Mitochondria-targeted Photodynamic Therapy Research Articles

A new near-infrared phosphorescent iridium(III) complex conjugated to a xanthene dye for mitochondria-targeted photodynamic therapy.

Iridium(iii) complexes are potent candidates for photodynamic therapy (PDT), but some key drawbacks still hamper clinical translation, such as poor operability in the phototherapeutic window, high dark toxicity, and low reactive oxygen species (ROS) production efficiency. In this work, a near-infrared phosphorescent Ir(iii) complex conjugated to a xanthene dye, NIR-Ir-XE, is reported with highly favourable properties for mitochondria-targeted imaging and cancer phototherapy. The generation of the triplet excited state of a xanthene moiety endows the NIR-Ir-XE to form singlet oxygen (1O2) for use as a photodynamic therapy agent after irradiation with visible light. Compared with the xanthene-free Ir(iii) counterpart (NIR-Ir-bpy), the xanthene-modified cyclometalated Ir(iii) photosensitizer NIR-Ir-XE exhibits higher 1O2 generation efficiency, negligible dark toxicity and a better therapeutic effect. Importantly, a clear correlation between cell death and intracellular generation of 1O2 derived from NIR-Ir-XE after light irradiation was demonstrated. The corresponding in vivo photo-antitumor performance was further demonstrated to be effective in tumor-bearing mice. The observed properties of NIR-Ir-XE qualify it as a promising PDT agent.

Mitochondria-Specific Agents for Photodynamic Cancer Therapy: A Key Determinant to Boost the Efficacy.

Mitochondria-targeted photodynamic therapy (Mt-PDT), which enables the photogenerated cytotoxic oxygen species with fatal oxidative damage to block mitochondrial functions, has been considered as a promising method to enhance the anticancer effectiveness. Aiming at the challenges of PDT, in the past few decades, numerous mitochondria-targeting molecular agents have been developed to boost the PDT efficacy via directly destroying the mitochondria or activating mitochondria-mediated cell death pathways. Herein, a review for recent advances of Mt-PDT is highlighted including: mitochondrial targeting design principles and strategies, therapeutic performance of mitochondria-targeted agents-mediated PDT as well as the agent-free Mt-PDT. In addition, it puts together the achievements of the combinatory mitochondria-anchoring PDT and other anticancer strategies, demonstrating the advantages provided by Mt-PDT. The existing challenges are discussed and future settlements for the development of mitochondria-specific agents are also forecasted.

Tuning the hydrophobicity of pyridinium-based probes to realize the mitochondria-targeted photodynamic therapy and mitophagy tracking

Targeting mitochondria and dynamically tracking mitophagy are profoundly important in the field of photodynamic therapy (PDT) which relies on the photosensitizers (PSs) under light irradiation. While simultaneously realizing the effective reactive oxygen species (ROS) generation, accurately mitochondrial targeting, and dynamic tracking in a single PS still is a challenging issue. In this context, a series of pyridinium-based cationic fluorogens with aggregation induced emission (AIE) has been developed for this issue. The hydrophobicity of these fluorogens can be finely tuned by modulating the length of the alkyl chains on pyridinium unit. The well-tuned hydrophobicity of TL8C with C8-alkyl chain gives rise to the specifically mitochondrial targeting capability of TL8C based on the appropriate synergistic effect of hydrophobic and electrostatic interaction. Meanwhile, TL8C can produce ROS in high efficiency. The excellent mitochondrial targeting and the effective ROS generation allow TL8C for the specifically mitochondria-targeted PDT as well as the real time monitoring of mitophagy.

Tetraphenylporphine-Modified Polymeric Nanoparticles Containing NIR Photosensitizer for Mitochondria-Targeting and Imaging-Guided Photodynamic Therapy.

Near-infrared (NIR) photodynamic therapy (PDT) is a promising antitumor strategy under NIR light irradiation to kill cancer cells. Mitochondria has a critical function in sustaining cellular viability and death, which is the ideal organelle for PDT. Here, we reported a tetraphenylporphine (TPP)-conjugated amphiphilic copolymer and an iodinated boron dipyrromethene photosensitizer (BDPI) with high singlet oxygen yield to form nanoparticles (PBDPI-TPP), which could realize mitochondria-targeting and improve the NIR imaging-guided PDT. The as-prepared mitochondria-targeting nanoplatform could show effective subcellular localization and bring about significant irreversible mitochondrial injury for enhanced PDT. Both in vitro and in vivo experiments revealed that the mitochondria-targeting PDT system could achieve a remarkable therapeutic effect, indicating that it is a promising nanoplatform for NIR imaging-guided PDT in cancer therapeutics.

Fine-tuning the electronic structure of heavy-atom-free BODIPY photosensitizers for fluorescence imaging and mitochondria-targeted photodynamic therapy.

Theranostics that combines both diagnosis and therapy into a single platform has recently emerged as a promising biomedical approach for cancer treatment; however, the development of efficient theranostic agents with excellent optical properties remains a challenge. Here, we report novel mitochondria-targeting BODIPY photosensitizers (R-BODs) that possess considerable singlet oxygen generation capabilities and good fluorescence properties for imaging-guided photodynamic therapy (PDT). The incorporation of sulfur atoms into the π-conjugated skeleton of BODIPY along with the introduction of different functional groups at the meso-position of the BODIPY core is essential for tuning the photophysical and photosensitizing properties. Notably, the MeOPh-substituted thiophene-fused BODIPY (MeO-BOD, R = p-methoxyphenyl) displayed the highest singlet oxygen generation capability (ΦΔ ≈ 0.85 in air-saturated acetonitrile) and a moderate fluorescence quantum yield (Φf = 17.11). Furthermore, MeO-BOD showed good biocompatibility, low dark toxicity and superior fluorescence imaging properties in living cells. More importantly, the PDT efficacy of mitochondria-specific anchoring of MeO-BOD was remarkably amplified with an extremely low half-maximal inhibitory concentration (IC50) value of 95 nM. We believe that the incorporation of an electron-donating group at the meso-position of the thiophene-fused BODIPY platform may be an effective approach for developing theranostic agents for precision cancer therapy.

A two-photon AIE fluorophore as a photosensitizer for highly efficient mitochondria-targeted photodynamic therapy

Nowadays, photodynamic therapy (PDT) has become an effective method for cancer therapy.

New strategy for precise cancer therapy: tumor-specific delivery of mitochondria-targeting photodynamic therapy agents and in situ O2-generation in hypoxic tumors.

Besides tumor hypoxia and limitation of superficial lesions, the short lifetime of photoinduced reactive oxygen species (ROS) is another factor repressing photodynamic therapy (PDT) efficacy. To overcome these problems, this study developed newly designed mitochondria-specific, H2O2-activatable, and O2-producing nanoparticles to achieve highly selective and efficient PDT and self-sufficiency of O2 in hypoxic tumors. The newly designed nanoparticles (BDPP NPs) are composed of a mitochondria-targeting photosensitizer and catalase in the aqueous core and a black hole quencher and fluorescent tracker in the polymeric shell, and modified with the tumor-targeting cyclic pentapeptide c(RGDfK). Once taken up by αvβ3 integrin-rich tumor cells, intracellular H2O2 easily penetrated the lipophilic shells into the aqueous cores of BDPP NPs, and it was catalyzed by catalase to quickly generate O2 gas, causing the rupture of the NPs to release the photosensitizer. Therefore in vivo tumor cell mitochondria targeting by BDPP can be realized together with the favorable hypoxia relief. In vitro and in vivo experiments demonstrate that the therapeutic efficiency was significantly improved by the mitochondria-specific feature and H2O2-controllable generation of 1O2. More importantly, BDPP NPs continuously generate O2 in the PDT process, which can be helpful for resolving the overconsumption of oxygen in PDT and enhancing the PDT efficiency of cancer chemotherapy. We anticipate that this work may provide new insight into the design of smart PDT systems to achieve highly selective in vivo PDT via targeting subcellular organelles and realize oxygen therapy in O2-deprived tumors.

A redox-activatable biopolymer-based micelle for sequentially enhanced mitochondria-targeted photodynamic therapy and hypoxia-dependent chemotherapy.

A tumor redox-activatable micellar nanoplatform based on the naturally occurring biomacromolecule hyaluronic acid (HA) was developed for complementary photodynamic/chemotherapy against CD44-positive tumors. Here HA was first conjugated with l-carnitine (Lc)-modified zinc phthalocyanine (ZnPc) via disulfide linkage and then co-assembled with tirapazamine (TPZ) to afford the physiologically stable micellar nanostructure. The mitochondria-targeted photodynamic activity of ZnPc-Lc could efficiently activate the mitochondrial apoptosis cascade and deplete the oxygen in the tumor intracellular environment to amplify the hypoxia-dependent cytotoxic effect of TPZ.

Cyclometalated iridium(iii) complex nanoparticles for mitochondria-targeted photodynamic therapy.

Cyclometalated Ir(iii) complexes, with a long triplet state lifetime and good photophysical properties, are good candidates for simultaneous imaging and photodynamic therapy (PDT). Herein, we synthesize a cyclometalated Ir(iii) complex, Ir(tiq)2ppy, whose triplet excited state lifetime is 2.9 μs and singlet oxygen generation quantum yield is approximately 100% (compared to tetraphenylporphyrin). Ir(tiq)2ppy nanoparticles (Ir(tiq)2ppy NPs) are prepared to achieve water solubility and mitochondria-targeting ability by co-precipitating with polystyrene grafted with carboxyl-terminated poly(ethylene glycol) (PS-PEG). Ir(tiq)2ppy NPs have higher PDT efficiency than Ir(tiq)2ppy at concentrations as low as 1.6 μg mL-1 for MCF-7 breast cancer cells under white light irradiation at quite low light intensity (5 mW cm-2). Besides, it is worth noting that the emission quenching of Ir(tiq)2ppy in aqueous solution has been conquered by using Ir(tiq)2ppy NPs, thus the distribution of the therapeutic agents in mitochondria can be tracked by confocal laser scanning microscopy (CLSM). The mechanism of killing cancer cells under irradiation is investigated, and the results indicate that cell death is caused by mitochondria-mediated apoptosis, which is induced by the ROS generated under light irradiation.

Mitochondria-targeted porphyrin-based photosensitizers containing triphenylphosphonium cations showing efficient in vitro photodynamic therapy effects

Subcellular organelle-targeted photosensitizers have recently reported to be effective photodynamic therapy (PDT) agents. In this work, three porphyrin-derived photosensitizers, containing one, two or four triphenylphosphonium targeting groups, were synthesized and characterized by NMR, HRMS, UV-vis and fluorescence spectroscopy. These photosensitizers showed similar photophysical properties to classical porphyrins and exhibited excellent [Formula: see text]O[Formula: see text] quantum yields in acetonitrile. Subcellular colocalization indicated that all three photosensitizers specifically stain the mitochondria of HeLa cells. Photosensitizer mito-dp, containing two triphenylphosphonium cations was found to be the most uptaken by cells and exhibited the best PDT effect with an effective phototoxicity (IC[Formula: see text] (light) [Formula: see text] 12.4 nM), suggestive of a higher practicable potential of mitochondria-targeted PDT agents in cancer therapy.

Defeating relapsed and refractory malignancies through a nano-enabled mitochondria-mediated respiratory inhibition and damage pathway

Hypoxia, which frequently reduces the sensitivity to many therapeutic interventions, including chemotherapy, radiotherapy and phototherapy, has been acknowledged as an important reason for poor prognosis. Burgeoning evidences have proved that the tumor hypoxia microenvironment can reduce the therapeutic effect on tumor through inhibiting the drug efficacy, limiting immune cell infiltration of tumors and accelerating tumor recurrence and metastasis. However, the relationship between oxygen supply and the proliferation of cancer cells is still ambiguous and argued. Different from the current commonly used oxygen supply strategies, this study concentrated on the reduction of endogenous oxygen consumption. Specifically, a novel photosensitizers (IR780) and metformin are packaged in PEG-PCL liposomes. Once such nanoparticles accumulated in tumor tissues, the tumor foci were irradiated through 808 nm laser, generated ROS to further release metformin and IR780. Metformin can directly inhibit the activity of complex Ⅰ in the mitochondrial electron transport chain, thus performed a potent inhibitor of cell respiration. After overcoming tumor hypoxia, the combination of mitochondria-targeted photodynamic therapy (PDT) and photothermic therapy (PTT) via IR780 may achieve superior synergistically therapeutic efficacy. Benefit from excellent characteristics of IR780, such synergistic PDT PTT with the inhibition of mitochondrial respiration can be monitored through near-infrared/photoacoustic dual-modal imaging. Such a conception of reducing endogenous oxygen consumption may offer a novel way to solve the important puzzles of hypoxia-induced tumor resistance to therapeutic interventions, not limited to phototherapy.

Multifunctional Two-Photon AIE Luminogens for Highly Mitochondria-Specific Bioimaging and Efficient Photodynamic Therapy.

In recent years, photodynamic therapy (PDT) has drawn much attention as a noninvasive and safe cancer therapy method due to its fine controllability, good selectivity, low systemic toxicity, and minimal drug resistance in contrast to the conventional methods (for example, chemotherapy, radiotherapy, and surgery). However, some drawbacks still remain for the current organic photosensitizers such as low singlet oxygen (1O2) quantum yield, poor photostability, inability of absorption in the near-infrared (NIR) region, short excitation wavelength, and limited action radius of singlet oxygen, which will strongly limit the PDT treatment efficiency. As a consequence, the development of efficient photosensitizers with high singlet oxygen quantum yield, strong fluorescent emission in the aggregated state, excellent photostability, NIR excitation wavelength ranging in the biological transparency window, and highly specific targeting to mitochondria is still in great demand for the enhancement of PDT treatment efficiency. In this study, two new two-photon AIEgens TPPM and TTPM based on a rigid D-π-A skeleton have been designed and synthesized. Both AIEgens TPPM and TTPM show strong aggregation-induced emission (AIE) with the emission enhancement up to 290-folds, large two-photon absorption with the two-photon absorption cross section up to 477 MG, and highly specific targeting to mitochondria in living cells with good biocompatibility. They can serve as two-photon bioprobes for the cell and deep tissue bioimaging with a penetration depth up to 150 μm. Furthermore, high 1O2 generation efficiency with high 1O2 quantum yield under white light irradiation has been found for both TPPM and TTPM and high PDT efficiency to HeLa cells under white light irradiation has also been proven. To the best of our knowledge, AIEgens in this work constitute one of the strongest emission enhancements and one of the highest 1O2 generation efficiencies in the reported organic AIEgens so far. The great AIE feature, large two-photon absorption, high specificity to mitochondria in living cells, and high PDT efficiency to living cells as well as excellent photostability and biocompatibility of these novel AIEgens TPPM and TTPM reveal great potential in clinical applications of two-photon cell and tissue bioimaging and image-guided and mitochondria-targeted photodynamic cancer therapy.

A pH-Activatable nanoparticle for dual-stage precisely mitochondria-targeted photodynamic anticancer therapy

Mitochondria-targeted photodynamic therapy (PDT) has emerged as one of the most efficient antitumor strategies. However, the therapeutic outcome of mitochondria-targeted PDT nanocarriers has been hampered by its poor capability of endosome escape and always-ON mode which induces normal tissue damage. To tackle these limitations, herein a novel pH-activatable nanoparticle is developed with dual-stage targeting capacity of early endosome and mitochondria for exponential activation of fluorescent signals and photodynamic efficacy. This nanoparticle is composed of pH-responsive mPEG-b-PDPA-Cy7.5 fluorescent copolymer and mitochondria-targeted photosensitizer (TPPa). The TPPa-encapsulated nanoparticles (M-TPPa) exhibit 111- and 151-fold enhancement in fluorescent signal and singlet oxygen generation (SOG) on encounting acidic pH environment, respectively. The M-TPPa can be quickly endocytosed by cancer cells and immediately dissociate at acidic early endosome to activate fluorescent signals and photoactivity. Subsequently, the activated TPPa quickly translocates from early endosome to mitochondria. Under laser irradiation, singlet oxygen could be generated in mitochondria, inducing intrinsic apoptosis in human HO8910 ovarian cancer cells. M-TPPa also exhibits high tumor imaging contrast and remarkable inhibition on tumor progression without obvious toxicity in HO8910-tumor bearing mice. Therefore, the rationally designed nanoparticles, with precise dual-targeting of distinct organelles and theranostic signal amplification, provides a promising strategy for efficient cancer treatment.

A mitochondria-targeted iridium(iii)-based photoacid generator induces dual-mode photodynamic damage within cancer cells.

A mitochondria-targeted photodynamic therapy (PDT) agent was designed and synthesized. Upon light irradiation, it can produce photoacid and its photolysis products can further sensitize 1O2 generation, causing dual-mode (oxygen-independent and oxygen-dependent) photodynamic damage in mitochondria and killing cancer cells effectively even under hypoxic conditions.

A cyanine-derivative photosensitizer with enhanced photostability for mitochondria-targeted photodynamic therapy.

A cyanine-derivative photosensitizer, CYBF2, was synthesized for photodynamic therapy of cancer. The photosensitizer can be activated by red-light with enhanced photostability compared to traditional cyanine photosensitizers. CYBF2 was able to generate singlet oxygen inside the cell mitochondria, which efficiently resulted in apoptosis of cancer cells.

Pyriplatin-Boron-Dipyrromethene Conjugates for Imaging and Mitochondria-Targeted Photodynamic Therapy.

Monofunctional pyriplatin analogues cis-[Pt(NH3)2(L)Cl](NO3) (1-3) having boron-dipyrromethene (BODIPY) pendants (L) with 1,3,5,7-tetramethyl-8-(4-pyridyl)-4,4'-difluoroboradiazaindacene moieties were designed and synthesized, and their photocytotoxic properties were studied. The Pt-BODIPY conjugates displayed an absorption band within 505-550 nm and a green emissive band near 535 nm in 1% DMSO/DMEM (Dulbecco's modified Eagle's medium) buffer. Complex cis-[Pt(NH3)2(4-Me-py)Cl](NO3) (4) was used as a control for determining the structural aspects by X-ray crystallography. The mono- and diiodinated BODIPY complexes 2 and 3 showed generation of singlet oxygen on light activation as evidenced from the 1,3-diphenylisobenzofuran (DPBF) titration experiments. The cytotoxicity of the BODIPY complexes was tested against A549 (human lung cancer), MCF-7 (human breast cancer), and HaCaT (human skin keratinocyte) cells in dark and visible light (400-700 nm, 10 J cm-2). While complexes 2 and 3 showed excellent photocytotoxicity (IC50 ≈ 0.05 μM), they remained essentially nontoxic in the dark (IC50 > 100 μM). The emissive bands of 1 and 2 were used for cellular imaging by confocal microscopy study, which showed their mitochondrial localization. This was further supported by platinum estimation from isolated mitochondria and mitochondrial depolarization through a JC-1 assay. The photomediated apoptotic cell death was evidenced from flow cytometric assays, annexin-V/FITC-PI (fluorescein isothiocyanate-propidium iodide) and cell cycle arrest in sub-G1 and G2/M phases. The complexes bind to 9-ethylguanine as a model nucleobase to form monoadducts. A mechanistic study on DNA photocleavage activity using pUC19 DNA showed singlet oxygen as the reactive oxygen species (ROS). The combination of photodynamic therapy with DNA cross-linking property enhanced the anticancer potential of the monofunctional BODIPY-conjugates of pyriplatins.

Mitochondria and plasma membrane dual-targeted chimeric peptide for single-agent synergistic photodynamic therapy

Mitochondria and cell membrane play important roles in maintaining cellular activity and stability. Here, a single-agent self-delivery chimeric peptide based nanoparticle (designated as M-ChiP) was developed for mitochondria and plasma membrane dual-targeted photodynamic tumor therapy. Without additional carrier, M-ChiP possessed high drug loading efficacy as well as the excellent ability of producing reactive oxygen species (ROS). Moreover, the dual-targeting property facilitated the effective subcellular localization of photosensitizer protoporphyrin IX (PpIX) to generate ROS in situ for enhanced photodynamic therapy (PDT). Notably, plasma membrane-targeted PDT would enhance the membrane permeability to improve the cellular delivery of M-ChiP, and even directly disrupt the cell membrane to induce cell necrosis. Additionally, mitochondria-targeted PDT would decrease mitochondrial membrane potential and significantly promote the cell apoptosis. Both in vitro and in vivo investigations indicated that this combinatorial PDT in mitochondria and plasma membrane could achieve the therapeutic effect maximization with reduced side effects. The single-agent self-delivery system with dual-targeting strategy was demonstrated to be a promising nanoplatform for synergistic tumor therapy.

A water soluble donor-acceptor-donor conjugated oligomer as a photosensitizer for mitochondria-targeted photodynamic therapy.

We designed a water soluble benzotriazole-cored donor-acceptor-donor molecule bearing four triphenylphosphonium moieties for mitochondria targeting. The organic molecule showed strong singlet oxygen sensitizing capability (ΦΔ 0.64), minimal dark cytotoxicity and high photocytotoxicity. The molecule is efficient in photodynamic killing of tumour cells under normal and hypoxia conditions using a very low light flux, and has potential in near-infrared two-photon imaging and photodynamic therapy.

Mitochondria-Targeted Photodynamic Therapy with a Galactodendritic Chlorin to Enhance Cell Death in Resistant Bladder Cancer Cells.

Here, we report the rational design of a new third-generation photosensitizer (PS), a chlorin conjugated with galactodendritic units, ChlGal8, to improve the effectiveness of bladder cancer treatment. ChlGal8 shows better photochemical and photophysical properties than a recently reported homologous porphyrin, PorGal8. In addition to inheriting excellent photostability, the ability to generate singlet oxygen, and the ability to interact with the proteins galectin-1 and human serum albumin (HSA), ChlGal8 exhibits high absorption in the red region of the electromagnetic spectrum. In vitro studies of anticancer activity of ChlGal8 revealed that once this PS is taken up by UM-UC-3 bladder cancer cells, it induces high cytotoxicity after a single dose of light irradiation. In HT-1376 bladder cancer cells resistant to therapy, a second light irradiation treatment enhanced in vitro and in vivo photodynamic efficacy. The enhanced phototoxicity in HT-1376 cancer cells seems to be due to the ability of ChlGal8 to accumulate in the mitochondria, via facilitative glucose transporter 1 (GLUT1), in the period between single and repeated irradiation. A photodynamic therapy (PDT) regimen using an extra dose of light irradiation and ChlGal8 as PS represents a promising strategy in treating resistant cancers in a clinical setting.

A Mitochondria-Targeted Photosensitizer Showing Improved Photodynamic Therapy Effects Under Hypoxia.

Organelle-targeted photosensitizers have been reported to be effective photodynamic therapy (PDT) agents. In this work, we designed and synthesized two iridium(III) complexes that specifically stain the mitochondria and lysosomes of living cells, respectively. Both complexes exhibited long-lived phosphorescence, which is sensitive to oxygen quenching. The photocytotoxicity of the complexes was evaluated under normoxic and hypoxic conditions. The results showed that HeLa cells treated with the mitochondria-targeted complex maintained a slower respiration rate, leading to a higher intracellular oxygen level under hypoxia. As a result, this complex exhibited an improved PDT effect compared to the lysosome-targeted complex, especially under hypoxia conditions, suggestive of a higher practicable potential of mitochondria-targeted PDT agents in cancer therapy.