-f)[1, 10]phenanthroline

The octahedral Ru(II) complexes containing the 2(2,6-dimethoxypyridine-3-yl)-1H-imidazo(4,5-f)[1, 10]phenanthroline ligand of type [Ru(N-N)₂(L)]²⁺, where N-N = phen (1,10-phenanthroline) (1), bpy (2,2^'-bipyridine) (2), and dmb (4,4^'-dimethyl-2,2^'-bipyridine) (3); L(dmpip) = (2(2,6-dimethoxypyridine-3-yl)1Himidazo(4,5-f)[1, 10]phenanthroline), have been synthesized and characterized by UV-visible absorption, molar conductivity, elemental analysis, mass, IR, and NMR spectroscopic techniques. The physicochemical properties of the Ru(II) complexes were determined by UV-Vis absorption spectroscopy. The DNA binding studies have been explored by UV-visible absorption, fluorescence titrations, and viscosity measurements. The supercoiled pBR322 DNA cleavage efficiency of Ru(II) complexes 1-3 was investigated. The antimicrobial activity of Ru(II) complexes was done against Gram-positive and Gram-negative microorganisms. The in vitro anticancer activities of all the complexes were investigated by cell viability assay, apoptosis, cellular uptake, mitochondrial membrane potential detection, and semi-quantitative PCR on HeLa cells. The result indicates that the synthesized Ru(II) complexes probably interact with DNA through an intercalation mode of binding with complex 1 having slightly stronger DNA binding affinity and anticancer activity than 2 and 3.

Upconversion-like Photolysis of BODIPY-Based Prodrugs via a One-Photon Process

Photochemical reactions at lower energy than the absorption window are currently achieved by multi-photon processes, including two-photon absorption and photon upconversion, which have limited energy utilization efficiency. Here, we report a one-photon strategy based on triplet-triplet energy transfer (TTET) between a photosensitizer and a photocleavable molecule to achieve photolysis at low energy. To verify this concept, we chose platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) as the photosensitizer and synthesized a boron-dipyrromethene (BODIPY)-based prodrug as the photocleavable molecule. Photolysis of the prodrug is achieved by TTET upon excitation of PtTPBP at 625 nm with a photolysis quantum yield of 2.8%. Another demonstration shows an unexpected higher photolysis quantum yield than the direct excitation at 530 nm. This strategy opens a new path for achieving photolysis at long wavelengths, benefiting the applications in biological studies, photopharmacology, and photoresponsive drug delivery.

A self-assembled Ru-Pt metallacage as a lysosome-targeting photosensitizer for 2-photon photodynamic therapy

Photodynamic therapy (PDT) is a treatment procedure that relies on cytotoxic reactive oxygen species (ROS) generated by the light activation of a photosensitizer. The photophysical and biological properties of photosensitizers are vital for the therapeutic outcome of PDT. In this work a 2D rhomboidal metallacycle and a 3D octahedral metallacage were designed and synthesized via the coordination-driven self-assembly of a Ru(II)-based photosensitizer and complementary Pt(II)-based building blocks. The metallacage showed deep-red luminescence, a large 2-photon absorption cross-section, and highly efficient ROS generation. The metallacage was encapsulated into an amphiphilic block copolymer to form nanoparticles to encourage cell uptake and localization. Upon internalization into cells, the nanoparticles selectively accumulate in the lysosomes, a favorable location for PDT. The nanoparticles are almost nontoxic in the dark, and can efficiently destroy tumor cells via the generation of ROS in the lysosomes under 2-photon near-infrared light irradiation. The superb PDT efficacy of the metallacage-containing nanoparticles was further validated by studies on 3D multicellular spheroids (MCS) and in vivo studies on A549 tumor-bearing mice.

Two Emissive Long-Lived Excited States of an Imidazole-Functionalized Ruthenium Dipyridophenazine Complex

A ruthenium(II) polypyridine-type complex based on the dipyridophenazine ligand with a directly fused imidazole unit (L1, dipyrido[3,2-a:2',3'-c]phenazine-10,11-imidazole) has been synthesized, and its electrochemical and photophysical properties have been studied. The cyclic voltammogram of [Ru(tbbpy)₂(L1)]²⁺ (C1) (tbbpy is 4,4'-tert-butyl-2,2'-bipyridine) shows a cathodic shift of the phenazine-based reduction process compared to similar molecules, while the first detected reduction wave (-1.34 V vs Fc/Fc⁺) is assigned to the imidazole unit within the molecule. On the basis of the TD-DFT calculations, the strong visible absorption band exhibited by C1 is assigned to a metal-to-ligand charge transfer (MLCT) transition with a concurrent ligand-centered (LC) transition. At room-temperature, C1 features emission (Φ = 0.04) from its lowest excited states with time constants of 1.2 and 18.3 μs. These lifetimes are assigned to emission processes from the ³MLCT and ³LC state, respectively. This is the first time that a long-lived dual emission has been observed for a ruthenium(II) complex bearing a directly fused extended π-system. Furthermore, the emission of C1 is quenched upon water addition. In contrast to related compounds based on a dipyridophenazine ligand, the excited state energy is not shifted, and the lifetime is drastically decreased to 169 ns.

Organoruthenated Nitroxoline Derivatives Impair Tumor Cell Invasion through Inhibition of Cathepsin B Activity

Lysosomal cysteine peptidase cathepsin B (catB) is an important tumor-promoting factor involved in tumor progression and metastasis representing a relevant target for the development of new antitumor agents. In the present study, we synthesized 11 ruthenium compounds bearing either the clinical agent nitroxoline that was previously identified as potent selective reversible inhibitor of catB activity or its derivatives. We demonstrated that organoruthenation is a viable strategy for obtaining highly effective and specific inhibitors of catB endo- and exopeptidase activity, as shown using enzyme kinetics and microscale thermophoresis. Furthermore, we showed that the novel metallodrugs by catB inhibition significantly impair processes of tumor progression in in vitro cell based functional assays at low noncytotoxic concentrations. Generally, by using metallodrugs we observed an improvement in catB inhibition, a reduction of extracellular matrix degradation and tumor cell invasion in comparison to free ligands, and a correlation with the reactivity of the monodentate halide leaving ligand.

Eleven ruthenium compounds bearing either the clinical agent nitroxoline or its potent cathepsin B (catB) inhibiting derivatives were evaluated as antimetastatic agents. We demonstrated that organoruthenation is a viable strategy for obtaining highly effective and specific inhibitors of catB activities, as shown using enzyme kinetics and microscale thermophoresis. Furthermore, we showed that the novel metallodrugs significantly impair processes of tumor progression in in vitro cell based functional assays at low noncytotoxic concentrations.

Pt(IV) Bifunctional Prodrug Containing 2-(2-Propynyl)octanoato Axial Ligand: Induction of Immunogenic Cell Death on Colon Cancer

The synthesis, characterization, and in vitro activity of a cyclohexane-1 R,2 R-diamine-based Pt(IV) derivative containing the histone deacetylase inhibitor rac-2-(2-propynyl)octanoato, namely, ( OC-6-44)-acetatodichlorido(cyclohexane-1 R,2 R-diamine)( rac-2-(2-propynyl)octanoato)platinum(IV), are reported together with those of its isomers containing enantiomerically enriched axial ligands. These Pt(IV) complexes showed comparable activity, of 2 orders of magnitude higher than reference drug oxaliplatin on three human (HCT 116, SW480, and HT-29) and one mouse (CT26) colon cancer cell lines. In vivo experiments were carried out on immunocompetent BALB/c mice bearing the same syngeneic tumor. The complex ( OC-6-44)-acetatodichlorido(cyclohexane-1 R,2 R-diamine)( rac-2-(2-propynyl)octanoato)platinum(IV) showed higher tumor mass Pt accumulation than oxaliplatin, due to its higher lipophilicity, with negligible nephro- and hepatotoxicities when administered intravenously. A remarkable tumor mass invasion by cytotoxic CD8+ T lymphocytes, following the Pt(IV) treatment, indicated a strong induction of immunogenic cell death.

Light-activated ruthenium (II)-bicalutamide prodrugs for prostate cancer

Targeted delivery of clinically approved anticancer drug to tumor sites is an effective way to achieve enhanced drug efficacy as well as reduced side effects and toxicity. Here bicalutamide is caged by the Ru(II) center through the nitrile group, and three photoactive Ru(II) complexes were designed and synthesized. Docking study showed that the ruthenium(II) fragments can effectively block the binding of complexes 1-3 with AR (androgen receptor) owing to the large steric structures, thus bicalutamide in complexes 1-3 could not interact with AR-LBD (ligand binding domain). Once irradiation with blue light (465nm), complexes 1-3 can release bicalutamide and anticancer Ru(II) fragments, which possesses dual-action of AR binding and DNA interaction simultaneously. In vitro cytotoxicity study on these complexes further confirmed that complexes 1-3 exhibited considerable cytotoxicity upon irradiation with blue light. Significantly, complex 3 could be activated at 660nm, which greatly increases the scope of complex 3 to treat deeper within tissue. Theoretical calculations showed that the lowest singlet excitation energy of complex 3 is lower than those of complexes 1-2, which explains the experimental results well. Moreover, the ³MC (metal centered) states of these complexes are more stable than their ³MLCT (metal to ligand charge transfer) states, indicating that the photoactive processes of these complexes are likely to result in ligand dissociation.

A dinuclear ruthenium(ii) phototherapeutic that targets duplex and quadruplex DNA

With the aim of developing a sensitizer for photodynamic therapy, a previously reported luminescent dinuclear complex that functions as a DNA probe in live cells was modified to produce a new iso-structural derivative containing RuII(TAP)2 fragments (TAP = 1,4,5,8-tetraazaphenanthrene). The structure of the new complex has been confirmed by a variety of techniques including single crystal X-ray analysis. Unlike its parent, the new complex displays Ru → L-based 3MLCT emission in both MeCN and water. Results from electrochemical studies and emission quenching experiments involving guanosine monophosphate are consistent with an excited state located on a TAP moiety. This hypothesis is further supported by detailed DFT calculations, which take into account solvent effects on excited state dynamics. Cell-free steady-state and time-resolved optical studies on the interaction of the new complex with duplex and quadruplex DNA show that the complex binds with high affinity to both structures and indicate that its photoexcited state is also quenched by DNA, a process that is accompanied by the generation of the guanine radical cation sites as photo-oxidization products. Like the parent complex, this new compound is taken up by live cells where it primarily localizes within the nucleus and displays low cytotoxicity in the absence of light. However, in complete contrast to [{RuII(phen)2}2(tpphz)]4+, the new complex is therapeutically activated by light to become highly phototoxic toward malignant human melanoma cell lines showing that it is a promising lead for the treatment of this recalcitrant cancer.

Molecular superoxide radical photogeneration in cancer cells by dipyridophenazine iridium(iii) complexes

The switch from Type II to Type I photochemical mechanism by new Ir(iii) complexes for improved PDT of cancer under hypoxia is demonstrated.

BODIPY derivatives as light-induced free radical generators for hypoxic cancer treatment

NBDP can self-assemble into nanoparticles (NBDP NPs), which could be internalized by cells via endocytosis. After being irradiated with an 808 nm laser, the BODIPY unit could convert photons into heat and further initiates the production of alkyl radicals. The generated tumor hyperthermia and alkyl radicals synergistically kill cancer cells.

New half-sandwich ruthenium(ii) complexes as proteosynthesis inhibitors in cancer cells

New Ru(ii) arene anticancer complexes with a non-coordinated CHO group that are able to inhibit the protein synthesis; this is a new mode of action for half-sandwich metal complexes.