Targeting and Imaging of Mitochondria Using Near-Infrared Cyanine Dye and Its Application to Multicolor Imaging

Water-Soluble Small Organic Fluorophores for Oncological Theragnostic Applications: Progress and Development

Cancer is one of the major noncommunicable diseases, responsible for millions of deaths every year worldwide. Though various cancer detection and treatment modalities are available today, many deaths occur owing to its late-stage detection and metastatic nature. Noninvasive detection using luminescence-based imaging tools is considered one of the promising techniques owing to its low cost, high sensitivity, and brightness. Moreover, these tools are unique and valuable as they can detect even the slightest changes in the cellular microenvironment. To achieve this, a fluorescent probe with strong tumor uptake and high spatial and temporal resolution, especially with high water solubility, is highly demanded. Recently, several water-soluble molecules with emission windows in the visible (400-700 nm), first near-infrared (NIR-I, 700-1000 nm), and second near-infrared (NIR-II, 1000-1700 nm) windows have been reported in literature. This review highlights recently reported water-soluble small organic fluorophores/dyes with applications in cancer diagnosis and therapeutics. We systematically highlight and describe the key concepts, structural classes of fluorophores, strategies for imparting water solubility, and applications in cancer therapy and diagnosis, i.e., theragnostics. We discuss examples of water-soluble fluorescent probes based on coumarin, xanthene, boron-dipyrromethene (BODIPY), and cyanine cores. Some other emerging classes of dyes based on carbocyclic and heterocyclic cores are also discussed. Besides, emerging molecular engineering methods to obtain such fluorophores are discussed. Finally, the opportunities and challenges in this research area are also delineated.

A New Phenothiazine-Based Fluorescent Sensor for Detection of Cyanide

A new fluorescent sensor for the detection of CN- was developed based on the conjugation of phenothiazine fluorophore and benzofuran unit. By the nucleophilic attacking of CN- to the fluoroacetylamino group in the sensor, the additional reaction of CN- and carbonyl group induced the ICT (intramolecular charge transfer) effect in the molecule and caused the fluorescence quenching sensor. The titration experiments show that the sensor has good sensitivity, selectivity and quick response for CN-. In addition, the fluorescent detection of CN- in the living cell and zebrafish experiments demonstrated the value of the sensor in tracing the CN- in biological systems.

Combination of quinoxaline with pentamethinium system: Mitochondrial staining and targeting

Pentamethinium indolium salts are promising fluorescence probes and anticancer agents with high mitochondrial selectivity. We synthesized two indolium pentamethinium salts: a cyclic form with quinoxaline directly incorporated in the pentamethinium chain (cPMS) and an open form with quinoxaline substitution in the γ-position (oPMS). To better understand their properties, we studied their interaction with mitochondrial phospholipids (cardiolipin and phosphatidylcholine) by spectroscopic methods (UV-Vis, fluorescence, and NMR spectroscopy). Both compounds displayed significant affinity for cardiolipin and phosphatidylcholine, which was associated with a strong change in their UV-Vis spectra. Nevertheless, we surprisingly observed that fluorescence properties of cPMS changed in complex with both cardiolipin and phosphatidylcholine, whereas those of oPMS only changed in complex with cardiolipin. Both salts, especially cPMS, display high usability in mitochondrial imaging and are cytotoxic for cancer cells. The above clearly indicates that conjugates of pentamethinium and quinoxaline group, especially cPMS, represent promising structural motifs for designing mitochondrial-specific agents.

Leptin Mediates Prostate Stromal Cell Proliferation, Smooth Muscle Contraction, and Mitochondrial Function in Benign Prostate Hyperplasia

Introduction

Leptin is a metabolic peptide hormone produced by adipocytes, with proven roles in proliferation of prostate cancer cells and of prostate cells in animal models of benign prostatic hyperplasia (BPH). Thus, the role of leptin as a molecular link connecting BPH and lower urinary tract symptoms (LUTS) suggestive of BPH with metabolic symptoms appears feasible but is still unknown. In fact, a connection between metabolic syndrome and BPH is becoming increasingly evident from epidemiologic studies. Key factors of Lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH/LUTS) are increased prostate smooth muscle tone, and prostate enlargement. Here, we examined the effects of leptin on contraction of human prostate smooth muscle and on growth of stromal cells.

Methods

We performed microarray analysis to identify genes (fold change ≥ 1.5) associated with BPH/LUTS progression, such as those involved in proliferation, apoptosis, and mitochondrial metabolism, in rat prostate tissue (data from GSE129561). We then used electric field stimulation (EFS) to induce frequency-dependent, neurogenic contractions of human prostate strips, which were enhanced by leptin. We also examined the effect of leptin on human prostate stromal cells (WPMY-1) and found increased cell proliferation and viability upon exposure. To explore the underlying mechanism, we conducted mitochondrial stress assay using near-infrared (NIR) fluorescent dye and flow cytometry (FACS) analysis and observed reduced cellular apoptosis and preserved mitochondrial membrane potential (∆ψM) after leptin treatment.

Results

Microarray analysis reveals that leptin regulates prostate smooth muscle contraction and stromal cell proliferation, shedding new light on its involvement in BPH/LUTS pathogenesis and mitochondrial function. We found that leptin enhanced the proliferation rate of prostate stromal cells relative to the control group (0.67 ± 0.05 vs 0.54 ± 0.08, p-value= 0.024). Moreover, leptin (100 ng/mL) potentiated the frequency-dependent, neurogenic contractions of prostate strips elicited by EFS (p= 0.047 between leptin and control group). We also show that leptin treatment increased the mitochondrial membrane potential of prostate stromal cells and inhibited mitochondrial apoptosis.

Discussion

Our results indicate that leptin stimulates the contractility and proliferation of smooth muscle and stromal cells in the human prostate, implying a potential role for leptin in exacerbating BPH/LUTS in obese men. Leptin modulation may be a beneficial therapeutic strategy for patients with metabolic syndrome and BPH/LUTS. Further studies are warranted to elucidate the mechanisms and implications of the leptin system in BPH/LUTS.

A cyanine-based NIR fluorescent Vemurafenib analog to probe BRAFV600E in cancer cells

BRAF represents one of the most frequently mutated protein kinase genes and BRAF^V600E mutation may be found in many types of cancer, including hairy cell leukemia (HCL), anaplastic thyroid cancer (ATC), colorectal cancer and melanoma. Herein, a fluorescent probe, based on the structure of the highly specific BRAF^V600E inhibitor Vemurafenib (Vem, 1) and featuring the NIR fluorophore cyanine-5 (Cy5), was straightforwardly synthesized and characterized (Vem-L-Cy5, 3), showing promising spectroscopic properties. Biological validation in BRAF^V600E-mutated cancer cells evidenced the ability of 3 to penetrate inside the cells, specifically binding to its elective target BRAF^V600E with high affinity, and inhibiting MEK phosphorylation and cell growth with a potency comparable to that of native Vem 1. Taken together, these data highlight Vem-L-Cy5 3 as a useful tool to probe BRAF^V600E mutation in cancer cells, and suitable to acquire precious insights for future developments of more informed BRAF inhibitors-centered therapeutic strategies.

Effect of Solubilizing Group on the Antibacterial Activity of Heptamethine Cyanine Photosensitizers

Antibiotic resistance of pathogenic bacteria dictates the development of novel treatment modalities such as antimicrobial photodynamic therapy (APDT) utilizing organic dyes termed photosensitizers that exhibit a high cytotoxicity upon light irradiation. Most of the clinically approved photosensitizers are porphyrins that are poorly excitable in the therapeutic near-IR spectral range. In contrast, cyanine dyes function well in the near-IR region, but their phototoxicity, in general, is very low. The introduction of iodine atoms in the cyanine molecules was recently demonstrated to greatly increase their phototoxicity. Herein, we synthesized a series of the new iodinated heptamethine cyanine dyes (ICy7) containing various solubilizing moieties, i.e., negatively charged carboxylic (ICy7COOH) and sulfonic (ICy7SO₃H) groups, positively charged triphenylphosphonium (ICy7PPh₃), triethylammonium (ICy7NEt₃) and amino (ICy7NH₂) groups, and neutral amide (ICy7CONHPr) group. The effect of these substituents on the photodynamic eradication of Gram-positive (S. aureus) and Gram-negative (E. coli and P. aeruginosa) pathogens was studied. Cyanine dyes containing the amide and triphenylphosphonium groups were found to be the most efficient for eradication of the investigated bacteria. These dyes are effective at low concentrations of 0.05 µM (33 J/cm²) for S. aureus, 50 µM (200 J/cm²) for E. coli, and 5 µM (100 J/cm²) for P. aeruginosa and considered, therefore, promising photosensitizers for APDT applications. The innovation of the new photosensitizers consisted of a combination of the heavy-atom effect that increases singlet oxygen generation with the solubilizing group's effect improving cell uptake, and with effective near-IR excitation. Such a combination helped to noticeably increase the APDT efficacy and should pave the way for the development of more advanced photosensitizers for clinical use.

Mitochondrial Targeting and Imaging with Small Organic Conjugated Fluorophores: A Review

The last decade has seen an increasingly large number of studies reporting on the development of novel small organic conjugated systems for mitochondrial imaging exploiting optical signal transduction pathways. Mitochondria are known to play a critical role in a number of key biological processes, including cellular metabolism. Importantly, irregularities on their working function are nowadays understood to be intimately linked to a range of clinical conditions, highlighting the importance of targeting mitochondria for therapeutic benefits. In this work we carry out an in-depth evaluation on the progress to date in the field to pave the way for the realization of superior alternatives to those currently existing. The manuscript is structured by commonly used chemical scaffolds and comprehensively covers key aspects factored in design strategies such as synthetic approaches as well as photophysical and biological characterization, to foster collaborative work among organic and physical chemists as well as cell biologists.

A novel active mitochondrion-selective fluorescent probe for the NIR fluorescence imaging and targeted photodynamic therapy of gastric cancer

The annual morbidity and mortality due to gastric cancer are still high across the world, posing a serious threat to public health. Improving the diagnosis rate of gastric cancer and exploring new treatments are urgent issues in the clinical field. In recent years, photosensitizer (PS)-based photodynamic therapy (PDT) has proven to be an effective cancer treatment strategy and can be used to treat a variety of cancers. Developing PSs with tumor-targeting ability and high singlet oxygen yield (Φ(¹O₂)) is the key to improving the PDT effect. Herein, we developed a novel diagnosis and treatment system (Cy₁₃₉₅-NPs). Our active thio-photosensitizer is based on the sulfur substitution strategy as it can reduce the S1-T1 energy gap, which can promote the process of intersystem crossing (ISC), thus resulting in high ROS generation efficiency. Cy₁₃₉₅-NPs exhibited stable spectral characteristics, satisfactory biocompatibility and high ¹O₂ yield under laser irradiation due to the introduction of the sulfur atom. In cellular studies, Cy₁₃₉₅-NPs could specifically target MKN45 cells via integrin α_vβ₃-mediated cRGD endocytosis and selectively aggregate in the mitochondria. Cy₁₃₉₅-NPs had no obvious cytotoxicity for MKN45 cells and exerted obvious phototoxicity due to the production of ¹O₂ under laser irradiation. The in vivo results showed that the fluorescence signal from the tumor site was obviously enhanced in 16-48 h, and Cy₁₃₉₅-NPs could selectively target solid tumors with a retention time of about 32 h. Under laser irradiation, Cy₁₃₉₅-NPs significantly inhibited tumor growth and led to significant tumor suppression and apoptosis. In summary, the developed Cy₁₃₉₅-NPs could actively target tumors and exert mitochondrial selectivity, showing an excellent fluorescence imaging effect. Under the irradiation of an 808 nm laser, Cy₁₃₉₅-NPs achieved good inhibition of gastric cancer cells both in vitro and in vivo, thus displaying the functions of tumor targeting, mitochondrial selectivity, fluorescence imaging and tumor inhibition. Our strategy provides a new diagnostic and treatment method for gastric cancers in clinical settings.

Recent advances in bioprobes and biolabels based on cyanine dyes

As a functional dye, cyanine dye promotes the widespread application of bioprobes in the fields of medicine, genetics and environment, owing to its advantages of good photophysical properties, excellent biocompatibility and low toxicity to biological systems. Nowadays, it is mainly used in the fields of life sciences such as fluorescent labeling of biological macromolecules, disease diagnosis, immunoassay and DNA detection, all of which lie at the core of this review. First, we briefly introduced the characteristics and principles of the cyanine dye bioprobe. Afterward, we paid attention to the recent progress of cyanine dye bioprobes widely used in the 10 years from 2010 to 2020. The application of cyanine dyes as bioprobes with different identification elements, including enzymes, organelles, immunity and DNAs, was mainly summarized. Finally, this review gave an outlook on the future development trend of cyanine dye bioprobes. This facilitates the construction of a new type of multifunctional fluorescent probe and promotes its clinical application.

Deep-red fluorogenic cyanine dyes carrying an amino group-terminated side chain for improved RNA detection and nucleolar RNA imaging

The introduction of an amino-group-terminated side chain into deep-red emissive benzo[c,d]indole–quinoline monomethine cyanine dye has led to the improved detection of RNAs as well as the imaging of nucleolar RNAs in cells.

The introduction of an amino-group-terminated side chain into deep-red emissive benzo[c,d]indole–quinoline monomethine cyanine dye has led to the improved detection of RNAs as well as the imaging of nucleolar RNAs in cells.

Fluorescent Materials for Monitoring Mitochondrial Biology

Mitochondria play important roles in diverse cellular processes such as energy production, cellular metabolism, and apoptosis to promote cell death. To investigate mitochondria-associated biological processes such as structure, dynamics, morphological change, metabolism, and mitophagy, there exists a continuous demand for visualizing and monitoring techniques elucidating mitochondrial biology and disease-relevancy. Due to the advantages of high sensitivity and practicality, fluorescence phenomena have been most widely used as scientific techniques for the visualization of biological phenomena and systems. In this review, we briefly overview the different types of fluorescent materials such as chemical probes, peptide- or protein-based probes, and nanomaterials for monitoring mitochondrial biology.

Nucleus-targeting imaging and enhanced cytotoxicity based on naphthalimide derivatives

Organelles possess critical biological effects in cellular processes. However, the relationship between organelle targeting and antitumour activity is a challenging issue. In this paper, a number of amide/acylhydrazine modified naphthalimide derivatives were designed and synthesized. Interestingly, amide modified naphthalimide derivatives NI-A-NH and NI-C-NH with (R)-piperdine and (S)-pyrrolidine functionalization exhibited enhanced cytotoxicity compared with acylhydrazine modified derivatives NI-A-2NH and NI-C-2NH. However, acylhydrazine modified derivatives NI-B-2NH and NI-D-2NH with (S)-piperdine and achiral piperdine conjugates possessed better cytotoxicity than NI-B-NH and NI-D-NH with amide modifications. Fluorescence imaging, DNA binding interactions and cell cycle analyses were further completed to clarify that the nucleus-targeting effects showed enhanced cytotoxic activity, strong DNA binding and the blocking of cells in S phase. These results provide a preliminary theoretical basis for the further design of organelle-targeting antitumour drugs.

Aggregation induced emission (AIE) materials for mitochondria imaging

Mitochondria are energy producing organelle of the eukaryotic cells. The main activities of mitochondria monitored by various marker molecules are autophagy detection, estimation of Reactive Oxygen Species (ROS), mitochondrial death and Photodynamic therapy in cancer cells. Due to the advantages of specificity and sensitivity, aggregation induced emission (AIE) is now popular for the mitochondria labeling. In this chapter, we would like to discuss three major types of AIEgens probe used in mitochondrial staining. There are three different types of AIEgens available for mitochondrial detection and sensing based on their different structural motifs. The first type of AIEgens is tetraphenylethene (TPE) based molecules. Due to simple engineering architecture, TPE based AIEgens are widely employed in bioimaging applications. AIEgen such as triphenylphosphine (TPP), and triphenylamine (TPA) are also employed as a novel building block. These are successfully used as exceptional lipid droplet (LD)-specific bio probes in cell imaging, assurance of cell combination, and photodynamic cancer cell removal. The third group is the miscellaneous AIEgens probe involved in mitochondria imaging.

Autophagy-Dependent Sensitization of Triple-Negative Breast Cancer Models to Topoisomerase II Poisons by Inhibition of the Nucleosome Remodeling Factor

Epigenetic regulators can modulate the effects of cancer therapeutics. To further these observations, we discovered that the bromodomain PHD finger transcription factor subunit (BPTF) of the nucleosome remodeling factor (NURF) promotes resistance to doxorubicin, etoposide, and paclitaxel in the 4T1 breast tumor cell line. BPTF functions in promoting resistance to doxorubicin and etoposide, but not paclitaxel, and may be selective to cancer cells, as a similar effect was not observed in embryonic stem cells. Sensitization to doxorubicin and etoposide with BPTF knockdown (KD) was associated with increased DNA damage, topoisomerase II (TOP2) crosslinking and autophagy; however, there was only a modest increase in apoptosis and no increase in senescence. Sensitization to doxorubicin was confirmed in vivo with the syngeneic 4T1 breast tumor model using both genetic and pharmacologic inhibition of BPTF. The effects of BPTF inhibition in vivo are autophagy dependent, based on genetic autophagy inhibition. Finally, treatment of 4T1, 66cl4, 4T07, MDA-MB-231, but not ER-positive 67NR and MCF7 breast cancer cells with the selective BPTF bromodomain inhibitor, AU1, recapitulates genetic BPTF inhibition, including in vitro sensitization to doxorubicin, increased TOP2-DNA crosslinks and DNA damage. Taken together, these studies demonstrate that BPTF provides resistance to the antitumor activity of TOP2 poisons, preventing the resolution of TOP2 crosslinking and associated autophagy. These studies suggest that BPTF can be targeted with small-molecule inhibitors to enhance the effectiveness of TOP2-targeted cancer chemotherapeutic drugs. IMPLICATIONS: These studies suggest NURF can be inhibited pharmacologically as a viable strategy to improve chemotherapy effectiveness.

Synthesis of novel cyanine dyes as antitumor agents

In this study, some novel cyanine dyes, 1, 3, and 5-15, were synthesized by a one-pot step reaction of pyridinium salts 2 and/or 4 with benzenaminium salt 1. N-{[1-Chloro-3,4-dihydronaphthalen-2-yl)methylene]benzenaminium} chloride 1 was obtained by the reaction of α-tetralone with Vilsmeier-Haack reagent, followed by a mixture of an equimolar ratio of anilin/ethanol (1:1). All new cyanine dyes were evaluated in vitro for their anticancer activity against two cell lines, that is, HepG2 (human hepatocellular liver carcinoma) and MCF-7 (breast cancer). The obtained results were compared with human lung fibroblasts (WI-38) and Vero cells (derived from the kidney of an African green monkey) as normal cells. In particular, some of these compounds, 6, 9, 13, and 14, were found to be the most potent derivatives against all the cancer cell lines, without effect on the normal cells. According to the structure-activity relationship, compound 13 (IC₅₀  = 8.8 µg/ml) exhibited a higher activity against HepG2 cells, as it contains the azo group and two phenyl rings and due to the presence of the π-conjugated system attached to the two pyridine rings. Compound 6 (IC₅₀  = 8 µg/ml) exhibited a higher activity against MCF-7 cells, as it contains two chlorine atoms and the π-conjugated system of the pyridine rings.

Fluorescence-based quantitative platform for ultrasensitive food allergen detection: From immunoassays to DNA sensors

Food allergies are global health issue with an increasing prevalence that affect food safety; hence, food allergen detection, labeling, and management are considered to be important priorities in the food industry. In this critical review, we provide a comprehensive overview of several fluorescence-based platforms based on different biorecognition ligands, such as antibodies, DNA, aptamers, and cells, for food allergen quantification. Traditional analytical methods are generally unsuitable for food manufacturers to accomplish the real-time identification of food allergens in food products. Therefore, it is important to develop simple, rapid, inexpensive, accurate, and sensitive methods to improve user accessibility. A fluorescence-based quantitative platform provides an excellent detection platform for food allergens because of its high sensitivity. This review summarizes the traditional antibody-based fluorescent techniques for food allergen detection, such as the time-resolved fluoroimmunoassay , immunofluorescence imaging, fluorescence enzyme-linked immune sorbent assay, flow injection fluoroimmunoassay, and fluorescence immunosensors. However, these methods suffer from disadvantages such as the significant rate of false-positive and false-negative results due to antibody cross-reactivity with nontarget food components in the complex food matrix and epitope degradation during food processing. Hence, different types of fluorescence-based immunoassays are suitable for standardization and quantification of allergens in fresh foods. In addition, we summarize new fluorescence-based quantitative platforms, including fluorescence genosensors, fluorescence cell sensors, and fluorescence aptamer sensors. With the advantages of high sensitivity and simple operation, fluorescence biosensors will have great potential in the future and could provide portable methods for multiallergen real-time detection in complex food systems.

PEGylated Bis-Quaternary Triphenyl-Phosphonium Tosylate Allows for Balanced Antibacterial Activity and Cytotoxicity

Quaternary triphenylphosphonium compounds (TPP⁺) have been widely recognized as an important antimicrobial because of their fast antimicrobial speed and broad antimicrobial spectrum. However, small-molecule TPP⁺ compounds have the defects of toxicity, which is the key factor that limits their practical applications. Here, two mono- and one bis-quaternary phosphonium tosylate compounds with different lengths of oligo(ethylene glycol) (OEG) chains and TPP⁺ as the active moiety were synthesized. Bis-TPP⁺ have a short OEG chain coupling two TPP⁺ at both ends, while mono-TPP⁺ attaches the OEG chain at one end in one molecule. In vitro antibacterial activities were evaluated against both Gram-positive as well as Gram-negative bacteria in terms of the inhibition zone (ZOI) and minimum inhibitory concentration (MIC). To investigate the antibacterial mechanism, β-galactosidase activity was monitored for measuring the degree of membrane permeability correlated to the abilities to disrupt the membranes of bacteria. Moreover, their structure-antibacterial activity and structure-cytotoxicity relationships were further analyzed. The results indicated that bis-TPP⁺ synthesized can reach the sterilization rate 90% or more against Escherichia coli and Staphylococcus aureus at MICs of 3.1 and 1.5 mg/mL, respectively, and meanwhile, the cell proliferation can reach more than 80%. This paper represents an excellent approach for development of bis-TPP⁺ bactericidal molecules that would achieve an optimal balance between antimicrobial activity and cytotoxicity.

Mitochondria-Targeting Organic Nanoparticles for Enhanced Photodynamic/Photothermal Therapy

Organelle-targeting techniques have been proved to be promising approaches for enhanced cancer treatment, especially phototherapy, because it can greatly improve the efficiency of photosensitizers. In this work, we designed and synthesized a mitochondria-targeting diketopyrrolopyrrole-based photosensitizer (DPP2+) for synergistic photodynamic/photothermal therapy upon irradiation. The obtained mitochondria-targeting nanoparticles (DPP2+ NPs) could produce thermal energy and singlet oxygen under 635 nm laser irradiation with ideal cytocompatibility. Importantly, DPP2+ NPs are more likely to enter the cells and target mitochondria. In in vitro and in vivo antitumor experiments, DPP2+ NPs showed highly effective antitumor effects, suggesting that mitochondria-targeting photosensitizers have potential for cancer treatment. The present work provides an alternative strategy to mitochondria-targeting molecular engineering and highlights the potential of organic nanomaterials in biomedical fields and cancer treatment.

Incorporating Thiourea into Fluorescent Probes: A Reliable Strategy for Mitochondrion-Targeted Imaging and Superoxide Anion Tracking in Living Cells

Three aggregation-induced emission active fluorescent compounds, TPA-Pyr-Octane, TPA-Pyr-Br, and TPA-Pyr-Thiourea (TPA = triphenylamine pyridinium), are synthesized; their tiny differences in chemical structures result in a huge difference in cell-imaging applications. Especially, incorporating thiourea into fluorescent probes is found as a reliable strategy for mitochondrion-targeted imaging and superoxide anion tracking in living cells, which is possibly due to the presence of hydrogen bonding between thiourea and mitochondrion proteins. This finding is very useful for the design of biosensors and delivery carriers in disease treatment.

GSH-Activatable NIR Nanoplatform with Mitochondria Targeting for Enhancing Tumor-Specific Therapy

Developing smart photosensitizers that are sensitive to tumor-specific signals for minimal side effects and enhanced antitumor efficacy is a tremendous challenge for tumor phototherapies. Herein, we construct a nanoplatform with glutathione (GSH)-activatable and mitochondria-targeted pro-photosensitizer encapsulated by ultrasensitive pH-responsive polymer for achieving imaging-guided tumor-specific photodynamic therapy (PDT). The GSH-activatable pro-photosensitizer, di-cyanine (DCy7), has been synthesized where two cyanine moieties are covalently conjugated by a disulfide bond, and the hydrophobic DCy7 is further encapsulated with an amphiphilic pH-responsive diblock copolymer POEGMA-b-PDPA to form P@DCy7 nanoparticles. Upon endocytosis by cancer cells, P@DCy7 nanoparticles dissociate at endosome first and then DCy7 is released to cytoplasm and subsequently activated by the high concentration of GSH, finally targets mitochondria for organelle-targeted PDT. Moreover, intracellular antioxidant GSH is consumed during the activation procedure that is beneficial to efficient PDT. These P@DCy7 nanoparticles display selective phototoxicity against tumor cells (HepG2 or 4T1 cells) over normal cells (BEAS-2B cells) in vitro, and their GSH-activatable enhanced PDT efficacy is further confirmed in tumor-bearing mice. Thus, P@DCy7 nanoparticles allow for accurate and highly efficient PDT with minimal side effects, providing an attractive nanoplatform for organelle-targeted precise PDT.