Senescence: A program in the road to cell elimination and cancer

Polyploid giant cancer cells: origin, possible pathways of formation, characteristics, and mechanisms of regulation

Polyploid giant cancer cells (PGCCs) are characterized by the presence of either a single enlarged nucleus or multiple nuclei and are closely associated with tumor progression and treatment resistance. These cells contribute significantly to cellular heterogeneity and can arise from various stressors, including radiation, chemotherapy, hypoxia, and environmental factors. The formation of PGCCs can occur through mechanisms such as endoreplication, cell fusion, cytokinesis failure, mitotic slippage, or cell cannibalism. Notably, PGCCs exhibit traits similar to cancer stem cells (CSCs) and generate highly invasive progeny through asymmetric division. The presence of PGCCs and their progeny is pivotal in conferring resistance to chemotherapy and radiation, as well as facilitating tumor recurrence and metastasis. This review provides a comprehensive analysis of the origins, potential formation mechanisms, stressors, unique characteristics, and regulatory pathways of PGCCs, alongside therapeutic strategies targeting these cells. The objective is to enhance the understanding of PGCC initiation and progression, offering novel insights into tumor biology.

Ageing microenvironment mediates lymphocyte carcinogenesis and lymphoma drug resistance: From mechanisms to clinical therapy (Review)

Cellular senescence has a complex role in lymphocyte carcinogenesis and drug resistance of lymphomas. Senescent lymphoma cells combine with immunocytes to create an ageing environment that can be reprogrammed with a senescence‑associated secretory phenotype, which gradually promotes therapeutic resistance. Certain signalling pathways, such as the NF‑κB, Wnt and PI3K/AKT/mTOR pathways, regulate the tumour ageing microenvironment and induce the proliferation and progression of lymphoma cells. Therefore, targeting senescence‑related enzymes or their signal transduction pathways may overcome radiotherapy or chemotherapy resistance and enhance the efficacy of relapsed/refractory lymphoma treatments. Mechanisms underlying drug resistance in lymphomas are complex. The ageing microenvironment is a novel factor that contributes to drug resistance in lymphomas. In terms of clinical translation, some senolytics have been used in clinical trials on patients with relapsed or refractory lymphoma. Combining immunotherapy with epigenetic drugs may achieve better therapeutic effects; however, senescent cells exhibit considerable heterogeneity and lymphoma has several subtypes. Extensive research is necessary to achieve the practical application of senolytics in relapsed or refractory lymphomas. This review summarises the mechanisms of senescence‑associated drug resistance in lymphoma, as well as emerging strategies using senolytics, to overcome therapeutic resistance in lymphoma.

The impact of the senescent microenvironment on tumorigenesis: Insights for cancer therapy

The growing global burden of cancer, especially among people aged 60 years and over, has become a key public health issue. This trend suggests the need for a deeper understanding of the various cancer types in order to develop universally effective treatments. A prospective area of research involves elucidating the interplay between the senescent microenvironment and tumor genesis. Currently, most oncology research focuses on adulthood and tends to ignore the potential role of senescent individuals on tumor progression. Senescent cells produce a senescence-associated secretory phenotype (SASP) that has a dual role in the tumor microenvironment (TME). While SASP components can remodel the TME and thus hinder tumor cell proliferation, they can also promote tumorigenesis and progression via pro-inflammatory and pro-proliferative mechanisms. To address this gap, our review seeks to investigate the influence of senescent microenvironment changes on tumor development and their potential implications for cancer therapies.

Drug repurposing for cancer therapy

Cancer, a complex and multifactorial disease, presents a significant challenge to global health. Despite significant advances in surgical, radiotherapeutic and immunological approaches, which have improved cancer treatment outcomes, drug therapy continues to serve as a key therapeutic strategy. However, the clinical efficacy of drug therapy is often constrained by drug resistance and severe toxic side effects, and thus there remains a critical need to develop novel cancer therapeutics. One promising strategy that has received widespread attention in recent years is drug repurposing: the identification of new applications for existing, clinically approved drugs. Drug repurposing possesses several inherent advantages in the context of cancer treatment since repurposed drugs are typically cost-effective, proven to be safe, and can significantly expedite the drug development process due to their already established safety profiles. In light of this, the present review offers a comprehensive overview of the various methods employed in drug repurposing, specifically focusing on the repurposing of drugs to treat cancer. We describe the antitumor properties of candidate drugs, and discuss in detail how they target both the hallmarks of cancer in tumor cells and the surrounding tumor microenvironment. In addition, we examine the innovative strategy of integrating drug repurposing with nanotechnology to enhance topical drug delivery. We also emphasize the critical role that repurposed drugs can play when used as part of a combination therapy regimen. To conclude, we outline the challenges associated with repurposing drugs and consider the future prospects of these repurposed drugs transitioning into clinical application.

The senescence journey in cancer immunoediting

Cancer progression is continuously controlled by the immune system which can identify and destroy nascent tumor cells or inhibit metastatic spreading. However, the immune system and its deregulated activity in the tumor microenvironment can also promote tumor progression favoring the outgrowth of cancers capable of escaping immune control, in a process termed cancer immunoediting. This process, which has been classified into three phases, i.e. "elimination", "equilibrium" and "escape", is influenced by several cancer- and microenvironment-dependent factors. Senescence is a cellular program primed by cells in response to different pathophysiological stimuli, which is based on long-lasting cell cycle arrest and the secretion of numerous bioactive and inflammatory molecules. Because of this, cellular senescence is a potent immunomodulatory factor promptly recruiting immune cells and actively promoting tissue remodeling. In the context of cancer, these functions can lead to both cancer immunosurveillance and immunosuppression. In this review, the authors will discuss the role of senescence in cancer immunoediting, highlighting its context- and timing-dependent effects on the different three phases, describing how senescent cells promote immune cell recruitment for cancer cell elimination or sustain tumor microenvironment inflammation for immune escape. A potential contribution of senescent cells in cancer dormancy, as a mechanism of therapy resistance and cancer relapse, will be discussed with the final objective to unravel the immunotherapeutic implications of senescence modulation in cancer.

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.

Autophagy and Senescence: The Molecular Mechanisms and Implications in Liver Diseases

The liver is the primary organ accountable for complex physiological functions, including lipid metabolism, toxic chemical degradation, bile acid synthesis, and glucose metabolism. Liver function homeostasis is essential for the stability of bodily functions and is involved in the complex regulation of the balance between cell proliferation and cell death. Cell proliferation-halting mechanisms, including autophagy and senescence, are implicated in the development of several liver diseases, such as cholestasis, viral hepatitis, nonalcoholic fatty liver disease, liver fibrosis, and hepatocellular carcinoma. Among various cell death mechanisms, autophagy is a highly conserved and self-degradative cellular process that recycles damaged organelles, cellular debris, and proteins. This process also provides the substrate for further metabolism. A defect in the autophagy machinery can lead to premature diseases, accelerated aging, inflammatory state, tumorigenesis, and cellular senescence. Senescence, another cell death type, is an active player in eliminating premalignant cells. At the same time, senescent cells can affect the function of neighboring cells by secreting the senescence-associated secretory phenotype and induce paracrine senescence. Autophagy can promote and delay cellular senescence under different contexts. This review decodes the roles of autophagy and senescence in multiple liver diseases to achieve a better understanding of the regulatory mechanisms and implications of autophagy and senescence in various liver diseases.

An immunosuppressive subtype of senescent tumor cells predicted worse immunotherapy response in lung adenocarcinoma

Senescent tumor cells (STCs) can induce immunosuppression, promoting tumor progression and therapy resistance. However, the specific characteristics of immunosuppressive STC have not been thoroughly investigated. This study aimed to characterize and elucidate the immunosuppressive phenotype of STC in lung adenocarcinoma by employing single-cell and bulk transcriptomics, as well as serum proteomics profiling. We identified senescence-related genes specific to tumors and identified Cluster10 of STC as the immunomodulatory subtype. Cluster10 exhibited a distinct secretome dominated by cytokines such as CXCL1, CXCL2, and CXCL8 and showed activation of transcription factors associated with cytokine secretion, including NFKB1, RELA, and STAT3. Notably, Cluster10 demonstrated the highest degree of intercellular communication among all cell types, with interactions as LGALS9-TIM3 and MIF-CD74. Furthermore, Cluster10 showed significant associations with poor prognosis and diminished response to immunotherapy. Analysis of serum proteomics data from our in-house cohort identified CXCL8 as a potential marker for predicting immunotherapeutic outcomes.

Tumor microenvironment and cellular senescence: Understanding therapeutic resistance and harnessing strategies

The tumor microenvironment (TME) is a major contributor to cancer malignancy including development of therapeutic resistance, a process mediated in part through intercellular crosstalk. Besides diverse soluble factors responsible for pro-survival pathway activation, immune evasion and extracellular matrix (ECM) remodeling further promote cancer resistance. Importantly, therapy-induced senescence (TIS) of cells in the TME is frequently observed in anticancer regimens, an off-target effect that can generate profound impacts on disease progression. By conferring the resistance and fueling the repopulation of remaining cancerous cells, TIS is responsible for tumor relapse and distant metastasis in posttreatment stage. This pathological trajectory can be substantially driven by the pro-inflammatory feature of senescent cells, termed as the senescence-associated secretory phenotype (SASP). Targeting strategies to selectively and efficiently remove senescent cells before they exert non-autonomous but largely deleterious effects, are emerging as an effective solution to prevent drug resistance acquired from a treatment-remodeled TME. In this review, we summarize the TME composition and key activities that affect tissue homeostasis and support treatment resistance. Promising opportunities that allow TME-manipulation and senescent cell-targeting (senotherapy) are discussed, with translational pipelines to overcome therapeutic barriers in clinical oncology projected.

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.

What Are the Reasons for Continuing Failures in Cancer Therapy? Are Misleading/Inappropriate Preclinical Assays to Be Blamed? Might Some Modern Therapies Cause More Harm than Benefit?

Over 50 years of cancer research has resulted in the generation of massive amounts of information, but relatively little progress has been made in the treatment of patients with solid tumors, except for extending their survival for a few months at best. Here, we will briefly discuss some of the reasons for this failure, focusing on the limitations and sometimes misunderstanding of the clinical relevance of preclinical assays that are widely used to identify novel anticancer drugs and treatment strategies (e.g., "synthetic lethality"). These include colony formation, apoptosis (e.g., caspase-3 activation), immunoblotting, and high-content multiwell plate cell-based assays, as well as tumor growth studies in animal models. A major limitation is that such assays are rarely designed to recapitulate the tumor repopulating properties associated with therapy-induced cancer cell dormancy (durable proliferation arrest) reflecting, for example, premature senescence, polyploidy and/or multinucleation. Furthermore, pro-survival properties of apoptotic cancer cells through phoenix rising, failed apoptosis, and/or anastasis (return from the brink of death), as well as cancer immunoediting and the impact of therapeutic agents on interactions between cancer and immune cells are often overlooked in preclinical studies. A brief review of the history of cancer research makes one wonder if modern strategies for treating patients with solid tumors may sometimes cause more harm than benefit.

Why Senescent Cells Are Resistant to Apoptosis: An Insight for Senolytic Development

Cellular senescence is a process that leads to a state of irreversible cell growth arrest induced by a variety of intrinsic and extrinsic stresses. Senescent cells (SnCs) accumulate with age and have been implicated in various age-related diseases in part via expressing the senescence-associated secretory phenotype. Elimination of SnCs has the potential to delay aging, treat age-related diseases and extend healthspan. However, once cells becoming senescent, they are more resistant to apoptotic stimuli. Senolytics can selectively eliminate SnCs by targeting the SnC anti-apoptotic pathways (SCAPs). They have been developed as a novel pharmacological strategy to treat various age-related diseases. However, the heterogeneity of the SnCs indicates that SnCs depend on different proteins or pathways for their survival. Thus, a better understanding of the underlying mechanisms for apoptotic resistance of SnCs will provide new molecular targets for the development of cell-specific or broad-spectrum therapeutics to clear SnCs. In this review, we discussed the latest research progresses and challenge in senolytic development, described the significance of regulation of senescence and apoptosis in aging, and systematically summarized the SCAPs involved in the apoptotic resistance in SnCs.

Cyclin-dependent kinase 1 as a potential target for lycorine against hepatocellular carcinoma

The pathological changes and possible underlying molecular mechanisms of hepatocellular carcinoma (HCC) are currently unclear. Effective treatment of this pathological state remains a challenge. The purpose of this study is to obtain some key genes with diagnostic and prognostic meaning and to identify potential therapeutic agents for HCC treatment. Here, CDK1, CCNB1 and CCNB2 were found to be highly expressed in HCC patients and accompanied by poor prognosis, and knockdown of them by siRNA drastically induced autophagy and senescence in hepatoma cells. Simultaneously, the anti-HCC effect of lycorine was comparable to that of interfering with these three genes, and lycorine significantly promoted the decrease both in protein and mRNA expression of CDK1. Molecular validation mechanistically demonstrated that lycorine might attenuate the degradation rate of CDK1 via interaction with it, which had been confirmed by cellular thermal shift assay and drug affinity responsive targets stability assay. Taken together, these findings suggested that CDK1, CCNB1 and CCNB2 could be regarded as potential diagnostic and prognostic biomarkers for HCC, and CDK1 might serve as a promising therapeutic target for lycorine against HCC.

Stress-Induced Polyploid Giant Cancer Cells: Unique Way of Formation and Non-Negligible Characteristics

Polyploidy is a conserved mechanism in cell development and stress responses. Multiple stresses of treatment, including radiation and chemotherapy drugs, can induce the polyploidization of tumor cells. Through endoreplication or cell fusion, diploid tumor cells convert into giant tumor cells with single large nuclei or multiple small nucleuses. Some of the stress-induced colossal cells, which were previously thought to be senescent and have no ability to proliferate, can escape the fate of death by a special way. They can remain alive at least before producing progeny cells through asymmetric cell division, a depolyploidization way named neosis. Those large and danger cells are recognized as polyploid giant cancer cells (PGCCs). Such cells are under suspicion of being highly related to tumor recurrence and metastasis after treatment and can bring new targets for cancer therapy. However, differences in formation mechanisms between PGCCs and well-accepted polyploid cancer cells are largely unknown. In this review, the methods used in different studies to induce polyploid cells are summarized, and several mechanisms of polyploidization are demonstrated. Besides, we discuss some characteristics related to the poor prognosis caused by PGCCs in order to provide readers with a more comprehensive understanding of these huge cells.

Biological functions of therapy-induced senescence in cancer

Therapy-induced cellular senescence is a state of stable growth arrest induced by common cancer treatments such as chemotherapy and radiation. In an oncogenic context, therapy-induced senescence can have different consequences. By blocking cellular proliferation and by facilitating immune cell infiltration, it functions as tumor suppressive mechanism. By fueling the proliferation of bystander cells and facilitating metastasis, it acts as a tumor promoting factor. This dual role is mainly attributed to the differential expression and secretion of a set of pro-inflammatory cytokines and tissue remodeling factors, collectively known as the Senescence-Associated Secretory Phenotype (SASP). Here, we describe cell-autonomous and non-cell-autonomous mechanisms that senescent cells activate in response to chemotherapy and radiation leading to tumor suppression and tumor promotion. We present the current state of knowledge on the stimuli that affect the activation of these opposing mechanisms and the effect of senescent cells on their micro-environment eg. by regulating the functions of immune cells in tumor clearance as well as strategies to eliminate senescent tumor cells before exerting their deleterious side-effects.