Triphenylphosphonium Group Research Articles

Mitoapocynin, a mitochondria targeted derivative of apocynin induces mitochondrial ROS generation and apoptosis in multiple cell types including cardiac myoblasts: a potential constraint to its therapeutic use.

Mitoapocynin is a triphenylphosphonium conjugated derivative of apocynin that specifically locates to the mitochondria. It has been developed as a mitochondrially targeted therapeutic antioxidant. We attempted to attenuate the mitochondrial ROS induced in H9c2 cardiac myoblast cells treated with norepinephrine. Mitoapocynin was a poor quencher of total ROS as detected by the fluoroprobe DCFH-DA. Using mitochondrial superoxide specific probe MitoSoxRed, we found that 5-10µM mitoapocynin itself induces superoxide over and above that is generated by the norepinephrine treatment. A supposedly control molecule to mitoapocynin, the synthetic compound PhC11TPP, having the triphenylphosphonium group and a benzene moiety with C11 aliphatic chain spacer was also found to be a robust inducer of mitochondrial ROS. Subsequent assays with several cell lines viz., NIH3T3, HEK293, Neuro2A, MCF-7 and H9c2, showed that prolonged exposure to mitoapocynin induces cell death by apoptosis that can be partially prevented by the general antioxidant N-acetyl cysteine. Analyses of mitochondrial electron transport complexes by Blue Native Polyacrylamide gel electrophoresis showed that both mitoapocynin and PhC11TPP disrupt the mitochondrial Complex I and V, and in addition, PhC11TPP also damages the Complex IV. Our data thus highlights the limitations of the therapeutic use of mitoapocynin as an antioxidant.

Quantum Sensors To Track Total Redox-Status and Oxidative Stress in Cells and Tissues Using Electron-Paramagnetic Resonance, Magnetic Resonance Imaging, and Optical Imaging

Total redox capacity (TRC) and oxidative stress (OxiStress) of biological objects (such as cells, tissues, and body fluids) are some of the most frequently analyzed parameters in life science. Development of highly sensitive molecular probes and analytical methods for detection of these parameters is a rapidly growing sector of BioTech's R&D industry. The aim of the present study was to develop quantum sensors for tracking the TRC and/or OxiStress in living biological objects using electron-paramagnetic resonance (EPR), magnetic resonance imaging (MRI), and optical imaging. We describe a two-set sensor system: (i) TRC sensor QD@CD-TEMPO and (ii) OxiStress sensor QD@CD-TEMPOH. Both redox sensors are composed of small-size quantum dots (QDs), coated with multinitroxide-functionalized cyclodextrin (paramagnetic CD-TEMPO or diamagnetic CD-TEMPOH) conjugated with triphenylphosphonium (TPP) groups. The TPP groups were added to achieve intracellular delivery and mitochondrial localization. Nitroxide residues interact simultaneously with various oxidizers and reducers, and the sensors are transformed from the paramagnetic radical form (QD@CD-TEMPO) into diamagnetic hydroxylamine form (QD@CD-TEMPOH) and vice-versa, because of nitroxide redox-cycling. These chemical transformations are accompanied by characteristic dynamics of their contrast features because of quenching of QD fluorescence by nitroxide radicals. The TRC sensor was applied for EPR analysis of cellular redox-status in vitro on isolated cells with different proliferative indexes, as well as for noninvasive MRI of redox imbalance and severe oxidative stress in vivo on mice with renal dysfunction.

Synthesis of Triphenylphosphonium Phospholipid Conjugates for the Preparation of Mitochondriotropic Liposomes.

Surface modification of liposomes with a ligand is facilitated by the conjugation of the ligand to a hydrophobic molecule that serves to anchor the ligand to the liposomal bilayer. We describe here a simple protocol to conjugate a triphenylphosphonium group to several commercially available functionalized phospholipids. The resulting triphenylphosphonium-conjugated lipids can be used to prepare liposomes that preferentially associate with mitochondria when exposed to live mammalian cells in culture.

Synthesis of Alkyl Triphenylphosphonium Ostruthin Derivatives as Potential Cytotoxic Candidates

AbstractOstruthin, isolated from Paramignya trimera, was used as a scaffold to design its alkyl triphenylphosphonium derivatives. With the optimal reaction conditions in hand, five alkyl triphenylphosphonium ostruthin derivatives (1–5) were synthesized. Ostruthin and its derivatives were tested for cytotoxicity against human PANC‐1 pancreatic, Hela cervical, and HepG2 liver cancer cell lines. Ostruthin and its hexyl and heptyl triphenylphosphonium derivatives (4 and 5) showed strong preferential cytotoxicity against PANC‐1 cells with the PC50 values of 10.3 and 14.4 μM, respectively. In addition, compounds 4 and 5 also exhibited potent cytotoxicity towards HeLa cells with the IC50 values of 24.8 and 18.5 μM, respectively. The hexyl triphenylphosphonium group in 4 was found to slightly enhance cytotoxicity against HepG2 cells. Further, the morphological changes and the live‐cell imaging result suggested the anticancer potential against HeLa cells of the synthesized ostruthin derivative 5.

Synthesis of triphenylphosphonium dibenzothiophene S-oxide derivatives and their effect on cell cycle as photodeoxygenation-based cytotoxic agents

Photodeoxygenation of Dibenzothiophene-S-oxide (DBTO) in UV-A light produces atomic oxygen [O(3P)] and the corresponding sulfide, dibenzothiophene (DBT). Recently, DBTO has been derivatized to study the effect of UV-A light-driven photodeoxygenation in lipids, proteins, and nucleic acids. In this study, two DBTO derivatives with triphenylphosphonium groups were synthesized to promote mitochondrial accumulation. The sulfone analogs of these derivatives were also synthesized and used as fluorescent mitochondrial dyes to assess localization in mitochondria of HeLa cells. These derivatives were then used to study the effect of photodeoxygenation on MDA-MB-231 breast cancer cell line using cell viability assays, cell cycle phase determination tests, and RNA-Seq analysis. The DBTO derivatives were found to significantly decrease cell viability only after UV-A irradiation as a result of generating corresponding sulfides that were found to significantly affect gene expression and cell cycle.

Enhanced antifungal activity of novel cationic chitosan derivative bearing triphenylphosphonium salt via azide-alkyne click reaction

As one of the most promising biopolymers for a variety of potential applications, chitosan has attracted much attention because of its unique biological, chemical, and physical properties. The functionalization of chitosan has been adopted to synthesize novel chitosan derivatives with improved water-solubility and excellent biological activities. In this paper, chitosan was functionalized with a triphenylphosphonium group by means of the copper (I) catalyzed azide-alkyne “click” reaction and has been investigated as potential polymer for agricultural antifungal biomaterial. The influence of chemical modification on the structural characteristics and water-solubility of chitosan was investigated by FTIR spectroscopy, 1H NMR spectroscopy, elemental analysis, and UV–vis spectrum. Furthermore, the antifungal property of target chitosan derivative against four plant threatening fungal pathogens was evaluated and in vitro investigation demonstrated that triphenylphosphonium salt incorporated chitosan backbone had excellent antifungal property compared with chitosan and intermediate chitosan derivative. Notably, target chitosan derivative displayed relatively strongest antifungal effect with over 80% inhibitory index against Botrytis cinerea at 1.0 mg/mL. The results of a detailed antifungal study indicated that cationic chitosan derivative bearing 1,2,3-triazole and triphenylphosphonium moieties provided a promising platform for preparation of novel cationic antifungal biomaterials in the field of agriculture.

Discovery of Mitochondrial Transcription Inhibitors Active in Pancreatic Cancer Cells.

Mitochondrial dysfunction is a hallmark of cancer cells and targeting cancer mitochondria has emerged as a promising anti-cancer therapy. Previously, we repurposed chlorambucil by conjugating it to a mitochondrial targeting triphenylphosphonium (TPP) group to design Mito-Chlor, a novel agent that acts on mitochondria DNA (mtDNA). Herein, we show that Mito-Chlor, but not chlorambucil, inhibits the nascent transcription of mtDNA. Clustering analysis of transcriptomic profile of our Bru-seq database led to the identification of another mitochondrial transcription inhibitor SQD1, which inhibits the proliferation of MIA PaCa-2 cells with an IC50 of 1.3 μM. Interestingly, Mito-Chlor reduces expression of mitochondrial proteins, interferes with mitochondria membrane potential, and impairs oxidative phosphorylation while SQD1 does not. Both compounds increased cellular and mitochondrial reactive oxygen species and stimulated similar signaling pathways in response to oxidative stress. As mitochondrial transcription inhibitors and redox modulators, SQD1 and Mito-Chlor are promising for the treatment of pancreatic cancer by blocking mitochondrial function.

Probing mitochondrial membrane potential

Mitochondrial membrane potential, an indicator of mitochondrial function, is perturbed in many diseases , including cancer and neurodegenerative diseases, but difficult to measure noninvasively. Now, Elena A. Goun of the Swiss Federal Institute of Technology, Lausanne (EPFL) and coworkers have devised a bioluminescent probe for monitoring mitochondrial membrane potential ( 2020, DOI: ). The probe comprises two parts, a triphenylphosphine-caged luciferin and a separate azido-triphenylphosphine. Both components use their triphenylphosphonium groups to target mitochondria, where they react via Staudinger ligation, uncaging the luciferin in the process. The luciferin is acted on by the enzyme luciferase, which the researchers engineer into cells and mice. The enzymatic reaction releases light, the intensity of which is proportional to the concentration of the two parts of the probe. The rate enhancement of the reaction in the mitochondria relative to the rest of the cell enables measurement of the mitochondrial membrane potential. The researchers used

Interaction of 1-acylamino-2,2-dichloroethenyl(triphenyl)phosphonium chlorides with alkanolamines

It is shown that the interaction of 1-acylamino-2,2-dichloroethenyl(triphenyl)-phosphonium chlorides with alkanolamines having a primary amino group results in the formation of 4-oxazolylphosphonium salts containing hydroxyalkylamine substituents at position 5 of the oxazole cycle. Under similar conditions the reaction of N-substituted alkanolamines with 1-acylamino-2,2-dichloroethenyl-(triphenyl)phosphonium chlorides leads to the formation of 1,3-oxazolidin-2-ylidene derivatives, in which the triphenylphosphonium group is located in the side chain. The structure of the new synthesized compounds has been reliably proven by elemental analysis, IR, 1Н, 13С, 31Р NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction.

Targeted photoresponsive carbazole-coumarin and drug conjugates for efficient combination therapy in leukemia cancer cells.

Phototriggered drug delivery systems (PTDDSs) facilitate controlled delivery of drugs loaded on photoactive platform to the target region under light stimulation. The present study investigated the synthesis and efficacy of carbazole-coumarin (CC)-fused heterocycles as a PTDDS platform for the photocontrolled release of a chemotherapeutic agent, chlorambucil, in an in vitro model of human breast and leukemia cancer cells. CC-fused heterocycles were constructed using 4-hydroxycarbazole as the starting material, and further modification of these heterocycles yielded two CC derivatives. CC-7 with an additional-COOH group and CC-8 with the triphenylphosphonium (TPP) group, a mitochondria-targeting ligand introduced in the carbazole ring, dissolved in polar solvents and exhibited emission bands at 360 and 450nm, respectively. The results indicate that visible light of 405nm triggers the photolysis of the CC-drug conjugate and efficiently delivers the drug in both in vitro cancer cell models. Cytotoxicity evaluation indicates the suppression of proliferation of both types of cells treated with CC-8 under synergy effect combining drug potency and photosensitization. Further, the lower IC50 of CC-8 toward leukemia cells suggests the efficacy of the TPP ligand in increasing the bioavailability of CC-drug conjugates in leukemia treatment. Studies on mitochondria-targeting drug delivery systems are required for improving the performance of anticancer drugs.

Synthesis, Anticancer, and Antibacterial Activity of Betulinic and Betulonic Acid C-28-Triphenylphosphonium Conjugates with Variable Alkyl Linker Length.

Conjugation of triterpenoids such as betulinic acid 1 with the Triphenylphosphonium (TPP) group is a powerful approach to generating medicinal compounds. Their development proposes structure optimization in respect of availability and activity towards target cells and organelles. Selection of 1 or its precursor betulonic acid 2 and the optimal linker is of particular importance for drug candidate identification among the TPP-triterpenoid conjugates. In this study, new C-28-TPP conjugated derivatives of 1 and 2 with the alkyl/alkoxyalkyl linkers of variable length were synthesized and compared regarding their anticancer, antibacterial, and mitochondriatargeted effects. The TPP conjugates of 1 and 2 [6a-f, 7a-f] were synthesized by the reaction of halogenalkyl esters [3a-f, 4a-f, 5] with triphenylphosphine in acetonitrile upon heating. Cytotoxicity (MTT assay), antibacterial activity (microdilution assay), and mitochondrial effects (flow cytofluorometry) were studied. Conjugation with the TPP group greatly increased the cytotoxicity of the triterpenoids up to 30 times. The conjugates were up to 10-17 times more active against MCF-7 (IC50 = 0.17μM, 72h, 6c) and PC-3 (IC50 = 0.14μM, 72h, 6a) cancer cells than for human skin fibroblasts. The enhanced antibacterial (bactericidal) activity of the TPP-triterpenoid conjugates with MIC for Gram-positive bacteria as low as 2μM (6a, 7a) was for the first time revealed. The conjugates were found to effectively inhibit fluorescence of 2′,7′-dichlorofluorescin probe in the cytosol upon oxidation, decrease transmembrane potential, and increase superoxide radical level in mitochondria. Relationships between the effects and structure of the TPP-triterpenoid conjugates were evaluated and discussed. Based on the results, 6a can be selected for further preclinical investigation as a potential anticancer compound.

Mitochondrial Relocation of a Common Synthetic Antibiotic: A Non-genotoxic Approach to Cancer Therapy

Tumor recurrence as a result of therapy-induced nuclear DNA lesions is a major issue in cancer treatment. Currently, only a few examples of potentially non-genotoxic drugs have been reported. Mitochondrial re-localization of ciprofloxacin, one of the most commonly prescribed synthetic antibiotics, is reported here as a new approach. Conjugating ciprofloxacin to a triphenyl phosphonium group (giving lead Mt-CFX), is used to enhance the concentration of ciprofloxacin in the mitochondria of cancer cells. The localization of Mt-CFX to the mitochondria induces oxidative damage to proteins, mtDNA, and lipids. A large bias in favor of mtDNA damage over nDNA was seen with Mt-CFX, contrary to classic cancer chemotherapeutics. Mt-CFX was found to reduce cancer growth in a xenograft mouse model and proved to be well tolerated. Mitochondrial relocalization of antibiotics could emerge as a useful approach to generating anticancer leads that promote cell death via the selective induction of mitochondrially-mediated oxidative damage.

Novel benzoate-lipophilic cations selectively induce cell death in human colorectal cancer cell lines

IntroductionColorectal cancer (CRC) is a critical health issue worldwide. The high rate of liver and lung metastasis associated with CRC creates a significant barrier to effective and efficient therapy. Tumour cells, including CRC cells, have metabolic alterations, such as high levels of glycolytic activity, increased cell proliferation and invasiveness, and chemo- and radio-resistance. However, the abnormally elevated mitochondrial transmembrane potential of these cells also provides an opportunity to develop drugs that selectively target the mitochondrial functions of tumour cells. MethodsIn this work, we used a new batch of benzoic acid esters with cytotoxic activities attached to the triphenylphosphonium group as a vehicle to target tumour mitochondria and improve their activity. We evaluated the cytotoxicity, selectivity, and mechanism of action of these derivatives, including the effects on energy stress-induced apoptosis and metabolic behaviour in the human CRC cell lines HCT-15 and COLO-205. ResultsThe benzoic acid derivatives selectively targeted the tumour cells with high potency and efficacy. The derivatives induced the uncoupling of the oxidative phosphorylation system, decreased the transmembrane potential, and reduced ATP levels while increasing AMPK activation, thereby triggering tumour cell apoptosis in both tumour cell lines tested. ConclusionThe benzoic acid derivatives studied here are promising candidates for assessing in vivo models of CRC, despite the diverse metabolic characteristics of these tumour cells.

Complex Mitochondrial Dysfunction Induced by TPP+-Gentisic Acid and Mitochondrial Translation Inhibition by Doxycycline Evokes Synergistic Lethality in Breast Cancer Cells.

The mitochondrion has emerged as a promising therapeutic target for novel cancer treatments because of its essential role in tumorigenesis and resistance to chemotherapy. Previously, we described a natural compound, 10-((2,5-dihydroxybenzoyl)oxy)decyl) triphenylphosphonium bromide (GA-TPP+C10), with a hydroquinone scaffold that selectively targets the mitochondria of breast cancer (BC) cells by binding to the triphenylphosphonium group as a chemical chaperone; however, the mechanism of action remains unclear. In this work, we showed that GA-TPP+C10 causes time-dependent complex inhibition of the mitochondrial bioenergetics of BC cells, characterized by (1) an initial phase of mitochondrial uptake with an uncoupling effect of oxidative phosphorylation, as previously reported, (2) inhibition of Complex I-dependent respiration, and (3) a late phase of mitochondrial accumulation with inhibition of α-ketoglutarate dehydrogenase complex (αKGDHC) activity. These events led to cell cycle arrest in the G1 phase and cell death at 24 and 48 h of exposure, and the cells were rescued by the addition of the cell-penetrating metabolic intermediates l-aspartic acid β-methyl ester (mAsp) and dimethyl α-ketoglutarate (dm-KG). In addition, this unexpected blocking of mitochondrial function triggered metabolic remodeling toward glycolysis, AMPK activation, increased expression of proliferator-activated receptor gamma coactivator 1-alpha (pgc1α) and electron transport chain (ETC) component-related genes encoded by mitochondrial DNA and downregulation of the uncoupling proteins ucp3 and ucp4, suggesting an AMPK-dependent prosurvival adaptive response in cancer cells. Consistent with this finding, we showed that inhibition of mitochondrial translation with doxycycline, a broad-spectrum antibiotic that inhibits the 28 S subunit of the mitochondrial ribosome, in the presence of GA-TPP+C10 significantly reduces the mt-CO1 and VDAC protein levels and the FCCP-stimulated maximal electron flux and promotes selective and synergistic cytotoxic effects on BC cells at 24 h of treatment. Based on our results, we propose that this combined strategy based on blockage of the adaptive response induced by mitochondrial bioenergetic inhibition may have therapeutic relevance in BC.

Sequential-targeting nanocarriers with pH-controlled charge reversal for enhanced mitochondria-located photodynamic-immunotherapy of cancer

Targeting delivery of photosensitizers to mitochondria as the most sensitive cellular organelles to reactive oxygen species (ROS) by positively charged polymeric nanocarriers (NCs) is one of the useful methods for efficient photodynamic therapy (PDT). However, the NCs with positively charged mitochondria-targeting moieties are easily cleaned during circulation, restricting their in vivo applications. Herein, to address this issue and enhance in vivo PDT efficacy, we developed a sequential-targeting delivery system consisting of mitochondria-targeting micelles as the core prepared from the cationic amphiphilic copolymer for loading chlorin e6 (Ce6) and a tumor-targeting pH-dependent charge transformational layer as the shell obtained from 2,3-dimethylmaleic anhydride modified Biotin-PEG4000-NH2 (BioPEGDMA) via electrostatic interaction. Concealed by the anionic shell, the as-prepared NCs showed longer retention within the first stage of tumor-targeting. Then, the accumulated NCs conversed to positive charge in tumor extracellular microenvironment (pH ∼ 6.5), which could be more effectively internalized by tumor cells, and the re-exposed triphenylphosphonium (TPP) groups endowed their second-stage targetability to the mitochondria. In vivo experiments revealed that the Ce6-loaded NCs exhibited remarkable tumor inhibition rates of 84.1% and 93.2% on BALB/c nude mice and Kunming mice, respectively, under 660 nm NIR irradiation, and stimulated immune responses with upregulated expression of IFN-γ, TNF-α and CD3+ in tumor tissues, and enhanced activation of CD3+/CD4+, CD3+/CD8+ T lymphocytes and DCs in both tumor tissues and lymph glands. This work provided a new pathway for the development of smart drug delivery system with advanced PDT efficacy. Statement of significanceAlthough the existing targeting delivery of photosensitizers to mitochondria by positively charged nanocarriers (NCs) have efficiently enhanced photodynamic therapy (PDT), their positive charges caused rapid clearance during circulation, which has restricted their in vivo applications. Therefore, we fabricated a novel sequential-targeting NC to solve the problem. The tumor accumulated NCs conversed to positive charge in tumor extracellular microenvironment, and the re-exposed triphenylphosphonium groups initiated second-stage targetability to mitochondria. This system exhibited remarkable tumor inhibition efficiency both in vitro and in vivo. Moreover, as we hypothesized, mitochondria-located PDT could promote immune response, resulting in improvement of PDT. The strategy of sequential targeting-based PDT in combination with augmented immune response showed a novel pathway for the development of smart drug delivery system with advanced PDT.

Triphenylphosphonium Analogues of Betulin and Betulinic Acid with Biological Activity: A Comprehensive Review.

Naturally occurring pentacyclic lupane triterpenoids such as betulin (1) or betulinic acid (2) and their synthetic derivatives display a broad spectrum of biological activities and, therefore, have been the subject of great interest. However, the use of these compounds as potential therapeutic agents is limited by their low bioavailability, high hydrophobicity, and insufficient intracellular accumulation. In this context, research on modifications of the parent structures that will improve their pharmacokinetic properties is particularly important. In the past few years, methods of synthesis as well as cytotoxic and antiparasitic properties of a series of lupane triterpenoids modified by introducing one or two triphenylphosphonium moieties at the C-2, C-3, C-28, or C-30 positions by carbon-carbon or ester bonds have been described. The presence of triphenylphosphonium groups affects not only physical properties but also the mechanism of action of a potential drug. This review summarizes published findings on synthetic methods and biological properties of the triphenylphosphonium derivatives of betulin and betulinic acid.

Triphenylphosphonium-Derived Protein Sulfenic Acid Trapping Agents: Synthesis, Reactivity, and Effect on Mitochondrial Function.

Redox-mediated protein modifications control numerous processes in both normal and disease metabolism. Protein sulfenic acids, formed from the oxidation of protein cysteine residues, play a critical role in thiol-based redox signaling. The reactivity of protein sulfenic acids requires their identification through chemical trapping, and this paper describes the use of the triphenylphosphonium (TPP) ion to direct known sulfenic acid traps to the mitochondria, a verified source of cellular reactive oxygen species. Coupling of the TPP group with the 2,4-(dioxocyclohexyl)propoxy (DCP) unit and the bicyclo[6.1.0]nonyne (BCN) group produces two new probes, DCP-TPP and BCN-TPP. DCP-TPP and BCN-TPP react with C165A AhpC-SOH, a model protein sulfenic acid, to form the expected adducts with second-order rate constants of k = 1.1 M-1 s-1 and k = 5.99 M-1 s-1, respectively, as determined by electrospray ionization time-of-flight mass spectrometry. The TPP group does not alter the rate of DCP-TPP reaction with protein sulfenic acid compared to dimedone but slows the rate of BCN-TPP reaction compared to a non-TPP-containing BCN-OH control by 4.6-fold. The hydrophobic TPP group may interact with the protein, preventing an optimal reaction orientation for BCN-TPP. Unlike BCN-OH, BCN-TPP does not react with the protein persulfide, C165A AhpC-SSH. Extracellular flux measurements using A549 cells show that DCP-TPP and BCN-TPP influence mitochondrial energetics, with BCN-TPP producing a drastic decrease in basal respiration, perhaps due to its faster reaction kinetics with sulfenylated proteins. Further control experiments with BCN-OH, TPP-COOH, and dimedone provide strong evidence for mitochondrial localization and accumulation of DCP-TPP and BCN-TPP. These results reveal the compatibility of the TPP group with reactive sulfenic acid probes as a mitochondrial director and support the use of the TPP group in the design of sulfenic acid traps.

Hydrophilic, Red-Emitting, and Thermally Activated Delayed Fluorescence Emitter for Time-Resolved Luminescence Imaging by Mitochondrion-Induced Aggregation in Living Cells.

Thermally activated delayed fluorescence (TADF) materials have provided new strategies for time‐resolved luminescence imaging (TRLI); however, the development of hydrophilic TADF luminophores for specific imaging in cells remains a substantial challenge. In this study, a mitochondria‐induced aggregation strategy for TRLI is proposed with the design and utilization of the hydrophilic TADF luminophore ((10‐(1,3‐dioxo‐2‐phenyl‐2,3‐dihydro‐1H‐benzo[de]isoquinolin‐6‐yl)‐9,9‐dimethyl‐9,10‐dihydroacridin‐2‐yl)methyl)triphenylphosphonium bromide (NID‐TPP). Using a nonconjugated linker to introduce a triphenylphosphonium (TPP+) group into the 6‐(9,9‐dimethylacridin‐10(9H)‐yl)‐2‐phenyl‐1H‐benzo[de]isoquinoline‐1,3(2H)‐dione (NID) TADF luminophore preserves the TADF emission of NID‐TPP. NID‐TPP shows clear aggregation‐induced delayed fluorescence enhancement behavior, which provides a practical strategy for long‐lived delayed fluorescence emission in an oxygen‐containing environment. Finally, the designed mitochondrion‐targeting TPP+ group in NID‐TPP induces the adequate accumulation of NID‐TPP and results in the first reported TADF‐based time‐resolved luminescence imaging and two‐photon imaging of mitochondria in living cells.

Effect of triphenylphosphonium moiety on spatial structure and biointeractions of stereochemical variants of YRFK motif.

Chemical modification of therapeutic peptides is an important approach to improving their physicochemical and pharmacokinetic properties. The triphenylphosphonium (TPP) cation has proved to be a powerful modifier; however, its effects on peptide structure and activity remain uncharacterized. In this study, cytoprotective tetrapeptides based on the YRFK opioid motif with L- or D-Arg residues were linked to (triphenylphosphonio)carboxylic acids with ethylene and pentylene spacers (TPP-3 and TPP-6 groups, respectively). The three-dimensional structure of the oligopeptides was analyzed by NMR spectroscopy, computational methods and circular dichroism (CD). A more compact and bent structure with segregated aromatic groups was revealed for the D-arginine-containing tetrapeptide and its TPP-6 derivative. The TPP moiety caused structure-organizing effect on the tetrapeptides, resulting in transition from random coil to β-sheet structures, and decreased the peptide backbone flexibility up to ten times. The TPP-3-modified oligopeptide with the lowest RMSD value (ca. 0.05Å) was characterized by intrapeptide hydrophobic interactions between the TPP and side groups of Tyr and Phe residues accompanied by strong CD induction. The TPP-6-modified oligopeptides showed enhanced ability to form intermolecular associates and disturb liposomal membranes. The relationship between the spatial structure of the oligopeptides and some of their biologically relevant interactions were additionally revealed and are discussed.

Dual-Mode Imaging Guided Multifunctional Theranosomes with Mitochondria Targeting for Photothermally Controlled and Enhanced Photodynamic Therapy in Vitro and in Vivo.

Photodynamic therapy (PDT) is commonly restricted by inefficient tumor selectivity during clinical study. Hence, a mitochondria-targeting multifunctional nanocarrier "theranosome (TNS)" was developed for near-infrared fluorescent (NIRF) imaging and photoacoustic (PA) imaging. What's more, the TNS can also enhance PDT efficacy. In this work, chlorin e6 (Ce6) undertakes reactive oxygen generation and fluorescence emission. Ce6 was quenched when being encapsulated into TNS together with IR780 iodide. When exposed under 808 nm NIR light, IR780 from the TNS can be photobleached; thus, the phototoxicity of Ce6 can be activated. The IR780 induced hyperthermia damaged tumor cells to perform photothermal therapy (PTT) effect. Then lysosomes disruption under PTT facilitated PDT effect induced by Ce6 through enhanced cytoplasmic delivery. Moreover, in vitro subcellular uptake experiments showed that triphenylphosphonium (TPP) group attached to the IR780/Ce6 TNS (ICT) could promote mitochondria targeting capacity. It can lead to PDT induced oxidizing damage to the mitochondria by mitochondrial membrane potential decreasing and cell apoptosis eventually. In in vivo antitumor studies, the TPP/IR780/Ce6 TNS (TICT) substantially repressed tumor growth in nude mice. Besides, we did not find any obvious side effects to normal tissues and organs. The results suggested the TICT conjugate provided a dual NIRF/PA tumor imaging modalities with spatial resolution and superior imaging contrast. This study offered an improved phototherapy for potential theranostic application.