A New Endoplasmic Reticulum (ER)-Targeting Fluorescent Probe for the Imaging of Cysteine in Living Cells

Old drug, new use: The thalidomide-based fluorescent probe for cysteine detection and imaging in living cells

Thalidomide, as a high-profile cereblon (CRBN) ligand, has attracted much attention because of its ability to target protein degradation. In this study, we are committed to developing a new fluorescent probe THD-1 based on thalidomide, aiming at improving the performance of cysteine fluorescent probe in optical properties and biocompatibility. The experimental results showed that THD-1, as a cysteine fluorescent probe, owned the characteristics of obvious colorimetric change, fast response time, good selectivity and high sensitivity. The mechanism of THD-1 sensing cysteine was further verified to ensure its reliability and effectiveness. It was also worth mentioning that THD-1 was successfully applied to the biological imaging of cysteine in living A549 cells, which highlighted its value in practical application. Overall, thalidomide, as a clinically approved drug, not only enriches the fluorescent skeleton library, but also paves a new way for the further development of fluorescent probes.

A two-photon fluorescent probe for highly selective detection of Cys over GSH and Hcy based on the Michael addition and transcyclization mechanism and its application in bioimaging and protein straining in SDS-PAGE

BACKGROUND

Cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), as three major biothiols are involved in a variety of physiological processes and play a crucial role in plant growth. Abnormal levels of Cys can cause plants to fail to grow properly. To date, although a very large number of fluorescent probes have been reported for the detection of biothiols, very few of them can be used for the selective discrimination of Cys from GSH and Hcy due to their structural similarity, and only a few of them can be used for plant imaging.

RESULTS

Here, three fluorescent probes (o-/m-/p-TMA) based on TMN fluorophore and the ortho-/meta-/para-substituted maleimide recognition groups were constructed to investigate the selective response effect of Cys. Compared to the o-/m-TMA, p-TMA can selectively detect Cys over GSH and Hcy with a rapid response time (10 min) and a low detection limit (0.26 μM). The theoretical calculation confirmed that the intermediate p-TMA-Cys-int has shorter interatomic reaction distances (3.827 Å) compared to o-/m-TMA-Cys (5.533/5.287 Å), making it more suitable for further transcyclization reactions. Additionally, p-TMA has been employed for selective tracking of exogenous and endogenous Cys in Arabidopsis thaliana using both single-/two-photon fluorescence imaging. Furthermore, single cell walls produced obvious two-photon fluorescence signals, indicating that p-TMA can be used for high-concentration Cys analysis in single cells. Surprisingly, p-TMA can be used as a fluorescent dye for protein staining in SDS-PAGE with higher sensitivity (7.49 μg/mL) than classical Coomassie brilliant blue (14.11 μg/mL).

SIGNIFICANCE

The outstanding properties of p-TMA make it a promising multifunctional molecular tool for the highly selective detection of Cys over GSH and Hcy in various complex environments, including water solutions, zebrafish, and plants. Additionally, it has the potential to be developed as a fluorescent dye for a simple and fast SDS-PAGE fluorescence staining method.

Synthesis and Characterization of Sulfonamide-Containing Naphthalimides as Fluorescent Probes

A tumor-targeting fluorescent probe has attracted increasing interest in fluorescent imaging for the noninvasive detection of cancers in recent years. Sulfonamide-containing naphthalimide derivatives (SN-2NI, SD-NI) were synthesized by the incorporation of N-butyl-4-ethyldiamino-1,8-naphthalene imide (NI) into sulfonamide (SN) and sulfadiazine (SD) as the tumor-targeting groups, respectively. These derivatives were further characterized by mass spectrometry (MS), nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV), and a fluorescence assay. In vitro properties, including cell cytotoxicity and the cell uptake of tumor cells, were also evaluated. Sulfonamide-containing naphthalimide derivatives possessed low cell cytotoxicity to B16F10 melanoma cells. Moreover, SN-2NI and SD-NI can be taken up highly by B16F10 cells and then achieve good green fluorescent images in B16F10 cells. Therefore, sulfonamide-containing naphthalimide derivatives can be considered to be the potential probes used to target fluorescent imaging in tumors.

Treatment evaluation of Rheumatoid arthritis by in situ fluorescence imaging of the Golgi cysteine

Rheumatoid arthritis (RA) is a long-term systemic inflammatory disease that causes severe joint pain. Golgi stress caused by redox imbalance significantly involves in acute and chronic inflammatory diseases, in which cysteine (Cys), as a representative reducing agent, may be an effective biomarker for RA. Hence, in order to achieve RA early detection and drugs evaluation, based on our previous work about innovative Golgi-targeting group, we established a phenylsulfonamide-modified fluorescence probe, Golgi-Cys, for the selective fluorescence imaging of Cys in Golgi apparatus in vivo. By application of Golgi-Cys, the Cys changes under Golgi stress in cells were elucidated. More importantly, we found that the probe can be effectively utilized for the RA detection and treatment evaluation in situ.

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Theoretical Insights on the Sensing Performance for Newly-synthesized Two-photon Fluorescent N2H4 Probes Based on Spirobifluorence

The development of fluorescent probe for hydrazine (N2H4) detection has attracted much attention due to the important role of N2H4 plays in the fields of medicine, agriculture, biology and environments. In this paper, the optical properties and water solubility of two novel two-photon fluorescent molecular probes (Probe1 and Probe2) before and after the reaction with N2H4 are studied by using the density function theory. The results show that electronic distribution and transition dipole moment of the probes are obviously changed after the reaction with N2H4, thus the optical properties of the molecules are influenced and the detection of N2H4 are realized. In addition, photoinduced electron transfer processes for Probe1 and Probe2 in the presence of N2H4 are theoretically characterized, which explains the experimental observations from the microscopic mechanism. Special attention has been paid on the analysis of the two-photon absorption for the probes with the absence and presence of N2H4 by the response theory method. Both probes with good water solubility show large variation on the two-photon absorption cross section when reacts with N2H4. In particular, the two-photon absorption response of Probe2 is more obvious, so it possesses preferable two-photon fluorescence microscopic imaging ability. More importantly, the receptor effect on the sensing performances of the probes are demonstrated, providing a theoretical reference for the design and synthesis on more efficient two-photon fluorescence N2H4 probes. Our study provides necessary information on the response mechanism of the studied chemosensors and helps to establish the relationship between the structure and optical properties of two-photon fluorescence N2H4 probes.

A Photoinduced Electron Transfer-Based Hypochlorite-Specific Fluorescent Probe for Selective Imaging of Proinflammatory M1 in a Rheumatoid Arthritis Model

The differentiation of the distinct phenotypes of macrophages is essential for monitoring the stage of inflammatory diseases for accurate diagnosis and treatment. Recent studies revealed that the level of hypochlorite (OCl^-) varies from activated M1 macrophages (killing pathogens) to M2 (resolution of inflammation) during inflammation. Thus, we developed a simple and efficient fluorescent probe for discriminating M1 from M0 and M2. Herein, fluorescent-based imaging is applied as an alternative to immunohistochemistry, which is challenging due to the tedious process and high cost. We developed a hypochlorite-specific probe PMS-T to differentiate M1 and M2, employing a metabolism-oriented live-cell distinction. This probe enables the detection of inflammatory rheumatoid arthritis in an ex vivo mouse model. Thus, it can be a potential chemical tool for monitoring inflammatory diseases, including rheumatoid arthritis, that may overcome the existing barriers of immunohistochemistry.

Theoretical study on a series of naphthalimide-contained two-photon fluorescent hypochlorite probe targeting endoplasmic reticulum: response mechanism and receptor effect

The development of detecting hypochlorous acid (HClO) in living endoplasmic reticulum has attracted much attention in the fields of biology, medicine, and pharmacy. In the present work, the one-photon absorption (OPA), one-photon emission (OPE), and two-photon absorption (TPA) properties of a series newly synthesized chemosensors with naphthalimide as the fluorophore were systematically investigated using time-dependent density functional theory in combination with response theory. Special emphasis is placed on evolution of the probes' optical properties in the presence of HClO. These compounds show drastic changes in their photoabsorption and photoemission properties when they react with HClO, indicating them to be excellent candidates as fluorescent chemosensors. To further understand the mechanisms of the two probes, we have employed the hole and electron analysis to investigate the charge transfer process for the photoemission of the molecules. The receptor effect is found to play a dominant role in the sensing performance of these probes. Specifically, two-photon absorption properties of the molecules are calculated. We have found that all probes show significant two-photon responses in the near-infrared light region. And the maximum two-photon absorption cross section of probe 2 is greatly enhanced with the presence of HClO, indicating that probe 2 can act as a potential two-photon excited fluorescent HClO probe. The theoretical investigations would be helpful to build the structure-property relationships for the naphthalimide-contained probes, providing information on the design of efficient two-photon fluorescent sensors that can be used for biological imaging of HClO in endoplasmic reticulum.

Subcellular delivery of lipid nanoparticles to endoplasmic reticulum and mitochondria

Primarily responsible for the biogenesis and metabolism of biomolecules, endoplasmic reticulum (ER) and mitochondria are gradually becoming the targets of therapeutic modulation, whose physiological activities and pathological manifestations determine the functional capacity and even the survival of cells. Drug delivery systems with specific physicochemical properties (passive targeting), or modified by small molecular compounds, polypeptides, and biomembranes demonstrating tropism for ER and mitochondria (active targeting) are able to reduce the nonselective accumulation of drugs, enhancing efficacy while reducing side effects. Lipid nanoparticles feature high biocompatibility, diverse cargo loading, and flexible structure modification, which are frequently used for subcellular organelle-targeted delivery of therapeutics. However, there is still a lack of systematic understanding of lipid nanoparticle-based ER and mitochondria targeting. Herein, we review the pathological significance of drug selectively delivered to the ER and mitochondria. We also summarize the molecular basis and application prospects of lipid nanoparticle-based ER and mitochondria targeting strategies, which may provide guidance for the prevention and treatment of associated diseases and disorders. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Recent progress in small-molecule fluorescent probes for endoplasmic reticulum imaging in biological systems

Endoplasmic reticulum (ER) is an indispensable organelle in eukaryotic cells involved in protein synthesis and processing, as well as calcium storage and release. Therefore, maintaining the quality of ER is of great importance for cellular homeostasis. Aberrant fluctuations of bioactive species in the ER will result in homeostasis disequilibrium and further cause ER stress, which has evolved to contribute to the pathogenesis of various diseases. Therefore, the real-time monitoring of various bioactive species in the ER is of high priority to ascertain the mysterious roles of ER, which will contribute to unveiling the corresponding mechanism of organism disturbances. Recently, fluorescence imaging has emerged as a robust technique for the direct visualization of molecular events due to its outstanding sensitivity, high temporal-spatial resolution and noninvasive nature. In this review, we comprehensively summarize the recent progress in design strategies, bioimaging applications, potential directions and challenges of ER-targetable small-molecular fluorescent probes.