Hypoxia-activated probe for NIR fluorescence and photoacoustic dual-mode tumor imaging

Fluorescent N-oxides: applications in bioimaging and sensing

N-Oxides, due to their zwitterionic nature and ability to form hydrogen bonds through the oxide ion, are highly water-soluble and widely used in biological and pharmacological studies. The N-oxide structural scaffold is introduced into molecules, enabling "turn-on" fluorescence via an intramolecular charge transfer (ICT) process. This process occurs when the N-O bond is cleaved, either through an enzymatic reaction under hypoxic conditions or by using Fe(II), which allows rapid and selective detection of Fe(II) at nanomolar concentrations both in vitro and in vivo. This review focuses on the literature published between 2010 and 2024, particularly emphasising N-oxide fluorophores and their applications in hypoxic cell lines, Fe(II) detection, and bioimaging.

A Contrast-Enhanced Tri-Modal MRI Technique for High-Performance Hypoxia Imaging of Breast Cancer

Personalized radiotherapy strategies enabled by the construction of hypoxia-guided biological target volumes (BTVs) can overcome hypoxia-induced radioresistance by delivering high-dose radiotherapy to targeted hypoxic areas of the tumor. However, the construction of hypoxia-guided BTVs is difficult owing to lack of precise visualization of hypoxic areas. This study synthesizes a hypoxia-responsive T1, T2, T2 mapping tri-modal MRI molecular nanoprobe (SPION@ND) and provides precise imaging of hypoxic tumor areas by utilizing the advantageous features of tri-modal magnetic resonance imaging (MRI). SPION@ND exhibits hypoxia-triggered dispersion-aggregation structural transformation. Dispersed SPION@ND can be used for routine clinical BTV construction using T1-contrast MRI. Conversely, aggregated SPION@ND can be used for tumor hypoxia imaging assessment using T2-contrast MRI. Moreover, by introducing T2 mapping, this work designs a novel method (adjustable threshold-based hypoxia assessment) for the precise assessment of tumor hypoxia confidence area and hypoxia level. Eventually this work successfully obtains hypoxia tumor target and accurates hypoxia tumor target, and achieves a one-stop hypoxia-guided BTV construction. Compared to the positron emission tomography-based hypoxia assessment, SPION@ND provides a new method that allows safe and convenient imaging of hypoxic tumor areas in clinical settings.

Dual/Multi-Modal Image-Guided Diagnosis and Therapy Based on Luminogens with Aggregation-Induced Emission

The combination of multiple imaging methods has made an indelible contribution to the diagnosis, surgical navigation, treatment, and prognostic evaluation of various diseases. Due to the unique advantages of luminogens with aggregation-induced emission (AIE), their progress has been significant in the field of organic fluorescent contrast agents. Herein, this manuscript summarizes the recent advancements in AIE molecules as contrast agents for optical image-based dual/multi-modal imaging. We particularly focus on the exceptional properties of each material and the corresponding application in the diagnosis and treatment of diseases.

Hypoxia-responsive AIEgens for precise disease theranostics

Specific biomarker-activatable probes have revolutionized theranostics, being beneficial for precision medicine. Hypoxia is a critical pathological characteristic prevalent in numerous major diseases such as cancers, cardiovascular disorders, inflammatory diseases, and acute ischemia. Aggregation-induced emission luminogens (AIEgens) have emerged as a promising tool to tackle the biomedical issues. Of particular significance are the hypoxia-responsive AIEgens, representing a kind of crucial probe capable of delicately sensing and responding to the hypoxic microenvironment, thereby enhancing the precision of disease diagnosis and treatment. In this review, we summarize the recent advances of hypoxia-responsive AIEgens for varied biomedical applications. The hypoxia-responsive structures based on AIEgens, such as azobenzene, nitrobenzene, and N-oxide are presented, which are in response to the reduction property to bring about significant alternations in response spectra and/or fluorescence intensity. The bioapplications including imaging and therapy of tumor and ischemia diseases are discussed. Moreover, the review sheds light on the future challenges and prospects in this field. This review aims to provide comprehensive guidance and understanding into the development of activatable bioprobes, especially the hypoxia-responsive AIEgens for improving the diagnosis and therapy outcome of related diseases.

Hypoxia-Directed and Self-Immolative Theranostic Agent: Imaging and Treatment of Cancer and Bacterial Infections

The impact of bacteria on cancer progression and treatment is becoming increasingly recognized. Cancer-associated bacteria are linked to metastases, reduced efficacy, and survival challenges. In this study, we present a sensitive hypoxia-activated prodrug, NR-NO2, which comprises an antibiotic combined with a chemotherapeutic. This prodrug demonstrates rapid and robust fluorescence enhancement and exhibits potent antibacterial activity against both Gram-positive and Gram-negative bacteria as well as tumor cells. Upon activation, NR-NO2 produces a distinct "fluorescence-on" signal, enabling real-time drug release monitoring. By leveraging elevated nitroreductase in cancer cells, NR-NO2 gives rise to heightened bacterial cytotoxicity while sparing normal cells. In A549 solid tumor-bearing mice, NR-NO2 selectively accumulated at tumor sites, displaying fluorescence signals under hypoxia superior to those of a corresponding prodrug-like control. These findings highlight the potential of NR-NO2 as a promising cancer therapy prodrug that benefits from targeted release, antibacterial impact, and imaging-based guidance.

Activatable probes with potential for intraoperative tumor-specific fluorescence-imaging guided surgery

Owing to societal development and aging population, the impact of cancer on human health and quality of life has increased. Early detection and surgical treatment are the most effective approaches for most cancer patients. As the scope of conventional tumor resection is determined by auxiliary examination and surgeon experience, there is often insufficient recognition of tiny tumors. The ability to detect such tumors can be improved by using fluorescent tumor-specific probes for surgical navigation. This review mainly describes the design principles and mechanisms of activatable probes for the fluorescence imaging of tumors. This type of probe is nonfluorescent in normal tissue but exhibits obvious fluorescence emission upon encountering tumor-specific substrates, such as enzymes or bioactive molecules, or changes in the microenvironment, such as a low pH. In some cases, a single-factor response does not guarantee the effective fluorescence labeling of tumors. Therefore, two-factor-activatable fluorescence imaging probes that react with two specific factors in tumor cells have also been developed. Compared with single biomarker testing, the simultaneous monitoring of multiple biomarkers may provide additional insight into the role of these substances in cancer development and aid in improving the accuracy of early cancer diagnosis. Research and progress in this field can provide new methods for precision medicine and targeted therapy. The development of new approaches for early diagnosis and treatment can effectively improve the prognosis of cancer patients and help enhance their quality of life.

Molecular Motion and Nonradiative Decay: Towards Efficient Photothermal and Photoacoustic Systems

Nonradiative decay invariably competes with radiative decay during the deexcitation process of matter. In the community of luminescence research, nonradiative decay has been deemed less attractive than radiative decay. However, all things in their being are good for something and so is nonradiative decay. As the molecular motion-facilitated nonradiative decay (MMFND) effect is inevitable in photophysical processes, it provides a new avenue to convert the harvested light energy into exploitable forms by harnessing molecular motion. In many cases, active molecular motion enables thermal deactivation from excited states. In this Minireview, recent advances in photothermal and photoacoustic systems with MMFND character are summarized. We believe that this presentation of the rational engineering of molecular motion for efficient photothermal generation will deepen the understanding of the relationship between molecular motion and nonradiative decay and navigate people to rethink the positive aspects of nonradiative decay for the establishment of new light-controllable techniques.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

NIR-I Dye-Based Probe: A New Window for Bimodal Tumor Theranostics

Near-infrared (NIR, 650-1700 nm) bioimaging has emerged as a powerful strategy in tumor diagnosis. In particular, NIR-I fluorescence imaging (650-950 nm) has drawn more attention, benefiting from the high quantum yield and good biocompatibility. Since their biomedical applications are slightly limited by their relatively low penetration depth, NIR-I fluorescence imaging probes have been under extensive development in recent years. This review summarizes the particular application of the NIR-I fluorescent dye-contained bimodal probes, with emphasis on related nanoprobes. These probes have enabled us to overcome the drawbacks of individual imaging modalities as well as achieve synergistic imaging. Meanwhile, the application of these NIR-I fluorescence-based bimodal probes for cancer theranostics is highlighted.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

Targeted contrast agents and activatable probes for photoacoustic imaging of cancer

Photoacoustic (PA) imaging has emerged as a powerful technique for the high resolution visualization of biological processes within deep tissue. Through the development and application of exogenous targeted contrast agents and activatable probes that can respond to a given cancer biomarker, researchers can image molecular events in vivo during cancer progression. This information can provide valuable details that can facilitate cancer diagnosis and therapy monitoring. In this tutorial review, we provide a step-by-step guide to select a cancer biomarker and subsequent approaches to design imaging agents for in vivo use. We envision this information will be a useful summary to those in the field, new members to the community, and graduate students taking advanced imaging coursework. We also highlight notable examples from the recent literature, with emphasis on the molecular designs and their in vivo PA imaging performance. To conclude, we provide our outlook and future perspective in this exciting field.

Trojan-Horse Diameter-Reducible Nanotheranostics for Macroscopic/Microscopic Imaging-Monitored Chemo-Antiangiogenic Therapy

Although nanotheranostics have displayed striking potential toward precise nanomedicine, their targeting delivery and tumor penetration capacities are still impeded by several biological barriers. Besides, the current antitumor strategies mainly focus on killing tumor cells rather than antiangiogenesis. Enlightened by the fact that the smart transformable self-targeting nanotheranostics can enhance their targeting efficiency, tumor penetration, and cellular uptake, we herein report carrier-free Trojan-horse diameter-reducible metal-organic nanotheranostics by the coordination-driven supramolecular sequential co-assembly of the chemo-drug pemetrexed (PEM), transition-metal ions (Fe^III), and antiangiogenesis pseudolaric acid B. Such nanotheranostics with both a high dual-drug payload efficiency and outstanding physiological stability are responsively decomposed into numerous ultra-small-diameter nanotheranostics under stimuli of the moderate acidic tumor microenvironment and then internalized into tumor cells through tumor-receptor-mediated self-targeting, synergistically enhancing tumor penetration and cellular uptake. Besides, such nanotheranostics enable visualization of self-targeting capacity under the macroscopic monitor of computed tomography/magnetic resonance imaging, thereby realizing efficient oncotherapy. Moreover, tumor microvessels are precisely monitored by optical coherence tomography angiography/laser speckle imaging during chemo-antiangiogenic therapy in vivo, visually verifying that such nanotheranostics possess an excellent antiangiogenic effect. Our work will provide a promising strategy for further tumor diagnosis and targeted therapy.

Progress in the past five years of small organic molecule dyes for tumor microenvironment imaging

The tumor microenvironment (TME) is the survival environment for tumor cell proliferation and metastasis in deep tissues.

Design and Characterization of Fibroblast Activation Protein Targeted Pan-Cancer Imaging Agent for Fluorescence-Guided Surgery of Solid Tumors

Tumor-targeted fluorescent dyes have been shown to significantly improve a surgeon's ability to locate and resect occult malignant lesions, thereby enhancing a patient’s chances of long term survival. Although several...

Aggregation-Induced Emission-Based Platforms for the Treatment of Bacteria, Fungi, and Viruses

The prevention and control of pathogenic bacteria, fungi, and viruses is a herculean task for all the countries since they greatly threaten global public health. Rapid detection and effective elimination of these pathogens is crucial for the treatment of related diseases. It is urgently demanded to develop new diagnostic and therapeutic strategies to combat bacteria, fungi, and viruses-induced infections. The emergence of aggregation-induced emission (AIE) luminogens (AIEgens) is a revolutionary breakthrough for the treatment of many diseases, including pathogenic infections. In this review, the main focus is on the applications of AIEgens for theranostic treatment of pathogenic bacteria, fungi, and viruses. Due to the AIE characteristic, AIEgens are promising fluorescent probes for the detection of bacteria, fungi, and viruses with excellent sensitivity and photostability. Moreover, AIEgen-based theranostic platforms can be fabricated by introducing bactericidal moieties or designing AIE photosensitizers and AIE photothermal agents. The current strategies and ongoing developments of AIEgens for the treatment of pathogenic bacteria, fungi, and viruses will be discussed in detail.