Enhancing the tumor cell selectivity of a rhodamine-decorated iridium(III) complex by conjugating with indomethacin for COX-2 targeted photodynamic therapy

Metal complexes with a twist: modified rhodamines as a promising theranostic approach for combating cancer

Rhodamines have been recognized for their exceptional optical properties, making them suitable for detection, imaging, and disease diagnosis. However, their use as photosensitizers in Photodynamic Therapy (PDT) has been limited by their low singlet oxygen production and limited tissue penetration. The development of rhodamine-metal complexes has overcome these limitations, offering a promising new approach for cancer treatment. These complexes in combination with structural and optical tuning of rhodamines, have been engineered to enhance tumour cell selectivity, improve reactive oxygen species (ROS) generation, and mitochondrial-targeted delivery. Notably, a variety of metal ions, including iridium(III), ruthenium(II) and platinum(II/IV) can form complexes with bright rhodamines with excellent optical responses and remarkable ROS generation. These breakthroughs have the potential to improve cancer diagnosis and therapeutic applications. Photophysical properties, photostability, and targeting agents, particularly in the near-infrared (NIR) range, will be discussed, with a focus on their applications in cancer detection, localization, and cytotoxicity.

808 nm Light-Triggered Cyanine-Decorated Iridium(III) Complexes for Antibacterial Photodynamic Therapy in Deep-Tissue

Acute bacterial skin and skin structure infections (ABSSSIs) pose significant global health challenges, exacerbated by rising antibiotic resistance. Antibacterial photodynamic therapy (APDT) has emerged as a promising strategy to combat these infections by utilizing a photosensitizer (PS) that generates reactive oxygen species (ROS) upon light activation. However, the limited tissue penetration of conventional organic PSs, which primarily absorb in the UV-vis spectra, has hindered their therapeutic potential for deeper infections. Herein, we introduce a novel iridium(III)-cyanine complex (Ir-cy) with strong near-infrared (NIR) absorption at 814 nm (up to 101 nm red-shifted from previous reports), specifically designed to enhance tissue penetration for APDT. Under 808 nm laser irradiation, Ir-cy demonstrated a substantial ROS generation capacity, achieving approximately 70% reduction in Staphylococcus aureus (S. aureus) colonies at a depth of 7.2 mm within a simulated tissue model. Comprehensive in vitro and in vivo evaluations further confirmed its potent antibacterial efficacy against S. aureus while maintaining excellent biocompatibility. These findings highlight the potential of Ir-cy as a highly effective NIR-active PS, paving the way for advanced therapeutic strategies targeting deep-tissue ABSSSIs through optimized APDT.

Leveraging the Photofunctions of Transition Metal Complexes for the Design of Innovative Phototherapeutics

Despite the advent of various medical interventions for cancer treatment, the disease continues to pose a formidable global health challenge, necessitating the development of new therapeutic approaches for more effective treatment outcomes. Photodynamic therapy (PDT), which utilizes light to activate a photosensitizer to produce cytotoxic reactive oxygen species (ROS) for eradicating cancer cells, has emerged as a promising approach for cancer treatment due to its high spatiotemporal precision and minimal invasiveness. However, the widespread clinical use of PDT faces several challenges, including the inefficient production of ROS in the hypoxic tumor microenvironment, the limited penetration depth of light in biological tissues, and the inadequate accumulation of photosensitizers at the tumor site. Over the past decade, there has been increasing interest in the utilization of photofunctional transition metal complexes as photosensitizers for PDT applications due to their intriguing photophysical and photochemical properties. This review provides an overview of the current design strategies used in the development of transition metal complexes as innovative phototherapeutics, aiming to address the limitations associated with PDT and achieve more effective treatment outcomes. The current challenges and future perspectives on the clinical translation of transition metal complexes are also discussed.

An NIR Type I Photosensitizer Based on a Cyclometalated Ir(III)-Rhodamine Complex for a Photodynamic Antibacterial Effect toward Both Gram-Positive and Gram-Negative Bacteria

Type I photosensitizers offer an advantage in photodynamic therapy (PDT) due to their diminished reliance on oxygen levels, thus circumventing the challenge of hypoxia commonly encountered in PDT. In this study, we present the synthesis and comprehensive characterization of a novel type I photosensitizer derived from a cyclometalated Ir(III)-rhodamine complex. Remarkably, the complex exhibits a shift in absorption and fluorescence, transitioning from "off" to "on" states in aprotic and protic solvents, respectively, contrary to initial expectations. Upon exposure to light, the complex demonstrates the effective generation of O2- and ·OH radicals via the type I mechanism. Additionally, it exhibits notable photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria, demonstrated through in vitro and in vivo experiments. This research offers valuable insights for the development of novel type I photosensitizers.

Iridium(III) complex induces apoptosis in HeLa cells by regulating mitochondrial and PI3K/AKT signaling pathways: In vitro and in vivo experiments

Cyclometalated iridium complexes with mitochondrial targeting show great potential as substitutes for platinum-based complexes because of their strong anti-cancer properties. Three novel cyclometalated iridium(III) compounds were synthesized and evaluated in five different cell lines as part of the ongoing systematic investigations of these compounds. The complexes were prepared using 4,7-dichloro-1,10-phenanthroline ligands. The cytotoxicity of complexes Ir1-Ir3 towards HeLa cells was shown to be high, with IC50 values of 0.83±0.06, 4.73±0.11, and 4.95±0.62 μM, respectively. Complex Ir1 could be ingested by HeLa cells in 3 h and has shown high selectivity toward mitochondria. Subsequent investigations demonstrated that Ir1 triggered apoptosis in HeLa cells by augmenting the generation of reactive oxygen species (ROS), reducing the mitochondrial membrane potential, and depleting ATP levels. Furthermore, the movement of cells was significantly suppressed and the progression of the cell cycle was arrested in the G0/G1 phase following the administration of Ir1. The Western blot analysis demonstrated that the induction of apoptosis in HeLa cells by Ir1 involves the activation of the mitochondria-dependent channel and the PI3K/AKT signaling pathway. No significant cytotoxicity was observed in zebrafish embryos at concentrations less than or equal to 16 µM, e.g., survival rate and developmental abnormalities. In vivo, antitumor assay demonstrated that Ir1 suppressed tumor growth in mice. Therefore, our work shows that complex Ir1 could be a promising candidate for developing novel antitumor drugs.

Indomethacin-based near-infrared photosensitizer for targeted photodynamic cancer therapy

Near-IR fluorescent sensitizers based on heptamethine cyanine (Cy820 and Cy820-IMC) were synthesized and their abilities to target and abolish tumor cells via photodynamic therapy (PDT) were explored. Some hepthamethine cyanine dyes can be transported into cancer cells via the organic anion transporting polypeptides (OATPs). In this study, we aimed to enhance the target ability of the sensitizer by conjugation Cy820 with indomethacin, a non-steroidal anti-inflammatory drug (NSAID), to obtain Cy820-IMC that aimed to target cyclooxygenase-2 (COX-2) which overexpresses in cancer cells. The results showed that Cy820-IMC internalized the cancer cells faster than Cy820 which was verified to be related to COX-2 level and OATPs. Based on PDT experiments, Cy820-IMC has higher photocytotoxicity index than Cy820, >7.13 and 4.90, respectively, implying that Cy820-IMC showed better PDT property than Cy820. However, Cy820 exhibits slightly higher normal-to-cancer cell toxicity ratio than Cy820-IMC, 6.58 and 3.63, respectively. Overall, Cy820-IMC has superior cancer targetability and enhanced photocytoxicity. These characteristics can be further improved towards clinically approved sensitizers for PDT.