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Aptamers have emerged as promising molecular probes for in vivo cancer imaging, but the reported \"always-on\" aptamer probes remain problematic because of high background and limited contrast. To address this problem, we designed an activatable aptamer probe (AAP) targeting membrane proteins of living cancer cells and achieved contrast-enhanced cancer visualization inside mice. The AAP displayed a quenched fluorescence in its free state and underwent a conformational alteration upon binding to target cancer cells with an activated fluorescence. As proof of concept, in vitro analysis and in vivo imaging of CCRF-CEM cancer cells were performed by using the specific aptamer, sgc8, as a demonstration. It was confirmed that the AAP could be specifically activated by target cancer cells with a dramatic fluorescence enhancement and exhibit improved sensitivity for CCRF-CEM cell analysis with the cell number of 118 detected in 200 μl binding buffer. In vivo studies demonstrated that activated fluorescence signals were obviously achieved in the CCRF-CEM tumor sites in mice. Compared to always-on aptamer probes, the AAP could substantially minimize the background signal originating from nontarget tissues, thus resulting in significantly enhanced image contrast and shortened diagnosis time to 15 min. Furthermore, because of the specific affinity of sgc8 to target cancer cells, the AAP also showed desirable specificity in differentiating CCRF-CEM tumors from Ramos tumors and nontumor areas. The design concept can be widely adapted to other cancer cell-specific aptamer probes for in vivo molecular imaging of cancer.

Background: Immune checkpoint inhibitors (ICIs) are effective against various advanced and metastatic cancers, but patient responses vary and can change over time, complicating treatment prediction. Therefore, better tools for patient stratification, response prediction, and response assessment are needed. This study presents the development and clinical translation of a fluorescently labelled ICI tracer pair used to perform multispectral fluorescent molecular imaging and simultaneously gain spatial and temporal insight in both programmed death ligand 1 (PD-L1) and programmed death receptor 1 (PD-1) expression. Methods: We conjugated the anti-PD-L1 antibody durvalumab to IRDye 680LT and the anti-PD-1 antibody nivolumab to IRDye 800CW. Tracers were developed and optimized for conjugation efficiency and purity to allow use in clinical trials. Stability was tested up to 12 months. An extended single-dose toxicity study in mice was performed for durvalumab-680LT and the unconjugated IRDye 680LT to demonstrate safety for first-in-human administration. Results: Durvalumab-680LT and nivolumab-800CW were successfully conjugated and purified. Conjugation optimization resulted in a robust production with labelling efficiencies of ≥88%. Long-term stability study of both tracers showed all parameters within end of shelf-life specifications for at least 12 months at 2–8 °C. No toxic effects were observed in doses up to 1000x the intended human dose for both IRDye 680LT and durvalumab-680LT, which are therefore considered safe for first-in-human use. Conclusions: We succeeded in the development and clinical translation of two novel fluorescent ICI tracers, durvalumab-680LT and nivolumab-800CW. Moreover, we demonstrated for the first time the safety of IRDye 680LT and durvalumab-680LT, enabling first-in-human use. Together, this makes durvalumab-680LT and nivolumab-800CW suitable for phase I/II clinical trials.

Folate receptor α (FRα) came into focus as an anticancer target many decades after the successful development of drugs targeting intracellular folate metabolism, such as methotrexate and pemetrexed. Binding to FRα is one of several methods by which folate is taken up by cells; however, this receptor is an attractive anticancer drug target owing to the overexpression of FRα in a range of solid tumours, including ovarian, lung and breast cancers. Furthermore, using FRα to better localize effective anticancer therapies to their target tumours using platforms such as antibody–drug conjugates, small-molecule drug conjugates, radioimmunoconjugates and, more recently, chimeric antigen receptor T cells could further improve the outcomes of patients with FRα-overexpressing cancers. FRα can also be harnessed for predictive biomarker research. Moreover, imaging FRα radiologically or in real time during surgery can lead to improved functional imaging and surgical outcomes, respectively. In this Review, we describe the current status of research into FRα in cancer, including data from several late-phase clinical trials involving FRα-targeted therapies, and the use of new technologies to develop FRα-targeted agents with improved therapeutic indices.Cancer cells, like non-malignant cells, are dependent on folate uptake for growth. However, cancer cells are much more reliant on folate receptors (FRs) and particularly FRα for folate uptake than non-malignant cells. In this Review, the authors describe the available data on the role of FRα as a biomarker and as a target of imaging probes, and of targeted therapies in patients with solid tumours.

Although ubiquitous in biological studies, the enhanced green and yellow fluorescent proteins (EGFP and EYFP) were not specifically optimized for neuroscience, and their underwhelming brightness and slow expression in brain tissue limits the fidelity of dendritic spine analysis and other indispensable techniques for studying neurodevelopment and plasticity. We hypothesized that EGFP’s low solubility in mammalian systems must limit the total fluorescence output of whole cells, and that improving folding efficiency could therefore translate into greater brightness of expressing neurons. By introducing rationally selected combinations of folding-enhancing mutations into GFP templates and screening for brightness and expression rate in human cells, we developed mGreenLantern, a fluorescent protein having up to sixfold greater brightness in cells than EGFP. mGreenLantern illuminates neurons in the mouse brain within 72 h, dramatically reducing lag time between viral transduction and imaging, while its high brightness improves detection of neuronal morphology using widefield, confocal, and two-photon microscopy. When virally expressed to projection neurons in vivo, mGreenLantern fluorescence developed four times faster than EYFP and highlighted long-range processes that were poorly detectable in EYFP-labeled cells. Additionally, mGreenLantern retains strong fluorescence after tissue clearing and expansion microscopy, thereby facilitating superresolution and whole-brain imaging without immunohistochemistry. mGreenLantern can directly replace EGFP/EYFP in diverse systems due to its compatibility with GFP filter sets, recognition by EGFP antibodies, and excellent performance in mouse, human, and bacterial cells. Our screening and rational engineering approach is broadly applicable and suggests that greater potential of fluorescent proteins, including biosensors, could be unlocked using a similar strategy.

Currently, there are no non-invasive tools to accurately diagnose wound and surgical site infections before they become systemic or cause significant anatomical damage. Fluorescence and photoacoustic imaging are cost-effective imaging modalities that can be used to noninvasively diagnose bacterial infections when paired with a molecularly targeted infection imaging agent. Here, we develop a fluorescent derivative of maltotriose (Cy7-1-maltotriose), which is shown to be taken up in a variety of gram-positive and gram-negative bacterial strains in vitro. In vivo fluorescence and photoacoustic imaging studies highlight the ability of this probe to detect infection, assess infection burden, and visualize the effectiveness of antibiotic treatment in E. coli -induced myositis and a clinically relevant S. aureus wound infection murine model. In addition, we show that maltotriose is an ideal scaffold for infection imaging agents encompassing better pharmacokinetic properties and in vivo stability than other maltodextrins (e.g. maltohexose). Sensitive diagnostic tools for bacterial infections of wounds and surgical sites are necessary to enable early detection and determine optimal means of treatment. Here, the authors develop a fluorescent and optoacoustic probe based on a maltotriose scaffold, which is selectively taken up by gram-positive and gram-negative bacteria.

Molecular imaging probes hold great promise in disease diagnostics and their therapeutic interventions. However, a single imaging modality sometimes lacks efficiency in all kinds of diseases. Conditions such as cancer, cardiovascular disorders, and neurodegenerative diseases critically require multimodal imaging to characterize complex biological environments accurately. Efficient targeting further enhances probe performance, improving diagnostic precision. This study explores the design rationale and application of bimodal probes designed for Magnetic Resonance (MR) and fluorescence (FL) imaging for their complementary strengths. MRI enables deep tissue visualization, while fluorescence offers high sensitivity and cellular-level resolution. Meticulous attention has been devoted to presenting methodologies aimed at improving the targeting efficacy of these probes. This involves the methodology to enhance targeting efficacy, including ligand-based strategies, nanoparticle functionalization, and molecularly imprinted polymers. The probes combine fluorescence for precise cellular imaging with MRI for in-depth tissue visualization, providing synergistic benefits that elevate their diagnostic potential. Moreover, we offer recent developments in Machine Learning and Artificial Intelligence-based computational approaches for image analysis, enabling more precise diagnosis across a range of diseases that may propel their diagnostic abilities for better therapeutic outcomes. Through systematic analysis and in vitro and in vivo evaluations, we demonstrate the ability of the probes to achieve superior spatial and temporal resolution, facilitating the accurate delineation of biological targets. The integration of these bimodal probes holds great promise for advancing our understanding of complex biological processes, enabling more precise diagnostics, and paving the way for targeted therapeutic interventions.

NIR-II fluorophores have shown great promise for biomedical applications with superior in vivo optical properties. To date, few small-molecule NIR-II fluorophores have been discovered with donor-acceptor-donor (D-A-D) or symmetrical structures, and upconversion-mitochondria-targeted NIR-II dyes have not been reported. Herein, we report development of D-A type thiopyrylium-based NIR-II fluorophores with frequency upconversion luminescence (FUCL) at ~580 nm upon excitation at ~850 nm. H4-PEG-PT can not only quickly and effectively image mitochondria in live or fixed osteosarcoma cells with subcellular resolution at 1 nM, but also efficiently convert optical energy into heat, achieving mitochondria-targeted photothermal cancer therapy without ROS effects. H4-PEG-PT has been further evaluated in vivo and exhibited strong tumor uptake, specific NIR-II signals with high spatial and temporal resolution, and remarkable NIR-II image-guided photothermal therapy. This report presents the first D-A type thiopyrylium NIR-II theranostics for synchronous upconversion-mitochondria-targeted cell imaging, in vivo NIR-II osteosarcoma imaging and excellent photothermal efficiency. Currently available mitochondria-targeted fluorescent dyes emit only one color in the visible or NIR-I and their applications are limited. Here, the authors develop upconversion mitochondria-targeted NIR-II fluorophores for synchronous upconversion-mitochondria-targeted cell imaging, in vivo NIR-II osteosarcoma imaging and photothermal efficiency

Tissue-clearing techniques are powerful tools for biological research and pathological diagnosis. Here, we describe advanced clear, unobstructed brain imaging cocktails and computational analysis (CUBIC) procedures that can be applied to biomedical research. This protocol enables preparation of high-transparency organs that retain fluorescent protein signals within 7–21 d by immersion in CUBIC reagents. A transparent mouse organ can then be imaged by a high-speed imaging system (>0.5 TB/h/color). In addition, to improve the understanding and simplify handling of the data, the positions of all detected cells in an organ (3–12 GB) can be extracted from a large image dataset (2.5–14 TB) within 3–12 h. As an example of how the protocol can be used, we counted the number of cells in an adult whole mouse brain and other distinct anatomical regions and determined the number of cells transduced with mCherry following whole-brain infection with adeno-associated virus (AAV)-PHP.eB. The improved throughput offered by this protocol allows analysis of numerous samples (e.g., >100 mouse brains per study), providing a platform for next-generation biomedical research.

Photoactivatable derivatives of the bright and photostable Janelia Fluor dyes enable improved multicolor single-particle tracking and facile localization microscopy in cells. Small-molecule fluorophores are important tools for advanced imaging experiments. We previously reported a general method to improve small, cell-permeable fluorophores which resulted in the azetidine-containing 'Janelia Fluor' (JF) dyes. Here, we refine and extend the utility of these dyes by synthesizing photoactivatable derivatives that are compatible with live-cell labeling strategies. Once activated, these derived compounds retain the superior brightness and photostability of the JF dyes, enabling improved single-particle tracking and facile localization microscopy experiments.

A simple and general chemical structure change to a panel of cell-permeable small-molecule fluorophores increases their brightness and photostability, which will enable improved single-molecule studies and super-resolution imaging. Specific labeling of biomolecules with bright fluorophores is the keystone of fluorescence microscopy. Genetically encoded self-labeling tag proteins can be coupled to synthetic dyes inside living cells, resulting in brighter reporters than fluorescent proteins. Intracellular labeling using these techniques requires cell-permeable fluorescent ligands, however, limiting utility to a small number of classic fluorophores. Here we describe a simple structural modification that improves the brightness and photostability of dyes while preserving spectral properties and cell permeability. Inspired by molecular modeling, we replaced the N , N -dimethylamino substituents in tetramethylrhodamine with four-membered azetidine rings. This addition of two carbon atoms doubles the quantum efficiency and improves the photon yield of the dye in applications ranging from in vitro single-molecule measurements to super-resolution imaging. The novel substitution is generalizable, yielding a palette of chemical dyes with improved quantum efficiencies that spans the UV and visible range.