ABSTRACT
Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD.
Subject(s)
Anti-Bacterial Agents/pharmacology , Escherichia coli/drug effects , Graphite/pharmacology , Methicillin-Resistant Staphylococcus aureus/drug effects , Photosensitizing Agents/pharmacology , Quantum Dots/chemistry , Animals , Anti-Bacterial Agents/chemistry , Cells, Cultured , Escherichia coli/metabolism , Escherichia coli Infections/drug therapy , Graphite/chemistry , Humans , Light , Methicillin-Resistant Staphylococcus aureus/metabolism , Mice , Mice, Inbred BALB C , Oxidative Stress/drug effects , Photosensitizing Agents/chemistry , Reactive Oxygen Species/metabolism , Staphylococcal Infections/drug therapyABSTRACT
The excellent photoluminescent properties of graphene quantum dots (GQD) makes them suitable candidates for biomedical applications, but their cytotoxicity has not been extensively studied. Here we show that electrochemically produced GQD irradiated with blue light (470 nm, 1W) generate reactive oxygen species, including singlet oxygen, and kill U251 human glioma cells by causing oxidative stress. The cell death induced by photoexcited GQD displayed morphological and/or biochemical characteristics of both apoptosis (phosphatidylserine externalization, caspase activation, DNA fragmentation) and autophagy (formation of autophagic vesicles, LC3-I/LC3-II conversion, degradation of autophagic target p62). Moreover, a genetic inactivation of autophagy-essential LC3B protein partly abrogated the photodynamic cytotoxicity of GQD. These data indicate potential usefulness of GQD in photodynamic therapy, but also raise concerns about their possible toxicity.
Subject(s)
Graphite/chemistry , Photosensitizing Agents/pharmacology , Quantum Dots , Apoptosis , Autophagy , Caspases/metabolism , Cell Line, Tumor , Cell Survival , DNA Fragmentation , Dose-Response Relationship, Drug , Electrochemistry/methods , Enzyme Activation , Flow Cytometry/methods , Humans , Luminescence , Microscopy, Electron, Transmission/methods , Oxidative Stress , Oxygen/chemistry , RNA Interference , Time FactorsABSTRACT
The design, synthesis and biological evaluation of a novel C,D-spirolactone analogue of paclitaxel is described. This is the first paclitaxel analogue without an oxetane D-ring that shows a significant cytotoxic effect (activity one order of magnitude lower than paclitaxel). More importantly, its cytotoxicity is a result of a different mechanism of action, involving mTOR inhibition-dependent autophagy instead of G(2)/M cell cycle arrest-dependent apoptosis.
