Anticancer Activity of Benzo[a]phenoxazine Compounds Promoting Lysosomal Dysfunction

Specific cancer therapy remains a problem to be solved. Breast and colorectal cancer are among the cancers with the highest prevalence and mortality rates. Although there are some therapeutic options, there are still few effective agents for those cancers, which constitutes a clinical problem that requires further research efforts. Lysosomes play an important role in cancer cells' survival, and targeting lysosomes has gained increased interest. In recent years, our team has been synthetizing and testing novel benzo[a]phenoxazine derivatives, as they have been shown to possess potent pharmacological activities. Here, we investigated the anticancer activity of three of the most potent derivatives from our library, C9, A36, and A42, on colorectal- and breast-cancer-derived cell lines, and compared this with the effect on non-neoplastic cell lines. We observed that the three compounds were selective for the cancer cells, namely the RKO colorectal cancer cell line and the MCF7 breast cancer cell line. In both models, the compounds reduced cell proliferation, cell survival, and cell migration, accumulated on the lysosome, and induced cell death accompanied by lysosomal membrane permeabilization (LMP), increasing the intracellular pH and ROS accumulation. Our results demonstrated that these compounds specifically target lysosomes from cancer cells, making them promising candidates as LMP inducers for cancer therapy.

A Hybrid Nanogel to Preserve Lysosome Integrity for Fluorescence Imaging

Fluorescence imaging of lysosomes provides a powerful tool to probe the lysosome physiology in living cells, yet the continuous light exposure inevitably causes lysosome damage and phototoxicity, which remains a formidable challenge. Here the long-term lysosome tracking with minimized photodamage was realized using a multifunctional nanoprobe, a platinum nanoparticle, and a quinacrine co-loaded nanogel. To construct the hybrid nanogel, cisplatin first functioned as cross-linker to withhold all components and then was reduced to a platinum nanoparticle in situ by ethanol. The platinum nanoparticle enabled a long-term quinacrine fluorescence imaging of lysosome by scavenging the light induced reactive oxygen species which could damage lysosomal membranes.

Small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes

In the past few years, the preparation of novel small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes has attracted considerable attention because of their wide applications in chemistry, biology, and medical science. This feature article summarizes the recent advances in the design and preparation of small-molecule fluorescent probes for specific detection of chemical species inside lysosomes. In addition, their properties and applications for the detection and imaging of pH, H2O2, HOCl, O2˙-, lipid peroxidation, H2S, HSO3-, thiols, NO, ONOO-, HNO, Zn2+, Cu2+, enzymes, etc. in lysosomes are discussed as well.

Organocatalyzed Controlled Radical Polymerizations

Radical polymerizations are responsible for a significant amount of the World's total polymer production. Free-radical polymerization provides a relatively inexpensive and facile route to produce bulk plastic products, however, it fails in the synthesis of precisely defined macromolecules. To address this issue, controlled radical polymerizations have been developed, which utilize a reversible deactivation mechanism for the synthesis of advanced polymeric architectures. In this chapter, we discuss the mechanisms and applications of organocatalyzed controlled radical polymerizations, specifically atom transfer radical polymerization, photo mediated reversible addition fragmentation chain-transfer polymerization, and reversible complexation mediated radical polymerization, as powerful new methods for precision polymer synthesis.

Dual site-controlled two-photon fluorescent probe for the imaging of lysosomal pH in living cells

Abnormal lysosomal pH is closely associated with many diseases, and real-time monitoring of lysosomal pH is important for understanding the lysosome physiological nature. Here, we present a novel lysosome-targeting two-photon fluorescent probe (MP-lys) for monitoring pH changes in living cells. As a dual site-controlled probe, MP-lys employed morpholine and piperazine groups as the lysosome-targeting groups and pH response sites. MP-lys showed rapid, reversible and sensitive fluorescence response to pH. MP-lys possessed lysosome-targeting properties, and could be used for two-photon imaging of chloroquine-induced pH variation in living cells.

One-Step Synthesis of Ultrasmall and Ultrabright Organosilica Nanodots with 100% Photoluminescence Quantum Yield: Long-Term Lysosome Imaging in Living, Fixed, and Permeabilized Cells

Water-dispersible nanomaterials with superbright photoluminescence (PL) emissions and narrow PL bandwidths are urgently desired for various imaging applications. Herein, for the first time, we prepared ultrasmall organosilica nanodots (OSiNDs) with an average size of ∼2.0 nm and ∼100% green-emitting PL quantum efficiency via a one-step hydrothermal treatment of two commercial reagents (a silane molecule and rose bengal). In particular, the structural reorganization and halide loss of rose bengal during the hydrothermal treatment contribute to the ultrahigh quantum yield and low phototoxicity of OSiNDs. Owing to their low pH-induced precipitation/aggregation property, the as-prepared OSiNDs can be used as excellent lysosomal trackers with many advantages: (1) They have superior lysosomal targeting ability with a Pearson's coefficient of 0.98; (2) The lysosomal monitoring time of OSiNDs is up to 48 h, which is much longer than those of commercial lysosomal trackers (<2 h); (3) They do not disturb the pH environment of lysosomes and can be used to visualize lysosomes in living, fixed, and permeabilized cells; (4) They exhibit intrinsic lysosomal tracking ability without the introduction of lysosome-targeting ligands (such as morpholine) and superior photostability; (5) The easy, cost-effective, and scalable synthetic method further ensures that these OSiNDs can be readily used as exceptional lysosomal trackers. We expect that the ultrasmall OSiNDs with superior fluorescence properties and easily modifiable surfaces could be applied as fluorescent nanoprobes, light-emitting diode phosphor, and anticounterfeiting material, which should be able to promote the preparation and application of silicon-containing nanomaterials.

A review: the trend of progress about pH probes in cell application in recent years

Intracellular pH values are some of the most important factors that govern biological processes and the acid-base homeostasis in cells, body fluids and organs sustains the normal operations of the body. Subcellular organelles including the acidic lysosomes and the alkalescent mitochondria undergo various processes such as intracellular digestion, ATP production and apoptosis. Due to their precise imaging capabilities, fluorescent probes have attracted great attention for the illustration of pH modulated processes. Furthermore, based on the unique acidic extracellular environment of acidic lysosomes, fluorescent probes can specifically be activated in cancer cells or tumors. In this review, recently reported lysosome and mitochondria specific pH imaging probes as well as pH-activatable cancer cell-targetable probes have been discussed.

Synthesis of near-infrared fluorescent rhodamines via an SNArH reaction and their biological applications

Seven rectilinearly π-extended NIR fluorescent rhodamines were synthesized via an intramolecular S_NAr^H reaction under mild conditions without any transition metal catalyst or extra oxidant.

A reversible frequency upconversion probe for real-time intracellular lysosome-pH detection and subcellular imaging

The probe NRH-Lyso shows an FUCL response to acidic pH and is a promising candidate for lysosome imaging in living cells.

Highly photostable wide-dynamic-range pH sensitive semiconducting polymer dots enabled by dendronizing the near-IR emitters

One constraint of semiconducting polymer dots (Pdots), especially those with near-IR emission, is their low effective emitter ratio (∼1.5 mole percent), which limits their pH sensing performance. The other critical issue of existing Pdot-based pH sensors is their poor photostability. To address these issues, we developed a series of Pdots by dendronizing the squaraine-based pH responsive near-IR emitter, which is covalently incorporated into the polyfluorene (PFO) backbone. The fluorescence self-quenching of the NIR squaraine emitter was effectively suppressed at a high emitter concentration of 5 mole percent. Through controlling the individually incomplete energy transfer from the amorphous PFO donor to the blue β-phase PFO and NIR squaraine emitter, we obtained a ratiometric pH sensor with simultaneously improved pH sensitivity, brightness, and photostability. The Pdots showed a fast and reversible pH response over the whole biological pH range of 4.7 to 8.5. Intracellular pH mapping was successfully demonstrated using this ultra-bright and photostable Pdot-based pH indicator.

Organocatalyzed Atom Transfer Radical Polymerization: Perspectives on Catalyst Design and Performance

The recent development of organocatalyzed atom transfer radical polymerization (O-ATRP) represents a significant advancement in the field of controlled radical polymerizations. A number of classes of photoredox catalysts have been employed thus far in O-ATRP. Analysis of the proposed mechanism gives insight into the relevant photophysical and chemical properties that determine catalyst performance. Discussion of each of the classes of O-ATRP catalysts highlights their previous uses, their roles in the development of O-ATRP, and the distinctive properties that govern their polymerization behavior, leading to a set of design principles for O-ATRP catalysts. Remaining challenges for O-ATRP are presented, as well as prospects for further improvement in the application scope of O-ATRP.

A tumor-targeting and lysosome-specific two-photon fluorescent probe for imaging pH changes in living cells

Lysosomal pH is closely related to the metastasis and apoptosis of cancer cells. Detecting lysosomal pH changes in cancer cells could be helpful for analyzing tumor progressions and in-depth study of the roles of lysosomes in tumor invasion and metastasis. Herein, we describe a novel tumor-targeting and lysosome-specific two-photon fluorescent probe (BN-lys) for imaging pH changes for the first time. Biotin was employed as the tumor-targeting module, and morpholine was selected as the lysosome-specific group and the pH site to control the fluorescence by photoinduced electron transfer (PET) mechanism. With a pK_a value of 5.36, BN-lys showed a fast and reversible fluorescence response to pH. Under the guidance of the biotin group, BN-lys displayed strong one-photon and two-photon fluorescence responses to lysosomal pH in cancer cells, while it displayed weak fluorescence in normal cells. Furthermore, BN-lys could be applied for the imaging of chloroquine-stimulated lysosomal pH changes in living cells. These features demonstrate that this probe could have practical applications in biological research.

Near-Infrared Probe Based on Rhodamine Derivative for Highly Sensitive and Selective Lysosomal pH Tracking

The development of near-infrared fluorescent probes with low pK_a, high selectivity, high photostability, and high sensitivity for lysosomal pH detection is of great importance. In the present work, we developed a novel near-infrared lysosomal pH probe (Lyso-hNR) based on a rhodamine derivative. Lyso-hNR showed fast, highly sensitive, and highly selective fluorescence response to acidic pH caused by the H⁺-induced structure changes from the nonfluorescent spirolactam form to the highly emissive open-ring form. Lyso-hNR displays a significant fluorescence enhancement at 650 nm (over 280-fold) from pH 7.0 to 4.0 with a pK_a value of 5.04. Live cell imaging data revealed that Lyso-hNR can selectively monitor lysosomal pH changes with excellent photostability and low cytotoxicity. In addition, Lyso-hNR can be successfully used in tracking lysosomal pH changes induced by chloroquine and those during apoptosis. All these features render Lyso-hNR a promising candidate to investigate lysosome-associated physiological and pathological processes.

Molecular engineering of a dual emission near-infrared ratiometric fluorophore for the detection of pH at the organism level

A near-infrared ratiometric fluorophore (NIR-HBT) was rationally designed and constructed by expanding both the excitation and emission wavelength of the classical ratiometric fluorophore 2-(benzothiazol-2-yl)phenol (HBT) into the near-infrared region. The NIR-HBT was easily synthesized by incorporating the HBT module into the hemicyanine skeleton and showed evident NIR ratiometric fluorophore characteristics. Further application of the new fluorophore for pH detection demonstrated that NIR-HBT possesses superior overall analytical performance and NIR-HBT was successfully applied for detection of acidosis caused by inflammation in living animal tissue, which indicated the potential application value of NIR-HBT in biological imaging and sensing.

Selective Imaging of Late Endosomes with a pH-Sensitive Diazaoxatriangulene Fluorescent Probe

Late endosomes are a major trafficking hub in the cell at the crossroads between endocytosis, autophagy, and degradation in lysosomes. Herein is disclosed the first small molecule allowing their selective imaging and monitoring in the form of a diazaoxatriangulene fluorophore, 1a (hexadecyl side chain). The compound is prepared in three steps from a simple carbenium precursor. In nanospheres, this pH-sensitive (pKa = 7.3), photochemically stable dye fluoresces in the red part of visible light (601 and 578 nm, acid and basic forms, respectively) with a quantum yield between 14 and 16% and an excited-state lifetime of 7.7-7.8 ns. Importantly, the protonated form 1a·H(+) provokes a specific staining of late endosome compartments (pH 5.0-5.5) after 5 h of incubation with HeLa cells. Not surprisingly, this late endosome marking depends on the intra-organelle pH, and changing the nature of the lipophilic chain provokes a loss of selectivity. Interestingly, fixation of the fluorophore is readily achieved with paraformaldehyde, giving the possibility to image both live and fixed cells.

Biscylometalated iridium(iii) complexes target mitochondria or lysosomes by regulating the lipophilicity of the main ligands

An efficient method that controls biscylometalated iridium(iii) complexes to target mitochondria or lysosomes was presented.

Nanoparticle-based luminescent probes for intracellular sensing and imaging of pH

Fluorescence imaging microscopy is an essential tool in biomedical research. Meanwhile, various fluorescent probes are available for the staining of cells, cell membranes, and organelles. Though, to monitor intracellular processes and dysfunctions, probes that respond to ubiquitous chemical parameters determining the cellular function such as pH, pO2 , and Ca(2+) are required. This review is focused on the progress in the design, fabrication, and application of photoluminescent nanoprobes for sensing and imaging of pH in living cells. The advantages of using nanoprobes carrying fluorescent pH indicators compared to single molecule probes are discussed as well as their limitations due to the mostly lysosomal uptake by cells. Particular attention is paid to ratiometric dual wavelength nanosensors that enable intrinsic referenced measurements. Referencing and proper calibration procedures are basic prerequisites to carry out reliable quantitative pH determinations in complex samples such as living cells. A variety of examples will be presented that highlight the diverseness of nanocarrier materials (polymers, micelles, silica, quantum dots, carbon dots, gold, photon upconversion nanocrystals, or bacteriophages), fluorescent pH indicators for the weak acidic range, and referenced sensing mechanisms, that have been applied intracellularly up to now. WIREs Nanomed Nanobiotechnol 2016, 8:378-413. doi: 10.1002/wnan.1366 For further resources related to this article, please visit the WIREs website.

A dual-emission fluorescence-enhanced probe for imaging copper(ii) ions in lysosomes

We have developed the first example of a fluorescence-enhanced and lysosome-targeted Cu²⁺ probe (Lys-Cu) with unique dual-channel emissions. The newly synthesized fluorescent probe Lys-Cu, which contains two recognition sites with different sensing mechanisms for Cu²⁺, displays fluorescence-enhanced dual-channel emissions with fluorescence response to Cu²⁺ in the lysosome pH environment. Fluorescence imaging shows that Lys-Cu is membrane-permeable and suitable for visualization of Cu²⁺ in lysosomes of living cells by dual-channel imaging.

A novel coumarin derivative as a sensitive probe for tracing intracellular pH changes

A novel coumarin derivative was synthesized and its application in live cell imaging was demonstrated.

Benzo[α]phenoxazines and benzo[α]phenothiazine from vitamin K3: synthesis, molecular structures, DFT studies and cytotoxic activity

Novel benzo[α]phenoxazines and benzo[α]phenothiazine from vitamin K3 are cytotoxic against HeLa, MCF-7 cell lines and potential topoisomerase II inhibitors.

Magnetic nanomaterials with near-infrared pH-activatable fluorescence via iron-catalyzed AGET ATRP for tumor acidic microenvironment imaging

This work provides a fluorescent/magnetic iron oxide nanomaterials prototype to visualize the solid tumor in vivo by sensing the tumor acidic microenvironment, and a satisfactory tumor-to-normal tissue signal ratio (T/N ratio) and a prolonged time-window for 4T1 tumor visualization were observed in vivo.

Colorimetric and ratiometric pH responses by the protonation of phenolate within hemicyanine

The indolium–phenol based tetramethylene hemicyanine has colorimetric and ratiometric optical responses under acidic and basic conditions.

A novel pH probe based on a rhodamine–rhodamine platform

A novel pH probe based on rhodamine–rhodanine platform.