👤 Nomura DK

Title: Biotin-Pt(IV)-Ru(II)-Boron-Dipyrromethene Prodrug as "Platin Bullet" for Targeted Chemo- and Photodynamic Therapy. Abstract: Using the principle of "Magic Bullet", a cisplatin-derived platinum(IV) prodrug heterobimetallic Pt(IV)-Ru(II) complex, cis,cis,trans-[Pt(NH3)2Cl2{Ru(tpy-BODIPY)(tpy-COO)}(biotin)]Cl2 (Pt-Ru-B, 2), having two axial ligands, namely, biotin as water-soluble B-vitamin for enhanced cellular uptake and a BODIPY-ruthenium(II) (Ru-B, 1) photosensitizer having N,N,N-donor tpy (4'-phenyl-2,2':6',2″-terpyridine) bonded to boron-dipyrromethene (BODIPY), is developed as a "Platin Bullet" for targeted photodynamic therapy (PDT). Pt-Ru-B exhibited intense absorption near 500 nm and emission near 513 nm (λex = 488 nm) in a 10% dimethyl sulfoxide-Dulbecco's phosphate-buffered saline medium (pH 7.2). The BODIPY complex on light activation generates singlet oxygen as the reactive oxygen species (ROS) giving a quantum yield (ΦΔ) of ∼0.64 from 1,3-diphenylisobenzofuran experiments. Pt-Ru-B exhibited preferential cellular uptake in cancer cells over noncancerous cells. The dichlorodihydrofluorescein diacetate assay confirmed the generation of cellular ROS. Confocal images revealed its mitochondrial internalization. Pt-Ru-B showed submicromolar photocytotoxicity in visible light (400-700 nm) in A549 and multidrug-resistant MDA-MB-231 cancer cells. It remained nontoxic in the dark and less toxic in nontumorigenic cells. Cellular apoptosis and alteration of the mitochondrial membrane potential were evidenced from the respective Annexin V-FITC/propidium iodide assay and JC-1 dye assay. A wound healing assay using A549 cells and Pt-Ru-B revealed inhibition of cancer cell migration, highlighting its potential as an antimetastatic agent. Show less

Novel bipyridine-based heterocyclic building block, 3,10-dichloro-benzo[f][1,10]phenanthroline and its Ruthenium(II) complex have been synthesized and fully characterized. The synthesized Ru(II)-complex is highly luminescent displaying emission at 590 nm with quantum yield of ∼0.8 in methanol. Ru(II) complex showed photocytotoxicity upon 400 nm blue light irradiation. Mechanistic study revealed that photoactivated Ru(II) complex generates reactive radical species which can damage the protein inside the cells and induce cell death even with short irradiation time. Show less

Photoreactive Ru(II) complexes capable of ejecting ligands have been used extensively for photocaging applications and for the creation of "photocisplatin" reagents. The incorporation of distortion into the structure of the coordination complex lowers the energy of dissociative excited states, increasing the yield of the photosubstitution reaction. While steric clash between ligands induced by adding substituents at the coordinating face of the ligand has been extensively utilized, a lesser known, more subtle approach is to distort the coordination sphere by altering the chelate ring size. Here a systematic study was performed to alter metal-ligand bond lengths, angles, and to cause intraligand distortion by introducing a "linker" atom or group between two pyridine rings. The synthesis, photochemistry, and photobiology of five Ru(II) complexes containing CH₂, NH, O, and S-linked dipyridine ligands was investigated. All systems where stable in the dark, and three of the five were photochemically active in buffer. While a clear periodic trend was not observed, this study lays the foundation for the creation of photoactive systems utilizing an alternative type of distortion to facilitate photosubstitution reactions. Show less

The β-diketone scaffold is a commonly used synthetic intermediate, and is a functional group found in natural products such as curcuminoids. This core structure can also act as a chelating ligand for a variety of metals. In order to assess the potential of this scaffold for medicinal inorganic chemistry, seven different κ²-O,O'-chelating ligands were used to construct Ru(II) complexes with polypyridyl co-ligands, and their biological activity was evaluated. The complexes demonstrated promising structure-dependent cytotoxicity. Three complexes maintained high activity in a tumor spheroid model, and all complexes demonstrated low in vivo toxicity in a zebrafish model. From this series, the best compound exhibited a ~ 30-fold window between cytotoxicity in a 3-D tumor spheroid model and potential in vivo toxicity. These results suggest that κ²-O,O'-ligands can be incorporated into Ru(II)-polypyridyl complexes to create favorable candidates for future drug development. Show less

Ferroptosis is a form of regulated cell death that is caused by the iron-dependent peroxidation of lipids1,2. The glutathione-dependent lipid hydroperoxidase glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting lipid hydroperoxides into non-toxic lipid alcohols3,4. Ferroptosis has previously been implicated in the cell death that underlies several degenerative conditions2, and induction of ferroptosis by the inhibition of GPX4 has emerged as a therapeutic strategy to trigger cancer cell death5. However, sensitivity to GPX4 inhibitors varies greatly across cancer cell lines6, which suggests that additional factors govern resistance to ferroptosis. Here, using a synthetic lethal CRISPR-Cas9 screen, we identify ferroptosis suppressor protein 1 (FSP1) (previously known as apoptosis-inducing factor mitochondrial 2 (AIFM2)) as a potent ferroptosis-resistance factor. Our data indicate that myristoylation recruits FSP1 to the plasma membrane where it functions as an oxidoreductase that reduces coenzyme Q10 (CoQ) (also known as ubiquinone-10), which acts as a lipophilic radical-trapping antioxidant that halts the propagation of lipid peroxides. We further find that FSP1 expression positively correlates with ferroptosis resistance across hundreds of cancer cell lines, and that FSP1 mediates resistance to ferroptosis in lung cancer cells in culture and in mouse tumour xenografts. Thus, our data identify FSP1 as a key component of a non-mitochondrial CoQ antioxidant system that acts in parallel to the canonical glutathione-based GPX4 pathway. These findings define a ferroptosis suppression pathway and indicate that pharmacological inhibition of FSP1 may provide an effective strategy to sensitize cancer cells to ferroptosis-inducing chemotherapeutic agents. Show less

The discovery of new light-triggered prodrugs based on ruthenium (II) complexes is a promising approach for photoactivated chemotherapy (PACT). The light-mediated activation of "strained" Ru(II) polypyridyl complexes resulted in ligand release and produced a ligand-deficient metal center capable of forming covalent adducts with biomolecules such as DNA. Based on the strategy of exploiting structural distortion to activate photochemistry, biologically active small molecules were coordinated to a Ru(II) scaffold to create light-triggered dual-action agents. Thirteen new Ru(II) complexes with pyridyl-pyrazol(in)e ligands were synthesized, and their photochemical reactivity and anticancer properties were investigated. Isomeric bidentate ligands were investigated, where "regular" ligands (where the coordinated nitrogens in the heterocycles are linked by C-C atoms) were compared to "inverse" isomers (where the coordinated nitrogens in the heterocycles are linked by C-N atoms). Coordination of the regular 3-(pyrid-2-yl)-pyrazol(in)es to a Ru(II) bis-dimethylphenanthroline scaffold yielded photoresponsive compounds with promising photochemical and biological properties, in contrast to the inverse 1-(pyrid-2-yl)-pyrazolines. The introduction of a phenyl ring to the 1N-pyrazoline cycle increased the distortion in complexes and improved ligand release upon light irradiation (470 nm) up to 5-fold in aqueous media. Compounds 1-8, containing pyridyl-pyrazol(in)e ligands, were at least 20-80-fold more potent than the parent pyridyl-pyrazol(in)es, and exhibited biological activity in the dark, with half-maximal inhibitory concentration (IC₅₀) values ranging from 0.2 to 7.6 μM in the HL60 cell line, with complete growth inhibition upon light irradiation. The diversification of coligands and introduction of a carboxylic acid into the Ru(II) complex resulted in compounds 9-12, with up to 146-fold improved phototoxicity indices compared with complexes 1-8. Show less

Ruthenium(II) complexes developed for photodynamic therapy (PDT) are almost exclusively tris-bidentate systems with C₂ or D₃ symmetry. This is due to the fact that this structural framework commonly produces long-lived excited states, which, in turn, allow for the generation of large amounts of singlet oxygen (¹O₂) and other reactive oxygen species. Complexes containing tridentate ligands would be advantageous for biological applications as they are generally achiral (D_2d or C_2v symmetry), which eliminates the possibility of multiple isomers which could exhibit potentially different interactions with chiral biological entities. However, Ru(II) complexes containing tridentate ligands are rarely studied as candidates for photobiological applications, such as PDT, since they almost exclusively exhibit low quantum yields and very short excited-state lifetimes and, thus, are not capable of generating sufficient ¹O₂ or engaging in electron transfer reactions. Here, we report a proof-of-concept approach to make bis-tridentate Ru(II) complexes useful for PDT applications by altering their photophysical properties through the inclusion of N-heterocyclic carbene (NHC) ligands. Three NHC and two terpyridine ligands were studied to evaluate the effects of structural and photophysical modulations of bis-substituted Ru(II) complexes. The NHC complexes were found to have superior excited-state lifetimes, ¹O₂ production, and photocytotoxicity. To the best of our knowledge, these complexes are the most potent light-activated bis-tridentate complexes reported. Show less

8-Hydroxyquinolines (HQ), including clioquinol, possess cytotoxic properties and are widely used as ligands for metal-based anticancer drug research. The number and identity of substituents on the HQ can have a profound effect on activity for a variety of inorganic compounds. Ruthenium complexes of HQ exhibit radically improved potencies, and operate by a new, currently unknown, mechanism of action. To define structure-activity relationships (SAR), a family of 22 Ru(II) coordination complexes containing mono-, di- and tri-substituted hydroxyquinoline ligands were synthesized and their biological activity evaluated. The complexes exhibited promising cytotoxic activity against a cancer cell line, and the SAR data revealed the 2- and 7-positions as key sites for the incorporation of halogens to improve potency. The Ru(II) complexes potently inhibited translation, as demonstrated by an in-cell translation assay. The effects were seen at 2-15-fold higher concentrations than those required to observe cytotoxicity, suggesting that prevention of protein synthesis may be a primary, but not the exclusive mechanism for the observed cytotoxic activity. Show less

Ruthenium complexes capable of light-triggered cytotoxicity are appealing potential prodrugs for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT). Two groups of Ru(II) polypyridyl complexes with 2-(2-pyridyl)-benzazole ligands were synthesized and investigated for their photochemical properties and anticancer activity to compare strained and unstrained systems that are likely to have different biological mechanisms of action. The structure-activity relationship was focused on the benzazole core bioisosterism and replacement of coligands in Ru(II) complexes. Strained compounds rapidly ejected the 2-(2-pyridyl)-benzazole ligand after light irradiation, and possessed strong toxicity in the HL-60 cell line both under dark and light conditions. In contrast, unstrained Ru(II) complexes were non-toxic in the absence of light, induced cytotoxicity at nanomolar concentrations after light irradiation, and are capable of light-induced DNA damage. The 90-220-fold difference in light and dark IC₅₀ values provides a large potential therapeutic window to allow for selective targeting of cells by exposure to light. Show less

Light-activated compounds are powerful tools and potential agents for medical applications, as biological effects can be controlled in space and time. Ruthenium polypyridyl complexes can induce cytotoxic effects through multiple mechanisms, including acting as photosensitizers for singlet oxygen (¹O₂) production, generating other reactive oxygen species (ROS), releasing biologically active ligands, and creating reactive intermediates that form covalent bonds to biological molecules. A structure-activity relationship (SAR) study was performed on a series of Ru(II) complexes containing isomeric tetramethyl-substituted bipyridyl-type ligands. Three of the ligand systems studied contained strain-inducing methyl groups and created photolabile metal complexes, which can form covalent bonds to biomolecules upon light activation, while the fourth was unstrained and resulted in photostable complexes, which can generate ¹O₂. The compounds studied included both bis-heteroleptic complexes containing two bipyridine ligands and a third, substituted ligand and tris-homoleptic complexes containing only the substituted ligand. The photophysics, electrochemistry, photochemistry, and photobiology were assessed. Strained heteroleptic complexes were found to be more photoactive and cytotoxic then tris-homoleptic complexes, and bipyridine ligands were superior to bipyrimidine. However, the homoleptic complexes exhibited an enhanced ability to inhibit protein production in live cells. Specific methylation patterns were associated with improved activation with red light, and photolabile complexes were generally more potent cytotoxic agents than the photostable ¹O₂-generating compounds. Show less

Two thermally activated ruthenium(ii) polypyridyl complexes, cis-Ru(bpy)2Cl2 and trans-Ru(qpy)Cl2 were investigated to determine the impact of the geometric arrangement of the exchangable ligands on the potential of the compounds to act as chemotherapeutics. In contrast to the geometry requirements for cisplatin, trans-Ru(qpy)Cl2 was 7.1-9.5× more cytotoxic than cis-Ru(bpy)2Cl2. This discovery could open up a new area of metal-based chemotherapeutic research. Show less

Two novel strained ruthenium(II) polypyridyl complexes containing a 2,3-dihydro-1,4-dioxino[2,3-f]-1,10-phenanthroline (dop) ligand selectively ejected a methylated ligand when irradiated with >400 nm light. The best compound exhibited a 1880-fold increase in cytotoxicity in human cancer cells upon light-activation and was 19-fold more potent than the well-known chemotherapeutic, cisplatin. Show less

Strained ruthenium (Ru) complexes have been synthesized and characterized as novel agents for photodynamic therapy (PDT). The complexes are inert until triggered by visible light, which induces ligand loss and covalent modification of DNA. An increase in cytotoxicity of 2 orders of magnitude is observed with light activation in cancer cells, and the compounds display potencies superior to cisplatin against 3D tumor spheroids. The use of intramolecular strain may be applied as a general paradigm to develop light-activated ruthenium complexes for PDT applications. Show less

Incorporation of biquinoline ligands into Ru(II) polypyridyl complexes produces light-activated systems that eject a ligand and photobind DNA after irradiation with visible and near-IR light. Structural analysis shows that distortion facilitates the photochemistry, and gel shift and cytotoxicity studies prove the compounds act as anti-cancer photodynamic therapy (PDT) agents in the tissue penetrant region. Show less