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.

A Novel Near-IR Absorbing Ruthenium(II) Complex as Photosensitizer for Photodynamic Therapy and its Cetuximab Bioconjugates

A novel Ru(II) cyclometalated photosensitizer (PS), Ru-NH2 , for photodynamic therapy (PDT) of formula [Ru(appy)(bphen)2 ]PF6 (where appy=4-amino-2-phenylpyridine and bphen=bathophenanthroline) and its cetuximab (CTX) bioconjugates, Ru-Mal-CTX and Ru-BAA-CTX (where Mal=maleimide and BAA=benzoylacrylic acid) were synthesised and characterised. The photophysical properties of Ru-NH2 revealed absorption maxima around 580 nm with an absorption up to 725 nm. The generation of singlet oxygen (1 O2 ) upon light irradiation was confirmed with a 1 O2 quantum yield of 0.19 in acetonitrile. Preliminary in vitro experiments revealed the Ru-NH2 was nontoxic in the dark in CT-26 and SQ20B cell lines but showed outstanding phototoxicity when irradiated, reaching interesting phototoxicity indexes (PI) >370 at 670 nm, and >150 at 740 nm for CT-26 cells and >50 with NIR light in SQ20B cells. The antibody CTX was successfully attached to the complexes in view of the selective delivery of the PS to cancer cells. Up to four ruthenium fragments were anchored to the antibody (Ab), as confirmed by MALDI-TOF mass spectrometry. Nonetheless, the bioconjugates were not as photoactive as the Ru-NH2 complex.

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.

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.

Antiproliferative Ruthenium Complexes Containing Curcuminoid Ligands Tested In Vitro on Human Ovarian Tumor Cell Line A2780, towards Their Capability to Modulate the NF-κBTranscription Factor, FGF-2 Growth Factor, and MMP-9 Pathway

So far, the polyphenolic components of turmeric have shown a significant pharmacological preventative activity for a wide spectrum of diseases, including oncological disorders. This type of natural product could be of great interest for the inhibition of cancer cell proliferation, displaying less side effects in comparison to classical chemotherapeutics. The poor bioavailability and quick metabolism of such natural compounds require new investigative methods to improve their stability in the organisms. A synthetic approach to increase the efficiency of curcuminoids is to coordinate them to metals through the beta-dicarbonyl moiety. We report the synthesis and the biological attempts on human ovarian carcinoma A2780 of ruthenium(II) complexes 1–4, containing curcuminoid ligands. The cytotoxicity of complexes 1–4 proves their antiproliferative capability, and a correlation between the IC50 values and NF-κB transcription factor, FGF-2, and MMP-9 levels was figured out through the principal component analysis (PCA).

Ruthenium photosensitizer anchored gold nanorods for synergistic photodynamic and photothermal therapy

Ruthenium polypyridyl complexes have been widely used as bioprobes and photosensitizers. However, several disadvantages including slow cellular uptake, nonspecific binding with biomolecules and toxicity limit their applications. In this study, a nanocarrier of human serum albumin coated gold nanorods was developed to deliver a ruthenium photosensitizer for PDT/PTT combination therapy. The HSA coating endowed the nanodrug with high biocompatibility and stability under physiological conditions. Ru-GNR-HSANPs generate ¹O₂ and hydroxyl radicals to kill cancer cells under blue light irradiation, and exhibit excellent photothermal anticancer effects under 808 nm light irradiation. Significant synergistic anticancer effects were achieved by combined PDT/PTT therapy. Importantly, Ru-GNR-HSANPs can have the synergistic PDT/PTT functions with no need of drug release from the carrier.

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.

UCNP@BSA@Ru nanoparticles with tumor-specific and NIR-triggered efficient PACT activity in vivo

Ru(ii)-based photoactivated chemotherapy (PACT) agents are promising; however, their short wavelength absorption (generally <550 nm) and poor tumor accumulation ability limit their in vivo applications. Herein, bovine serum albumin (BSA) coated lanthanide-doped upconversion nanoparticles (NaYF4:Yb:Tm@NaYF4 (UCNPs)) were loaded with a Ru(ii) PACT agent, i.e. [Ru(dip)2(spc)]+ (dip = 4,7-diphenyl-1,10-phenanthroline; spc = 2-sulfonic acid pyridine-3-carboxylic acid). The resultant UCNP@BSA@Ru can transfer [Ru(dip)2(spc)]+ to tumor cells in vitro as well as tumor tissues in vivo highly efficiently and selectively owing to the targeting ability of BSA and the enhanced permeability and retention effect of the nanoparticles. The subsequent near infrared (NIR) light irradiation at 980 nm or visible light irradiation at 470 nm can initiate dissociation of the spc ligand, and the released Ru(ii) aqua compounds ([Ru(dip)2(H2O)2]2+) may exert a potent cytotoxicity towards a series of cancer cells but a much weaker effect on the normal IOSE80 cells. The in vivo (mouse) results showed that UCNP@BSA@Ru could inhibit tumor growth upon 980 nm irradiation more efficiently than in the dark and more efficiently than cisplatin (in the dark).

Autocatalytic photodegradation of [Ru(II)(2,2'-bipyridine)2DAD]+ (DADH = 1,2-dihydroxyanthracene-9,10-dione) by hydrogen peroxide under acidic aqueous conditions

As part of a continuing effort to identify ruthenium agents capable of the photorelease of anthraquinone-based ligands the complexes Δ/Λ-[Ru(bpy)2DAD]+ (bpy = 2,2'-bipyridine) were produced by the reaction of 1,2-dihydroxyanthracene-9,10-dione (DADH) with chirally pure Δ/Λ-[Ru(bpy)2(py)2][(+)-O,O'-dibenzoyl-d-tartrate]·12H2O (py = pyridine). A very subtle difference in the chemical shift of the hydroxyl proton in their high-field 1H NMR spectra was observed, supporting that the OH proton is susceptible to a small change in environment at the metal centre. The excited state lifetime of the complexes, as measured by femtosecond pump-probe spectroscopy, was 7.1 (±0.8) ps in water (pH 2) and 13 (±1) ps in MeCN. Illumination of a sample of Λ-[Ru(bpy)2DAD]+ in water (pH 2) in the presence of hydrogen peroxide resulted in decomposition of the complex. The decay profile, as monitored at several wavelengths, was sigmoidal indicating the reaction was autocatalytic, in which the product formed catalysed decomposition of the starting complex. A mechanism is proposed that relies on participation of the uncoordinated hydroxyl group on the anthraquinone ligand in promoting water loss and radical formation in the excited state. The radical is oxidised by peroxide to generate the ruthenium(iii) complex, which behaves as an oxidant in the autocatalytic process.

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.

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

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

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.

796 nm Activation of a Photocleavable Ruthenium(II) Complex Conjugated to an Upconverting Nanoparticle through Two Phosphonate Groups

The biological application of photoactivatable ruthenium anticancer prodrugs is limited by the need to use poorly penetrating high-energy visible light for their activation. Upconverting nanoparticles (UCNPs), which produce high-energy light under near-infrared (NIR) excitation, can solve this issue, provided that they form stable, water (H2O)-dispersible nanoconjugates with the prodrug and that there is efficient energy transfer from the UCNP to the ruthenium complex. Herein, we report on the synthesis and photochemistry of the ruthenium(II) polypyridyl complex [Ru(bpy)2(3H)](PF6)2 ([1](PF6)2), where bpy = 2,2-bipyridine and 3H is a photocleavable bis(thioether) ligand modified with two phosphonate moieties. This ligand was coordinated to the ruthenium center through its thioether groups and could be dissociated under blue-light irradiation. Complex [1](PF6)2 was bound to the surface of NaYF4:Yb3+,Tm3+@NaYF4:Nd3+@NaYF4 core-shell-shell (CSS-)UCNPs through its bis(phosphonate) group, thereby creating a H2O-dispersible, thermally stable nanoconjugate (CSS-UCNP@[1]). Conjugation to the nanoparticle surface was found to be most efficient in neutral to slightly basic conditions, resulting in up to 2.4 × 103 RuII ions per UCNP. The incorporation of a neodymium-doped shell layer allowed for the generation of blue light using low-energy, deep-penetrating light (796 nm). This wavelength prevents the undesired heating seen with conventional UCNPs activated at 980 nm. Irradiation of CSS-UCNP@[1] with NIR light led to activation of the ruthenium complex [1](PF6)2. Although only one of the two thioether groups was dissociated under irradiation at 50 W·cm-2, we provide the first demonstration of the photoactivation of a ruthenium thioether complex using 796 nm irradiation of a H2O-dispersible nanoconjugate.

Persistent Luminescence Nanoplatform with Fenton-like Catalytic Activity for Tumor Multimodal Imaging and Photoenhanced Combination Therapy

Reactive oxygen species-mediated tumor chemodynamic therapy and photodynamic therapy have captured extensive attention in practical cancer combination therapies. However, the severe treatment conditions and the hypoxic microenvironment of solid tumors significantly limit the efficacy of these therapies. This work demonstrates the design and fabrication of a multifunctional persistent luminescence nanoplatform (PHFI, refers to PLNP-HSA-Fe³⁺-IR780) for cancer multimodal imaging and effective photoenhanced combination therapy. The near-infrared-emitted persistent luminescence nanoparticles (PLNP) was modified with human serum albumin (HSA) combined with an IR780 probe and Fe³⁺. The synthesized PHFI possesses high longitudinal relaxivity, obvious photoacoustic contrast signals, and long-lasting persistent luminescence, indicating that PHFI can be used for cancer magnetic resonance imaging, photoacoustic imaging, and persistent luminescence multimodal imaging. PHFI shows intrinsic photoenhanced Fenton-like catalytic activities as well as photodynamic and photothermal effects and thereby can effectively overcome severe treatment conditions for killing tumor cells. It is worth noting that PHFI serving as a rechargeable internal light source for photoenhanced combination therapy was first disclosed. We believe that our work shows the great potential of PHFI for cancer theranostics and will advance the development of PLNP-based nanoplatforms in tumor catalytic therapy.

Sulfur Nanoparticles with Novel Morphologies Coupled with Brain-Targeting Peptides RVG as a New Type of Inhibitor Against Metal-Induced Aβ Aggregation

Functionalized nanomaterials, which have been applied widely to inhibit amyloid-β protein (Aβ) aggregation, show enormous potential in the field of prevention and treatment of Alzheimer's disease (AD). A significant body of data has demonstrated that the morphology and size of nanomaterials have remarkable effects on their biological behaviors. In this work, we proposed and designed three kinds of brain-targeting sulfur nanoparticles (RVG@Met@SNPs) with novel morphologies (volute-like, tadpole-like, and sphere-like) and investigated the effect of different RVG@Met@SNPs on Aβ-Cu²⁺ complex aggregation and their corresponding neurotoxicity. Among them, the sphere-like nanoparticles (RVG@Met@SS) exhibited the most effective inhibitory activity, due to their unique mini size effect, and they reduced 61.6% the Aβ-Cu²⁺ complex aggregation and increased 92.4% SH-SY5Y cell viability in a dose of 10 μg/mL. In vitro and in vivo, the abilities of different morphologies of RVG@Met@SNPs to cross the blood-brain barrier (BBB) and target brain parenchymal cells were significantly different. Moreover, improvements in learning disability and cognitive loss were shown in the transgenic AD mice model using the Morris water maze test after multiple doses of RVG@Met@SNPs treatment. In general, the purpose of this research is to develop a biological application of sulfur nanoparticles and to provide a novel functionalized nanomaterial to treat AD.

Transglutaminase mediated PEGylation of nanobodies for targeted nano-drug delivery

Targeted delivery of anticancer drugs that selectively accumulate in malignant cells could enhance drug efficacy and reduce side effects of conventional chemotherapy. In this work, we designed a single domain antibody (nanobody) based drug delivery system for targeted delivery of anticancer drugs. An anti-EGFR nanobody (Nb) was constructed with a C₃-tag and a Q-tag for site specific modifications under physiological conditions. The site specific PEGylation of the nanobody was achieved via a transglutaminase catalyzed reaction through the coupling of the Q-tag with PEG-NH₂. As a proof of concept, the PEGylated nanobody was tethered to HSA coated upconversion nanoparticles (UCNPs) through the C₃-tag, and an anticancer drug, doxorubicin (DOX), was loaded. Results showed that the Nb-conjugated drug delivery system exhibits superior specificity to the EGFR positive tumor cells. The drug delivery system is highly accumulated in the EGFR positive tumor cells (A431), whereas there was no detectable accumulation in the EGFR negative cells (MCF-7). Consequently, the drug loaded particles demonstrated significantly higher anti-proliferation to A431 cells than to MCF-7 cells. This work provides an effective approach for site-specific modification of nanobodies for the construction of targeted drug delivery systems.

Construction of a hypoxia responsive upconversion nanosensor for tumor imaging by fluorescence resonance energy transfer from carbon dots to ruthenium complex

Hypoxia responsive upconversion nano-aggregates are synthesized which can be excited by NIR light to give oxygen dependent phosphorescence emission via the FRET process.

Developing a pH-sensitive Al(OH)3 layer-mediated UCNP@Al(OH)3/Au nanohybrid for photothermal therapy and fluorescence imaging in vivo

A pH-responsive and hydrophilic Al(OH)₃ mediating layer makes possible the promising integration of photothermal therapy and fluorescence imaging based on upconversion nanoparticles (UCNPs).

Pompon-like RuNPs-Based Theranostic Nanocarrier System with Stable Photoacoustic Imaging Characteristic for Accurate Tumor Detection and Efficient Phototherapy Guidance

Even though numerous therapeutic methods exist for cancer treatment, many fail to achieve ideal outcomes or have severe side effects. Here, we describe a theranostic nanocarrier system with improved tumor vasculature detection and tumor margin quantification that increases the accuracy and guidance efficiency of phototherapy. Novel pompon-like RuNPs with superb photothermal properties and high encapsulation efficiency were first synthesized via the polyol reducing method. Based on these RuNPs, we then developed a multifunctional theranostic system, pRu-pNIPAM@RBT, composed of poly(N-isopropylacrylamide) as the thermal-response switch and of [Ru(bpy)₂(tip)]²⁺ as the photosensitizer of PDT and the contrast agent of biomedical imaging. We demonstrate that the pRu-pNIPAM@RBT can generate intracellular hyperthermia and reactive oxygen species (ROS) for simultaneous photothermal therapy (PTT) and photodynamic therapy (PDT) by laser activation. In contrast to other studies, our work highlights the integration of quantitative analysis of infrared thermal imaging and PA imaging data, which can distinguish between tumor and healthy tissues and guide the destructive but precise phototherapy and decrease nonspecific tissue injury. Considering the excellent in vivo antitumor phototherapeutic effects, this strategy may help preclinical researchers gain insight into theoretical as well as practical aspects of precision cancer therapy.

Near infrared light-mediated photoactivation of cytotoxic Re(i) complexes by using lanthanide-doped upconversion nanoparticles

Photoactivation of cytotoxic Re(i) complexes by using lanthanide doped upconversion nanoparticles upon near infrared illumination was demonstrated to selectively activate Re(i) complexes in tumor cells for enhanced anti-cancer effect.