Oxidative photocatalysis on membranes triggers non-canonical pyroptosis.

Intracellular membranes composing organelles of eukaryotes include membrane proteins playing crucial roles in physiological functions. However, a comprehensive understanding of the cellular responses triggered by intracellular membrane-focused oxidative stress remains elusive. Herein, we report an amphiphilic photocatalyst localised in intracellular membranes to damage membrane proteins oxidatively, resulting in non-canonical pyroptosis. Our developed photocatalysis generates hydroxyl radicals and hydrogen peroxides via water oxidation, which is accelerated under hypoxia. Single-molecule magnetic tweezers reveal that photocatalysis-induced oxidation markedly destabilised membrane protein folding. In cell environment, label-free quantification reveals that oxidative damage occurs primarily in membrane proteins related to protein quality control, thereby aggravating mitochondrial and endoplasmic reticulum stress and inducing lytic cell death. Notably, the photocatalysis activates non-canonical inflammasome caspases, resulting in gasdermin D cleavage to its pore-forming fragment and subsequent pyroptosis. These findings suggest that the oxidation of intracellular membrane proteins triggers non-canonical pyroptosis.

Controlling Morphologies of Redox-Responsive Polymeric Nanocarriers for a Smart Drug Delivery System.

Redox-responsive nanocarriers using disulfides or thiols have received considerable attention owing to the higher levels of glutathione (GSH) in cancer cells than those in extracellular fluids. Nevertheless, the normal-to-cancer-cell selectivity of these nanocarriers has not yet been clarified. Nanocarriers exhibit different cytotoxicities depending on the morphologies they adopt under the redox-active conditions typically existing in cancerous cells. Therefore, not only GSH levels but also reactive oxygen species (ROS) levels and other complex cancerous cell conditions must be considered for the development of smart drug delivery systems. In this article, we review the structural design of redox-responsive polymers that exhibit different morphological changes in environments akin to cancerous cells (e. g., GSH- and ROS-abundant conditions). In addition, we propose a molecular design for the spatiotemporal control of nanocarrier morphology depending on the levels of both GSH and ROS upon photoirradiation to increase the cytotoxicity difference between normal and cancer cells.

Dual-Modulated Release of a Cytotoxic Photosensitizer Using Photogenerated Reactive Oxygen Species and Glutathione.

Reversible thiol-disulfide exchange chemistry is of particular interest in drug delivery systems. However, high levels of glutathione (GSH) in cancer cells are hard to distinguish from GSH in normal cells, resulting in unmanageable cytotoxic drug release. This study investigates the spatiotemporally-controlled irreversible degradation of Ir-based photosensitizer (TIr3)-encapsulating nanogels (IrNG) through the hyperoxidation of resulting intracellular thiols using reactive oxygen species (ROS). A highly cytotoxic TIr3 was stably encapsulated within IrNG through hydrophobic interactions and reversible crosslinking between its disulfide bonds and thiols in the absence of light, resulting in high biocompatibility under normal cellular conditions. However, upon photoirradiation, TIr3 generated high levels of ROS, irreversibly oxidizing the thiols to induce electrostatic repulsion between the polymer molecules, resulting in the TIr3 release and induction of cancer cell apoptosis.

Singlet Oxygen Generation from Polyaminoglycerol by Spin-Flip-Based Electron Transfer.

Reactive oxygen species have drawn attention owing to their strong oxidation ability. In particular, the singlet oxygen (1O2) produced by energy transfer is the predominant species for controlling oxidation reactions efficiently. However, conventional 1O2 generators, which rely on enhanced energy transfer, frequently suffer from poor solubility, low stability, and low biocompatibility. Herein, we introduce a hyperbranched aliphatic polyaminoglycerol (hPAG) as a 1O2 generator, which relies on spin-flip-based electron transfer. The coexistence of a lone pair electron on the nitrogen atom and a hydrogen-bonding donor (the protonated form of nitrogen and hydroxyl group) affords proximity between hPAG and O2. Subsequent direct electron transfer after photo-irradiation induces hPAG•+-O2 •- formation, and the following spin-flip process generates 1O2. The spin-flip-based electron transfer pathway is analyzed by a series of photophysical, electrochemical, and computational studies. The 1O2 generator, hPAG, is successfully employed in photodynamic therapy and as an antimicrobial reagent.

Analysing the mechanism of mitochondrial oxidation-induced cell death using a multifunctional iridium(III) photosensitiser.

Mitochondrial oxidation-induced cell death, a physiological process triggered by various cancer therapeutics to induce oxidative stress on tumours, has been challenging to investigate owing to the difficulties in generating mitochondria-specific oxidative stress and monitoring mitochondrial responses simultaneously. Accordingly, to the best of our knowledge, the relationship between mitochondrial protein oxidation via oxidative stress and the subsequent cell death-related biological phenomena has not been defined. Here, we developed a multifunctional iridium(III) photosensitiser, Ir-OA, capable of inducing substantial mitochondrial oxidative stress and monitoring the corresponding change in viscosity, polarity, and morphology. Photoactivation of Ir-OA triggers chemical modifications in mitochondrial protein-crosslinking and oxidation (i.e., oxidative phosphorylation complexes and channel and translocase proteins), leading to microenvironment changes, such as increased microviscosity and depolarisation. These changes are strongly related to cell death by inducing mitochondrial swelling with excessive fission and fusion. We suggest a potential mechanism from mitochondrial oxidative stress to cell death based on proteomic analyses and phenomenological observations.

Reduction-Triggered Self-Cross-Linked Hyperbranched Polyglycerol Nanogels for Intracellular Delivery of Drugs and Proteins.

Owing to the unique advantages of combining the characteristics of hydrogels and nanoparticles, nanogels are actively investigated as a promising platform for advanced biomedical applications. In this work, a self-cross-linked hyperbranched polyglycerol nanogel is synthesized using the thiol-disulfide exchange reaction based on a novel disulfide-containing polymer. A series of structural analyses confirm the tunable size and cross-linking density depending on the type of polymer (homo- or copolymer) and the amount of reducing agent, dithiothreitol, used in the preparation of the nanogels. The nanogels retain not only small molecular therapeutics irrespective of hydrophilic and hydrophobic nature but also large enzymes such as ß-galactosidase by exploiting the self-cross-linking chemistry. Their superior biocompatibility together with the controllable release of active therapeutic agents suggests the applicability of nanogels in smart drug delivery systems.