Characterizing OXPHOS inhibitor-mediated alleviation of hypoxia using high-throughput live cell-imaging

BACKGROUND

Hypoxia is a common feature of many solid tumors and causes radiotherapy and immunotherapy resistance. Pharmacological inhibition of oxidative phosphorylation (OXPHOS) has emerged as a therapeutic strategy to reduce hypoxia. However, the OXPHOS inhibitors tested in clinical trials caused only moderate responses in hypoxia alleviation or trials were terminated due to dose-limiting toxicities. To improve the therapeutic benefit, FDA approved OXPHOS inhibitors (e.g. atovaquone) were conjugated to triphenylphosphonium (TPP+) to preferentially target cancer cell's mitochondria. In this study, we evaluated the hypoxia reducing effects of several mitochondria-targeted OXPHOS inhibitors and compared them to non-mitochondria-targeted OXPHOS inhibitors using newly developed spheroid models for diffusion-limited hypoxia.

METHODS

B16OVA murine melanoma cells and MC38 murine colon cancer cells expressing a HIF-Responsive Element (HRE)-induced Green Fluorescent Protein (GFP) with an oxygen-dependent degradation domain (HRE-eGFP-ODD) were generated to assess diffusion-limited hypoxia dynamics in spheroids. Spheroids were treated with IACS-010759, atovaquone, metformin, tamoxifen or with mitochondria-targeted atovaquone (Mito-ATO), PEGylated mitochondria-targeted atovaquone (Mito-PEG-ATO) or mitochondria-targeted tamoxifen (MitoTam). Hypoxia dynamics were followed and quantified over time using the IncuCyte Zoom Live Cell-Imaging system.

RESULTS

Hypoxic cores developed in B16OVA.HRE and MC38.HRE spheroids within 24 h hours after seeding. Treatment with IACS-010759, metformin, atovaquone, Mito-PEG-ATO and MitoTam showed a dose-dependent reduction of hypoxia in both B16OVA.HRE and MC38.HRE spheroids. Mito-ATO only alleviated hypoxia in MC38.HRE spheroids while tamoxifen was not able to reduce hypoxia in any of the spheroid models. The mitochondria-targeted OXPHOS inhibitors demonstrated stronger anti-hypoxic effects compared to the non-mito-targeted OXPHOS inhibitors.

CONCLUSIONS

We successfully developed a high-throughput spheroid model in which hypoxia dynamics can be quantified over time. Using this model, we showed that the mitochondria-targeted OXPHOS inhibitors Mito-ATO, Mito-PEG-ATO and MitoTam reduce hypoxia in tumor cells in a dose-dependent manner, potentially sensitizing hypoxic tumor cells for radiotherapy.

Fine-tuning bromide AIE probes for Hg2+ detection in mitochondria with wash-free staining

Mercury ions (Hg2+) primarily target mitochondria in the cells. Therefore, the development of novel probes that specifically target mitochondria in the presence of Hg2+ is of immense importance. Most previously reported probes that utilize the softness of S, Te, O, and/or N atoms for Hg2+ binding often face problems such as fluorescence quenching and off-target signals. In this study, bromide-hydrocarbon pyridinium salts were designed to target the mitochondria and chelate Hg2+ via Hg-Br coordination bonds. As a prototype, four aggregation-induced emission (AIE) fluorogens, namely TPP-Br, TPP-Cl, R1, and R2, with a similar D-π-A structure but slight differences in their halogen substituents, were designed. Among them, only TPP-Br achieved the highly selective and sensitive detection of Hg2+ by triggering its AIE properties, resulting in remarkable emission enhancement (80-fold), colorimetry, and the Tyndall effect. TPP-Br exhibited high selectivity and sensitivity to Hg2+ with a detection limit of 0.35 μM, rapid response time (<10 s), and large Stokes shift of 185 nm. Their interaction modes were studied using a combination of 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy, fluorescent lifetime decay, and theoretical calculations. TPP-Br exhibited a low emission background in cells, whereas in the presence of Hg2+, mitochondria were lit up with wash-free staining. This study provides a powerful tool for accurately diagnosing mercury poisoning-related diseases in mitochondria.

A unique phenothiazine-based fluorescent probe using benzothiazolium as a reactivity regulator for the specific detection of hypochlorite in drinking water and living organisms

As a common disinfectant and an essential reactive oxygen species (ROS), hypochlorite (ClO-) plays vital roles in both water treatment and cell metabolism, but its abnormal level can cause serious harm to human health. Therefore, quantifying ClO- level in drinking water and living organisms is extremely significant. Herein, we decorated different cationic heterocycles on phenothiazine core to construct three fluorescent probes for ClO-. According to the results, only benzothiazolium moiety reasonably adjusted the electron cloud density at sulfur atom of phenothiazine core for the specific oxidation with ClO-, thus endowing the prepared probe PT-BT with a perfect selectivity for ClO-. Meanwhile, PT-BT exhibited a low detection limit (38 nM) and a fast response (within 20 s) toward ClO-. Furthermore, this probe was utilized to fabricate a ready-to-use test strip, which could quantitatively measure ClO- level in real water samples by a portable smartphone sensing platform. Notably, PT-BT targeted mitochondria efficiently, and successfully visualized endogenous ClO- in living cells and zebrafish larvae. Especially, PT-BT was able to monitor the dynamic change of ClO- level in inflammatory mice. These results strongly manifested that probe PT-BT was a promising tool for detecting ClO- in drinking water and living organisms.

"Closed-Loop" O2-Economizer Induced In Situ Therapeutic Vaccine against Hypoxic Tumors

Therapeutic tumor vaccines, which use tumor antigens to stimulate a cancer patient's immune system to eventually kill the tumor tissues, have emerged as one of the most attractive strategies in anticancer research. Especially, exploring in situ vaccines has become a potential field in cancer immunotherapy. However, due to the hypoxic tumor microenvironment, the generation of tumor antigens is always mild and not sufficient. Hence, in this study, we designed a closed-loop mitochondrial oxygen-economizer (TPCA) to induce enhanced phototherapy-driven in situ vaccines. The O2-economizer was developed by the integration of the photosensitizer CyI and the mitochondrial inhibitor atovaquone into the PAMAM dendrimer. In vitro and in vivo studies showed that TPCA could enter the mitochondria through (3-propylcarboxyl) triphenylphosphine bromide (TPP) and effectively restrict the respiration of tumor cells to reduce tumor hypoxia, thus providing continuous oxygen for enhanced iodinated cyanine dye mediated photodynamic therapy, which could further induce in situ vaccines for ablating the primary tumor directly and inhibiting the tumor metastasis and recurrence. Furthermore, the antitumor mechanism revealed that O2-economizer-based oxygen-boosted PDT elicited immunogenic cancer cell death with enhanced exposure and release of DAMPs and altered the immunosuppressive tumor microenvironment with increased recruitment of T cells in tumors, thereby inducing in situ vaccines and provoking the systematic antitumor responses against CT26 tumors. This study will provide innovative approaches for local, abscopal, and metastatic tumor treatment.

Modulation of Near-Infrared Mitochondria-Targetable fluorescent probe for H2S bioimaging through the modification of heavy atom iodine

H₂S is correlated with mitochondrial dysfunction, which results in the death of cells. Two near-infrared fluorescent probes, Mito-HS-1 and Mito-HS-2, were designed for mitochondrial H₂S imaging. Initially, the synthesis protocol of expensive IR-780-based hemicyanine (HXPI) was optimized with an appreciate yield of 80 % as compared with 14-56 % previously reported. Iodine atom was introduced to HXPI to obtain iodine-HXPI whose Stokes shift was increased to be 90 nm. On account of the rapid and fast nucleophilic attack of H₂S, HXPI-based Mito-HS-1 could be applied for the real time imaging of mitochondrial H₂S. Besides some similar optical properties with Mito-HS-1, iodine-HXPI-based Mito-HS-2 exhibited wider linear range (3-150 μM), more stable fluorescent imaging and more favorable specificity in vitro. Both Mito-HS-1 and Mito-HS-2 could be used to image exogenous H₂S in cells, with Mito-HS-2 showing fairly better signal-to-noise. Additionally, the Pearson correlation coefficient of two probes demonstrated that they could successfully monitor mitochondrial H₂S in A549 cells and Hela cells.

Screening of H2S donors with a red emission mitochondria-targetable fluorescent probe: Toward discovering a new therapeutic strategy for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by various factors such as neuroinflammation, oxidative stress, mitochondrial dysfunction, and neuronal apoptosis. Recent studies have shown that H2S supplementation reverses neuronal loss and mitigates motor deficits in PD patients through anti-inflammatory, antioxidant, improved mitochondrial function and proautophagic. Therefore, the discovery and use of H2S donors may be an exciting and intriguing strategy for the treatment of PD. Herein, we report a red emission mitochondria-targetable fluorescent probe, Rho-H2S, which can specifically and sensitively detect H2S with a limit of detection of 62.5 nM. Bioimaging experiments have shown that the probe has excellent mitochondrial targeting and good imaging capabilities for the detection of exogenous and endogenous H2S in cells. More importantly, based on the Rho-H2S probe, we first confirmed the sulforaphane (SFN) among 15 glucosinolate and isothiocyanate compounds from cruciferous vegetables with an outstanding ability to release H2S and we further proved that SFN could alleviate the symptoms of PD in vivo. All results demonstrate that Rho-H2S could be an effective tool for screening H2S donors and can contribute to the development of new therapeutic strategies for PD.

Bioimaging and detecting endogenous and exogenous cyanide in foods, living cells and mice based on a turn-on mitochondria-targeted fluorescent probe

A novel fluorescent probe, with advanced features including "turn-on" fluorescence response, high sensitivity, good compatibility, and mitochondria-targeting function, has been synthesized based on structural design for detecting and visualizing cyanide in foods and biological systems. An electron-donating triphenylamine group (TPA) was employed as the fluorescent and an electron-accepting 4-methyl-N-methyl-pyridinium iodide (Py) moiety was used as a mitochondria-targeted localization unit, which formed intramolecular charge transfer (ICT) system. The "turn-on" fluorescence response of the probe (TPA-BTD-Py, TBP) toward cyanide is attributed two reasons, one is the insertion of an electron-deficient benzothiadiazole (BTD) group into the conjugated system between TPA and Py, and the other is the inhibition of ICT induced by the nucleophilic addition of CN^-. Two active sites for reacting with CN^- were involved in TBP molecule and high response sensitivity were observed in tetrahydrofuran solvent containing 3 % H₂O. The response time could be reduced to 150 s, the linear range was 0.25-50 μM, and the limit of detection was 0.046 μM for CN^- analysis. The TBP probe was successfully applied to the detection of cyanide in food samples prepared in aqueous solution, including the sprouting potato, bitter almond, cassava, and apple seeds. Furthermore, TBP exhibited low cytotoxicity, clear mitochondria-localizing capability in HeLa cells and excellent fluorescence imaging of exogenous and endogenous CN^- in living PC12 cells. Moreover, exogenous CN^- with intraperitoneal injection in nude mice could be well monitored visually by the "turn-on" fluorescence. Therefore, the strategy based on structural design provided good prospects for optimizing fluorescent probes.

Dual-key-and-lock AIE probe for thiosulfate and Ag+ detection in mitochondria

Ag⁺ ion detection has attracted much attention due to its important role in chemical and biological processes, as well as its potential threat to the environment and human health. Herein, we firstly constructed a dual-key-and-lock sensing strategy for Ag⁺ detection based on three-component co-assembly. An aggregation-induced emission luminogen (AIEgen), namely triphenylamine-thiophene-pyridinium (abbreviated to TPA-T-Py), showed unique co-assembly capability with Ag⁺ and S₂O₃^2- in PBS buffer (pH 7.4, 0.01 M). Cell imaging further proved that mitochondria can be lit up by TPA-T-Py under the dual key stimulation, which was successfully used for Ag⁺ and S₂O₃^2- detection in vitro. In brief, we provide a promising strategy for the construction of dual-lock imaging agents with organelle-targeting ability.

Hyperbaric oxygen enhanced the chemotherapy of mitochondrial targeting molecule IR-780 in bladder cancer

BACKGROUND

Bladder cancer has a high rate of recurrence and drug resistance due to the lack of effective therapies. IR-780 iodide, a near-infrared (NIR) mitochondria-targeting fluorescent agent, has been demonstrated to achieve higher selectivity than other drugs in different tumor types and exhibited tumor-killing effects in some cancers. However, this therapeutic strategy is rarely studied in bladder cancer.

MATERIAL AND METHODS

The accumulation of IR-780 in bladder cancer was measured by NIR imaging. Human bladder cell lines (T24, 5637, and TCCSUP) were treated with IR-780 or combined IR-780 and hyperbaric oxygen (HBO). Cell viability, cell apoptosis, cellular ATP production, mitochondrial reactive oxygen species (ROS), and plasma membrane potential were detected. Mitochondrial complex I protein NDUFS1 was measured by western blot. To confirm the anti-tumor efficacy of IR-780 + HBO, mouse bladder cell line (MB49) tumor-bearing mice were established and tumor size and weight were recorded. Besides, cell apoptosis and tumor size were assessed in drug-resistant bladder cancer cells (T24/DDP) and xenografts to evaluate the effect of IR-780 + HBO on drug-resistant bladder cancer.

RESULTS

IR-780 selectively accumulated in bladder cancer (bladder cancer cells, transplanted tumors, and bladder cancer tissue from patients) and could induce cancer cell apoptosis by targeting the mitochondrial complex I protein NDUFS1. The combination with HBO could significantly enhance the anti-tumor effect of IR-780 in vitro by promoting cancer cell uptake and inducing excessive mitochondrial ROS production, while suppressing tumor growth and recurrence in animal models without causing apparent toxicity. Moreover, this combination antitumor strategy was also demonstrated in drug-resistant bladder cancer cells (T24/DDP) and xenografts.

CONCLUSION

We identified for the first time a combination of IR-780 and HBO (IR-780 + HBO), which exhibits mitochondria-targeting and therapeutic capabilities, as a novel treatment paradigm for bladder cancer.

Mitochondria as a target of third row transition metal-based anticancer complexes

In pursuit of better treatment options for malignant tumors, metal-based complexes continue to show promise as attractive chemotherapeutics due to tunability, novel mechanisms, and potency exemplified by platinum agents. The metabolic character of tumors renders the mitochondria and other metabolism pathways fruitful targets for medicinal inorganic chemistry. Cumulative understanding of the role of mitochondria in tumorigenesis has ignited research in mitochondrial targeting metal-based complexes to overcome resistance and inhibit tumor growth with high potency and selectivity. Here, we discuss recent progress made in third row transition metal-based mitochondrial targeting agents with the goal of stimulating an active field of research toward new clinical anticancer agents and the elucidation of novel mechanisms of action.

ROS-triggered self-disintegrating and pH-responsive astaxanthin nanoparticles for regulating the intestinal barrier and colitis

Smart delivery systems with stimuli-responsive capability are able to improve the bioaccessibility through increasing the solubility, physicochemical stability and biocompatibility of bioactive compounds. In this study, the astaxanthin nanoparticles with reactive oxygen species (ROS) and pH dual-response function were design and constructed using poly (propylene sulfide) covalently modified sodium alginate as carriers based on ultrasonic assisted self-assembly strategy. Atomic force microscope and scanning electron microscope analysis showed that the nanoparticles were spherical in shape with a size of around 260 nm. Meanwhile, the astaxanthin nanoparticles showed both pH and ROS stimuli-responsive release characteristics. In vitro cell experiments showed that astaxanthin nanoparticles significantly inhibited the production of ROS and mitochondrial depolarization induced by oxidative stress. In vivo colitis experiment of mice revealed that astaxanthin nanoparticles could significantly relieve colitis, protect the integrity of colon tissue and restore the expression of tight junction proteins ZO-1 and occludin. The abundance of Lactobacillus and Lachnospiraceae, and the ratio of Firmicutes/Bacteroidota of gut microbiota were significantly improved after intervention of the stimuli-responsive astaxanthin nanoparticles. This work provided a simple strategy for constructing ROS/pH dual response delivery system, which provided an experimental basis for improving the oral bioavailability of hydrophobic active compounds.

Synthesis and discovery of mitochondria-targeting oleanolic acid derivatives for potential PI3K inhibition

Oleanolic acid and its derivatives have been widely reported for their antitumor activities. Recently, the introduction of a triphenylphosphonium cation moiety has been described to improve the selectivity and cytotoxicity of pentacyclic triterpenoids by targeting the mitochondria of human cancer cells. In this work, a series of novel mitochondria-targeting oleanolic acid derivatives were synthesized and their antitumor activities assessed. The majority of the compounds are more cytotoxicity to cancer cells than normal cells, especially for 6c with IC₅₀ of 0.81 μM in A549 cells, which showed a slight increase compared to doxorubicin (0.97 μM). Mechanism studies demonstrated that 6c induced apoptosis of A549 cells in a dose-dependent manner, and reactive oxygen species production, mitochondrial membrane potential depolarization, and particularly pro-apoptotic proteins upregulated by western blotting experiment may be responsible for the results. Moreover, 6c arrested the cell cycle at G2/M phase and cell migration in A549 cells. Compound 6c had a comparable or somewhat improved activity to the positive control LY294002 in molecular docking studies and in vitro testing, demonstrating that the apoptosis mechanism may involve inhibition of the PI3K-Akt pathway. These results augur well for the use of 6c as a novel triphenylphosphonium-conjugated anticancer agent.

Mitochondria-targeting multifunctional nanoplatform for cascade phototherapy and hypoxia-activated chemotherapy

Despite considerable progress has been achieved in hypoxia-associated anti-tumor therapy, the efficacy of utilizing hypoxia-activated prodrugs alone is not satisfied owing to the inadequate hypoxia within the tumor regions. In this work, a mitochondrial targeted nanoplatform integrating photodynamic therapy, photothermal therapy and hypoxia-activated chemotherapy has been developed to synergistically treat cancer and maximize the therapeutic window. Polydopamine coated hollow copper sulfide nanoparticles were used as the photothermal nanoagents and thermosensitive drug carriers for loading the hypoxia-activated prodrug, TH302, in our study. Chlorin e6 (Ce6) and triphenyl phosphonium (TPP) were conjugated onto the surface of the nanoplatform. Under the action of TPP, the obtained nanoplatform preferentially accumulated in mitochondria to restore the drug activity and avoid drug resistance. Using 660 nm laser to excite Ce6 can generate ROS and simultaneously exacerbate the cellular hypoxia. While under the irradiation of 808 nm laser, the nanoplatform produced local heat which can increase the release of TH302 in tumor cells, ablate cancer cells as well as intensify the tumor hypoxia levels. The aggravated tumor hypoxia then significantly boosted the anti-tumor efficiency of TH302. Both in vitro and in vivo studies demonstrated the greatly improved anti-cancer activity compared to conventional hypoxia-associated chemotherapy. This work highlights the potential of using a combination of hypoxia-activated prodrugs plus phototherapy for synergistic cancer treatment.

An ESIPT-based fluorescent probe with fast-response for detection of hydrogen sulfide in mitochondria

Excited-state intramolecular proton transfer (ESIPT) has recently received considerable attention due to its dual fluorescent changes and large Stokes shift. Hydrogen sulfide (H₂S) is a gas signal molecule that plays important roles in modulating the functions of different systems. Herein, by modifying 2-(2́-hydroxyphenyl) benzothiazole (HBT) scaffold, a novel near-infrared mitochondria-targeted fluorescent probe HBTP-H₂S has been rationally designed based on excited-state intramolecular proton transfer (ESIPT) effect. The nucleophilic addition reaction of the H₂S with probe HBTP-H₂S caused the break of the conjugated skeleton, resulting the shifting of maximum emission peak from 658 nm to 470 nm. HBTP-H₂S showed fast-response response time, good selectivity and a large Stokes shift (188 nm) toward H₂S. Most importantly, inspired by the inherent advantages of the probe, HBTP-H₂S was successfully employed to monitor mitochondrial H₂S in HepG2 cells.

Mitochondria-targeted accumulation of oxygen-irrelevant free radicals for enhanced synergistic low-temperature photothermal and thermodynamic therapy

BACKGROUND

Although lower temperature (< 45 °C) photothermal therapy (LPTT) have attracted enormous attention in cancer therapy, the therapeutic effect is still unsatisfying when applying LPTT alone. Therefore, combining with other therapies is urgently needed to improve the therapeutic effect of LPTT. Recently reported oxygen-irrelevant free radicals based thermodynamic therapy (TDT) exhibit promising potential for hypoxic tumor treatment. However, overexpression of glutathione (GSH) in cancer cells would potently scavenge the free radicals before their arrival to the specific site and dramatically diminish the therapeutic efficacy.

METHODS AND RESULTS

In this work, a core-shell nanoplatform with an appropriate size composed of arginine-glycine-aspartate (RGD) functioned polydopamine (PDA) as a shell and a triphenylphosphonium (TPP) modified hollow mesoporous manganese dioxide (H-mMnO2) as a core was designed and fabricated for the first time. This nanostructure endows a size-controllable hollow cavity mMnO2 and thickness-tunable PDA layers, which effectively prevented the pre-matured release of encapsulated azo initiator 2,2'-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIBI) and revealed pH/NIR dual-responsive release performance. With the mitochondria-targeting ability of TPP, the smart nanocomposites (AIBI@H-mMnO2-TPP@PDA-RGD, AHTPR) could efficiently induce mitochondrial associated apoptosis in cancer cells at relatively low temperatures (< 45 °C) via selectively releasing oxygen-irrelevant free radicals in mitochondria and facilitating the depletion of intracellular GSH, exhibiting the advantages of mitochondria-targeted LPTT/TDT. More importantly, remarkable inhibition of tumor growth was observed in a subcutaneous xenograft model of osteosarcoma (OS) with negligible side effects.

CONCLUSIONS

The synergistic therapy efficacy was confirmed by effectively inducing cancer cell death in vitro and completely eradicating the tumors in vivo. Additionally, the excellent biosafety and biocompatibility of the nanoplatforms were confirmed both in vitro and in vivo. Taken together, the current study provides a novel paradigm toward oxygen-independent free-radical-based cancer therapy, especially for the treatment of hypoxic solid tumors.

Multifunctional Nanoaggregates Composed of Active CPUL1 and a Triphenylphosphine Derivative for Mitochondria-Targeted Drug Delivery and Cell Imaging

We report that active substance (CPUL1) and triphenylphosphine (TPP) derivative could self-assemble into multifunctional nanoaggregates (CPUL1-TPP NAs) through electrostatic and π-π stacking interactions. CPUL1 was wrapped tightly inside the nanoparticles as well as CPUL1 and TPP derivative self-assembled into stable and compact nanoparticles in water. The positive surface charge of CPUL1-TPP NAs made them much easier to be endocytosed to enter cytoplasm, accumulate in the mitochondria and induce cell apoptosis based on their mitochondria targeting ability, fluorescence property and fast cell uptake characteristic, which showed better antitumor efficacy on HUH7 hepatoma cells in vitro than that of free CPUL1.

Mitochondria-targeted Pt(IV) prodrugs conjugated with an aggregation-induced emission luminogen against breast cancer cells by dual modulation of apoptosis and autophagy inhibition

Theranostic anticancer agents with dual functions of diagnosis and therapy are in highly demand for breast cancer. Herein, a triphenylphosphonium (TPP)-decorated aggregation-induced emission (AIE)-based Pt(IV) prodrug ACPt was developed, which exhibited superior anticancer performance with novel anticancer mechanism of dual modulation of apoptosis and autophagy inhibition. The experimental data showed that ACPt induced increased reactive oxygen species (ROS), and decreased mitochondrial membrane potential (MMP). The morphology and function of mitochondria were also severely damaged and ACPt showed strong inhibition to both mitochondrial and glycolytic bioenergetics. Moreover, DNA damage and cell cycle arrest in the S-phase were also observed after the ACPt treatment, eventually leading to the apoptosis and autophagy inhibition of cancer cells. Furthermore, ACPt also indicated excellent anti-proliferation activity in 3D multicellular tumor spheroids (MCTSs), suggesting the potential to inhibit solid tumors in vivo. Our observation demonstrated that ACPt could serve as a promising anticancer theranostic agent toward breast cancers for prodrug activation monitoring and image-guided chemotherapy.

Concurrent impairment of nucleus and mitochondria for synergistic inhibition of cancer metastasis

Cancer metastasis, which increases the mortality in a short period of time, has been considered as the main challenge in tumor treatment. However, tumor growth suppression also should not be ignored in cancer metastasis treatment. Recently, accumulating evidences have suggested that mitochondria play an important role in mitigating caner metastasis. Nucleus, as the repository of genetic information, plays a key role in cell proliferation. However, it remains elusive that the concurrent impairment of nucleus and mitochondria may achieve better anti-tumor and anti-metastatic effects. Here, we designed a mitochondria-penetrating peptide modified doxorubicin (MPP-Dox) loaded N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer conjugates (PM), as well as a nuclear accumulating HPMA copolymer Dox conjugates (PN) by the nuclear tendency of Dox. After co-delivering the two copolymers (abbreviation for PMN), PM promoted cell apoptosis and inhibited tumor metastasis by damaging mitochondria, whereas PN suppressed cell proliferation and promoted apoptosis by destroying nucleus. Importantly, PM and PN complemented each other as expected. The mitochondrial dysfunction and tumor metastasis inhibition of PM was improved by PN, while cell proliferation suppression and apoptosis by nucleus destroying of PN was enhanced by PM. As a result, tumor growth of breast cancer 4T1 cells in vivo was significantly restrained and lung metastasis was potently decreased and almost eradicated, fully reflecting the advantages of organelle targeting combination therapy. As a consequence, our work showed that concurrent impairment of nucleus and mitochondria was feasible and beneficial to metastatic cancer treatment.

Cathepsin B-responsive multifunctional peptide conjugated gold nanorods for mitochondrial targeting and precise photothermal cancer therapy

Nanomaterials have shown great potential in cancer therapy, but the phenomenon of poor tumor recognition without cellular organelle accumulation usually leads to reduced therapeutic effects and enhanced side effects. Herein, we resolved this issue by employing a multifunctional peptide coating mainly composed of, from the inside out, a mitochondrial targeting segment, a cathepsin B-responsive segment and a zwitterionic antifouling segment. Then gold nanorods were modified with a peptide via ligand exchange, displaying excellent photothermal property and superior stability both before and after enzyme treatment. The in vitro and in vivo results showed that this nanoplatform possessed good biocompatibility, satisfactory mitochondria targeting ability, prolonged blood circulation lifetime and enhanced cellular uptake in tumors. This nanoplatform promoted effective near-infrared light-triggered subcellular hyperthermia treatment in vitro and exhibited excellent tumor ablation ability in vivo. These findings suggested that this multifunctional nanoplatform could significantly enhance the therapeutic efficiency of photothermal therapy based on activated mitochondrial targeting.

Mitochondria-targeting graphene oxide nanocomposites for fluorescence imaging-guided synergistic phototherapy of drug-resistant osteosarcoma

BACKGROUND

Osteosarcoma (OS) is the most common primary malignant bone tumor occurring in children and young adults. Drug-resistant osteosarcoma often results in chemotherapy failure. Therefore, new treatments aimed at novel therapeutic targets are urgently needed for the treatment of drug-resistant osteosarcoma. Mitochondria-targeted phototherapy, i.e., synergistic photodynamic/photothermal therapy, has emerged as a highly promising strategy for treating drug-resistant tumors. This study proposed a new nano-drug delivery system based on near-infrared imaging and multifunctional graphene, which can target mitochondria and show synergistic phototherapy, with preferential accumulation in tumors.

METHODS AND RESULTS

Based on our previous study, (4-carboxybutyl) triphenyl phosphonium bromide (TPP), a mitochondria-targeting ligand, was conjugated to indocyanine green (ICG)-loaded, polyethylenimine-modified PEGylated nanographene oxide sheets (TPP-PPG@ICG) to promote mitochondrial accumulation after cellular internalization. Thereafter, exposure to a single dose of near-infrared irradiation enabled synergistic photodynamic and photothermal therapy, which simultaneously inhibited adenosine triphosphate synthesis and mitochondrial function. Induction of intrinsic apoptosis assisted in surmounting drug resistance and caused tumor cell death. After fluorescence imaging-guided synergistic phototherapy, the mitochondria-targeting, multifunctional graphene-based, drug-delivery system showed highly selective anticancer efficiency in vitro and in vivo, resulting in marked inhibition of tumor progression without noticeable toxicity in mice bearing doxorubicin-resistant MG63 tumor cells.

CONCLUSION

The mitochondria-targeting TPP-PPG@ICG nanocomposite constitutes a new class of nanomedicine for fluorescence imaging-guided synergistic phototherapy and shows promise for treating drug-resistant osteosarcoma.

Azole-triphenylphosphonium conjugates combat antifungal resistance and alleviate the development of drug-resistance

Azole antifungals are commonly used to treat fungal infections but have resulted in the occurrence of drug resistance. Therefore, developing azole derivatives (AZDs) that can both combat established drug-resistant fungal strains and evade drug resistance is of great importance. In this study, we synthesized a series of AZDs with a fluconazole (FLC) skeleton conjugated with a mitochondria-targeting triphenylphosphonium cation (TPP⁺). These AZDs displayed potent activity against both azole-sensitive and azole-resistant Candida strains without eliciting obvious resistance. Moreover, two representative AZDs, 20 and 25, exerted synergistic antifungal activity with Hsp90 inhibitors against C. albicans strains resistant to the combination treatment of FLC and Hsp90 inhibitors. AZD 25, which had minimal cytotoxicity, was effective in preventing C. albicans biofilm formation. Mechanistic investigation revealed that AZD 25 inhibited the biosynthesis of the fungal membrane component ergosterol and interfered with mitochondrial function. Our findings provide an alternative approach to address fungal resistance problems.

Triphenylphosphonium-functionalized nanocomposites as carriers of a platinum diimine complex for photodynamic therapy

The photodamage induced by PDT usually occurs at the site where the photosensitizers accumulate in the tumor cells, thus the modulation of intrinsic apoptosis by mitochondria-targeting PDT drugs might be a promising way to enhance the therapeutic efficacy of PDT drugs against tumor cells. Novel triphenylphosphonium-functionalized nanocomposites employed as carriers of a photoactive platinum diimine complex have been fabricated and characterized. Upon irradiation, the IC₅₀ value of photosensitizer-loaded triphenylphosphonium-functionalized nanocomposites was found to be 17.4 or 14.4 times lower than that of the photosensitizer studied alone against HCT116 cells or A549 cells, respectively. The results suggested that the triphenylphosphonium- functionalized nanocomposites as drug delivery vehicles could significantly enhance the photodynamic efficacy of the photosensitizer.

Selective antitumor activity of drug-free TPGS nanomicelles with ROS-induced mitochondrial cell death

D-a-tocopheryl polyethylene glycol succinate (TPGS) as a FDA-approved safe adjuvant has shown an excellent application in the targeting delivery of antitumor drugs and overcoming multidrug resistance. Beside, TPGS can result in apoptogenic activity toward many tumor types because it can induce mitochondrial dysfunction. Therefore, TPGS can serve as an antineoplastic agent. However, the current research on the selective antitumor activity of TPGS is ignored. To reveal the issue, herein we develop a mitochondria-targeting drug-free TPGS nanomicelles with the hydrodynamic diameter of about 100 nm and outstanding serum stability by weak interaction-driven self-assembly of the amphiphilic TPGS polymer. Moreover, such drug-free TPGS nanomicelles intravenously injected into tumor-bearing mice exhibit long blood circulation time, superior tumor enrichment, and inhibit the tumor growth via inducing excessive reactive oxygen species (ROS) generation within tumor cells. Further in vitro and in vivo researches jointly demonstrate that drug-free TPGS nanomicelles have more significant antitumor effect on HeLa cells compared with that of other tumor cells. On the contrary, drug-free TPGS nanomicelles display the low toxicity toward normal cells and tissues. Taken together, these new findings confirm that TPGS drug-free nanomicelles represent simple, multifunctional, safe, and efficient antineoplastic agents, which can be expected to bring new light on the development of drug-free polymers for tumor therapy.

A mitochondria-targeting magnetothermogenic nanozyme for magnet-induced synergistic cancer therapy

Magnetic hyperthermia therapy (MHT) and chemodynamic therapy (CDT) are non-invasive in situ treatments without depth limitations and with minimum adverse effects on surrounding healthy tissue. We herein report a mitochondria-targeting magnetothermogenic nanozyme (Ir@MnFe2O4 NPs) for highly efficient cancer therapy. An iridium(III) complex (Ir) acts as a mitochondria-targeting agent on the surface of MnFe2O4 NPs. On exposure to an alternating magnetic field (AMF), the Ir@MnFe2O4 NPs induce a localized increase in temperature causing mitochondrial damage (MHT effect). Meanwhile glutathione (GSH) reduces Fe(III) to Fe(II) on the NPs surface, which in turn catalyzes the conversion of H2O2 to cytotoxic •OH (CDT effect). The depletion of GSH (a •OH scavenger) increases CDT efficacy, while the localized increase in temperature increases the rate of conversion of both Fe(III) to Fe(II) and H2O2 to •OH further enhancing the CDT effect. In addition, the disruption of cellular redox homeostasis due to CDT, leads to greater sensitivity of the cell towards MHT. This nanoplatform integrates these excellent therapeutic properties, with two-photon microscopy (TPM) (demonstrated in vitro) and magnetic resonance imaging (MRI) (demonstrated in vivo) to enable the precise and effective treatment of cancer.

Conjugation of Triphenylphosphonium Cation to Hydrophobic Moieties to Prepare Mitochondria-Targeting Nanocarriers

The contribution of mitochondrial dysfunctions to diseases such as cancer, diabetes, cardiovascular, and neurodegenerative diseases has made mitochondria an attractive pharmacological target. To deliver biologically active molecules to mitochondria, however, cellular and mitochondrial barriers must be first overcome. The mitochondrial transmembrane electric potential (negative inside) is among the most commonly used strategies to deliver molecules to mitochondria as it allows the accumulation of positively charged molecules. Thus, therapeutic molecules are either covalently conjugated to lipophilic cations like triphenylphosphonium (TPP) or loaded into nanocarriers conjugated to TPP.

Mitochondria-targeting turn-on fluorescent probe for HClO detection and imaging in living cells

Hypochlorous/hypochlorite (HClO/ClO^-), one of the most important signal molecule, plays a crucial role in many cellular signaling pathways. It is reported that the HClO/ClO^- level in mitochondria is important to maintain the normal mitochondrial function. Herein, we present two simple fluorescent probes BAC and mitochondria-targeting fluorescent probe TACB for the detection of ClO^-. Probes BAC &TACB could be sensitively and selectivity detecting ClO^- at the nanomolar levels with the detection limit of 1.64 × 10^-9 M and 9.86 × 10^-8 M, respectively. Additionally, probes BAC &TACB with the response unit of CO moiety could selectively detect ClO^- over other various analytes such as anions, metal ions and OH, ¹O₂, H₂O₂. The response time of probe TACB for ClO^- (<20 s), implying that it could offer a real-time analytical assay of ClO^-. Finally, probe BAC was used for monitoring the ClO^- in HEK293T cells and probe TACB could be utilized to track the fluctuations of exogenous ClO^- levels in the mitochondria of Hela cells.

A novel "turn-on" mitochondria-targeting near-infrared fluorescent probe for determination and bioimaging cellular hydrogen sulfide

Hydrogen sulfide (H₂S) has been regarded as an important gas transmitter playing vital role in cytoprotective processes and redox signaling. It is very meaningful to monitor and analyze it in biosystem for obtaining important physiological and pathological information. Despite numerous fluorescent probes for cellular H₂S have been reported in past decades, only a few have capability to detect mitochondrial H₂S with near-infrared (NIR) emission. Therefore, a new mitochondria-targeting NIR fluorescent probe (Mito-NSH) for detection of cellular H₂S was developed by introducing 2,4-dinitrophenyl ether into a novel dye (Mito-NOH). A large "turn-on" NIR fluorescence response was obtained due to thiolysis of ether to hydroxyl group when Mito-NSH was treated with NaHS. Moreover, Mito-NSH could quantitatively detect H₂S at concentration ranging from 0 to 30 μM with a detection limit of 68.2 nM, and it exerts some superior optical properties, such as large stokes shift (107 nm), highly selectively mitochondria location, fast response and high selectivity to H₂S. More impressively, it was successfully applied to imaging exogenous and endogenously generated H₂S in living HeLa cells via confocal fluorescence microscopy.

Fluorescence detection of intracellular pH changes in the mitochondria-associated process of mitophagy using a hemicyanine-based fluorescent probe

Intracellular pH behaves as a vital parameter in the physiological and pathological processes. Novel small molecule probes for precise and dynamic monitoring of pH fluctuations in cellular physiological processes are still highly required. Herein, we present a hemicyanine-based probe (HcPH) detection of the pH changes during the intracellular process of mitochondria-associated autophagy. HcP-H exhibits highly reversible and ratiometric fluorescence detection of pH variation due to the deprotonation/protonation process, showing orange fluorescence (λ_em = 557 nm) in basic media (pH 8.0) and green fluorescence (λ_em = 530 nm) in acidic media (pH 6.2), respectively. Organelle localization experiment in HeLa cells demonstrates that this probe could selectively accumulate in mitochondria, showing almost overlap with that of Mito-Tracker Green FM. More importantly, Fluorescence imaging of HcP-H in HeLa cells subjected to the nutrient deprivation has demonstrated that this probe could monitor the intracellular pH changes in the mitochondria-associated process of mitophagy. It is clearly confirmed that HcP-H would serve as a promising fluorescent probe for tracing mitophagy in living cells.

Mitochondria-targeting theranostics

BACKGROUND

Interest in subcellular organelle-targeting theranostics is substantially increasing due to the significance of subcellular organelle-targeting drug delivery for maximizing therapeutic effects and minimizing side effects, as well as the significance of theranostics for delivering therapeutics at the correct locations and doses for diseases throughout diagnosis. Among organelles, mitochondria have received substantial attention due to their significant controlling functions in cells.

MAIN BODY

With the necessity of subcellular organelle-targeting drug delivery and theranostics, examples of mitochondria-targeting moieties and types of mitochondria-targeting theranostics were introduced. In addition, the current studies of mitochondria-targeting theranostic chemicals, chemical conjugates, and nanosystems were summarized.

CONCLUSION

With the current issues of mitochondria-targeting theranostic chemicals, chemical conjugates, and nanosystems, their potentials and alternatives are discussed.

Mitochondria-targeting drug conjugates for cytotoxic, anti-oxidizing and sensing purposes: current strategies and future perspectives

Mitochondrial targeting is a promising approach for solving current issues in clinical application of chemotherapy and diagnosis of several disorders. Here, we discuss direct conjugation of mitochondrial-targeting moieties to anticancer drugs, antioxidants and sensor molecules. Among them, the most widely applied mitochondrial targeting moiety is triphenylphosphonium (TPP), which is a delocalized cationic lipid that readily accumulates and penetrates through the mitochondrial membrane due to the highly negative mitochondrial membrane potential. Other moieties, including short peptides, dequalinium, guanidine, rhodamine, and F16, are also known to be promising mitochondrial targeting agents. Direct conjugation of mitochondrial targeting moieties to anticancer drugs, antioxidants and sensors results in increased cytotoxicity, anti-oxidizing activity and sensing activity, respectively, compared with their non-targeting counterparts, especially in drug-resistant cells. Although many mitochondria-targeted anticancer drug conjugates have been investigated in vitro and in vivo, further clinical studies are still needed. On the other hand, several mitochondria-targeting antioxidants have been analyzed in clinical phases I, II and III trials, and one conjugate has been approved for treating eye disease in Russia. There are numerous ongoing studies of mitochondria-targeted sensors.

Mitochondria-targeting BODIPY-loaded micelles as novel class of photosensitizer for photodynamic therapy

In this paper, a series of novel BODIPY-based photosensitizers have been designed and synthesized for photodynamic therapy. BODIPY3 was screened out as the most potential photosensitizer due to its excellent optical properties, high singlet oxygen efficiency and good photostability. However, as an organic photosensitizer, BODIPY3 still suffered from the drawbacks of insolubility and instability in aqueous system. In view of these problems, DSPE-PEG2000 was used to trap BODIPY3 into the hydrophobic core of micelles to obtain well-dispersing nano complexes BODIPY3-PEG₃ in aqueous system. More importantly, BODIPY3-PEG₃ not only has better solubility and stability in aqueous media but can generate significant singlet oxygen (¹O₂, one of the reactive oxygen species, the real cytotoxic agent in photodynamic therapy) in living cells and exhibit high light cytotoxicity to three cancer cell lines. The mechanism studies indicated the mitochondrial localization of BODIPY3-PEG₃ was able to generate ROS in mitochondria, which further result in mitochondrial dysfunction and photoinduced apoptosis via caspase-8 and caspase-3 pathway.

Targeted reversal and phosphorescence lifetime imaging of cancer cell metabolism via a theranostic rhenium(I)-DCA conjugate

Cancer cell metabolism is quite different from normal cells. Targeting cancer metabolism and untuning the tumor metabolic machine has emerged as a promising strategy for cancer therapy. We have developed a multi-functional Re-dca conjugate (Re-dca 2) by conjugating the metabolic modulator dichloroacetate (DCA) to mitochondria-targeted rhenium(I) complex, allowing its efficient penetration into cancer cells and selective accumulation in mitochondria, thus achieving the cancer cell metabolism reversal from glycolysis to glucose oxidation at pharmacologically relevant DCA doses. Mechanism studies confirm the inhibition effect of Re-dca 2 on the activity of pyruvate dehydrogenase kinase (PDK) and capture the metabolic reversal window in Re-dca 2 treated NCI-1229 cells at the early stage of drug treatment, resulting in selective killing of malignant cells cocultured with normal cells, significant inhibition of cancer cell metastasis and invasion, as well as excellent anti-angiogenesis activities in zebrafish embryos. By comparison, DCA-free Re(I) analogue is also investigated under the same conditions. Although this analogue also exhibits cytotoxicity due to the Re(I) core, metabolic reversal is not induced by this analogue and its anti-metastasis activity is much lower than Re-dca 2, indicating the synergistic effect of Re(I) core and DCA moiety on cancer therapy. In vivo anti-cancer investigations also indicate that the mitochondria-targeted Re-dca 2 can effectively inhibit the tumor growth without affecting the body weight of nude mice, and the therapeutic effect is much better than the DCA-free Re(I) analogue 2a. Simultaneously, the O₂-sensitive phosphorescent lifetimes of Re-dca 2 can be utilized for PLIM imaging of intracellular oxygen consumption, thus reflecting the Re-dca 2 induced glycolysis-to-glucose oxidation reversal at the early drug treatment stage. The excellent phosphorescence of Re-dca 2 can also be utilized for real-time tracking of mitochondrial morphological changes during treatment. In a word, rational design of phosphorescent metallodrug and metabolic modulator conjugates for synergistic treatment is a promising strategy for simultaneous untuning and tracking tumor metabolic machine, thus providing new clues for cancer therapy and mechanisms.

A nontoxic, photostable and high signal-to-noise ratio mitochondrial probe with mitochondrial membrane potential and viscosity detectivity

Herein, we reported a yellow emission probe 1-methyl-4-(6-morpholino-1, 3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl) pyridin-1-ium iodide which could specifically stain mitochondria in living immortalized and normal cells. In comparison to the common mitochondria tracker (Mitotracker Deep Red, MTDR), this probe was nontoxic, photostable and ultrahigh signal-to-noise ratio, which could real-time monitor mitochondria for a long time. Moreover, this probe also showed high sensitivity towards mitochondrial membrane potential and intramitochondrial viscosity change. Consequently, this probe was used for imaging mitochondria, detecting changes in mitochondrial membrane potential and intramitochondrial viscosity in physiological and pathological processes.

Nanopreparations for mitochondria targeting drug delivery system: Current strategies and future prospective

Mitochondria are a novel and promising therapeutic target for diagnosis, treatment and prevention of a lot of human diseases such as cancer, metabolic diseases and neurodegenerative disease. Owing to the mitochondrial special bilayer structure and highly negative potential nature, therapeutic molecules have multiple difficulties in reaching mitochondria. To overcome multiple barriers for targeting mitochondria, the researchers developed various pharmaceutical preparations such as liposomes, polymeric nanoparticles and inorganic nanoparticles modified by mitochondriotropic moieties like dequalinium (DQA), triphenylphosphonium (TPP), mitochondrial penetrating peptides (MPPs) and mitochondrial protein import machinery that allow specific targeting. The targeted formulations exhibited enhanced pharmacological effect and better therapeutic effect than their untargeted counterpart both in vitro and in vivo. Nanocarriers may be used for bio-therapeutic delivery into specific mitochondria that possess a great potential treatment of mitochondria related diseases.

Triphenyl phosphonium coated nano-quercetin for oral delivery: Neuroprotective effects in attenuating age related global moderate cerebral ischemia reperfusion injury in rats

Cerebral ischemia-reperfusion is a classic example of reactive oxygen species (ROS) mediated acute damage to brain. Post-ischemic reperfusion induced oxygen free radicals production causes damage to brain cell mitochondria. Antioxidants like quercetin (Qc) have potentials to manage oxidative stress related pathophysiology. However low oral bioavailability and poor cell membrane permeability restrict its therapeutic efficacy. To overcome these hurdles mitochondria specific delivery of Qc nanocapsules was designed to efficiently counteract cerebral ischemia-reperfusion induced cell death and neurodegeneration in young and aged rats. The orally deliverable quercetin loaded polymeric nanocapsules (N1QC) were made mitochondria specific by using triphenylphosphonium cation as one of the matrix components. N1QC demonstrated higher brain uptake and remarkable mitochondrial localization post cerebral ischemia-reperfusion. This unique controlled mitochondrial delivery of quercetin ameliorated histopathological severity by preserving mitochondrial structural and functional integrity through sequestering ROS thus modulating mitochondrial ROS mediated apoptotic cell death in young and aged rats.

Functional nanosome for enhanced mitochondria-targeted gene delivery and expression

Mitochondria dysfunction plays a role in many human diseases. Therapeutic techniques for these disorders require novel delivery systems that can specifically target and penetrate mitochondria. In this study, we report a novel nanosome composed of dequalinium-DOTAP-DOPE (1,2 dioleoyl-3-trimethylammonium-propane-1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) (DQA80s) as a potential mitochondria-targeting delivery vector. The functional DQAsome, DQA80s, showed enhanced transfection efficiency compared to a vector DQAsomes in HeLa cells and dermal fibroblasts. In addition, DQA80s/pDNA complexes exhibited rapid escape from the endosome into the cytosol. We observed the delivery of pDNA to mitochondria in living cells using flow cytometry, confocal microscopy, and TME imaging. More specifically, we confirmed our results by co-localization of hmtZsGreen constructs to mitochondria when delivered via DQAsomes and DQA80s in living cells. The mitochondria-targeting DQAsomes and DQA80s induced mitochondrial dysfunction through depolarization of mitochondrial membrane potential. Our data demonstrate that DQA80s show promise for use as a mitochondria-targeted carrier system for treatment of mitochondria diseases in vivo.

A fluorescent carbon-dots-based mitochondria-targetable nanoprobe for peroxynitrite sensing in living cells

Mitochondria, the power generators in cell, are a primary organelle of oxygen consumption and a main source of reactive oxygen/nitrogen species (ROS/RNS). Peroxynitrite (ONOO^-), known as a kind of RNS, has been considered to be a significant factor in many cell-related biological processes, and there is great desire to develop fluorescent probes that can sensitively and selectively detect peroxynitrite in living cells. Herein, we developed a fluorescent carbon-dots (C-dots) based mitochondria-targetable nanoprobe with high sensitivity and selectivity for peroxynitrite sensing in living cells. The C-dots with its surface rich in amino groups was synthesized using o-phenylenediamine as carbon precursor, and it could be covalently conjugated with a mitochondria-targeting moiety, i.e. triphenylphosphonium (TPP). In the presence of peroxynitrite, the fluorescence of the constructed nanoprobe (C-dots-TPP) was efficiently quenched via a mechanism of photoinduced electron transfer (PET). The nanoprobe exhibited relatively high sensitivity (limit of detection: 13.5nM) and selectivity towards peroxynitrite in aqueous buffer. The performance of the nanoprobe for fluorescence imaging of peroxynitrite in mitochondria was investigated. The results demonstrated that the nanoprobe showed fine mitochondria-targeting ability and imaging contrast towards peroxynitrite in living cells. We anticipate that the proposed nanoprobe will provide a facile tool to explore the role played by peroxynitrite in cytobiology.

Microwave pumped high-efficient thermoacoustic tumor therapy with single wall carbon nanotubes

The ultra-short pulse microwave could excite to the strong thermoacoustic (TA) shock wave and deeply penetrate in the biological tissues. Based on this, we developed a novel deep-seated tumor therapy modality with mitochondria-targeting single wall carbon nanotubes (SWNTs) as microwave absorbing agents, which act efficiently to convert ultra-short microwave energy into TA shock wave and selectively destroy the targeted mitochondria, thereby inducing apoptosis in cancer cells. After the treatment of SWNTs (40 μg/mL) and ultra-short microwave (40 Hz, 1 min), 77.5% of cancer cells were killed and the vast majority were caused by apoptosis that initiates from mitochondrial damage. The orthotopic liver cancer mice were established as deep-seated tumor model to investigate the anti-tumor effect of mitochondria-targeting TA therapy. The results suggested that TA therapy could effectively inhibit the tumor growth without any observable side effects, while it was difficult to achieve with photothermal or photoacoustic therapy. These discoveries implied the potential application of TA therapy in deep-seated tumor models and should be further tested for development into a promising therapeutic modality for cancer treatment.

Targeted fluorescent probes for detection of oxidative stress in the mitochondria

Mitochondrial oxidative stress has been implicated in aging, neurodegenerative diseases, diabetes, stroke, ischemia/reperfusion injury, age-related macular degeneration (AMD) and cancer. Recently, we developed two new mitochondria-targeting fluorescent probes, MitoProbes I/II, which specifically localize in mitochondria and employed both in vivo and in vitro for detection of mitochondrial oxidative stress. Here, we report the design and synthesis of these agents, as well as their utility for real-time imaging of mitochondrial oxidative stress in cells.

Mitophagy induced by nanoparticle-peptide conjugates enabling an alternative intracellular trafficking route

The intracellular behaviors of nanoparticles are fundamentally important for the evaluation of their biosafety and the designs of nano carrier-assisted drug delivery with high therapeutic efficacy. It is still in a great need to discover how functionalized nanoparticles are transported inside the cells, for instance, in a complicated fashion of translocation between different types of cell organelles. Here we report a new understanding of the interactions between nanoparticles and cells by the development of polyoxometalates nanoparticle-peptide conjugates and investigation of their intracellular trafficking behaviors. The as-prepared nanoparticles are featured with a unique combination of fluorescence and high contrast for synchrotron X-ray-based imaging. Functional surface modification with peptides facilitates effective delivery of the nanoparticles onto the target organelle (mitochondria) and subsequent intracellular trafficking in a dynamic mode. Interestingly, our experimental results have revealed that autophagy of mitochondria (mitophagy) can be induced by NP-peptide as a cellular response for recycling the damaged organelles, through molecular mediation associated with the change of mitochondrial membrane potential. The biological effects induced by NP-peptide reciprocally affect the distribution patterns and fates of nanoparticles in the cell metabolism by providing an alternative route of intracellular trafficking. The new understanding of the mutual activities between nanoparticles and cells will enrich our approaches in the development of nanobiotechnology and nano-medicine for disease treatments.