Self-Illuminated, Oxygen-Supplemented Photodynamic Therapy via a Multienzyme-Mimicking Nanoconjugate

Self-Chemiluminescence-Triggered Ir(III) Complex Photosensitizer for Photodynamic Therapy against Hypoxic Tumor

The limited optical penetration depth and hypoxic tumor microenvironment (TME) are key factors that hinder the practical applications of conventional photodynamic therapy (PDT). To fundamentally address these issues, self-luminescent photosensitizers (PSs) can achieve efficient PDT. Herein, a self-chemiluminescence (CL)-triggered Ir complex PS, namely, IrL2, with low-O2-dependence type I photochemical processes is reported for efficient PDT. The rational design achieves efficient chemiluminescence resonance energy transfer (CRET) from covalently bonded luminol units to the Ir complex in IrL2 under the catalysis of H2O2 and hemoglobin (Hb) to generate O2•- and 1O2. Liposome IrL2H nanoparticles (NPs) are constructed by loading IrL2 and Hb. The intracellular H2O2 and loaded Hb catalyze the luminol part of IrL2H, and the Ir2 part is then excited to produce types I and II reactive oxygen species (ROS) through CRET, inducing cell death, even under hypoxic conditions, and promoting cell apoptosis. IrL2H is used for tumor imaging and inhibits tumor growth in 4T1-bearing mouse models through intratumoral injection without external light sources. This work provides new designs for transition metal complex PSs that conquer the limitations of external light sources and the hypoxic TME in PDT.

Nanomaterials for light-mediated therapeutics in deep tissue

Light-mediated therapeutics, including photodynamic therapy, photothermal therapy and light-triggered drug delivery, have been widely studied due to their high specificity and effective therapy. However, conventional light-mediated therapies usually depend on the activation of light-sensitive molecules with UV or visible light, which have poor penetration in biological tissues. Over the past decade, efforts have been made to engineer nanosystems that can generate luminescence through excitation with near-infrared (NIR) light, ultrasound or X-ray. Certain nanosystems can even carry out light-mediated therapy through chemiluminescence, eliminating the need for external activation. Compared to UV or visible light, these 4 excitation modes penetrate more deeply into biological tissues, triggering light-mediated therapy in deeper tissues. In this review, we systematically report the design and mechanisms of different luminescent nanosystems excited by the 4 excitation sources, methods to enhance the generated luminescence, and recent applications of such nanosystems in deep tissue light-mediated therapeutics.

Unleashing the potential of 5-Aminolevulinic acid: Unveiling a promising target for cancer diagnosis and treatment beyond photodynamic therapy

The therapeutic properties of 5-aminolevulinic acid (5-ALA) have been extensively studied for cancer detection and treatment using photodynamic therapy (PDT). When administered externally, 5-ALA is converted to protoporphyrin IX (PpIX) in cancer cells, which generates reactive oxygen species (ROS) upon exposure to light. This process enables targeted cell death induction and cancer detection. Given the highly conserved nature of heme biosynthesis over billions of years, we hypothesized that natural mechanisms might exist to prevent excessive accumulation of PpIX or heme resulting from 5-ALA overload. Therefore, we anticipated alterations in protein expression profiles upon exogenous administration of 5-ALA. To understand cellular responses to 5-ALA, we investigated protein expression changes and identified OR1B1 as a promising target in bladder, prostate, lung, and cervical cancer cells. OR1B1 expression was observed only with 5-ALA and ferrous chloride, highlighting the central role of heme in this discovery. Immunofluorescence and electron microscopy confirmed OR1B1's sub-cellular localization. These findings suggest that 5-ALA transformation in cancer cells and OR1B1 expression have potential for enhancing cancer detection and developing alternative treatments, including immunotherapy. This approach overcomes the limitations of PDT and opens new avenues for effective and targeted cancer interventions.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.