Activatable senoprobes and senolytics: Novel strategies to detect and target senescent cells

Bioorthogonally Activatable Photosensitizer for NIR Fluorescence Imaging-Guided Highly Selective Elimination of Senescent Tumor Cells and Chemotherapy Enhancement

Chemotherapy is a primary modality in cancer treatment, but it may induce cellular senescence, which in turn triggers the release of senescence-associated secretory phenotypes (SASPs) that promote tumor growth and metastasis. To selectively identify senescent cells and mitigate their negative impact on cancer therapy, herein, we have developed a β-galactosidase (β-Gal)-activated and self-immobilizing photosensitizer CyGF-DBCO-T. This photosensitizer can be selectively activated and fluorescently label proteins in situ within senescent cells, enabling near-infrared (NIR) fluorescence imaging-guided photodynamic therapy (PDT) for the precise ablation of these cells. First, we developed an activatable NIR fluorescent probe CyGF-N3 that can specifically in situ label senescent cells. Subsequently, DBCO-T with free radicals underwent a bioorthogonal click reaction with activated CyGF-N3 in senescent cells to generate the photosensitizer CyO-DBCO-T. Under light irradiation, CyO-DBCO-T generated singlet oxygen (1O2) in situ, thereby enabling precise PDT with fluorescence guidance and photoactivation. Both CyGF-N3 and DBCO-T were encapsulated in biotinylated liposomes (CyGF-N3@LIP-B and DBCO-T@LIP-B), which enhanced their water solubility, tumor targeting, and in vivo circulation time. This promoted the accumulation of the probes in senescent tumor cells, thus enabling intense fluorescence imaging of tumor senescence regions in mice and enhancing the efficacy of PDT. This dual-module strategy, guided by fluorescence imaging for PDT, has achieved selective identification and precise ablation of senescent tumor cells in a chemotherapy-induced senescence model, effectively alleviating chemotherapy resistance and suppressing tumor growth.

The context-dependent effect of cellular senescence: From embryogenesis and wound healing to aging

Aging is characterized by a steady loss of physiological integrity, leading to impaired function and increased vulnerability to death. Cell senescence is a biological process that progresses with aging and is believed to be a key driver of age-related diseases. Senescence, a hallmark of aging, also demonstrates its beneficial physiological aspects as an anti-cancer, pro-regenerative, homeostatic, and developmental mechanism. A transitory response in which the senescent cells are quickly formed and cleared may promote tissue regeneration and organismal fitness. At the same time, senescence-related secretory phenotypes associated with extended senescence can have devastating effects. The fact that the interaction between senescent cells and their surroundings is very context-dependent may also help to explain this seemingly opposing pleiotropic function. Further, mitochondrial dysfunction is an often-unappreciated hallmark of cellular senescence and figures prominently in multiple feedback loops that induce and maintain the senescent phenotype. This review summarizes the mechanism of cellular senescence and the significance of acute senescence. We concisely introduced the context-dependent role of senescent cells and SASP, aspects of mitochondrial biology altered in the senescent cells, and their impact on the senescent phenotype. Finally, we conclude with recent therapeutic advancements targeting cellular senescence, focusing on acute injuries and age-associated diseases. Collectively, these insights provide a future roadmap for the role of senescence in organismal fitness and life span extension.

Recent Advances in Anti-Aging Therapeutic Strategies Targeting DNA Damage Response and Senescence-Associated Secretory Phenotype-Linked Signaling Cascade

Aging is considered the contributory accumulation of abruptions occurring through cell signaling cascades, which ultimately cause changes in physical functions, cell fate, and damage across all organ systems. DNA damage response (DDR) also occurs through telomere shortening, tumor formation, mitochondrial dysfunction, and so forth. Cellular aging occurs through cell cycle arrest, which is the result of extended DDR cascade signaling networks via MDC1, 53BP1, H2AX, ATM, ARF, P53, P13-Akt, BRAF, Sirtuins, NAD + , and so forth. These persistent cell cycle arrests initiated by DDR and other associated stress-induced signals promote a permanent state of cell cycle arrest called senescence-associated secretory phenotype (SASP). However, cellular aging gets accelerated with faulty DNA repair systems, and the produced senescent cells further generate various promoting contributors to age-related dysfunctional diseases including SASP. Any changes to these factors contribute to age-related disease development. Therefore, this review explores anti-aging factors targeting DDR and SASP regulation and their detailed signaling networks. In addition, it allows researchers to identify anti-aging targets and anti-aging therapeutic strategies based on identified and nonidentified targets.

Cellular senescence and PAPP-A

Cellular senescence and its accompanying secretome have major impact on growth and aging of mammalian organisms. A novel protease, PAPP-A, regulates the bioavailability of an important growth factor, insulin-like growth factor (IGF)-I, and has major impact on growth and aging. This short review will explore a new perspective of cellular senescence and PAPP-A.

Mechanisms and strategies of immunosenescence effects on non-small cell lung cancer (NSCLC) treatment: A comprehensive analysis and future directions

Non-small cell lung cancer (NSCLC), the most prevalent form of lung cancer, remains a leading cause of cancer-related mortality worldwide, particularly among elderly individuals. The phenomenon of immunosenescence, characterized by the progressive decline in immune cell functionality with aging, plays a pivotal role in NSCLC progression and contributes to the diminished efficacy of therapeutic interventions in older patients. Immunosenescence manifests through impaired immune surveillance, reduced cytotoxic responses, and increased chronic inflammation, collectively fostering a pro-tumorigenic microenvironment. This review provides a comprehensive analysis of the molecular, cellular, and genetic mechanisms of immunosenescence and its impact on immune surveillance and the tumor microenvironment (TME) in NSCLC. We explore how aging affects various immune cells, including T cells, B cells, NK cells, and macrophages, and how these changes compromise the immune system's ability to detect and eliminate tumor cells. Furthermore, we address the challenges posed by immunosenescence to current therapeutic strategies, particularly immunotherapy, which faces significant hurdles in elderly patients due to immune dysfunction. The review highlights emerging technologies, such as single-cell sequencing and CRISPR-Cas9, which offer new insights into immunosenescence and its potential as a therapeutic target. Finally, we outline future research directions, including strategies for rejuvenating the aging immune system and optimizing immunotherapy for older NSCLC patients, with the goal of improving treatment efficacy and survival outcomes. These efforts hold promise for the development of more effective, personalized therapies for elderly patients with NSCLC.

Improved Therapeutic Efficiency of Senescent Cell-specific, Galactose-Functionalized Micelle Nanocarriers

Cellular senescence has recently been recognized as one of the hallmarks of cancer, aging, as well as many age-related disorders, sparking significant interest in the development of senolytics, compounds that can remove senescent cells. However, most current pharmacological strategies face challenges related to non-specific delivery, leading to significant side effects that hinder safe and effective treatments. To address these issues, galactose-functionalized amphiphiles are synthesized that can self-assemble into micelles and be loaded with a senolytic cargo. These galactose-micelles are responsive to the lysosomal β-galactosidase enzyme, present in elevated amounts in senescent cells, and are employed for specific delivery of the senolytic Bcl2-inhibitor Navitoclax. This novel formulation showed reduced delivery and toxicity to non-senescent cells, thereby increasing the senolytic index of Navitoclax and making it suitable for future in vivo experimental designs to improve selectivity and safety profiles.

Nanodevice-Mediated Immune Cell Recruitment: Targeting Senescent Cells via MMP-3-Responsive CXCL12-Coated Nanoparticles

Senescent cells are involved in age-related disorders in different organs and are therapeutic targets for fibrotic and chronic pathologies. Immune-modulating agents, able to enhance senescent cell detection and elimination by endogenous immune cells, have emerged as pharmacological strategies. We report herein a nanoparticle for immune cell-mediated senolytic therapy designed to recruit immune cells in response to specific enzymatic matrix metalloproteinase-3 (MMP-3) activity in the senescence-associated secretory phenotype. For this, mesoporous silica nanoparticles (MSNs) are coated with a peptide substrate of the metalloproteinase MMP-3, and the peptide is decorated with chemokine CXCL12 that enhances immune cell recruitment (NPs@CXCL12). Controlled release studies confirmed the progressive and specific release of CXCL12 in the presence of MMP-3. The ability of immune cell recruitment in response to a senescent microenvironment (senescent WI-38 fibroblasts) is confirmed by Transwell migration assays with green fluorescent Jurkat T-cells, showing NPs@CXCL12 has an enhanced chemotaxis effect toward senescent cells compared to free CXCL12 (2-fold). Moreover, the cytotoxic capacity of human primary natural killer (NK) cells over senescent WI-38 is also confirmed, and their migration trajectories in response to NPs@CXCL12 or free CXCL12 are monitored by using a microfluidic device. Results confirm the ability of NPs@CXCL12 to generate a chemotactic gradient able to attract NK cells. When compared with free CXCL12, the NPs@CXCL12 system showed a reduction of up to 15.56% in the population of NK cells migrating toward free CXCL12 under competitive conditions. This study demonstrates the potential of designing nanoparticles to recruit immune cells under specific responses to eliminate senescent cells. Results confirm that NPs@CXCL12 can effectively establish a chemotactic gradient to attract NK cells.

Development of Calcium-Dependent Phospholipase A2 Inhibitors to Target Cellular Senescence and Oxidative Stress in Neurodegenerative Diseases

Significance: Cellular senescence is a critical process underlying aging and is associated with age-related diseases such as Alzheimer's disease. Lipids are implicated in cellular senescence. Fatty acids, particularly eicosanoids, have been associated with various forms of senescence and inflammation, and the associated reactive oxygen species production has been proposed as a therapeutic target for mitigating senescence. When overactivated, calcium-dependent phospholipase A2 (cPLA2) catalyzes the conversion of arachidonic acid into eicosanoids such as leukotrienes and prostaglandins. Recent Advances: With a growing understanding of the importance of lipids as mediators and modulators of senescence, cPLA2 has emerged as a compelling drug target. cPLA2 overactivation plays a significant role in several pathways associated with senescence, including neuroinflammation and oxidative stress. Critical Issues: Previous cPLA2 inhibitors have shown potential in ameliorating inflammation and oxidative stress, but the dominant hurdles in the central nervous system-targeting drug discovery are specificity and blood-brain barrier penetrance. Future Directions: With the need for more effective drugs against neurological diseases, we emphasize the significance of discovering new brain-penetrant, potent, and specific cPLA2 inhibitors. We discuss how the recently developed Virtual Synthon Hierarchical Enumeration Screening, an iterative synthon-based approach for fast structure-based virtual screening of billions of compounds, provides an efficient exploration of large chemical spaces for the discovery of brain-penetrant cPLA2 small-molecule inhibitors. Antioxid. Redox Signal. 41, 1100-1116.

Photoacoustic polydopamine-indocyanine green (PDA-ICG) nanoprobe for detection of senescent cells

Cellular senescence is considered an important tumour suppression mechanism in response to damage and oncogenic stress in early lesions. However, when senescent cells are not immune-cleared and persist in the tumour microenvironment, they can drive a variety of tumour-promoting activities, including cancer initiation, progression, and metastasis. Additionally, there is compelling evidence demonstrating a direct connection between chemo(radio)therapy-induced senescence and the development of drug resistance and cancer recurrence. Therefore, detection of senescent cells in tissues holds great promise for predicting cancer occurrence earlier, assessing tumour progression, aiding patient stratification and prognosis, and informing about the efficacy of potential senotherapies. However, effective detection of senescent cells is limited by lack of biomarkers and readout strategies suitable for in vivo clinical imaging. To this end, a nanoprobe composed of biocompatible polydopamine (PDA) nanoparticle doped with FDA-approved indocyanine green (ICG) dye, namely PDA-ICG, was designed as a contrast agent for senescence detection using photoacoustic imaging (PAI). In an in vitro model of chemotherapy-induced senescence, PDA-ICG nanoprobe showed an elevated uptake in senescent cells relative to cancer cells. In addition to its improved photostability, 2.5-fold enhancement in photoacoustic signal relative to ICG was observed. Collectively, the results indicate that the PDA-ICG nanoprobe has the potential to be used as a contrast agent for senescence detection of chemotherapy-induced senescence using PAI.

Emerging insights in senescence: pathways from preclinical models to therapeutic innovations

Senescence is a crucial hallmark of ageing and a significant contributor to the pathology of age-related disorders. As committee members of the young International Cell Senescence Association (yICSA), we aim to synthesise recent advancements in the identification, characterisation, and therapeutic targeting of senescence for clinical translation. We explore novel molecular techniques that have enhanced our understanding of senescent cell heterogeneity and their roles in tissue regeneration and pathology. Additionally, we delve into in vivo models of senescence, both non-mammalian and mammalian, to highlight tools available for advancing the contextual understanding of in vivo senescence. Furthermore, we discuss innovative diagnostic tools and senotherapeutic approaches, emphasising their potential for clinical application. Future directions of senescence research are explored, underscoring the need for precise, context-specific senescence classification and the integration of advanced technologies such as machine learning, long-read sequencing, and multifunctional senoprobes and senolytics. The dual role of senescence in promoting tissue homoeostasis and contributing to chronic diseases highlights the complexity of targeting these cells for improved clinical outcomes.

Therapy-Induced Senescence: Novel Approaches for Markers Identification

Therapy-induced senescence (TIS) represents a major cellular response to anticancer treatments. Both malignant and non-malignant cells in the tumor microenvironment undergo TIS and may be harmful for cancer patients since TIS cells develop a senescence-associated secretory phenotype (SASP) that can sustain tumor growth. The SASP also modulates anti-tumor immunity, although the immune populations involved and the final results appear to be context-dependent. In addition, senescent cancer cells are able to evade senescence growth arrest and to resume proliferation, likely contributing to relapse. So, research data suggest that TIS induction negatively affects therapy outcomes in cancer patients. In line with this, new interventions aimed at the removal of senescent cells or the reprogramming of their SASP, called senotherapy, have become attractive therapeutic options. To date, the lack of reliable, cost-effective, and easy-to-use TIS biomarkers hinders the application of recent anti-senescence therapeutic approaches in the clinic. Hence, the identification of biomarkers for the detection of TIS tumor cells and TIS non-neoplastic cells is a high priority in cancer research. In this review article, we describe the current knowledge about TIS, outline critical gaps in our knowledge, and address recent advances and novel approaches for the discovery of TIS biomarkers.

Combining rejuvenation interventions in rodents: a milestone in biomedical gerontology whose time has come

INTRODUCTION

Longevity research has matured to the point where significantly postponing age-related decline in physical and mental function is now achievable in the laboratory and foreseeable in the clinic. The most promising strategies involve rejuvenation, i.e. reducing biological age, not merely slowing its progression.

AREAS COVERED

We discuss therapeutic strategies for rejuvenation and results achieved thus far, with a focus on in vivo studies. We discuss the implications of interventions which act on mean or maximum lifespan and those showing effects in accelerated disease models. While the focus is on work conducted in mice, we also highlight notable insights in the field from studies in other model organisms.

EXPERT OPINION

Rejuvenation was originally proposed as easier than slowing aging because it targets initially inert changes to tissue structure and composition, rather than trying to disentangle processes that both create aging damage and maintain life. While recent studies support this hypothesis, a true test requires a panel of rejuvenation interventions targeting multiple damage categories simultaneously. Considerations of cost, profitability, and academic significance have dampened enthusiasm for such work, but it is vital. Now is the time for the field to take this key step toward the medical control of aging.

Cellular senescence in lung cancer: Molecular mechanisms and therapeutic interventions

Lung cancer stands as the primary contributor to cancer-related fatalities worldwide, affecting both genders. Two primary types exist where non-small cell lung cancer (NSCLC), accounts for 80-85% and SCLC accounts for 10-15% of cases. NSCLC subtypes include adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. Smoking, second-hand smoke, radon gas, asbestos, and other pollutants, genetic predisposition, and COPD are lung cancer risk factors. On the other hand, stresses such as DNA damage, telomere shortening, and oncogene activation cause a prolonged cell cycle halt, known as senescence. Despite its initial role as a tumor-suppressing mechanism that slows cell growth, excessive or improper control of this process can cause age-related diseases, including cancer. Cellular senescence has two purposes in lung cancer. Researchers report that senescence slows tumor growth by constraining multiplication of impaired cells. However, senescent cells also demonstrate the pro-inflammatory senescence-associated secretory phenotype (SASP), which is widely reported to promote cancer. This review will look at the role of cellular senescence in lung cancer, describe its diagnostic markers, ask about current treatments to control it, look at case studies and clinical trials that show how senescence-targeting therapies can be used in lung cancer, and talk about problems currently being faced, and possible solutions for the same in the future.

Chemical Strategies for the Detection and Elimination of Senescent Cells

Cellular senescence can be defined as an irreversible stopping of cell proliferation that arises in response to various stress signals. Cellular senescence is involved in diverse physiological and pathological processes in different tissues, exerting effects on processes as differentiated as embryogenesis, tissue repair and remodeling, cancer, aging, and tissue fibrosis. In addition, the development of some pathologies, aging, cancer, and other age-related diseases has been related to senescent cell accumulation. Due to the complexity of the senescence phenotype, targeting senescent cells is not trivial, is challenging, and is especially relevant for in vivo detection in age-related diseases and tissue samples. Despite the elimination of senescent cells (senolysis) using specific drugs (senolytics) that have been shown to be effective in numerous preclinical disease models, the clinical translation is still limited due to the off-target effects of current senolytics and associated toxicities. Therefore, the development of new chemical strategies aimed at detecting and eliminating senescent cells for the prevention and selective treatment of senescence-associated diseases is of great interest. Such strategies not only will contribute to a deeper understanding of this rapidly evolving field but also will delineate and inspire new possibilities for future research.In this Account, we report our recent research in the development of new chemical approaches for the detection and elimination of senescent cells based on new probes, nanoparticles, and prodrugs. The designed systems take advantage of the over-representation in senescent cells of certain biomarkers such as β-galactosidase and lipofuscin. One- and two-photon probes, for higher tissue penetration, have been developed. Moreover, we also present a renal clearable fluorogenic probe for the in vivo detection of the β-galactosidase activity, allowing for correlation with the senescent burden in living animals. Moreover, as an alternative to molecular-based probes, we also developed nanoparticles for senescence detection. Besides, we describe advances in new therapeutic agents to selectively eradicate senescent cells using β-galactosidase activity-sensitive gated nanoparticles loaded with cytotoxic or senolytic agents or new prodrugs aiming to increase the selectivity and reduction of off-target toxicities of current drugs. Moreover, new advances therapies have been applied in vitro and in vivo. Studies with the probes, nanoparticles, and prodrugs have been applied in several in vitro and in vivo models of cancer, fibrosis, aging, and drug-induced cardiotoxicity in which senescence plays an important role. We discuss the benefits of these chemical strategies toward the development of more specific and sophisticated probes, nanoparticles, and prodrugs targeting senescent cells.

A navitoclax-loaded nanodevice targeting matrix metalloproteinase-3 for the selective elimination of senescent cells

Cellular senescence is implicated in the occurrence and progression of multiple age-related disorders. In this context, the selective elimination of senescent cells, senolysis, has emerged as an effective therapeutic strategy. However, the heterogeneous senescent phenotype hinders the discovery of a universal and robust senescence biomarker that limits the effective of senolytic with off-target toxic effects. Therefore, the development of more selective strategies represents a promising approach to increase the specificity of senolytic therapy. In this study, we have developed an innovative nanodevice for the selective elimination of senescent cells (SCs) based on the specific enzymatic activity of the senescent secretome. The results revealed that when senescence is induced in proliferating WI-38 by ionizing radiation (IR), the cells secrete high levels of matrix metalloproteinase-3 (MMP-3). Based on this result, mesoporous silica nanoparticles (MSNs) were loaded with the senolytic navitoclax (Nav) and coated with a specific peptide which is substrate of MMP-3 (NPs(Nav)@MMP-3). Studies in cells confirmed the preferential release of cargo in IR-induced senescent cells compared to proliferating cells, depending on MMP-3 levels. Moreover, treatment with NPs(Nav)@MMP-3 induced a selective decrease in the viability of SCs as well as a protective effect on non-proliferating cells. These results demonstrate the potential use of NPs to develop enhanced senolytic therapies based on specific enzymatic activity in the senescent microenvironment, with potential clinical relevance. STATEMENT OF SIGNIFICANCE: The common β-galactosidase activity has been exploited to develop nanoparticles for the selective elimination of senescent cells. However, the identification of new senescent biomarkers is a key factor for the development of improved strategies. In this scenario, we report for the first time the development of NPs targeting senescent cells based on specific enzymatic activity of the senescent secretome. We report a navitoclax-loaded nanodevice responsive to the matrix metalloproteinase-3 (MMP-3) associated with the senescent phenotype. Our nanosystem achieves the selective release of navitoclax in an MMP-3-dependent manner while limiting off-target effects on non-senescent cells. This opens the possibility of using nanoparticles able to detect an altered senescent environment and selectively release its content, thus enhancing the efficacy of senolytic therapies.

Detection and Elimination of Senescent Cells with a Self-Assembled Senescence-Associated β-Galactosidase-Activatable Nanophotosensitizer

Senescent cells have become an important therapeutic target for many age-related dysfunctions and diseases. We report herein a novel nanophotosensitizing system that is responsive to the senescence-associated β-galactosidase (β-gal) for selective detection and elimination of these cells. It involves a dimeric zinc(II) phthalocyanine linked to a β-galactose unit via a self-immolative linker. This compound can self-assemble in aqueous media, forming stable nanoscale particles in which the phthalocyanine units are stacked and self-quenched for fluorescence emission and singlet oxygen production. Upon internalization into senescent HeLa cells, these nanoparticles interact with the overproduced senescence-associated β-gal inside the cells to trigger the disassembly process through enzymatic cleavage of the glycosidic bonds, followed by self-immolation to release the photoactive monomeric phthalocyanine units. These senescent cells can then be lit up with fluorescence and eliminated through the photodynamic action upon light irradiation with a half-maximal inhibitory concentration of 0.06 μM.

Molecularly Targeted Fluorescent Sensors for Visualizing and Tracking Cellular Senescence

Specific identification and monitoring of senescent cells are essential for the in-depth understanding and regulation of senescence-related life processes and diseases. Fluorescent sensors providing real-time and in situ information with spatiotemporal resolution are unparalleled tools and have contributed greatly to this field. This review focuses on the recent progress in fluorescent sensors for molecularly targeted imaging and real-time tracking of cellular senescence. The molecular design, sensing mechanisms, and biological activities of the sensors are discussed. The sensors are categorized by the types of markers and targeting ligands. Accordingly, their molecular recognition and fluorescent performance towards senescence biomarkers are summarized. Finally, the perspective and challenges in this field are discussed, which are expected to assist future design of next-generation sensors for monitoring cellular senescence.

Exploring the Communication of the SASP: Dynamic, Interactive, and Adaptive Effects on the Microenvironment

Cellular senescence is a complex cell state that can occur during physiological ageing or after exposure to stress signals, regardless of age. It is a dynamic process that continuously evolves in a context-dependent manner. Senescent cells interact with their microenvironment by producing a heterogenous and plastic secretome referred to as the senescence-associated secretory phenotype (SASP). Hence, understanding the cross-talk between SASP and the microenvironment can be challenging due to the complexity of signal exchanges. In this review, we first aim to update the definition of senescence and its associated biomarkers from its discovery to the present day. We detail the regulatory mechanisms involved in the expression of SASP at multiple levels and develop how SASP can orchestrate microenvironment modifications, by focusing on extracellular matrix modifications, neighboring cells' fate, and intercellular communications. We present hypotheses on how these microenvironmental events may affect dynamic changes in SASP composition in return. Finally, we discuss the various existing approaches to targeting SASP and clarify what is currently known about the biological effects of these modified SASPs on the cellular environment.

Senolytic and senomorphic interventions to defy senescence-associated mitochondrial dysfunction

The accumulation of senescent cells in the aging individual is associated with an increase in the occurrence of age-associated pathologies that contribute to poor health, frailty, and mortality. The number and type of senescent cells is viewed as a contributor to the body's senescence burden. Cellular models of senescence are based on induction of senescence in cultured cells in the laboratory. One type of senescence is triggered by mitochondrial dysfunction. There are several indications that mitochondria defects contribute to body aging. Senotherapeutics, targeting senescent cells, have been shown to induce their lysis by means of senolytics, or repress expression of their secretome, by means of senomorphics, senostatics or gerosuppressors. An outline of the mechanism of action of various senotherapeutics targeting mitochondria and senescence-associated mitochondria dysfunction will be here addressed. The combination of geroprotective interventions together with senotherapeutics will help to strengthen mitochondrial energy metabolism, biogenesis and turnover, and lengthen the mitochondria healthspan, minimizing one of several molecular pathways contributing to the aging phenotype.

Senescence and senotherapies in biliary atresia and biliary cirrhosis

BACKGROUND

Premature senescence occurs in adult hepatobiliary diseases and worsens the prognosis through deleterious liver remodeling and hepatic dysfunction. Senescence might also arises in biliary atresia (BA), the first cause of pediatric liver transplantation. Since alternatives to transplantation are needed, our aim was to investigate premature senescence in BA and to assess senotherapies in a preclinical model of biliary cirrhosis.

METHODS

BA liver tissues were prospectively obtained at hepatoportoenterostomy (n=5) and liver transplantation (n=30) and compared to controls (n=10). Senescence was investigated through spatial whole transcriptome analysis, SA-β-gal activity, p16 and p21 expression, γ-H2AX and senescence-associated secretory phenotype (SASP). Human allogenic liver-derived progenitor cells (HALPC) or dasatinib and quercetin (D+Q) were administrated to two-month-old Wistar rats after bile duct ligation (BDL).

RESULTS

Advanced premature senescence was evidenced in BA livers from early stage and continued to progress until liver transplantation. Senescence and SASP were predominant in cholangiocytes, but also present in surrounding hepatocytes. HALPC but not D+Q reduced the early marker of senescence p21 in BDL rats and improved biliary injury (serum γGT and Sox9 expression) and hepatocytes mass loss (Hnf4a).

CONCLUSIONS

BA livers displayed advanced cellular senescence at diagnosis that continued to progress until liver transplantation. HALPC reduced early senescence and improved liver disease in a preclinical model of BA, providing encouraging preliminary results regarding the use of senotherapies in pediatric biliary cirrhosis.

Senescence induces proteolytically-active PAPP-A secretion and association with extracellular vesicles in human pre-adipocytes

Senescence is a cellular response to various stressors characterized by irreversible cell cycle arrest, resistance to apoptosis and expression of a senescence-associated secretory phenotype (SASP). Interestingly, studies where senescent cells were deleted in mice produced beneficial effects similar to those where the zinc metalloproteinase, PAPP-A, was deleted in mice. In this study, we investigated the effect of senescence on PAPP-A secretion and activity in primary cultures of adult human pre-adipocytes. Cultured pre-adipocytes were isolated from subcutaneous (Sub) and omental (Om) fat. Senescence was induced with low dose etoposide. PAPP-A protein was measured by an ultrasensitive PAPP-A ELISA. PAPP-A proteolytic activity was measured by a specific substrate cleavage assay. Senescence significantly increased PAPP-A levels in both Sub and Om conditioned medium (CM) 8- to 15-fold over non-senescent CM. Proteolytic activity reflected PAPP-A protein with 12- to 18-fold greater activity in senescent CM versus non-senescent CM. Furthermore, PAPP-A was found at high levels on the surface of extracellular vesicles secreted by senescent pre-adipocytes and was proteolytically active. In conclusion, we identified enzymatically active PAPP-A as a component of human pre-adipocyte SASP. This recognition warrants further investigation of PAPP-A as a new biomarker for senescence and a potential therapeutic target to control of the spread of senescence in adipose tissue.

Recent Advances in Strategies for Imaging Detection and Intervention of Cellular Senescence

Cellular senescence is a stable cell cycle arrest state that can be triggered by a wide range of intrinsic or extrinsic stresses. Increased burden of senescent cells in various tissues is thought to contribute to aging and age-related diseases. Thus, the detection and interventions of senescent cells are critical for longevity and treatment of disease. However, the highly heterogeneous feature of senescence makes it challenging for precise detection and selective clearance of senescent cells in different age-related diseases. To address this issue, considerable efforts have been devoted to developing senescence-targeting molecular theranostic strategies, based on the potential biomarkers of cellular senescence. Herein, we review recent advances in the field of anti-senescence research and highlight the specific visualization and elimination of senescent cells. Additionally, the challenges in this emerging field are outlined.

β-Galactosidase-Activatable Nile Blue-Based NIR Senoprobe for the Real-Time Detection of Cellular Senescence

Cellular senescence is a stable cell cycle arrest in response to stress or other damage stimuli to maintain tissue homeostasis. However, the accumulation of senescent cells can lead to the progression of various senescence-related disorders. In this paper, we describe the development of a β-galactosidase-activatable near-infrared (NIR) senoprobe, NBGal, for the detection of senescent cells based on the use of the FDA-approved Nile blue (NB) fluorophore. NBGal was validated in chemotherapeutic-induced senescence cancer models in vitro using SK-Mel 103 and 4T1 cell lines. In vivo monitoring of cellular senescence was evaluated in orthotopic triple-negative breast cancer-bearing mice treated with palbociclib to induce senescence. In all cases, NBGal exhibited a selective tracking of senescent cells mainly ascribed to the overexpressed β-galactosidase enzyme responsible for hydrolyzing the NBGal probe generating the highly emissive NB fluorophore. In this way, NBGal has proven to be a qualitative, rapid, and minimally invasive probe that allows the direct detection of senescent cells in vivo.

Immune senescence in non-small cell lung cancer management: therapeutic relevance, biomarkers, and mitigating approaches

INTRODUCTION

Lung cancer and mainly non-small cell lung cancer (NSCLC) still remain a prevalent malignancy worldwide despite sustained screening approaches. Furthermore, a significant proportion of the cases are diagnosed at advanced stages when conservative therapy is often unsuccessful. Cell senescence is an endogenous antitumor weapon but when it is upregulated exerts opposite activities favoring tumor metastasizing and poor response to therapy. However, little is known about this dangerous relationship between cell senescence and NSCLC outcome or on potential approaches to mitigate its unfavorable consequences.

AREAS COVERED

We discuss cell senescence focusing on immune senescence, its cell and humoral effectors (namely immune senescence associated secretory phenotype-iSASP), its impact on NSCLC outcome, and its biomarkers. Senotherapeutics as mitigating approaches are also considered based on the availability of experimental data pertinent to NSCLC.

EXPERT OPINION

Characterization of NSCLC subsets in which immune senescence is a risk factor for poor prognosis and poor therapeutic response might be very helpful in supporting the addition of senotherapeutics to conventional cancer therapy. This approach has the potential to improve disease outcome but more studies in this area are necessary.

New Trends in Aging Drug Discovery

Aging is considered the main risk factor for many chronic diseases that frequently appear at advanced ages. However, the inevitability of this process is being questioned by recent research that suggests that senescent cells have specific features that differentiate them from younger cells and that removal of these cells ameliorates senescent phenotype and associated diseases. This opens the door to the design of tailored therapeutic interventions aimed at reducing and delaying the impact of senescence in life, that is, extending healthspan and treating aging as another chronic disease. Although these ideas are still far from reaching the bedside, it is conceivable that they will revolutionize the way we understand aging in the next decades. In this review, we analyze the main and well-validated cellular pathways and targets related to senescence as well as their implication in aging-associated diseases. In addition, the most relevant small molecules with senotherapeutic potential, with a special emphasis on their mechanism of action, ongoing clinical trials, and potential limitations, are discussed. Finally, a brief overview of alternative strategies that go beyond the small molecule field, together with our perspectives for the future of the field, is provided.

Cellular senescence: a key therapeutic target in aging and diseases

Cellular senescence is a hallmark of aging defined by stable exit from the cell cycle in response to cellular damage and stress. Senescent cells (SnCs) can develop a characteristic pathogenic senescence-associated secretory phenotype (SASP) that drives secondary senescence and disrupts tissue homeostasis, resulting in loss of tissue repair and regeneration. The use of transgenic mouse models in which SnCs can be genetically ablated has established a key role for SnCs in driving aging and age-related disease. Importantly, senotherapeutics have been developed to pharmacologically eliminate SnCs, termed senolytics, or suppress the SASP and other markers of senescence, termed senomorphics. Based on extensive preclinical studies as well as small clinical trials demonstrating the benefits of senotherapeutics, multiple clinical trials are under way. This Review discusses the role of SnCs in aging and age-related diseases, strategies to target SnCs, approaches to discover and develop senotherapeutics, and preclinical and clinical advances of senolytics.

In Vitro and In Vivo Modeling of Normal and Leukemic Bone Marrow Niches: Cellular Senescence Contribution to Leukemia Induction and Progression

Cellular senescence is recognized as a dynamic process in which cells evolve and adapt in a context dependent manner; consequently, senescent cells can exert both beneficial and deleterious effects on their surroundings. Specifically, senescent mesenchymal stromal cells (MSC) in the bone marrow (BM) have been linked to the generation of a supporting microenvironment that enhances malignant cell survival. However, the study of MSC's senescence role in leukemia development has been straitened not only by the availability of suitable models that faithfully reflect the structural complexity and biological diversity of the events triggered in the BM, but also by the lack of a universal, standardized method to measure senescence. Despite these constraints, two- and three dimensional in vitro models have been continuously improved in terms of cell culture techniques, support materials and analysis methods; in addition, research on animal models tends to focus on the development of techniques that allow tracking leukemic and senescent cells in the living organism, as well as to modify the available mice strains to generate individuals that mimic human BM characteristics. Here, we present the main advances in leukemic niche modeling, discussing advantages and limitations of the different systems, focusing on the contribution of senescent MSC to leukemia progression.