Photoinduced Storage and Thermal Release of Singlet Oxygen from 1,2‐Dihydropyridine Endoperoxides

Photosensitizer-singlet oxygen sensor conjugated silica nanoparticles for photodynamic therapy and bioimaging

Intracellular singlet oxygen (1O2) generation and detection help optimize the outcome of photodynamic therapy (PDT). Theranostics programmed for on-demand phototriggered 1O2 release and bioimaging have great potential to transform PDT. We demonstrate an ultrasensitive fluorescence turn-on sensor-sensitizer-RGD peptide-silica nanoarchitecture and its 1O2 generation-releasing-storing-sensing properties at the single-particle level or in living cells. The sensor and sensitizer in the nanoarchitecture are an aminomethyl anthracene (AMA)-coumarin dyad and a porphyrin or CdSe/ZnS quantum dots (QDs), respectively. The AMA in the dyad quantitatively quenches the fluorescence of coumarin by intramolecular electron transfer, the porphyrin or QD moiety generates 1O2, and the RGD peptide facilitates intracellular delivery. The small size, below 200 nm, as verified by scanning electron microscopy and differential light scattering measurements, of the architecture within the 1O2 diffusion length enables fast and efficient intracellular fluorescence switching by the tandem ultraviolet (UV)-visible or visible-near-infrared (NIR) photo-triggering. While the red emission and 1O2 generation by the porphyrin are continually turned on, the blue emission of coumarin is uncaged into 230-fold intensity enhancement by on-demand photo-triggering. The 1O2 production and release by the nanoarchitecture enable spectro-temporally controlled cell imaging and apoptotic cell death; the latter is verified from cytotoxic data under dark and phototriggering conditions. Furthermore, the bioimaging potential of the TCPP-based nanoarchitecture is examined in vivo in B6 mice.

A Targeting Singlet Oxygen Battery for Multidrug-Resistant Bacterial Deep-Tissue Infections

Traditional photodynamic therapy (PDT) is dependent on externally applied light and oxygen, and the depth of penetration of these factors can be insufficient for the treatment of deep infections. The short half-life and short diffusion distance of reactive oxygen species (ROS) also limit the antibacterial efficiency of PDT. Herein, we designed a targeting singlet oxygen delivery system, CARG-Py, for irradiation-free and oxygen-free PDT. This system was converted to the "singlet oxygen battery" CARG-1 O2 and released singlet oxygen without external irradiation or oxygen. CARG-1 O2 is composed of pyridones coupled to a targeting peptide that improves the utilization of singlet oxygen in deep multidrug-resistant bacterial infections. CARG-1 O2 was shown to damage DNA, protein, and membranes by increasing the level of reactive oxygen inside bacteria; the attacking of multiple biomolecular sites caused the death of methicillin-resistant Staphylococcus aureus (MRSA). An in vivo study in a MRSA-infected mouse model of pneumonia demonstrated the potential of CARG-1 O2 for the efficient treatment of deep infections. This work provides a new strategy to improve traditional PDT for irradiation- and oxygen-free treatment of deep infections while improving convenience of PDT.

Dark Dynamic Therapy: Photosensitization without Light Excitation Using Chemiluminescence Resonance Energy Transfer in a Dioxetane-Erythrosin B Conjugate

Reactive oxygen species (e.g., singlet oxygen) are the primary cytotoxic agents used in the clinically approved technique photodynamic therapy (PDT). Although singlet oxygen has high potential to effectively kill tumor cells, its production via light excitation of a photosensitizer has been limited by the penetration depth and delivery of light in tissue. To produce singlet oxygen without light excitation, we describe the use of Schaap's chemiluminescent scaffold comprising an adamantylidene-dioxetane motif. Functionalizing this scaffold with a photosensitizer, Erythrosin B, resulted in spontaneous chemiluminescence resonance energy transfer (CRET) leading to the production of singlet oxygen. We show that this compound is cell permeable and that the singlet oxygen produced via CRET is remarkably efficient in killing cancer cells at low micromolar concentrations. Moreover, we demonstrate that protection of the phenol on the chemiluminescent scaffold with a nitroreductase-responsive trigger group allows for cancer-selective dark dynamic cell death. Here, we present the concept of dark dynamic therapy using a small cell-permeable molecule capable of producing the effects of PDT in cells, without light.