Clearance of therapy-induced senescent tumor cells by the senolytic ABT-263 via interference with BCL-XL -BAX interaction

Therapy-induced senescent cancer cells contribute to cancer progression by promoting ribophorin 1-dependent PD-L1 upregulation

Conventional chemotherapy- and radiotherapy-induced cancer senescence, which is characterized by poor proliferation, drug resistance, and senescence-associated secretory phenotype, has gained attention as contributing to cancer relapse and the development of an immunosuppressive tumor microenvironment. However, the association between cancer senescence and anti-tumor immunity is not fully understood. Here, we demonstrate that senescent cancer cells increase the level of PD-L1 by promoting its transcription and glycosylation. We identify ribophorin 1 as a key regulator of PD-L1 glycosylation during cancer senescence. Ribophorin 1 depletion reduces this elevated level of PD-L1 through the ER-lysosome-associated degradation pathway, thereby increasing the susceptibility of senescent cancer cells to T-cell-mediated killing. Consistently, ribophorin 1 depletion suppresses tumor growth by decreasing PD-L1 levels and boosting cytotoxic T lymphocyte activity in male mice. Moreover, ribophorin 1-targeted or anti-PD-1 therapy reduces the number of senescent cancer cells in irradiated tumors and suppresses cancer recurrence through the activation of cytotoxic T lymphocytes. These results provide crucial insights into how senescent cancer cells can escape T-cell immunity following cancer treatment and thereby contribute to cancer recurrence. Our findings also highlight the therapeutic promise of targeting senescent cancer cells for cancer treatment.

Regulation of the Cilia as a Potential Treatment for Senescence and Tumors: A Review

Millions of people worldwide die from malignant tumors every year, and the current clinical treatment is still based on radiotherapy and chemotherapy. Immunotherapy-adjuvant chemotherapy is widely applied, yet resistance to various factors persists in the management of advanced malignancies. Recently researchers have gradually discovered that the integrity of primary cilia is closely related to many diseases. The phenotypic changes in primary cilia are found in some cases of progeria, tumorigenesis, and drug resistance. Primary cilia seem to mediate signaling during these diseases. Hedgehog inhibitors have emerged in recent years to treat tumors by controlling signaling proteins on primary cilia. There is evidence for the use of anti-tumor drugs to treat senescence-related disease. Considering the close relationship between aging and obesity, as well as the obesity is the phenotype of many ciliopathies. Therefore, we speculate that some anti-tumor or anti-aging drugs can treat ciliopathies. Additionally, there is evidence suggesting that anti-aging drugs for tumor treatment, in which the process may be mediated by cilia. This review elucidates for the first time that cilia may be involved in the regulation of senescence, metabolic, tumorigenesis, and tumor resistance and hypothesizes that cilia can be regulated to treat these diseases in the future.

Uncovering cellular senescence as a therapeutic target in NF2-related vestibular schwannoma

BACKGROUND

Vestibular schwannomas (VS) are complex and heterogeneous human tumors arising from the Schwann cell compartment of the vestibulocochlear nerve. VS cause significant neurological deficit such as hearing loss and vestibular impairment, and in some cases death due to brainstem compression. There is an urgent need to find pharmacotherapies for VS since surgical removal and stereotactic radiosurgery are the only effective treatments. Cancer therapy based in the combination of drug-induced senescence and senolytics may provide an innovative pharmacological alternative for VS management.

METHODS

Senescence-associated β-galactosidase (SA-β-GAL) activity detection assay, real-time polymerase chain reaction (RT-PCR), western blotting and immunofluorescence, together with viability assays were used to analyze the response to different chemotherapy drugs of the human VS HEI-193 cell line. Human VS tumor paraffin sections were also studied for SA-β-GAL-stained cells.

RESULTS

We found that chemotherapy compounds induced genotoxic stress and cellular senescence in HEI-193 VS cells, as characterized by increased SA-β-GAL activity, growth arrest, increased levels of the cyclin-dependent kinase inhibitor p21 and the accumulation of DNA damage. These cellular senescence markers were also accompanied by an increase of senescence-associated secretory phenotype (SASP): IL6, IL8, IL1B and MMP1. Induction of senescence by chemotherapy rendered HEI-193 VS cells as druggable targets for senolytic compounds, as navitoclax. Thus, treatment with navitoclax selectively eliminated bleomycin-induced senescent HEI-193 VS cells by activating the extrinsic and intrinsic apoptosis pathways. Our data also show the presence of senescent cells, SA-β-GAL-positive stain, in human VS tumors, which are not present in healthy great auricular nerve sections.

CONCLUSIONS

These findings suggest that a one-two punch strategy of pro-senescence therapy induced by chemotherapy treatment followed by senolytic therapy represents a new paradigm for the pharmacological treatment of VS.

The crosstalk between senescence, tumor, and immunity: molecular mechanism and therapeutic opportunities

Cellular senescence is characterized by a stable cell cycle arrest and a hypersecretory, proinflammatory phenotype in response to various stress stimuli. Traditionally, this state has been viewed as a tumor-suppressing mechanism that prevents the proliferation of damaged cells while activating the immune response for their clearance. However, senescence is increasingly recognized as a contributing factor to tumor progression. This dual role necessitates a careful evaluation of the beneficial and detrimental aspects of senescence within the tumor microenvironment (TME). Specifically, senescent cells display a unique senescence-associated secretory phenotype that releases a diverse array of soluble factors affecting the TME. Furthermore, the impact of senescence on tumor-immune interaction is complex and often underappreciated. Senescent immune cells create an immunosuppressive TME favoring tumor progression. In contrast, senescent tumor cells could promote a transition from immune evasion to clearance. Given these intricate dynamics, therapies targeting senescence hold promise for advancing antitumor strategies. This review aims to summarize the dual effects of senescence on tumor progression, explore its influence on tumor-immune interactions, and discuss potential therapeutic strategies, alongside challenges and future directions. Understanding how senescence regulates antitumor immunity, along with new therapeutic interventions, is essential for managing tumor cell senescence and remodeling the immune microenvironment.

Senolysis by ABT-263 is associated with inherent apoptotic dependence of cancer cells derived from the non-senescent state

Cellular senescence is a stress response that cells can employ to resist cell death. Senescent cells rely on anti-apoptotic signaling for their survival, which can be targeted by senolytic agents, like the BCL-XL, BCL-2, BCL-W inhibitor ABT-263. However, the response to ABT-263 of senescent cancer cells ranges from highly sensitive to refractory. Using BH3 profiling, we identify here apoptotic blocks in cancer cells that are resistant to this senolytic treatment and discover a correlation between mitochondrial apoptotic priming and cellular sensitivity to ABT-263 in senescence. Intriguingly, ABT-263 sensitivity correlates with overall mitochondrial apoptotic priming, not only in senescence but also in the parental state. Moreover, we confirm that ABT-263 exposure increases dependency on MCL-1, which is most enhanced in ABT-263 sensitive cells. ABT-263 resistant cells however upregulate MCL-1, while sensitive cells exhibit low levels of this anti-apoptotic protein. Overall, our data indicate that the response of senescent cells to ABT-263 is predetermined by the mitochondrial apoptotic priming state of the parental cells, which could serve as a predictive biomarker for response to senolytic therapy.

Targeting treatment resistance in cervical cancer: A new avenue for senolytic therapies

Cervical cancer poses a significant global health challenge, particularly impacting women in economically developing nations. This disparity stems from a combination of factors, including inadequate screening infrastructure and resource limitations. However, the foremost contributor is the widespread lack of awareness and limited accessibility to Human Papillomavirus (HPV) vaccination, which is a key preventative measure against cervical cancer development. Despite advancements in cervical cancer prevention, treatment resistance remains a major hurdle in achieving improved patient outcomes. Cellular senescence, specifically the senescence-associated secretory phenotype (SASP) and its bidirectional relationship with the immune system, has been implicated in resistance to conventional cervical cancer chemotherapy treatments. The exact mechanisms by which this state of growth arrest and the associated changes in immune regulation contribute to cervical cancer progression and the associated drug resistance are not entirely understood. This underscores the necessity for innovative strategies to address the prevalence of treatment-resistant cervical cancer, with one promising avenue being the utilisation of senolytics. Senolytics are agents that have promising efficacy in clearing senescent cells from tumour tissues, however neither the utilisation of senolytics for addressing senescence-induced treatment resistance nor the potential integration of immunotherapy as senolytic agents in cervical cancer treatment has been explored to date. This review provides a concise overview of the mechanisms underlying senescence induction and the pivotal role of the immune system in this process. Additionally, it explores various senolytic approaches that hold significant potential for advancing cervical cancer research.

Granulocyte colony-stimulating factor mediates bone loss via the activation of IL-1β/JNK signaling pathway in murine Staphylococcus aureus-induced osteomyelitis

Staphylococcus aureus (S. aureus)-induced bone loss is a significant challenge in the treatment of osteomyelitis. Our previous study was the first to confirm that granulocyte colony-stimulating factor (G-CSF) mediates S. aureus-induced bone loss. However, the underlying mechanism remains unknown. The objective of this study was to elucidate this. We found G-CSF mediated BMSC senescence and increased IL-1β concentration of serum and bone marrow in mice after S. aureus infection. Furthermore, we demonstrated that G-CSF promoted the expression of IL1b in murine bone marrow-derived neutrophils. Notably, we identified that IL-1β mediated BMSC (bone marrow mesenchymal stromal cell) senescence in mice after S. aureus infection. Importantly, IL-1β neutralizing antibody effectively alleviated BMSC senescence and bone loss caused by S. aureus infection in mice. In terms of molecular mechanism, we found IL-1β induced BMSC senescence by JNK/P53 and JNK/BCL2 pathways. Collectively, G-CSF promotes IL-1β production which induces BMSC senescence via JNK/P53 and JNK/BCL2 pathways, leading to S. aureus-induced bone loss. This study identified novel targets for preventing and treating S. aureus-induced bone loss in osteomyelitis.

Inhibition of PERK-mediated unfolded protein response acts as a switch for reversal of residual senescence and as senolytic therapy in glioblastoma

BACKGROUND

Glioblastoma due to recurrence is clinically challenging with 10-15 months overall survival. Previously we showed that therapy-induced senescence (TIS) in glioblastoma reverses causing recurrence. Here, we aim to delineate the TIS reversal mechanism for potential therapeutic intervention to prevent glioblastoma (GBM) recurrence.

METHODS

Residual senescent (RS) and end of residual senescence (ERS) cells were captured from GBM patient-derived primary-cultures and cell lines mimicking clinical scenarios. RNA-sequencing, transcript/protein validations, knock-down/inhibitor studies, ChIP RT-PCR, biochemical assays, and IHCs were performed for the mechanistics of TIS reversal. In vivo validations were conducted in GBM orthotopic mouse model.

RESULTS

Transcriptome analysis showed co-expression of endoplasmic reticulum (ER) stress-unfolded protein response (UPR) and senescence-associated secretory phenotype (SASP) with TIS induction and reversal. Robust SASP production and secretion by RS cells could induce senescence, Reactive oxygen specis (ROS), DNA damage, and ER stress in paracrine fashion independent of radiation. Neutralization of most significantly enriched cytokine from RS-secretome IL1β, suppressed SASP, and delayed senescence reversal. Mechanistically, with SASP and massive protein accumulation in ER, RS cells displayed stressed ER morphology, upregulated ER stress markers, and PERK pathway activation via peIF2α-ATF4-CHOP which was spontaneously resolved in ERS. ChIP RT-PCR showed CHOP occupancy at CXCL8/IL8, CDKN1A/p21, and BCL2L1/BCLXL aiding survival. PERK knockdown/inhibition with GSK2606414 in combination with radiation led to sustained ER stress and senescence without SASP. PERKi in RS functioned as senolytic via apoptosis and prevented recurrence in vitro and in vivo ameliorating overall survival.

CONCLUSION

We demonstrate that PERK-mediated UPR regulates senescence reversal and its inhibition can be exploited as a potential seno-therapeutic option in glioblastoma.

A BPTF Inhibitor That Interferes with the Multidrug Resistance Pump to Sensitize Murine Triple-Negative Breast Cancer Cells to Chemotherapy

Triple-negative breast cancer (TNBC) is associated with a generally poor prognosis due to its highly aggressive and metastatic nature, lack of targetable receptors, as well as the frequent development of resistance to chemotherapy. We previously reported that AU1, a small molecule developed as an inhibitor of BPTF (bromodomain PHD finger-containing transcription factor), was capable of sensitizing preclinical models of TNBC to chemotherapy in part via the promotion of autophagy. In studies reported here, we identify an additional property of this compound, specifically that sensitization is associated with the inhibition of the P-glycoprotein (P-gp) efflux pump. In silico molecular docking studies indicate that AU1 binds to active regions of the efflux pump in a manner consistent with the inhibition of the pump function. This work identifies a novel chemical structure that can influence multidrug efflux, an established mechanism of drug resistance in TNBC, that has not yet been successfully addressed by clinical efforts.

The senolytic drug ABT-263 accelerates ovarian aging in older female mice

Previous studies have reported that senolytic drugs can reverse obesity-mediated accumulation of senescent cells in the ovary and protect against cisplatin-induced ovarian injury by removing senescent cells. Early intervention with ABT-263 has been shown to mitigate ovarian aging. However, it remains unknown whether treatment with ABT-263 could rejuvenate the aged ovary in reproductively old females. Therefore, the current study was aimed to investigate whether advanced age intervention with ABT-263 could ameliorate age-related decline in ovarian function. Fourteen 16-month-old mice with a C57/BL6 background were treated with ABT-263 (N = 7) or vehicle (N = 7) for two weeks. Mice were initially treated with ABT-263 (60 mg/kg/d) or vehicle for 7 consecutive days. After a 7-day break, the treatment was repeated for another 7 consecutive days. Six 2-month-old mice with C57BL/6 were used as a young control. The hormonal levels, estrus cycles, ovarian reserve, ovarian cell proliferation and apoptosis, ovarian fibrosis, and steroidogenic gene expression of ovarian stromal cells were evaluated. ABT-263 treatment did not rescue abnormal estrus cycles and sex hormonal levels, or inhibit the formation of multinucleated giant cells and ovarian stromal cell apoptosis in aged ovaries. However, it reduced ovarian fibrosis and preserved the steroidogenic gene expression of ovarian stromal cells in aged ovaries. Importantly, ABT-263 treatment further depleted ovarian follicles in aged mice. In conclusion, ABT-263 treatment accelerated the depletion of ovarian follicles in aged mice, suggesting that senolytic drugs for reproductively old female may adversely affect female fertility.

The dual role of cellular senescence in human tumor progression and therapy

Cellular senescence, one of the hallmarks of cancer, is characterized by cell cycle arrest and the loss of most normal cellular functions while acquiring a hypersecretory, proinflammatory phenotype. The function of senescent cells in cancer cells varies depending on the cellular conditions. Before the occurrence of cancer, senescent cells act as a barrier to prevent its development. But once cancer has occurred, senescent cells play a procancer role. However, few of the current studies have adequately explained the diversity of cellular senescence across cancers. Herein, we concluded the latest intrinsic mechanisms of cellular senescence in detail and emphasized the senescence-associated secretory phenotype as a key contributor to heterogeneity of senescent cells in tumor. We also discussed five kinds of inducers of cellular senescence and the advancement of senolytics in cancer, which are drugs that tend to clear senescent cells. Finally, we summarized the various effects of senescent cells in different cancers and manifested that their functions may be diametrically opposed under different circumstances. In short, this paper contributes to the understanding of the diversity of cellular senescence in cancers and provides novel insight for tumor therapy.

Cellular senescence and metabolic reprogramming: Unraveling the intricate crosstalk in the immunosuppressive tumor microenvironment

The intrinsic oncogenic mechanisms and properties of the tumor microenvironment (TME) have been extensively investigated. Primary features of the TME include metabolic reprogramming, hypoxia, chronic inflammation, and tumor immunosuppression. Previous studies suggest that senescence-associated secretory phenotypes that mediate intercellular information exchange play a role in the dynamic evolution of the TME. Specifically, hypoxic adaptation, metabolic dysregulation, and phenotypic shifts in immune cells regulated by cellular senescence synergistically contribute to the development of an immunosuppressive microenvironment and chronic inflammation, thereby promoting the progression of tumor events. This review provides a comprehensive summary of the processes by which cellular senescence regulates the dynamic evolution of the tumor-adapted TME, with focus on the complex mechanisms underlying the relationship between senescence and changes in the biological functions of tumor cells. The available findings suggest that components of the TME collectively contribute to the progression of tumor events. The potential applications and challenges of targeted cellular senescence-based and combination therapies in clinical settings are further discussed within the context of advancing cellular senescence-related research.

Cellular senescence and SASP in tumor progression and therapeutic opportunities

Cellular senescence (CS), a permanent and irreversible arrest of the cell cycle and proliferation leading to the degeneration of cellular structure and function, has been implicated in various key physiological and pathological processes, particularly in cancer. Initially, CS was recognized as a barrier to tumorigenesis, serving as an intrinsic defense mechanism to protect cells from malignant transformation. However, increasing evidence suggests that senescent cells can promote tumor progression to overt malignancy, primarily through a set of factors known as senescence-associated secretory phenotypes (SASPs), including chemokines, growth factors, cytokines, and stromal metalloproteinases. These factors significantly reshape the tumor microenvironment (TME), enabling tumors to evade immune destruction. Interestingly, some studies have also suggested that SASPs may impede tumor development by enhancing immunosurveillance. These opposing roles highlight the complexity and heterogeneity of CS and SASPs in diverse cancers. Consequently, there has been growing interest in pharmacological interventions targeting CS or SASPs in cancer therapy, such as senolytics and senomorphics, to either promote the clearance of senescent cells or mitigate the harmful effects of SASPs. In this review, we will interpret the concept of CS, delve into the role of SASPs in reshaping the TME, and summarize recent advances in anti-tumor strategies targeting CS or SASPs.

Therapeutic Senolysis of Axitinib-Induced Senescent Human Lung Cancer Cells

BACKGROUND

Tyrosine kinase inhibitors (TKIs) inhibit receptor-mediated signals in cells. Axitinib is a TKI with high specificity for vascular endothelial growth factor receptors (VEGFRs).

AIM

We determined whether axitinib could induce senescence in human cancer cells and be lysed by the senolytic drug ABT-263.

METHODS

Human lung and breast adenocarcinoma cell lines were used. These cells were cultured with axitinib or a multi-target TKI lenvatinib. The expression of β-galactosidase, VEGFRs, Ki-67, reactive oxygen species (ROS) of cancer cells, and their BrdU uptake were evaluated by flow cytometry. The mRNA expression of p21 and IL-8 was examined by quantitative PCR. The effects of TKIs on phosphorylation of Akt and Erk1/2, as downstream molecules of VEGFR signaling, were examined by immunoblot. The in vivo anti-cancer effect was examined using a xenograft mice model.

RESULTS

Axitinib, but not lenvatinib, induced cellular senescence (increased cell size and enhanced expression of β-galactosidase) in all adenocarcinoma cell lines. Axitinib-induced senescence was unrelated to the expression of VEGFRs on cancer cells. ROS were involved in axitinib-induced senescence. Axitinib-induced senescent lung adenocarcinoma A549 cells were drastically lysed by ABT-263. In A549-xenografted mice, combination therapy with axitinib and ABT-263 significantly suppressed tumor growth with the induction of apoptotic cancer cells.

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.

Therapy-Induced Cellular Senescence: Potentiating Tumor Elimination or Driving Cancer Resistance and Recurrence?

Cellular senescence has been increasingly recognized as a hallmark of cancer, reflecting its association with aging and inflammation, its role as a response to deregulated proliferation and oncogenic stress, and its induction by cancer therapies. While therapy-induced senescence (TIS) has been linked to resistance, recurrence, metastasis, and normal tissue toxicity, TIS also has the potential to enhance therapy response and stimulate anti-tumor immunity. In this review, we examine the Jekyll and Hyde nature of senescent cells (SnCs), focusing on how their persistence while expressing the senescence-associated secretory phenotype (SASP) modulates the tumor microenvironment through autocrine and paracrine mechanisms. Through the SASP, SnCs can mediate both resistance and response to cancer therapies. To fulfill the unmet potential of cancer immunotherapy, we consider how SnCs may influence tumor inflammation and serve as an antigen source to potentiate anti-tumor immune response. This new perspective suggests treatment approaches based on TIS to enhance immune checkpoint blockade. Finally, we describe strategies for mitigating the detrimental effects of senescence, such as modulating the SASP or targeting SnC persistence, which may enhance the overall benefits of cancer treatment.

Cellular Senescence in Germ Cell Neoplasia In Situ (GCNIS) and Other Histological Types of Testicular Cancer

Background and Objectives: The presence and contribution of senescent cells in premalignant lesions is well documented, but not in germ cell neoplasia in situ. The purpose of this study is to identify the presence of senescent cells in pre-malignant testicular conditions and in different histological types of testicular cancer. Materials and Methods: Thirty patients who underwent orchiectomy due to testicular tumors were included. Formalin-fixed paraffin-embedded (FFPE) testicular tissue for each patient was available. Sections from these specimens were examined by immunohistochemical analysis with the following markers: GL13 for cellular senescence, p21WAF1/Cip1 for cell cycle arrest, and Ki67 for cell proliferation. Results: Thirteen (43.3%) suffered from seminoma with a mean total proportion of GCNIS senescence of 20.81 ± 6.81%. In the group of embryonal testicular tumors, nine (30%) patients were included, with an average rate of 6.64 ± 5.42% of senescent cells in GCNIS. One (3.3%) patient suffered from chondrosarcoma in which 7.9% of GL13+ cells were detected in GCNIS. Four (13.4%) patients suffered from teratoma and three (10%) from yolk sac tumors, while GCNIS senescence was detected in a range of 4.43 ± 1.78% and 3.76 ± 1.37%, respectively. Conclusions: Cellular senescence was detected in both germ cell neoplasia in situ and testicular cancer, but was more prevalent within the premalignant lesions.

Multi-omics and single cell characterization of cancer immunosenescence landscape

Cellular senescence (CS) is closely related to tumor progression. However, the studies about CS genes across human cancers have not explored the relationship between cancer senescence signature and telomere length. Additionally, single-cell analyses have not revealed the evolutionary trends of malignant cells and immune cells at the CS level. We defined a CS-associated signature, called "senescence signature", and found that patients with higher senescence signature had worse prognosis. Higher senescence signature was related to older age, higher genomic instability, longer telomeres, increased lymphocytic infiltration, higher pro-tumor immune infiltrates (Treg cells and MDSCs), and could predict responses to immune checkpoint inhibitor therapy. Single-cell analysis further reveals malignant cells and immune cells share a consistent evolutionary trend at the CS level. MAPK signaling pathway and apoptotic processes may play a key role in CS, and senescence signature may effectively predict sensitivity of MEK1/2 inhibitors, ERK1/2 inhibitors and BCL-2 family inhibitors. We also developed a new CS prediction model of cancer survival and established a portal website to apply this model ( https://bio-pub.shinyapps.io/cs_nomo/ ).

Senescent cell-derived vaccines: a new concept towards an immune response against cancer and aging?

Two recent seminal works have untangled the intricate role of tumor-associated senescent cells in cancer progression, or regression, by guiding our immune system against cancer cells. The characterization of these unique, yet diverse cell populations, should be considered, particularly when contemplating the use of senolytics, which are drugs that selectively eliminate senescent cells, in a cancer framework. Here, we will describe the current knowledge in this field. In particular, we will discuss how the presence of senescent cells in tumors could be used as a therapeutic target in immunogenic cancers and how we may hypothetically design an adaptive anti-aging vaccine.

Macrophages and tumor-associated macrophages in the senescent microenvironment: From immunosuppressive TME to targeted tumor therapy

In-depth studies of the tumor microenvironment (TME) have helped to elucidate its cancer-promoting mechanisms and inherent characteristics. Cellular senescence, which acts as a response to injury and can the release of senescence-associated secretory phenotypes (SASPs). These SASPs release various cytokines, chemokines, and growth factors, remodeling the TME. This continual development of a senescent environment could be associated with chronic inflammation and immunosuppressive TME. Additionally, SASPs could influence the phenotype and function of macrophages, leading to the recruitment of tumor-associated macrophages (TAMs). This contributes to tumor proliferation and metastasis in the senescent microenvironment, working in tandem with immune regulation, angiogenesis, and therapeutic resistance. This comprehensive review covers the evolving nature of the senescent microenvironment, macrophages, and TAMs in tumor development. We also explored the links between chronic inflammation, immunosuppressive TME, cellular senescence, and macrophages. Moreover, we compiled various tumor-specific treatment strategies centered on cellular senescence and the current challenges in cellular senescence research. This study aimed to clarify the mechanism of macrophages and the senescent microenvironment in tumor progression and advance the development of targeted tumor therapies.

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.

Adaptations of membrane trafficking in cancer and tumorigenesis

Membrane trafficking, a fundamental cellular process encompassing the transport of molecules to specific organelles, endocytosis at the plasma membrane and protein secretion, is crucial for cellular homeostasis and signalling. Cancer cells adapt membrane trafficking to enhance their survival and metabolism, and understanding these adaptations is vital for improving patient responses to therapy and identifying therapeutic targets. In this Review, we provide a concise overview of major membrane trafficking pathways and detail adaptations in these pathways, including COPII-dependent endoplasmic reticulum (ER)-to-Golgi vesicle trafficking, COPI-dependent retrograde Golgi-to-ER trafficking and endocytosis, that have been found in cancer. We explore how these adaptations confer growth advantages or resistance to cell death and conclude by discussing the potential for utilising this knowledge in developing new treatment strategies and overcoming drug resistance for cancer patients.

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.

Senotherapy, cancer, and aging

INTRODUCTION

We aimed to highlight the effects of senotherapy on the prevention and treatment of cancer in older individuals. The aim of senotherapy is to eliminate senescent cells. These cells express the senescence-associated secretory phenotype (SASP). With production of inflammatory cytokines, growth factors, and different type of proteases, the SASP is responsible for aging-associated disability and diseases. All mammalian cells experience senescence. The main agents of aging include fibroblasts and adipose cells. Senescent tumor cells may undergo genomic reprogramming and re-enter cell cycle with a stem cell phenotype.

MATERIALS AND METHODS

We conducted a Medline search for the following key words: senotherapy, senolysis, senomorphic agents. We provide a narrative review of the finding.

RESULTS

Different agents may eliminate senescent cells from cell cultures and murine models. These include metformin, rapamycin, desatinib, quercitin, fisetin, ruloxitinib, and BCL2 inhibitors. A randomized controlled study of metformin in 3,000 patients aged 65-79 without glucose intolerance aiming to establish whether senotherapy may prevent or reverse disability and aging associated diseases, including cancer, is ongoing. Senotherapy prolongs the life span and decreases the incidence of cancer in experimental animal models, as well as delays and reverses disability. Senescent tumor cells are found prior to treatment and after chemotherapy and radiation. These elements may be responsible for tumor recurrence and treatment refractoriness.

DISCUSSION

Senotherapy may have substantial effects on cancer management including decreased incidence and aggressiveness of cancer, improved tolerance of antineoplastic treatment, and prevention of relapse after primary treatment. Senotherapy may ameliorate several complications of cancer chemotherapy.

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.

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.

Senolysis of gemcitabine-induced senescent human pancreatic cancer cells

INTRODUCTION

Gemcitabine (GEM) is often used to treat pancreatic cancer. Many anti-cancer drugs induce cancer cell death, but some cells survive after cell cycle arrest. Such a response to DNA damage is termed cellular senescence. Certain drugs, including the Bcl-2-family inhibitor ABT-263, kill senescent cells; this is termed senolysis. In this study, we examined the therapeutic benefits of ABT-263 in GEM-induced senescence of human pancreatic cancer cells.

METHODS AND RESULTS

Of four pancreatic cancer cell lines (PANC-1, AsPC-1, CFPAC-1, and PANC10.05), GEM induced senescent features in PANC-1 and AsPC-1 cells, including increases in the cell sizes and expression levels of mRNAs encoding interleukin (IL)-6/IL-8 and induction of β-galactosidase. Successive treatment with GEM and ABT-263 triggered apoptosis in PANC-1 and AsPC-1 cells and suppressed colony formation significantly. Senolysis of GEM-induced senescent pancreatic cancer cells by ABT-263 was triggered by a Bcl-xL inhibitor, but not by a Bcl-2 inhibitor, suggesting a central role for Bcl-xL in senolysis. In a xenograft mouse model, combined treatment with GEM and ABT-737 (an ABT-263 analog exhibiting the same specificity) suppressed in vivo growth of AsPC-1 significantly.

CONCLUSION

Together, our results indicate that sequential treatment with GEM and senolytic drugs effectively kill human pancreatic cancer cells.

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.

Therapy-induced senescent cancer cells exhibit complement activation and increased complement regulatory protein expression

Therapy-induced senescence (TIS) is a primary response to chemotherapy, contributing to untoward treatment outcomes such as evasion of immunosurveillance. Despite the established role of the complement system in the immune response to cancer, the role of complement in mediating the immune response against senescent tumor cells remains poorly understood. To explore this relationship, we exposed lung adenocarcinoma (A549), breast adenocarcinoma (MCF7) and pancreatic carcinoma (Panc-1) cell lines to sublethal doses of either etoposide or doxorubicin to trigger TIS. Identification of TIS was based on morphological changes, upregulation of the senescence-associated β-galactosidase, p21Cip1 induction and lamin B1 downregulation. Using immunofluorescence microscopy, quantitative PCR, ELISA of conditioned media and in silico analysis, we investigated complement activation, complement protein expression, C3 levels in the conditioned media of senescent cells and secreted complement proteins as part of the senescence-associated secretory phenotype (SASP), respectively. In cell lines undergoing TIS, complement-related changes included (i) activation of the terminal pathway, evidenced by the deposition of C5b-9 on senescent cells; (ii) an increase in the expression of CD59 and complement factor H and (iii) in A549 cells, an elevation in the expression of C3 with its secretion into the medium. In addition, increased C3 expression was observed in breast cancer samples expressing TIS hallmarks following exposure to neoadjuvant chemotherapy. In conclusion, TIS led to the activation of complement, upregulation of complement regulatory proteins and increased C3 expression. Complement appears to play a role in shaping the cancer microenvironment upon senescence induction.

Autophagy and senescence facilitate the development of antiestrogen resistance in ER positive breast cancer

Estrogen receptor positive (ER+) breast cancer is the most common breast cancer diagnosed annually in the US with endocrine-based therapy as standard-of-care for this breast cancer subtype. Endocrine therapy includes treatment with antiestrogens, such as selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs). Despite the appreciable remission achievable with these treatments, a substantial cohort of women will experience primary tumor recurrence, subsequent metastasis, and eventual death due to their disease. In these cases, the breast cancer cells have become resistant to endocrine therapy, with endocrine resistance identified as the major obstacle to the medical oncologist and patient. To combat the development of endocrine resistance, the treatment options for ER+, HER2 negative breast cancer now include CDK4/6 inhibitors used as adjuvants to antiestrogen treatment. In addition to the dysregulated activity of CDK4/6, a plethora of genetic and biochemical mechanisms have been identified that contribute to endocrine resistance. These mechanisms, which have been identified by lab-based studies utilizing appropriate cell and animal models of breast cancer, and by clinical studies in which gene expression profiles identify candidate endocrine resistance genes, are the subject of this review. In addition, we will discuss molecular targeting strategies now utilized in conjunction with endocrine therapy to combat the development of resistance or target resistant breast cancer cells. Of approaches currently being explored to improve endocrine treatment efficacy and patient outcome, two adaptive cell survival mechanisms, autophagy, and "reversible" senescence, are considered molecular targets. Autophagy and/or senescence induction have been identified in response to most antiestrogen treatments currently being used for the treatment of ER+ breast cancer and are often induced in response to CDK4/6 inhibitors. Unfortunately, effective strategies to target these cell survival pathways have not yet been successfully developed. Thus, there is an urgent need for the continued interrogation of autophagy and "reversible" senescence in clinically relevant breast cancer models with the long-term goal of identifying new molecular targets for improved treatment of ER+ breast cancer.

Single-cell Transcriptome Analysis Identifies Senescent Osteocytes as Contributors to Bone Destruction in Breast Cancer Metastasis

Breast cancer bone metastases increase fracture risk and are a major cause of morbidity and mortality among women. Upon colonization by tumor cells, the bone microenvironment undergoes profound reprogramming to support cancer progression that disrupts the balance between osteoclasts and osteoblasts, leading to bone lesions. Whether such reprogramming affects matrix-embedded osteocytes remains poorly understood. Here, we demonstrate that osteocytes in breast cancer bone metastasis develop premature senescence and a distinctive senescence-associated secretory phenotype (SASP) that favors bone destruction. Single-cell RNA sequencing identified osteocytes from mice with breast cancer bone metastasis enriched in senescence and SASP markers and pro-osteoclastogenic genes. Using multiplex in situ hybridization and AI-assisted analysis, we detected osteocytes with senescence-associated distension of satellites, telomere dysfunction, and p16Ink4a expression in mice and patients with breast cancer bone metastasis. In vitro and ex vivo organ cultures showed that breast cancer cells promote osteocyte senescence and enhance their osteoclastogenic potential. Clearance of senescent cells with senolytics suppressed bone resorption and preserved bone mass in mice with breast cancer bone metastasis. These results demonstrate that osteocytes undergo pathological reprogramming by breast cancer cells and identify osteocyte senescence as an initiating event triggering bone destruction in breast cancer metastases.

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.

Damage-Induced Senescent Immune Cells Regulate Regeneration of the Zebrafish Retina

Zebrafish spontaneously regenerate their retinas in response to damage through the action of Müller glia (MG). Even though MG are conserved in higher vertebrates, the capacity to regenerate retinal damage is lost. Recent work has focused on the regulation of inflammation during tissue regeneration, with temporal roles for macrophages and microglia. Senescent cells that have withdrawn from the cell cycle have mostly been implicated in aging but are still metabolically active, releasing a variety of signaling molecules as part of the senescence-associated secretory phenotype. Here, we discover that in response to retinal damage, a subset of cells expressing markers of microglia/macrophages also express markers of senescence. These cells display a temporal pattern of appearance and clearance during retina regeneration. Premature removal of senescent cells by senolytic treatment led to a decrease in proliferation and incomplete repair of the ganglion cell layer after N-methyl-D-aspartate damage. Our results demonstrate a role for modulation of senescent cell responses to balance inflammation, regeneration, plasticity, and repair as opposed to fibrosis and scarring.

Understanding Cancer's Defense against Topoisomerase-Active Drugs: A Comprehensive Review

In recent years, the emergence of cancer drug resistance has been one of the crucial tumor hallmarks that are supported by the level of genetic heterogeneity and complexities at cellular levels. Oxidative stress, immune evasion, metabolic reprogramming, overexpression of ABC transporters, and stemness are among the several key contributing molecular and cellular response mechanisms. Topo-active drugs, e.g., doxorubicin and topotecan, are clinically active and are utilized extensively against a wide variety of human tumors and often result in the development of resistance and failure to therapy. Thus, there is an urgent need for an incremental and comprehensive understanding of mechanisms of cancer drug resistance specifically in the context of topo-active drugs. This review delves into the intricate mechanistic aspects of these intracellular and extracellular topo-active drug resistance mechanisms and explores the use of potential combinatorial approaches by utilizing various topo-active drugs and inhibitors of pathways involved in drug resistance. We believe that this review will help guide basic scientists, pre-clinicians, clinicians, and policymakers toward holistic and interdisciplinary strategies that transcend resistance, renewing optimism in the ongoing battle against cancer.

Cisplatin Provokes Peripheral Nociception and Neuronal Features of Therapy-Induced Senescence and Calcium Dysregulation in Rats

Therapy-Induced Senescence (TIS) is a form of senescence that is typically described in malignant cells in response to the exposure of cancer chemotherapy or radiation but can also be precipitated in non-malignant cells. TIS has been shown to contribute to the development of several cancer therapy-related adverse effects; however, evidence on its role in mediating chemotherapy-induced neurotoxicity, such as Chemotherapy-induced Peripheral Neuropathy (CIPN), is limited. We here show that cisplatin treatment over two cycles (cumulative dose of 23 mg/kg) provoked mechanical allodynia and thermal hyperalgesia in Sprague-Dawley rats. Isolation of dorsal root ganglia (DRG) from the cisplatin-treated rats demonstrated robust SA-β-gal upregulation at both day 8 (after the first cycle) and day 18 (after the second cycle), decreased lmnb1 expression, increased expression of cdkn1a and cdkn2a, and of several factors of the Senescence-associated Secretory Phenotype (SASP) (Il6, Il1b, and mmp9). Moreover, single-cell calcium imaging of cultured DRGs revealed a significant increase in terms of the magnitude of KCl-evoked calcium responses in cisplatin-treated rats compared to vehicle-treated rats. No significant change was observed in terms of the magnitude of capsaicin-evoked calcium responses in cisplatin-treated rats compared to vehicle-treated rats but with decreased area under the curve of the responses in cisplatin-treated rats. Further evidence to support the contribution of TIS to therapy adverse effects is required but should encourage the use of senescence-modulating agents (senotherapeutics) as novel palliative approaches to mitigate chemotherapy-induced neurotoxicity.

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.

Targeting therapy-induced senescence as a novel strategy to combat chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a treatment-limiting adverse effect of anticancer therapy that complicates the lifestyle of many cancer survivors. There is currently no gold-standard for the assessment or management of CIPN. Subsequently, understanding the underlying mechanisms that lead to the development of CIPN is essential for finding better pharmacological therapy. Therapy-induced senescence (TIS) is a form of senescence that is triggered in malignant and non-malignant cells in response to the exposure to chemotherapy. Recent evidence has also suggested that TIS develops in the dorsal root ganglia of rodent models of CIPN. Interestingly, several components of the senescent phenotype are commensurate with the currently established primary processes implicated in the pathogenesis of CIPN including mitochondrial dysfunction, oxidative stress, and neuroinflammation. In this article, we review the literature that supports the hypothesis that TIS could serve as a holistic mechanism leading to CIPN, and we propose the potential for investigating senotherapeutics as means to mitigate CIPN in cancer survivors.

Cellular senescence and frailty: a comprehensive insight into the causal links

Senescent cells may have a prominent role in driving inflammation and frailty. The impact of cellular senescence on frailty varies depending on the assessment tool used, as it is influenced by the criteria or items predominantly affected by senescent cells and the varying weights assigned to these items across different health domains. To address this challenge, we undertook a thorough review of all available studies involving gain- or loss-of-function experiments as well as interventions targeting senescent cells, focusing our attention on those studies that examined outcomes based on the individual frailty phenotype criteria or specific items used to calculate two humans (35 and 70 items) and one mouse (31 items) frailty indexes. Based on the calculation of a simple "evidence score," we found that the burden of senescent cells related to musculoskeletal and cerebral health has the strongest causal link to frailty. We deem that insight into these mechanisms may not only contribute to clarifying the role of cellular senescence in frailty but could additionally provide multiple therapeutic opportunities to help the future development of a desirable personalized therapy in these extremely heterogeneous patients.

Advances in molecular targeted therapies to increase efficacy of (chemo)radiation therapy

Recent advances in understanding the tumor's biology in line with a constantly growing number of innovative technologies have prompted characterization of patients' individual malignancies and may display a prerequisite to treat cancer at its patient individual tumor vulnerability. In recent decades, radiation- induced signaling and tumor promoting local events for radiation sensitization were explored in detail, resulting the development of novel molecular targets. A multitude of pharmacological, genetic, and immunological principles, including small molecule- and antibody-based targeted strategies, have been developed that are suitable for combined concepts with radiation (RT) or chemoradiation therapy (CRT). Despite a plethora of promising experimental and preclinical findings, however, so far, only a very limited number of clinical trials have demonstrated a better outcome and/or patient benefit when RT or CRT are combined with targeted agents. The current review aims to summarize recent progress in molecular therapies targeting oncogenic drivers, DNA damage and cell cycle response, apoptosis signaling pathways, cell adhesion molecules, hypoxia, and the tumor microenvironment to impact therapy refractoriness and to boost radiation response. In addition, we will discuss recent advances in nanotechnology, e.g., RNA technologies and protein-degrading proteolysis-targeting chimeras (PROTACs) that may open new and innovative ways to benefit from molecular-targeted therapy approaches with improved efficacy.

Therapy-induced senescent tumor cells in cancer relapse

Cellular senescence is characterized by a generally irreversible cell cycle arrest and the secretion of bioactive factors known as the senescence-associated secretory phenotype (SASP). In an oncogenic context, senescence is considered a tumor suppressive mechanism as it prevents cell proliferation and inhibits the progression from pre-malignant to malignant disease. However, recent studies have demonstrated that senescent tumor cells, which could spontaneously exist within cancer tissues or arise in response to various cancer interventions (the so-called therapy-induced senescence, TIS), can acquire pro-tumorigenic properties and are capable of driving local and metastatic relapse. This highlights the complex and multifaceted nature of cellular senescence in cancer biology. Here, we summarize the current knowledge of the pathological function of therapy-induced senescent tumor cells and discuss possible mechanisms by which tumor cell senescence contributes to cancer relapse. We also discuss implications for future studies toward targeting these less appreciated cells.

The Combination of Radiation with PARP Inhibition Enhances Senescence and Sensitivity to the Senolytic, Navitoclax, in Triple Negative Breast Tumor Cells

Despite significant advances in the treatment of triple-negative breast cancer, this disease continues to pose a clinical challenge, with many patients ultimately suffering from relapse. Tumor cells that recover after entering into a state of senescence after chemotherapy or radiation have been shown to develop a more aggressive phenotype, and to contribute to disease recurrence. By combining the PARP inhibitor (PARPi), talazoparib, with radiation, senescence was enhanced in 4T1 and MDA-MB-231 triple-negative breast cancer cell lines (based on SA-β-gal upregulation, increased expression of CDKN1A and the senescence-associated secretory phenotype (SASP) marker, IL6). Subsequent treatment of the radiation- and talazoparib-induced senescent 4T1 and MDA-MB231 cells with navitoclax (ABT-263) resulted in significant apoptotic cell death. In immunocompetent tumor-bearing mice, navitoclax exerted a modest growth inhibitory effect when used alone, but dramatically interfered with the recovery of 4T1-derived tumors induced into senescence with ionizing radiation and talazoparib. These findings support the potential utility of a senolytic strategy in combination with the radiotherapy/PARPi combination to mitigate the risk of disease recurrence in triple-negative breast cancer.

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.

Aging and oral squamous cell carcinoma development: the role of cellular senescence

The gradual accumulation and inadequate renewal of senescent cells over time drive organismal aging. Senescent cells undergo altered gene expression and release inflammatory mediators collectively termed the senescence-associated secretory phenotype (SASP), which significantly contributes to a spectrum of age-related disorders, including cancer. In the context of carcinogenesis, the SASP produced by senescent cells has been implicated in the promotion of epithelial cancers, including oral squamous cell carcinoma (OSCC), the most common form of oral cancer. Senescent cells within the tumor microenvironment release factors that amplify the growth and invasiveness of neighboring cancer cells. Senotherapeutics, including senolytics and senomorphics, emerge as promising modalities to target senescent cells and their associated inflammatory factors, thereby opening novel avenues for augmenting the efficacy of cancer treatments. Here, we review the general aspects of cellular senescence, focusing on the relation between senescence-related inflammation with cancer development. We also analyze the available evidence linking cellular senescence with OSCC, highlighting possible clinical applications.

NOXA expression is downregulated in human breast cancer undergoing incomplete pathological response and senescence after neoadjuvant chemotherapy

Neoadjuvant chemotherapy (NAC) is a frequently utilized approach to treat locally advanced breast cancer, but, unfortunately, a subset of tumors fails to undergo complete pathological response. Apoptosis and therapy-induced senescence (TIS) are both cell stress mechanisms but their exact role in mediating the pathological response to NAC is not fully elucidated. We investigated the change in expression of PAMIP1, the gene encoding for the pro-apoptotic protein, NOXA, following NAC in two breast cancer gene datasets, and the change in NOXA protein expression in response to NAC in 55 matched patient samples (pre- and post-NAC). PAMIP1 expression significantly declined in post-NAC in the two sets, and in our cohort, 75% of the samples exhibited a downregulation in NOXA post-NAC. Matched samples that showed a decline in NOXA post-NAC were examined for TIS based on a signature of downregulated expression of Lamin-B1 and Ki-67 and increased p16INK4a, and the majority exhibited a decrease in Lamin B1 (66%) and Ki-67 (80%), and increased p16INK4a (49%). Since our cohort consisted of patients that did not develop complete pathological response, such findings have clinical implications on the role of TIS and NOXA downregulation in mediating suboptimal responses to the currently established NAC.

Senescence in cancer: Advances in detection and treatment modalities

Senescence is a form of irreversible cell cycle arrest. Senescence plays a dual role in cancer, as both a tumor suppressor by preventing the growth of damaged cells and a cancer promoter by creating an inflammatory milieu. Stress-induced premature senescence (SIPS) and replicative senescence are the two major sub-types of senescence. Senescence plays a dual role in cancer, depending on the context and kind of senescence involved. SIPS can cause cancer by nurturing an inflammatory environment, whereas replicative senescence may prevent cancer. Major pathways that are involved in senescence are the p53-p21, p16INK4A-Rb pathway along with mTOR, MAPK, and PI3K pathways. The lack of universal senescence markers makes it difficult to identify senescent cells in vivo. A combination of reliable detection methods of senescent cells in vivo is of utmost importance and will help in early detection and open new avenues for future treatment. New strategies that are being developed in order to tackle these shortcomings are in the field of fluorescent probes, nanoparticles, positron emission tomography probes, biosensors, and the detection of cell-free DNA from liquid biopsies. Along with detection, eradication of these senescent cells is also important to prevent cancer reoccurrence. Recently, the field of nano-senolytic and immunotherapy has also been emerging. This review provides up-to-date information on the various types of advancements made in the field of detection and treatment modalities for senescent cells that hold promise for the future treatment and prognosis of cancer, as well as their limitations and potential solutions.

Cytoprotective, Cytotoxic and Cytostatic Roles of Autophagy in Response to BET Inhibitors

The bromodomain and extra-terminal domain (BET) family inhibitors are small molecules that target the dysregulated epigenetic readers, BRD2, BRD3, BRD4 and BRDT, at various transcription-related sites, including super-enhancers. BET inhibitors are currently under investigation both in pre-clinical cell culture and tumor-bearing animal models, as well as in clinical trials. However, as is the case with other chemotherapeutic modalities, the development of resistance is likely to constrain the therapeutic benefits of this strategy. One tumor cell survival mechanism that has been studied for decades is autophagy. Although four different functions of autophagy have been identified in the literature (cytoprotective, cytotoxic, cytostatic and non-protective), primarily the cytoprotective and cytotoxic forms appear to function in different experimental models exposed to BET inhibitors (with some evidence for the cytostatic form). This review provides an overview of the cytoprotective, cytotoxic and cytostatic functions of autophagy in response to BET inhibitors in various tumor models. Our aim is to determine whether autophagy targeting or modulation could represent an effective therapeutic strategy to enhance the response to these modalities and also potentially overcome resistance to BET inhibition.

BRD4 Inhibition as a Strategy to Prolong the Response to Standard of Care in Estrogen Receptor-Positive Breast Cancer

Breast cancer is the most commonly occurring malignancy in women and the second most common cause of cancer-related deaths. ER+ breast cancer constitutes approximately 70% of all breast cancer cases. The standard of care for ER+ breast cancer involves estrogen antagonists such as tamoxifen or fulvestrant in combination with CDK4/6 inhibitors such as palbociclib. However, these treatments are often not curative, with disease recurrence and metastasis being responsible for patient mortality. Overexpression of the epigenetic regulator, BRD4, has been shown to be a negative prognostic indicator in breast cancer, and BET family inhibitors such as ARV-825 and ABBV-744 have garnered interest for their potential to improve and prolong the response to current therapeutic strategies. The current work examined the potential of utilizing ARV-825 and ABBV-744 to increase the effectiveness of tamoxifen or fulvestrant plus palbociclib. ARV-825 was effective in both p53 wild-type (WT) breast tumor cells and in cells lacking functional p53 either alone or in combination with tamoxifen, while the effectiveness of ABBV-744 was limited to fulvestrant plus palbociclib in p53 WT cells. These differential effects may be related to the capacity to suppress c-Myc, a downstream target of BRD4.

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.

Targeting Senescence as a Therapeutic Opportunity for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is associated with an elevated risk of recurrence and poor prognosis. Historically, only chemotherapy was available as systemic treatment, but immunotherapy and targeted therapies currently offer prolonged benefits. TNBC is a group of diseases with heterogeneous treatment sensitivity, and resistance is inevitable and early for a large proportion of the intrinsic subtypes. Although senescence induction by anticancer therapy offers an immediate favorable clinical outcome once the rate of tumor progression reduces, these cells are commonly dysfunctional and metabolically active, culminating in treatment-resistant repopulation associated with worse prognosis. This heterogeneous response can also occur without therapeutic pressure in response to damage or oncogenic stress, playing a relevant role in the carcinogenesis. Remarkably, there is preclinical and exploratory clinical evidence to support a relevant role of senescence in treatment resistance. Therefore, targeting senescent cells has been a scientific effort in many malignant tumors using a variety of targets and strategies, including increasing proapoptotic and decreasing antiapoptotic stimuli. Despite promising results, there are some challenges to applying this technology, including the best schedule of combination, assessment of senescence, specific vulnerabilities, and the best clinical scenarios. This review provides an overview of senescence in TNBC with a focus on future-proofing senotherapy strategies.