Efficient photodynamic therapy of cancer using chemotherapeutic porphyrin–ruthenium metalla-cubes

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

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

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

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

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

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

Theoretical investigation of [Ru(bpy)2(HAT)]2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene; bpy = 2,2'-bipyridine): Photophysics and reactions in excited state

In this article, Density Functional Theory based calculations, including dispersion corrections, PBE0(D3BJ)/Def2-TZVP(-f), were performed to elucidate the photophysics of the [Ru(bpy)₂(HAT)]²⁺ complex in water. In addition, the thermodynamics of the charge and electron transfer excited state reactions of this complex with oxygen, nitric oxide and Guanosine-5'-monophosphate nucleotide (GMP) were investigated. The first singlet excite state, S₁, strongly couples with the second and third triplet excited states (T₂ and T₃) giving rise to a high intersystem crossing rate of 6.26 × 10¹¹ s^-1 which is ∼10⁶ greater than the fluorescence rate decay. The thermodynamics of the excited reactions revealed that all electron transfer reactions investigated are highly favorable, due mainly to the high stability of the triply charged radical cation ²PS^•3+ species formed after the electron has been transferred. Excited state electron transfer from the GMP nucleotide to the complex is also highly favorable (ΔG_sol = -92.6 kcal/mol), showing that this complex can be involved in the photooxidation of DNA, in line with experimental findings. Therefore, the calculations allow to conclude that the [Ru(bpy)₂(HAT)]²⁺ complex can act in Photodynamic therapy through both mechanisms type I and II, through electron transfer from and to the complex and triplet-triplet energy transfer, generating ROS, RNOS and through DNA photooxidation. In addition, the work also opens a perspective of using this complex for the in-situ generation of the singlet nitroxyl (¹NO^-) species, which can have important applications for the generation of HNO and may have, therefore, important impact for physiological studies involving HNO.

Bioconjugate Supramolecular Pd2+ Metallacages Penetrate the Blood Brain Barrier In Vitro and In Vivo

The biomedical application of discrete supramolecular metal-based structures, specifically self-assembled metallacages, is still an emergent field of study. Capitalizing on the knowledge gained in recent years on the development of 3-dimensional (3D) metallacages as novel drug delivery systems and theranostic agents, we explore here the possibility to target [Pd₂L₄]⁴⁺ cages (L = 3,5-bis(3-ethynylpyridine)phenyl ligand) to the brain. In detail, a new water-soluble homoleptic cage (C^PepH3) tethered to a blood brain barrier (BBB)-translocating peptide was synthesized by a combination of solid-phase peptide synthesis (SPPS) and self-assembly procedures. The cage translocation efficacy was assessed by inductively coupled mass spectrometry (ICP-MS) in a BBB cellular model in vitro. Biodistribution studies of the radiolabeled cage [[^99mTcO₄]^- ⊂ C^PepH3] in the CD1 mice model demonstrate its brain penetration properties in vivo. Further DFT studies were conducted to model the structure of the [[^99mTcO₄]^- ⊂ cage] complex. Moreover, the encapsulation capabilities and stability of the cage were investigated using the [ReO₄]^- anion, the "cold" analogue of [^99mTcO₄]^-, by ¹H NMR spectroscopy. Overall, our study constitutes another proof-of-concept of the unique potential of supramolecular coordination complexes for modifying the physiochemical and biodistribution properties of diagnostic species.

Unmasking Arene Ruthenium Building Blocks

We have, like many others, contributed to the development and to the popularity of arene ruthenium assemblies. From early on, our research was driven by applications, mainly biological (therapeutic, drug delivery, DNA interactions, photodynamic therapy, imaging). For nearly 15 years, we have focused on the use of arene ruthenium building block as a tool to construct added-value objects. In this account, we want to give the basic reasons behind our choice, and uncover our most successful examples, with an emphasis on the foreseen applications.

Theoretical exploration of the photophysical properties of two-component RuII-porphyrin dyes as promising assemblies for a combined antitumor effect

Due to the extraordinary success of porphyrins in photodynamic therapy (PDT) and Ru compounds as chemotherapeutics, a series of RuII-porphyrin complexes have recently been synthesized and proposed as promising dual-action therapeutic agents. The results of a careful DFT and TDDFT investigation on four mononuclear pyridyl triphenylporphyrin RuII-arene complexes are herein reported and compared with those obtained for the metal-free derivatives. The investigation aims at shedding light on the modulation of the photophysical properties of the light absorber upon metalation and exploring the hydrolysis process of the RuII-moiety in the presence of the bulky porphyrin unit. Type I and Type II photoreactions were analyzed computing absorption spectra, singlet-triplet energy gaps, spin orbit coupling constants and vertical electron affinity (VEA) along with ionization potentials (VIP) for all the investigated compounds, while the chloride/water exchange reaction kinetics were determined by exploring the first and second aquation reactions of the Ru-moiety. Despite the highly similar photophysical properties displayed by the members of this class of compounds, an analysis of the hydrolysis processes in the dark allows to point out an interesting difference related to the type of pyridylporphyrin isomer and could be a preliminary explanation of the greater phototoxicity experimentally found for 3'-pyridyl substituted compounds.

Self-Assembly of Porphyrin-Containing Metalla-Assemblies and Cancer Photodynamic Therapy

In this report, we describe the synthesis of two porphyrin-containing Pt(II) supramolecular assemblies via coordination-driven self-assembly. X-ray crystallographic analysis on one assembly reveals that the metalla-assembly formation imposes large interchromophore distances, leading to a higher ¹O₂ generation efficiency, relative to the corresponding small molecular precursors. The metalla-assemblies were examined as photosensitizers for photodynamic therapy as the potential reduction of the unfavorable self-aggregation phenomenon. In vivo and in vitro investigations demonstrate that the metalla-assemblies exhibit enhanced anticancer activity with minimal dose requirement and side effects comparable to the small molecule precursors. Thus, our work demonstrates that self-assembly provides a promising methodology for enhancing the therapeutic effectiveness of anticancer agents.

Dual function of lectins — new perspectives in targeted photodynamic therapy

Porphyrins and phthalocyanines are photosensitizers (PS) that are used in clinical imaging, detection of cancer cells and are particularly applied in photodynamic therapy (PDT). Many scientists have been focused on the design of different porphyrin compounds. However, similar to other anti-cancer agents, they cannot selectively recognize tumor tissues. Scientists are seeking new methods to overcome this problem and to find appropriate targeted delivery strategies. Plant lectins are especially suitable molecules for such targeting as they preferentially recognize specific antigens on the glycosylated cancer cells. This review will give more detailed information about the dual function of lectins and their interactions with PSs, which is a new perspective in targeted PDT. The implications and potential applications of such studies will also be discussed.

Synthesis of highly water soluble tetrabenzoporphyrins and their application toward photodynamic therapy

Novel tetraaryl-(pyridinium-4-yl)-tetrabenzoporphyrins have been successfully synthesized via a Heck-based sequence reaction. These tetrabenzoporphyrins were substituted with eight pyridyl groups at the fused benzene rings. Methylation of the pyridyl groups with methyl iodide afforded highly water soluble tetrabenzoporphyrins carrying eight ionic groups. The extended [Formula: see text]-conjugation broadened and red-shifted the absorption band of these porphyrins to 650–750 nm. These cationic tetrabenzoporphyrins showed non-toxicity in the dark up to 100 uM. High phototoxicity with IC[Formula: see text] values lower than 18 [Formula: see text]M were obtained for these tetrabenzoporphyrins.

Exo-Functionalized Metallacages as Host-Guest Systems for the Anticancer Drug Cisplatin

Within the framework of designing new self-assembled metallosupramolecular architectures for drug delivery, seven [Pd2L4]4+ metallacages (L = 2,6-bis(pyridine-3-ylethynyl)pyridine) featuring different groups in exo-position, selected to enhance the cage solubility in aqueous environment, were synthesized. Thus, carboxylic acids, sugars, and PEG groups were tethered to the bispyridyl ligands directly or via disulfide bond formation, as well as via click chemistry. The ligands and respective cages were characterized by different methods, including NMR spectroscopy and high-resolution electrospray mass spectrometry (HR-ESI-MS). While the two ligands featuring carboxylic acid-functionalized groups showed improved solubility in water, the other ligands were soluble only in organic solvents. Unfortunately, all the respective self-assembled cages were also insoluble in water. Afterwards, the encapsulation properties of the anticancer drug cisplatin in selected [Pd2L4]X4 cages (X =NO 3 - ,BF 4 - ) were studied by 1H, 1H DOSY, and 195Pt NMR spectroscopy. The effect of the counter ions as well as of the polarity of the solvent in the drug encapsulation process were also investigated, and provided useful information on the host-guest properties of these experimental drug delivery systems. Our results provide further experimental support for previous studies that suggest the desolvation of guests from surrounding solvent molecules and the resulting solvent rearrangement may actually be the primary driving force for determining guest binding affinities in metallacages, in the absence of specific functional group interactions.

Remarkable Electronic Effect on the meso-Tetra(thienyl)porphyrins

Complexes derived from meso-tetra(thienyl)porphyrins (TThP) and meso-tetra(pyridyl)porphyrin (TPyP) containing peripheral ruthenium complexes with general formulas {TPyP[RuCl(dppb)(5,5'-Mebipy)]₄}(PF₆)₄, {TThP[RuCl(dppb)(5,5'-Mebipy)]₄}(PF₆)₄, and {TThP-me-[RuCl(dppb)(5,5'-Mebipy)]₄}(PF₆)₄ [5,5'-Mebipy = 5,5'-dimethyl-2,2'-bipyridine and dppb = 1,4-bis(diphenylphosphino)butane] were synthesized and characterized by spectroscopy techniques (¹H- and ³¹P{¹H}-NMR, IR, UV/vis, fluorescence, and electron paramagnetic resonance (EPR)), cyclic voltammetry, coulometry, molar conductivity, and elemental analysis. Voltammetry and UV/vis studies demonstrated differentiated electronic properties for ruthenium appended with TThP and TThP-me when compared to ruthenium appended with TPyP. The UV/vis analysis for the ruthenium complex derived from TThP and TThP-me, as well as the Soret and Q bands, characteristics of porphyrins, showed a band at 700 nm referring to the Ru → S electronic transition, and porphyrin TThP-me showed another band at 475 nm from the Ru-N transition. The attribution of these bands was confirmed by spectroelectrochemical analysis. Cyclic voltammetry analysis for the ruthenium complex derived from TPyP exhibited only an electrochemical process with E_1/2 = 0.47 V assigned to the Ru(II)/Ru(III) redox pair (Fc/Fc⁺). On the other hand, two processes were observed for the ruthenium complexes derived from TThP and TThP-me, with E_1/2 around 0.17 and 0.47 V, which were attributed to the formation of a mixed valence tetranuclear species containing Ru(II) and Ru(III) ions, showing that the peripheral groups are not oxidized at the same potential. Fluorescence spectroscopic experiments show the existence of a mixed state of emission in the supramolecular porphyrin moieties. The results suggest the formation of Ru(II)-Ru(III) mixed valence complexes when oxidation potential was applied around 0.17 V in the {TThP[RuCl(dppb)(5,5'-Mebipy)]₄}(PF₆)₄ and {TThP-me-[RuCl(dppb)(5,5'-Mebipy)]₄}(PF₆)₄ species.

Multinuclear Ru(ii) and Ir(iii) decorated tetraphenylporphyrins as efficient PDT agents

Two novel multi-metallic porphyrin complexes were synthesised and evaluated as effective PDT agents against human breast epithelial cells (SKBR-3).

Peripherally Metalated Porphyrins with Applications in Catalysis, Molecular Electronics and Biomedicine

Porphyrins are conjugated, stable chromophores with a central core that binds a variety of metal ions and an easily functionalized peripheral framework. By combining the catalytic, electronic or cytotoxic properties of selected transition metal complexes with the binding and electronic properties of porphyrins, enhanced characteristics of the ensemble are generated. This review article focuses on porphyrins bearing one or more peripheral transition metal complexes and discusses their potential applications in catalysis or biomedicine. Modulation of the electronic properties and intramolecular communication through coordination bond linkages in bis-porphyrin scaffolds is also presented.

Self-Assembled Cofacial Zinc-Porphyrin Supramolecular Nanocapsules as Tuneable 1 O2 Photosensitizers

We demonstrate the benefits of using cofacial Zn-porphyrins as structural synthons in coordination-driven self-assembled prisms to produce cage-like singlet oxygen (¹ O₂ ) photosensitizers with tunable properties. In particular, we describe the photosensitizing and emission properties of palladium- and copper-based supramolecular capsules, and demonstrate that the nature of the bridging metal nodes in these discrete self-assembled prisms strongly influences ¹ O₂ generation at the Zn-porphyrin centers. The Pd^II -based prism is a particularly robust photosensitizer, whereas the Cu^II self-assembled prism is a dormant photosensitizer that could be switched to a ON state upon disassembly of the suprastructure. Furthermore, the well-defined cavity within the prisms allowed encapsulation of pyridine-based ligands and fullerene derivatives, which led to a remarkable guest tuning of the ¹ O₂ production.

The Promise of Self-Assembled 3D Supramolecular Coordination Complexes for Biomedical Applications

In the supramolecular chemistry field, coordination-driven self-assembly has provided the basis for tremendous growth across many subdisciplines, spanning from fundamental investigations regarding the design and synthesis of new architectures to defining different practical applications. Within this framework, supramolecular coordination complexes (SCCs), defined as large chemical entities formed from smaller precursor building blocks of ionic metal nodes and organic multidentate ligands, resulting in intricate and well-defined supramolecular structures, hold great promise. Notably, interest in the construction of discrete 3D molecular architectures, such as those offered by SCCs, has experienced extraordinary progress because of their potential application as sensors, catalysts, probes, and containers and in basic host-guest chemistry. Despite numerous synthetic efforts and a number of inherent favorable properties, the field of 3D SCCs for biomedical applications is still in its infancy. This Viewpoint focuses on 3D SCCs, specifically metallacages and helicates, first briefly presenting the fundamentals in terms of the synthesis and characterization of their host-guest properties, followed by an overview of the possible biological applications with representative examples. Thus, emphasis will be given in particular to metallacages as drug delivery systems and to chiral helicates as DNA recognition domains. Overall, we will provide an update on the state-of-the-art literature and will define the challenges in this fascinating research area at the interface of different disciplines.

M2L4 coordination capsules with tunable anticancer activity upon guest encapsulation

Guest encapsulation can modulate the cytotoxicity of anthracene-based nano-capsules and broaden their applications from metallodrugs to biocompatible delivery systems.

Fine control on the photochemical and photobiological properties of Ru(II) arene complexes

A series of six Ru(arene) complexes, [(η(6)-p-cymene)Ru(dpb)(py-R)](2+) (1-6, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline, py-R = 4-substituted pyridine, R = N(CH3)2, NH2, OCH3, H, COOCH3 and NO2), were synthesized and their photochemical and photobiological properties were compared in detail. The electron push/pull character of the R groups has a significant impact on both ligand photodissociation and (1)O2 generation of the complexes. The photoinduced DNA covalent binding capabilities increase from 1 to 6 under both aerobic and anaerobic conditions, and DNA photocleavage occurs simultaneously in aerobic environments. 4 has the most potent phototoxicity against human lung carcinoma A549 cells among the examined complexes. The substituent effect may be ascribed to the influences of the R groups on the energy levels of (3)MC and (3)MLCT states as well as the energy gaps between (3)MC, (3)MLCT and dpb-based (3)IL states. Similar chemical modification on bidentate and arene ligands or other sites of the pyridine ligand may lead to more efficient agents with PDT and/or PACT activities.

The contrasting catalytic efficiency and cancer cell antiproliferative activity of stereoselective organoruthenium transfer hydrogenation catalysts

The rapidly growing area of catalytic ruthenium chemistry has provided new complexes with potential as organometallic anticancer agents with novel mechanisms of action.

A Porphyrin Coordination Cage Assembled from Four Silver(I) Triazolyl-Pyridine Complexes

The synthesis of a zinc(II) porphyrin 1 with four appended triazolyl-pyridine chelates is reported. Complexation of the porphyrin peripheral ligands with Ag(I) ions in a 1:2 binding stoichiometry afforded quantitatively the coordination cage [Ag4 (1)2 ](4+) . The assembly and disassembly processes of the cage were investigated in solution using UV/Vis spectroscopy. The mathematical analysis of the data obtained in the UV/Vis titration of 1 with Ag(I) confirmed the assembly in CH2 Cl2 /MeOH (90:10) solution of a species having a 1:2 porphyrin/silver stoichiometry and assigned to it an overall stability constant of 5.0×10(26)  M(-5) . The use of a model system allowed an independent assessment of a microscopic binding constant value (Km ) for the interaction between the triazolyl-pyridine ligand and Ag(I) . The coincidence that existed between the Km values extracted from the model system and the titration of 1 provided an indication of the quality and fit of the data analysis. It also allowed the calculation of the average effective molarity (EM) value for the three intramolecular processes that led to the cage assembly as 2.6 mM. Simulated speciation profiles supported the conclusion that at millimolar concentration and working under strict stoichiometric control of the silver/porphyrin ratio, the cage [Ag4 (1)2 ](4+) was the species exclusively assembled in solution. On the other hand, when the concentration of added Ag(I) was approximately 2.6 mM, 50 % of the coordination cage disassembled into open aggregates.

Phototoxic Activity and DNA Interactions of Water-Soluble Porphyrins and Their Rhenium(I) Conjugates

In the search for alternative photosensitizers for use in photodynamic therapy (PDT), herein we describe two new water-soluble porphyrins, a neutral fourfold-symmetric compound and a +3-charged tris-methylpyridinium derivative, in which either four or one [1,4,7]-triazacyclononane (TACN) units are connected to the porphyrin macrocycle through a hydrophilic linker; we also report their corresponding tetracationic Re(I) conjugates. The in vitro (photo)toxic effects of the compounds toward the human cell lines HeLa (cervical cancer), H460M2 (non-small-cell lung carcinoma), and HBL-100 (non-tumorigenic epithelial cells) are reported. Three of the compounds are not cytotoxic in the dark up to 100 μm, and the fourfold-symmetric couple revealed very good phototoxic indexes (PIs). The intracellular localization of all derivatives was studied in HeLa cells by confocal fluorescence microscopy. Although low nuclear localization was observed for some of them, it still prompted us to investigate their capacity to bind both quadruplex and duplex DNA; we observed significant selectivity in the tris-methylpyridinium derivatives for G-quadruplex interactions.

Fusion of photodynamic therapy and photoactivated chemotherapy: a novel Ru(II) arene complex with dual activities of photobinding and photocleavage toward DNA

Transition metal complexes with dual functions of DNA photobinding via coordination and DNA photocleavage via(1)O2 may present potent antitumor activities with high selectivity and a wide anticancer spectrum. We herein report such a complex, [(η(6)-p-cymene)Ru(dpb)(py)](2+) (dpb = 2,3-bis(2-pyridyl)benzoquinoxaline, py = pyridine, 1). The highly delocalized nature of dpb provides 1 with long wavelength-absorbing properties and a long-lived excited state, facilitating (1)O2 generation. Additionally, the bulky nature of dpb leads to a distorted coordination geometry, and allow the (3)MC (metal-centered) state to be more accessible. From this, dissociation of py and dpb may occur, followed by the coordination of the resultant Ru fragment to nucleic bases if DNA is present. The dissociation of dpb can turn on fluorescence of its own, enabling real-time imaging of the photoactivation process. The fascinating properties of 1 and the underlying mechanisms that occur may provide guidelines for developing more efficient metallodrugs with dual potential for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT).

Biologically active [Pd2L4](4+) quadruply-stranded helicates: stability and cytotoxicity

There is emerging interest in the anti-proliferative effects of metallosupramolecular systems due to the different size and shape of these metallo-architectures compared to traditional small molecule drugs. Palladium(II)-containing systems are the most abundant class of metallosupramolecular complexes, yet their biological activity has hardly been examined. Here a small series of [Pd2(L)4](BF4)4 quadruply-stranded, dipalladium(II) architectures were screened for their cytotoxic effects against three cancer cell lines and one non-malignant line. The helicates exhibited a range of cytotoxic properties, with the most cytotoxic complex [Pd2(hextrz)4](BF4)4 possessing low micromolar IC50 values against all of the cell lines tested, while the other helicates displayed moderate or no cytotoxicity. Against the MDA-MB-231 cell line, which is resistant to platinum-based drugs, [Pd2(hextrz)4](BF4)4 was 7-fold more active than cisplatin. Preliminary mechanistic studies indicate that the [Pd2(hextrz)4](BF4)4 helicate does not induce cell death in the same way as clinically used metal complexes such as cisplatin. Rather than interacting with DNA, the helicate appears to disrupt the cell membrane. These studies represent the first biological characterisation of quadruply-stranded helicate architectures, and provide insight into the design requirements for the development of biologically active and stable palladium(II)-containing metallosupramolecular architectures.

Combination of Ru(ii) complexes and light: new frontiers in cancer therapy

The synergistic action of light, oxygen and a photosensitizer (PS) has found applications for decades in medicine under the name of photodynamic therapy (PDT) for the treatment of skin diseases and, more recently, for the treatment of cancer. However, of the thirteen PSs currently approved for the treatment of cancer over more than 10 countries, only two contain a metal ion. This fact is rather surprising considering that nowadays around 50% of conventional chemotherapies involve the use of cisplatin and other platinum-containing drugs. In this perspective article, we review the opportunities brought by the use of Ru(ii) complexes as PSs in PDT. In addition, we also present the recent achievements in the application of Ru(ii) complexes in photoactivated chemotherapy (PACT). In this strategy, the presence of oxygen is not required to achieve cell toxicity. This is of significance since tumors are generally hypoxic. Importantly, this perspective article focuses particularly on the Ru(ii) complexes for which an in vitro biological evaluation has been performed and the mechanism of action (partially) unveiled.

Biologically relevant arene ruthenium metalla-assemblies

Arene ruthenium complexes have become popular building blocks for the preparation of metalla-assemblies with biological applications, opening a new era for arene ruthenium complexes.

‘Click’ to functionalise: synthesis, characterisation and enhancement of the physical properties of a series of exo- and endo-functionalised Pd2L4nanocages

Facile CuAAC ‘click’ chemistry has been utilised toexo-functionalise Pd₂L₄host nanocages with electrochemically active, emissive and solubilising groups.