Single-cell transcriptomics identifies Mcl-1 as a target for senolytic therapy in cancer

Targeting metabolism to influence cellular senescence a promising anti-cancer therapeutic strategy

Metabolic disorders are considered the hallmarks of cancer and metabolic reprogramming is emerging as a new strategy for cancer treatment. Exogenous and endogenous stressors can induce cellular senescence; the interactions between cellular senescence and systemic metabolism are dynamic. Cellular senescence disrupts metabolic homeostasis in various tissues, which further promotes senescence, creating a vicious cycle facilitating tumor occurrence, recurrence, and altered outcomes of anticancer treatments. Therefore, the regulation of cellular senescence and related secretory phenotypes is considered a breakthrough in cancer therapy; moreover, proteins involved in the associated pathways are prospective therapeutic targets. Although studies on the association between cellular senescence and tumors have emerged in recent years, further elucidation of this complex correlation is required for comprehensive knowledge. In this paper, we review the research progress on the correlation between cell aging and metabolism, focusing on the strategies of targeting metabolism to modulate cellular senescence and the progress of relevant research in the context of anti-tumor therapy. Finally, we discuss the significance of improving the specificity and safety of anti-senescence drugs, which is a potential challenge in cancer therapy.

Androgen deprivation-induced senescence confers sensitivity to a senolytic strategy in prostate cancer

We have previously demonstrated that androgen-dependent prostate cancer (PCa) cell lines enter a state of senescence following exposure to androgen deprivation therapies (ADT). ADT-induced senescence was found to be transient, as senescent cells develop castration resistance and re-emerge into a proliferative state even under continuous androgen deprivation in vitro. Moreover, the BCL-XL/BCL-2 inhibitor, ABT-263 (navitoclax), an established senolytic agent, promoted apoptosis of senescent PCa cells, suppressing proliferative recovery and subsequent tumor cell outgrowth. As this strategy has not previously been validated in vivo, we used a clinically relevant, syngeneic murine model of PCa, where mice were either castrated or castrated followed by the administration of ABT-263. Our results largely confirm the outcomes previously reported in vitro; specifically, castration alone results in a transient tumor growth suppression with characteristics of senescence, which is prolonged by exposure to ABT-263. Most critically, mice that underwent castration followed by ABT-263 experienced a statistically significant prolongation in survival, with an increase of 14.5 days in median survival time (56 days castration alone vs. 70.5 days castration + ABT-263). However, as is often the case in studies combining the promotion of senescence with a senolytic (the "one-two" punch approach), the suppression of tumor growth by the inclusion of the senolytic agent was transient, allowing for tumor regrowth once the drug treatment was terminated. Nevertheless, the results of this work suggest that the "one-two" punch senolytic strategy in PCa may effectively interfere with, diminish, or delay the development of the lethal castration-resistant phenotype.

Role of cellular senescence in inflammation and regeneration

Cellular senescence is the state in which cells undergo irreversible cell cycle arrest and acquire diverse phenotypes. It has been linked to chronic inflammation and fibrosis in various organs as well as to individual aging. Therefore, eliminating senescent cells has emerged as a potential target for extending healthy lifespans. Cellular senescence plays a beneficial role in many biological processes, including embryonic development, wound healing, and tissue regeneration, which is mediated by the activation of stem cells. Therefore, a comprehensive understanding of cellular senescence, including both its beneficial and detrimental effects, is critical for developing safe and effective treatment strategies to target senescent cells. This review provides an overview of the biological and pathological roles of cellular senescence, with a particular focus on its beneficial or detrimental functions among its various roles.

p53/MDM2 signaling pathway in aging, senescence and tumorigenesis

A wealth of evidence has emerged that there is an association between aging, senescence and tumorigenesis. Senescence, a biological process by which cells cease to divide and enter a status of permanent cell cycle arrest, contributes to aging and aging-related diseases, including cancer. Aging populations have the higher incidence of cancer due to a lifetime of exposure to cancer-causing agents, reduction of repairing DNA damage, accumulated genetic mutations, and decreased immune system efficiency. Cancer patients undergoing cytotoxic therapies, such as chemotherapy and radiotherapy, accelerate aging. There is growing evidence that p53/MDM2 (murine double minute 2) axis is critically involved in regulation of aging, senescence and oncogenesis. Therefore, in this review, we describe the functions and mechanisms of p53/MDM2-mediated senescence, aging and carcinogenesis. Moreover, we highlight the small molecular inhibitors, natural compounds and PROTACs (proteolysis targeting chimeras) that target p53/MDM2 pathway to influence aging and cancer. Modification of p53/MDM2 could be a potential strategy for treatment of aging, senescence and tumorigenesis.

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.

Single-cell senescence identification reveals senescence heterogeneity, trajectory, and modulators

Cellular senescence underlies many aging-related pathologies, but its heterogeneity poses challenges for studying and targeting senescent cells. We present here a machine learning program senescent cell identification (SenCID), which accurately identifies senescent cells in both bulk and single-cell transcriptome. Trained on 602 samples from 52 senescence transcriptome datasets spanning 30 cell types, SenCID identifies six major senescence identities (SIDs). Different SIDs exhibit different senescence baselines, stemness, gene functions, and responses to senolytics. SenCID enables the reconstruction of senescent trajectories under normal aging, chronic diseases, and COVID-19. Additionally, when applied to single-cell Perturb-seq data, SenCID helps reveal a hierarchy of senescence modulators. Overall, SenCID is an essential tool for precise single-cell analysis of cellular senescence, enabling targeted interventions against senescent cells.

Unveiling Novel Double-Negative Prostate Cancer Subtypes Through Single-Cell RNA Sequencing Analysis

Recent advancements in single-cell RNA sequencing (scRNAseq) have facilitated the discovery of previously unrecognized subtypes within prostate cancer (PCa), offering new insights into disease heterogeneity and progression. In this study, we integrated scRNAseq data from multiple studies, comprising both publicly available cohorts and data generated by our research team, and established the HuPSA (Human Prostate Single cell Atlas) and the MoPSA (Mouse Prostate Single cell Atlas) datasets. Through comprehensive analysis, we identified two novel double-negative PCa populations: KRT7 cells characterized by elevated KRT7 expression, and progenitor-like cells marked by SOX2 and FOXA2 expression, distinct from NEPCa, and displaying stem/progenitor features. Furthermore, HuPSA-based deconvolution allowed for the re-classification of human PCa specimens, validating the presence of these novel subtypes. Leveraging these findings, we developed a user-friendly web application, "HuPSA-MoPSA" (https://pcatools.shinyapps.io/HuPSA-MoPSA/), for visualizing gene expression across all newly-established datasets. Our study provides comprehensive tools for PCa research and uncovers novel cancer subtypes that can inform clinical diagnosis and treatment strategies.

Cellular senescence in cancer: molecular mechanisms and therapeutic targets

Aging exhibits several hallmarks in common with cancer, such as cellular senescence, dysbiosis, inflammation, genomic instability, and epigenetic changes. In recent decades, research into the role of cellular senescence on tumor progression has received widespread attention. While how senescence limits the course of cancer is well established, senescence has also been found to promote certain malignant phenotypes. The tumor-promoting effect of senescence is mainly elicited by a senescence-associated secretory phenotype, which facilitates the interaction of senescent tumor cells with their surroundings. Targeting senescent cells therefore offers a promising technique for cancer therapy. Drugs that pharmacologically restore the normal function of senescent cells or eliminate them would assist in reestablishing homeostasis of cell signaling. Here, we describe cell senescence, its occurrence, phenotype, and impact on tumor biology. A "one-two-punch" therapeutic strategy in which cancer cell senescence is first induced, followed by the use of senotherapeutics for eliminating the senescent cells is introduced. The advances in the application of senotherapeutics for targeting senescent cells to assist cancer treatment are outlined, with an emphasis on drug categories, and the strategies for their screening, design, and efficient targeting. This work will foster a thorough comprehension and encourage additional research within this field.

Therapeutic strategies targeting cellular senescence for cancer and other diseases

Cellular senescence occurs in response to endogenous or exogenous stresses and is characterized by stable cell cycle arrest, alterations in nuclear morphology and secretion of proinflammatory factors, referred to as the senescence-associated secretory phenotype (SASP). An increase of senescent cells is associated with the development of several types of cancer and aging-related diseases. Therefore, senolytic agents that selectively remove senescent cells may offer opportunities for developing new therapeutic strategies against such cancers and aging-related diseases. This review outlines senescence inducers and the general characteristics of senescent cells. We also discuss the involvement of senescent cells in certain cancers and diseases. Finally, we describe a series of senolytic agents and their utilization in therapeutic strategies.

Prognostic significance of a signature based on senescence-related genes in colorectal cancer

Colorectal cancer, recognized as a quintessential age-related disease, underscores the intricate interplay between aging mechanisms and disease pathogenesis. Cellular senescence, a DNA damage-induced cellular stress response, is characterized by cell cycle arrest, the expression of an inflammatory senescence-associated secretory phenotype, and alterations in extracellular matrix metabolism. It is widely recognized as a fundamental and evolutionarily conserved mechanism of aging. Guided by geroscience principles, which assert that the pathogenesis of age-related diseases involves cellular mechanisms of aging, this study delves into the role of senescence-related genes in colon cancer progression. Leveraging a gene set reflective of senescence-associated pathways, we employed uni- and multivariate Cox proportional hazards survival analysis combined with the determination of the false discovery rate to analyze correlations between gene expression and survival. The integrated database of 1130 colon cancer specimens with available relapse-free survival time and relapse event data from ten independent cohorts provided a robust platform for survival analyses. We identified senescence-related genes associated with differential expression levels linked to shorter survival. Our findings unveil a prognostic signature utilizing cellular senescence-related genes (hazard ratio: 2.73, 95% CI 2.12-3.52, p = 6.4E - 16), offering valuable insights into survival prediction in colon cancer. Multivariate analysis underscored the independence of the senescence-related signature from available epidemiological and pathological variables. This study highlights the potential of senescence-related genes as prognostic biomarkers. Overall, our results underscore the pivotal role of cellular senescence, a fundamental mechanism of aging, in colon cancer progression.

Revolutionizing Diabetic Foot Ulcer Care: The Senotherapeutic Approach

Diabetic foot ulcers (DFUs) are a prevalent and profoundly debilitating complication that afflicts individuals with diabetes mellitus (DM). These ulcers are associated with substantial morbidity, recurrence rates, disability, and mortality, imposing substantial economic, psychological, and medical burdens. Timely detection and intervention can mitigate the morbidity and disparities linked to DFU. Nevertheless, current therapeutic approaches for DFU continue to grapple with multifaceted limitations. A growing body of evidence emphasizes the crucial role of cellular senescence in the pathogenesis of chronic wounds. Interventions that try to delay cellular senescence, eliminate senescent cells (SnCs), or suppress the senescence-associated secretory phenotype (SASP) have shown promise for helping chronic wounds to heal. In this context, targeting cellular senescence emerges as a novel therapeutic strategy for DFU. In this comprehensive review, we look at the pathology and treatment of DFU in a systematic way. We also explain the growing importance of investigating SnCs in DFU and highlight the great potential of senotherapeutics that target SnCs in DFU treatment. The development of efficacious and safe senotherapeutics represents a pioneering therapeutic approach aimed at enhancing the quality of life for individuals affected by DFU.

A Conversation with ChatGPT on Contentious Issues in Senescence and Cancer Research

Artificial intelligence (AI) platforms, such as Generative Pretrained Transformer (ChatGPT), have achieved a high degree of popularity within the scientific community due to their utility in providing evidence-based reviews of the literature. However, the accuracy and reliability of the information output and the ability to provide critical analysis of the literature, especially with respect to highly controversial issues, has generally not been evaluated. In this work, we arranged a question/answer session with ChatGPT regarding several unresolved questions in the field of cancer research relating to therapy-induced senescence (TIS), including the topics of senescence reversibility, its connection to tumor dormancy, and the pharmacology of the newly emerging drug class of senolytics. ChatGPT generally provided responses consistent with the available literature, although occasionally overlooking essential components of the current understanding of the role of TIS in cancer biology and treatment. Although ChatGPT, and similar AI platforms, have utility in providing an accurate evidence-based review of the literature, their outputs should still be considered carefully, especially with respect to unresolved issues in tumor biology. SIGNIFICANCE STATEMENT: Artificial Intelligence platforms have provided great utility for researchers to investigate biomedical literature in a prompt manner. However, several issues arise when it comes to certain unresolved biological questions, especially in the cancer field. This work provided a discussion with ChatGPT regarding some of the yet-to-be-fully-elucidated conundrums of the role of therapy-induced senescence in cancer treatment and highlights the strengths and weaknesses in utilizing such platforms for analyzing the scientific literature on this topic.

Butein inhibits oral squamous cell carcinoma growth via promoting MCL-1 ubiquitination

Oral squamous cell carcinoma (OSCC) is the most common malignant head and neck carcinoma type. Myeloid cell leukemia-1 (MCL-1), an anti-apoptotic BCL-1 protein, has been verified to be among the most highly upregulated pathologic proteins in human cancers linked to tumor relapse, poor prognosis and therapeutic resistance. Herein, therapeutic targeting MCL-1 is an attractive focus for cancer treatment. The present study found that butein, a potential phytochemical compound, exerted profound antitumor effects on OSCC cells. Butein treatment significantly inhibited cell viability, proliferation capacity and colony formation ability, and activated cell apoptotic process. Further potential mechanism investigation showed that promoting MCL-1 ubiquitination and degradation is the major reason for butein-mediated OSCC cell cytotoxicity. Our results uncovered that butein could facilitate E3 ligase FBW7 combined with MCL-1, which contributed to an increase in the ubiquitination of MCL-1 Ub-K48 and degradation. The results of both in vitro cell experiments and in vivo xenograft models imply a critical antitumor function of butein with the well-tolerated feature, and it might be an attractive and promising agent for OSCC treatment.

Integrative analysis of senescence-related genes identifies robust prognostic clusters with distinct features in hepatocellular carcinoma

INTRODUCTION

Senescence refers to a state of permanent cell growth arrest and is regarded as a tumor suppressive mechanism, whereas accumulative evidence demonstrate that senescent cells play an adverse role during cancer progression. The scarcity of specific and reliable markers reflecting senescence level in cancer impede our understanding of this biological basis.

OBJECTIVES

Senescence-related genes (SRGs) were collected for integrative analysis to reveal the role of senescence in hepatocellular carcinoma (HCC).

METHODS

Consensus clustering was used to subtype HCC based on SRGs. Several computational methods, including single sample gene set enrichment analysis (ssGSEA), fuzzy c-means algorithm, were performed. Data of drug sensitivities were utilized to screen potential therapeutic agents for different senescence patients. Additionally, we developed a method called signature-related gene analysis (SRGA) for identification of markers relevant to phenotype of interest. Experimental strategies consisting quantitative real-time PCR (qRT-PCR), β-galactosidase assay, western blot, and tumor-T cell co-culture system were used to validate the findings in vitro.

RESULTS

We identified three robust prognostic clusters of HCC patients with distinct survival outcome, mutational landscape, and immune features. We further extracted signature genes of senescence clusters to construct the senescence scoring system and profile senescence level in HCC at bulk and single-cell resolution. Senescence-induced stemness reprogramming was confirmed both in silico and in vitro. HCC patients with high senescence were immune suppressed and sensitive to Tozasertib and other drugs. We suggested that MAFG, PLIN3, and 4 other genes were pertinent to HCC senescence, and MAFG potentially mediated immune suppression, senescence, and stemness.

CONCLUSION

Our findings provide insights into the role of SRGs in patients stratification and precision medicine.

Retinoic acid receptor activation reprograms senescence response and enhances anti-tumor activity of natural killer cells

Cellular senescence can exert dual effects in tumors, either suppressing or promoting tumor progression. The senescence-associated secretory phenotype (SASP), released by senescent cells, plays a crucial role in this dichotomy. Consequently, the clinical challenge lies in developing therapies that safely enhance senescence in cancer, favoring tumor-suppressive SASP factors over tumor-promoting ones. Here, we identify the retinoic-acid-receptor (RAR) agonist adapalene as an effective pro-senescence compound in prostate cancer (PCa). Reactivation of RARs triggers a robust senescence response and a tumor-suppressive SASP. In preclinical mouse models of PCa, the combination of adapalene and docetaxel promotes a tumor-suppressive SASP that enhances natural killer (NK) cell-mediated tumor clearance more effectively than either agent alone. This approach increases the efficacy of the allogenic infusion of human NK cells in mice injected with human PCa cells, suggesting an alternative therapeutic strategy to stimulate the anti-tumor immune response in "immunologically cold" tumors.

Radiotherapy-Induced Astrocyte Senescence Promotes an Immunosuppressive Microenvironment in Glioblastoma to Facilitate Tumor Regrowth

Accumulating evidence suggests that changes in the tumor microenvironment caused by radiotherapy are closely related to the recurrence of glioma. However, the mechanisms by which such radiation-induced changes are involved in tumor regrowth have not yet been fully investigated. In the present study, how cranial irradiation-induced senescence in non-neoplastic brain cells contributes to glioma progression is explored. It is observed that senescent brain cells facilitated tumor regrowth by enhancing the peripheral recruitment of myeloid inflammatory cells in glioblastoma. Further, it is identified that astrocytes are one of the most susceptible senescent populations and that they promoted chemokine secretion in glioma cells via the senescence-associated secretory phenotype. By using senolytic agents after radiotherapy to eliminate these senescent cells substantially prolonged survival time in preclinical models. The findings suggest the tumor-promoting role of senescent astrocytes in the irradiated glioma microenvironment and emphasize the translational relevance of senolytic agents for enhancing the efficacy of radiotherapy in gliomas.

Characterization of BCL-X L , MCL-1, and BAX Protein Expression in Response to Neoadjuvant Chemotherapy in Breast Cancer

The use of chemotherapy has improved the overall treatment of breast cancer, which is frequently administered in the form of neoadjuvant chemotherapy (NAC). Apoptosis is an established cell stress response to NAC in preclinical models; however, there is limited understanding of its role in clinical cancer, specifically, its contribution to favorable pathologic responses in breast cancer therapy. Here, we aimed to characterize the change in protein expression of 3 apoptosis-associated biomarkers, namely, BCL-X L , MCL-1, and BAX in breast cancer in response to NAC. For this, we utilized a set of 68 matched invasive breast cancer FFPE samples that were collected before (pre) and after (post) the exposure to NAC therapy that were characterized by incomplete pathologic response. Immunohistochemistry (IHC) analysis suggested that most of the samples show a decrease in the protein expression of all 3 markers following exposure to NAC as 90%, 69%, and 76% of the matched samples exhibited a decrease in expression for BCL-X L , MCL-1, and BAX, respectively. The median H-score of BCL-X L post-NAC was 150/300 compared with 225/300 pre-NAC ( P value <0.0001). The median H-score of MCL-1 declined from 200 pre-NAC to 160 post-NAC ( P value <0.0001). The median H-score of BAX protein expression decreased from 260 pre-NAC to 190 post-NAC ( P value <0.0001). There was no statistically significant association between the expression of these markers and stage, grade, and hormone receptor profiling (luminal status). Collectively, our data indicate that the expression of apoptosis regulatory proteins changes following exposure to NAC in breast cancer tissue, developing a partial pathologic response.

Amide Alkaloids as Privileged Sources of Senomodulators for Therapeutic Purposes in Age-Related Diseases

Nature is an important source of bioactive compounds and has continuously made a large contribution to the discovery of new drug leads. Particularly, plant-derived compounds have long been identified as highly interesting in the field of aging research and senescence. Many plants contain bioactive compounds that have the potential to influence cellular processes and provide health benefits. Among them, Piper alkaloids have emerged as interesting candidates in the context of age-related diseases and particularly senescence. These compounds have been shown to display a variety of features, including antioxidant, anti-inflammatory, neuroprotective, and other bioactive properties that may help counteracting the effects of cellular aging processes. In the review, we will put the emphasis on piperlongumine and other related derivatives, which belong to the Piper alkaloids, and whose senomodulating potential has emerged during the last several years. We will also provide a survey on their potential in therapeutic perspectives of age-related diseases.

Therapy-induced senescence is finally escapable, what is next?

Several breakthrough articles have recently confirmed the ability of tumor cells to escape the stable cell cycle arrest imposed by Therapy-Induced Senescence (TIS). Subsequently, accepting the hypothesis that TIS is escapable should encourage serious reassessments of the fundamental roles of senescence in cancer treatment. The potential for escape from TIS undermines the well-established tumor suppressor function of senescence, proposes it as a mechanism of tumor dormancy leading to disease recurrence and invites for further investigation of its unfavorable contribution to cancer therapy outcomes. Moreover, escaping TIS strongly indicates that the elimination of senescent tumor cells, primarily through pharmacological means, is a suitable approach for increasing the efficacy of cancer treatment, one that still requires further exploration. This commentary provides an overview of the recent evidence that unequivocally demonstrated the ability of therapy-induced senescent tumor cells in overcoming the terminal growth arrest fate and provides future perspectives on the roles of TIS in tumor biology.

Cooperative pro-tumorigenic adaptation to oncogenic RAS through epithelial-to-mesenchymal plasticity

In breast cancers, aberrant activation of the RAS/MAPK pathway is strongly associated with mesenchymal features and stemness traits, suggesting an interplay between this mitogenic signaling pathway and epithelial-to-mesenchymal plasticity (EMP). By using inducible models of human mammary epithelial cells, we demonstrate herein that the oncogenic activation of RAS promotes ZEB1-dependent EMP, which is necessary for malignant transformation. Notably, EMP is triggered by the secretion of pro-inflammatory cytokines from neighboring RAS-activated senescent cells, with a prominent role for IL-6 and IL-1α. Our data contrast with the common view of cellular senescence as a tumor-suppressive mechanism and EMP as a process promoting late stages of tumor progression in response to signals from the tumor microenvironment. We highlighted here a pro-tumorigenic cooperation of RAS-activated mammary epithelial cells, which leverages on oncogene-induced senescence and EMP to trigger cellular reprogramming and malignant transformation.

Current senolytics: Mode of action, efficacy and limitations, and their future

Senescence is a cellular state characterized by its near-permanent halted cell cycle and distinct secretory phenotype. Although senescent cells have a variety of beneficial physiological functions, progressive accumulation of these cells due to aging or other conditions has been widely shown to provoke deleterious effects on the normal functioning of the same or higher-level biological organizations. Recently, erasing senescent cells in vivo, using senolytics, could ameliorate diseases identified with an elevated number of senescent cells. Since then, researchers have struggled to develop new senolytics each with different selectivity and potency. In this review, we have gathered and classified the proposed senolytics and discussed their mechanisms of action. Moreover, we highlight the heterogeneity of senolytics regarding their effect sizes, and cell type specificity as well as comment on the exploited strategies to improve these features. Finally, we suggest some prospective routes for the novel methods for ablation of senescent cells.

Therapy-induced normal tissue damage promotes breast cancer metastasis

Disseminated tumor cells frequently exhibit a period of dormancy, rendering them chemotherapy insensitive; conversely, the systemic delivery of chemotherapies can result in normal tissue damage. Using multiple mouse and human breast cancer models, we demonstrate that prior chemotherapy administration enhances metastatic colonization and outgrowth. In vitro, chemotherapy-treated fibroblasts display a pro-tumorigenic senescence-associated secretory phenotype (SASP) and are effectively eliminated by targeting the anti-apoptotic protein BCL-xL. In vivo, chemotherapy treatment induces SASP expression in normal tissues; however, the accumulation of senescent cells is limited, and BCL-xL inhibitors are unable to reduce chemotherapy-enhanced metastasis. This likely reflects that chemotherapy-exposed stromal cells do not enter a BCL-xL-dependent phenotype or switch their dependency to other anti-apoptotic BCL-2 family members. This study highlights the role of the metastatic microenvironment in controlling outgrowth of disseminated tumor cells and the need to identify additional approaches to limit the pro-tumorigenic effects of therapy-induced normal tissue damage.

Doxorubicin-induced senescence promotes resistance to cell death by modulating genes associated with apoptotic and necrotic pathways in prostate cancer DU145 CD133+/CD44+ cells

Cancer stem cells (CSCs) are the most important cause of cancer treatment failure. Traditional cancer treatments, such as chemotherapy and radiotherapy, damage healthy cells alongside malignant cells, leading to severe adverse effects. Therefore, inducing cellular senescence without triggering apoptosis, which further damages healthy cells, may be an alternative strategy. However, there is insufficient knowledge regarding senescence induction in CSCs that show resistance to treatment and stemness properties. The present study aims to elucidate the effects of senescence induction on proliferation, cell cycle, and apoptosis in prostate CSCs and non-CSCs. Prostate CSCs were isolated from DU145 cancer cells using the FACS method. Subsequently, senescence induction was performed in RWPE-1, DU145, prostate CSCs, and non-CSCs by using different concentrations of Doxorubicin (DOX). Cellular senescence was detected using the senescence markers SA-β-gal, Ki67, and senescence-associated heterochromatin foci (SAHF). The effects of senescence on cell cycle and apoptosis were evaluated using the Muse Cell Analyzer, and genes in signaling pathways associated with the apoptotic/necrotic pathway were analyzed by real-time PCR. Prostate CSCs were isolated with 95.6 ± 1.4% purity according to CD133+/CD44+ characteristics, and spheroid formation belonging to stem cells was observed. After DOX-induced senescence, we observed morphological changes, SA-β-gal positivity, SAHF, and the lack of Ki67 in senescent cells. Furthermore; we detected G2/M cell cycle arrest and downregulation of various apoptosis-related genes in senescent prostate CSCs. Our results showed that DOX is a potent inducer of senescence for prostate CSCs, inhibits proliferation by arresting the cell cycle, and senescent prostate CSCs develop resistance to apoptosis.

Therapy-induced senescence as a component of tumor biology: Evidence from clinical cancer

Therapy-Induced Senescence (TIS) is an established response to anticancer therapy in a variety of cancer models. Ample evidence has characterized the triggers, hallmarks, and functional outcomes of TIS in preclinical studies; however, limited evidence delineates TIS in clinical cancer (human tumor samples). We examined the literature that investigated the induction of TIS in samples derived from human cancers and highlighted the major findings that suggested that TIS represents a main constituent of tumor biology. The most frequently utilized approach to identify TIS in human cancers was to investigate the protein expression of senescence-associated markers (such as cyclins, cyclin-dependent kinase inhibitors, Ki67, DNA damage repair response markers, DEC1, and DcR1) via immunohistochemical techniques using formalin-fixed paraffin-embedded (FFPE) tissue samples and/or testing the upregulation of Senescence-Associated β-galactosidase (SA-β-gal) in frozen sections of unfixed tumor samples. Collectively, and in studies where the extent of TIS was determined, TIS was detected in 31-66% of tumors exposed to various forms of chemotherapy. Moreover, TIS was not only limited to both malignant and non-malignant components of tumoral tissue but was also identified in samples of normal (non-transformed) tissue upon chemo- or radiotherapy exposure. Nevertheless, the available evidence continues to be limited and requires a more rigorous assessment of in vivo senescence based on novel approaches and more reliable molecular signatures. The accurate assessment of TIS will be beneficial for determining its relevant contribution to the overall outcome of cancer therapy and the potential translatability of senotherapeutics.

Multiparametric senescent cell phenotyping reveals targets of senolytic therapy in the aged murine skeleton

Senescence drives organismal aging, yet the deep characterization of senescent cells in vivo remains incomplete. Here, we apply mass cytometry by time-of-flight using carefully validated antibodies to analyze senescent cells at single-cell resolution. We use multiple criteria to identify senescent mesenchymal cells that are growth-arrested and resistant to apoptosis. These p16 + Ki67-BCL-2+ cells are highly enriched for senescence-associated secretory phenotype and DNA damage markers, are strongly associated with age, and their percentages are increased in late osteoblasts/osteocytes and CD24high osteolineage cells. Moreover, both late osteoblasts/osteocytes and CD24high osteolineage cells are robustly cleared by genetic and pharmacologic senolytic therapies in aged mice. Following isolation, CD24+ skeletal cells exhibit growth arrest, senescence-associated β-galactosidase positivity, and impaired osteogenesis in vitro. These studies thus provide an approach using multiplexed protein profiling to define senescent mesenchymal cells in vivo and identify specific skeletal cell populations cleared by senolytics.

Targeting MCL-1 protein to treat cancer: opportunities and challenges

Evading apoptosis has been linked to tumor development and chemoresistance. One mechanism for this evasion is the overexpression of prosurvival B-cell lymphoma-2 (BCL-2) family proteins, which gives cancer cells a survival advantage. Mcl-1, a member of the BCL-2 family, is among the most frequently amplified genes in cancer. Targeting myeloid cell leukemia-1 (MCL-1) protein is a successful strategy to induce apoptosis and overcome tumor resistance to chemotherapy and targeted therapy. Various strategies to inhibit the antiapoptotic activity of MCL-1 protein, including transcription, translation, and the degradation of MCL-1 protein, have been tested. Neutralizing MCL-1's function by targeting its interactions with other proteins via BCL-2 interacting mediator (BIM)S2A has been shown to be an equally effective approach. Encouraged by the design of venetoclax and its efficacy in chronic lymphocytic leukemia, scientists have developed other BCL-2 homology (BH3) mimetics-particularly MCL-1 inhibitors (MCL-1i)-that are currently in clinical trials for various cancers. While extensive reviews of MCL-1i are available, critical analyses focusing on the challenges of MCL-1i and their optimization are lacking. In this review, we discuss the current knowledge regarding clinically relevant MCL-1i and focus on predictive biomarkers of response, mechanisms of resistance, major issues associated with use of MCL-1i, and the future use of and maximization of the benefits from these agents.

Bcl-2 family inhibitors sensitize human cancer models to therapy

BH3 mimetics, targeting the Bcl-2 family anti-apoptotic proteins, represent a promising therapeutic opportunity in cancers. ABT-199, the first specific Bcl-2 inhibitor, was approved by FDA for the treatment of several hematological malignancies. We have recently discovered IS21, a novel pan BH3 mimetic with preclinical antitumor activity in several tumor types. Here, we evaluated the efficacy of IS21 and other BH3 mimetics, both as single agents and combined with the currently used antineoplastic agents in T-cell acute lymphoblastic leukemia, ovarian cancer, and melanoma. IS21 was found to be active in T-cell acute lymphoblastic leukemia, melanoma, lung, pancreatic, and ovarian cancer cell lines. Bcl-xL and Mcl-1 protein levels predicted IS21 sensitivity in melanoma and ovarian cancer, respectively. Exploring IS21 mechanism of action, we found that IS21 activity depends on the presence of BAX and BAK proteins: complexes between Bcl-2 and Bcl-xL proteins and their main binding partners were reduced after IS21 treatment. In combination experiments, BH3 mimetics sensitized leukemia cells to chemotherapy, ovarian cancer cells and melanoma models to PARP and MAPK inhibitors, respectively. We showed that this enhancing effect was related to the potentiation of the apoptotic pathway, both in hematologic and solid tumors. In conclusion, our data suggest the use of inhibitors of anti-apoptotic proteins as a therapeutic strategy to enhance the efficacy of anticancer treatment.

A Redox Homeostasis Modulatory Hydrogel with GLRX3+ Extracellular Vesicles Attenuates Disc Degeneration by Suppressing Nucleus Pulposus Cell Senescence

Characterized by nucleus pulposus (NP) cell senescence and extracellular matrix (ECM) degradation, disc degeneration is a common pathology for various degenerative spinal disorders. To date, effective treatments for disc degeneration are absent. Here, we found that Glutaredoxin3 (GLRX3) is an important redox-regulating molecule associated with NP cell senescence and disc degeneration. Using a hypoxic preconditioning method, we developed GLRX3⁺ mesenchymal stem cell-derived extracellular vehicles (EVs-GLRX3), which enhanced the cellular antioxidant defense, thus preventing reactive oxygen species (ROS) accumulation and senescence cascade expansion in vitro. Further, a disc tissue-like biopolymer-based supramolecular hydrogel, which was injectable, degradable, and ROS-responsive, was proposed to deliver EVs-GLRX3 for treating disc degeneration. Using a rat model of disc degeneration, we demonstrated that the EVs-GLRX3-loaded hydrogel attenuated mitochondrial damage, alleviated the NP senescence state, and restored ECM deposition by modulating the redox homeostasis. Our findings suggested that modulation of redox homeostasis in the disc can rejuvenate NP cell senescence and thus attenuate disc degeneration.

Reshaping of the tumor microenvironment by cellular senescence: An opportunity for senotherapies

Cellular senescence is a stress response associated with aging and disease, including cancer. Senescent cells undergo a stable cell cycle arrest, undergo a change in morphology and metabolic reprogramming, and produce a bioactive secretome termed the senescence-associated secretory phenotype (SASP). In cancer, senescence is an important barrier to tumor progression. Induction of senescence in preneoplastic cells limits cancer initiation, and many cancer therapies act in part by inducing senescence in cancer cells. Paradoxically, senescent cells lingering in the tumor microenvironment (TME) can contribute to tumor progression, metastasis, and therapy resistance. In this review, we discuss the different types of senescent cells present in the TME and how these senescent cells and their SASP reshape the TME, affect immune responses, and influence cancer progression. Furthermore, we will highlight the importance of senotherapies, including senolytic drugs that eliminate senescent cells and impede tumor progression and metastasis by restoring anti-tumor immune responses and influencing the TME.

A patent review of selective CDK9 inhibitors in treating cancer

INTRODUCTION

The dysregulation of CDK9 protein is greatly related to the proliferation and differentiation of various cancers due to its key role in the regulation of RNA transcription. Moreover, CDK9 inhibition can markedly downregulate the anti-apoptotic protein Mcl-1 which is essential for the survival of tumors. Thus, targeting CDK9 is considered to be a promising strategy for antitumor drug development, and the development of selective CDK9 inhibitors has gained increasing attention.

AREAS COVERED

This review focuses on the development of selective CDK9 inhibitors reported in patent publications during the period 2020-2022, which were searched from SciFinder and Cortellis Drug Discovery Intelligence.

EXPERT OPINION

Given that pan-CDK9 inhibitors may lead to serious side effects due to poor selectivity, the investigation of selective CDK9 inhibitors has attracted widespread attention. CDK9 inhibitors make some advance in treating solid tumors and possess the therapeutic potential in EGFR-mutant lung cancer. CDK9 inhibitors with short half-life and intravenous administration might result in transient target engagement and contribute to a better safety profile in vivo. However, more efforts are urgently needed to accelerate the development of CDK9 inhibitors, including the research on new binding modes between ligand and receptor or new protein binding sites.

Senescent Tumor Cells Are Frequently Present at the Invasion Front: Implications for Improving Disease Control in Patients with Locally Advanced Prostate Cancer

INTRODUCTION

Local tumor invasion is a critical factor for the outcome of men with prostate cancer. In particular, seminal vesicle invasion (SVI) has been reported to be associated with a more unfavorable prognosis. A better understanding of the functional state of invading prostate cancer cells is crucial to develop novel therapeutic strategies for patients with locally advanced disease.

METHODS

The prognostic impact of local tumor progression was ascertained in over 1,000 men with prostate cancer. Prostate cancer specimens were stained by double-immunohistochemistry for the proliferation marker Ki-67 and the senescence marker p16INK4A. The migratory properties of senescent prostate cancer cells were analyzed in vitro using a wound healing assay and immunofluorescence microscopy for p16INK4A.

RESULTS

We confirm the notion that patients with SVI have a more unfavorable prognosis than patients with extraprostatic extension alone. Surprisingly, we found that the tumor invasion front frequently harbors p16INK4A-positive and Ki-67-negative, i.e., senescent, tumor cells. While the intraprostatic tumor periphery was a hotspot for both proliferation and expression of p16INK4A, the area of SVI showed less proliferative activity but was at the same time a hotspot of cells with increased nuclear p16INK4A expression. Senescence was associated with an accelerated migration of prostate cancer cells in vitro.

CONCLUSION

This proof-of-concept study shows that invading prostate cancer cells frequently show signs of cellular senescence. This finding may open new avenues for neoadjuvant and adjuvant treatment concepts in men with locally advanced prostate cancer.

Involvement of Bcl-2 Family Proteins in Tetraploidization-Related Senescence

The B-cell lymphoma 2 (Bcl-2) family of proteins is the main regulator of apoptosis. However, multiple emerging evidence has revealed that Bcl-2 family proteins are also involved in cellular senescence. On the one hand, the different expression of these proteins determines the entry into senescence. On the other hand, entry into senescence modulates the expression of these proteins, generally conferring resistance to apoptosis. With some exceptions, senescent cells are characterized by the upregulation of antiapoptotic proteins and downregulation of proapoptotic proteins. Under physiological conditions, freshly formed tetraploid cells die by apoptosis due to the tetraploidy checkpoint. However, suppression of Bcl-2 associated x protein (Bax), as well as overexpression of Bcl-2, favors the appearance and survival of tetraploid cells. Furthermore, it is noteworthy that our laboratory has shown that the joint absence of Bax and Bcl-2 antagonist/killer (Bak) favors the entry into senescence of tetraploid cells. Certain microtubule inhibitory chemotherapies, such as taxanes and vinca alkaloids, induce the generation of tetraploid cells. Moreover, the combined use of inhibitors of antiapoptotic proteins of the Bcl-2 family with microtubule inhibitors increases their efficacy. In this review, we aim to shed light on the involvement of the Bcl-2 family of proteins in the senescence program activated after tetraploidization and the possibility of using this knowledge to create a new therapeutic strategy targeting cancer cells.

A three-marker signature identifies senescence in human breast cancer exposed to neoadjuvant chemotherapy

PURPOSE

Despite the beneficial effects of chemotherapy, therapy-induced senescence (TIS) manifests itself as an undesirable byproduct. Preclinical evidence suggests that tumor cells undergoing TIS can re-emerge as more aggressive divergents and contribute to recurrence, and thus, senolytics were proposed as adjuvant treatment to eliminate senescent tumor cells. However, the identification of TIS in clinical samples is essential for the optimal use of senolytics in cancer therapy. In this study, we aimed to detect and quantify TIS using matched breast cancer samples collected pre- and post-exposure to neoadjuvant chemotherapy (NAC).

METHODS

Detection of TIS was based on the change in gene and protein expression levels of three senescence-associated markers (downregulation of Lamin B1 and Ki-67 and upregulation of p16^INK4a).

RESULTS

Our analysis revealed that 23 of 72 (31%) of tumors had a shift in the protein expression of the three markers after exposure to NAC suggestive of TIS. Gene expression sets of two independent NAC-treated breast cancer samples showed consistent changes in the expression levels of LMNB1, MKI67 and CDKN2A.

CONCLUSIONS

Collectively, our study shows a more individualized approach to measure TIS hallmarks in matched breast cancer samples and provides an estimation of the extent of TIS in breast cancer clinically. Results from this work should be complemented with more comprehensive identification approaches of TIS in clinical samples in order to adopt a more careful implementation of senolytics in cancer treatment.

Emerging Therapeutic Approaches to Target the Dark Side of Senescent Cells: New Hopes to Treat Aging as a Disease and to Delay Age-Related Pathologies

Life expectancy has drastically increased over the last few decades worldwide, with important social and medical burdens and costs. To stay healthy longer and to avoid chronic disease have become essential issues. Organismal aging is a complex process that involves progressive destruction of tissue functionality and loss of regenerative capacity. One of the most important aging hallmarks is cellular senescence, which is a stable state of cell cycle arrest that occurs in response to cumulated cell stresses and damages. Cellular senescence is a physiological mechanism that has both beneficial and detrimental consequences. Senescence limits tumorigenesis, lifelong tissue damage, and is involved in different biological processes, such as morphogenesis, regeneration, and wound healing. However, in the elderly, senescent cells increasingly accumulate in several organs and secrete a combination of senescence associated factors, contributing to the development of various age-related diseases, including cancer. Several studies have revealed major molecular pathways controlling the senescent phenotype, as well as the ones regulating its interactions with the immune system. Attenuating the senescence-associated secretory phenotype (SASP) or eliminating senescent cells have emerged as attractive strategies aiming to reverse or delay the onset of aging diseases. Here, we review current senotherapies designed to suppress the deleterious effect of SASP by senomorphics or to selectively kill senescent cells by "senolytics" or by immune system-based approaches. These recent investigations are promising as radical new controls of aging pathologies and associated multimorbidities.

Apolipoprotein E induces pathogenic senescent-like myeloid cells in prostate cancer

Tumor cells promote the recruitment of immunosuppressive neutrophils, a subset of myeloid cells driving immune suppression, tumor proliferation, and treatment resistance. Physiologically, neutrophils are known to have a short half-life. Here, we report the identification of a subset of neutrophils that have upregulated expression of cellular senescence markers and persist in the tumor microenvironment. Senescent-like neutrophils express the triggering receptor expressed on myeloid cells 2 (TREM2) and are more immunosuppressive and tumor-promoting than canonical immunosuppressive neutrophils. Genetic and pharmacological elimination of senescent-like neutrophils decreases tumor progression in different mouse models of prostate cancer. Mechanistically, we have found that apolipoprotein E (APOE) secreted by prostate tumor cells binds TREM2 on neutrophils, promoting their senescence. APOE and TREM2 expression increases in prostate cancers and correlates with poor prognosis. Collectively, these results reveal an alternative mechanism of tumor immune evasion and support the development of immune senolytics targeting senescent-like neutrophils for cancer therapy.

Identification of anoikis-related molecular patterns to define tumor microenvironment and predict immunotherapy response and prognosis in soft-tissue sarcoma

Background: Soft-tissue sarcoma (STS) is a massive threat to human health due to its high morbidity and malignancy. STS also represents more than 100 histologic and molecular subtypes, with different prognosis. There is growing evidence that anoikis play a key role in the proliferation and invasion of tumors. However, the effects of anoikis in the immune landscape and the prognosis of STS remain unclear. Methods: We analyzed the genomic and transcriptomic profiling of 34 anoikis-related genes (ARGs) in patient cohort of pan-cancer and STS from The Cancer Genome Atlas (TCGA) database. Single-cell transcriptome was used to disclose the expression patterns of ARGs in specific cell types. Gene expression was further validated by real-time PCR and our own sequencing data. We established the Anoikis cluster and Anoikis subtypes by using unsupervised consensus clustering analysis. An anoikis scoring system was further built based on the differentially expressed genes (DEGs) between Anoikis clusters. The clinical and biological characteristics of different groups were evaluated. Results: The expressions of most ARGs were significantly different between STS and normal tissues. We found some common ARGs profiles across the pan-cancers. Network of 34 ARGs demonstrated the regulatory pattern and the association with immune cell infiltration. Patients from different Anoikis clusters or Anoikis subtypes displayed distinct clinical and biological characteristics. The scoring system was efficient in prediction of prognosis and immune cell infiltration. In addition, the scoring system could be used to predict immunotherapy response. Conclusion: Overall, our study thoroughly depicted the anoikis-related molecular and biological profiling and interactions of ARGs in STS. The Anoikis score model could guide the individualized management.

Distinct mechanisms mediating therapy-induced cellular senescence in prostate cancer

BACKGROUND

Prostate cancer (PCa) is an age-related malignancy in men with a high incidence rate. PCa treatments face many obstacles due to cancer cell resistance and many bypassing mechanisms to escape therapy. According to the intricacy of PCa, many standard therapies are being used depending on PCa stages including radical prostatectomy, radiation therapy, androgen receptor (AR) targeted therapy (androgen deprivation therapy, supraphysiological androgen, and AR antagonists) and chemotherapy. Most of the aforementioned therapies have been implicated to induce cellular senescence. Cellular senescence is defined as a stable cell cycle arrest in the G1 phase and is one of the mechanisms that prevent cancer proliferation.

RESULTS

In this review, we provide and analyze different mechanisms of therapy-induced senescence (TIS) in PCa and their effects on the tumor. Interestingly, it seems that different molecular pathways are used by cancer cells for TIS. Understanding the complexity and underlying mechanisms of cellular senescence is very critical due to its role in tumorigenesis. The most prevalent analyzed pathways in PCa as TIS are the p53/p21^WAF1/CIP1, the p15^INK4B/p16^INK4A/pRb/E2F/Cyclin D, the ROS/ERK, p27^Kip1/CDK/pRb, and the p27^Kip1/Skp2/C/EBP β signaling. Despite growth inhibition, senescent cells are highly metabolically active. In addition, their secretome, which is termed senescence-associated secretory phenotype (SASP), affects within the tumor microenvironment neighboring non-tumor and tumor cells and thereby may regulate the growth of tumors. Induction of cancer cell senescence is therefore a double-edged sword that can lead to reduced or enhanced tumor growth.

CONCLUSION

Thus, dependent on the type of senescence inducer and the specific senescence-induced cellular pathway, it is useful to develop pathway-specific senolytic compounds to specifically targeting senescent cells in order to evict senescent cells and thereby to reduce SASP side effects.

Senolytic Therapy: A Potential Approach for the Elimination of Oncogene-Induced Senescent HPV-Positive Cells

Senescence represents a unique cellular stress response characterized by a stable growth arrest, macromolecular alterations, and wide spectrum changes in gene expression. Classically, senescence is the end-product of progressive telomeric attrition resulting from the repetitive division of somatic cells. In addition, senescent cells accumulate in premalignant lesions, in part, as a product of oncogene hyperactivation, reflecting one element of the tumor suppressive function of senescence. Oncogenic processes that induce senescence include overexpression/hyperactivation of H-Ras, B-Raf, and cyclin E as well as inactivation of PTEN. Oncogenic viruses, such as Human Papilloma Virus (HPV), have also been shown to induce senescence. High-risk strains of HPV drive the immortalization, and hence transformation, of cervical epithelial cells via several mechanisms, but primarily via deregulation of the cell cycle, and possibly, by facilitating escape from senescence. Despite the wide and successful utilization of HPV vaccines in reducing the incidence of cervical cancer, this measure is not effective in preventing cancer development in individuals already positive for HPV. Accordingly, in this commentary, we focus on the potential contribution of oncogene and HPV-induced senescence (OIS) in cervical cancer. We further consider the potential utility of senolytic agents for the elimination of HPV-harboring senescent cells as a strategy for reducing HPV-driven transformation and the risk of cervical cancer development.

Targeting senescence as an anticancer therapy

Cellular senescence is a stress response elicited by different molecular insults. Senescence results in cell cycle exit and is characterised by multiple phenotypic changes such as the production of a bioactive secretome. Senescent cells accumulate during ageing and are present in cancerous and fibrotic lesions. Drugs that selectively kill senescent cells (senolytics) have shown great promise for the treatment of age-related diseases. Senescence plays paradoxical roles in cancer. Induction of senescence limits cancer progression and contributes to therapy success, but lingering senescent cells fuel progression, recurrence, and metastasis. In this review, we describe the intricate relation between senescence and cancer. Moreover, we enumerate how current anticancer therapies induce senescence in tumour cells and how senolytic agents could be deployed to complement anticancer therapies. "One-two punch" therapies aim to first induce senescence in the tumour followed by senolytic treatment to target newly exposed vulnerabilities in senescent tumour cells. "One-two punch" represents an emerging and promising new strategy in cancer treatment. Future challenges of "one-two punch" approaches include how to best monitor senescence in cancer patients to effectively survey their efficacy.

Can 3D bioprinting solve the mystery of senescence in cancer therapy?

Tumor dormancy leading to cancer relapse is still a poorly understood mechanism. Several cell states such as quiescence and diapause can explain the persistence of tumor cells in a dormant state, but the potential role of tumor cell senescence has been met with hesitance given the historical understanding of the senescent growth arrest as irreversible. However, recent evidence has suggested that senescence might contribute to dormancy and relapse, although its exact role is not fully developed. This limited understanding is largely due to the paucity of reliable study models. The current 2D cell modeling is overly simplistic and lacks the appropriate representation of the interactions between tumor cells (senescent or non-senescent) and the other cell types within the tumor microenvironment (TME), as well as with the extracellular matrix (ECM). 3D cell culture models, including 3D bioprinting techniques, offer a promising approach to better recapitulate the native cancer microenvironment and would significantly improve our understanding of cancer biology and cellular response to treatment, particularly Therapy-Induced Senescence (TIS), and its contribution to tumor dormancy and cancer recurrence. Fabricating a novel 3D bioprinted model offers excellent opportunities to investigate both the role of TIS in tumor dormancy and the utility of senolytics (drugs that selectively eliminate senescent cells) in targeting dormant cancer cells and mitigating the risk for resurgence. In this review, we discuss literature on the possible contribution of TIS in tumor dormancy, provide examples on the current 3D models of senescence, and propose a novel 3D model to investigate the ultimate role of TIS in mediating overall response to therapy.