A ruthenium(II) anthraquinone complex as the theranostic agent combining hypoxia imaging and HIF-1α inhibition

Investigation of the Relationship between Electronic Structures and Bioactivities of Polypyridyl Ru(II) Complexes

Ruthenium (Ru)-based organometallic drugs have gained attention as chemotherapeutic and bioimaging agents due to their fewer side effects and excellent physical optical properties. Tuning the electronic structures of Ru complexes has been proven to increase the cytotoxicity of cancer cells and the luminescent efficiency of the analytical probes. However, the relationship between electronic structures and bioactivities is still unclear due to the potential enhancement of both electron donor and acceptor properties. Thus, we investigated the relationship between the electronic structures of Ru(II) complexes and cytotoxicity by optimizing the electron-withdrawing (complex 1), electron-neutral (complex 2), and electron-donating (complex 3) ligands through DFT calculations, bioactivities tests, and docking studies. Our results indicated that it was not sufficient to consider only either the effect of electron-withdrawing or electron-donating effects on biological activities instead of the total electronic effects. Furthermore, these complexes with electron-donating substituents (complex 3) featured unique "off-on" luminescent emission phenomena caused by the various "HOMO-LUMO" distributions when they interacted with DNA, while complex with electron-withdrawing substituent showed an "always-on" signature. These findings offer valuable insight into the development of bifunctional chemotherapeutic agents along with bioimaging ability.

Synthesis, characterization, photophysical, lipophilicity, and in vitro fluorescence studies of mono-, di-, and trinuclear Ru(II) polypyridyl complexes of pyridinyl benzimidazole derivatives

The synthesis, characterization, and photophysical properties of mononuclear ruthenium(II) complexes [Ru(bpy)₂(py-BIm-Bz)](ClO₄)₂ (1) and [Ru(phen)₂(py-BIm-Bz)](ClO₄)₂ (2), dinuclear complexes [(bpy)₂Ru-μ₂-(py-BIm-Xy)-Ru(bpy)₂](ClO₄)₄ (3) and [(phen)₂Ru-μ₂-(py-BIm-Xy)-Ru(phen)₂](ClO₄)₄ (4), and trinuclear complexes [((bpy)₂Ru)₃-μ₃-(py-BIm-Ms)](ClO₄)₆ (5) and [((phen)₂Ru)₃-μ₃-(py-BIm-Ms)](ClO₄)₆ (6) of pyridinyl benzimidazole ligands with 2,2'-bipyridine or 1,10-phenanthroline ancillary ligands as fluorescent imaging probes are reported. The ligand py-BIm-Bz crystallizes with inherent disorder due to the competing π-π interactions between two (2-pyridinyl)benzimidazole moieties aligned in parallel and in the opposite direction. The complex 2 forms non-merohedrally twinned crystal with the twin law matrix [0.259 -0.776 0.741, 0.000 -1.000 0.000, 1.259 -0.776 -0.259] and a batch scale factor (BASF) of 0.05. The electronic absorption spectra of the complexes 1-6 differ typically in the π-π* transitions of the ancillary ligands. The complexes exhibit orange-red fluorescence at 624-634 nm at room temperature with quantum yield (0.096 - 0.117) higher than that of [Ru(bpy)₃]²⁺ and a hypsochromic shift of the emission maxima in frozen acetonitrile (λ_em = 613-628 nm) due to the rigidochromic effect. The excited state lifetime of these complexes are in the range 72-194 ns with the mononuclear complexes exhibiting the highest values. The complexes 1-6 are nontoxic (IC₅₀ > 275 μM) toward both HeLa and Vero cell lines. They are hydrophilic and the logP_o/w values are in the -0.53 to -1.46 range. The confocal microscopic study of cellular localization of the complexes on the HeLa cells co-stained with the nuclear staining DAPI dye shows their localization in the cytoplasm and the nuclear membrane penetration increases with nuclearity.

Hydrogen peroxide assisted photorelease of an anthraquinone-based ligand from [Ru(2,2'-bipyridine)2(9,10-dioxo-9,10-dihydroanthracen-1-olate)]Cl in aqueous solution

A new class of light-activated ruthenium(ii) complex was designed as a potential blocker of biological functioning, especially for targeting redox reactions within mitochondria under light activation. Based on our concepts the complex [Ru(bipy)2(1-hydroxyanthra-9,10 quinone)]Cl (RU1) was prepared and studied to understand the preliminary reaction mechanisms and its excited state behaviour through a series of stability tests, electrochemistry, UV-Visible kinetics and femtosecond transient absorption spectroscopy experiments. Under white light in the presence of H2O2 two different reactions (fast and slow) appear to take place. The complex loses the quinone-based ligand and a resulting Ru(iii) or Ru(v) species is produced. The complex RU1 shows potential to consume H2O2 from the one carbon metabolism in mitochondria, and hence may cut the energy cycle pathway of tumor cells.

Novel anthraquinone compounds as anticancer agents and their potential mechanism

Anthraquinones exhibit a unique anticancer activity. Since their discovery, medicinal chemists have made several structural modifications, resulting in the design and synthesis of a large number of novel anthraquinone compounds with different biological activities. In general, anthraquinone compounds have been considered to have anticancer activity mainly through DNA damage, cycle arrest and apoptosis. However, recent studies have shown that novel anthraquinone compounds may also inhibit cancer through paraptosis, autophagy, radiosensitising, overcoming chemoresistance and other methods. This Review article provides an overview of novel anthraquinone compounds that have been developed as anticancer agents in recent years and focuses on their anticancer mechanism.

Esterification of the free carboxylic group from the lutidinic acid ligand as a tool to improve the cytotoxicity of Ru(ii) complexes

The esterification of the free carboxyl group in ruthenium complexes improves the complex interactions with biomolecules, lipophilicity, and cellular uptake, making them more selective against tumor cells than cisplatin.