Reactive Reductive Species Participating Photodynamic Therapy for Cancer Treatment.

Although the development of oxidative photodynamic therapy (O-PDT) based on reactive oxygen species (ROS) has led to great progress in cancer treatment, tumor hypoxia, cellular adaptation and intrinsic antioxidant defenses are still obstacles at this stage. Fortunately, with the discovery and development of reactive reductive species (RRS) in the PDT process, reductive PDT (R-PDT) is receiving increasing research interest. R-PDT with oxygen-independence is an effective reduction therapy that promises excellent therapeutic efficacy in extremely hypoxic or even anaerobic environments. In the concept, we introduce representative strategies to boost the type-I photosensitizing pathway, and then focus on the most recent R-PDT involving hydrogen radical (H⋅) and the single electron transfer (SET) process.

Photoluminescent Properties and Mechanism of Novel Cyanine-Borondifluoride Curcuminoid Hybrids as Red-to-Near Infrared and Endoplasmic Reticulum-Targeting Dyes.

Synthesis-oriented design led us to the discovery of a series of novel cyanine-borondifluoride curcuminoid hybrids called Nanchang Red (NCR) dyes that overcome the intrinsic low synthetic yields of symmetrical cyanine-difluoroboronate (BF2 )-hybridized NIR dyes. The hybridization endows NCR dyes with high molar extinction coefficients, efficient red-to-NIR emission, and enlarged Stokes shifts. Quantum chemical calculations revealed that the asymmetrical layout of the three key electron-withdrawing and electron-donating fragments results in a special pattern of partial charge separation and inconsistent degrees of charge delocalization on their π-conjugated backbones. While the nature of the hemicyanine fragment exerts significant influence on the excitation modes of NCR dyes, the borondifluoride hemicurcuminoid fragment is the major contributor to the enlarged Stokes shifts. Cell imaging experiments illustrated that a subtle change in the N-heterocycle of the hemicyanine fragment has a remarkable effect on the subcellular localization of NCR dyes. Unlike other previously reported cyanine-BF2 hybridized dyes, which mainly target mitochondria, the benzothiazole and indole-based NCR dyes accumulate in both the endoplasmic reticulum (ER) and lipid droplets of HeLa cells, whereas the benzoxazole and quinoline-based NCR dyes stain the ER specifically.

Photocatalytic Generation of Hydrogen Radical (H⋠) with GSH for Photodynamic Therapy.

As a reactive hydrogen species, the hydrogen radical (H⋅) scarcely sees applications in tumor biological therapy due to the very limited bio-friendly sources of H⋅. In this work, we report that TAF can act as an organic photosensitizer as well as an efficient photocatalytic H⋅ generator with reduced glutathione (GSH) as a fuel. The photoactivation of TAF leads to cell death in two ways including triple amplification of oxidative stress via ferroptosis-apoptosis under normoxia and apoptosis through biological reductions under hypoxia. TAF presents excellent biosafety with ultrahigh photocytotoxicity index at an order of magnitude of 102 -103 on both normoxic and hypoxic cells. The in vitro data suggest that H⋅ therapy is promising to overcome the challenge of tumor hypoxia at low doses of both photocatalyst and light. In addition, the capability of near-infrared two-photon excitation would benefit broad biological applications.

Dithiol-Activated Bioorthogonal Chemistry for Endoplasmic Reticulum-Targeted Synergistic Chemophototherapy.

The controlled intracellular release of nitrite is still an unmet challenge due to the lack of bio-friendly donors, and the antitumor effect of nitrite is limited by its physiologically inert activity. Herein, we designed benzothiadiazole-based organic nitrite donors that are stable against bio-relevant species but selectively respond to dithiol species through SN Ar/intramolecular cyclization tandem reactions in the aqueous media. The bioorthogonal system was established to target the endoplasmic reticulum (ER) of liver cancer HepG2 cells. The nitrite and nonivamide were coupled to induce elevation of intracellular levels of calcium ions as well as reactive oxygen/nitrogen species, which resulted in ER stress and mitochondrial dysfunction. We demonstrated that a combination of photoactivation and "click to release" strategy could enhance antitumor effect in cellular level and show good potential for cancer precision therapy.

Intrinsic Mitochondrial Reactive Oxygen Species (ROS) Activate the In†Situ Synthesis of Trimethine Cyanines in Cancer Cells.

Environment-responsive in situ synthesis of molecular fluorescent dyes is challenging. Herein, we develop a photoextension strategy to make trimethine cyanines with decent conversion efficiency (up to 81 %) using 1-butyl 2,3,3-trimethyl 3H-indole derivatives as the sole precursors, and demonstrate a free radical mechanism. In the inducer-extension stage, free radicals and reactive oxygen species (ROS) were able to mediate similar reactions with no assistance of light. We explored a Mito-extension strategy to in situ synthesize trimethine cyanines in the living cells. The cellular ROS-dependence provided a foundation for preferential cyanine expression in cancer cells. Finally, we applied an iodized precursor as an intrinsic ROS-activated theranostic agent that integrated mitochondria-targeted cyanine synthesis, cell imaging and phototherapy.

Cascade Reactions by Nitric Oxide and Hydrogen Radical for Anti-Hypoxia Photodynamic Therapy Using an Activatable Photosensitizer.

Organelle-targeted activatable photosensitizers are attractive to improve the specificity and controllability of photodynamic therapy (PDT), however, they suffer from a big problem in the photoactivity under both normoxia and hypoxia due to the limited diversity of phototoxic species (mainly reactive oxygen species). Herein, by effectively photocaging a π-conjugated donor-acceptor (D-A) structure with an N-nitrosamine substituent, we established a unimolecular glutathione and light coactivatable photosensitizer, which achieved its high performance PDT effect by targeting mitochondria through both type I and type II (dual type) reactions as well as secondary radicals-participating reactions. Of peculiar interest, hydrogen radical (H•) was detected by electron spin resonance technique. The generation pathway of H• via reduction of proton and its role in type I reaction were discussed. We demonstrated that the synergistic effect of multiple reactive species originated from tandem cascade reactions comprising reduction of O2 by H• to form O2•-/HO2• and downstream reaction of O2•- with •NO to yield ONOO-. With a relatively large two-photon absorption cross section for photoexcitation in the near-infrared region (166 ± 22 GM at 800 nm) and fluorogenic property, the new photosensitizing system is very promising for broad biomedical applications, particularly low-light dose PDT, in both normoxic and hypoxic environments.

Photoactivated In Situ Generation of Near Infrared Cyanines for Spatiotemporally Controlled Fluorescence Imaging in Living Cells.

Photoactivated trimerization of 2,3,3-trimethyl-3H-indole derivatives created near infrared fluorophore Cy5. The synthetic method is air-tolerant, photosensitizer free, metal free, and condensation agent free. Living cells make Cy5 on a time scale of minutes under white light irradiation at a low power intensity, with the monomer as the only exogenous agent. The new method is promising to find applications in cell studies for in situ spatiotemporally controlled fluorescence imaging in living cells.

GSH and H2 O2 Co-Activatable Mitochondria-Targeted Photodynamic Therapy under Normoxia and Hypoxia.

Currently, photosensitizers (PSs) that are microenvironment responsive and hypoxia active are scarcely available and urgently desired for antitumor photodynamic therapy (PDT). Presented herein is the design of a redox stimuli activatable metal-free photosensitizer (aPS), also functioning as a pre-photosensitizer as it is converted to a PS by the mutual presence of glutathione (GSH) and hydrogen peroxide (H2 O2 ) with high specificity on a basis of domino reactions on the benzothiadiazole ring. Superior to traditional PSs, the activated aPS contributed to efficient generation of reactive oxygen species including singlet oxygen and superoxide ion through both type 1 and type 2 pathways, alleviating the aerobic requirement for PDT. Equipped with a triphenylphosphine ligand for mitochondria targeting, mito aPS showed excellent phototoxicity to tumor cells with low light fluence under both normoxic and hypoxic conditions, after activation by intracellular GSH and H2 O2 . The mito aPS was also compatible to near infrared PDT with two photon excitation (800 nm) for extensive bioapplications.

A photosynthesis-inspired supramolecular system: caging photosensitizer and photocatalyst in apoferritin.

Inspired by the bioinorganic structure of natural [FeFe]-hydrogenase ([FeFe]-H2ase) that possesses iron sulfur clusters to catalyze proton reduction to hydrogen (H2), we design a supramolecular photosystem by sequentially integrating hydrophobic ruthenium complex (as a photosensitizer) and diiron dithiolate complex (as a photocatalyst) into the inner surface or cavity of apoferritin via noncovalent interactions. This platform allows photosensitizer and catalyst to localize in a close proximity and short-distance electron transfer process to occur within a confined space. The resulted uniform core-shell nanocomposites were stable and well dispersed in water, and showed enhanced H2 generation activity in acidic solution as compared to the homogenous system without apoferritin participation.

Mitochondria Targeting Fluorescent Probes Based on through Bond-Energy Transfer for Mutually Imaging Signaling Molecules H2 S and H2 O2.

Reactive signaling molecules participate in varieties of biochemical reactions, and methods to detect their mutual existence and crosstalk are in urgent demand. A benzothiadiazole-based handle was designed to fluorescently respond to the co-existence of H2 S and H2 O2 under pseudo-physiological conditions on a basis of a thiyl-radical-mediated mechanism that accounts for the rapid and efficient domino-like reaction processes. Then the handle motif was attached to a rhodamine moiety by means of an ethynylene linkage, and achieved a significant H2 S-H2 O2 mutual response in the mitochondria of living cells. Theoretical calculations supported that a through bond energy transfer mechanism contributes to the drastic fluorescence response.

An S-alkyl thiocarbamate-based biosensor for highly sensitive and selective detection of hypochlorous acid.

We reported a near-infrared biosensor that features a dihydromethylene blue and an S-alkyl thiocarbamate linker to detect hypochlorous acid in a drastic fluorescence turn-on response. We achieved high sensitivity at the nanomolar level and high selectivity that resolves the interference issue with mercury ions and other transition metal ions. We demonstrated the response mechanism by analysing the released segments, and investigated the imaging capability to detect both exogenous and endogenous hypochlorous acid in living cells.

Precisely tunable engineering of sub-30 nm monodisperse oligonucleotide nanoparticles.

Advancement of RNAi therapies is mainly hindered by the development of efficient delivery vehicles. The ability to create small size (<30 nm) oligonucleotide nanoparticles is essential for many aspects of the delivery process but is often overlooked. In this report, we describe diblock star polymers that can reproducibly complex double-stranded oligonucleotides into monodisperse nanoparticles with 15, 23, or 30 nm in diameter. The polymer-nucleic acid nanoparticles have a core-shell architecture with dense PEG brush coating. We characterized these nanoparticles using ITC, DLS, FRET, FCS, TIRF, and TEM. In addition to small size, these nanoparticles have neutral zeta-potentials, making the presented polymer architecture a very attractive platform for investigation of yet poorly studied polyplex size range for siRNA and antisense oligonucleotide delivery applications.

Polymer-Drug Conjugates Codeliver a Temozolomide Intermediate and Nitric Oxide for Enhanced Chemotherapy against Glioblastoma Multiforme.

Polymer-drug conjugates (PDCs) provide possibilities for the development of multiresponsive drug delivery and release platforms utilized in cancer therapy. The delivery of Temozolomide (TMZ, a DNA methylation agent) by PDCs has been developed to improve TMZ stability under physiological conditions for the treatment of glioblastoma multiforme (GBM); however, with inefficient chemotherapeutic efficacy. In this work, we synthesized an amphiphilic triblock copolymer (P1-SNO) with four pendant functionalities, including (1) a TMZ intermediate (named MTIC) as a prodrug moiety, (2) a disulfide bond as a redox-responsive trigger to cage MTIC, (3) S-nitrosothiol as a light/heat-responsive donor of nitric oxide (NO), and (4) a poly(ethylene glycol) chain to enable self-assembly in aqueous media. P1-SNO was demonstrated to liberate MTIC in the presence of reduced glutathione and release gaseous NO upon exposure to light or heat. The in vitro results revealed a synergistic effect of released MTIC and NO on both TMZ-sensitive and TMZ-resistant GBM cells. The environment-responsive PDC system for codelivery of MTIC and NO is promising to overcome the efficacy issue in TMZ-based cancer therapy.

Recent advances for enhanced photodynamic therapy: from new mechanisms to innovative strategies.

Photodynamic therapy (PDT) has been developed as a potential cancer treatment approach owing to its non-invasiveness, spatiotemporal control and limited side effects. Currently, great efforts have been made to improve the PDT effect in terms of safety and efficiency. In this review, we highlight recent advances in innovative strategies for enhanced PDT, including (1) the development of novel radicals, (2) design of activatable photosensitizers based on the TME and light, and (3) photocatalytic NADH oxidation to damage the mitochondrial electron transport chain. Additionally, the new mechanisms for PDT are also presented as an inspiration for the design of novel PSs. Finally, we discuss the current challenges and future prospects in the clinical practice of these innovative strategies. It is hoped that this review will provide a new angle for understanding the relationship between the intratumoural redox environment and PDT mechanisms, and new ideas for the future development of smart PDT systems.

Tunable thioesters as "reduction" responsive functionality for traceless reversible protein PEGylation.

Disulfide has been the only widely used functionality to serve as a reduction responsive trigger in drug delivery. We introduce thioester as a novel thiol responsive chemistry for drug delivery, whose reactivity can be conveniently modulated by choosing the appropriate steric environment around the thioester. Compared with disulfides, thioesters are facile to synthesize and have an order of magnitude broader kinetic tunability. A novel traceless reversible protein PEGylation reagent is developed based on thioester chemistry.

Synthesis and DNA Cleavage Activity of Cationic Methylene-Blue-Backboned Polymers.

Methods of DNA cleavage have broad bioapplications in gene editing, disease treatment, and biosensor design. The traditional method for DNA cleavage is mainly through oxidation or hydrolysis mediated by small molecules or transition metal complexes. However, DNA cleavage by artificial nucleases using organic polymers has been rarely reported. Methylene blue has been extensively studied in the fields of biomedicine and biosensing due to its excellent singlet oxygen yield, redox properties, and good DNA affinity. Methylene blue mainly relies on light and oxygen for DNA cleavage, and the cutting rate is slow. Here, we synthesize cationic methylene-blue-backboned polymers (MBPs) that can bind DNA efficiently and induce DNA cleavage through free radical mechanisms in the absence of light and exogenous reagents, showing high-efficiency nuclease activity. In addition, MBPs with different structures showed selectivity for DNA cleavage, and the cleavage efficiency of the flexible structure was significantly higher than that of the rigid structure. Studies on the DNA cleavage mechanism have shown that the cleavage mechanism of MBPs is not through the common ROS-mediated oxidative cleavage pathway, but through the radical of MBP• inducing DNA cleavage. Meanwhile, MBPs can simulate topoisomerase I (Topo I)-mediated topological rearrangement of superhelical DNA. This work paved a way for the application of MBPs in the field of artificial nucleases.

It takes more than an imine: the role of the central atom on the electron-accepting ability of benzotriazole and benzothiadiazole oligomers.

We report on the comparison of the electronic and photophysical properties of a series of related donor-acceptor-donor oligomers incorporating the previously known 2H-benzo[d][1,2,3]triazole (BTz) moiety as the acceptor and the recently reported BTzTD acceptor, a hybrid of BTz and 2,1,3-benzothiadiazole (BTD). Although often implied in the polymer literature that BTz has good acceptor character, we show that this moiety is best described as a weak acceptor. We present electrochemical, computational, and photophysical evidence supporting our assertion that BTzTD is a strong electron acceptor while maintaining the alkylation ability of the BTz moiety. Our results show that the identity of the central atom (N or S) in the benzo-fused heterocyclic ring plays an important role in both the electron-accepting and the electron-donating ability of acceptor moieties with sulfur imparting a greater electron-accepting ability and nitrogen affording greater electron-donating character. We report on the X-ray crystal structure of a BTzTD trimer, which exhibits greater local aromatic character in the region of the triazole ring and contains an electron-deficient sulfur that imparts strong electron-accepting ability. Additionally, we examine the transient absorption spectra of BTzTD and BTz oligomers and report that the BTz core promotes efficient intersystem crossing to the triplet state, while the presence of the thiadiazole moiety in BTzTD leads to a negligible triplet yield. Additionally, while BTz does not function as a good acceptor, oligomers containing this moiety do function as excellent sensitizers for the generation of singlet oxygen.

Conjugated polyelectrolyte dendrimers: aggregation, photophysics, and amplified quenching.

Conjugated polyelectrolyte dendrimers (CPDs) are monodisperse macromolecules that feature a fully π-conjugated dendrimer core surrounded on the periphery by ionic solubilizing groups. CPDs are soluble in water and polar organic solvents, and they exhibit photophysics characteristic of the π-conjugated chromophores comprising the dendrimer core. Here we describe the synthesis and photophysical characterization of series of three generations of CPDs based on a phenylene ethynylene repeat unit structure that is surrounded by an array of anionic sodium carboxylate groups. Molecular dynamics simulations indicate that the first-generation CPD is flat while the second- and third-generation CPDs adopt oblate structures. Photophysical studies, including absorption, fluorescence spectroscopy, and lifetimes, show that the ester protected precursor dendrimers exhibit highly efficient blue fluorescence in THF solution emanating from the phenylene ethynylene chromophore that is in the dendrimer core. By contrast, the water-soluble CPDs have much lower fluorescence quantum yields and the absorption and fluorescence spectra exhibit features of strong chromophore-chromophore interactions. The results are interpreted as suggesting that the CPDs exist as dimer or multimer aggregates, even in very dilute solution. Fluorescence quenching of the anionic CPDs with the dication electron acceptor N,N'-dimethylviologen (MV(2+)) is very efficient, with Stern-Volmer quenching constants (K(SV)) increasing with generation number. The third-generation CPD exhibits highly efficient amplified quenching, with K(SV) ∼ 5 × 10(6) M(-1).

Noncovalent Engineering of Apoferritin with a PEGylated [FeFe] Hydrogenase Mimic for In Situ Polymerization.

Apoferritin can act as a scaffold for functionalization in the inner and outer surfaces. However, traditional covalent modification methods have a risk of disrupting the structure and physicochemical properties of apoferritin. Herein, we report a method for designing versatile apoferritin-based nanosystems through noncovalent interaction between a PEGylated [FeFe]-hydrogenase mimic (FeFe-PEG-N3) and apoferritin. FeFe-PEG-N3 can be anchored into the threefold channels of apoferritin via program injection, at a number of ∼8 per protein. We also engineered apoferritin with an FeFe-PEG-N3/ATRP initiator conjugate for in situ and noninvasive atom transfer radical polymerization (ATRP) at the apoferritin surface. This "grafting-from" method for noncovalent apoferritin engineering has the advantages of simple preparation, good controllability, and high efficiency and affords opportunities for the construction of multifunctional apoferritin-based nanosystems for broad applications such as drug delivery and catalysis.

Cationic conjugated polymers for optical detection of DNA methylation, lesions, and single nucleotide polymorphisms.

Simple, rapid, and sensitive technologies to detect nucleic acid modifications have important applications in genetic analysis, clinical diagnosis, and molecular biology. Because genetic modifications such as single nucleotide polymorphisms (SNP), DNA methylation, and other lesions can serve as hallmarks of human disease, interest in such methods has increased in recent years. This Account describes a new strategy for the optical detection of these DNA targets using cationic conjugated polymers (CCPs). Because of their unique signal amplification properties, researchers have extensively investigated conjugated polymers as optical transducers in highly sensitive biosensors. Recently, we have shown that cationic polyfluorene can detect SNPs within the DNA of clinical samples. When we incorporated deoxyguanosine triphosphate (dGTP-Fl) into the DNA chain at an SNP site where the target/probe pair is complementary, we observed higher fluorescence resonance energy transfer (FRET) efficiency between cationic polyfluorene and fluorescein label on the dGTP. By monitoring the change in emission intensity of cationic polyfluorene or fluorescein, we identified the homozygous or heterozygous SNP. The high sensitivity of this assay results from the 10-fold enhancement of fluorescein emission intensity by the FRET from polyfluorene. This method can detect allele frequencies (the proportion of all copies of a gene that is made up of a particular gene variant) as low as 2%. Using this novel method, we clearly discriminated among the SNP genotypes of 76 individuals of Chinese ancestry. Improving on this initial system, we designed a method for multicolor and one-tube SNP genotyping assays based on cationic polyfluorene using fluorescein-labeled deoxyuridine triphosphate (dUTP-Fl) and Cy3-labeled deoxycytidine triphosphate (dCTP-Cy3) in extension reactions. We also developed a one-step method for direct detection of SNP genotypes from genomic DNA by combining allele-specific PCR with CCPs. In 2008, we developed a new method for DNA methylation detection based on single base extension reaction and CCPs. Treatment of DNA with bisulfite followed by PCR amplification converts unmethylated DNA into a C/T polymorphism, which allows us to characterize the methylation status of the target DNA. Furthermore, we used CCPs to detect DNA lesions caused by ultraviolet light irradiation for the first time. By monitoring the color change of cationic polythiophene before and after DNA cleavage, we also detected oxidative damage to DNA by hydroxyl radical. These CCP-based new assays avoid primer labeling, cumbersome workups, and sophisticated instruments, leading to simpler procedures and improved sensitivity. We expect that these features could lead to major advances in human disease diagnostics and genomic study in the near future.