AND-gate contrast agents for enhanced fluorescence-guided surgery

Dual-locked fluorescent probes for precise diagnosis and targeted treatment of tumors

Cancer continues to pose a significant threat to global health, with its high mortality rates largely attributable to delayed diagnosis and non-specific treatments. Early and accurate diagnosis is crucial, yet it remains challenging due to the subtle and often undetectable early molecular changes. Traditional single-target fluorescent probes often fail to accurately identify cancer cells, relying solely on single biomarkers and consequently leading to high rates of false positives and inadequate specificity. In contrast, dual-locked fluorescent probes represent a breakthrough, designed to enhance diagnostic precision. By requiring the simultaneous presence of two specific tumor-associated biomarkers or microenvironmental conditions, these probes significantly reduce non-specific activations typical of conventional single-analyte probes. This review discusses the structural designs, response mechanisms, and biological applications of dual-locked probes, highlighting their potential in tumor imaging and treatment. Importantly, the review addresses the challenges, and perspectives in this field, offering a comprehensive look at the current state and future potential of dual-locked fluorescent probes in oncology.

Structure Tailoring of Hemicyanine Dyes for In Vivo Shortwave Infrared Imaging

In vivo bioimaging using shortwave infrared (SWIR) (1000-2000 nm) molecular dyes enables deeper penetration and higher contrast compared to visible and near-infrared-I (NIR-I, 700-900 nm) dyes. Developing new SWIR molecules is still quite challenging. This study developed SRHCYs, a panel of fluorescent dyes based on hemicyanine, with adjustable absorbance (830-1144 nm) and emission (886-1217 nm) wavelength. The photophysical attributes of these dyes are precisely tailored by strengthening the donor parts and extending polymethine chains. SRHCY-3, with its clickable azido group, was chosen for high-performance imaging of blood vessels in living mice, enabling the precise detection of brain and lung cancer. The combination of these probes achieved in vivo multicolor imaging with negligible optical crosstalk. This report presents a series of SWIR hemicyanine dyes with promising spectroscopic properties for high-contrast bioimaging and multiplexing detection.

Tuning nanoparticle core composition drives orthogonal fluorescence amplification for enhanced tumour imaging

Tumour detection with high selectivity and sensitivity is crucial for delineating tumour margins and identifying metastatic foci during image-guided surgery. Optical nanoprobes with preferential tumour accumulation is often limited by inefficient amplification of biological signals. Here, we report the design of a library of hydrophobic core-tunable ultra-pH-sensitive nanoprobes (HUNPs) for orthogonally amplifying tumour microenvironmental signals on multiple tumour models. We find that tuning the hydrophobicity of nanoparticle core composition with non-ionizable monomers can enhance cellular association of HUNPs by more than ten-fold, resulting in a high cellular internalization efficiency of HUNPs with up to 50% in tumours. Combining high tumour accumulation and high cell internalization efficiency, HUNPs show orthogonally amplified fluorescence signals, permitting the precise locating and delineating margins between malignant lesions and normal tissues with high contrast-to-noise ratio and resolution. Our study provides key strategies to design nanomedicines with high intracellular bioavailability for cancer detection, drug/gene delivery, and therapy.

Molecularly targeted protease-activated probes for visualization of glioblastoma: a comparison with 5-ALA

OBJECTIVE

The highly infiltrative growth of glioblastoma (GBM) makes distinction between the tumor and normal brain tissue challenging. Therefore, fluorescence-guided surgery is often used to improve visual identification of radiological tumor margins. The aim of this study was to evaluate the ability of recently developed molecularly targeted near-infrared (NIR) protease-activated probes to visualize GBM tissue and to compare the most promising candidate with the gold standard, 5-aminolevulinic acid (5-ALA).

METHODS

Single-substrate probes 6QC-ICG and 6QC-Cy5 (cysteine cathepsin cleavable), double-substrate probes AG2-FNIR and AG2-Cy5 (cysteine cathepsin and caspase 3 cleavable), and 5-ALA were administered intravenously to mice with orthotopic tumors. Activation of the probes was also evaluated in cell cultures in vitro and in biopsy material from patients with GBM ex vivo. The tumor to normal brain tissue fluorescence ratio (TNR) was quantified in brain sections using preclinical and clinical visualization platforms, and in tissue homogenates and cell suspensions using spectrofluorimetry. Subcellular localization of the fluorophores was visualized by confocal microscopy.

RESULTS

In vitro, the single-substrate probe 6QC-ICG was cleaved in glioma cells and macrophages, and the resulting fluorophore accumulated intracellularly. In experimental GBMs, both single- and double-substrate probes visualized tumor tissue, while in healthy brain tissue the signal was minimal. TNR was highest for 6QC-ICG and AG2-FNIR, but the signal intensity was higher for 6QC-ICG. Using xenograft and syngeneic mouse models, as well as human GBM biopsy material ex vivo, the authors confirmed the ability of 6QC-ICG to specifically visualize the glioma tissue using preclinical and clinical visualization platforms. Finally, a comparison with 5-ALA in animals coadministered with both compounds revealed a higher TNR for 6QC-ICG in experimental GBMs.

CONCLUSIONS

The cysteine cathepsin-cleavable probe 6QC-ICG is activated by glioma cells and tumor-associated macrophages, leading to a high contrast between tumor and nontumorous brain tissue that is superior to that of the current standard, 5-ALA. In addition to a well-defined mechanism of action, protease-activated probes that use NIR fluorophores (e.g., indocyanine green) have the advantage of low absorption and scattering of the NIR light and lower tissue autofluorescence. These results suggest that 6QC-ICG has the potential to become the targeted agent in intraoperative detection of GBM tissue using fluorescence imaging.

A pan-cancer dye for solid-tumour screening, resection and wound monitoring via short-wave and near-infrared fluorescence imaging

The efficacy of fluorescence-guided surgery in facilitating the real-time delineation of tumours depends on the optical contrast of tumour tissue over healthy tissue. Here we show that CJ215-a commercially available, renally cleared carbocyanine dye sensitive to apoptosis, and with an absorption and emission spectra suitable for near-infrared fluorescence imaging (wavelengths of 650-900 nm) and shortwave infrared (SWIR) fluorescence imaging (900-1,700 nm)-can facilitate fluorescence-guided tumour screening, tumour resection and the assessment of wound healing. In tumour models of either murine or human-derived breast, prostate and colon cancers and of fibrosarcoma, and in a model of intraperitoneal carcinomatosis, imaging of CJ215 with ambient light allowed for the delineation of nearly all tumours within 24 h after intravenous injection of the dye, which was minimally taken up by healthy organs. At later timepoints, CJ215 provided tumour-to-muscle contrast ratios up to 100 and tumour-to-liver contrast ratios up to 18. SWIR fluorescence imaging with the dye also allowed for quantifiable non-contact wound monitoring through commercial bandages. CJ215 may be compatible with existing and emerging clinical solutions.

Dual-Locked Fluorescent Probes Activated by Aminopeptidase N and the Tumor Redox Environment for High-Precision Imaging of Tumor Boundaries

Clear delineation of tumor margins is essential for accurate resection and decreased recurrence rate in the clinic. Fluorescence imaging is emerging as a promising alternative to traditional visual inspection by surgeons for intraoperative imaging. However, traditional probes lack accuracy in tumor diagnosis, making it difficult to depict tumor boundaries accurately. Herein, we proposed an offensive and defensive integration (ODI) strategy based on the "attack systems (invasive peptidase) and defense systems (reductive microenvironment)" of multi-dimensional tumor characteristics to design activatable fluorescent probes for imaging tumor boundaries precisely. Screened out from a series of ODI strategy-based probes, ANQ performed better than traditional probes based on tumor unilateral correlation by distinguishing between tumor cells and normal cells and minimizing false-positive signals from living metabolic organs. To further improve the signal-to-background ratio in vivo, derivatized FANQ, was prepared and successfully applied to distinguish orthotopic hepatocellular carcinoma tissues from adjacent tissues in mice models and clinical samples. This work highlights an innovative strategy to develop activatable probes for rapid diagnosis of tumors and high-precision imaging of tumor boundaries, providing more efficient tools for future clinical applications in intraoperative assisted resection.

Machine-Learning-Assisted Rational Design of Si─Rhodamine as Cathepsin-pH-Activated Probe for Accurate Fluorescence Navigation

High-performance fluorescent probes stand as indispensable tools in fluorescence-guided imaging, and are crucial for precise delineation of focal tissue while minimizing unnecessary removal of healthy tissue. Herein, machine-learning-assisted strategy to investigate the current available xanthene dyes is first proposed, and a quantitative prediction model to guide the rational synthesis of novel fluorescent molecules with the desired pH responsivity is constructed. Two novel Si─rhodamine derivatives are successfully achieved and the cathepsin/pH sequentially activated probe Si─rhodamine─cathepsin-pH (SiR─CTS-pH) is constructed. The results reveal that SiR─CTS-pH exhibits higher signal-to-noise ratio of fluorescence imaging, compared to single pH or cathepsin-activated probe. Moreover, SiR─CTS-pH shows strong differentiation abilities for tumor cells and tissues and accurately discriminates the complex hepatocellular carcinoma tissues from normal ones, indicating its significant application potential in clinical practice. Therefore, the continuous development of xanthene dyes and the rational design of superior fluorescent molecules through machine-learning-assisted model broaden the path and provide more advanced methods to researchers.

Polymer-Tethered Quenched Fluorescent Probes for Enhanced Imaging of Tumor-Associated Proteases

Fluorescence-based contrast agents enable real-time detection of solid tumors and their neovasculature, making them ideal for use in image-guided surgery. Several agents have entered late-stage clinical trials or secured FDA approval, suggesting they are likely to become the standard of care in cancer surgeries. One of the key parameters to optimize in contrast agents is molecular size, which dictates much of the pharmacokinetic and pharmacodynamic properties of the agent. Here, we describe the development of a class of protease-activated quenched fluorescent probes in which a N-(2-hydroxypropyl)methacrylamide copolymer is used as the primary scaffold. This copolymer core provides a high degree of probe modularity to generate structures that cannot be achieved with small molecules and peptide probes. We used a previously validated cathepsin substrate and evaluated the effects of length and type of linker, as well as the positioning of the fluorophore/quencher pair on the polymer core. We found that the polymeric probes could be optimized to achieve increased overall signal and tumor-to-background ratios compared to the reference small molecule probe. Our results also revealed multiple structure-activity relationship trends that can be used to design and optimize future optical imaging probes. Furthermore, they confirm that a hydrophilic polymer is an ideal scaffold for use in optical imaging contrast probes, allowing a highly modular design that enables efficient optimization to maximize probe accumulation and overall biodistribution properties.

Dual Enzyme-Locked Activation Reporter for Accurate Liver Cancer Surveillance

Activatable probes with a higher signal-to-background ratio and accuracy are essential for monitoring liver cancer as well as intraoperative fluorescence navigation. However, the presence of only one biomarker is usually not sufficient to meet the high requirement of a signal-to-background ratio in cancer surveillance, leading to the risk of misdiagnosis. In this work, a dual-locked activation response probe, Si-NTR-LAP, for nitroreductase and leucine aminopeptidase was reported. This dual-locked probe provides better tumor recognition and a higher signal-to-noise ratio than that of single-locked probes (Si-LAP and Si-NTR). In both the subcutaneous tumor model and the more complex orthotopic hepatocellular carcinoma model, the probe was able to identify tumor tissue with high specificity and accurately differentiate the boundaries between tumor tissue and normal tissue. Therefore, the dual-locked probe may provide a new and practical strategy for applying to real patient tumor tissue samples.

Programmable melanoma-targeted radio-immunotherapy via fusogenic liposomes functionalized with multivariate-gated aptamer assemblies

Radio-immunotherapy exploits the immunostimulatory features of ionizing radiation (IR) to enhance antitumor effects and offers emerging opportunities for treating invasive tumor indications such as melanoma. However, insufficient dose deposition and immunosuppressive microenvironment (TME) of solid tumors limit its efficacy. Here we report a programmable sequential therapeutic strategy based on multifunctional fusogenic liposomes (Lip@AUR-ACP-aptPD-L1) to overcome the intrinsic radio-immunotherapeutic resistance of solid tumors. Specifically, fusogenic liposomes are loaded with gold-containing Auranofin (AUR) and inserted with multivariate-gated aptamer assemblies (ACP) and PD-L1 aptamers in the lipid membrane, potentiating melanoma-targeted AUR delivery while transferring ACP onto cell surface through selective membrane fusion. AUR amplifies IR-induced immunogenic death of melanoma cells to release antigens and damage-associated molecular patterns such as adenosine triphosphate (ATP) for triggering adaptive antitumor immunity. AUR-sensitized radiotherapy also upregulates matrix metalloproteinase-2 (MMP-2) expression that combined with released ATP to activate ACP through an "and" logic operation-like process (AND-gate), thus triggering the in-situ release of engineered cytosine-phosphate-guanine aptamer-based immunoadjuvants (eCpG) for stimulating dendritic cell-mediated T cell priming. Furthermore, AUR inhibits tumor-intrinsic vascular endothelial growth factor signaling to suppress infiltration of immunosuppressive cells for fostering an anti-tumorigenic TME. This study offers an approach for solid tumor treatment in the clinics.

Recent advances in ratiometric fluorescence imaging of enzyme activity in vivo

Among molecular imaging modalities that can monitor enzyme activity in vivo, optical imaging provides sensitive, molecular-level information at low-cost using safe and non-ionizing wavelengths of light. Yet, obtaining quantifiable optical signals in vivo poses significant challenges. Benchmarking using ratiometric signals can overcome dependence on dosing, illumination variability, and pharmacokinetics to provide quantitative in vivo optical data. This review highlights recent advances using fluorescent probes that are processed by enzymes to induce photophysical changes that can be monitored by ratiometric imaging. These diverse strategies include caged fluorophores that change photophysical properties upon enzymatic cleavage, as well as multi-fluorophore systems that are triggered by enzymatic cleavage to alter optical outputs in one or more fluorescent channels. The strategies discussed here have great potential for further development as well as potential broad applications for targeting diverse enzymes important for a wide range of human diseases.

A Dual-Cascade Activatable Near-Infrared Fluorescent Probe for Precise Intraoperative Imaging of Tumor

Accurate intraoperative tumor delineation is critical to achieving successful surgical outcomes. However, conventional techniques typically suffer from poor specificity and low sensitivity and are time-consuming, which greatly affects intraoperative decision-making. Here, we report a cascade activatable near-infrared fluorescent (NIRF) probe IR780SS@CaP that can sequentially respond to tumor acidity and elevated glutathione levels for accurate intraoperative tumor localization. Compared with nonactivatable and single-factor activatable probes, IR780SS@CaP with a cascade strategy can minimize nonspecific activation and false positive signals in a complicated biological environment, affording a superior tumor-to-normal tissue ratio to facilitate the delineation of abdominal metastases. Small metastatic lesions that were less than 1 mm in diameter can be precisely identified by IR780SS@CaP and completely excised under NIRF imaging guidance. This study could benefit tumor diagnosis and image-guided tumor surgery by providing real-time information and reliable decision support, thus reducing the risk of both recurrence and complications to improve patient outcomes.

Silicon-Rhodamine Functionalized Evocalcet Probes Potently and Selectively Label Calcium Sensing Receptors In Vitro, In Vivo, and Ex Vivo

The calcium sensing receptor (CaSR) is a ubiquitously expressed G-protein coupled receptor (GPCR) that regulates extracellular calcium signals via the parathyroid glands. CaSR has recently also been implicated in noncalcitropic pathophysiologies like asthma, gut inflammation, and cancer. To date, molecular tools that enable the bioimaging of CaSR in tissues are lacking. Based on in silico analyses of available structure-activity relationship data on CaSR ligands, we designed and prepared silicon-rhodamine (SiR) conjugates of the clinically approved drug evocalcet. The new probes EvoSiR4 and EvoSiR6, with differing linker lengths at the evocalcet carboxyl end, both showed a 6-fold and 3-fold increase in potency toward CaSR (EC50 < 45 nM) compared to evocalcet and the evocalcet-linker conjugate, respectively, in an FLIPR-based cellular functional assay. The specificity of the EvoSiR probes toward CaSR binding and the impact of albumin was evaluated in live cell experiments. Both probes showed strong albumin binding, which facilitated the clearance of nonspecific binding interactions. Accordingly, in zebrafish embryos, EvoSiR4 specifically labeled the high CaSR expressing neuromasts of the lateral line in vivo. EvoSiR4 was also assessed in human parathyroid tissues ex vivo, showing a specific absolute CaSR-associated fluorescence compared to that of parathyroid autofluorescence. In summary, functionalization of evocalcet by SiR led to the preparation of potent and specific fluorescent CaSR probes. EvoSiR4 is a versatile small-molecular probe that can be employed in CaSR-related biomedical analyses where antibodies are not applicable.

Polymer-tethered quenched fluorescent probes for enhanced imaging of tumor associated proteases

Fluorescence-based contrast agents enable real-time detection of solid tumors and their neovasculature, making them ideal for use in image-guided surgery. Several agents have entered late-stage clinical trials or secured FDA approval, suggesting they are likely to become standard of care in cancer surgeries. One of the key parameters to optimize in contrast agent is molecular size, which dictates much of the pharmacokinetic and pharmacodynamic properties of the agent. Here, we describe the development of a class of protease-activated quenched fluorescent probes in which a N-(2-hydroxypropyl)methacrylamide copolymer is used as the primary scaffold. This copolymer core provides a high degree of probe modularity to generate structures that cannot be achieved with small molecules and peptide probes. We used a previously validated cathepsin substrate and evaluated the effects of length and type of linker as well as positioning of the fluorophore/quencher pair on the polymer core. We found that the polymeric probes could be optimized to achieve increased over-all signal and tumor-to-background ratios compared to the reference small molecule probe. Our results also revealed multiple structure-activity relationship trends that can be used to design and optimize future optical imaging probes. Furthermore, they confirm that a hydrophilic polymer is an ideal scaffold for use in optical imaging contrast probes, allowing a highly modular design that enables efficient optimization to maximize probe accumulation and overall biodistribution properties.

Bienzyme-Locked Activatable Fluorescent Probes for Specific Imaging of Tumor-Associated Mast Cells

Tumor-associated mast cells (TAMCs) have been recently revealed to play a multifaceted role in the tumor microenvironment. Noninvasive optical imaging of TAMCs is thus highly desired to gain insights into their functions in cancer immunotherapy. However, due to the lack of a single enzyme that is specific to mast cells, a common probe design approach based on single-enzyme activation is not applicable. Herein, we reported a bienzyme-locked molecular probe (THCMC) based on a photoinduced electron transfer-intramolecular charge-transfer hybrid strategy for in vivo imaging of TAMCs. The bienzyme-locked activation mechanism ensures that THCMC exclusively turns on near-infrared (NIR) fluorescence only in the presence of both tryptase and chymase specifically coexpressed by mast cells. Thus, THCMC effectively distinguishes mast cells from other leukocytes, including T cells, neutrophils, and macrophages, a capability lacking in single-locked probes. Such a high specificity of THCMC allows noninvasive tracking of the fluctuation of TAMCs in the tumor of living mice during cancer immunotherapy. The results reveal that the decreased intratumoral signal of THCMC after combination immunotherapy correlates well with the reduced population of TAMCs, accurately predicting the inhibition of tumor growth. Thus, this study not only presents the first NIR fluorescent probe specific for TAMCs but also proposes a generic bienzyme-locked probe design approach for in vivo cell imaging.

Activity-Based Fluorescence Diagnostics for Cancer

Fluorescence imaging is one of the most promising approaches to achieve intraoperative assessment of the tumor/normal tissue margins during cancer surgery. This is critical to improve the patients' prognosis, and therefore various molecular fluorescence imaging probes have been developed for the identification of cancer lesions during surgery. Among them, "activatable" fluorescence probes that react with cancer-specific biomarker enzymes to generate fluorescence signals have great potential for high-contrast cancer imaging due to their low background fluorescence and high signal amplification by enzymatic turnover. Over the past two decades, activatable fluorescence probes employing various fluorescence control mechanisms have been developed worldwide for this purpose. Furthermore, new biomarker enzymatic activities for specific types of cancers have been identified, enabling visualization of various types of cancers with high sensitivity and specificity. This Review focuses on recent advances in the design, function and characteristics of activatable fluorescence probes that target cancer-specific enzymatic activities for cancer imaging and also discusses future prospects in the field of activity-based diagnostics for cancer.

Activatable Near-Infrared Versatile Fluorescent and Chemiluminescent Dyes Based on the Dicyanomethylene-4H-pyran Scaffold: From Design to Imaging and Theranostics

Activatable fluorescent and chemiluminescent dyes with near-infrared emission have indispensable roles in the fields of bioimaging, molecular prodrugs, and phototheranostic agents. As one of the most popular fluorophore scaffolds, the dicyanomethylene-4H-pyran scaffold has been applied to fabricate a large number of versatile activatable optical dyes for analytes detection and diseases diagnosis and treatment by virtue of its high photostability, large Stokes shift, considerable two-photon absorption cross-section, and structural modifiability. This review discusses the molecular design strategies, recognition mechanisms, and both in vitro and in vivo bio-applications (especially for diagnosis and therapy of tumors) of activatable dicyanomethylene-4H-pyran dyes. The final section describes the current shortcomings and future development prospects of this topic.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

A pan-cancer agent for screening, resection and wound monitoring via NIR and SWIR imaging

Fluorescence guided surgery (FGS) facilitates real time tumor delineation and is being rapidly established clinically. FGS efficacy is tied to the utilized dye and provided tumor contrast over healthy tissue. Apoptosis, a cancer hallmark, is a desirable target for tumor delineation. Here, we preclinically in vitro and in vivo, validate an apoptosis sensitive commercial carbocyanine dye (CJ215), with absorption and emission spectra suitable for near infrared (NIR, 650-900nm) and shortwave infrared (SWIR, 900-1700nm) fluorescence imaging (NIRFI, SWIRFI). High contrast SWIRFI for solid tumor delineation is demonstrated in multiple murine and human models including breast, prostate, colon, fibrosarcoma and intraperitoneal colorectal metastasis. Organ necropsy and imaging highlighted renal clearance of CJ215. SWIRFI and CJ215 delineated all tumors under ambient lighting with a tumor-to-muscle ratio up to 100 and tumor-to-liver ratio up to 18, from 24 to 168 h post intravenous injection with minimal uptake in healthy organs. Additionally, SWIRFI and CJ215 achieved non-contact quantifiable wound monitoring through commercial bandages. CJ215 provides tumor screening, guided resection, and wound healing assessment compatible with existing and emerging clinical solutions.

In Situ Track-Generated DNA Walker for AND-Gate Logic Imaging of Telomerase and Flap Endonuclease 1 Activities in Living Cells

In situ monitoring of the actions of correlated enzymes in living cells is crucial for expanding our understanding of disease progression and evaluating drug efficacy. However, due to the diverse functions of different enzymes, currently available methods for comprehensive analysis of these events are limited. Here, we present an in situ track-generated DNA walker for AND-gate logic imaging of telomerase (TE) and flap endonuclease 1 (FEN1) activities in live cells. TE is in charge of generating the tracks for the walking strands by extending the TE primer on a gold nanoparticle, while FEN1 is responsible for recognizing the overlapping structure formed by the walking strands and the tracks and then cleaving the fluorescent reporter to produce signals. By utilizing the DNA walker, we successfully determined the expression levels and activities of TE and FEN1 in various cancer cell lines, offering promising prospects for screening inhibitors and investigating the biomolecular mechanisms of diseases.

Recent Advances in the Development of Non-Invasive Imaging Probes for Cancer Immunotherapy

The last two decades have witnessed a major revolution in the field of tumor immunology including clinical progress using various immunotherapy strategies. These advances have highlighted the potential for approaches that harness the power of the immune system to fight against cancer. While cancer immunotherapies have shown significant clinical successes, patient responses vary widely due to the complex and heterogeneous nature of tumors and immune responses, calling for reliable biomarkers and therapeutic strategies to maximize the benefits of immunotherapy. Especially, stratifying responding individuals from non-responders during the early stages of treatment could help avoid long-term damage and tailor personalized treatments. In efforts to develop non-invasive means for accurately evaluating and predicting tumor response to immunotherapy, multiple affinity-based agents targeting immune cell markers and checkpoint molecules have been developed and advanced to clinical trials. In addition, researchers have recently turned their attention to substrate and activity-based imaging probes that can provide real-time, functional assessment of immune response to treatment. Here, we highlight some of those recently designed probes that image functional proteases as biomarkers of cancer immunotherapy with a focus on their chemical design and detection modalities and discuss challenges and opportunities for the development of imaging tools utilized in cancer immunotherapy.

Strategies for quantifying the enzymatic activities of glycoside hydrolases within cells and in vivo

Within their native milieu of the cell, the activities of enzymes are controlled by a range of factors including protein interactions and post-translational modifications. The involvement of these factors in fundamental cell biology and the etiology of diseases is stimulating interest in monitoring enzyme activities within tissues. The creation of synthetic substrates, and their use with different imaging modalities, to detect and quantify enzyme activities has great potential to propel these areas of research. Here we describe the latest developments relating to the creation of substrates for imaging and quantifying the activities of glycoside hydrolases, focusing on mammalian systems. The limitations of current tools and the difficulties within the field are summarised, as are prospects for overcoming these challenges.

An Activatable Near-Infrared Fluorescent Probe for Precise Detection of the Pulmonary Metastatic Tumors: A Traditional Molecule Having a Stunning Turn

An accurate detection of lung metastasis is of great significance for making better treatment choices and improving cancer prognosis, but remains a big challenge in clinical practice. In this study, we propose a reinventing strategy to develop a pH-activatable near-infrared (NIR) fluorescent nanoprobe, pulmonary metastasis tracer (denoted as PMT), based on assembly of NIR dye IR780 and calcium phosphate (CaP). By delicately tuning the intermolecular interactions during the assembly process and dye doping content, as well as the synthetic condition of probe, the fluorescence of PMT could be finely adjusted via the tumor acidity-triggered disassembly. Notably, the selected PMT9 could sharply convert subtle pH variations into a distinct fluorescence signal to generate high fluorescence ON/OFF contrast, dramatically reducing the background signals. Benefiting from such preferable features, PMT9 is able to precisely identify not only the tumor sites in orthotopic lung cancer models but also the pulmonary metastases in mice with remarkable signal-to-background ratio (SBR). This study provides a unique strategy to turn shortcomings of traditional dye IR780 during in vivo imaging into advantages and further expand the application of fluorescent probe to image lung associated tumor lesions.

Target-triggered enzyme-free amplification for highly efficient AND-gated bioimaging in living cells

Rapid, simultaneous, and sensitive detection of biomolecules has important application prospects in disease diagnosis and biomedical research. However, because the content of intracellular endogenous target biomolecules is usually very low, traditional detection methods can't be used for effective detection and imaging, and to enhance the detection sensitivity, signal amplification strategies are frequently required. The hybridization chain reaction (HCR) has been used to detect many disease biomarkers because of its simple operation, good reproducibility, and no enzyme involvement. Although HCR signal amplification methods have been employed to detect and image intracellular biomolecules, there are still false positive signals. Therefore, a target-triggered enzyme-free amplification system (GHCR system) was developed, as a fluorescent AND-gated sensing platform for intracellular target probing. The false positive signals can be well avoided and the accuracy of detection and imaging can be improved by using the design of the AND gate. Two cancer markers, GSH and miR-1246, were used as two orthogonal inputs for the AND gated probe. The AND-gated probe only works when GSH and miR-1246 are the inputs at the same time, and FRET signals can be the output. In addition to the use of AND-gated imaging, FRET-based high-precision ratiometric fluorescence imaging was employed. FRET-based ratiometric fluorescent probes have a higher ability to resist interference from the intracellular environment, they can avoid false positive signals well, and they are expected to have good specificity. Due to the advantages of HCR, AND-gated, and FRET fluorescent probes, the GHCR system exhibited highly efficient AND-gated FRET bioimaging for intracellular endogenous miRNAs with a lower detection limit of 18 pM, which benefits the applications of ratiometric intracellular biosensing and bioimaging and offers a novel concept for advancing the diagnosis and therapeutic strategies in the field of cancer.

Precise tumor delineation in clinical tissues using a novel acidic tumor microenvironment activatable near-infrared fluorescent contrast agent

Tumor selective near-infrared (NIR) fluorescent contrast agents has the potential to greatly enhance the efficiency and precision of tumor surgery by enabling real-time tumor margin identification for tumor resection guided by imaging. However, the development of these agents is still challenging. In this study, based on the acidic tumor microenvironment (TME), we designed and synthesized a novel pH-sensitive NIR fluorescent contrast agent OBD from β-carboline. The fluorescence quantum yield of OBD exhibited a notable increase at pH 3.6, approximately 12-fold higher compared to its value at pH 7.4. After cellular uptake, OBD lighted up the cancer cells with high specificity and accumulated in the mitochondria. Spraying OBD emitted selective fluorescence in xenograft tumor tissues with tumor-to-normal tissue ratios (TNR) as high as 11.18, implying successful image-guided surgery. Furthermore, OBD was also shown to track metastasis in spray mode. After simple topical spray, OBD rapidly and precisely visualized the tumor margins of clinical colon and liver tissues with TNR over 4.2. Therefore, the small-molecule fluorescent contrast agent OBD has promising clinical applications in tumor identification during surgery.

Enzyme and MicroRNA Dual-Regulated Photodynamic Molecular Beacons for Cell-Selective Amplification of Antitumor Efficacy

Photodynamic molecular beacons (PMBs) are highly appealing for activatable photodynamic therapy (PDT), but their applications are hindered by limited therapeutic efficacy. Here, by molecular engineering of enzyme-responsive units in the loop region of DNA-based PMBs, we present for the first time the modular design of an enzyme/microRNA dual-regulated PMB (D-PMB) to achieve cancer-cell-selective amplification of PDT efficacy. In the design, the "inert" photosensitizers in D-PMB could be repeatedly activated in the presence of both tumor-specific enzyme and miRNA, leading to amplified generation of cytotoxic singlet oxygen species and therefore enhanced PDT efficacy in vitro and in vivo. By contrast, low photodynamic activity could be observed in healthy cells, as D-PMB activation has been largely avoided by the dual-regulatable design. This work presents a cooperatively activated PDT strategy, which enables enhanced therapeutic efficacy with improved tumor-specificity and thus conceptualizes an approach to expand the repertoire of designing smart tumor treatment modality.

Enzyme-Triggered DNA Sensor Technology for Spatially-Controlled, Cell-Selective Molecular Imaging

ConspectusWith unparalleled programmability, DNA has evolved as a powerful scaffold for engineering intricate and dynamic systems that can perform diverse tasks. By allowing serial detection of molecular targets in complex cellular milieus, increasingly sophisticated DNA sensors have not only promoted significant advances in unveiling the fundamental mechanisms of various pathophysiological processes but also provided a useful toolkit for disease diagnostics based on molecular signatures. Despite much progress, an inherent limitation of DNA-based sensors is that they often lack spatial control and cell-type selectivity for the sensing activity because of their "always active" design mechanism. Since most molecular targets of interests are not exclusive to disease cells, they are also shared by normal cells, the application of such biosensors for disease-specific imaging is limited by inadequate signal-to-background ratios due to indistinguishable signal response in both disease and normal cells. Therefore, imparting biosensors with spatial controllability remains a key issue to achieve molecular imaging with high sensitivity and cell specificity.As a biocatalyst, enzyme has been found to be closely related with the pathological conditions of numerous diseases. For example, many nucleases, protease, and kinases have been identified overexpressed in disease cells and considered as important biomarkers of cancer, inflammation, and neurological diseases. Recently, we have envisioned that such pathophysiology-associated enzymes could be leveraged as endogenous triggers to achieve spatial control over the molecular imaging activity of the DNA-based sensors with improved cell-specificity. In this Account, we outline the research efforts from our group on the development of endogenous enzyme-triggered, DNA-based sensor technology that enables spatially controlled, cell-type selective molecular imaging. With programmable DNA design and further engineering of enzymatically cleavable sites, a series of DNAzyme- and aptamer-based sensors have been developed for enzyme-controlled imaging of various molecular targets (e.g., metal ions and small molecules) in a cancer cell-selective manner. In particular, by introduction of PNA as bridge molecules to engineer DNA-based sensors with functional peptides, the conceptual design of protease-activated DNA biosensors has been established for spatioselective molecular imaging in cancer cells and extracellular tumor microenvironments. Furthermore, enzyme-triggered signal amplification approaches, such as enzymatically activated molecular beacon and catalytic hairpin assembly, have been developed for spatially selective RNA imaging in specific disease cells (e.g., inflammatory cells and cancer cells), which enables enhanced disease-site specificity and thus improved signal-to-background ratio. The signal amplification strategy is further expanded to cell-selective amplified imaging of non-RNA species through the combination with functional DNA design. Finally, the challenges and potential future directions in this burgeoning field are discussed. We hope this Account offers insights into rational design of enzymatically controlled, DNA-based sensor platforms for opening new frontiers in spatially resolved, cell-selective molecular imaging. We believe that the continuing advances in DNA-based molecular sensing technology together with the discoveries of diverse disease-associated enzymes will promise to usher a new era of diagnosis.

Single-institution experience of 500 pulmonary resections guided by intraoperative molecular imaging

OBJECTIVE

Intraoperative molecular imaging (IMI) using tumor-targeted optical contrast agents can improve thoracic cancer resections. There are no large-scale studies to guide surgeons in patient selection or imaging agent choice. Here, we report our institutional experience with IMI for lung and pleural tumor resection in 500 patients over a decade.

METHODS

Between December 2011 and November 2021, patients with lung or pleural nodules undergoing resection were preoperatively infused with 1 of 4 optical contrast tracers: EC17, TumorGlow, pafolacianine, or SGM-101. Then, during resection, IMI was used to identify pulmonary nodules, confirm margins, and identify synchronous lesions. We retrospectively reviewed patient demographic data, lesion diagnoses, and IMI tumor-to-background ratios (TBRs).

RESULTS

Five hundred patients underwent resection of 677 lesions. We found that there were 4 types of clinical utility of IMI: detection of positive margins (n = 32, 6.4% of patients), identification of residual disease after resection (n = 37, 7.4%), detection of synchronous cancers not predicted on preoperative imaging (n = 26, 5.2%), and minimally invasive localization of nonpalpable lesions (n = 101 lesions, 14.9%). Pafolacianine was most effective for adenocarcinoma-spectrum malignancies (mean TBR, 2.84), and TumorGlow was most effective for metastatic disease and mesothelioma (TBR, 3.1). False-negative fluorescence was primarily seen in mucinous adenocarcinomas (mean TBR, 1.8), heavy smokers (>30 pack years; TBR, 1.9), and tumors greater than 2.0 cm from the pleural surface (TBR, 1.3).

CONCLUSIONS

IMI may be effective in improving resection of lung and pleural tumors. The choice of IMI tracer should vary by the surgical indication and the primary clinical challenge.

An AND-gate bioluminescent probe for precise tumor imaging

Sensitivity and specificity are two indispensable requirements to ensure diagnostic accuracy. Dual-locked probes with "AND-gate" logic theory have emerged as a powerful tool to enhance imaging specificity, avoid "false positive" results, and realize correlation analysis. In addition, bioluminescence imaging (BLI) is an excitation-free optical modality with high sensitivity and low background and can thus be combined with a dual-locked strategy for precise disease imaging. Here, we developed a novel AND-gate bioluminescent probe, FK-Luc-BH, which is capable of responding to two different tumor biomarkers (cathepsin L and ClO^-). The good specificity of FK-Luc-BH was proven, as an obvious BL signal could only be observed in the solution containing both cathepsin L (CTSL) and ClO^-. 4T1-fLuc cells and tumors treated with FK-Luc-BH exhibited significantly higher BL signals than those treated with unresponsive control compound Ac-Luc-EA or cotreated with FK-Luc-BH and a ClO^- scavenger/cathepsin inhibitor, demonstrating the ability of FK-Luc-BH to precisely recognize tumors in which CTSL and ClO^- coexist.

Protease Activated Probes for Real-Time Ratiometric Imaging of Solid Tumors

Surgery is the preferred treatment option for most solid tumors. However, inaccurate detection of cancer borders leads to either incomplete removal of malignant cells or excess excision of healthy tissue. While fluorescent contrast agents and imaging systems improve tumor visualization, they can suffer from low signal-to-background and are prone to technical artifacts. Ratiometric imaging has the potential to eliminate many of these issues such as uneven probe distribution, tissue autofluorescence, and changes in positioning of the light source. Here, we describe a strategy to convert quenched fluorescent probes into ratiometric contrast agents. Conversion of the cathepsin-activated probe, 6QC-Cy5, into a two-fluorophore probe, 6QC-RATIO, significantly improved signal-to-background in vitro and in a mouse subcutaneous breast tumor model. Tumor detection sensitivity was further enhanced using a dual-substrate AND-gate ratiometric probe, Death-Cat-RATIO, that fluoresces only after orthogonal processing by multiple tumor-specific proteases. We also designed and built a modular camera system that was coupled to the FDA-approved da Vinci Xi robot, to enable real-time imaging of ratiometric signals at video frame rates compatible with surgical workflows. Our results demonstrate that ratiometric camera systems and imaging probes have the potential to be clinically implemented to improve surgical resection of many types of cancer.

Acidic tumor microenvironment-activatable fluorescent diagnostic probe for the rapid identification and resection of human tumors via spraying

A fluorescent diagnostic probe for real-time intraoperative image-guided tumor resection can significantly improve the efficiency and quality of oncological therapy, but their development is challenging. Herein, a novel fluorescent diagnostic probe called HLTC based on β-carboline was designed and synthesized. HLTC was found to show a ∼10-fold enhancement of fluorescence quantum field with pH from 7.4 to 4.0, indicating its imaging potential in acid environment which is a typical hallmark of the tumor microenvironment (TME). Following fluorescence microscopy imaging showed HLTC could emit specific signals in cancer cells and sections, by both one-photon excitation and two-photon excitation. Importantly, HLTC enabled the precise and rapid delineation of both transplanted tumor and clinical tumor tissues within several minutes of simple topical spray. The tumor-to-background ratio (TBR) was up to 10.2 ± 1.0 at clinical liver cancer tissues and 9.9 ± 0.3 at clinical colon cancer tissues, allowing precise tumor margin identification and the effective guidance of surgical tumor resection. Furthermore, CCK8 assay, pharmacokinetic evaluation, blood analysis and H&E staining were performed, which verified high biocompatibility and biosafety of HLTC at working concentration. These results reveal the exciting potential of this small-molecule fluorescent diagnostic probe for real-time fluorescence-based navigation during surgical tumor resection.

Activatable near-infrared probes for the detection of specific populations of tumour-infiltrating leukocytes in vivo and in urine

Tracking the immune microenvironment of tumours is essential for understanding the mechanisms behind the effectiveness of cancer immunotherapies. Molecular imaging of tumour-infiltrating leukocytes (TILs) can be used to non-invasively monitor the tumour immune microenvironment, but current imaging agents do not distinguish TILs from leukocytes resident in other tissues. Here we report a library of activatable molecular probes for the imaging, via near-infrared fluorescence, of specific TILs (including M1 macrophages, cytotoxic T lymphocytes and neutrophils) in vivo in real time and also via excreted urine, owing to the probes' renal clearance. The fluorescence of the probes is activated only in the presence of both tumour and leukocyte biomarkers, which allows for the imaging of populations of specific TILs in mouse models of cancers with sensitivities and specificities similar to those achieved via flow-cytometric analyses of biopsied tumour tissues. We also show that the probes enable the non-invasive evaluation of the immunogenicity of different tumours, the dynamic monitoring of responses to immunotherapies and the accurate prediction of tumour growth under various treatments.

Non-invasive molecular imaging for precision diagnosis of metastatic lymph nodes: opportunities from preclinical to clinical applications

Lymph node metastasis is an indicator of the invasiveness and aggressiveness of cancer. It is a vital prognostic factor in clinical staging of the disease and therapeutic decision-making. Patients with positive metastatic lymph nodes are likely to develop recurrent disease, distant metastasis, and succumb to death in the coming few years. Lymph node dissection and histological analysis are needed to detect whether regional lymph nodes have been infiltrated by cancer cells and determine the likely outcome of treatment and the patient's chances of survival. However, these procedures are invasive, and tissue biopsies are prone to sampling error. In recent years, advanced molecular imaging with novel imaging probes has provided new technologies that are contributing to comprehensive management of cancer, including non-invasive investigation of lymphatic drainage from tumors, identifying metastatic lymph nodes, and guiding surgeons to operate efficiently in patients with complex lesions. In this review, first, we outline the current status of different molecular imaging modalities applied for lymph node metastasis management. Second, we summarize the multi-functional imaging probes applied with the different imaging modalities as well as applications of cancer lymph node metastasis from preclinical studies to clinical translations. Third, we describe the limitations that must be considered in the field of molecular imaging for improved detection of lymph node metastasis. Finally, we propose future directions for molecular imaging technology that will allow more personalized treatment plans for patients with lymph node metastasis.

An exploratory human study of superstable homogeneous lipiodol-indocyanine green formulation for precise surgical navigation in liver cancer

The clinical applications of transcatheter arterial embolization (TAE) conversion therapy combined with hepatectomy have been severely restricted by ill-defined tumoral boundaries and miniscule hidden lesions. Fluorescent surgical navigation is a promising method for overcoming these barriers. However, sufficient delivery of the fluorescent probe into the tumor region after long-term TAE is challenging due to blockade of the tumor-supplying artery. Here, a super-stable homogeneous intermix formulating technology (SHIFT) to physically mix lipiodol and indocyanine green (ICG) formulation (SHIFT and ICG) for fluorescent surgical navigation after long-term TAE conversion therapy is provided. Through the retrospective study of 45 clinical liver cancer patients, it is found that SHIFT and ICG formulation have excellent tumor deposition effect and safety. During surgical resection after long-term TAE conversion therapy, SHIFT and ICG could clearly identify in real time the full tumor regions and boundaries and had a high signal-to-normal tissues ratio-even the indistinguishable satellite lesions could be identified with a strong fluorescence intensity. Meanwhile, SHIFT and ICG could improve operative, anesthetic, and postoperative variables associated with postoperative complications. This simple and effective SHIFT could provide precise fluorescent navigation for surgical resection following long-term embolization therapy in clinical practice and has great potential for a translational pipeline.

Self-healing, EMI shielding, and antibacterial properties of recyclable cellulose liquid metal hydrogel sensor

Flexible hydrogels are promising materials for the preparation of artificial intelligence electronics and wearable devices. Introducing a rigid conductive material into the hydrogels can improve their electrical conductivities. However, it may have poor interfacial compatibility with the flexible hydrogel matrix. Therefore, we prepared a hydrogel containing flexible and highly ductile liquid metal (LM). The hydrogel can be used as a strain sensor to monitor human motion. The hydrogel showed many properties (i.e., recyclability, EMI shielding properties (33.14 dB), antibacterial (100 %), strain sensitivity (gauge factor = 2.92), and self-healing) that cannot be achieved simultaneously by a single hydrogel. Furthermore, the recycling of LM and their application to hydrogel-based EMI shielding materials have not been investigated previously. Due to its excellent properties, the prepared flexible hydrogel has great potential for applications in artificial intelligence, personal healthcare, and wearable devices.

Spatial Chemoproteomics for Mapping the Active Proteome

Functional regulation of cell signaling through dynamic changes in protein activity state as well as spatial organization represent two dynamic, complex, and conserved phenomena in biology. Seemingly separate areas of -omics method development have focused on building tools that can detect and quantify protein activity states, as well as map sub-cellular and intercellular protein organization. Integration of these efforts, through the development of chemical tools and platforms that enable detection and quantification of protein functional states with spatial resolution provide opportunities to better understand heterogeneity in the proteome within cell organelles, multi-cellular tissues, and whole organisms. This review provides an overview of and considerations for major classes of chemical proteomic probes and technologies that enable protein activity mapping from sub-cellular compartments to live animals.

Tuning the Cellular Uptake and Retention of Rhodamine Dyes by Molecular Engineering for High-Contrast Imaging of Cancer Cells

Probes allowing high-contrast discrimination of cancer cells and effective retention are powerful tools for the early diagnosis and treatment of cancer. However, conventional small-molecule probes often show limited performance in both aspects. Herein, we report an ingenious molecular engineering strategy for tuning the cellular uptake and retention of rhodamine dyes. Introduction of polar aminoethyl leads to the increased brightness and reduced cellular uptake of dyes, and this change can be reversed by amino acetylation. Moreover, these modifications allow cancer cells to take up more dyes than normal cells (16-fold) through active transport. Specifically, we further improve the signal contrast (56-fold) between cancer and normal cells by constructing activatable probes and confirm that the released fluorophore can remain in cancer cells with extended time, enabling long-term and specific tumor imaging.

Cysteine Cathepsins in Breast Cancer: Promising Targets for Fluorescence-Guided Surgery

The majority of breast cancer patients is treated with breast-conserving surgery (BCS) combined with adjuvant radiation therapy. Up to 40% of patients has a tumor-positive resection margin after BCS, which necessitates re-resection or additional boost radiation. Cathepsin-targeted near-infrared fluorescence imaging during BCS could be used to detect residual cancer in the surgical cavity and guide additional resection, thereby preventing tumor-positive resection margins and associated mutilating treatments. The cysteine cathepsins are a family of proteases that play a major role in normal cellular physiology and neoplastic transformation. In breast cancer, the increased enzymatic activity and aberrant localization of many of the cysteine cathepsins drive tumor progression, proliferation, invasion, and metastasis. The upregulation of cysteine cathepsins in breast cancer cells indicates their potential as a target for intraoperative fluorescence imaging. This review provides a summary of the current knowledge on the role and expression of the most important cysteine cathepsins in breast cancer to better understand their potential as a target for fluorescence-guided surgery (FGS). In addition, it gives an overview of the cathepsin-targeted fluorescent probes that have been investigated preclinically and in breast cancer patients. The current review underscores that cysteine cathepsins are highly suitable molecular targets for FGS because of favorable expression and activity patterns in virtually all breast cancer subtypes. This is confirmed by cathepsin-targeted fluorescent probes that have been shown to facilitate in vivo breast cancer visualization and tumor resection in mouse models and breast cancer patients. These findings indicate that cathepsin-targeted FGS has potential to improve treatment outcomes in breast cancer patients.

Cysteine cathepsins: A long and winding road towards clinics

Biomedical research often focuses on properties that differentiate between diseased and healthy tissue; one of the current focuses is elevated expression and altered localisation of proteases. Among these proteases, dysregulation of cysteine cathepsins can frequently be observed in inflammation-associated diseases, which tips the functional balance from normal physiological to pathological manifestations. Their overexpression and secretion regularly exhibit a strong correlation with the development and progression of such diseases, making them attractive pharmacological targets. But beyond their mostly detrimental role in inflammation-associated diseases, cysteine cathepsins are physiologically highly important enzymes involved in various biological processes crucial for maintaining homeostasis and responding to different stimuli. Consequently, several challenges have emerged during the efforts made to translate basic research data into clinical applications. In this review, we present both physiological and pathological roles of cysteine cathepsins and discuss the clinical potential of cysteine cathepsin-targeting strategies for disease management and diagnosis.

Enzyme-Activatable Chemokine Conjugates for In Vivo Targeting of Tumor-Associated Macrophages

Increased levels of tumor-associated macrophages (TAMs) are indicators of poor prognosis in most cancers. Although antibodies and small molecules blocking the recruitment of macrophages to tumors are under evaluation as anticancer therapies, these strategies are not specific for macrophage subpopulations. Herein we report the first enzyme-activatable chemokine conjugates for effective targeting of defined macrophage subsets in live tumors. Our constructs exploit the high expression of chemokine receptors (e.g., CCR2) and the activity of cysteine cathepsins in TAMs to target these cells selectively over other macrophages and immune cells (e.g., neutrophils, T cells, B cells). Furthermore, we demonstrate that cathepsin-activatable chemokines are compatible with both fluorescent and therapeutic cargos, opening new avenues in the design of targeted theranostic probes for immune cells in the tumor microenvironment.

Enzyme-Activatable Chemokine Conjugates for In Vivo Targeting of Tumor-Associated Macrophages

Increased levels of tumor-associated macrophages (TAMs) are indicators of poor prognosis in most cancers. Although antibodies and small molecules blocking the recruitment of macrophages to tumors are under evaluation as anticancer therapies, these strategies are not specific for macrophage subpopulations. Herein we report the first enzyme-activatable chemokine conjugates for effective targeting of defined macrophage subsets in live tumors. Our constructs exploit the high expression of chemokine receptors (e.g., CCR2) and the activity of cysteine cathepsins in TAMs to target these cells selectively over other macrophages and immune cells (e.g., neutrophils, T cells, B cells). Furthermore, we demonstrate that cathepsin-activatable chemokines are compatible with both fluorescent and therapeutic cargos, opening new avenues in the design of targeted theranostic probes for immune cells in the tumor microenvironment.

Emerging Biomaterials Imaging Antitumor Immune Response

Immunotherapy is one of the most promising clinical modalities for the treatment of malignant tumors and has shown excellent therapeutic outcomes in clinical settings. However, it continues to face several challenges, including long treatment cycles, high costs, immune-related adverse events, and low response rates. Thus, it is critical to predict the response rate to immunotherapy by using imaging technology in the preoperative and intraoperative. Here, the latest advances in nanosystem-based biomaterials used for predicting responses to immunotherapy via the imaging of immune cells and signaling molecules in the immune microenvironment are comprehensively summarized. Several imaging methods, such as fluorescence imaging, magnetic resonance imaging, positron emission tomography imaging, ultrasound imaging, and photoacoustic imaging, used in immune predictive imaging, are discussed to show the potential of nanosystems for distinguishing immunotherapy responders from nonresponders. Nanosystem-based biomaterials aided by various imaging technologies are expected to enable the effective prediction and diagnosis in cases of tumors, inflammation, and other public diseases.

A simple and smart AND-gate DNA nanoprobe for correlated enzymes tracking and cell-selective imaging

Accurate cancer diagnosis and effective drug therapy entail sensitive and dynamic monitoring of intracellular key enzymes, since their expression level is closely related to disease progression. Simultaneous monitoring of correlated enzymes is promising to help unveiling mystery of cytobiological events during tumor progression and drug response, while is challenged by lacking of a robust and simple simultaneous detection strategy. In order to construct a simple and smart strategy which is complex design-avoided and doesn't need other auxiliary enzyme, here we develop an AND-gate strategy for simultaneously monitoring correlated enzymes which both are upregulated in cancer cells (telomerase and apurinic/apyrimidinic endonuclease 1). An innovative AND-gate DNA nanoprobe has been designed to avoid mutual interference and background noise, guaranteeing an enhanced fluorescent signal output upon catalyzation of dual enzymes. This AND-gate strategy achieves sensitive detection of two enzymes in an individual manner in test tube, through which the diagnostic potential of bladder cancer has been validated by telomerase detection in clinical urine sample. The AND-gate strategy enables specific intracellular imaging of dual enzymes in different cancer cell lines. Importantly, in contrast to traditional single-targeting strategies, AND-gate imaging of dual enzymes significantly improves cancer cell selectivity. Moreover, this strategy dynamically monitors enzymatic activity changes during chemoresistance induced by chemotherapeutic treatment. This simple and smart strategy has foreseeable prospect in the fields of disease diagnosis, drug prognosis evaluation, and precise fluorescence-guided surgery.

A Cathepsin-Targeted Quenched Activity-Based Probe Facilitates Enhanced Detection of Human Tumors during Resection

PURPOSE

Fluorescence-guided surgery using tumor-targeted contrast agents has been developed to improve the completeness of oncologic resections. Quenched activity-based probes that fluoresce after covalently binding to tumor-specific enzymes have been proposed to improve specificity, but none have been tested in humans. Here, we report the successful clinical translation of a cathepsin activity-based probe (VGT-309) for fluorescence-guided surgery.

EXPERIMENTAL DESIGN

We optimized the specificity, dosing, and timing of VGT-309 in preclinical models of lung cancer. To evaluate clinical feasibility, we conducted a canine study of VGT-309 during pulmonary tumor resection. We then conducted a randomized, double-blind, dose-escalation study in healthy human volunteers receiving VGT-309 to evaluate safety. Finally, we tested VGT-309 in humans undergoing lung cancer surgery.

RESULTS

In preclinical models, we found highly specific tumor cell labeling that was blocked by a broad spectrum cathepsin inhibitor. When evaluating VGT-309 for guidance during resection of canine tumors, we found that the probe selectively labeled tumors and demonstrated high tumor-to-background ratio (TBR; range: 2.15-3.71). In the Phase I human study, we found that VGT-309 was safe at all doses studied. In the ongoing Phase II trial, we report two cases in which VGT-309 localized visually occult, non-palpable tumors (TBRs = 2.83 and 7.18) in real time to illustrate its successful clinical translation and potential to improve surgical management.

CONCLUSIONS

This first-in-human study demonstrates the safety and feasibility of VGT-309 to label human pulmonary tumors during resection. These results may be generalizable to other cancers due to cathepsin overexpression in many solid tumors.

A versatile fluorescence-quenched substrate for quantitative measurement of glucocerebrosidase activity within live cells

Loss of activity of the lysosomal glycosidase β-glucocerebrosidase (GCase) causes the lysosomal storage disease Gaucher disease (GD) and has emerged as the greatest genetic risk factor for the development of both Parkinson disease (PD) and dementia with Lewy bodies. There is significant interest into how GCase dysfunction contributes to these diseases, however, progress toward a full understanding is complicated by presence of endogenous cellular factors that influence lysosomal GCase activity. Indeed, such factors are thought to contribute to the high degree of variable penetrance of GBA mutations among patients. Robust methods to quantitatively measure GCase activity within lysosomes are therefore needed to advance research in this area, as well as to develop clinical assays to monitor disease progression and assess GCase-directed therapeutics. Here, we report a selective fluorescence-quenched substrate, LysoFQ-GBA, which enables measuring endogenous levels of lysosomal GCase activity within living cells. LysoFQ-GBA is a sensitive tool for studying chemical or genetic perturbations of GCase activity using either fluorescence microscopy or flow cytometry. We validate the quantitative nature of measurements made with LysoFQ-GBA using various cell types and demonstrate that it accurately reports on both target engagement by GCase inhibitors and the GBA allele status of cells. Furthermore, through comparisons of GD, PD, and control patient-derived tissues, we show there is a close correlation in the lysosomal GCase activity within monocytes, neuronal progenitor cells, and neurons. Accordingly, analysis of clinical blood samples using LysoFQ-GBA may provide a surrogate marker of lysosomal GCase activity in neuronal tissue.