Photoactivated chemotherapy (PACT): the potential of excited-state d-block metals in medicine

Dual Photoreactive Ternary Ruthenium(II) Terpyridyl Complexes: A Comparative Study on Visible-Light-Induced Single-Step Dissociation of Bidentate Ligands and Generation of Singlet Oxygen

The versatile and tunable ligand-exchange dynamics in ruthenium(II)-polypyridyl complexes imposed by the modulation of the steric and electronic effects of the coordinated ligands provide an unlimited scope for developing phototherapeutic agents. The photorelease of a bidentate ligand from the Ru-center is better suited for potent Ru(II)-based photocytotoxic agents with two available labile sites for cross-linking with biological targets augmented with possible phototriggered 1O2 generation. Herein, we introduced a phenyl-terpyridine (ptpy) ligand in the octahedral Ru(II) core of [Ru(ptpy)(L-L)Cl]+ to induce structural distortion for the possible photorelease of electronically distinct bidentate ligands (L-L). For a systematic study, we designed four Ru(II) polypyridyl complexes: [Ru(ptpy)(L-L)Cl](PF6), ([1]-[4]), where L-L = 1,2-bis(phenylthio)ethane (SPH) [1], N,N,N',N'-tetramethylethylenediamine (TMEN) [2], N1,N2-diphenylethane-1,2-diimine (BPEDI) [3], and bis[2-(diphenylphosphino)phenyl]ether (DPE-Phos) [4]. The detailed photochemical studies suggest a single-step dissociation of L-L from the bis-thioether (SPH) complex [1] and diamine (TMEN) complex [2], while no photosubstitution was observed for [3] and [4]. Complex [1] and [2] demonstrated a dual role, involving both photosubstitution and 1O2 generation, while [3] and [4] solely exhibited poor to moderate 1O2 production. The interplay of excited states leading to these behaviors was rationalized from the lifetimes of the 3MLCT excited states by using transient absorption spectroscopy, suggesting intricate relaxation dynamics and 1O2 generation upon excitation. Therefore, the photolabile complexes [1] and [2] could potentially act as dual photoreactive agents via the phototriggered release of L-L (PACT) and/or 1O2-mediated PDT mechanisms, while [4] primarily can be utilized as a PDT agent.

RuBi-Ruxolitinib: A Photoreleasable Antitumor JAK Inhibitor

We describe the synthesis and biological testing of ruthenium-bipyridine ruxolitinib (RuBiRuxo), a photoreleasable form of ruxolitinib, a JAK inhibitor used as an antitumoral agent in cutaneous T-cell lymphomas (CTCL). This novel caged compound is synthesized efficiently, is stable in aqueous solution at room temperature, and is photoreleased rapidly by visible light. Irradiation of RuBiRuxo reduces cell proliferation and induces apoptosis in a light- and time-dependent manner in a CTCL cell line. This effect is specific and is mediated by a decreased phosphorylation of STAT proteins. Our results demonstrate the potential of ruthenium-based photocompounds and light-based therapeutic approaches for the potential treatment of cutaneous lymphomas and other pathologies.

A detailed density functional theory exploration of the photodissociation mechanism of ruthenium complexes for photoactivated chemotherapy

Polypyridyl Ru(II) complexes have attracted much attention due to their potential as light-activatable anticancer agents in photoactivated chemotherapy (PACT). The action of ruthenium-based PACT compounds relies on the breaking of a coordination bond between the metal center and an organic ligand via a photosubstitution reaction. Here, a detailed computational investigation of the photophysical properties of a novel trisheteroleptic ruthenium complex, [Ru(dpp)(bpy)(mtmp)]2+ (dpp = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2'-bipyridine and mtmp = 2-methylthiomethylpyridine), has been carried out by means of DFT and its time-dependent extension. All the aspects of the mechanism by which, upon light irradiation, the mtmp protecting group is released and the corresponding aquated complex, able to bind to DNA inducing cell death, is formed have been explored in detail. All the involved singlet and triplet states have been fully described, providing the calculation of the corresponding energy barriers. The involvement of solvent molecules in photosubstitution and the role played by pyridyl-thioether chelates as caging groups have been elucidated.

A colorimetric approach for monitoring the reduction of platinum(iv) complexes in aqueous solution

We report the synthesis of 4-nitrophenyl (4-NP) functionalised Pt(iv) complexes as a colorimetric strategy for monitoring Pt(iv) reduction in aqueous solution. Treatment of each 4-NP functionalised Pt(iv) complex with the biological reductant sodium ascorbate led to a colour change from clear to yellow, which was attributed to the reduction of Pt(iv) to Pt(ii) and simultaneous release of 4-nitroaniline. Trends in reduction profiles and a photocatalysed reduction for each Pt(iv) complex were observed.

Ruthenium-Cathepsin Inhibitor Conjugates for Green Light-Activated Photodynamic Therapy and Photochemotherapy

Dysregulated cathepsin activity is linked to various human diseases including metabolic disorders, autoimmune conditions, and cancer. Given the overexpression of cathepsin in the tumor microenvironment, cathepsin inhibitors are promising pharmacological agents and drug delivery vehicles for cancer treatment. In this study, we describe the synthesis and photochemical and biological assessment of a dual-action agent based on ruthenium that is conjugated with a cathepsin inhibitor, designed for both photodynamic therapy (PDT) and photochemotherapy (PCT). The ruthenium-cathepsin inhibitor conjugate was synthesized through an oxime click reaction, combining a pan-cathepsin inhibitor based on E64d with the Ru(II) PCT/PDT fragment [Ru(dqpy)(dppn)], where dqpy = 2,6-di(quinoline-2-yl)pyridine and dppn = benzo[i]dipyrido[3,2-a:2',3'-c]phenazine. Photochemical investigations validated the conjugate's ability to release a triazole-containing cathepsin inhibitor for PCT and to generate singlet oxygen for PDT upon exposure to green light. Inhibition studies demonstrated the conjugate's potent and irreversible inactivation of purified and intracellular cysteine cathepsins. Two Ru(II) PCT/PDT agents based on the [Ru(dqpy)(dppn)] moiety were evaluated for photoinduced cytotoxicity in 4T1 murine triple-negative breast cancer cells, L929 fibroblasts, and M0, M1, and M2 macrophages. The cathepsin inhibitor conjugate displayed notable selectivity for inducing cell death under irradiation compared to dark conditions, mitigating toxicity in the dark observed with the triazole control complex [Ru(dqpy)(dppn)(MeTz)]2+ (MeTz = 1-methyl-1H-1,2,4-triazole). Notably, our lead complex is among a limited number of dual PCT/PDT agents activated with green light.

Reversible Photoinduced Ligand Substitution in a Luminescent Chromium(0) Complex

Light-triggered dissociation of ligands forms the basis for many compounds of interest for photoactivated chemotherapy (PACT), in which medicinally active substances are released or "uncaged" from metal complexes upon illumination. Photoinduced ligand dissociation is usually irreversible, and many recent studies performed in the context of PACT focused on ruthenium(II) polypyridines and related heavy metal complexes. Herein, we report a first-row transition metal complex, in which photoinduced dissociation and spontaneous recoordination of a ligand unit occurs. Two scorpionate-type tridentate chelates provide an overall six-coordinate arylisocyanide environment for chromium(0). Photoexcitation causes decoordination of one of these six ligating units and coordination of a solvent molecule, at least in tetrahydrofuran and 1,4-dioxane solvents, but far less in toluene, and below detection limit in cyclohexane. Transient UV-vis absorption spectroscopy and quantum chemical simulations point to photoinduced ligand dissociation directly from an excited metal-to-ligand charge-transfer state. Owing to the tridentate chelate design and the substitution lability of the first-row transition metal, recoordination of the photodissociated arylisocyanide ligand unit can occur spontaneously on a millisecond time scale. This work provides insight into possible self-healing mechanisms counteracting unwanted photodegradation processes and seems furthermore relevant in the contexts of photoswitching and (photo)chemical information storage.

Photo-responsive hydrogels based on a ruthenium complex: synthesis and degradation

We report the synthesis of a photo responsive metallo-hydrogel based on a ruthenium(II) complex as a functional cross-linker. This metal complex contains reactive 4AAMP (= 4-(acrylamidomethyl)pyridine) ligands, which can be cleaved by light-induced ligand substitution. Ru[(bpy)2(4AAMP)2] cross-links 4-arm-PEG-SH macromonomers by thia-Michael-addition to the photocleavable 4AAMP ligand for the preparation of the hydrogel. Irradiation with green light at 529 nm leads to photodegradation of the metallo-hydrogel due to the ligand dissociation, which can be adjusted by adjusting the Ru[(bpy)2(4AAMP)2] concentration. The ligand substitution forming [Ru(bpy)2(L)2]2+ (L = H2O and CH3CN) can be monitored by 1H NMR spectroscopy and UV-visible absorption. The control of degradation by light irradiation plays a significant role in modulating the elasticity and stiffness of the light sensitive metallo-hydrogel network. The photo-responsive hydrogel is a viable substrate for cell cultures.

Optical modulation of cell nucleus penetration and singlet oxygen release of a switchable platinum complex

The activation of anticancer molecules with visible light constitutes an elegant strategy to target tumors and to improve the selectivity of treatments. In this context, we report here a visible-light activatable bis-platinum complex (DHP-Pt2) incorporating an organic photo-switchable ligand based on the dimethyldihydropyrene moiety. Illumination of this metal complex with red light (660 nm) under air readily produces the corresponding endoperoxide form (CPDO2-Pt2). These two metal complexes exhibit different DNA binding properties and, more importantly, we show that only the photogenerated CPDO2-Pt2 is able to penetrate into cancer cell nuclei, where it is then capable of releasing cytotoxic singlet oxygen. This study represents the first proof-of-concept showing that dimethyldihydropyrene derivatives can be used to transport and deliver singlet oxygen into cancer cell nuclei upon visible-light activation.

Recent Advances in Organometallic NIR Iridium(III) Complexes for Detection and Therapy

Iridium(III) complexes are emerging as a promising tool in the area of detection and therapy due to their prominent photophysical properties, including higher photostability, tunable phosphorescence emission, long-lasting phosphorescence, and high quantum yields. In recent years, much effort has been devoted to develop novel near-infrared (NIR) iridium(III) complexes to improve signal-to-noise ratio and enhance tissue penetration. In this review, we summarize different classes of organometallic NIR iridium(III) complexes for detection and therapy, including cyclometalated ligand-enabled NIR iridium(III) complexes and NIR-dye-conjugated iridium(III) complexes. Moreover, the prospects and challenges for organometallic NIR iridium(III) complexes for targeted detection and therapy are discussed.

Primary processes in photophysics and photochemistry of a potential light-activated anti-cancer dirhodium complex

Photophysics and photochemistry of a potential light-activated cytotoxic dirhodium complex [Rh2(µ-O2CCH3)2(bpy)(dppz)](O2CCH3)2, where bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine (Complex 1 or Rh2) in aqueous solutions was studied by means of stationary photolysis and time-resolved methods in time range from hundreds of femtoseconds to microseconds. According to the literature, Complex 1 demonstrates both oxygen-dependent (due to singlet oxygen formation) and oxygen-independent cytotoxicity. Photoexchange of an acetate ligand to a water molecule was the only observed photochemical reaction, which rate was increased by oxygen removal from solutions. Photoexcitation of Complex 1 results in the formation of the lowest triplet electronic excited state, which lifetime is less than 10 ns. This time is too short for diffusion-controlled quenching of the triplet state by dissolved oxygen resulting in 1O2 formation. We proposed that singlet oxygen is produced by photoexcitation of weakly bound van der Waals complexes [Rh2…O2], which are formed in solutions. If this is true, no oxygen-independent light-induced cytotoxicity of Complex 1 exists. Residual cytotoxicity deaerated solutions are caused by the remaining [Rh2…O2] complexes.

A Trojan horse approach for enhancing the cellular uptake of a ruthenium nitrosyl complex

Ruthenium nitrosyl (RuNO) complexes continue to attract significant research interest due to several appealing features that make these photoactivatable nitric oxide (NO˙) donors attractive for applications in photoactivated chemotherapy. Interesting examples of molecular candidates capable of delivering cytotoxic concentrations of NO˙ in aqueous media have been discussed. Nevertheless, the question of whether most of these highly polar and relatively large molecules are efficiently incorporated by cells remains largely unanswered. In this paper, we present the synthesis and the chemical, photophysical and photochemical characterization of RuNO complexes functionalized with 17α-ethinylestradiol (EE), a semisynthetic steroidal hormone intended to act as a molecular Trojan horse for the targeted delivery of RuNO complexes. The discussion is centered around two main molecular targets, one containing EE (EE-Phtpy-RuNO) and a reference compound lacking this biological recognition fragment (Phtpy-RuNO). While both complexes displayed similar optical absorption profiles and NO˙ release efficiencies in aqueous media, important differences were found regarding their cellular uptake towards dermal fibroblasts, with EE-Phtpy-RuNO gratifyingly displaying a remarkable 10-fold increase in cellular uptake when compared to Phtpy-RuNO, thus demonstrating the potential drug-targeting capabilities of this biomimetic steroidal conjugate.

Acetylacetonate Ruthenium Nitrosyls: A Gateway to Nitric Oxide Release in Water under Near-Infrared Excitation by Two-Photon Absorption

A fundamental challenge for phototriggered therapies is to obtain robust molecular frameworks that can withstand biological media. Photoactivatable nitric oxide (NO) releasing molecules (photoNORMs) based on ruthenium nitrosyl (RuNO) complexes are among the most studied systems due to several appealing features that make them attractive for therapeutic applications. Nevertheless, the propensity of the NO ligand to be attacked by nucleophiles frequently manifests as significant instability in water for this class of photoNORMs. Our approach to overcome this limitation involved enhancing the Ru-NO π-backbonding to lower the electrophilicity at the NO by replacing the commonly employed 2,2'-bipyridine (bpy) ligand by an anionic, electron-rich, acetylacetonate (acac). A versatile and convenient synthetic route is developed and applied for the preparation of a large library of RuNO photoNORMs with the general formula [RuNO(tpy)(acac)]2+ (tpy = 2,2':6',2″-terpyridine). A combined theoretical and experimental analysis of the Ru-NO bonding in these complexes is presented, supported by extensive single-crystal X-ray diffraction experiments and by topological analyses of the electron charge density by DFT. The enhanced π-back-bonding, systematically evidenced by several techniques, resulted in a remarkable stability in water for these complexes, where significant NO release efficiencies were recorded. We finally demonstrate the possibility of obtaining sophisticated water-stable multipolar NO-delivery platforms that can be activated in the near-IR region by two-photon absorption (TPA), as demonstrated for an octupolar complex with a TPA cross section of 1530 GM at λ = 800 nm and for which NO photorelease was demonstrated under TPA irradiation in aqueous media.

Ruthenium-Based Photoactivated Chemotherapy

Ruthenium(II) polypyridyl complexes form a vast family of molecules characterized by their finely tuned photochemical and photophysical properties. Their ability to undergo excited-state deactivation via photosubstitution reactions makes them quite unique in inorganic photochemistry. As a consequence, they have been used, in general, for building dynamic molecular systems responsive to light but, more particularly, in the field of oncology, as prodrugs for a new cancer treatment modality called photoactivated chemotherapy (PACT). Indeed, the ability of a coordination bond to be selectively broken under visible light irradiation offers fascinating perspectives in oncology: it is possible to make poorly toxic agents in the dark that become activated toward cancer cell killing by simple visible light irradiation of the compound inside a tumor. In this Perspective, we review the most important concepts behind the PACT idea, the relationship between ruthenium compounds used for PACT and those used for a related phototherapeutic approach called photodynamic therapy (PDT), and we discuss important questions about real-life applications of PACT in the clinic. We conclude this Perspective with important challenges in the field and an outlook.

GSH resistant, luminescent 2-(pyren-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline-based Ru(II)/Ir(III)/Re(I) complexes for phototoxicity in triple-negative breast cancer cells

Selective chemotherapeutic strategies necessitate the emergence of a photosensitive scaffold to abate the nuisance of cancer. In the current context, photo-activated chemotherapy (PACT) has, therefore, appeared to be very effective to vanquish the vehemence of triple-negative breast cancer (TNBC). Metal complexes have been identified to act well against cancer cell microenvironment (high GSH content, low pH, and hypoxia), and thus they have been employed in the treatment of various types of cancer. As TNBC is very challenging to treat owing to its poor prognosis, lack of a specific target, high chance of relapse, and strong metastatic ability, herein we have aspired to design GSH-resistant phototoxic Ru(II)/Ir(III)/Re(I) based pyrene imidazophenathroline complexes to selectively avert the triple-negative breast cancer. The application of complexes, [RuL], [IrL], and [ReL] in the absence and in the presence of GSH against MDA-MB-231TNBC cells, has revealed that they are very active upon irradiation of visible light compared to dark due to the creation of copious singlet oxygen (1O2) as reactive oxygen species (ROS). Among three synthesized complexes, [IrL] has shown outstanding potency (IC50 = 3.70 in the absence of GSH and IC50 = 3.90 in the presence of GSH). Also, the complex, [IrL] is capable of interacting with DNA with the highest binding constant (Kb = 0.023 × 106 M-1) along with higher protein binding affinity (KBSA = 0.0321 × 106 M-1). Here, it has been unveiled that all the complexes have been entitled to involve DNA covalent interaction through the available sites of both adenine and guanine bases.

Interrogating bioinspired ESIPT/PCET-based Ir(iii)-complexes as organelle-targeted phototherapeutics: a redox-catalysis under hypoxia to evoke synergistic ferroptosis/apoptosis

Installing proton-coupled electron transfer (PCET) in Ir-complexes is indeed a newly explored phenomenon, offering high quantum efficiency and tunable photophysics; however, the prospects for its application in various fields, including interrogating biological systems, are quite open and exciting. Herein, we developed various organelle-targeted Ir(iii)-complexes by leveraging the photoinduced PCET process to see the opportunities in phototherapeutic application and investigate the underlying mechanisms of action (MOAs). We diversified the ligands' nature and also incorporated a H-bonded benzimidazole-phenol (BIP) moiety with π-conjugated ancillary ligands in Ir(iii) to study the excited-state intramolecular proton transfer (ESIPT) process for tuning dual emission bands and to tempt excited-state PCET. These visible or two-photon-NIR light activatable Ir-catalysts generate reactive hydroxyl radicals (˙OH) and simultaneously oxidize electron donating biomolecules (1,4-dihydronicotinamide adenine dinucleotide or glutathione) to disrupt redox homeostasis, downregulate the GPX4 enzyme, and amplify oxidative stress and lipid peroxide (LPO) accumulation. Our homogeneous photocatalytic platform efficiently triggers organelle dysfunction mediated by a Fenton-like pathway with spatiotemporal control upon illumination to evoke ferroptosis poised with the synergistic action of apoptosis in a hypoxic environment leading to cell death. Ir2 is the most efficient photochemotherapy agent among others, which provided profound cytophototoxicity to 4T1 and MCF-7 cancerous cells and inhibited solid hypoxic tumor growth in vitro and in vivo.

Small Molecule Interactions with Biomacromolecules: DNA Binding Interactions of a Manganese(III) Schiff Base Complex with Potential Anticancer Activities

A manganese(III) complex, [MnIII(L)(SCN)(enH)](NO3)·H2O (1•H2O) (H2L = 2-((E)-(2-((E)-2-hydroxy-3-methoxybenzylidene-amino)-ethyl-imino)methyl)-6-methoxyphenol), has been synthesized and characterized by single-crystal X-ray diffraction analysis. The interaction of 1•H2O with DNA was studied by monitoring the decrease in absorbance of the complex at λ = 324 nm with the increase in DNA concentration, providing an opportunity to determine the binding constant of the 1•H2O-ct-DNA complex as 5.63 × 103 M-1. Similarly, fluorescence titration was carried out by adding ct-DNA gradually and monitoring the increase in emission intensity at 453 nm on excitation at λex = 324 nm. A linear form of the Benesi-Hildebrand equation yields a binding constant of 4.40 × 103 M-1 at 25 °C, establishing the self-consistency of our results obtained from absorption and fluorescence titrations. The competitive displacement reactions of dyes like ethidium bromide, Hoechst, and DAPI (4',6-diamidine-2'-phenylindole dihydrochloride) from dye-ct-DNA conjugates by 1•H2O were analyzed, and the corresponding KSV values are 1.05 × 104, 1.25 × 104, and 1.35 × 104 M-1 and the Kapp values are 2.16 × 103, 8.34 × 103, and 9.0 × 103 M-1, from which it is difficult to infer the preference of groove binding over intercalation by these DNA trackers. However, the molecular docking experiments and viscosity measurement clearly indicate the preference for minor groove binding over intercalation, involving a change in Gibbs free energy of -8.56 kcal/mol. The 1•H2O complex was then evaluated for its anticancer potential in breast cancer MCF-7 cells, which severely abrogates the growth of the cells in both 2D and 3D mammospheres, indicating its promising application as an anticancer drug through a minor groove binding interaction with ct-DNA.

Interactions of Mn complexes with DNA: the relevance of therapeutic applications towards cancer treatment

Manganese (Mn) is one of the most significant bio-metals that helps the body to form connective tissue, bones, blood clotting factors, and sex hormones. It is necessary for fat and carbohydrate metabolism, calcium absorption, blood sugar regulation, and normal brain and nerve functions. It accelerates the synthesis of proteins, vitamin C, and vitamin B. It is also involved in the catalysis of hematopoiesis, regulation of the endocrine level, and improvement of immune function. Again, Mn metalloenzymes like arginase, glutamine synthetase, phosphoenolpyruvate decarboxylase, and Mn superoxide dismutase (MnSOD) contribute to the metabolism processes and reduce oxidative stress against free radicals. Recent investigations have revealed that synthetic Mn-complexes act as antibacterial and antifungal agents. As a result, chemists and biologists have been actively involved in developing Mn-based drugs for the treatment of various diseases including cancer. Therefore, any therapeutic drugs based on manganese complexes would be invaluable for the treatment of cancer/infectious diseases and could be a better substitute for cisplatin and other related platinum based chemotherapeutic drugs. From this perspective, attempts have been made to discuss the interactions and nuclease activities of Mn(II/III/IV) complexes with DNA through which one can evaluate their therapeutic applications.

Visible light-activatable platinum(IV) prodrugs harnessing CD36 for ovarian cancer therapy

We hereby engineered photoactivatable Pt(IV) metallodrugs that harness CD36 to target ovarian cancer cells. Pt(IV) compounds mimic the structure of fatty acids and take advantage of CD36 as a "Trojan horse" to gain entry into the cells. We confirmed that CD36-dependent entry occurs using graphite furnace atomic absorption spectroscopy with ovarian cancer cells expressing different levels of CD36 and a CD36 inhibitor, SSO. Once the Pt(IV) metallodrugs enter the cancer cells, they can be activated to form Pt(II) with characteristics of cisplatin under visible light (490 nm) irradiation, promoting photoinduced electron transfer from the attached fluorophore to the metal center. This light-induced activation can increase the cytotoxicity of the Pt(IV) metallodrugs by up to 20 times toward ovarian cancer cells, inducing DNA damage and enabling efficient elimination of drug-resistant cancer cells.

Cyclic Ruthenium-Peptide Conjugates as Integrin-Targeting Phototherapeutic Prodrugs for the Treatment of Brain Tumors

To investigate the potential of tumor-targeting photoactivated chemotherapy, a chiral ruthenium-based anticancer warhead, Λ/Δ-[Ru(Ph₂phen)₂(OH₂)₂]²⁺, was conjugated to the RGD-containing Ac-MRGDH-NH₂ peptide by direct coordination of the M and H residues to the metal. This design afforded two diastereoisomers of a cyclic metallopeptide, Λ-[1]Cl₂ and Δ-[1]Cl₂. In the dark, the ruthenium-chelating peptide had a triple action. First, it prevented other biomolecules from coordinating with the metal center. Second, its hydrophilicity made [1]Cl₂ amphiphilic so that it self-assembled in culture medium into nanoparticles. Third, it acted as a tumor-targeting motif by strongly binding to the integrin (K_d = 0.061 μM for the binding of Λ-[1]Cl₂ to α_IIbβ₃), which resulted in the receptor-mediated uptake of the conjugate in vitro. Phototoxicity studies in two-dimensional (2D) monolayers of A549, U87MG, and PC-3 human cancer cell lines and U87MG three-dimensional (3D) tumor spheroids showed that the two isomers of [1]Cl₂ were strongly phototoxic, with photoindexes up to 17. Mechanistic studies indicated that such phototoxicity was due to a combination of photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) effects, resulting from both reactive oxygen species generation and peptide photosubstitution. Finally, in vivo studies in a subcutaneous U87MG glioblastoma mice model showed that [1]Cl₂ efficiently accumulated in the tumor 12 h after injection, where green light irradiation generated a stronger tumoricidal effect than a nontargeted analogue ruthenium complex [2]Cl₂. Considering the absence of systemic toxicity for the treated mice, these results demonstrate the high potential of light-sensitive integrin-targeted ruthenium-based anticancer compounds for the treatment of brain cancer in vivo.

Near-infrared-activated anticancer platinum(IV) complexes directly photooxidize biomolecules in an oxygen-independent manner

Conventional light-driven cancer therapeutics require oxygen and visible light to indirectly damage biomolecules, limiting their efficacy in deep, hypoxic tumours. Here we report the use of near-infrared-activated small-molecule Pt(IV) photooxidants to directly oxidize intracellular biomolecules in an oxygen-independent manner, achieving controllable and effective elimination of cancer stem cells. These Pt(IV) complexes accumulate in the endoplasmic reticulum and show low toxicity in the dark. Upon irradiation, the resultant metal-enhanced photooxidation effect causes them to robustly photooxidize survival-related biomolecules, induce intense oxidative stress, disrupt intracellular pH (pHi) homeostasis and initiate nonclassical necrosis. In vivo experiments confirm that the lead photooxidant can effectively inhibit tumour growth, suppress metastasis and activate the immune system. Our study validates the concept of metal-enhanced photooxidation and the subsequent chemotherapeutic applications, supporting the development of such localized photooxidants to directly damage intracellular biomolecules and decrease pHi as a strategy for effective metal-based drugs.

Ligand Rigidity Steers the Selectivity and Efficiency of the Photosubstitution Reaction of Strained Ruthenium Polypyridyl Complexes

While photosubstitution reactions in metal complexes are usually thought of as dissociative processes poorly dependent on the environment, they are, in fact, very sensitive to solvent effects. Therefore, it is crucial to explicitly consider solvent molecules in theoretical models of these reactions. Here, we experimentally and computationally investigated the selectivity of the photosubstitution of diimine chelates in a series of sterically strained ruthenium(II) polypyridyl complexes in water and acetonitrile. The complexes differ essentially by the rigidity of the chelates, which strongly influenced the observed selectivity of the photosubstitution. As the ratio between the different photoproducts was also influenced by the solvent, we developed a full density functional theory modeling of the reaction mechanism that included explicit solvent molecules. Three reaction pathways leading to photodissociation were identified on the triplet hypersurface, each characterized by either one or two energy barriers. Photodissociation in water was promoted by a proton transfer in the triplet state, which was facilitated by the dissociated pyridine ring acting as a pendent base. We show that the temperature variation of the photosubstitution quantum yield is an excellent tool to compare theory with experiments. An unusual phenomenon was observed for one of the compounds in acetonitrile, for which an increase in temperature led to a surprising decrease in the photosubstitution reaction rate. We interpret this experimental observation based on complete mapping of the triplet hypersurface of this complex, revealing thermal deactivation to the singlet ground state through intersystem crossing.

Photodynamic therapy: Innovative approaches for antibacterial and anticancer treatments

Photodynamic therapy is an alternative treatment mainly for cancer but also for bacterial infections. This treatment dates back to 1900 when a German medical school graduate Oscar Raab found a photodynamic effect while doing research for his doctoral dissertation with Professor Hermann von Tappeiner. Unexpectedly, Raab revealed that the toxicity of acridine on paramecium depends on the intensity of light in his laboratory. Photodynamic therapy is therefore based on the administration of a photosensitizer with subsequent light irradiation within the absorption maxima of this substance followed by reactive oxygen species formation and finally cell death. Although this treatment is not a novelty, there is an endeavor for various modifications to the therapy. For example, selectivity and efficiency of the photosensitizer, as well as irradiation with various types of light sources are still being modified to improve final results of the photodynamic therapy. The main aim of this review is to summarize anticancer and antibacterial modifications, namely various compounds, approaches, and techniques, to enhance the effectiveness of photodynamic therapy.

Stimuli-Responsive Gene Delivery Nanocarriers for Cancer Therapy

Gene therapy provides a promising approach in treating cancers with high efficacy and selectivity and few adverse effects. Currently, the development of functional vectors with safety and effectiveness is the intense focus for improving the delivery of nucleic acid drugs for gene therapy. For this purpose, stimuli-responsive nanocarriers displayed strong potential in improving the overall efficiencies of gene therapy and reducing adverse effects via effective protection, prolonged blood circulation, specific tumor accumulation, and controlled release profile of nucleic acid drugs. Besides, synergistic therapy could be achieved when combined with other therapeutic regimens. This review summarizes recent advances in various stimuli-responsive nanocarriers for gene delivery. Particularly, the nanocarriers responding to endogenous stimuli including pH, reactive oxygen species, glutathione, and enzyme, etc., and exogenous stimuli including light, thermo, ultrasound, magnetic field, etc., are introduced. Finally, the future challenges and prospects of stimuli-responsive gene delivery nanocarriers toward potential clinical translation are well discussed. The major objective of this review is to present the biomedical potential of stimuli-responsive gene delivery nanocarriers for cancer therapy and provide guidance for developing novel nanoplatforms that are clinically applicable.

Shine, Shine, Ruthenium Caged Drug

This is a highlight on the paper by Bonnet et al.: A Lock-and-Kill Anticancer Photoactivated Chemotherapy Agent. which constitutes an important step toward establishing photoactivated chemotherapy (PACT) as a widespread tool to treat different health issues, specially tumors. PACT can be a useful technique to deliver already tested drugs, where the effect of the desired molecule is directed only to its target after light irradiation, even in the cases in which it is difficult to achieve a precise delivery in the desired organ or tissue. Ruthenium-polipyridyl caged-compounds are near ideal devices to deliver a drug in that precise fashion, albeit they usually fail in revealing their actual location due to their weak light emission properties. The mentioned work introduces a simple and clever idea: the use of a covalently linked fluorophore to map the caged-compounds in-vivo distribution prior to the eventual irradiation to activate the chemotherapy.

Water-Soluble Carbon Monoxide-Releasing Molecules (CORMs)

Carbon monoxide-releasing molecules (CORMs) are promising candidates for producing carbon monoxide in the mammalian body for therapeutic purposes. At higher concentrations, CO has a harmful effect on the mammalian organism. However, lower doses at a controlled rate can provide cellular signaling for mandatory pharmacokinetic and pathological activities. To date, exploring the therapeutic implications of CO dose as a prodrug has attracted much attention due to its therapeutic significance. There are two different methods of CO insertion, i.e., indirect and direct exogenous insertion. Indirect exogenous insertion of CO suggests an advantage of reduced toxicity over direct exogenous insertion. For indirect exogenous insertion, researchers are facing the issue of tissue selectivity. To solve this issue, developers have considered the newly produced CORMs. Herein, metal carbonyl complexes (MCCs) are covalently linked with CO molecules to produce different CORMs such as CORM-1, CORM-2, and CORM-3, etc. All these CORMs required exogenous CO insertion to achieve the therapeutic targets at the optimized rate under peculiar conditions or/and triggering. Meanwhile, the metal residue was generated from i-CORMs, which can propagate toxicity. Herein, we explain CO administration, water-soluble CORMs, tissue accumulation, and cytotoxicity of depleted CORMs and the kinetic profile of CO release.

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.

Amphiphilic Metallodrug Assemblies with Red-Light-Enhanced Cellular Internalization and Tumor Penetration for Anticancer Phototherapy

Metallodrugs are widely used in cancer treatment. The modification of metallodrugs with polyethylene glycol (PEGylation) prolongs blood circulation and improves drug accumulation in tumors; it represents a general strategy for drug delivery. However, PEGylation hinders cellular internalization and tumor penetration, which reduce therapeutic efficacy. Herein, the red-light-enhanced cellular internalization and tumor penetration of a PEGylated anticancer agent, PEGylated Ru complex (Ru-PEG), are reported upon. Ru-PEG contains a red-light-cleavable PEG ligand, anticancer Ru complex moiety, and fluorescent pyrene group for imaging and self-assembly. Ru-PEG self-assembles into vesicles that circulate in the bloodstream and accumulate in the tumors. Red-light irradiation induces dePEGylation and changes the Ru-PEG vesicles to large compound micelles with smaller diameters and higher zeta potentials, which enhance tumor penetration and cellular internalization. Red-light irradiation also generates intracellular ¹ O₂ , which induces the death of cancer cells. This work presents a new strategy to enhance the cellular internalization and tumor penetration of anticancer agents for efficient phototherapy.

Organogold(III) Complexes Display Conditional Photoactivities: Evolving From Photodynamic into Photoactivated Chemotherapy in Response to O2 Consumption for Robust Cancer Therapy

Photodynamic therapy (PDT) is a spatiotemporally controllable, powerful approach in combating cancers but suffers from low activity under hypoxia, whereas photoactivated chemotherapy (PACT) operates in an O₂ -independent manner but compromises the ability to harness O₂ for potent photosensitization. Herein we report that cyclometalated gold(III)-alkyne complexes display a PDT-to-PACT evolving photoactivity for efficient cancer treatment. On the one hand, the gold(III) complexes can act as dual photosensitizers and substrates, leading to conditional PDT activity in oxygenated condition that progresses to highly efficient PACT (ϕ up to 0.63) when O₂ is depleted in solution and under cellular environment. On the other hand, the conditional PDT-to-PACT reactivity can be triggered by external photosensitizers in a similar manner in vitro and in vivo, giving additional tumor-selectivity and/or deep tissue penetration by red-light irradiation that leads to robust anticancer efficacy.

Luminescent and Photofunctional Transition Metal Complexes: From Molecular Design to Diagnostic and Therapeutic Applications

There has been emerging interest in the exploitation of the photophysical and photochemical properties of transition metal complexes for diagnostic and therapeutic applications. In this Perspective, we highlight the major recent advances in the development of luminescent and photofunctional transition metal complexes, in particular, those of rhenium(I), ruthenium(II), osmium(II), iridium(III), and platinum(II), as bioimaging reagents and phototherapeutic agents, with a focus on the molecular design strategies that harness and modulate the interesting photophysical and photochemical behavior of the complexes. We also discuss the current challenges and future outlook of transition metal complexes for both fundamental research and clinical applications.

Light Triggers the Antiproliferative Activity of Naphthalimide-Conjugated (η6-arene)ruthenium(II) Complexes

We report the synthesis and characterization of three half-sandwich Ru(II) arene complexes [(η⁶-arene)Ru(N,N')L][PF₆]₂ containing arene = p-cymene, N,N' = bipyridine, and L = pyridine meta- with methylenenaphthalimide (C1), methylene(nitro)naphthalimide (C2), or methylene(piperidinyl)naphthalimide (C3). The naphthalimide acts as an antenna for photoactivation. After 3 h of irradiation with blue light, the monodentate pyridyl ligand had almost completely dissociated from complex C3, which contains an electron donor on the naphthalimide ring, whereas only 50% dissociation was observed for C1 and C2. This correlates with the lower wavelength and strong absorption of C3 in this region of the spectrum (λ_max = 418 nm) compared with C1 and C2 (λ_max = 324 and 323 nm, respectively). All the complexes were relatively non-toxic towards A549 human lung cancer cells in the dark, but only complex C3 exhibited good photocytoxicity towards these cancer cells upon irradiation with blue light (IC₅₀ = 10.55 ± 0.30 μM). Complex C3 has the potential for use in photoactivated chemotherapy (PACT).

Unravelling the role of [Ru(bpy)2(OH2)2]2+ complexes in photo-activated chemotherapy

Photoactivated chemotherapy (PACT) has emerged as a promising strategy to selectively target cancer cells by using light irradiation to generate cytotoxic complexes in situ through a mechanism involving ligand-loss. Due to their rich optical properties and excited state chemistry, Ru polypyridyl complexes have attracted significant attention for PACT. However, studying PACT is complicated by the fact that many of these Ru complexes can also undergo excited-state electron transfer to generate ¹O₂ species. In order to deconvolute the biological roles of possible photo-decomposition products without the added complication of excited-state electron transfer chemistry, we have developed a methodology to systematically investigate each product individually, and assess the structure-function relationship. Here, we synthesized a series of eight distinct Ru polypyridyl complexes: Ru-Xa ([Ru(NN)₃]²⁺), Ru-Xb ([Ru(NN)₂py₂]²⁺), and Ru-Xc ([Ru(NN)(OH₂)₂]²⁺) where NN = 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, or dimethyl 2,2'-bipyridine-4,4'-dicarboxylate and py = pyridine. The cytotoxicity of these complexes was investigated in two cell lines amenable to PACT: H23 (breast cancer) and T47D (lung cancer). We confirmed that light irradiation of Ru-Xa and Ru-Xb complexes generate Ru-Xc complexes through UV-visible spectroscopy, and observed that the Ru-Xc complexes are the most toxic against the cancer cell lines. In addition, we have shown that ligand release and biological activity including bovine serum albumin (BSA) binding, lipophilicity, and DNA interaction are altered when different groups are appended to the bipyridine ligands. We believe that the methodology presented here will enhance the development of more potent and selective PACT agents moving forward.

Materials and device design for advanced phototherapy systems

Phototherapy has recently emerged as a promising solution for cancer treatment due to its multifunctionality and minimal invasiveness. Notwithstanding the limited penetration depth of light through skin, the ability of photopharmaceutical device systems to deliver light to desired lesions is important. The device system deploys advanced biocompatible materials and fabrication technologies for electronics, and eventually enables more efficient phototherapy. In this review, we focus on diverse optical electronics to illuminate the lesion site with light. Then, moving on to the phototherapy, we highlight photo-thermal therapy with light absorbing materials, photo-activated chemotherapy with light sensitive materials, and photo-dynamic therapy using photosensitizers. Furthermore, we introduce a drug delivery system that can deliver these photopharmaceutical agents spatiotemporally to the tumor site. To this end, we provide a general overview of materials and devices for phototherapy and discuss critical issues and pending limitations of such phototherapy.

Photosubstitution in a trisheteroleptic ruthenium complex inhibits conjunctival melanoma growth in a zebrafish orthotopic xenograft model

In vivo data are rare but essential for establishing the clinical potential of ruthenium-based photoactivated chemotherapy (PACT) compounds, a new family of phototherapeutic drugs that are activated via ligand photosubstitution. Here a novel trisheteroleptic ruthenium complex [Ru(dpp)(bpy)(mtmp)](PF₆)₂ ([2](PF₆)₂, dpp = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, mtmp = 2-methylthiomethylpyridine) was synthesized and its light-activated anticancer properties were validated in cancer cell monolayers, 3D tumor spheroids, and in embryonic zebrafish cancer models. Upon green light irradiation, the non-toxic mtmp ligand is selectively cleaved off, thereby releasing a phototoxic ruthenium-based photoproduct capable notably of binding to nuclear DNA and triggering DNA damage and apoptosis within 24–48 h. In vitro, fifteen minutes of green light irradiation (21 mW cm⁻², 19 J cm⁻², 520 nm) were sufficient to generate high phototherapeutic indexes (PI) for this compound in a range of cancer cell lines including lung (A549), prostate (PC3Pro4), conjunctival melanoma (CRMM1, CRMM2, CM2005.1) and uveal melanoma (OMM1, OMM2.5, Mel270) cancer cell lines. The therapeutic potential of [2](PF₆)₂ was further evaluated in zebrafish embryo ectopic (PC3Pro4) or orthotopic (CRMM1, CRMM2) tumour models. The ectopic model consisted of red fluorescent PC3Pro4-mCherry cells injected intravenously (IV) into zebrafish, that formed perivascular metastatic lesions at the posterior ventral end of caudal hematopoietic tissue (CHT). By contrast, in the orthotopic model, CRMM1- and CRMM2-mCherry cells were injected behind the eye where they developed primary lesions. The maximally-tolerated dose (MTD) of [2](PF₆)₂ was first determined for three different modes of compound administration: (i) incubating the fish in prodrug-containing water (WA); (ii) injecting the prodrug intravenously (IV) into the fish; or (iii) injecting the prodrug retro-orbitally (RO) into the fish. To test the anticancer efficiency of [2](PF₆)₂, the embryos were treated 24 h after engraftment at the MTD. Optimally, four consecutive PACT treatments were performed on engrafted embryos using 60 min drug-to-light intervals and 90 min green light irradiation (21 mW cm⁻², 114 J cm⁻², 520 nm). Most importantly, this PACT protocol was not toxic to the zebrafish. In the ectopic prostate tumour models, where [2](PF₆)₂ showed the highest photoindex in vitro (PI > 31), the PACT treatment did not significantly diminish the growth of primary lesions, while in both conjunctival melanoma orthotopic tumour models, where [2](PF₆)₂ showed more modest photoindexes (PI ∼ 9), retro-orbitally administered PACT treatment significantly inhibited growth of the engrafted tumors. Overall, this study represents the first demonstration in zebrafish cancer models of the clinical potential of ruthenium-based PACT, here against conjunctival melanoma.

A new tris-heteroleptic photoactivated chemotherapy ruthenium complex induces apoptosis upon green light activation in a zebrafish orthothopic conjunctival melanoma xenograft model.

Dissociation of Bipyridine and Coordination with Nitrosyl: Cyclometalated Ruthenium Nitrosyl Complex

A novel family of ruthenium nitrosyl complexes [Ru(bpy)(C^∧N)(MeCN)NO](PF₆)₂ (2a-2e, bpy = 2,2'-bipyridine, HC^∧N = 2-phenylpyridine and its derivatives) has been prepared by reacting cyclometalated ruthenium complexes [Ru(bpy)₂(C^∧N)][PF₆] (1a-1e) with NO⁺, which were comprehensively characterized by mass, IR, NMR, and UV-vis spectra as well as the single-crystal X-ray structure determinations. Herein, the coordination geometry of Ru atoms in 2a-2e is a distorted octahedron and {Ru^II-NO⁺}⁶ is present in these complexes. Theoretical calculations suggest that the reactions involving dissociation of one bipyridine and coordination with NO⁺ proceed spontaneously (ΔG < 0) and the transformation from 1a-1e to the intermediates is dominated by substituents (ΔG_RI varies from -1.19 to -1.53 eV), which influence the binding energy between Ru(II) and NO⁺ in complexes 2a-2e (-89.42 to -101.17 kcal/mol) and thus control the photorelease of NO on a certain scale. The weak absorption bands in the visible region could be attributed to the contribution of dπ(Ru^II) → π*(NO⁺), which were enhanced greatly under light, indicating the possible release of NO. The photoinduced NO, as well as singlet oxygen (¹O₂), was then confirmed by EPR spectra, and the amount of NO released from 2a-2e was estimated via Griess reagent assay. The cytotoxicity of these complexes with or without visible light irradiation was also investigated using an MTT assay.

The Rationale for "Laser-Induced Thermal Therapy (LITT) and Intratumoral Cisplatin" Approach for Cancer Treatment

Cisplatin is one of the most widely used anticancer drugs in the treatment of various types of solid human cancers, as well as germ cell tumors, sarcomas, and lymphomas. Strong evidence from research has demonstrated higher efficacy of a combination of cisplatin and derivatives, together with hyperthermia and light, in overcoming drug resistance and improving tumoricidal efficacy. It is well known that the antioncogenic potential of CDDP is markedly enhanced by hyperthermia compared to drug treatment alone. However, more recently, accelerators of high energy particles, such as synchrotrons, have been used to produce powerful and monochromatizable radiation to induce an Auger electron cascade in cis-platinum molecules. This is the concept that makes photoactivation of cis-platinum theoretically possible. Both heat and light increase cisplatin anticancer activity via multiple mechanisms, generating DNA lesions by interacting with purine bases in DNA followed by activation of several signal transduction pathways which finally lead to apoptosis. For the past twenty-seven years, our group has developed infrared photo-thermal activation of cisplatin for cancer treatment from bench to bedside. The future development of photoactivatable prodrugs of platinum-based agents injected intratumorally will increase selectivity, lower toxicity and increase efficacy of this important class of antitumor drugs, particularly when treating tumors accessible to laser-based fiber-optic devices, as in head and neck cancer. In this article, the mechanistic rationale of combined intratumor injections of cisplatin and laser-induced thermal therapy (CDDP-LITT) and the clinical application of such minimally invasive treatment for cancer are reviewed.

Low-Intensity Light-Responsive Anticancer Activity of Platinum(II) Complex Nanocolloids on 2D and 3D In Vitro Cancer Cell Model

This study aimed to evaluate the therapeutic efficacy of low-intensity visible light responsive nanocolloids of a Pt-based drug using a 2D and three-dimensional (3D) in vitro cancer cell model. Biocompatible and biodegradable polymeric nanocolloids, obtained using the ultrasonication method coupled with Layer by Layer technology, were characterized in terms of size (100 ± 20 nm), physical stability, drug loading (78%), and photoactivation through spectroscopy studies. The in vitro biological effects were assessed in terms of efficacy, apoptosis induction, and DNA-Pt adducts formation. Biological experiments were performed both in dark and under visible light irradiation conditions, exploiting the complex photochemical properties. The light-stimuli responsive nanoformulation gave a significant enhancement in drug bioactivity. This allowed us to achieve satisfying results by using nanomolar drug concentration (50 nM), which was ineffective in darkness condition. Furthermore, our nanocolloids were validated in 3D in vitro spheroids using confocal microscopy and cytofluorimetric assay to compare their behavior on culture in 2D monolayers. The obtained results confirmed that these nanocolloids are promising tools for delivering Pt-based drugs.

Alkylgold(III) Complexes Undergo Unprecedented Photo-Induced β-Hydride Elimination and Reduction for Targeted Cancer Therapy

Spatiotemporally controllable activation of prodrugs within tumors is highly desirable for cancer therapy to minimize toxic side effects. Herein we report that stable alkylgold(III) complexes can undergo unprecedented photo-induced β-hydride elimination, releasing alkyl ligands and forming gold(III)-hydride intermediates that could be quickly converted into bioactive [Au^III -S] adducts; meanwhile, the remaining alkylgold(III) complexes can photo-catalytically reduce [Au^III -S] into more bioactive Au^I species. Such photo-reactivities make it possible to functionalize gold complexes on the auxiliary alkyl ligands without attenuating the metal-biomacromolecule interactions. As a result, the gold(III) complexes containing glucose-functionalized alkyl ligands displayed efficient and tumor-selective uptake; notably, after one- or two-photon activation, the complexes exhibited high thioredoxin reductase (TrxR) inhibition, potent cytotoxicity, and strong antiangiogenesis and antitumor activities in vivo.

Applications of Antimicrobial Photodynamic Therapy against Bacterial Biofilms

Antimicrobial photodynamic therapy and allied photodynamic antimicrobial chemotherapy have shown remarkable activity against bacterial pathogens in both planktonic and biofilm forms. There has been little or no resistance development against antimicrobial photodynamic therapy. Furthermore, recent developments in therapies that involve antimicrobial photodynamic therapy in combination with photothermal hyperthermia therapy, magnetic hyperthermia therapy, antibiotic chemotherapy and cold atmospheric pressure plasma therapy have shown additive and synergistic enhancement of its efficacy. This paper reviews applications of antimicrobial photodynamic therapy and non-invasive combination therapies often used with it, including sonodynamic therapy and nanozyme enhanced photodynamic therapy. The antimicrobial and antibiofilm mechanisms are discussed. This review proposes that these technologies have a great potential to overcome the bacterial resistance associated with bacterial biofilm formation.

BODIPY-dipicolylamine complexes of platinum(II): X-ray structure, cellular imaging and organelle-specific near-IR light type-II PDT

Dipicolylamine (dpa) based platinum(II) complexes [Pt(L1-3)Cl]Cl (1-3), where L2 and L3 are green and red light BODIPY-tagged dpa ligands and L1 is a benzyl derivative of dpa, were synthesized and characterized and their in vitro cytotoxicity was studied. The perchlorate salt of complex 2 was structurally characterized. It showed a PtN₃Cl core with a deformed square-planar geometry. At pH 7.2, complexes 2 and 3 showed strong absorption bands at 500 nm (ε ∼6.8 × 10⁴ dm³ mol^-1 cm^-1) and 653 nm (ε ∼1.0 × 10⁵ dm³ mol^-1 cm^-1) in a 1 : 1 (v/v) mixture of dimethyl sulfoxide and Dulbecco's phosphate-buffered saline (DMSO/DPBS), respectively. They displayed respective emission bands at 515 and 677 nm having fluorescence quantum yield values of 0.36 and 0.25. Complex 3 generated singlet oxygen, as evidenced from the 1,3-diphenylisobenzofuran titration experiments and mechanistic DNA photocleavage study. It showed high photocytotoxicity in red light (600-720 nm) with half-maximal inhibitory concentration (IC₅₀) values of 1.73 and 2.67 μM in HeLa and A549 cells. The complexes showed significantly reduced chemo-PDT activity in a non-cancerous HPL1D cell line and in the dark. The 2',7'-dichlorofluorescein diacetate assay revealed reactive oxygen species-mediated type-II photodynamic therapy (PDT) activity. Cellular imaging of A549 cancer cells using complexes 2 and 3 revealed their preferential localization in mitochondria and endoplasmic reticulum. The annexin V-FITC/PI assay confirmed apoptotic cell damage. Cell cycle analysis indicated arrest in the G1 phase upon red light irradiation. Pt-DNA adduct formation was proposed from a DNA binding experiment with green light active complex 2 and 9-ethylguanine as a nucleobase from the mass spectral study.

DFT Study on the Substituent Effect of Anticancer Picoline-Diazido-Pt(IV) Compounds

The geometric structure of azido Pt(IV) compounds containing picoline was calculated by using density functional theory(DFT) at the LSDA/SDD level. The ESP distribution shows the possible reaction sites of the compounds. In addition, the frequency calculation results assigned the infrared spectra of these compounds, and specified important stretching and bending vibrations. The HOMO-LUMO energy gaps of these compounds are also calculated to explain the charge transfer of the molecules. The distribution of Mulliken charges and natural atomic charges of these atoms is also calculated. Natural bond orbital(NBO) analysis explains the intramolecular interactions and their electron density.

Phototherapeutic anticancer strategies with first-row transition metal complexes: a critical review

Photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) are therapeutic techniques based on a photosensitizer (PS) and light. These techniques allow the spatial and temporal control of the activation of drugs with light. Transition metal complexes are attractive compounds as photoactivatable prodrugs since their excited states can be appropriately designed by subtle modifications of the ligands, the metal centre, or the oxidation state. However, most metal-based PSs contain heavy metals such as Ru, Os, Ir, Pt or Au, which are expensive and non-earth-abundant, contrary to first-row transition metals. In this context, the exploration of the photochemical properties of complexes based on first-row transition metals appears to be extremely promising. This did encourage several groups to develop promising PSs based on these metals. This review presents up-to-date state-of-the-art information on first-row-transition metal complexes, from titanium to zinc in regard to their application as PSs for phototherapeutic applications.

Cytotoxicity of Metal-Based Photoactivated Chemotherapy (PACT) Compounds

Metal-based compounds have been used to treat cancer for decades, with cisplatin being the most common and widely used. Photodynamic therapy (PDT) is another clinical modality used to fight cancer, which uses a photosensitizer (PS) that localizes in cancer tissues. This PS is activated by the illumination of the tumor with visible light. Photoactivated chemotherapy (PACT) is a new concept that brings these two ideas together. Like PDT , PACT aims at sparing healthy tissues while maintaining toxicity against cancerous cells. Unlike PDT , which often stops working when the concentration of dioxygen in illuminated tissues is too low, light activation of PACT compounds remains efficient in hypoxic cancer cells. This chapter addresses the methodology to experimentally measure the phototoxicity of PACT compounds in cancer cell lines, under both normoxic and hypoxic conditions.

Photodynamic therapy with mitochondria-targeted biscyclometallated Ir(III) complexes. Multi-action mechanism and strong influence of the cyclometallating ligand

Photodynamic therapy is an alternative to classical chemotherapy due to its potential to reduce side effects by a controlled activation of a photosensitizer through local irradiation with light. The photosensitizer then interacts with oxygen and generates reactive oxygen species. Iridium biscyclometallated complexes are very promising photosensitizers due to their exceptional photophysical properties and their ability to target mitochondria. Four Ir(III) biscyclometallated complexes of formula [Ir(C^N)₂(N^N')]Cl, where N^N' is a ligand containing a benzimidazolyl fragment, have been synthesized and characterized. The C^N ligands were 2-phenylpyridinate (ppy) and 2-(2,4-difluorophenyl)pyridinate (dfppy). The complexes exhibited high photostability. The electrochemical and photophysical properties were modulated by both the cyclometallating and the ancillary ligands. The dfppy derivatives yielded the highest emission energy values, quantum yields of phosphorescence and excited state lifetimes. All complexes generated ¹O₂ in aerated solutions upon irradiation. Biological studies revealed that these complexes have a moderate cytotoxicity in the dark against different human cancer cell lines: prostate (PC-3), colon (CACO-2) and melanoma (SK-MEL-28), and against non-malignant fibroblasts (CCD-18Co). However, derivatives with ppy ligands ([1a]Cl, [2a]Cl) yielded a relevant photodynamic activity upon light irradiation (450 nm, 24.1 J cm^-2), with phototoxicity indexes (EC_50,dark/EC_50,light) of 20.8 and 17.3, respectively, achieved in PC-3 cells. Mechanistic studies showed that these complexes are taken up by the cells through endocytosis and preferentially accumulate in mitochondria. Upon photoactivation, the complexes induced mitochondrial membrane depolarization and DNA damage, thus triggering cell death, mainly by apoptosis. Complex [1a]Cl is also able to oxidize NADH. This mitochondria-targeted photodynamic mechanism greatly inhibited the reproductive capacity of cancer cells and provides a valuable alternative to traditional chemotherapy for the controlled treatment of cancer.

Phosphorescent NIR emitters for biomedicine: applications, advances and challenges

Application of NIR (near-infrared) emitting transition metal complexes in biomedicine is a rapidly developing area of research. Emission of this class of compounds in the "optical transparency windows" of biological tissues and the intrinsic sensitivity of their phosphorescence to oxygen resulted in the preparation of several commercial oxygen sensors capable of deep (up to whole-body) and quantitative mapping of oxygen gradients suitable for in vivo experimental studies. In addition to this achievement, the last decade has also witnessed the increased growth of successful alternative applications of NIR phosphors that include (i) site-specific in vitro and in vivo visualization of sophisticated biological models ranging from 3D cell cultures to intact animals; (ii) sensing of various biologically relevant analytes, such as pH, reactive oxygen and nitrogen species, RedOx agents, etc.; (iii) and several therapeutic applications such as photodynamic (PDT), photothermal (PTT), and photoactivated cancer (PACT) therapies as well as their combinations with other therapeutic and imaging modalities to yield new variants of combined therapies and theranostics. Nevertheless, emerging applications of these compounds in experimental biomedicine and their implementation as therapeutic agents practically applicable in PDT, PTT, and PACT face challenges related to a critically important improvement of their photophysical and physico-chemical characteristics. This review outlines the current state of the art and achievements of the last decade and stresses the most promising trends, major development prospects, and challenges in the design of NIR phosphors suitable for biomedical applications.

Photoactivable Ruthenium-Based Coordination Polymer Nanoparticles for Light-Induced Chemotherapy

Green light photoactive Ru-based coordination polymer nanoparticles (CPNs), with chemical formula [[Ru(biqbpy)]_1.5(bis)](PF₆)₃ (biqbpy = 6,6'-bis[N-(isoquinolyl)-1-amino]-2,2'-bipyridine; bis = bis(imidazol-1-yl)-hexane), were obtained through polymerization of the trans-[Ru(biqbpy)(dmso)Cl]Cl complex (Complex 1) and bis bridging ligands. The as-synthesized CPNs (50 ± 12 nm diameter) showed high colloidal and chemical stability in physiological solutions. The axial bis(imidazole) ligands coordinated to the ruthenium center were photosubstituted by water upon light irradiation in aqueous medium to generate the aqueous substituted and active ruthenium complexes. The UV-Vis spectral variations observed for the suspension upon irradiation corroborated the photoactivation of the CPNs, while High Performance Liquid Chromatography (HPLC) of irradiated particles in physiological media allowed for the first time precisely quantifying the amount of photoreleased complex from the polymeric material. In vitro studies with A431 and A549 cancer cell lines revealed an 11-fold increased uptake for the nanoparticles compared to the monomeric complex [Ru(biqbpy)(N-methylimidazole)₂](PF₆)₂ (Complex 2). After irradiation (520 nm, 39.3 J/cm²), the CPNs yielded up to a two-fold increase in cytotoxicity compared to the same CPNs kept in the dark, indicating a selective effect by light irradiation. Meanwhile, the absence of ¹O₂ production from both nanostructured and monomeric prodrugs concluded that light-induced cell death is not caused by a photodynamic effect but rather by photoactivated chemotherapy.