A mitochondria-targeted ratiometric fluorescent sensor based on naphthalimide derivative-functionalized silica-based nanodots for imaging formaldehyde in living cells and zebrafish

A mitochondria-targeted ratiometric fluorescent sensor (Mito-Si-NA) for formaldehyde (FA) has been constructed by functionalizing silica-based nanodots (silica-based ND). As the fluorescence reference and carrier, the silica-based ND conjugate with small molecule probe for FA via covalent. Further modifying with mitochondria targeting moiety enables the sensor to specifically target mitochondria. In the presence of FA, the emission of silica-based ND remain constant to act as an internal reference (445 nm) while the response signal of small molecule probe was gradually enhanced (545 nm). This sensor exhibits excellent selectivity towards FA with great changes of fluorescence intensity ratio values (I545/I445). The FA ratiometric fluorescence imaging in mitochondria was achieved successfully. In addition, the sensor was also successfully used for imaging FA in zebrafish. The good performance of Mito-Si-NA for FA bioimaging confirms that Mito-Si-NA is an appealing imaging tool to monitor FA in mitochondria and shows great potential to study the functions of FA on mitochondria.

A dual-lock-controlled mitochondria-targeted ratiometric fluorescence probe for simultaneous detection of atherosclerosis-related HClO and viscosity

Precise detection of inflammatory microenvironment-related viscosity and hypochlorous acid (HClO) contributes to illuminating the pathogenesis and further diagnosing of atherosclerosis (AS). Herein, a dual-lock-controlled mitochondria-targeted fluorescence probe (NS) for simultaneous imaging of HClO and viscosity in AS-related foam cells is presented. NS performs linear increase in green-fluorescence along with increased viscosity (excited at 425 nm), permitting "off-on" fluorescence imaging of viscosity. Meanwhile, upon HClO activation, NS exhibits red-shifted and enhanced fluorescence in orange, thus leading to ratiometric fluorescence quantification of HClO (excited at 465 nm). Such dual-lock-controlled effect makes NS realize simultaneous imaging of viscosity and HClO with high sensitivity and selectivity via "off-on" and ratiometric fluorescence readouts, respectively. Besides, endowed with mitochondria-targeting capacity, NS achieves in situ imaging of mitochondria viscosity and HClO in living RAW264.7 cells. Importantly, for the first time, NS realizes simultaneous imaging of mitochondria viscosity and HClO in macrophage-derived foam cells, revealing the close association between HClO level and viscosity change in mitochondria during foaming translation of macrophages in atherogenesis. This work not only provides a novel strategy and tool to image organelle-located viscosity and HClO in living systems, but also holds great potential in early diagnosis of AS.

A long-wavelength mitochondria-targeted fluorescent probe for imaging of peroxynitrite during dexamethasone treatment

Peroxynitrite (ONOO^-), as a strong oxidizing reactive nitrogen substance (RNS), is generated endogenously by cells. Its visualization research is crucial to understand relevant disease processes. Herein, we reported a long-wavelength mitochondria-targeted fluorescence "turn on" probe TL. The probe TL could react with ONOO^- by using 4-(Bromomethyl)benzeneboronic as a reactive site, which exhibited outstanding characteristics for detection of ONOO^-, thus improving response time (about 50 s), sensitivity (DL, 10.1 nM), and emission wavelength (667 nm). Besides, TL displayed well mitochondria targeting and biological visualizing of exogenous and endogenous ONOO^- in biological systems. Finally, TL was used to monitor high concentration of dexamethasone-induced an up-regulation of ONOO^-. This indicated that TL has excellent potential to study the fluctuation of ONOO^- in the physiological and pathological system.

A mitochondria-targeted fluorescent probe for imaging of endogenous carbon monoxide in living cells

Carbon monoxide (CO), a vital gasotransmitter, plays critical functions in many physiological processes. Mitochondrial CO is closely related to mitochondrial respiration, thus the detection and imaging of mitochondrial CO in living cells is very important and has attracted much attention recently. In this paper, we developed a hemicyanine-based off-on fluorescent probe, CO-H1, which was used for monitoring endogenous mitochondrial CO levels in living cells. After reacted with CO in the presence of PdCl₂, the fluorescence of CO-H1 was enhanced notably, accompanied by a significant red shift of absorption. CO-H1 exhibits low cytotoxicity, high sensitivity (detection limit of 0.048 μM), and good selectivity for CO. When incubated with living cells, probe CO-H1 mainly entered the mitochondria. CO-H1 was successfully applied to imaging the exogenous/endogenous mitochondrial CO in living cells, suggesting its potential application for further studying the biological functions of mitochondrial CO in living cells.

Investigation of mitochondrial targeting ability of sydnones and sydnonimines and mitochondria-targeted delivery of celecoxib

Mitochondria are considered to be a promising target in cancer diagnosis and therapeutics. Recently, sydnone and sydnonimine, as mesoionic bioorthogonal reagents, have been used in cell labeling and drug delivery. Here we investigated the mitochondrial targeting ability of sydnones and sydnonimines for the first time. Experimental results show that sydnone and sydnonimine themselves have high mitochondrial distribution. However, the introduction of a phenyl group into the C₄ position of sydnone dramatically decreases the mitochondrial affinity. In addition, we took advantage of mitochondrial targeting ability and click-and-release reaction of sydnonimine to evaluate anticancer activities of in-mitochondria delivery of celecoxib against HeLa and HepG2 cells, indicating that celecoxib-induced cancer cell death may not involve mitochondria-related pathway.

A mitochondria-targeted near-infrared fluorescent probe for detection and imaging of HSO3- in living cells

Sulfur dioxide, an essential gas signaling molecule mainly produced in mitochondria, plays important roles in many physiological and pathological processes. Herein, a near-infrared fluorescent probe, A1, with good mitochondria targeting ability was developed for colorimetric and fluorescence detection of HSO₃^-. Probe A1 has a conjugated cyanine structure that can selectively react with HSO₃^- through the nucleophilic addition. The reaction with HSO₃^- destroys the conjugated structure of probe A1, resulting in fluorescence quenching, and accompaniedby color change of probe A1 solution from purple-red to colorless. Probe A1 showed high selectivity and good sensitivity to HSO₃^- in PBS. And the limit of detection was calculated to be 1.28 and 0.037 μM for colorimetry and fluorescence spectrophotometry respectively. In addition, probe A1 mainly entered the mitochondria in living cells, and was successfully used for imaging the exogenous/endogenous HSO₃^- in cells. These results suggest the potential applications of probe A1 in biological systems.

Mitochondria-targeted cyclometalated iridium (III) complex for H(2)S-responsive intracellular redox regulation as potent photo-oxidation anticancer agent

Owing to the safety and low toxicity, photodynamic therapy (PDT) for cancer treatment has received extensive attention. However, the excess H₂S in cancer cells reduces the PDT efficiency, because H₂S indirectly depletes the reactive oxygen species (ROS). To improve anticancer efficiency, a mitochondria-targeted iridium(III) complex Ir-MMB has been developed as H₂S consumer and photo-oxidation anticancer agent. On the one hand, complex Ir-MMB can consume H₂S with sensitive phosphorescence turn-on, which has been successfully applied to exogenous and endogenous H₂S response imaging in living cells. On the other hand, Ir-MMB can enhance its anticancer activity and cause photo-oxidation damage via catalyzing the oxidation of reduced form of nicotinamide-adenine dinucleotide (NADH) to NAD⁺ and producing H₂O₂ under light, and ultimately results in cell apoptosis through mitochondrial depolarization and ROS production.

Mitochondria-targeted nanozymes eliminate oxidative damage in retinal neovascularization disease

Retinal neovascularization is typically accompanied by hypoxia-induced oxidative injury in the vascular system. This study developed an ultrasmall (6-8 nm) platinum (Pt) nanozyme loaded mitochondria-targeted liposome (Pt@MitoLipo) to alleviate hypoxia and eliminate excess reactive oxygen species (ROS) for effective retinal neovascularization disease therapy. Pt nanozymes possess superoxide dismutase (SOD) and catalase (CAT) cascade enzyme-like activities, which convert cytotoxic O₂^•- and H₂O₂ into nontoxic H₂O and O₂. Triphenylphosphonium (TPP)-conjugated liposomes were coated on the surface of Pt nanozymes to increase their biocompatibility and help them penetrate the cell membrane, escape from the lysosomal barrier, and target mitochondria, thus achieving precise scavenging of mitochondrial O₂^•- and relief from hypoxia. Using an oxygen-induced retinopathy (OIR) mouse model, we demonstrated that Pt@MitoLipo nanozymes significantly suppressed hypoxia-induced abnormal neovascularization and facilitated avascular normalization of the retina in vivo without any noticeable toxicity. This study provides a promising way to break through cellular barriers and target scavenging mitochondrial O₂^•- and illustrates the potential of ROS-scavenging and hypoxia relief in retinal neovascularization disease therapy.

A novel heptamethine cyanine photosensitizer for FRET-amplified photodynamic therapy and two-photon imaging in A-549 cells

In this study, a new cyanine-based photosensitizer Cy-N-Rh was developed for photodynamic therapy. Based on fluorescence resonance energy transfer (FRET) mechanism, utilizing the absorption of the donor rhodamine (Rh), the acceptor heptamethine cyanine unit (Cy) was indirectly excited to produce singlet oxygen (¹O₂). The efficiency of energy transfer from the donor Rh to the acceptor Cy was 78.5%. Meanwhile, the singlet oxygen yield of Cy-N-Rh (Φ_Δ = 12.00%) was much higher than that of the acceptor Cy (Φ_Δ = 4.35%) without FRET. Moreover, the dual cation gave Cy-N-Rh with excellent mitochondria-targeting ability with Pearson's correlation coefficients of 0.90 and 0.91, respectively. In the MTT test, Cy-N-Rh had low dark cytotoxicity with cell survival rate above 90% and high photo cytotoxicity with cell survival rate below 40%. The cell apoptosis assay also demonstrated the role of the photosensitizer Cy-N-R visually. More importantly, Cy-N-Rh fulfilled two-photon excitation fluorescence imaging under the 800 nm femtosecond laser. All results indicate that this design strategy provides a new method for the development of higher-level cyanine photosensitizers.

Enhancement of antitumor immunotherapy using mitochondria-targeted cancer cell membrane-biomimetic MOF-mediated sonodynamic therapy and checkpoint blockade immunotherapy

Immunotherapeutic interventions represent a promising approach to treating cancer, with strategies such as immune checkpoint blockade (ICB), immunogenic sonodynamic therapy (SDT), and immune adjuvant T cell delivery having exhibited clinical promise. In this report, we describe the use of cancer cell membrane-coated triphenylphosphonium (TPP) decorated nano-metal-organic framework (nMOF) constructs [Zr-TCPP(TPP)/R837@M] that were used to generate homologous, mitochondria-targeted platforms with a high rate of sonosensitizer loading. This construct was utilized to simultaneously promote tumor antigen presentation via enhancing SDT while synergistically promoting dendritic cell (DC) maturation through the delivery of the Toll-like receptor agonist R837. In vitro, these functionalized nMOFs were readily internalized by homologous tumor cells in which they were efficiently targeted to the mitochondria, promoting DC activation through the induction of immunogenic cell death (ICD) following ultrasound exposure. Moreover, this nanoplatform was able to achieve in vivo synergy with anti-CTLA-4 ICB to reverse immunosuppression tumor microenvironment (TME), thus achieving more robust antitumor efficacy capable of suppressing metastatic disease progression and facilitating the development of durable antitumor memory responses. Together, these results highlight a promising approach to achieving enhanced SDT activity while overcoming an immunosuppressive TME, thereby achieving more robust antitumor immunity.

AIPE-Active Ir(III) complexes with tuneable photophysical properties and application in mitochondria-targeted dual-mode photodynamic therapy

Aggregation-induced phosphorescence emission (AIPE) materials based on transition metal Ir(III) complexes have significant advantages in bioimaging and photodynamic therapy (PDT) due to the long lifetime, the reduced photobleaching and the good reactive oxygen species (ROS) generation. Herein, four cationic Ir(III) complexes (Ir1-Ir4) have been synthesized and studied. Tunable phosphorescence from green to red with the excellent properties of AIPE and long lifetimes can be achieved by varying the substituents. Moreover, these phosphorescence Ir(III) complexes exhibited dual-mode PDT potential (type I and type II). Complex Ir4 showed great prospect in bioimaging and PDT with the large Stokes shift (259 nm), the long lifetime (9.85 μs) and the high ROS yield (0.73). Confocal microscopy demonstrated that Ir4 accumulated in the mitochondria selectively and possessed remarkable photostability (reduced photobleaching up to 600 s). The results indicate that Ir4 may be used in dual-mode PDT guided by mitochondria-targeted imaging. This work provides an in-depth understanding of the relationship between structure and photophysical properties and facilitates the study in PDT applications.

A multimodal fluorescent probe for portable colorimetric detection of pH and it's application in mitochondrial bioimaging

Mitochondria, as vital energy supplying organelles, play important roles in cellular metabolism, which are closely related with mitochondrial pH (∼8.0). In this work, a novel multimodal fluorescent probe was employed for ratiometric and colorimetric detection of pH. The probe is designed to work by controlling benzothiazole phenol-hemicyanine system as the interaction site and hemicyanine connected by conjugate bonds as the mitochondrial targeting, which also could make the fluorescence of probe red-shifted. This system results in a perfect ratiometric fluorescent response, whose emission changed from red to blue under pH 2.0-10.0, having a broad linear range (pH = 3.0-10.0). And the marked colour change (light yellow to deep purple via naked eye under pH 2.0-11.0) could be used to construct the test strip colorimetry and smartphone APP detection method, realizing the fast, portable, and accurate detection of pH in vitro and environment. Besides, the probe owns the characteristics of easy loading, high selectivity and staining ability of mitochondria, and low cytotoxicity, thereby allowing imaging of pH values and real-time monitor the subcellular mitochondria pH changes caused by drugs in living cells. It thus could be used to monitor the organ-specific dynamics related to transitions between pathological and physiological states.

Mitochondria-targeted phosphorescent cyclometalated iridium(III) complex for bioimaging of H2S

The selective visualization of H₂S in mitochondria is still a challenge, but it correlates closely with mitochondrial damage and some related diseases. In this work, a cyclometalated iridium complex Ir-DNB, [Ir(ppy)₂(N^N)](PF₆) (ppy = 2-phenylpyridine, N^N = (4'-methyl-[2,2'-bipyridin]-4-yl)methyl 2-((2,4-dinitrophenyl) thio)benzoate) has been explored for the detection of mitochondrial H₂S. Adding H₂S to a solution of complex Ir-DNB results in a clearly luminescence enhancement, and displays high selectivity and sensitivity. Moreover, this complex displays negligible toxicity and good mitochondrial localization to HeLa cells, and has also been successfully used for endogenous and exogenous H₂S imaging in vitro and in vivo.

Multifunctional AIE iridium (III) photosensitizer nanoparticles for two-photon-activated imaging and mitochondria targeting photodynamic therapy

Developing novel photosensitizers for deep tissue imaging and efficient photodynamic therapy (PDT) remains a challenge because of the poor water solubility, low reactive oxygen species (ROS) generation efficiency, serve dark cytotoxicity, and weak absorption in the NIR region of conventional photosensitizers. Herein, cyclometalated iridium (III) complexes (Ir) with aggregation-induced emission (AIE) feature, high photoinduced ROS generation efficiency, two-photon excitation, and mitochondria-targeting capability were designed and further encapsulated into biocompatible nanoparticles (NPs). The Ir-NPs can be used to disturb redox homeostasis in vitro, result in mitochondrial dysfunction and cell apoptosis. Importantly, in vivo experiments demonstrated that the Ir-NPs presented obviously tumor-targeting ability, excellent antitumor effect, and low systematic dark-toxicity. Moreover, the Ir-NPs could serve as a two-photon imaging agent for deep tissue bioimaging with a penetration depth of up to 300 μm. This work presents a promising strategy for designing a clinical application of multifunctional Ir-NPs toward bioimaging and PDT.

Mitochondria-targeted and ultrasound-responsive nanoparticles for oxygen and nitric oxide codelivery to reverse immunosuppression and enhance sonodynamic therapy for immune activation

Background: Sonodynamic therapy (SDT) is a promising strategy to inhibit tumor growth and activate antitumor immune responses for immunotherapy. However, the hypoxic and immunosuppressive tumor microenvironment limits its therapeutic efficacy and suppresses immune response. Methods: In this study, mitochondria-targeted and ultrasound-responsive nanoparticles were developed to co-deliver oxygen (O2) and nitric oxide (NO) to enhance SDT and immune response. This system (PIH-NO) was constructed with a human serum albumin-based NO donor (HSA-NO) to encapsulate perfluorodecalin (FDC) and the sonosensitizer (IR780). In vitro, the burst release of O2 and NO with US treatment to generate reactive oxygen species (ROS), the mitochondria targeting properties and mitochondrial dysfunction were evaluated in tumor cells. Moreover, in vivo, tumor accumulation, therapeutic efficacy, the immunosuppressive tumor microenvironment, immunogenic cell death, and immune activation after PIH-NO treatment were also studied in 4T1 tumor bearing mice. Results: PIH-NO could accumulate in the mitochondria and relive hypoxia. After US irradiation, O2 and NO displayed burst release to enhance SDT, generated strongly oxidizing peroxynitrite anions, and led to mitochondrial dysfunction. The release of NO increased blood perfusion and enhanced the accumulation of the formed nanoparticles. Owing to O2 and NO release with US, PIH-NO enhanced SDT to inhibit tumor growth and amplify immunogenic cell death in vitro and in vivo. Additionally, PIH-NO promoted the maturation of dendritic cells and increased the number of infiltrating immune cells. More importantly, PIH-NO polarized M2 macrophages into M1 phenotype and depleted myeloid-derived suppressor cells to reverse immunosuppression and enhance immune response. Conclusion: Our findings provide a simple strategy to co-deliver O2 and NO to enhance SDT and reverse immunosuppression, leading to an increase in the immune response for cancer immunotherapy.

A mitochondria-targeted thiazoleorange-based photothermal agent for enhanced photothermal therapy for tumors

Organic small molecules with near-infrared (NIR) absorption hold great promise as the phototheranostic agents for clinical translation by virtue of their inherent merits such as well-defined chemical structure, high purity and good reproducibility. Probes that happen to be based on cyanine dyes exhibit strong NIR-absorbing and efficient photothermal conversion, representing a new class of photothermal agents (PAs) for photothermal therapy (PTT), and taking into account the heat susceptibility of Mitochondria (Mito), we designed and prepared a mitochondria-targeted organic small molecule (Mito-BWQ) based on thiazole orange maternal unit that can effectively kill tumor cells through the hyperpyrexia generated in the lesions under exogenous laser irradiation. The Confocal laser scanning microscope was employed to determine the preferential targeting of Mito-BWQ to the mitochondria of MCF-7 cells and U87 cells. When subjected to 600 nm laser radiation, Mito-BWQ produced an increase in temperature in test systems and this increase was dependent on both the laser power and probe concentration. In vitro tests, cytotoxicity was observed when cells were incubated with Mito-BWQ and exposed to laser irradiation. The PTT in vivo also showed that Mito-BWQ performed remarkably in tumor inhibition. This study thus provides a vital starting point for the creation of thiazole orange-based PTT formulations and promotes further advances in the field of PAs-based anticancer research and therapy.

Hsp90 inhibitor-loaded IR780 micelles for mitochondria-targeted mild-temperature photothermal therapy in xenograft models of human breast cancer

Mitochondria-targeted mild-temperature photothermal therapy (MT-PTT) is a promising strategy that can maximize anticancer effects and reduce adverse reactions. Here, a novel photosensitizer with mitochondrial targeting based on IR780 iodide and heat shock protein 90 inhibitor (BIIB021), which can passively accumulate in MCF-7 cells and achieve effective MT-PTT effect is synthesized. The prepared PEG-IR780-BIIB021 nano-micelles possess considerable biocompatibility and biological stability, with an encapsulation efficiency of about 84% for BIIB021. They can selectively enrich in mitochondria, and release BIIB021 after NIR irradiation to reduce cell tolerance to heat, thereby reducing the mitochondrial membrane potential and rapidly affecting key intrinsic apoptotic factors (Cyt-C, Caspase-9, Bcl-2 and Bax) to achieve the effect of MT-PTT. It is believed that mitochondria-targeted MT-PTT generated by the PEG-IR780-BIIB021 nano-micelles is a promising therapeutic strategy in clinical practice.

Stimuli-responsive and cellular targeted nanoplatforms for multimodal therapy of skin cancer

Interdisciplinary applications of nanopharmaceutical sciences have tremendous potential for enhancing pharmacokinetics, efficacy and safety of cancer therapy. The limitations of conventional therapeutic platforms used for skin cancer therapy have been largely overcome by the use of nanoplatforms. This review discusses various nanotechnological approaches experimented for the treatment of skin cancer. The review describes various polymeric, lipidic and inorganic nanoplatforms for efficient therapy of skin cancer. The stimuli-responsive nanoplatforms such as pH-responsive as well as temperature-responsive platforms have also been reviewed. Different strategies for potentiating the nanoparticles application for cancer therapy such as surface engineering, conjugation with drugs, stimulus-responsive and multimodal effect have also been discussed and compared with the available conventional treatments. Although, nanopharmaceuticals face challenges such as toxicity, cost and scale-up, efforts put-in to improve these drawbacks with continuous research would deliver exciting and promising results in coming days.

X-ray induced photodynamic therapy (PDT) with a mitochondria-targeted liposome delivery system

In this study, we constructed multifunctional liposomes with preferentially mitochondria-targeted feature and gold nanoparticles-assisted synergistic photodynamic therapy. We systemically investigated the in vitro X-ray triggered PDT effect of these liposomes on HCT 116 cells including the levels of singlet oxygen, mitochondrial membrane potential, cell apoptosis/necrosis and the expression of apoptosis-related proteins. The results corroborated that synchronous action of PDT and X-ray radiation enhance the generation of cytotoxic reactive oxygen species produced from the engineered liposomes, causing mitochondrial dysfunction and increasing the levels of apoptosis.

A novel pyridinium-based fluorescent probe for ratiometric detection of peroxynitrite in mitochondria

Peroxynitrite (ONOO^-) is a primary kind of reactive oxygen species. Excessive ONOO^- can induce oxidative damage to biomolecules and further results in various diseases. So, quantitative monitoring ONOO^- with excellent selectivity and sensitivity is imperative for elucidating its role in biological processes. In this study, a novel pyridinium fluorescent ONOO^- probe (CPC) has been constructed base on ICT-modulated by combining coumarin fluorophore and diphenylphosphinate recognition group. The fluorescence response of CPC for ONOO^- is realized via the removal of diphenylphosphinate group. The probe CPC shows prominent features for detection of ONOO^- including fast response rate (within 3 min), excellent selectivity and sensitivity, distinct colorimetric (red to green), and a large emission wavelength shift (105 nm). The emission intensity ration (I₅₃₈/I₆₄₃) exhibits 153-fold enhancement along with the increasing ONOO^- and the detection limit is as low as 1.60 × 10^-8 M. These good response properties make CPC possible to quantitative detection of ONOO^- concentration. By using the strategy, the ratiometric CPC has been employed to detection of mitochondrial ONOO^- in live cell successfully.

A bond energy transfer based difunctional fluorescent sensor for Cys and bisulfite

In living cells, cysteine (Cys) and bisulfite are involved in many important physiological processes. Their unbalance in vivo would lead to multiple diseases. So, it is vital to develop difuntional sensor for Cys and bisulfite. As we known, cysteine could metabolized into bisulfite by the metabolic processes of cysteine in the animal level. Therefore, we designed and synthesized a mitochondria-targeted long-wavelength ratio fluorescence sensor Z2 for Cys and bisulfite simultaneous detection. Z2 exhibitted excellent selectivity, good anti-interference, fast response and low detection limit. The sensor exhibited obviously two channels fluorescence response for Cys and bisulfite orderly. Z2 is widely used for imaging Cys and bisulfite in MCF-7 cells, zebrafish, and mice, and successfully imaging Cys metabolism in these livings. We hope this bifunctional ratio fluorescence sensor Z2 will be a useful tool to monitor Cys and SO₂ levels in living systems.

Synthesis, photophysical and anticancer properties of mitochondria-targeted phosphorescent cyclometalated iridium(III) N-heterocyclic carbene complexes

Metal N-Heterocyclic carbene (NHC) complexes are expected to be new opportunities for the development of anticancer metallodrugs. In this work, two near-infrared (NIR) emitting iridium(III)-NHC complexes Ir1 and Ir2 have been explored as mitochondria-targeted anticancer and photodynamic agents. These complexes are more cytotoxic than cisplatin against the cancer cells screened, and display higher cytotoxicity in the presence of 450 nm and 630 nm LED light. Colocalization and quantitative studies indicated that these complexes could specially localize to mitochondria. Mechanism studies show that these complexes increase intracellular reactive oxygen species (ROS) level, reduce mitochondrial membrane potential (MMP) and induce some degree of early apoptosis. Further studies found that Ir1could induce mitophagy at dark and necrocytosis under the irradiation of 630 nm LED light. The in vitro and in vivo photoxicity studies revealed that Ir1 is a promising photodynamic therapy (PDT) agent and could significantly inhibit tumor growth.

A new "off-on" NIR fluorescence probe for determination and bio-imaging of mitochondrial hypochlorite in living cells and zebrafish

Hypochlorite anion (ClO^-) has been recognized as host defense destructing incursive bacteria and pathogens, a signal molecule inducing occurrence of apoptosis and a noxious agent when it is overproduced. It is significant to detect ClO^- in mitochondria for getting meaningful physiological and pathological information. Compared with the fluorescence probes of emission wavelength in ultraviolet or visible region, those with near-infrared (NIR) fluorescence signal are advantageous due to the deeper tissue penetrability and less photo-bleaching effect. In this work, a new "off-on" NIR ClO^--specific fluorescence probe (Mito-NClO) especially located in mitochondria was designed and synthesized by condensation of diaminomaleonitrile with a new fluorophore (Mito-NCHO). A marked "turn-on" NIR fluorescence signal was observed on account of the oxidation of the imine bond by NaClO. Moreover, in the range from 0 to 20 μM, this probe had the capability to quantitatively detect ClO^- with a detection limit as low as 90.2 nM. Additionally, the probe exerted other excellent properties, including larger stokes shift (117 nm), better aqueous solubility, high selectivity toward ClO^-, rapid response and selective mitochondrial location. Furthermore, the bio-imaging experiments clearly demonstrated that Mito-NClO facilitated the visualization of exogenous and endogenous ClO^- in living HeLa cells and zebrafish model. Therefore, we speculate that the probe Mito-NClO can be served as an ideal tool for the monitoring of ClO^- in biosystems.

Design and synthesis a mitochondria-targeted dihydronicotinamide as radioprotector

Radiation-induced damage to the mitochondrial macromolecules and electron transfer chain (ETC), causing the generation of primary and secondary reactive oxygen (ROS) species. The continuous ROS production after radiation will trigger cell oxidative stress and ROS-mediated nucleus apoptosis and autophagy signaling pathways. Scavenging radiation-induced ROS effectively can help mitochondria to maintain their physiological function and relief cells from oxidative stress. Nicotinamide is a critical endogenous antioxidant helping to neutralize ROS in vivo. In this study, we designed and synthetized a novel mitochondrial-targeted dihydronicotinamide (Mito-N) with the help of mitochondrial membrane potential to enter the mitochondria and scavenge ROS. According to experiment results, Mito-N significantly increased cell viability by 30.75% by neutralizing the accumulated ROS and resisting DNA strands breaks after irradiation. Furthermore, the mice survival rate also improved with the treatment of Mito-N, by effectively ameliorating the hematopoietic system infliction under lethal dose irradiation.

Developing glutathione-activated catechol-type diphenylpolyenes as small molecule-based and mitochondria-targeted prooxidative anticancer theranostic prodrugs

Developing concise theranostic prodrugs is highly desirable for personalized and precision cancer therapy. Herein we used the glutathione (GSH)-mediated conversion of 2,4-dinitrobenzenesulfonates to phenols to protect a catechol moiety and developed stable pro-catechol-type diphenylpolyenes as small molecule-based prooxidative anticancer theranostic prodrugs. These molecules were synthesized via a modular route allowing creation of various pro-catechol-type diphenylpolyenes. As a typical representative, PDHH demonstrated three unique advantages: (1) capable of exploiting increased levels of GSH in cancer cells to in situ release a catechol moiety followed by its in situ oxidation to o-quinone, leading to preferential redox imbalance (including generation of H₂O₂ and depletion of GSH) and final selective killing of cancer cells over normal cells, and is also superior to 5-fluorouracil and doxorubicin, the widely used chemotherapy drugs, in terms of its ability to kill preferentially human colon cancer SW620 cells (IC₅₀ = 4.3 μM) over human normal liver L02 cells (IC₅₀ = 42.3 μM) with a favourable in vitro selectivity index of 9.8; (2) permitting a turn-on fluorescent monitoring for its release, targeting mitochondria and therapeutic efficacy without the need of introducing additional fluorophores after its activation by GSH in cancer cells; (3) efficiently targeting mitochondria without the need of introducing additional mitochondria-directed groups.

New Platinum(II) agent induces bimodal death of apoptosis and autophagy against A549 cancer cell

Agents with multiple modes of tumor cell death can be effective chemotherapeutic drugs. One example of a bimodal chemotherapeutic approach is an agent that can induce both apoptosis and autophagic death. Thus far, no clinical anticancer drug has been shown to simultaneously induce both these pathways. Mono-functional platinum complexes are potent anticancer drug candidates which act through mechanisms distinct from cisplatin. Here, we describe the synthesis and characterize of two mono-functional platinum complexes containing 8-substituted quinoline derivatives as ligands. In comparison to cisplatin, n-Mon-Pt-1 exhibited a greater in vitro cytotoxicity, was more effective in resistant cells and elicited a better anticancer effect. Mechanistic experiments indicate that n-Mon-Pt-1 mainly accumulates in mitochondria, and stimulates significant TrxR inhibition, ROS release and an ER stress response, ultimately resulting in a simultaneous induction of apoptosis and autophagy. Importantly, compared to cisplatin, n-Mon-Pt-1 exhibits lower acute toxicity and better anticancer activity in a murine tumor model.

Mitochondria-targeted platinum(II) complexes induce apoptosis-dependent autophagic cell death mediated by ER-stress in A549 cancer cells

Agents with multiple modes of tumor cell death can be effective chemotherapeutic drugs. One example of a bimodal chemotherapeutic approach is an agent that can induce both apoptosis and autophagic death. Thus far, no clinical anticancer drug has been shown to simultaneously induce both these pathways. Mono-functional platinum complexes are potent anticancer drug candidates which act through mechanisms distinct from cisplatin. Here, we describe the synthesis and characterize of two mono-functional platinum complexes containing 8-substituted quinoline derivatives as ligands, [PtL₁Cl]Cl [L₁ = (Z)-1-(pyridin-2-yl)-N-(quinolin-8-ylmethylene) methanamine] (Mon-Pt-1) and [PtL₂Cl]Cl [L₂ = (Z)-2-(pyridin-2-yl)-N-(quinolin-8-ylmethylene) ethanamine] (Mon-Pt-2). In comparison to cisplatin, Mon-Pt-2 exhibited a greater in vitro cytotoxicity, was more effective in resistant cells and elicited a better anticancer effect. Mechanistic experiments indicate that Mon-Pt-2 mainly accumulates in mitochondria, and stimulates significant TrxR inhibition ROS release and an ER stress response, mediated by mitochondrial dysfunction, ultimately resulting in a simultaneous induction of apoptosis and autophagy. Importantly, compared to cisplatin, Mon-Pt-2 exhibits lower acute toxicity and better anticancer activity in a murine tumor model. To the best of our knowledge, Mon-Pt-2 is the first mono-functional platinum complex inducing pro-death autophagy and apoptosis of cancer cells.

Design of mitochondria-targeted colorimetric and ratiometric fluorescent probes for rapid detection of SO2 derivatives in living cells

Two mitochondria-targeted colorimetric and ratiometric fluorescent probes for SO₂ derivatives were constructed based on the SO₂ derivatives-triggered Michael addition reaction. The probes exhibit high specificity toward HSO₃^-/SO₃^2- by interrupting their conjugation system resulting in a large ratiometric blue shift of 46-121nm in their emission spectrum. The two well-resolved emission bands can ensure accurate detection of HSO₃^-. The detection limits were calculated to be 1.09 and 1.35μM. Importantly, probe 1 and probe 2 were successfully used to fluorescence ratiometric imaging of endogenous HSO₃^- in BT-474 cells.

A novel mitochondria-targeted near-infrared fluorescence probe for ultrafast and ratiometric detection of SO2 derivatives in live cells

A novel mitochondria-targeted ratiometric near-infrared fluorescence probe NDMBT for Sulfur dioxide (SO₂) derivatives was constructed based on the SO₂ derivatives-triggered Michael addition reaction. It displayed ultrafast response time (within 10s), large hypsochromic shift (260nm), high photostability, excellent selectivity and high sensitivity in aqueous media with a detection limit of 43nM. More importantly, it was successfully applied to imaging of the enzymatically generated SO₂ derivatives in mitochondria of live cells.

A mitochondria-targeted turn-on fluorescent probe for the detection of glutathione in living cells

A novel turn-on red fluorescent BODIPY-based probe (Probe 1) for the detection of glutathione was developed. Such a probe carries a para-dinitrophenoxy benzyl pyridinium moiety at the meso position of a BODIPY dye as self-immolative linker. Probe 1 responds selectively to glutathione with the detection limit of 109nM over other amino acids, common metal ions, reactive oxygen species, reactive nitrogen species, and reactive sulfur species. A novel electrostatic interaction to modulate the SNAr attack of glutathione was believed to play significant role for the observed selective response to glutathione. The cleavage of dinitrophenyl ether by glutathione leads to the production of para-hydroxybenzyl moiety which is able to self-immolate through an intramolecular 1,4-elimination reaction to release the fluorescent BODIPY dye. The low toxic probe has been successfully used to detect mitochondrial glutathione in living cells.

A mitochondria-targeted ratiometric two-photon fluorescent probe for biological zinc ions detection

A mitochondria-targeted ratiometric two-photon fluorescent probe (Mito-MPVQ) for biological zinc ions detection was developed based on quinolone platform. Mito-MPVQ showed large red shifts (68 nm) and selective ratiometric signal upon Zn(2+) binding. The ratio of emission intensity (I488 nm/I420 nm) increases dramatically from 0.45 to 3.79 (ca. 8-fold). NMR titration and theoretical calculation confirmed the binding of Mito-MPVQ and Zn(2+). Mito-MPVQ also exhibited large two-photon absorption cross sections (150 GM) at nearly 720 nm and insensitivity to pH within the biologically relevant pH range. Cell imaging indicated that Mito-MPVQ could efficiently located in mitochondria and monitor mitochondrial Zn(2+) under two-photon excitation with low cytotoxicity.

A mitochondria-targeted ratiometric fluorescent probe for rapid, sensitive and specific detection of biological SO2 derivatives in living cells

In this study, we report a ratiometric fluorescent probe (CZBI) for sulfur dioxide (SO2) derivatives based on the conjugate of carbazole and benzo[e]indolium, which displays colorimetric and ratiometric fluorescence dual response to HSO3(-). The probe can quantitatively detect HSO3(-) with high specificity, fast response (within 40s) as well as low detection limit (10nM). A 1,4-nucleophilic addition reaction was proposed for the sensing mechanism of this probe, which was confirmed by (1)H NMR and HR-MS spectra. Fluorescence co-localization studies demonstrated that CZBI was a specific mitochondria-targeted fluorescent probe for SO2 derivatives with excellent cell membrane permeability. Furthermore, fluorescence imaging of HeLa cells indicated that CZBI could be used for monitoring the intrinsically generated intracellular SO2 derivatives in living cells by ratiometric fluorescence imaging. Thus, CZBI has a great potential application for exploring the role played by SO2 derivatives in biology.

Mitochondria-targeted ratiometric fluorescent probe for real time monitoring of pH in living cells

Pyridinium functioned 7-hydroxy coumarin was presented as the first mitochondria-targeted ratiometric fluorescent probe CP for real time monitoring pH in living cells. Compared with commercially available mitochondrial trackers, CP possesses high specificity to mitochondria in living cells as well as good biocompatibility. Meanwhile, CP displays excellent pH sensitivity and anti-interference capability. Confocal image experiments confirm that CP can monitor mitochondrial pH changes associated with the mitochondrial acidification, cellular apoptosis and stress response efficiently in real time.

Intramitochondrial accumulation of cationic Atto520-biotin proceeds via voltage-dependent slow permeation through lipid membrane

Conjugation to penetrating cations is a general approach for intramitochondrial delivery of physiologically active compounds, supported by a high membrane potential of mitochondria having negative sign on the matrix side. By using fluorescence correlation spectroscopy, we found here that Atto520-biotin, a conjugate of a fluorescent cationic rhodamine-based dye with the membrane-impermeable vitamin biotin, accumulated in energized mitochondria in contrast to biotin-rhodamine 110. The energy-dependent uptake of Atto520-biotin by mitochondria, being slower than that of the conventional mitochondrial dye tetramethyl-rhodamine ethyl ester, was enhanced by the hydrophobic anion tetraphenylborate (TPB). Atto520-biotin also exhibited accumulation in liposomes driven by membrane potential resulting from potassium ion gradient in the presence valinomycin. The induction of electrical current across planar bilayer lipid membrane by Atto520-biotin proved the ability of the compound to permeate through lipid membrane in a cationic form. Atto520-biotin stained mitochondria in a culture of L929 cells, and the staining was enhanced in the presence of TPB. Therefore, the fluorescent Atto520 moiety can serve as a vehicle for intramitochondrial delivery of hydrophilic drugs. Of importance for biotin-streptavidin technology, binding of Atto520-biotin to streptavidin was found to cause quenching of its fluorescence similar to the case of fluorescein-4-biotin.