Senescence and the SASP: many therapeutic avenues.

Cellular senescence is a stress response that elicits a permanent cell cycle arrest and triggers profound phenotypic changes such as the production of a bioactive secretome, referred to as the senescence-associated secretory phenotype (SASP). Acute senescence induction protects against cancer and limits fibrosis, but lingering senescent cells drive age-related disorders. Thus, targeting senescent cells to delay aging and limit dysfunction, known as "senotherapy," is gaining momentum. While drugs that selectively kill senescent cells, termed "senolytics" are a major focus, SASP-centered approaches are emerging as alternatives to target senescence-associated diseases. Here, we summarize the regulation and functions of the SASP and highlight the therapeutic potential of SASP modulation as complimentary or an alternative to current senolytic approaches.

Senolytic and senomorphic agent procyanidin C1 alleviates structural and functional decline in the aged retina.

Increased cellular senescence burden contributes in part to age-related organ dysfunction and pathologies. In our study, using mouse models of natural aging, we observed structural and functional decline in the aged retina, which was accompanied by the accumulation of senescent cells and senescence-associated secretory phenotype factors. We further validated the senolytic and senomorphic properties of procyanidin C1 (PCC1) both in vitro and in vivo, the long-term treatment of which ameliorated age-related retinal impairment. Through high-throughput single-cell RNA sequencing (scRNA-seq), we comprehensively characterized the retinal landscape after PCC1 administration and deciphered the molecular basis underlying the senescence burden increment and elimination. By exploring the scRNA-seq database of age-related retinal disorders, we revealed the role of cellular senescence and the therapeutic potential of PCC1 in these pathologies. Overall, these results indicate the therapeutic effects of PCC1 on the aged retina and its potential use for treating age-related retinal disorders.

Targeting senescent cells to reshape the tumor microenvironment and improve anticancer efficacy.

Cancer is daunting pathology with remarkable breadth and scope, spanning genetics, epigenetics, proteomics, metalobomics and cell biology. Cellular senescence represents a stress-induced and essentially irreversible cell fate associated with aging and various age-related diseases, including malignancies. Senescent cells are characterized of morphologic alterations and metabolic reprogramming, and develop a highly active secretome termed as the senescence-associated secretory phenotype (SASP). Since the first discovery, senescence has been understood as an important barrier to tumor progression, as its induction in pre-neoplastic cells limits carcinogenesis. Paradoxically, senescent cells arising in the tumor microenvironment (TME) contribute to tumor progression, including augmented therapeutic resistance. In this article, we define typical forms of senescent cells commonly observed within the TME and how senescent cells functionally remodel their surrounding niche, affect immune responses and promote cancer evolution. Furthermore, we highlight the recently emerging pipelines of senotherapies particularly senolytics, which can selectively deplete senescent cells from affected organs in vivo and impede tumor progression by restoring therapeutic responses and securing anticancer efficacies. Together, co-targeting cancer cells and their normal but senescent counterparts in the TME holds the potential to achieve increased therapeutic benefits and restrained disease relapse in future clinical oncology.

Dual Inhibition of CDK4/6 and XPO1 Induces Senescence With Acquired Vulnerability to CRBN-Based PROTAC Drugs.

BACKGROUND & AIMS: Despite the increasing number of treatment options available for liver cancer, only a small proportion of patients achieve long-term clinical benefits. Here, we aim to develop new therapeutic approaches for liver cancer. METHODS: A compound screen was conducted to identify inhibitors that could synergistically induce senescence when combined with cyclin-dependent kinase (CDK) 4/6 inhibitor. The combination effects of CDK4/6 inhibitor and exportin 1 (XPO1) inhibitor on cellular senescence were investigated in a panel of human liver cancer cell lines and multiple liver cancer models. A senolytic drug screen was performed to identify drugs that selectively killed senescent liver cancer cells. RESULTS: The combination of CDK4/6 inhibitor and XPO1 inhibitor synergistically induces senescence of liver cancer cells in vitro and in vivo. The XPO1 inhibitor acts by causing accumulation of RB1 in the nucleus, leading to decreased E2F signaling and promoting senescence induction by the CDK4/6 inhibitor. Through a senolytic drug screen, cereblon (CRBN)-based proteolysis targeting chimera (PROTAC) ARV-825 was identified as an agent that can selectively kill senescent liver cancer cells. Up-regulation of CRBN was a vulnerability of senescent liver cancer cells, making them sensitive to CRBN-based PROTAC drugs. Mechanistically, we find that ubiquitin specific peptidase 2 (USP2) directly interacts with CRBN, leading to the deubiquitination and stabilization of CRBN in senescent liver cancer cells. CONCLUSIONS: Our study demonstrates a striking synergy in senescence induction of liver cancer cells through the combination of CDK4/6 inhibitor and XPO1 inhibitor. These findings also shed light on the molecular processes underlying the vulnerability of senescent liver cancer cells to CRBN-based PROTAC therapy.

CD4+CD57+ senescent T cells as promoters of systemic lupus erythematosus pathogenesis and the therapeutic potential of senolytic BCL-2 inhibitor.

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by persistent activation of immune cells and overproduction of autoantibodies. The accumulation of senescent T and B cells has been observed in SLE and other immune-mediated diseases. However, the exact mechanistic pathways contributing to this process in SLE remain incompletely understood. In this study, we found that in SLE patients: (1) the frequency of CD4+CD57+ senescent T cells was significantly elevated and positively correlated with disease activity; (2) the expression levels of B-lymphoma-2 (BCL-2) family and interferon-induced genes (ISGs) were significantly upregulated; and (3) in vitro, the cytokine IL-15 stimulation increased the frequency of senescent CD4+ T cells and upregulated the expression of BCL-2 family and ISGs. Further, treatment with ABT-263 (a senolytic BCL-2 inhibitor) in MRL/lpr mice resulted in decreased: (1) frequency of CD4+CD44hiCD62L-PD-1+CD153+ senescent CD4+ T cells; (2) frequency of CD19+CD11c+T-bet+ age-related B cells; (3) level of serum antinuclear antibody; (4) proteinuria; (5) frequency of Tfh cells; and (6) renal histopathological abnormalities. Collectively, these results indicated a dominant role for CD4+CD57+ senescent CD4+ T cells in the pathogenesis of SLE and senolytic BCL-2 inhibitor ABT-263 may be the potential treatment in ameliorating lupus phenotypes.

Senescent Cells: Emerging Targets for Human Aging and Age-Related Diseases.

Aging is a major risk factor for numerous human pathologies, including cardiovascular, metabolic, musculoskeletal, and neurodegenerative conditions and various malignancies. While our understanding of aging is far from complete, recent advances suggest that targeting fundamental aging processes can delay, prevent, or alleviate age-related disorders. Cellular senescence is physiologically beneficial in several contexts, but it has causal roles in multiple chronic diseases. New studies have illustrated the promising feasibility and safety to selectively ablate senescent cells from tissues, a therapeutic modality that holds potential for treating multiple chronic pathologies and extending human healthspan. Here, we review molecular links between cellular senescence and age-associated complications and highlight novel therapeutic avenues that may be exploited to target senescent cells in future geriatric medicine.

Senolytic Drugs: Reducing Senescent Cell Viability to Extend Health Span.

Senescence is the consequence of a signaling mechanism activated in stressed cells to prevent proliferation of cells with damage. Senescent cells (Sncs) often develop a senescence-associated secretory phenotype to prompt immune clearance, which drives chronic sterile inflammation and plays a causal role in aging and age-related diseases. Sncs accumulate with age and at anatomical sites of disease. Thus, they are regarded as a logical therapeutic target. Senotherapeutics are a new class of drugs that selectively kill Sncs (senolytics) or suppress their disease-causing phenotypes (senomorphics/senostatics). Since 2015, several senolytics went from identification to clinical trial. Preclinical data indicate that senolytics alleviate disease in numerous organs, improve physical function and resilience, and suppress all causes of mortality, even if administered to the aged. Here, we review the evidence that Sncs drive aging and disease, the approaches to identify and optimize senotherapeutics, and the current status of preclinical and clinical testing of senolytics.

Transplanting old organs promotes senescence in young recipients.

In clinical organ transplantation, donor and recipient ages may differ substantially. Old donor organs accumulate senescent cells that have the capacity to induce senescence in naïve cells. We hypothesized that the engraftment of old organs may induce senescence in younger recipients, promoting age-related pathologies. When performing isogeneic cardiac transplants between age-mismatched C57BL/6 old donor (18 months) mice and young and middle-aged C57BL/6 (3- or 12- month-old) recipients , we observed augmented frequencies of senescent cells in draining lymph nodes, adipose tissue, livers, and hindlimb muscles 30 days after transplantation. These observations went along with compromised physical performance and impaired spatial learning and memory abilities. Systemic levels of the senescence-associated secretory phenotype factors, including mitochondrial DNA (mt-DNA), were elevated in recipients. Of mechanistic relevance, injections of mt-DNA phenocopied effects of age-mismatched organ transplantation on accelerating aging. Single treatment of old donor animals with senolytics prior to transplantation attenuated mt-DNA release and improved physical capacities in young recipients. Collectively, we show that transplanting older organs induces senescence in transplant recipients, resulting in compromised physical and cognitive capacities. Depleting senescent cells with senolytics, in turn, represents a promising approach to improve outcomes of older organs.

A second generation of senotherapies: the development of targeted senolytics, senoblockers and senoreversers for healthy ageing.

Cellular senescence, a form of terminal cell cycle arrest, is as a key driver of organismal ageing and an important factor in age-related diseases. Insights into the senescent phenotype have led to the development of novel therapeutic strategies, collectively known as senotherapies, that aim to ameliorate the detrimental effects of senescent cell accumulation in tissues. The senotherapeutic field has rapidly evolved over the past decade, with clinical translation of the first drugs discovered currently underway. What began as the straightforward removal of senescent cells using repurposed compounds, which were given the name of senolytics, has grown into an expanding field that uses different state of the art approaches to achieve the goal of preventing the build-up of senescent cells in the body. Here, we summarize the emergence of a new generation of senotherapies, based on improving the efficacy and safety of the original senolytics by making them targeted, but also branching out into drugs that prevent senescence (senoblockers) or revert it (senoreversers).The use of nanotechnology, specific antibodies, cell-based approaches and restored immunosurveillance is likely to revolutionize the field of senotherapies in the near future, hopefully allowing it to realize its full clinical potential.

Characterisation of premature cell senescence in Alzheimer's disease using single nuclear transcriptomics.

Aging is associated with cell senescence and is the major risk factor for AD. We characterized premature cell senescence in postmortem brains from non-diseased controls (NDC) and donors with Alzheimer's disease (AD) using imaging mass cytometry (IMC) and single nuclear RNA (snRNA) sequencing (> 200,000 nuclei). We found increases in numbers of glia immunostaining for galactosidase beta (> fourfold) and p16INK4A (up to twofold) with AD relative to NDC. Increased glial expression of genes related to senescence was associated with greater ß-amyloid load. Prematurely senescent microglia downregulated phagocytic pathways suggesting reduced capacity for ß-amyloid clearance. Gene set enrichment and pseudo-time trajectories described extensive DNA double-strand breaks (DSBs), mitochondrial dysfunction and ER stress associated with increased ß-amyloid leading to premature senescence in microglia. We replicated these observations with independent AD snRNA-seq datasets. Our results describe a burden of senescent glia with AD that is sufficiently high to contribute to disease progression. These findings support the hypothesis that microglia are a primary target for senolytic treatments in AD.

Application potential of senolytics in clinical treatment.

Of the factors studied in individual ageing, the accumulation of senescent cells has been considered as an essential cause of organ degeneration to eventually initiate age-related diseases. Cellular senescence is attributed to the accumulation of damage for an inducement in the activation of cell cycle inhibitory pathways, resulting the cell permanently withdraw from the cell proliferation cycle. Further, senescent cells will activate the inflammatory factor secretion pathway to promote the development of various age-related diseases. Senolytics, a small molecule compound, can delay disease development and extend mammalian lifespan. The evidence from multiple trials shows that the targeted killing of senescent cells has a significant clinical application for the treatment of age-related diseases. In addition, senolytics are also significant for the development of ageing research in solid organ transplantation, which can fully develop the potential of elderly organs and reduce the age gap between demand and supply. We conclude that the main characteristics of cellular senescence, the anti-ageing drug senolytics in the treatment of chronic diseases and organ transplantation, and the latest clinical progress of related researches in order to provide a theoretical basis for the prevention and treatment of ageing and related diseases.

Quercetin and dasatinib, two powerful senolytics in age-related cardiovascular disease.

Cellular senescence is characteristic of the development and progression of multiple age-associated diseases. Accumulation of senescent cells in the heart contributes to various age-related pathologies. Several compounds called senolytics have been designed to eliminate these cells within the tissues. In recent years, the use and study of senolytics increased, representing a promising field for finding accessible and safe therapies for cardiovascular disease (CVD) treatment. This mini-review discusses the changes in the aging heart and the participation of senescent cells in CVD, as well as the use of senolytics to prevent the progression of myocardial damage, mainly the effect of dasatinib and quercetin. In particular, the mechanisms and physiological effects of senolytics therapies in the aged heart are discussed.

Combined dasatinib and quercetin treatment contributes to skin rejuvenation through selective elimination of senescent cells in vitro and in vivo.

The skin's protective functions are compromised over time by both endogenous and exogenous aging. Senescence is well-documented in skin phenotypes, such as wrinkling and sagging, a consequence of the senescence-associated secretory phenotype (SASP) that involves the accumulation of senescent fibroblasts, chronic inflammation, and collagen remodeling. Although therapeutic approaches for eliminating senescent cells from the skin are available, their efficacy remains unclear. Accordingly, we aimed to examine the effects of dasatinib in combination with quercetin (D + Q) on senescent human skin fibroblasts and aging human skin. Senescence was induced in human dermal fibroblasts (HDFs) using approaches such as long-term passaging, ionizing radiation, and doxorubicin treatment. The generated senescent cells were treated with D + Q or vehicle. Additionally, a mouse-human chimera model was generated by subcutaneously transplanting whole-skin grafts of aged individuals onto nude mice. Mouse models were administered D + Q or vehicle by oral gavage for 30 days. Subsequently, skin samples were harvested and stained for senescence-associated beta-galactosidase. Senescence-associated markers were assessed by western blotting, reverse transcription-quantitative PCR and histological analyses. Herein, D + Q selectively eliminated senescent HDFs in all cellular models of induced senescence. Additionally, D + Q-treated aged human skin grafts exhibited increased collagen density and suppression of the SASP compared with control grafts. No adverse events were observed during the study period. Collectively, D + Q could ameliorate skin aging through selective elimination of senescent dermal fibroblasts and suppression of the SASP. Our findings suggest that D + Q could be developed as an effective therapeutic approach for combating skin aging.

Design and optimization of piperlongumine analogs as potent senolytics.

Selective removal of senescent cells (SnCs) offers a promising therapeutic strategy to treat chronic and age-related diseases. Our prior investigations led to the discovery of piperlongumine (PL) and its derivatives as senolytic agents. In this study, our medicinal chemistry campaign on both the α,ß-unsaturated δ-valerolactam ring and the phenyl ring of PL culminated in the identification of compound 24, which exhibited an impressive 50-fold enhancement in senolytic activity against senescent WI-38 fibroblasts compared to PL.

Potential Clinical Implications of Senotherapies for Cardiovascular Disease.

Aging is a major risk factor for cardiovascular diseases (CVDs) and accumulating evidence indicates that biological aging has a significant effect on the onset and progression of CVDs. In recent years, therapies targeting senescent cells (senotherapies), particularly senolytics that selectively eliminate senescent cells, have been developed and show promise for treating geriatric syndromes and age-associated diseases, including CVDs. In 2 pilot studies published in 2019 the senolytic combination, dasatinib plus quercetin, improved physical function in patients with idiopathic pulmonary fibrosis and eliminated senescent cells from adipose tissue in patients with diabetic kidney disease. More than 30 clinical trials using senolytics are currently underway or planned. In preclinical CVD models, senolytics appear to improve heart failure, ischemic heart disease, valvular heart disease, atherosclerosis, aortic aneurysm, vascular dysfunction, dialysis arteriovenous fistula patency, and pre-eclampsia. Because senotherapies are completely different strategies from existing treatment paradigms, they might alleviate diseases for which there are no current effective treatments or they could be used in addition to current therapies to enhance efficacy. Moreover, senotherapies might delay, prevent, alleviate or treat multiple diseases in the elderly and reduce polypharmacy, because senotherapies target fundamental aging mechanisms. We comprehensively summarize the preclinical evidence about senotherapies for CVDs and discuss future prospects for their clinical application.

Escape from senescence: molecular basis and therapeutic ramifications.

Cellular senescence constitutes a stress response mechanism in reaction to a plethora of stimuli. Senescent cells exhibit cell-cycle arrest and altered function. While cell-cycle withdrawal has been perceived as permanent, recent evidence in cancer research introduced the so-called escape-from-senescence concept. In particular, under certain conditions, senescent cells may resume proliferation, acquiring highly aggressive features. As such, they have been associated with tumour relapse, rendering senescence less effective in inhibiting cancer progression. Thus, conventional cancer treatments, incapable of eliminating senescence, may benefit if revisited to include senolytic agents. To this end, it is anticipated that the assessment of the senescence burden in everyday clinical material by pathologists will play a crucial role in the near future, laying the foundation for more personalised approaches. Here, we provide an overview of the investigations that introduced the escape-from-senescence phenomenon, the identified mechanisms, as well as the major implications for pathology and therapy. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Recent Advances in Pathology: the 2023 Annual Review Issue of The Journal of Pathology.

The 2023 Annual Review Issue of The Journal of Pathology, Recent Advances in Pathology, contains 12 invited reviews on topics of current interest in pathology. This year, our subjects include immuno-oncology and computational pathology approaches for diagnostic and research applications in human disease. Reviews on the tissue microenvironment include the effects of apoptotic cell-derived exosomes, how understanding the tumour microenvironment predicts prognosis, and the growing appreciation of the diverse functions of fibroblast subtypes in health and disease. We also include up-to-date reviews of modern aspects of the molecular basis of malignancies, and our final review covers new knowledge of vascular and lymphatic regeneration in cardiac disease. All of the reviews contained in this issue are written by expert groups of authors selected to discuss the recent progress in their particular fields and all articles are freely available online (https://pathsocjournals.onlinelibrary.wiley.com/journal/10969896). © 2023 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Senotherapeutics to Counteract Senescent Cells Are Prominent Topics in the Context of Anti-Ageing Strategies.

Cellular senescence is implicated in ageing and associated with a broad spectrum of age-related diseases. Importantly, a cell can initiate the senescence program irrespective of the organism's age. Various stress signals, including those defined as ageing hallmarks and alterations leading to cancer development, oncogene activation, or loss of cancer-suppressive functions, can trigger cellular senescence. The primary outcome of these alterations is the activation of nuclear factor (NF)-κB, thereby inducing the senescence-associated secretory phenotype (SASP). Proinflammatory cytokines and chemokines, components of this phenotype, contribute to chronic systemic sterile inflammation, commonly referred to as inflamm-ageing. This inflammation is linked to age-related diseases (ARDs), frailty, and increased mortality in older individuals. Additionally, senescent cells (SCs) accumulate in multiple tissues with age and are believed to underlie the organism functional decline, as demonstrated by models. An escalating effort has been dedicated to identify senotherapeutics that selectively target SCs by inducing apoptosis; these drugs are termed senolytics. Concurrently, small molecules that suppress senescent phenotypes without causing cell death are known as senomorphics. Both natural and synthetic senotherapeutics, along with immunotherapies employing immune cell-mediated clearance of SCs, currently represent the most promising strategies to combat ageing and ARDs. Indeed, it is fascinating to observe that information regarding the immune reaction to SCs indicates that regulation by specific lymphocyte subsets, elevated in the oldest centenarians, plays a role in attaining extreme longevity. Regardless, the application of methods already utilized in cancer treatment, such as CAR cells and monoclonal antibodies, broadens the spectrum of potential approaches to be utilized.

Endothelial Senescence: From Macro- to Micro-Vasculature and Its Implications on Cardiovascular Health.

Endothelial cells line at the most inner layer of blood vessels. They act to control hemostasis, arterial tone/reactivity, wound healing, tissue oxygen, and nutrient supply. With age, endothelial cells become senescent, characterized by reduced regeneration capacity, inflammation, and abnormal secretory profile. Endothelial senescence represents one of the earliest features of arterial ageing and contributes to many age-related diseases. Compared to those in arteries and veins, endothelial cells of the microcirculation exhibit a greater extent of heterogeneity. Microcirculatory endothelial senescence leads to a declined capillary density, reduced angiogenic potentials, decreased blood flow, impaired barrier properties, and hypoperfusion in a tissue or organ-dependent manner. The heterogeneous phenotypes of microvascular endothelial cells in a particular vascular bed and across different tissues remain largely unknown. Accordingly, the mechanisms underlying macro- and micro-vascular endothelial senescence vary in different pathophysiological conditions, thus offering specific target(s) for therapeutic development of senolytic drugs.

Senolysis Enabled by Senescent Cell-Sensitive Bioorthogonal Tetrazine Ligation.

Although the clearance of senescent cells has been proven to slow down the aging process and promote anti-cancer chemotherapy, the development of senolytics remains challenging. Herein, we report a senolytic strategy enabled by senescent cell-sensitive bioorthogonal tetrazine ligation. Our design is based on linking dihydrotetrazine (Tz) to a galactose (Gal) moiety that serves both as a recognition moiety for senescence-associated ß-galactosidase and a caging group for the control of tetrazine activity. Gal-Tz enables efficient click-release of a fluorescent hemicyanine and doxorubicin from a trans-cyclooctene-caged prodrug to detect and eliminate senescent HeLa and A549 cells over non-senescent counterparts with a 16.44 senolytic index. Furthermore, we leverage the strategy for the selective activation and delivery of proteolysis-targeting chimeras (PROTACs) as senolytics. PROTAC prodrug TCO-ARV-771 can be selectively activated by Gal-Tz and delivered into senescent HeLa and A549 cells to induce the degradation of bromodomain-containing protein 4. Senolytic PROTACs may offer an efficient way for intervention on cell senescence thanks to their unique capacity to degrade target proteins in a sub-stoichiometric and catalytic fashion. The results of this study establish the bioorthogonal tetrazine ligation approach as a viable strategy for selective removal of senescent cells.