Light-Sensitive Ruthenium Complex-Loaded Cross-linked Polymeric Nanoassemblies for the Treatment of Cancer

Knockdown of BACE1 by a multistage brain-targeting polyion complex improved memory and learning behaviors in APP/PS1 transgenic mouse model

Cleavage of Amyloid precursor protein (APP) by the β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the rate-limiting step in the production of amyloid-β (Aβ) synaptotoxins. The siRNA-mediated silencing to attenuate the expression of BACE1 to ameliorate cognitive dysfunction in mice had been investigated. To improve therapeutic gene delivery to the central nervous system, cationic copolymer poly(ethylene glycol)-b-poly[N-(N'-{N''-[N'''-(2-aminoethyl)-2-aminoethyl]-2-aminoethyl}-2-aminoethyl)aspartamide]-cholesterol was synthesized, then RVG29 and Tet1 peptides were exploited as ligands to construct a dual-targeting brain gene delivery polyion complex (Tet1/RVG29-PIC). The cell uptake of a coculture cell model showed that the Tet1/RVG29-PIC exhibited notable transport characteristics and possessed affinity towards nerve cells. In vivo transfection, Tet1/RVG29-PIC possessed the highest expression of luciferase in brain compared with that of RVG29-PIC or Tet1-PIC, which were 1.25 and 1.22 times respectively. Silence BACE1 expression using siRNA-expressing plasmid loaded Tet1/RVG29-PIC that improved behavioral deficits in the APP/PS1 mouse model, demonstrating the favorable brain delivery properties of Tet1/RVG29-PIC by synergistical engagement of GT1B and nicotinic acetylcholine receptors. Our results suggested that the nanoformulation has the potential to be exploited as a multistage-targeting gene vector for the CNS disease therapy.

Biotin-conjugated Ru(II) complexes with AIE characteristics as mitochondria-targeted photosensitizers for enhancing photodynamic therapy by disrupting cellular redox balance

The potential use of Ru(II) complexes as photosensitizers (PSs) in photodynamic therapy (PDT) has gained significant attention. In comparison with fluorophores with aggregation-caused quenching (ACQ), fluorophores with aggregation-induced emission (AIE) characteristics exhibit sustained fluorescence and dispersibility in aqueous solutions. PSs with AIE characteristics have received much attention in recent years. Herein, we reported two novel biotin-conjugated Ru(II) polypyridyl complexes (Ru1 and Ru2) with AIE characteristics. When exposed to 460 nm (10 mW cm-2) light, Ru1 and Ru2 exhibited outstanding photostability and photocatalytic activity. Ru1 and Ru2 could efficiently generate singlet oxygen and induce pUC19 DNA photolysis when exposed to 460 nm light. Interestingly, both Ru1 and Ru2 also functioned as catalysts for NADH oxidation when exposed to 460 nm light. The presence of biotin fragments in Ru1 and Ru2 enhanced the specific uptake of these complexes by tumor cells. Both complexes showed minimal toxicity to selected cells in the dark. Nevertheless, the phototoxicity of both complexes significantly increased upon 460 nm light irradiation for 15 min. Further experiments revealed that Ru2 primarily accumulated in mitochondria and might bind to mitochondrial DNA. Under 460 nm light irradiation, Ru2 induced the generation of reactive oxygen species (ROS) and NADH depletion disrupting intracellular redox homeostasis in A549 cells, activating the mitochondrial apoptosis pathway resulting in up-regulation of apoptotic marker caspase-3, effectively damaged A549 cell DNA and arrested A549 cell cycle in the S phase. In vivo anti-tumor experiments were conducted to assess the effects of Ru2 on tumor growth in A549 tumor-bearing mice. The results showed that Ru2 effectively inhibited tumor growth under 460 nm light irradiation conditions. These findings indicate that Ru2 has great potential as a targeted photosensitizer for mitochondrial targeting imaging and photodynamic therapy of tumors.

In Situ Bioconjugation of a Maleimide-Functionalized Ruthenium-Based Photosensitizer to Albumin for Photodynamic Therapy

Maleimide-containing prodrugs can quickly and selectively react with circulating serum albumin following their injection in the bloodstream. The drug-albumin complex then benefits from longer blood circulation times and better tumor accumulation. Herein, we have applied this strategy to a previously reported highly phototoxic Ru polypyridyl complex-based photosensitizer to increase its accumulation at the tumor, reduce off-target cytotoxicity, and therefore improve its pharmacological profile. Specifically, two complexes were synthesized bearing a maleimide group: one complex with the maleimide directly incorporated into the bipyridyl ligand, and the other has a hydrophilic linker between the ligand and the maleimide group. Their interaction with albumin was studied in-depth, revealing their ability to efficiently bind both covalently and noncovalently to the plasma protein. A crucial finding is that the maleimide-functionalized complexes exhibited significantly lower cytotoxicity in noncancerous cells under dark conditions compared to the nonfunctionalized complex, which is a highly desirable property for a photosensitizer. The binding to albumin also led to a decrease in the phototoxicity of the Ru bioconjugates in comparison to the nonfunctionalized complex, probably due to a decreased cellular uptake. Unfortunately, this decrease in phototoxicity was not compensated by a dramatic increase in tumor accumulation, as was demonstrated in a tumor-bearing mouse model using inductively coupled plasma mass spectrometry (ICP-MS) studies. Consequently, this study provides valuable insight into the future design of in situ albumin-binding complexes for photodynamic therapy in order to maximize their effectiveness and realize their full potential.

Encapsulation of Ru(II) Polypyridine Complexes for Tumor-Targeted Anticancer Therapy

Ru(II) polypyridine complexes have attracted much attention as anticancer agents because of their unique photophysical, photochemical, and biological properties. Despite their promising therapeutic profile, the vast majority of compounds are associated with poor water solubility and poor cancer selectivity. Among the different strategies employed to overcome these pharmacological limitations, many research efforts have been devoted to the physical or covalent encapsulation of the Ru(II) polypyridine complexes into nanoparticles. This article highlights recent developments in the design, preparation, and physicochemical properties of Ru(II) polypyridine complex-loaded nanoparticles for their potential application in anticancer therapy.

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.

Polymeric Nanosystems Applied for Metal-Based Drugs and Photosensitizers Delivery: The State of the Art and Recent Advancements

Nanotechnology-based approaches for targeting the delivery and controlled release of metal-based therapeutic agents have revealed significant potential as tools for enhancing the therapeutic effect of metal-based agents and minimizing their systemic toxicities. In this context, a series of polymer-based nanosized systems designed to physically load or covalently conjugate metal-based therapeutic agents have been remarkably improving their bioavailability and anticancer efficacy. Initially, the polymeric nanocarriers were applied for platinum-based chemotherapeutic agents resulting in some nanoformulations currently in clinical tests and even in medical applications. At present, these nanoassemblies have been slowly expanding for nonplatinum-containing metal-based chemotherapeutic agents. Interestingly, for metal-based photosensitizers (PS) applied in photodynamic therapy (PDT), especially for cancer treatment, strategies employing polymeric nanocarriers have been investigated for almost 30 years. In this review, we address the polymeric nanocarrier-assisted metal-based therapeutics agent delivery systems with a specific focus on non-platinum systems; we explore some biological and physicochemical aspects of the polymer–metallodrug assembly. Finally, we summarize some recent advances in polymeric nanosystems coupled with metal-based compounds that present potential for successful clinical applications as chemotherapeutic or photosensitizing agents. We hope this review can provide a fertile ground for the innovative design of polymeric nanosystems for targeting the delivery and controlled release of metal-containing therapeutic agents.

Intraligand Excited States Turn a Ruthenium Oligothiophene Complex into a Light-Triggered Ubertoxin with Anticancer Effects in Extreme Hypoxia

Ru(II) complexes that undergo photosubstitution reactions from triplet metal-centered (3MC) excited states are of interest in photochemotherapy (PCT) due to their potential to produce cytotoxic effects in hypoxia. Dual-action systems that incorporate this stoichiometric mode to complement the oxygen-dependent photosensitization pathways that define photodynamic therapy (PDT) are poised to maintain antitumor activity regardless of the oxygenation status. Herein, we examine the way in which these two pathways influence photocytotoxicity in normoxia and in hypoxia using the [Ru(dmp)2(IP-nT)]2+ series (where dmp = 2,9-dimethyl-1,10-phenanthroline and IP-nT = imidazo[4,5-f][1,10]phenanthroline tethered to n = 0-4 thiophene rings) to switch the dominant excited state from the metal-based 3MC state in the case of Ru-phen-Ru-1T to the ligand-based 3ILCT state for Ru-3T and Ru-4T. Ru-phen-Ru-1T, having dominant 3MC states and the largest photosubstitution quantum yields, are inactive in both normoxia and hypoxia. Ru-3T and Ru-4T, with dominant 3IL/3ILCT states and long triplet lifetimes (τTA = 20-25 μs), have the poorest photosubstitution quantum yields, yet are extremely active. In the best instances, Ru-4T exhibit attomolar phototoxicity toward SKMEL28 cells in normoxia and picomolar in hypoxia, with phototherapeutic index values in normoxia of 105-1012 and 103-106 in hypoxia. While maximizing excited-state deactivation through photodissociative 3MC states did not result in bonafide dual-action PDT/PCT agents, the study has produced the most potent photosensitizer we know of to date. The extraordinary photosensitizing capacity of Ru-3T and Ru-4T may stem from a combination of very efficient 1O2 production and possibly complementary type I pathways via 3ILCT excited states.

Light-responsive and Protic Ruthenium Compounds Bearing Bathophenanthroline and Dihydroxybipyridine Ligands Achieve Nanomolar Toxicity towards Breast Cancer Cells

We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)2 Ru(n,n'-dhbp)]Cl2 with n = 6 and 4 in 1A and 2A , respectively). Full characterization data are reported for 1A and 2A and single crystal X-ray diffraction for 1A . Both 1A and 2A are diprotic acids. We have studied 1A , 1B , 2A , and 2B (B = deprotonated forms) by UV-vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy 3 MLCT states relative to the acidic forms. Complexes 1A and 2A produce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC50 light values as low as 0.50 μM with PI values as high as >200 vs. MCF7. Computational studies were used to predict the energies of the 3 MLCT and 3 MC states. An inaccessible 3 MC state for 2B suggests a rationale for why photodissociation does not occur with the 4,4'-dhbp ligand. Low dark toxicity combined with an accessible 3 MLCT state for 1 O2 generation explains the excellent photocytotoxicity of 2.

Fine-Feature Modifications to Strained Ruthenium Complexes Radically Alter Their Hypoxic Anticancer Activity†

In an earlier study of π-expansive ruthenium complexes for photodynamic and photochemo-therapies, it was shown that a pair of structural isomers differing only in the connection point of a naphthalene residue exhibited vastly different biological activity. These isomers are further explored in this paper through the activity of their functionalized derivatives. In normoxia, the inactive 2-NIP isomer (5) can be made as photocytotoxic as the active 1-NIP isomer (1) by functionalizing with methyl or methoxy groups, while methoxy variants of the 1-NIP isomer became inactive. In all cases, the singlet oxygen sensitization quantum yield was below 1%. Hypoxic photocytotoxicity was attenuated, with only three of the series showing any activity, notwithstanding the photodissociative ligands. The results here are consistent with the earlier findings in that seemingly minor structural modifications on the non-strained ligand can dramatically modulate the normoxic and hypoxic activity of these strained compounds and that these changes appear to exert a greater influence on photocytotoxicity than singlet oxygen sensitization or rates of photosubstitution in cell-free conditions would suggest.

The Development of Ru(II)-Based Photoactivated Chemotherapy Agents

Photoactivated chemotherapy (PACT) is a novel cancer treatment method that has drawn increasing attention due to its high selectivity and low side effects by spatio-temporal control of irradiation. Compared with photodynamic therapy (PDT), oxygen-independent PACT is more suitable for treating hypoxic tumors. By finely tuning ligand structures and coordination configurations, many Ru(II) complexes can undergo photoinduced ligand dissociation, and the resulting Ru(II) aqua species and/or free ligands may have anticancer activity, showing their potential as PACT agents. In this mini-review, we summarized the progress in Ru(II)-based PACT agents, as well as challenges that researchers in this field still face.

Photo-induced mitochondrial DNA damage and NADH depletion by -NO2 modified Ru(II) complexes

Two mitochondria-localized Ru(ii) complexes with photo-labile ligands were reported to exert one- and two-photon activatable anticancer activity through a dual-function mechanism, i.e. mitochondrial DNA covalent binding after photo-induced ligand dissociation and photo-catalyzed NADH depletion, thus displaying good activity towards cisplatin-resistant cancer cells under both normoxic and hypoxic conditions.

Diatom-like silica-protein nanocomposites for sustained drug delivery of ruthenium polypyridyl complexes

Inspired by the unique glass cell wall of diatom, we design a new nanostructure of human serum albumin nanoparticle (HSANP) coated with silica (HSA/SiO₂), which consists of a core-satellite assembly of small silica nanoparticles on a single HSANP. The HSA/SiO₂ nanoparticles are used for delivering ruthenium polypyridyl complexes into cells. The silica coating increases the Ru loading efficiency, and prevents the burst release of Ru from HSA/SiO₂. The Ru release rate can be controlled by adjusting the amount of coated silica on HSANP, affording a drug delivery system with controlled drug release rate. The Ru-HSA/SiO₂ nanoparticles show high stability in physiological condition, and significantly increase the Ru uptake into cells, which proceeds via clathrin-mediated endocytosis into the lysosomes. The silica coating takes no effect on the fluorescence intensity and ROS generation of loaded Ru in HSA/SiO₂. Furthermore, Ru4-HSA/SiO₂ exhibit weak cytotoxicity in dark, however, the nanodrug can be activated by light irradiation and generate ROS to damage cells, thus achieving an excellent photodynamic therapy efficiency. Therefore, the diatom-like nanostructure can function as sustained drug delivery nanocarrier of ruthenium polypyridyl complex and can be used for bioimaging and photodynamic therapy.

Biological activities of polypyridyl-type ligands: implications for bioinorganic chemistry and light-activated metal complexes

Polypyridyl coordinating ligands are common in metal complexes used in medicinal inorganic chemistry. These ligands possess intrinsic cytotoxicity, but detailed data on this phenomenon are sparse, and cytotoxicity values vary widely and are often irreproducible. To provide new insights into the biological effects of bipyridyl-type ligands and structurally related metal-binding systems, reports of free ligand cytotoxicity were reviewed. The cytotoxicity of 25 derivatives of 2,2'-bipyridine and 1,10-phenanthroline demonstrates that there is no correlation between IC₅₀ values and ligand properties such as pKa, log D, polarizability volume, and electron density, as indicated by NMR shifts. As a result of these observations, as well as the various reported mechanisms of action of polypyridyl ligands, we offer the hypothesis that biological effects are governed by the availability of and affinity for specific metal ions within the experimental model.

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

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

Incorporation of Ru(II) Polypyridyl Complexes into Nanomaterials for Cancer Therapy and Diagnosis

Ru(II) polypyridyl complexes are compounds of great interest in cancer therapy due to their unique photophysical, photochemical, and biological properties. For effective treatment, they must be able to penetrate tumor cells effectively and selectively. The development of nanoscale carriers capable of delivering Ru(II) polypyridyl complexes has the potential to passively or selectively enhance their cellular uptake in tumor cells. Many different strategies have been explored to incorporate Ru(II) polypyridyl complexes into a variety of nanosized constructs, ranging from organic to inorganic materials. Herein, recent developments in nanomaterials loaded with Ru(II) polypyridyl complexes are highlighted. Their rational design, preparation, and physicochemical properties are described, and their potential applications in cancer therapy are eventually discussed.

The synthesis, characterization, DNA/BSA/HSA interactions, molecular modeling, antibacterial properties, and in vitro cytotoxic activities of novel parent and niosome nano-encapsulated Ho(iii) complexes

Based on the importance of metal-centered complexes that can interact with DNA, this research focused on the synthesis of a new Ho(iii) complex. This complex was isolated and characterized via elemental analysis, and FT-IR, fluorescence, and UV-vis spectroscopy. Additional confirmation of the Ho(iii) complex structure was obtained via single-crystal X-ray diffraction. DNA interaction studies were carried out via circular dichroism (CD) spectroscopy, UV-vis absorption spectroscopy, viscosity measurements and emission spectroscopy; it was proposed that the metal complex acts as an effective DNA binder based on studies in the presence of fish DNA (FS-DNA), showing high binding affinity to DNA in the presence of hydrophobic and electron donating substituents. Also, the interactions of this complex with human (HSA) and bovine serum albumin (BSA) proteins were studied via fluorescence spectroscopy techniques and the obtained results reveal an excellent propensity for binding in both cases. Furthermore, the interactions of the Ho(iii) complex with DNA, BSA and HSA were confirmed via molecular docking analysis. The antimicrobial activities of the Ho(iii) complex were tested against Gram-negative bacteria and Gram-positive bacteria. In addition, a niosome nano-encapsulated Ho(iii) complex was synthesized, and the parent and encapsulated complexes were evaluated as potential antitumor candidates. The main structure of the Ho(iii) complex is maintained after encapsulation using niosome nanoparticles. The MTT method was used to assess the anticancer properties of the Ho(iii) complex and its encapsulated form toward human lung carcinoma and breast cancer cell lines. The anticancer activity in the encapsulated form was more than that of the parent Ho(iii) complex. In conclusion, these compounds could be considered as new antitumor candidates.

Nanostructured polymer assemblies stabilize photoactivatable anticancer ruthenium complexes under physiological conditions

Photoactivatable ruthenium (Ru) complexes are promising compounds for anticancer phototherapy. They must be stable under physiological conditions before they are transported to cancer cells. In this paper, we systematically studied the stabilities of two Ru-containing block copolymers (Ru complexes as side group or in main chain, respectively) and their corresponding Ru complexes in different media, including saline, bovine serum albumin (BSA) solution, Dulbecco's Modified Eagle's Medium (DMEM, pH 6.5) and DMEM (pH 5.5) with 1.0 mM glutathione (GSH). Their stabilities were studied by monitoring the metal-to-ligand charge transfer (MLCT) bands of the Ru moieties via UV-Vis absorption spectroscopy. The MLCT bands of Ru complexes changed to varying degrees within a day in the above-mentioned media, indicating that they were instable. In contrast, the MLCT bands of Ru-containing polymer assemblies did not change significantly under the same conditions. These results showed that the self-assembled nanostructures protected the Ru moieties and improved their stability. In addition, these nanostructured polymer assemblies could be activated by red light. Therefore, the studied Ru-containing polymer assemblies are more suitable for in vivo applications than their low-molecular weight analogues.

A nuclear permeable Ru(ii)-based photoactivated chemotherapeutic agent towards a series of cancer cells: in vitro and in vivo studies

Ru(ii) polypyridyl complexes which can undergo photo-induced ligand dissociation and DNA covalent binding are considered as potential photoactivated chemotherapeutic (PACT) agents. Herein four pyridine-2-sulfonate (py-SO3-) ligand based Ru(ii) complexes [Ru(N-N)2(py-SO3)]+ (1-4) were synthesized and studied. All the complexes can undergo fast py-SO3- ligand dissociation and DNA covalent binding upon visible light irradiation. However, only complex 4 exhibited high photo-induced anticancer activities towards a series of cancer cells, with half maximal inhibitory concentration (IC50) values in 100-300 nM regions and phototoxicity index (PI) values of about 100. In particular, complex 4 can also kill cisplatin resistant SKOV-3 and A549 cancer cells with IC50 values in 200-400 nM regions and PI values of about 50, which should be the first report of Ru(ii) based PACT agents that are also effective towards cisplatin resistant cancer cells. Complex 4 exhibited much higher cell uptake and nuclear accumulation levels, which may be the main reasons for its high anticancer activities. The in vivo anticancer experiments indicated that complex 4 can inhibit tumor growth significantly with fewer side effects. Our results may provide guidelines for developing novel photoactivatable Ru(ii) anticancer agents.

Combinatorial photochemotherapy on liver cancer stem cells with organoplatinum(ii) metallacage-based nanoparticles

Liver cancer is a kind of lethal and aggressive malignant neoplasm with a high rate of relapse and metastasis after therapy. An important cause for the relapse and metastasis is the existence of liver cancer stem cells (CSCs), which have high resistance to chemotherapy and high tumorigenic potential. Therefore, it is crucial to develop new methods to eradicate CSCs in tumors. Herein, we develop a photodynamic therapy (PDT) that features bimodal metallacage-loaded nanoparticles (MNPs) for integrated chemotherapy. This platform achieves chemo-photodynamic combinational therapy. Organoplatinum(ii) metallacage-loaded nanoparticles show excellent ability to kill liver CSCs, decreasing their mobility and sphenoid formation ability under near-infrared laser irradiation. Importantly, MNPs can successfully penetrate into 3D tumor spheroids, which display higher drug resistance compared to traditional 2D cultured cells. This destroys CSCs and prevents subsequent tumor formation in vivo. With the excellent combinational therapeutic results in hand, the working mechanisms of MNPs were then studied. MNPs under NIR light irradiation can generate reactive oxygen species (ROS), resulting in damage of mitochondrial membrane and subsequent cell apoptosis with chemotherapeutic platinum. This study proves the great potential of MNPs for combinational cancer therapy, providing a new insight for the next generation of nanomedicines.

Biocompatible ruthenium polypyridyl complexes as efficient radiosensitizers

A biocompatible ruthenium polypyridyl complex has been rationally designed, which could self-assemble into nanoparticles in aqueous solution to enhance the solubility and biocompatibility, and could synergistically realize simultaneous cancer chemo-radiotherapy.

Red and Near-Infrared Light-Cleavable Polymers

Photocleavable polymers have attracted much attention in drug delivery, photopatterning, and controlling cell behavior. Photolysis is usually induced by UV light. However, UV light cannot penetrate deeply into biological tissue and may damage biological components. Therefore, conventional UV-light-cleavable polymers are problematic for deep-tissue biomedical applications. In this feature article, red and near-infrared light-cleavable polymers are reviewed, and their potential applications are highlighted. The remaining challenges in the field of photocleavable polymers are discussed.

111In-labelled polymeric nanoparticles incorporating a ruthenium-based radiosensitizer for EGFR-targeted combination therapy in oesophageal cancer cells

Radiolabelled, drug-loaded nanoparticles may combine the theranostic properties of radionuclides, the controlled release of chemotherapy and cancer cell targeting. Here, we report the preparation of poly(lactic-co-glycolic acid) (PLGA) nanoparticles surface conjugated to DTPA-hEGF (DTPA = diethylenetriaminepentaacetic acid, hEGF = human epidermal growth factor) and encapsulating the ruthenium-based DNA replication inhibitor and radiosensitizer Ru(phen)2(tpphz)2+ (phen = 1,10-phenanthroline, tpphz = tetrapyridophenazine) Ru1. The functionalized PLGA surface incorporates the metal ion chelator DTPA for radiolabelling and the targeting ligand for EGF receptor (EGFR). Nanoparticles radiolabelled with 111In are taken up preferentially by EGFR-overexpressing oesophageal cancer cells, where they exhibit radiotoxicity through the generation of cellular DNA damage. Moreover, nanoparticle co-delivery of Ru1 alongside 111In results in decreased cell survival compared to single-agent formulations; an effect that occurs through DNA damage enhancement and an additive relationship between 111In and Ru1. Substantially decreased uptake and radiotoxicity of nanoparticles towards normal human fibroblasts and oesophageal cancer cells with normal EGFR levels is observed. This work demonstrates nanoparticle co-delivery of a therapeutic radionuclide plus a ruthenium-based radiosensitizer can achieve combinational and targeted therapeutic effects in cancer cells that overexpress EGFR.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Platinum complexes as light promoted anticancer agents: a redefined strategy for controlled activation

Site-specific delivery and amenable activation of prodrugs are indispensible criteria for designing novel anticancer agents. Platinum based drugs vanguard the chemotherapeutic regimes and over the years significant attention has been paid to achieve more efficacious drugs with fewer adverse effects. The switch from platinum(ii) drugs to the inert platinum(iv) analogues proved advantageous but the new prodrugs still suffered from unspecific cytotoxic actions. Thus the photoactivation of an inert platinum prodrug specifically within neoplastic cells provided the desired spatio-temporal control over drug activation by means of illumination, thereby limiting the cytotoxic events to only at the targeted tumors. This article collates research on platinum complexes which exhibit potential light mediated anticancer effects and provides insights into the underlying mechanisms of activation. Fine tuning of the coordination sphere results in dramatic alteration of the redox and spectral properties of both ground and excited states and the cellular properties of the molecules. This concise article highlights the various light promoted strategies employed to attain a controlled release of active platinum(ii) and/or reactive oxygen species such as photoreduction, photocaging, photodissociation and photosensitization. Such dual action photoactive metal complexes with improved aqueous solubility and versatility are promising candidates for combination therapy which is likely to be the future of anticancer research.

Upconverting nanoparticles for the near infrared photoactivation of transition metal complexes: new opportunities and challenges in medicinal inorganic photochemistry

The article highlights the emergent use of upconverting nanoparticles as tools for the near infrared photoactivation of transition metal complexes, identifying opportunities and challenges of this approach in the context of medicinal inorganic chemistry.

The development of anticancer ruthenium(ii) complexes: from single molecule compounds to nanomaterials

Cancer is rapidly becoming the top killer in the world. Most of the FDA approved anticancer drugs are organic molecules, while metallodrugs are very scarce. The advent of the first metal based therapeutic agent, cisplatin, launched a new era in the application of transition metal complexes for therapeutic design. Due to their unique and versatile biochemical properties, ruthenium-based compounds have emerged as promising anti-cancer agents that serve as alternatives to cisplatin and its derivertives. Ruthenium(iii) complexes have successfully been used in clinical research and their mechanisms of anticancer action have been reported in large volumes over the past few decades. Ruthenium(ii) complexes have also attracted significant attention as anticancer candidates; however, only a few of them have been reported comprehensively. In this review, we discuss the development of ruthenium(ii) complexes as anticancer candidates and biocatalysts, including arene ruthenium complexes, polypyridyl ruthenium complexes, and ruthenium nanomaterial complexes. This review focuses on the likely mechanisms of action of ruthenium(ii)-based anticancer drugs and the relationship between their chemical structures and biological properties. This review also highlights the catalytic activity and the photoinduced activation of ruthenium(ii) complexes, their targeted delivery, and their activity in nanomaterial systems.

Tethered polymer nanoassemblies for sustained carfilzomib release and prolonged suppression of proteasome activity

AIM

Proteasome inhibitors, such as carfilzomib (CFZ), have shown potential to treat various types of cancers in preclinical models, but clinical applications are limited likely due to formulation and delivery issues. Results & methodology: Tethered polymer nanoassemblies (TNAs) were synthesized by tethering hydrophilic polymers and hydrophobic groups to charged polymer scaffolds, and then end-capping remaining amines on scaffold. Drug entrapment and drug release half-lives increased as charge was removed from scaffold. TNAs with sustained CFZ release maintained drug efficacy after preincubation and increased duration of proteasome inhibition in cancer cells compared with free CFZ.

CONCLUSION

TNAs fine-tuned CFZ release as charge was removed from polymer scaffold, which allowed for sustained proteasome inhibition in cancer cells and potentially enhanced anticancer efficacy.

Development of Halofluorochromic Polymer Nanoassemblies for the Potential Detection of Liver Metastatic Colorectal Cancer Tumors Using Experimental and Computational Approaches

PURPOSE

To develop polymer nanoassemblies (PNAs) modified with halofluorochromic dyes to allow for the detection of liver metastatic colorectal cancer (CRC) to improve therapeutic outcomes.

METHODS

We combine experimental and computational approaches to evaluate macroscopic and microscopic PNA distributions in patient-derived xenograft primary and orthotropic liver metastatic CRC tumors. Halofluorochromic and non-halofluorochromic PNAs (hfPNAs and n-hfPNAs) were prepared from poly(ethylene glycol), fluorescent dyes (Nile blue, Alexa546, and IR820), and hydrophobic groups (palmitate), all of which were covalently tethered to a cationic polymer scaffold [poly(ethylene imine) or poly(lysine)] forming particles with an average diameter < 30 nm.

RESULTS

Dye-conjugated PNAs showed no aggregation under opsonizing conditions for 24 h and displayed low tissue diffusion and cellular uptake. Both hfPNAs and n-hfPNAs accumulated in primary and liver metastatic CRC tumors within 12 h post intravenous injection. In comparison to n-hfPNAs, hfPNAs fluoresced strongly only in the acidic tumor microenvironment (pH < 7.0) and distinguished small metastatic CRC tumors from healthy liver stroma. Computational simulations revealed that PNAs would steadily accumulate mainly in acidic (hypoxic) interstitium of metastatic tumors, independently of the vascularization degree of the tissue surrounding the lesions.

CONCLUSION

The combined experimental and computational data confirms that hfPNAs detecting acidic tumor tissue can be used to identify small liver metastatic CRC tumors with improved accuracy.

An Overview Of Photosubstitution Reactions Of Ru(II) Imine Complexes And Their Application In Photobiology And Photodynamic Therapy

This article is a short review that presents a short review of photosubstitution reactions of Ru(II) imine complexes and illustrates their use in the development of therapeutic agents. The review begins with an overview of the photophysical behavior and common photoreactions of Ru(II) imine complexes, with select examples from the literature since the 1960s. It is followed by a more detailed picture of the application of knowledge gained over the years in the development of Ru(II) complexes for photobiology and photodynamic therapy.

A GSH-activatable ruthenium(ii)-azo photosensitizer for two-photon photodynamic therapy

The first dinuclear ruthenium(ii)-azo complex was developed as a glutathione (GSH)-activatable photosensitizer for use in two-photon photodynamic therapy upon irradiation in the NIR region.

Protein Nanocages for Delivery and Release of Luminescent Ruthenium(II) Polypyridyl Complexes

In this report, noncovalent encapsulation of hydrophobic ruthenium(II) polyridyl complexes, Ru(bpy)2dppz(2+) and Ru(phen)2dppz(2+), into apoferritin cavity was achieved with high loading contents by effective prevention of Ru complex-induced protein aggregation, without disruption of protein native architecture. The Ru-loaded luminescent nanocomposites have demonstrated improved water solubility, easy manipulation, reduced cytotoxicity, and enhanced cellular uptake as compared to the nontreated Ru complexes.

A dual-fluorescent nano-carrier for delivering photoactive ruthenium polypyridyl complexes

A photo-responsive diagnostic conjugate was generated by loading a photoactive polypyridyl ruthenium complex onto a dual-fluorescent nanocarrier, resulting in photo-induced cytotoxicity.