ABSTRACT
The biological properties of two water-soluble organic cations based on polypyridyl structures commonly used as ligands for photoactive transition metal complexes designed to interact with biomolecules are investigated. A cytotoxicity screen employing a small panel of cell lines reveals that both cations show cytotoxicity toward cancer cells but show reduced cytotoxicity to noncancerous HEK293 cells with the more extended system being notably more active. Although it is not a singlet oxygen sensitizer, the more active cation also displayed enhanced potency on irradiation with visible light, making it active at nanomolar concentrations. Using the intrinsic luminescence of the cations, their cellular uptake was investigated in more detail, revealing that the active compound is more readily internalized than its less lipophilic analogue. Colocalization studies with established cell probes reveal that the active cation predominantly localizes within lysosomes and that irradiation leads to the disruption of mitochondrial structure and function. Stimulated emission depletion (STED) nanoscopy and transmission electron microscopy (TEM) imaging reveal that treatment results in distinct lysosomal swelling and extensive cellular vacuolization. Further imaging-based studies confirm that treatment with the active cation induces lysosomal membrane permeabilization, which triggers lysosome-dependent cell-death due to both necrosis and caspase-dependent apoptosis. A preliminary toxicity screen in the Galleria melonella animal model was carried out on both cations and revealed no detectable toxicity up to concentrations of 80 mg/kg. Taken together, these studies indicate that this class of synthetically easy-to-access photoactive compounds offers potential as novel therapeutic leads.
Subject(s)
Antineoplastic Agents , Cations , Phenazines , Humans , Antineoplastic Agents/pharmacology , Antineoplastic Agents/chemistry , Antineoplastic Agents/chemical synthesis , Cations/chemistry , Cations/pharmacology , Phenazines/chemistry , Phenazines/pharmacology , Lysosomes/metabolism , Lysosomes/drug effects , HEK293 Cells , Apoptosis/drug effects , Drug Screening Assays, Antitumor , Cell Line, Tumor , Animals , Theranostic Nanomedicine , Molecular StructureABSTRACT
With the aim of developing photostable near-infrared cell imaging probes, a convenient route to the synthesis of heteroleptic OsII complexes containing the Os(TAP)2 fragment is reported. This method was used to synthesize the dinuclear OsII complex, [{Os(TAP)2}2tpphz]4+ (where tpphz = tetrapyrido[3,2-a:2',3'-c:3â³,2''-h:2â´,3'''-j]phenazine and TAP = 1,4,5,8- tetraazaphenanthrene). Using a combination of resonance Raman and time-resolved absorption spectroscopy, as well as computational studies, the excited state dynamics of the new complex were dissected. These studies revealed that, although the complex has several close lying excited states, its near-infrared, NIR, emission (λmax = 780 nm) is due to a low-lying Os â TAP based 3MCLT state. Cell-based studies revealed that unlike its RuII analogue, the new complex is neither cytotoxic nor photocytotoxic. However, as it is highly photostable as well as live-cell permeant and displays NIR luminescence within the biological optical window, its properties make it an ideal probe for optical microscopy, demonstrated by its use as a super-resolution NIR STED probe for nuclear DNA.
Subject(s)
Coordination Complexes/chemistry , DNA/analysis , Luminescent Agents/chemistry , Animals , Cattle , Cell Line, Tumor , Coordination Complexes/chemical synthesis , Coordination Complexes/toxicity , Humans , Luminescent Agents/chemical synthesis , Luminescent Agents/toxicity , Microscopy, Confocal , Osmium/chemistry , Osmium/toxicityABSTRACT
Drug resistance to platinum chemotherapeutics targeting DNA often involves abrogation of apoptosis and has emerged as a significant challenge in modern, non-targeted chemotherapy. Consequently, there is great interest in the anti-cancer properties of metal complexes-particularly those that interact with DNA-and mechanisms of consequent cell death. Herein we compare a parent cytotoxic complex, [Ru(phen)2(tpphz)]2+ [phen = 1,10-phenanthroline, tpphz = tetrapyridyl[3,2- a:2',3'- c:3â³,2â³- h:2â´,3â´- j]phenazine], with a mononuclear analogue with a modified intercalating ligand, [Ru(phen)2(taptp)]2+ [taptp = 4,5,9,18-tetraazaphenanthreno[9,10- b] triphenylene], and two structurally related dinuclear, tpphz-bridged, heterometallic complexes, RuRe and RuPt. All three of these structural changes result in a switch from intercalation to groove-binding DNA interaction and concomitant reduction in cytotoxic potency, but no significant change in relative cytotoxicity toward platinum-resistant A2780CIS cancer cells, indicating that the DNA interaction mode is not critical for the mechanism of platinum resistance. All variants exhibited a light-switch effect, which for the first time was exploited to investigate timing of cell death by live-cell microscopy. Surprisingly, cell death occurred rapidly as a consequence of oncosis, characterized by loss of cytoplasmic volume control, absence of significant mitochondrial membrane potential loss, and lack of activation of apoptotic cell death markers. Importantly, a novel, quantitative proteomic analysis of the A2780 cell genome following exposure of the cells to either mononuclear complex reveals changes in protein expression associated with global cell responses to oxidative stress and DNA replication/repair cellular pathways. This combination of multiple targeting modalities and induction of a non-apoptotic death mechanism makes these complexes highly promising chemotherapeutic cytotoxicity leads.
