PD-L1 siRNA hitched polyethyleneimine-elastase constituting nanovesicle induces tumor immunogenicity and PD-L1 silencing for synergistic antitumor immunotherapy

BACKGROUND

PD-1/PD-L1 blockade has become a powerful method to treat malignant tumors. However, a large proportion of patients still do not benefit from this treatment, due to low tumor immunogenicity and low tumor penetration of the agents. Recently, neutrophil elastase has been shown to induce robust tumor immunogenicity, while the insufficient enzyme activity at the tumor site restricted its anti-tumor application. Here, we designed polyethyleneimine-modified neutrophil elastase (PEI-elastase) loaded with PD-L1small interfering RNA (PD-L1 siRNA) for improving enzymatic activity and delivering siRNA to tumor, which was expected to solve the above-mentioned problems.

RESULTS

We first demonstrated that PEI-elastase possessed high enzymatic activity, which was also identified as an excellent gene-delivery material. Then, we synthesized anti-tumor lipopolymer (P-E/S Lip) by encapsulating PEI-elastase and PD-L1siRNA with pH-responsive anionic liposomes. The P-E/S Lip could be rapidly cleaved in tumor acidic environment, leading to exposure of the PEI-elastase/PD-L1 siRNA. Consequently, PEI-elastase induced powerful tumor immunogenicity upon direct tumor killing with minimal toxicity to normal cells. In parallel, PEI-elastase delivered PD-L1siRNA into the tumor and reduced PD-L1 expression. Orthotopic tumor administration of P-E/S Lip not only attenuated primary tumor growth, but also produced systemic anti-tumor immune response to inhibit growth of distant tumors and metastasis. Moreover, intravenous administration of P-E/S Lip into mice bearing subcutaneous tumors leaded to an effective inhibition of established B16-F10 tumor and 4T1 tumor, with histological analyses indicating an absence of detectable toxicity.

CONCLUSIONS

In our study, a protease-based nanoplatform was used to cooperatively provoke robust tumor immunogenicity and down-regulate PD-L1 expression, which exhibited great potential as a combination therapy for precisely treating solid tumors.

Phosphinate Esters as Novel Warheads for Quenched Activity-Based Probes Targeting Serine Proteases

Quenched activity-based probes (qABP) are invaluable tools to visualize aberrant protease activity. Unfortunately, most studies so far have only focused on cysteine proteases, and only a few studies describe the synthesis and use of serine protease qABPs. We recently used phosphinate ester electrophiles as a novel type of reactive group to construct ABPs for serine proteases. Here, we report on the construction of qABPs based on the phosphinate warhead, exemplified by probes for the neutrophil serine proteases. The most successful probes show sub-stoichiometric reaction with human neutrophil elastase, efficient fluorescence quenching, and rapid unquenching of fluorescence upon reaction with target proteases.

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.

A fluorogenic, peptide-based probe for the detection of Cathepsin D in macrophages

Cathepsin D is a protease that is an effector in the immune response of macrophages, yet to date, only a limited number of probes have been developed for its detection. Herein, we report a water soluble, highly sensitive, pH insensitive fluorescent probe for the detection of Cathepsin D activity that provides a strong OFF/ON signal upon activation and with bright emission at 515 nm. The probe was synthesised using a combination of solid and solution-phase chemistries, with probe optimisation to increase its water solubility and activation kinetics by addition of a long PEG chain (5 kDa) at the C-terminus. A BODIPY fluorophore allowed detection of Cathepsin D across a wide pH range, important as the protease is active both at the low pH found in lysosomes and also in higher pH phagolysosomes, and in the cytosol. The probe was successfully used to detect Cathepsin D activity in macrophages challenged by exposure to bacteria.

Moving into the red - a near infra-red optical probe for analysis of human neutrophil elastase in activated neutrophils and neutrophil extracellular traps

Neutrophils are the first immune cells recruited for defence against invading pathogens; however, their dysregulated activation and subsequent release of the enzyme human neutrophil elastase is associated with several, inflammation-based, diseases. Herein, we describe a FRET-based, tri-branched (one quencher, three fluorophores) near infrared probe that provides an intense OFF/ON amplified fluorescence signal for specific detection of human neutrophil elastase. The probe allowed selective detection of activated neutrophils and labelling of neutrophil extracellular traps.

A Tandem-Locked Fluorescent NETosis Reporter for the Prognosis Assessment of Cancer Immunotherapy

NETosis, the peculiar type of neutrophil death, plays important roles in pro-tumorigenic functions and inhibits cancer immunotherapy. Non-invasive real-time imaging is thus imperative for prognosis of cancer immunotherapy yet remains challenging. Herein, we report a Tandem-locked NETosis Reporter 1 (TNR1 ) that activates fluorescence signals only in the presence of both neutrophil elastase (NE) and cathepsin G (CTSG) for the specific imaging of NETosis. In the aspect of molecular design, the sequence of biomarker-specific tandem peptide blocks can largely affect the detection specificity towards NETosis. In live cell imaging, the tandem-locked design allows TNR1 to differentiate NETosis from neutrophil activation, while single-locked reporters fail to do so. The near-infrared signals from activated TNR1 in tumor from living mice were consistent with the intratumoral NETosis levels from histological results. Moreover, the near-infrared signals from activated TNR1 negatively correlated with tumor inhibition effect after immunotherapy, thereby providing prognosis for cancer immunotherapy. Thus, our study not only demonstrates the first sensitive optical reporter for noninvasive monitoring of NETosis levels and evaluation of cancer immunotherapeutic efficacy in tumor-bearing living mice, but also proposes a generic approach for tandem-locked probe design.

Moonlighting chromatin: when DNA escapes nuclear control

Extracellular chromatin, for example in the form of neutrophil extracellular traps (NETs), is an important element that propels the pathological progression of a plethora of diseases. DNA drives the interferon system, serves as autoantigen, and forms the extracellular scaffold for proteins of the innate immune system. An insufficient clearance of extruded chromatin after the release of DNA from the nucleus into the extracellular milieu can perform a secret task of moonlighting in immune-inflammatory and occlusive disorders. Here, we discuss (I) the cellular events involved in the extracellular release of chromatin and NET formation, (II) the devastating consequence of a dysregulated NET formation, and (III) the imbalance between NET formation and clearance. We include the role of NET formation in the occlusion of vessels and ducts, in lung disease, in autoimmune diseases, in chronic oral disorders, in cancer, in the formation of adhesions, and in traumatic spinal cord injury. To develop effective therapies, it is of utmost importance to target pathways that cause decondensation of chromatin during exaggerated NET formation and aggregation. Alternatively, therapies that support the clearance of extracellular chromatin are conceivable.

Fluorogenic Granzyme A Substrates Enable Real-Time Imaging of Adaptive Immune Cell Activity

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near-infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity-based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild-type and GzmA knock-out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen-driven recognition of cancer cells in real time.

Fluorogenic Granzyme A Substrates Enable Real-Time Imaging of Adaptive Immune Cell Activity

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near-infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity-based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild-type and GzmA knock-out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen-driven recognition of cancer cells in real time.

Coumarin-based turn-on fluorescence probe with a large Stokes shift for detection of endogenous neutrophil elastase in live cells and zebrafish

Neutrophil elastase (NE), a serine proteinase, is a significant biomarker which is closely related to the progress of diseases. However, only few probes have been reported for detection of NE activity and cell imaging. And these probes have exhibited small Stokes shift, which leads to high fluorescence interferences. Furthermore, only one probe among them is able to image NE in vivo successfully. To overcome the above problems, we designed a novel coumarin-based fluorescent probe HNCOU-NE with large Stokes shift to visualize NE activity in living cells and zebrafish. The new probe HNCOU-NE for NE contains fluorophore HNCOU as the reporter and pentafluoroethyl as the enzyme-active trigger moiety. As expected, HNCOU-NE displays perfect detecting performance for sensing of NE, including good water solubility, large Stokes shift, high affinity and wide linear response concentration. In addition, HNCOU-NE has been successfully utilized for NE real-time detection and imaging in different living cells, exhibiting low cytotoxicity and excellent biocompatibility. Most importantly, endogenous NE fluorescence imaging experiments reveals that HNCOU-NE can distinguish liver cancer cells (HepG2) and other cells (293T, HeLa and SKOV3), illustrating its specific ability to diagnose liver cancer cells. Besides, probe HNCOU-NE also has the ability to specifically detect endogenous NE activity in living zebrafish. All the results indicate that HNCOU-NE is a valuable probe for qualitative and quantitative sensing of NE activity in vitro and in vivo.

Activity-Based Probes for Proteases Pave the Way to Theranostic Applications

Proteases are important enzymes in health and disease. Their activities are regulated at multiple levels. In fact, proteases are synthesized as inactive proenzymes (zymogens) that are activated by proteolytic removal of their pro-peptide sequence and can remain active or their activity can be attenuated by complex formation with specific endogenous inhibitors or by limited proteolysis or degradation. Consequently, quite often, only a fraction of the protease molecules is in the active/functional form, thus, the abundance of a protease is not always linearly proportional to the (patho)physiological function(s). Therefore, assays to determine the active forms of proteases are needed, not only in research but also in molecular diagnosis and therapy. Activity-based probes (ABPs) are chemical entities that bind covalently to the active enzyme/protease. ABPs carry a detection tag to enable localization and quantification of specific enzymatic/proteolytic activities with applications in molecular imaging and diagnosis. Moreover, ABPs act as suicide inhibitors of proteases, which can be exploited for delineation of the functional role(s) of a given protease in (patho) biological context and as potential therapeutics. In this sense, ABPs represent new theranostic agents. We outline recent developments pertaining to ABPs for proteases with potential therapeutic applications, with the aim to highlight their importance in theranostics.

Activatable Fluorophores for Imaging Immune Cell Function

Optical imaging has become an essential tool to study biomolecular processes in live systems with unprecedented spatial resolution. New fluorescent technologies and advances in optical microscopy have revolutionized the ways in which we can study immune cells in real time. For example, activatable fluorophores that emit signals after target recognition have enabled direct imaging of immune cell function with enhanced readouts and minimal background. In this Account, we summarize recent advances in the chemical synthesis and implementation of activatable fluorescent probes to monitor the activity and the role of immune cells in different pathological processes, from infection to inflammatory diseases or cancer. In addition to the contributions that our group has made to this field, we review the most relevant literature disclosed over the past decade, providing examples of different activatable architectures and their application in diagnostics and drug discovery. This Account covers the imaging of the three major cell types in the immune system, that is, neutrophils, macrophages, and lymphocytes. Attracted by the tunability and target specificity of peptides, many groups have designed strategies based on fluorogenic peptides whose fluorescence emission is regulated by the reaction with enzymes (e.g., MMPs, cathepsins, granzymes), or through Förster resonance energy transfer (FRET) mechanisms. Selective imaging of immune cells has been also achieved by targeting different intracellular metabolic routes, such as lipid biogenesis. Other approaches involve the implementation of diversity-oriented fluorescence libraries or the use of environmentally sensitive fluorescent scaffolds (e.g., molecular rotors). Our group has made important progress by constructing probes to image metastasis-associated macrophages in tumors, apoptotic neutrophils, or cytotoxic natural killer (NK) cells against cancer cells, among other examples. The chemical probes covered in this Account have been successfully validated in vitro in cell culture systems, and in vivo in relevant models of inflammation and cancer. Overall, the range of chemical structures and activation mechanisms reported to sense immune cell function is remarkable. However, the emergence of new strategies based on new molecular targets or activatable mechanisms that are yet to be discovered will open the door to track unexplored roles of immune cells in different biological systems. We anticipate that upcoming generations of activatable probes will find applications in the clinic to help assessing immunotherapies and advance precision medicine. We hope that this Account will evoke new ideas and innovative work in the design of fluorescent probes for imaging cell function.

Peptide probes for proteases - innovations and applications for monitoring proteolytic activity

Proteases are excellent biomarkers for a variety of diseases, offer multiple opportunities for diagnostic applications and are valuable targets for therapy. From a chemistry-based perspective this review discusses and critiques the most recent advances in the field of substrate-based probes for the detection and analysis of proteolytic activity both in vitro and in vivo.

Peptide-Derived Biosensors and Their Applications in Tumor Immunology-Related Detection

Small-molecular targeting peptides possess features of biocompatibility, affinity, and specificity, which is widely applied in molecular recognition and detection. Moreover, peptides can be developed into highly ordered supramolecular assemblies with boosting binding affinities, diverse functions, and enhanced stabilities suitable for biosensors construction. In this Review, we summarize recent progress of peptide-based biosensors for precise detection, especially on tumor-related analysis, as well as further provide a brief overview of the progress in tumor immune-related detection. Also, we are looking forward to the prospective future of peptide-based biosensors.

COVID-19-related cardiac complications from clinical evidences to basic mechanisms: opinion paper of the ESC Working Group on Cellular Biology of the Heart

The pandemic of coronavirus disease (COVID)-19 is a global threat, causing high mortality, especially in the elderly. The main symptoms and the primary cause of death are related to interstitial pneumonia. Viral entry also into myocardial cells mainly via the angiotensin converting enzyme type 2 (ACE2) receptor and excessive production of pro-inflammatory cytokines, however, also make the heart susceptible to injury. In addition to the immediate damage caused by the acute inflammatory response, the heart may also suffer from long-term consequences of COVID-19, potentially causing a post-pandemic increase in cardiac complications. Although the main cause of cardiac damage in COVID-19 remains coagulopathy with micro- (and to a lesser extent macro-) vascular occlusion, open questions remain about other possible modalities of cardiac dysfunction, such as direct infection of myocardial cells, effects of cytokines storm, and mechanisms related to enhanced coagulopathy. In this opinion paper, we focus on these lesser appreciated possibilities and propose experimental approaches that could provide a more comprehensive understanding of the cellular and molecular bases of cardiac injury in COVID-19 patients. We first discuss approaches to characterize cardiac damage caused by possible direct viral infection of cardiac cells, followed by formulating hypotheses on how to reproduce and investigate the hyperinflammatory and pro-thrombotic conditions observed in the heart of COVID-19 patients using experimental in vitro systems. Finally, we elaborate on strategies to discover novel pathology biomarkers using omics platforms.