Senolytics for Cancer Therapy: Is All That Glitters Really Gold?

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.

Biomarkers of Cellular Senescence and Aging: Current State-of-the-Art, Challenges and Future Perspectives

Population aging has increased the global prevalence of aging-related diseases, including cancer, sarcopenia, neurological disease, arthritis, and heart disease. Understanding aging, a fundamental biological process, has led to breakthroughs in several fields. Cellular senescence, evinced by flattened cell bodies, vacuole formation, and cytoplasmic granules, ubiquitously plays crucial roles in tissue remodeling, embryogenesis, and wound repair as well as in cancer therapy and aging. The lack of universal biomarkers for detecting and quantifying senescent cells, in vitro and in vivo, constitutes a major limitation. The applications and limitations of major senescence biomarkers, including senescence-associated β-galactosidase staining, telomere shortening, cell-cycle arrest, DNA methylation, and senescence-associated secreted phenotypes are discussed. Furthermore, explore senotherapeutic approaches for aging-associated diseases and cancer. In addition to the conventional biomarkers, this review highlighted the in vitro, in vivo, and disease models used for aging studies. Further, technologies from the current decade including multi-omics and computational methods used in the fields of senescence and aging are also discussed in this review. Understanding aging-associated biological processes by using cellular senescence biomarkers can enable therapeutic innovation and interventions to improve the quality of life of older adults.

Cellular Aging and Senescence in Cancer: A Holistic Review of Cellular Fate Determinants

This comprehensive review navigates the complex relationship between cellular aging, senescence, and cancer, unraveling the determinants of cellular fate. Beginning with an overview of cellular aging's significance in cancer, the review explores processes, changes, and molecular pathways influencing senescence. The review explores senescence as a dual mechanism in cancer, acting as a suppressor and contributor, focusing on its impact on therapy response. This review highlights opportunities for cancer therapies that target cellular senescence. The review further examines the senescence-associated secretory phenotype and strategies to modulate cellular aging to influence tumor behavior. Additionally, the review highlights the mechanisms of senescence escape in aging and cancer cells, emphasizing their impact on cancer prognosis and resistance to therapy. The article addresses current advances, unexplored aspects, and future perspectives in understanding cellular aging and senescence in cancer.

Emerging Roles of Vitamin B12 in Aging and Inflammation

Vitamin B12 (cobalamin) is an essential nutrient for humans and animals. Metabolically active forms of B12-methylcobalamin and 5-deoxyadenosylcobalamin are cofactors for the enzymes methionine synthase and mitochondrial methylmalonyl-CoA mutase. Malfunction of these enzymes due to a scarcity of vitamin B12 leads to disturbance of one-carbon metabolism and impaired mitochondrial function. A significant fraction of the population (up to 20%) is deficient in vitamin B12, with a higher rate of deficiency among elderly people. B12 deficiency is associated with numerous hallmarks of aging at the cellular and organismal levels. Cellular senescence is characterized by high levels of DNA damage by metabolic abnormalities, increased mitochondrial dysfunction, and disturbance of epigenetic regulation. B12 deficiency could be responsible for or play a crucial part in these disorders. In this review, we focus on a comprehensive analysis of molecular mechanisms through which vitamin B12 influences aging. We review new data about how deficiency in vitamin B12 may accelerate cellular aging. Despite indications that vitamin B12 has an important role in health and healthy aging, knowledge of the influence of vitamin B12 on aging is still limited and requires further research.

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.

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.

Epigenetic dynamics of aging and cancer development: current concepts from studies mapping aging and cancer epigenomes

PURPOSE OF REVIEW

This review emphasizes the role of epigenetic processes as incidental changes occurring during aging, which, in turn, promote the development of cancer.

RECENT FINDINGS

Aging is a complex biological process associated with the progressive deterioration of normal physiological functions, making age a significant risk factor for various disorders, including cancer. The increasing longevity of the population has made cancer a global burden, as the risk of developing most cancers increases with age due to the cumulative effect of exposure to environmental carcinogens and DNA replication errors. The classical 'somatic mutation theory' of cancer cause is being challenged by the observation that multiple normal cells harbor cancer driver mutations without resulting in cancer. In this review, we discuss the role of age-associated epigenetic alterations, including DNA methylation, which occur across all cell types and tissues with advancing age. There is an increasing body of evidence linking these changes with cancer risk and prognosis.

SUMMARY

A better understanding about the epigenetic changes acquired during aging is critical for comprehending the mechanisms leading to the age-associated increase in cancer and for developing novel therapeutic strategies for cancer treatment and prevention.

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.

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.

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.

Implications of cellular senescence in paediatric pituitary tumours

The long-standing view of senescent cells as passive and dysfunctional biological remnants has recently shifted into a new paradigm where they are main players in the development of many diseases, including cancer. The senescence programme represents a first line of defence that prevents tumour cell growth but also leads to the secretion of multiple pro-inflammatory and pro-tumourigenic factors that fuel tumour initiation, growth, and progression. Here, we review the main molecular features and biological functions of senescent cells in cancer, including the outcomes of inducing or targeting senescence. We discuss evidence on the role of cellular senescence in pituitary tumours, with an emphasis on adamantinomatous craniopharyngioma (ACP) and pituitary adenomas. Although senescence has been proposed to be a tumour-preventing mechanism in pituitary adenomas, research in ACP has shown that senescent cells are tumour-promoting in both murine models and human tumours. Future studies characterizing the impact of targeting senescent cells may result in novel therapies against pituitary tumours.

Integrated multicomponent interventions to support healthy aging of the whole person

Healthy aging is an integrated "whole person" process that involves an individual's biology, behavior, and social/physical environment. With the recent development of antiaging drugs, careful consideration of the respective roles of pharmacologic and nonpharmacologic approaches to both health and aging is in order. Recent advances in understanding the cellular and molecular mechanisms of aging are providing new measures that can be used as clinical outcomes in studying the impact of antiaging interventions in humans. This paper outlines the strategic interest of the National Center for Complementary and Integrative Health (NCCIH) in supporting the development, testing, and implementation of effective, scalable, and integrated multicomponent interventions to support healthy aging of the whole person.

The senescent mesothelial matrix accentuates colonization by ovarian cancer cells

Ovarian cancer is amongst the most morbid of gynecological malignancies due to its diagnosis at an advanced stage, a transcoelomic mode of metastasis, and rapid transition to chemotherapeutic resistance. Like all other malignancies, the progression of ovarian cancer may be interpreted as an emergent outcome of the conflict between metastasizing cancer cells and the natural defense mounted by microenvironmental barriers to such migration. Here, we asked whether senescence in coelom-lining mesothelia, brought about by drug exposure, affects their interaction with disseminated ovarian cancer cells. We observed that cancer cells adhered faster on senescent human and murine mesothelial monolayers than on non-senescent controls. Time-lapse epifluorescence microscopy showed that mesothelial cells were cleared by a host of cancer cells that surrounded the former, even under sub-confluent conditions. A multiscale computational model predicted that such colocalized mesothelial clearance under sub-confluence requires greater adhesion between cancer cells and senescent mesothelia. Consistent with the prediction, we observed that senescent mesothelia expressed an extracellular matrix with higher levels of fibronectin, laminins and hyaluronan than non-senescent controls. On senescent matrix, cancer cells adhered more efficiently, spread better, and moved faster and persistently, aiding the spread of cancer. Inhibition assays using RGD cyclopeptides suggested the adhesion was predominantly contributed by fibronectin and laminin. These findings led us to propose that the senescence-associated matrisomal phenotype of peritoneal barriers enhances the colonization of invading ovarian cancer cells contributing to the metastatic burden associated with the disease.

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.

N7-methylguanosine methylation of tRNAs regulates survival to stress in cancer

Tumour progression and therapy tolerance are highly regulated and complex processes largely dependent on the plasticity of cancer cells and their capacity to respond to stress. The higher plasticity of cancer cells highlights the need for identifying targetable molecular pathways that challenge cancer cell survival. Here, we show that N7-guanosine methylation (m7G) of tRNAs, mediated by METTL1, regulates survival to stress conditions in cancer cells. Mechanistically, we find that m7G in tRNAs protects them from stress-induced cleavage and processing into 5' tRNA fragments. Our analyses reveal that the loss of tRNA m7G methylation activates stress response pathways, sensitising cancer cells to stress. Furthermore, we find that the loss of METTL1 reduces tumour growth and increases cytotoxic stress in vivo. Our study uncovers the role of m7G methylation of tRNAs in stress responses and highlights the potential of targeting METTL1 to sensitise cancer cells to chemotherapy.

Pro-Apoptotic Activity of MCL-1 Inhibitor in Trametinib-Resistant Melanoma Cells Depends on Their Phenotypes and Is Modulated by Reversible Alterations Induced by Trametinib Withdrawal

BACKGROUND

Although BRAFV600/MEK inhibitors improved the treatment of melanoma patients, resistance is acquired almost inevitably.

METHODS

Trametinib withdrawal/rechallenge and MCL-1 inhibition in trametinib-resistance models displaying distinct p-ERK1/2 levels were investigated.

RESULTS

Trametinib withdrawal/rechallenge caused reversible changes in ERK1/2 activity impacting the balance between pro-survival and pro-apoptotic proteins. Reversible alterations were found in MCL-1 levels and MCL-1 inhibitors, BIM and NOXA. Taking advantage of melanoma cell dependency on MCL-1 for survival, we used S63845. While it was designed to inhibit MCL-1 activity, we showed that it also significantly reduced NOXA levels. S63845-induced apoptosis was detected as the enhancement of Annexin V-positivity, caspase-3/7 activation and histone H2AX phosphorylation. Percentages of Annexin V-positive cells were increased most efficiently in trametinib-resistant melanoma cells displaying the p-ERK1/2low/MCL-1low/BIMhigh/NOXAlow phenotype with EC50 values at concentrations as low as 0.1 μM. Higher ERK1/2 activity associated with increased MCL-1 level and reduced BIM level limited pro-apoptotic activity of S63845 further influenced by a NOXA level.

CONCLUSIONS

Our study supports the notion that the efficiency of an agent designed to target a single protein can largely depend on the phenotype of cancer cells. Thus, it is important to define appropriate phenotype determinants to stratify the patients for the novel therapy.

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.

Targeting Inhibitor of Apoptosis Proteins to Overcome Chemotherapy Resistance-A Marriage between Targeted Therapy and Cytotoxic Chemotherapy

Precision oncology is the ultimate goal of cancer treatment, i.e., to treat cancer and only cancer, leaving all the remaining cells and tissues as intact as possible. Classical chemotherapy and radiotherapy, however, are still effective in many patients with cancer by effectively inducing apoptosis of cancer cells. Cancer cells might resist apoptosis via the anti-apoptotic effects of the inhibitor of apoptosis proteins. Recently, the inhibitors of those proteins have been developed with the goal of enhancing the cytotoxic effects of chemotherapy and radiotherapy, and one of them, xevinapant, has already demonstrated effectiveness in a phase II clinical trial. This class of drugs represents an example of synergism between classical cytotoxic chemo- and radiotherapy and new targeted therapy.

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.

New Horizons in cellular senescence for clinicians

Cellular senescence has emerged as a fundamental biological mechanism underpinning the ageing process and has been implicated in the pathogenesis of an increasing number of age-related conditions. Cellular senescence is a cell fate originally defined as an irreversible loss of replicative potential although it is now clear that it can be induced by a variety of mechanisms independent of replication and telomere attrition. The drivers include a persistent DNA damage response causing multiple alterations in cellular function. Senescent cells secrete a range of mediators that drive chronic inflammation and can convert other cells to the senescent state-the senescence-associated secretory phenotype. Much research to date has been conducted in animal models, but it is now clear that senescent cells accompany ageing in humans and their presence is an important driver of disease across systems. Proof-of-concept work suggests that preventing or reversing senescence may be a viable strategy to counteract human ageing and age-related disease. Possible interventions include exercise, nutrition and senolytics/senostatic drugs although there are a number of potential limitations to the use of senotherapeutics. These interventions are generally tested for single-organ conditions, but the real power of this approach is the potential to tackle multiple age-related conditions. The litmus test for this exciting new class of therapies, however, will be whether they can improve healthy life expectancy rather than merely extending lifespan. The outcomes measured in clinical studies need to reflect these aims if senotherapeutics are to gain the trust of clinicians, patients and the public.

Antagonizing the irreversible thrombomodulin-initiated proteolytic signaling alleviates age-related liver fibrosis via senescent cell killing

Cellular senescence is a stress-induced, stable cell cycle arrest phenotype which generates a pro-inflammatory microenvironment, leading to chronic inflammation and age-associated diseases. Determining the fundamental molecular pathways driving senescence instead of apoptosis could enable the identification of senolytic agents to restore tissue homeostasis. Here, we identify thrombomodulin (THBD) signaling as a key molecular determinant of the senescent cell fate. Although normally restricted to endothelial cells, THBD is rapidly upregulated and maintained throughout all phases of the senescence program in aged mammalian tissues and in senescent cell models. Mechanistically, THBD activates a proteolytic feed-forward signaling pathway by stabilizing a multi-protein complex in early endosomes, thus forming a molecular basis for the irreversibility of the senescence program and ensuring senescent cell viability. Therapeutically, THBD signaling depletion or inhibition using vorapaxar, an FDA-approved drug, effectively ablates senescent cells and restores tissue homeostasis in liver fibrosis models. Collectively, these results uncover proteolytic THBD signaling as a conserved pro-survival pathway essential for senescent cell viability, thus providing a pharmacologically exploitable senolytic target for senescence-associated diseases.

The Cross Talk between Cellular Senescence and Melanoma: From Molecular Pathogenesis to Target Therapies

Melanoma is a malignant skin tumor that originates from melanocytes. The pathogenesis of melanoma involves a complex interaction that occurs between environmental factors, ultraviolet (UV)-light damage, and genetic alterations. UV light is the primary driver of the skin aging process and development of melanoma, which can induce reactive oxygen species (ROS) production and the presence of DNA damage in the cells, and results in cell senescence. As cellular senescence plays an important role in the relationship that exists between the skin aging process and the development of melanoma, the present study provides insight into the literature concerning the topic at present and discusses the relationship between skin aging and melanoma, including the mechanisms of cellular senescence that drive melanoma progression, the microenvironment in relation to skin aging and melanoma factors, and the therapeutics concerning melanoma. This review focuses on defining the role of cellular senescence in the process of melanoma carcinogenesis and discusses the targeting of senescent cells through therapeutic approaches, highlighting the areas that require more extensive research in the field.

Cellular senescence and the blood-brain barrier: Implications for aging and age-related diseases

The blood-brain barrier (BBB) is a critical physiochemical interface that regulates communication between the brain and blood. It is comprised of brain endothelial cells which regulate the BBB's barrier and interface properties and is surrounded by supportive brain cell types including pericytes and astrocytes. Recent reports have suggested that the BBB undergoes dysfunction during normative aging and in disease. In this review, we consider the effect of cellular senescence, one of the nine hallmarks of aging, on the BBB. We first characterize known normative age-related changes at the BBB, and then evaluate changes in neurodegenerative diseases, with an emphasis on if/how cellular senescence is influencing these changes. We then discuss what insight has been gained from in vitro and in vivo studies of cellular senescence at the BBB. Finally, we evaluate mechanisms by which cellular senescence in peripheral pathologies can indirectly or directly affect BBB function.

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.

The role of cellular senescence and SASP in tumour microenvironment

Cellular senescence refers to a state of irreversible cell cycle arrest that can be induced by various cellular stresses and is known to play a pivotal role in tumour suppression. While senescence-associated growth arrest can inhibit the proliferation of cancer-prone cells, the altered secretory profile of senescent cells, termed the senescence-associated secretory phenotype, can contribute to the microenvironment that promotes tumour development. Although the senescence-associated secretory phenotype and its effects on tumorigenesis are both highly context dependent, mechanisms underlying such diversity are becoming better understood, thereby allowing the creation of new strategies to effectively target the senescence-associated secretory phenotype and senescent cells for cancer therapy. In this review, we discuss the current knowledge on cellular senescence and the senescence-associated secretory phenotype to develop a structural understanding of their roles in the tumour microenvironment and provide perspectives for future research, including the possibility of senotherapy for the treatment of cancer.

The hypoxia-inducible factor-1α in stemness and resistance to chemotherapy in gastric cancer: Future directions for therapeutic targeting

Hypoxia-inducible factor-1α (HIF-1α) is a crucial mediator of intra-tumoral heterogeneity, tumor progression, and unresponsiveness to therapy in tumors with hypoxia. Gastric tumors, one of the most aggressive tumors in the clinic, are highly enriched in hypoxic niches, and the degree of hypoxia is strongly correlated with poor survival in gastric cancer patients. Stemness and chemoresistance in gastric cancer are the two root causes of poor patient outcomes. Based on the pivotal role of HIF-1α in stemness and chemoresistance in gastric cancer, the interest in identifying critical molecular targets and strategies for surpassing the action of HIF-1α is expanding. Despite that, the understanding of HIF-1α induced signaling in gastric cancer is far from complete, and the development of efficacious HIF-1α inhibitors bears various challenges. Hence, here we review the molecular mechanisms by which HIF-1α signaling stimulates stemness and chemoresistance in gastric cancer, with the clinical efforts and challenges to translate anti-HIF-1α strategies into the clinic.

Targeting chemoresistant senescent pancreatic cancer cells improves conventional treatment efficacy

Pancreatic cancer is one of the deadliest cancers owing to its late diagnosis and of the strong resistance to available treatments. Despite a better understanding of the disease in the last two decades, no significant improvement in patient care has been made. Senescent cells are characterized by a stable proliferation arrest and some resistance to cell death. Increasing evidence suggests that multiple lines of antitumor therapy can induce a senescent-like phenotype in cancer cells, which may participate in treatment resistance. In this study, we describe that gemcitabine, a clinically-used drug against pancreatic cancer, induces a senescent-like phenotype in highly chemoresistant pancreatic cancer cells in vitro and in xenografted tumors in vivo. The use of ABT-263, a well-described senolytic compound targeting Bcl2 anti-apoptotic proteins, killed pancreatic gemcitabine-treated senescent-like cancer cells in vitro. In vivo, the combination of gemcitabine and ABT-263 decreased tumor growth, whereas their individual administration had no effect. Together these data highlight the possibility of improving the efficacy of conventional chemotherapies against pancreatic cancer by eliminating senescent-like cancer cells through senolytic intervention. Further studies testing different senolytics or their combination with available treatments will be necessary to optimize preclinical data in mouse models before transferring these findings to clinical trials.

Cellular Senescence as a Brake or Accelerator for Oncogenic Transformation and Role in Lymphatic Metastasis

Cellular senescence-the irreversible cell cycle arrest driven by a variety of mechanisms and, more specifically, the senescence-associated secretory phenotype (SASP)-is an important area of research in the context of different age-related diseases, such as cardiovascular disease and cancer. SASP factors play both beneficial and detrimental roles in age-related disease progression depending on the source of the SASPs, the target cells, and the microenvironment. The impact of senescence and the SASP on different cell types, the immune system, and the vascular system has been widely discussed. However, the impact of replicative or stress-induced senescence on lymphatic biology and pathological lymphangiogenesis remains underexplored. The lymphatic system plays a crucial role in the maintenance of body fluid homeostasis and immune surveillance. The perturbation of lymphatic function can hamper normal physiological function. Natural aging or stress-induced premature aging influences the lymphatic vessel structure and function, which significantly affect the role of lymphatics in tumor dissemination and metastasis. In this review, we focus on the role of senescence on lymphatic pathobiology, its impact on cancer, and potential therapeutic interventions to manipulate the aged or senescent lymphatic system for disease management.

Obesity triggers tumoral senescence and renders poorly immunogenic malignancies amenable to senolysis

Obesity is a major risk factor for cancer. Conventional thought suggests that elevated adiposity predisposes to heightened inflammatory stress and potentiates tumor growth, yet underlying mechanisms remain ill-defined. Here, we show that tumors from patients with a body mass index >35 carry a high burden of senescent cells. In mouse syngeneic tumor models, we correlated a pronounced accretion of senescent cancer cells with poorly immunogenic tumors when mice were subjected to diet-induced obesity (DIO). Highly immunogenic tumors showed lesser senescence burden suggesting immune-mediated elimination of senescent cancer cells, likely targeted as a consequence of their senescence-associated secretory phenotype. Treatment with the senolytic BH3 mimetic small molecule inhibitor ABT-263 selectively stalled tumor growth in mice with DIO to rates comparable to regular diet-fed mice. Thus, consideration of body adiposity in the selection of cancer therapy may be a critical determinant for disease outcome in poorly immunogenic malignancies.

Drugging non-coding RNAs-A new light of hope in senescence-related cancer therapy

Cancer is the most prevalent disease of concern worldwide for several decades. Diverse therapeutic aspects are in applications to control this phenomenal disease and also for decennaries. Among many causes and consequences of cancer, senescence has gained much interest in recent times. Senescence, also termed aging, is the natural process that induces cancer in neighboring cells through Senescence-Associated-Secretory Phenotypes (SASPs) production. As a cure or preventive measure of cancer progression, studies already light upon multiple proteins and their roles in associated pathways but the aspect of different non-coding RNAs (ncRNAs) is emerging recently and is under extensive research. Different approaches toward controlling senescence and inhibiting senescent cell accumulation are other aspects of cancer procurement. Thus, the role of ncRNA molecules in senescence and aging is getting much more interest as an alternate therapy for cancer treatment. In this review, at first, the roles of different ncRNAs related to several cellular processes are described. Then we tried to highlight the roles of different non-coding RNAs in senescence-induced cancer formation that extends with increasing age and emphasized non-coding RNAs as a therapeutic target solely or in combination with small molecules where drugging of small molecules targeting these non-coding RNAs can control cancer development.

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.

Senotherapies: A novel strategy for synergistic anti-tumor therapy

Cellular senescence was initially considered an effective antitumor mechanism, and senescence-induced therapy has previously been regarded as an efficient treatment. However, increasing studies have discovered that persistent senescent cells (SNCs) might have unanticipated negative repercussions for antitumor treatment. The long-term build-up of SNCs exacerbates toxic side effects, treatment resistance, and poor prognosis, and tumor cells that undergo senescence escape can acquire stemness to repopulate the tumor, leading to cancer recurrence. Thus, senotherapies that eliminate SNCs could be used as a new strategy for synergistic antitumor therapy. In this review, we summarize the adverse effects of SNCs in tumor development and the mechanisms by which senescent tumor cells escape senescence, discuss the relationship between senescence and polyploidy, and highlight the potential of senotherapies as an emerging adjuvant antitumor treatment strategy. Such a strategy is expected to provide new approaches for antitumor drug development from the perspective of cellular senescence.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

cFLIP suppression and DR5 activation sensitize senescent cancer cells to senolysis

Senolytics, drugs that kill senescent cells, have been proposed to improve the response to pro-senescence cancer therapies; however, this remains challenging due to a lack of broadly acting senolytic drugs. Using CRISPR/Cas9-based genetic screens in different senescent cancer cell models, we identify loss of the death receptor inhibitor cFLIP as a common vulnerability of senescent cancer cells. Senescent cells are primed for apoptotic death by NF-κB-mediated upregulation of death receptor 5 (DR5) and its ligand TRAIL, but are protected from death by increased cFLIP expression. Activation of DR5 signaling by agonistic antibody, which can be enhanced further by suppression of cFLIP by BRD2 inhibition, leads to efficient killing of a variety of senescent cancer cells. Moreover, senescent cells sensitize adjacent non-senescent cells to killing by DR5 agonist through a bystander effect mediated by secretion of cytokines. We validate this 'one-two punch' cancer therapy by combining pro-senescence therapy with DR5 activation in different animal models.

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.

Alleviation of cisplatin-induced neuropathic pain, neuronal apoptosis, and systemic inflammation in mice by rapamycin

Platinum-based chemotherapeutic treatment of cancer patients is associated with debilitating adverse effects. Several adverse effects have been well investigated, and can be managed satisfactorily, but chemotherapy-induced peripheral neuropathy (CIPN) remains poorly treated. Our primary aim in this study was to investigate the neuroprotective effect of the immunomodulatory drug rapamycin in the mitigation of cisplatin-induced neurotoxicity. Pain assays were performed in vivo to determine whether rapamycin would prevent or significantly decrease cisplatin-induced neurotoxicity in adult male Balb/c mice. Neuropathic pain induced by both chronic and acute exposure to cisplatin was measured by hot plate assay, cold plate assay, tail-flick test, and plantar test. Rapamycin co-treatment resulted in significant reduction in cisplatin-induced nociceptive-like symptoms. To understand the underlying mechanisms behind rapamycin-mediated neuroprotection, we investigated its effect on certain inflammatory mediators implicated in the propagation of chemotherapy-induced neurotoxicity. Interestingly, cisplatin was found to significantly increase peripheral IL-17A expression and CD8- T cells, which were remarkably reversed by the pre-treatment of mice with rapamycin. In addition, rapamycin reduced the cisplatin-induced neuronal apoptosis marked by decreased neuronal caspase-3 activity. The rapamycin neuroprotective effect was also associated with reversal of the changes in protein expression of p21^Cip1, p53, and PUMA. Collectively, rapamycin alleviated some features of cisplatin-induced neurotoxicity in mice and can be further investigated for the treatment of cisplatin-induced peripheral neuropathy.

Cellular senescence and the tumour microenvironment

The senescence-associated secretory phenotype (SASP), where senescent cells produce a variety of secreted proteins including inflammatory cytokines, chemokines, matrix remodelling factors, growth factors and so on, plays pivotal but varying roles in the tumour microenvironment. The effects of SASP on the surrounding microenvironment depend on the cell type and process of cellular senescence induction, which is often associated with innate immunity. Via SASP-mediated paracrine effects, senescent cells can remodel the surrounding tissues by modulating the character of adjacent cells, such as stromal, immune cells, as well as cancer cells. The SASP is associated with both tumour-suppressive and tumour-promoting effects, as observed in senescence surveillance effects (tumour-suppressive) and suppression of anti-tumour immunity in most senescent cancer-associated fibroblasts and senescent T cells (tumour-promoting). In this review, we discuss the features and roles of senescent cells in tumour microenvironment with emphasis on their context-dependency that determines whether they promote or suppress cancer development. Potential usage of recently developed drugs that suppress the SASP (senomorphics) or selectively kill senescence cells (senolytics) in cancer therapy are also discussed.

Pro-tumorigenic role of type 2 diabetes-induced cellular senescence in colorectal cancer

Colorectal cancer (CRC) is the second leading cause of cancer-related mortality worldwide. The disease still remains incurable and highly lethal in the advanced stage, representing a global health concern. Therefore, it is essential to understand the causes and risk factors leading to its development. Because age-related cellular senescence and type 2 diabetes (T2D) have been recognised as risk factors for CRC development, the recent finding that type 2 diabetic patients present an elevated circulating volume of senescent cells raises the question whether type 2 diabetes facilitates the process of CRC tumorigenesis by inducing premature cell senescence. In this review, we will discuss the mechanisms according to which T2D induces cellular senescence and the role of type 2 diabetes-induced cellular senescence in the pathogenesis and progression of colorectal cancer. Lastly, we will explore the current therapeutic approaches and challenges in targeting senescence.

Simple Detection of Unstained Live Senescent Cells with Imaging Flow Cytometry

Cellular senescence is a hallmark of aging and a promising target for therapeutic approaches. The identification of senescent cells requires multiple biomarkers and complex experimental procedures, resulting in increased variability and reduced sensitivity. Here, we propose a simple and broadly applicable imaging flow cytometry (IFC) method. This method is based on measuring autofluorescence and morphological parameters and on applying recent artificial intelligence (AI) and machine learning (ML) tools. We show that the results of this method are superior to those obtained measuring the classical senescence marker, senescence-associated beta-galactosidase (SA-β-Gal). We provide evidence that this method has the potential for diagnostic or prognostic applications as it was able to detect senescence in cardiac pericytes isolated from the hearts of patients affected by end-stage heart failure. We additionally demonstrate that it can be used to quantify senescence “in vivo” and can be used to evaluate the effects of senolytic compounds. We conclude that this method can be used as a simple and fast senescence assay independently of the origin of the cells and the procedure to induce senescence.

GCN2 inhibition sensitizes arginine-deprived hepatocellular carcinoma cells to senolytic treatment

Hepatocellular carcinoma (HCC) is a typically fatal malignancy exhibiting genetic heterogeneity and limited therapy responses. We demonstrate here that HCCs consistently repress urea cycle gene expression and thereby become auxotrophic for exogenous arginine. Surprisingly, arginine import is uniquely dependent on the cationic amino acid transporter SLC7A1, whose inhibition slows HCC cell growth in vitro and in vivo. Moreover, arginine deprivation engages an integrated stress response that promotes HCC cell-cycle arrest and quiescence, dependent on the general control nonderepressible 2 (GCN2) kinase. Inhibiting GCN2 in arginine-deprived HCC cells promotes a senescent phenotype instead, rendering these cells vulnerable to senolytic compounds. Preclinical models confirm that combined dietary arginine deprivation, GCN2 inhibition, and senotherapy promote HCC cell apoptosis and tumor regression. These data suggest novel strategies to treat human liver cancers through targeting SLC7A1 and/or a combination of arginine restriction, inhibition of GCN2, and senolytic agents.

Clinical and Biological Aspects of Disseminated Tumor Cells and Dormancy in Breast Cancer

Progress in detection and treatment have drastically improved survival for early breast cancer patients. However, distant recurrence causes high mortality and is typically considered incurable. Cancer dissemination occurs via circulating tumor cells (CTCs) and up to 75% of breast cancer patients could harbor micrometastatses at time of diagnosis, while metastatic recurrence often occurs years to decades after treatment. During clinical latency, disseminated tumor cells (DTCs) can enter a state of cell cycle arrest or dormancy at distant sites, and are likely shielded from immune detection and treatment. While this is a challenge, it can also be seen as an outstanding opportunity to target dormant DTCs on time, before their transformation into lethal macrometastatic lesions. Here, we review and discuss progress made in our understanding of DTC and dormancy biology in breast cancer. Strides in our mechanistic insights of these features has led to the identification of possible targeting strategies, yet, their integration into clinical trial design is still uncertain. Incorporating minimally invasive liquid biopsies and rationally designed adjuvant therapies, targeting both proliferating and dormant tumor cells, may help to address current challenges and improve precision cancer care.

Considering therapy-induced senescence as a mechanism of tumour dormancy contributing to disease recurrence

The capability of tumour cells to escape from therapy-induced senescence, as well as cell-non-autonomous functions of senescence, support the premise that senescence could serve as one pathway to tumour dormancy (among others that include quiescence and diapause) that is permissive for disease recurrence. Consequently, the pharmacologic targeting of senescent tumour cells could mitigate the risk for cancer resurgence, thereby enhancing the therapeutic efficacy of cancer chemotherapy.

Cellular senescence in neuroblastoma

Neuroblastoma is a tumour that arises from the sympathoadrenal lineage occurring predominantly in children younger than five years. About half of the patients are diagnosed with high-risk tumours and undergo intensive multi-modal therapy. The success rate of current treatments for high-risk neuroblastoma is disappointingly low and survivors suffer from multiple therapy-related long-term side effects. Most chemotherapeutics drive cancer cells towards cell death or senescence. Senescence has long been considered to represent a terminal non-proliferative state and therefore an effective barrier against tumorigenesis. This dogma, however, has been challenged by recent observations that infer a much more dynamic and reversible nature for this process, which may have implications for the efficacy of therapy-induced senescence-oriented treatment strategies. Neuroblastoma cells in a dormant, senescent-like state may escape therapy, whilst their senescence-associated secretome may promote inflammation and invasiveness, potentially fostering relapse. Conversely, due to its distinct molecular identity, senescence may also represent an opportunity for the development of novel (combination) therapies. However, the limited knowledge on the molecular dynamics and diversity of senescence signatures demands appropriate models to study this process in detail. This review summarises the molecular knowledge about cellular senescence in neuroblastoma and investigates current and future options towards therapeutic exploration.

Exploiting senescence for the treatment of cancer

Senescence is a cellular response to a variety of stress signals that is characterized by a stable withdrawal from the cell cycle and major changes in cell morphology and physiology. While most research on senescence has been performed on non-cancer cells, it is evident that cancer cells can also mount a senescence response. In this Review, we discuss how senescence can be induced in cancer cells. We describe the distinctive features of senescent cancer cells and how these changes in cellular physiology might be exploited for the selective eradication of these cells (senolysis). We discuss activation of the host immune system as a particularly attractive way to clear senescent cancer cells. Finally, we consider the challenges and opportunities provided by a 'one-two punch' sequential treatment of cancer with pro-senescence therapy followed by senolytic therapy.

Cellular Senescence: Molecular Targets, Biomarkers, and Senolytic Drugs

Cellular senescence is defined as irreversible cell cycle arrest caused by various processes that render viable cells non-functional, hampering normal tissue homeostasis. It has many endogenous and exogenous inducers, and is closely connected with age, age-related pathologies, DNA damage, degenerative disorders, tumor suppression and activation, wound healing, and tissue repair. However, the literature is replete with contradictory findings concerning its triggering mechanisms, specific biomarkers, and detection protocols. This may be partly due to the wide range of cellular and in vivo animal or human models of accelerated aging that have been used to study senescence and test senolytic drugs. This review summarizes recent findings concerning senescence, presents some widely used cellular and animal senescence models, and briefly describes the best-known senolytic agents.