Senescence-associated secretory phenotype favors the emergence of cancer stem-like cells

Adaptive response of resistant cancer cells to chemotherapy

Despite advances in cancer therapeutics and the integration of personalized medicine, the development of chemoresistance in many patients remains a significant contributing factor to cancer mortality. Upon treatment with chemotherapeutics, the disruption of homeostasis in cancer cells triggers the adaptive response which has emerged as a key resistance mechanism. In this review, we summarize the mechanistic studies investigating the three major components of the adaptive response, autophagy, endoplasmic reticulum (ER) stress signaling, and senescence, in response to cancer chemotherapy. We will discuss the development of potential cancer therapeutic strategies in the context of these adaptive resistance mechanisms, with the goal of stimulating research that may facilitate the development of effective cancer therapy.

ROCK inhibition modulates the senescence-associated secretory phenotype (SASP) in oral keratinocytes

Senescent cells accumulate in different organs and develop a senescence‐associated secretory phenotype (SASP), associated with the development of age‐related pathologies. The constitution of the SASP varies among cell types and with the method of senescence induction; nevertheless, there is substantial overlap among SASPs, especially the presence of pro‐inflammatory cytokines such as IL‐1β, IL‐1α, IL‐6 and IL‐8. These cytokines are highly conserved among SASPs and are implicated in the development of several cancers. Here, we report that ROCK inhibition by Y‐27632 reduces levels of IL‐1α, IL‐1β, IL‐6 and IL‐8 secreted by senescent normal and dysplastic oral keratinocytes without affecting the permanent cell growth arrest. The data indicate some inflammatory genes downregulated by Y‐27632 remain downregulated even after repeated passage in the absence of Y‐27632. We propose ROCK kinase inhibition as a novel alternative to current strategies to modulate the inflammatory components of the SASP, without compromising the permanent cell growth arrest. This observation potentially has wide clinical applications, given the involvement of senescence in cancer and a wide range of age‐related disease. It also suggests care should be exercised when using Y‐27632 to facilitate cell expansion of primary cells, as its effects on gene expression are not entirely reversible.

Discussion of some 'knowns' and some 'unknowns' about the tumour suppressor p53

Activation of the tumour suppressor p53 upon cellular stress can induce a number of different cellular processes. The diverse actions of these processes are critical for the protective function of p53 in preventing the development of cancer. However, it is still not fully understood which process(es) activated by p53 is/are critical for tumour suppression and how this might differ depending on the type of cells undergoing neoplastic transformation and the nature of the drivers of oncogenesis. Moreover, it is not clear why upon activation of p53 some cells undergo cell cycle arrest and senescence whereas others die by apoptosis. Here we discuss some of the cellular processes that are crucial for p53-mediated tumour suppression and the factors that could impact cell fate upon p53 activation. Finally, we describe therapies aimed either at activating wild-type p53 or at changing the behaviour of mutant p53 to unleash tumour growth suppressive processes for therapeutic benefit in malignant disease.

Endothelial cells under therapy-induced senescence secrete CXCL11, which increases aggressiveness of breast cancer cells

The effects of senescence associated secretory phenotype (SASP) from therapy-induced senescent endothelial cells on tumor microenvironment (TME) remains to be clarified. Here, we investigated effects of ionizing radiation (IR)- and doxorubicin-induced senescent HUVEC on TME. MDA-MB-231 cancer cells treated with conditioned medium (CM) from senescent HUVEC or co-cultured with senescent HUVEC significantly increased cancer cell proliferation, migration, and invasion. We found that CXCL11 plays a principal role in the senescent CM-induced aggressive activities of MDA-MB-231 cells. When we treated HUVEC with a neutralizing anti-CXCL11 antibody or CXCL11 SiRNA, or treated MDA-MB-231 cells with CXCR3 SiRNA, we observed synergistic diminution of the ability of the HUVEC SASP to alter the migration and spheroid invasion of cancer cells. ERK activation was involved in the HUVEC SASP-induced aggressive activity of MDA-MB-231 cells. Finally, we observed the in vivo effect of CXCL11 from the senescent HUVEC in tumor-bearing mice. Together, our results demonstrate that SASP from endothelial cells experiencing therapy-induced senescence promotes the aggressive behavior of cancer cells, and that CXCL11 can potentially be targeted to prevent the adverse effects of therapy-induced senescent endothelial cells on the tumor microenvironment.

BH3 mimetics selectively eliminate chemotherapy-induced senescent cells and improve response in TP53 wild-type breast cancer

TP53 wild-type breast tumors rarely undergo a complete pathological response after chemotherapy treatment. These patients have an extremely poor survival rate and studies show these tumors preferentially undergo senescence instead of apoptosis. These senescent cells persist after chemotherapy and secrete cytokines and chemokines comprising the senescence associated secretory phenotype, which promotes survival, proliferation, and metastasis. We hypothesized that eliminating senescent tumor cells would improve chemotherapy response and extend survival. Previous studies have shown "senolytic" agents selectively kill senescent normal cells, but their efficacy in killing chemotherapy-induced senescent cancer cells is unknown. We show that ABT-263, a BH3 mimetic that targets antiapoptotic proteins BCL2/BCL-XL/BCL-W, had no effect on proliferating cells, but rapidly and selectively induced apoptosis in a subset of chemotherapy-treated cancer cells, though sensitivity required days to develop. Low NOXA expression conferred resistance to ABT-263 in some cells, necessitating additional MCL1 inhibition. Gene editing confirmed breast cancer cells relied on BCL-XL or BCL-XL/MCL1 for survival in senescence. In a mouse model of breast cancer, ABT-263 treatment following chemotherapy led to apoptosis, greater tumor regression, and longer survival. Our results reveal cancer cells that have survived chemotherapy by entering senescence can be eliminated using BH3 mimetic drugs that target BCL-XL or BCL-XL/MCL1. These drugs could help minimize residual disease and extend survival in breast cancer patients that otherwise have a poor prognosis and are most in need of improved therapies.

Senescence-Associated Pro-inflammatory Cytokines and Tumor Cell Plasticity

The well-recognized cell phenotypic heterogeneity in tumors is a great challenge for cancer treatment. Dynamic interconversion and movement within a spectrum of different cell phenotypes (cellular plasticity) with the acquisition of specific cell functions is a fascinating biological puzzle, that represent an additional difficulty for cancer treatment and novel therapies development. The understanding of the molecular mechanisms responsible for moving or stabilizing tumor cells within this spectrum of variable states constitutes a valuable tool to overcome these challenges. In particular, cell transitions between epithelial and mesenchymal phenotypes (EMT-MET) and de-and trans-differentiation processes are relevant, since it has been shown that they confer invasiveness, drug resistance, and metastatic ability, due to the simultaneous acquisition of stem-like cell properties. Multiple drivers participate in these cell conversions events. In particular, cellular senescence and senescence-associated soluble factors have been shown to unveil stem-like cell properties and cell plasticity. By modulating gradually the composition of their secretome and the time of exposure, senescent cells may have differential effect not only on tumor cells but also on surrounding cells. Intriguingly, tumor cells that scape from senescence acquire stem-like cell properties and aggressiveness. The reinforcement of senescence and inflammation by soluble factors and the participation of immune cells may provide a dynamic milieu having varied effects on cell transitions, reprogramming, plasticity, stemness and therefore heterogeneity. This will confer different epithelial/mesenchymal traits (hybrid phenotype) and stem-like cell properties, combinations of which, in a particular cell context, could be responsible for different cellular functions during cancer progression (survival, migration, invasion, colonization or proliferation). Additionally, cooperative behavior between cell subpopulations with different phenotypes/stemness functions could also modulate their cellular plasticity. Here, we will discuss the role of senescence and senescence-associated pro-inflammatory cytokines on the induction of cellular plasticity, their effect role in establishing particular states within this spectrum of cell phenotypes and how this is accompanied by stem-like cell properties that, as the epithelial transitions, may also have a continuum of characteristics providing tumor cells with functional adaptability specifically useful in the different stages of carcinogenesis.

Beyond Tumor Suppression: Senescence in Cancer Stemness and Tumor Dormancy

Here, we provide an overview of the importance of cellular fate in cancer as a group of diseases of abnormal cell growth. Tumor development and progression is a highly dynamic process, with several phases of evolution. The existing evidence about the origin and consequences of cancer cell fate specification (e.g., proliferation, senescence, stemness, dormancy, quiescence, and cell cycle re-entry) in the context of tumor formation and metastasis is discussed. The interplay between these dynamic tumor cell phenotypes, the microenvironment, and the immune system is also reviewed in relation to cancer. We focus on the role of senescence during cancer progression, with a special emphasis on its relationship with stemness and dormancy. Selective interventions on senescence and dormancy cell fates, including the specific targeting of cancer cell populations to prevent detrimental effects in aging and disease, are also reviewed. A new conceptual framework about the impact of synthetic lethal strategies by using senogenics and then senolytics is given, with the promise of future directions on innovative anticancer therapies.

DNA damage response and resistance of cancer stem cells

The cancer stem cell (CSC) model defines tumors as hierarchically organized entities, containing a small population of tumorigenic CSC, or tumour-initiating cells, placed at the apex of this hierarchy. These cells may share common qualities with chemo- and radio-resistant cancer cells and contribute to self-renewal activities resulting in tumour formation, maintenance, growth and metastasis. Yet, it remains obscure what self-defense mechanisms are utilized by these cells against the chemotherapeutic drugs or radiotherapy. Recently, attention has been focused on the pivotal role of the DNA damage response (DDR) in tumorigenesis. In line with this note, an increased DDR that prevents CSC and chemoresistant cells from genotoxic pressure of chemotherapeutic drugs or radiation may be responsible for cancer metastasis. In this review, we focus on the current knowledge concerning the role of DDR in CSC and resistant cancer cells and describe the existing opportunities of re-sensitizing such cells to modulate therapeutic treatment effects.

Berberine ameliorates cellular senescence and extends the lifespan of mice via regulating p16 and cyclin protein expression

Although aging and senescence have been extensively studied in the past few decades, however, there is lack of clinical treatment available for anti‐aging. This study presents the effects of berberine (BBR) on the aging process resulting in a promising extension of lifespan in model organisms. BBR extended the replicative lifespan, improved the morphology, and boosted rejuvenation markers of replicative senescence in human fetal lung diploid fibroblasts (2BS and WI38). BBR also rescued senescent cells with late population doubling (PD). Furthermore, the senescence‐associated β‐galactosidase (SA‐β‐gal)‐positive cell rates of late PD cells grown in the BBR‐containing medium were ~72% lower than those of control cells, and its morphology resembled that of young cells. Mechanistically, BBR improved cell growth and proliferation by promoting entry of cell cycles from the G₀ or G₁ phase to S/G₂‐M phase. Most importantly, BBR extended the lifespan of chemotherapy‐treated mice and naturally aged mice by ~52% and ~16.49%, respectively. The residual lifespan of the naturally aged mice was extended by 80%, from 85.5 days to 154 days. The oral administration of BBR in mice resulted in significantly improved health span, fur density, and behavioral activity. Therefore, BBR may be an ideal candidate for the development of an anti‐aging medicine.

Chemotherapy-induced senescent cancer cells engulf other cells to enhance their survival

In chemotherapy-treated breast cancer, wild-type p53 preferentially induces senescence over apoptosis, resulting in a persisting cell population constituting residual disease that drives relapse and poor patient survival via the senescence-associated secretory phenotype. Understanding the properties of tumor cells that allow survival after chemotherapy treatment is paramount. Using time-lapse and confocal microscopy to observe interactions of cells in treated tumors, we show here that chemotherapy-induced senescent cells frequently engulf both neighboring senescent or nonsenescent tumor cells at a remarkable frequency. Engulfed cells are processed through the lysosome and broken down, and cells that have engulfed others obtain a survival advantage. Gene expression analysis showed a marked up-regulation of conserved macrophage-like program of engulfment in chemotherapy-induced senescent cell lines and tumors. Our data suggest compelling explanations for how senescent cells persist in dormancy, how they manage the metabolically expensive process of cytokine production that drives relapse in those tumors that respond the worst, and a function for their expanded lysosomal compartment.

A biomimetic 3D model of hypoxia-driven cancer progression

The fate of tumors depends both on the cancer cells' intrinsic characteristics and on the environmental conditions where the tumors reside and grow. Engineered in vitro models have led to significant advances in cancer research, allowing the investigation of cells in physiological environments and the study of disease mechanisms and processes with enhanced relevance. Here we present a biomimetic cancer model based on a collagen matrix synthesized through a biologically inspired process. We compared in this environment the responses of two breast tumor lineages characterized by different molecular patterns and opposite clinical behaviors: MCF-7 that belong to the luminal A subtype connected to an indolent course, and basal-like MDA-MB-231 connected to high-grade and aggressive disease. Cancer cells in the biomimetic matrix recreate a hypoxic environment that affects their growth dynamics and phenotypic features. Hypoxia induces apoptosis and the selection of aggressive cells that acquire expression signatures associated with glycolysis, angiogenesis, cell-matrix interaction, epithelial to mesenchymal transition and metastatic ability. In response to hypoxia MDA-MB-231 migrate on the collagen fibrils and undergo cellular senescence, while MCF-7 do not exhibit these behaviors. Our biomimetic model mimics the evolution of tumors with different grade of aggressiveness fostered by a hypoxic niche and provides a relevant technology to dissect the events involved in cancer progression.

Unmasking senescence: context-dependent effects of SASP in cancer

Cellular senescence plays a critical role in tumorigenesis. Once thought of as a tissue culture artefact by some researchers, senescence is now a major field of study. Although there are common molecular mechanisms that enforce the growth arrest that characterizes the phenotype, the impact of senescence is varied and can, in some instances, have opposite effects on tumorigenesis. It has become clearer that the cell of origin and the tissue in question dictate the impact of senescence on tumorigenesis. In this Review, we unravel this complexity by focusing on how senescence impacts tumorigenesis when it arises within incipient tumour cells versus stromal cells, and how these roles can change in different stages of disease progression. In addition, we highlight the diversity of the senescent phenotype and its functional output beyond growth arrest: the senescence-associated secretory phenotype (SASP). Fortunately, a number of new genetic and pharmacologic tools have been developed that are now allowing the senescence phenotype to be parsed further.

Cellular plasticity and metastasis in breast cancer: a pre- and post-malignant problem

As a field we have made tremendous strides in treating breast cancer, with a decline in the past 30 years of overall breast cancer mortality. However, this progress is met with little affect once the disease spreads beyond the primary site. With a 5-year survival rate of 22%, 10-year of 13%, for those patients with metastatic breast cancer (mBC), our ability to effectively treat wide spread disease is minimal. A major contributing factor to this ineffectiveness is the complex make-up, or heterogeneity, of the primary site. Within a primary tumor, secreted factors, malignant and pre-malignant epithelial cells, immune cells, stromal fibroblasts and many others all reside alongside each other creating a dynamic environment contributing to metastasis. Furthermore, heterogeneity contributes to our lack of understanding regarding the cells' remarkable ability to undergo epithelial/non-cancer stem cell (CSC) to mesenchymal/CSC (E-M/CSC) plasticity. The enhanced invasion & motility, tumor-initiating potential, and acquired therapeutic resistance which accompanies E-M/CSC plasticity implicates a significant role in metastasis. While most work trying to understand E-M/CSC plasticity has been done on malignant cells, recent evidence is emerging concerning the ability for pre-malignant cells to undergo E-M/CSC plasticity and contribute to the metastatic process. Here we will discuss the importance of E-M/CSC plasticity within malignant and pre-malignant populations of the tumor. Moreover, we will discuss how one may potentially target these populations, ultimately disrupting the metastatic cascade and increasing patient survival for those with mBC.

Senescence cell-associated extracellular vesicles serve as osteoarthritis disease and therapeutic markers

Senescent cells (SnCs) are increasingly recognized as central effector cells in age-related pathologies. Extracellular vesicles (EVs) are potential cellular communication tools through which SnCs exert central effector functions in the local tissue environment. To test this hypothesis in a medical indication that could be validated clinically, we evaluated EV production from SnCs enriched from chondrocytes isolated from human arthritic cartilage. EV production increased in a dose-responsive manner as the concentration of SnCs increased. The EVs were capable of transferring senescence to nonsenescent chondrocytes and inhibited cartilage formation by non-SnCs. microRNA (miR) profiles of EVs isolated from human arthritic synovial fluid did not fully overlap with the senescent chondrocyte EV profiles. The effect of SnC clearance was tested in a murine model of posttraumatic osteoarthritis. miR and protein profiles changed after senolytic treatment but varied depending on age. In young animals, senolytic treatment altered expression of miR-34a, -30c, -125a, -24, -92a, -150, and -186, and this expression correlated with cartilage production. The primary changes in EV contents in aged mice after senolytic treatment, which only reduced pain and degeneration, were immune related. In sum, EV contents found in synovial fluid may serve as a diagnostic for arthritic disease and indicator for therapeutic efficacy of senolytic treatment.

Intraarticular senescent chondrocytes impair the cartilage regeneration capacity of mesenchymal stem cells

Background

Senescent cells exert a significant influence over their surrounding cellular environment. Senescent chondrocytes (SnChos) were found to be accumulated in degenerated cartilage present in joints affected by osteoarthritis. The influence of SnChos on exogenously transplanted stem cells has yet to be reported.

Methods

In this study, we evaluated the interactions between SnChos and bone marrow mesenchymal stem cells (BMSCs) when co-cultured as well as in the intra-articular senescent microenvironment (IASM). The effect of IASM on cartilage regeneration was also assessed.

Results

It was found that a small fraction of SnChos induced BMSC cellular senescence and apoptosis. SnChos also inhibited proliferation, facilitated stemness, and suppressed chondrogenic differentiation of BMSCs. BMSCs induced the apoptosis of SnChos, reduced the proportion of SnChos, stimulated SnChos proliferation, and revealed a bidirectional effect on SnChos inflammaging. IASM significantly suppressed the survival, proliferation, and appropriate differentiation of grafted BMSCs in vivo, all of which impaired cartilage regeneration. Anti-senescence agent ABT-263 was able to partly rescue the cells from the negative effects of SnChos.

Conclusions

The SnChos and BMSCs interacted with each other at cellular senescence, apoptosis, proliferation, differentiation, and cell functions. This interaction impaired the cartilage repair of MSCs. Anti-senescence agent provided a possible solution for this impairment.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1193-1) contains supplementary material, which is available to authorized users.

Pro- and anti-tumorigenic functions of the senescence-associated secretory phenotype

Introduction: Cellular senescence is a stable form of cell cycle exit. Though they no longer divide, senescent cells remain metabolically active and secrete a plethora of proteins collectively termed the senescence-associated secretory phenotype (SASP). Although senescence-associated cell cycle exit likely evolved as an anti-tumor mechanism, the SASP contains both anti- and pro-tumorigenic potential.Areas covered: In this review, we briefly discuss the discovery of senescent cells and its relationship to cancer and aging. We also describe the initiation and regulation of the SASP upon senescence stimulus onset. We focus on both the pro- and anti-tumorigenic properties of the SASP. Finally, we speculate on the potential benefits of therapy-induced senescence combined with selective SASP inhibition for the treatment of cancer.Expert opinion: Further identification and characterization of the SASP factors that are pro-tumorigenic and those that are anti-tumorigenic in specific contexts will be crucial in order to develop personalized therapeutics for the successful treatment of cancer.

Genome Damage Sensing Leads to Tissue Homeostasis in Drosophila

DNA repair is a critical cellular process required for the maintenance of genomic integrity. It is now well appreciated that cells employ several DNA repair pathways to take care of distinct types of DNA damage. It is also well known that a cascade of signals namely DNA damage response or DDR is activated in response to DNA damage which comprise cellular responses, such as cell cycle arrest, DNA repair and cell death, if the damage is irreparable. There is also emerging literature suggesting a cross-talk between DNA damage signaling and several signaling networks within a cell. Moreover, cell death players themselves are also well known to engage in processes outside their canonical function of apoptosis. This chapter attempts to build a link between DNA damage, DDR and signaling from the studies mainly conducted in mammals and Drosophila model systems, with a special emphasis on their relevance in overall tissue homeostasis and development.

Calcium channel α2δ1 subunit (CACNA2D1) enhances radioresistance in cancer stem-like cells in non-small cell lung cancer cell lines

Purpose

Radiotherapy is a major treatment method for patients with non-small cell lung cancer (NSCLC). However, the presence of radioresistant cancer stem cells (CSCs) may be associated with disease relapse or a poor outcome after radiotherapy. Voltage-gated calcium channel α2δ1 subunit (encoded by the gene CACNA2D1) isoform 5 is a marker of CSCs in hepatocellular carcinoma. This study aimed to investigate the radiosensitivity of α2δ1-high cells in NSCLC cell lines.

Materials and methods

NSCLC cell lines A549, H1975, H1299, and PC9 were used. CACNA2D1-knockdown and CACNA2D1-overexpressing cell lines were established by lentiviral infection. Colony formation assay was performed to determine radiosensitivity. Sphere formation assay in serum-free medium was performed to evaluate self-renewal capacity. Proteins associated with DNA damage repair were analyzed by immunofluorescence or Western blot. The monoclonal antibody of α2δ1 was applied alone or in combination with radiation either in vitro or in vivo to determine the anti-tumor effect of the antibody.

Results

α2δ1-high cells showed greater sphere-forming efficiency than α2δ1-low cells and were relatively resistant to radiation. CACNA2D1 knockdown in A549 cells enhanced radiosensitivity, whereas CACNA2D1 overexpression in PC9 and H1975 cells reduced radiosensitivity, suggesting that α2δ1 imparted radioresistance to NSCLC cells. Analysis of proteins involved in DNA damage repair suggested that α2δ1 enhanced the efficiency of DNA damage repair. The monoclonal antibody of α2δ1 had a synergistic effect with that of radiation to block the self-renewal of α2δ1-high cells and enhanced the radiosensitivity of α2δ1-positive cells in colony formation assays. The combination of the α2δ1 antibody with radiation repressed A549 xenograft growth in vivo.

Conclusion

α2δ1 enhances radioresistance in cancer stem-like cells in NSCLC. The α2δ1 monoclonal antibody sensitizes α2δ1-high cells to radiation, suggesting that the antibody may be used to improve the treatment outcome when combined with radiation in NSCLC.

Induction of multiple myeloma cancer stem cell apoptosis using conjugated anti-ABCG2 antibody with epirubicin-loaded microbubbles

Background

Multiple myeloma (MM) currently remains largely incurable. Cancer stem cells (CSCs) are believed to be responsible for drug resistance and eventual relapse. In this study, we exploited a novel agent to evaluate its inhibitory effect on MM CSCs.

Methods

Epirubicin (EPI)-loaded lipid microbubbles (MBs) conjugated with anti-ABCG2 monoclonal antibody (EPI-MBs + mAb) were developed and their effect on MM 138⁻CD34⁻ CSCs isolated from human MM RPMI 8226 cell line plus ultrasound exposure in vitro and in vivo in a nonobese diabetic/severe combined immunodeficient mouse model were assessed.

Results

EPI-MBs + mAb combined with ultrasound led to a significant decrease in the clone formation ability and the mitochondrial membrane potential along with an increase in MM CSC apoptosis. Moreover, treatment with EPI-MBs + mAb with ultrasound exposure remarkably inhibited the growth of MM CSC-derived tumors in xenograft nonobese diabetic/severe combined immunodeficient mice compared with a single agent or EPI-MBs + mAb without ultrasound exposure. The inhibitive efficacy was also correlated with an increased expression of caspase-3, Bax, and TUNEL and decreased expressions of PCNA, Bcl-2, and CD31.

Conclusions

Our findings reveal that the EPI-MBs + mAb combined with therapeutic ultrasound may confer an effective approach for treatment of MM by induction of an apoptotic pathway in MM CSCs.

Non-Cell Autonomous Effects of the Senescence-Associated Secretory Phenotype in Cancer Therapy

In addition to promoting various forms of cell death, most conventional anti-tumor therapies also promote senescence. There is now extensive evidence that therapy-induced senescence (TIS) might be transient, raising the concern that TIS could represent an undesirable outcome of therapy by providing a mechanism for tumor dormancy and eventual disease recurrence. The senescence-associated secretory phenotype (SASP) is a hallmark of TIS and may contribute to aberrant effects of cancer therapy. Here, we propose that the SASP may also serve as a major driver of escape from senescence and the re-emergence of proliferating tumor cells, wherein factors secreted from the senescent cells contribute to the restoration of tumor growth in a non-cell autonomous fashion. Accordingly, anti-SASP therapies might serve to mitigate the deleterious outcomes of TIS. In addition to providing an overview of the putative actions of the SASP, we discuss recent efforts to identify and eliminate senescent tumor cells.

Paracrine roles of cellular senescence in promoting tumourigenesis

Senescent cells activate genetic programmes that irreversibly inhibit cellular proliferation, but also endow these cells with distinctive metabolic and signalling phenotypes. Although senescence has historically been considered a protective mechanism against tumourigenesis, the activities of senescent cells are increasingly being associated with age-related diseases, including cancer. An important feature of senescent cells is the secretion of a vast array of pro-inflammatory cytokines, chemokines, and growth factors collectively known as the senescence-associated secretory phenotype (SASP). Recent research has shown that SASP paracrine signalling can mediate several pro-tumourigenic effects, such as enhancing malignant phenotypes and promoting tumour initiation. In this review, we summarise the paracrine activities of senescent cells and their role in tumourigenesis through direct effects on growth and proliferation of tumour cells, tumour angiogenesis, invasion and metastasis, cellular reprogramming and emergence of tumour-initiating cells, and tumour interactions with the local immune environment. The evidence described here suggests cellular senescence acts as a double-edged sword in cancer pathogenesis, which demands further attention in order to support the use of senolytic or SASP-modulating compounds for cancer treatment.

Oncogene-induced senescence: a potential breakpoint mechanism against malignant transformation in plasma cell disorders

Oncogene-induced senescence (OIS) is a cellular tumor-suppressive mechanism present in several premalignant conditions. Here, we analyze the possible impact of OIS on malignant transformation in plasma cell disorders. Tumor samples from 125 patients with different disease stages were analyzed immunohistochemically for expression of senescence markers. Protein expression of cyclin-dependent kinase inhibitor p21^Cip1/Waf1 was significantly higher in smoldering multiple myeloma (SMM) compared to monoclonal gammopathy of undetermined significance (MGUS) (p = .02) or symptomatic multiple myeloma (MM) (p = .005). SMM plasma cells expressing p21^Cip1/Waf1 were negative for Ki67, consistent with senescence. While p27^Kip1 was highly expressed in healthy controls, MGUS and SMM, expression decreased significantly in MM (p = .02). SMM plasma cells displayed a mutually exclusive expression of p21^Cip1/Waf1/p27^Kip1 suggesting compensatory mechanisms of senescence. In conclusion, we found markers of cellular senescence differentially expressed in SMM compared to MGUS and MM supporting the hypothesis of OIS as a breakpoint mechanism against malignant transformation in plasma cell disorders.

Senescence Elicits Stemness: A Surprising Mechanism for Cancer Relapse

Cellular senescence is traditionally viewed as a permanent form of cell cycle arrest that restrains tumorigenesis. In a recent study in Nature, however, Milanovic et al. (2018) challenge this conventional view, showing that senescence can counterintuitively promote cancer stemness and tumor aggressiveness. This finding suggests that attacking senescence can be exploited in cancer therapy.

Senescent cells and osteoarthritis: a painful connection

Senescent cells (SnCs) are associated with age-related pathologies. Osteoarthritis is a chronic disease characterized by pain, loss of cartilage, and joint inflammation, and its incidence increases with age. For years, the presence of SnCs in cartilage isolated from patients undergoing total knee artificial implants has been noted, but these cells' relevance to disease was unclear. In this Review, we summarize current knowledge of SnCs in the multiple tissues that constitute the articular joint. New evidence for the causative role of SnCs in the development of posttraumatic and age-related arthritis is reviewed along with the therapeutic benefit of SnC clearance. As part of their senescence-associated secretory phenotype, SnCs secrete cytokines that impact the immune system and its response to joint tissue trauma. We present concepts of the immune response to tissue trauma as well as the interactions with SnCs and the local tissue environment. Finally, we discuss therapeutic implications of targeting SnCs in treating osteoarthritis.

On metabolic reprogramming and tumor biology: A comprehensive survey of metabolism in breast cancer

Altered metabolism in tumor cells has been a focus of cancer research for as long as a century but has remained controversial and vague due to an inhomogeneous overall picture. Accumulating genomic, metabolomic, and lastly panomic data as well as bioenergetics studies of the past few years enable a more comprehensive, systems-biologic approach promoting deeper insight into tumor biology and challenging hitherto existing models of cancer bioenergetics. Presenting a compendium on breast cancer-specific metabolome analyses performed thus far, we review and compile currently known aspects of breast cancer biology into a comprehensive network, elucidating previously dissonant issues of cancer metabolism. As such, some of the aspects critically discussed in this review include the dynamic interplay or metabolic coupling between cancer (stem) cells and cancer-associated fibroblasts, the intratumoral and intertumoral heterogeneity and plasticity of cancer cell metabolism, the existence of distinct metabolic tumor compartments in need of separate yet simultaneous therapeutic targeting, the reliance of cancer cells on oxidative metabolism and mitochondrial power, and the role of pro-inflammatory, pro-tumorigenic stromal conditioning. Comprising complex breast cancer signaling networks as well as combined metabolomic and genomic data, we address metabolic consequences of mutations in tumor suppressor genes and evaluate their contribution to breast cancer predisposition in a germline setting, reasoning for distinct personalized preventive and therapeutic measures. The review closes with a discussion on central root mechanisms of tumor cell metabolism and rate-limiting steps thereof, introducing essential strategies for therapeutic targeting.

Cyclin D1 unbalances the redox status controlling cell adhesion, migration, and drug resistance in myeloma cells

The interactions of multiple myeloma (MM) cells with their microenvironment are crucial for pathogenesis. MM cells could interact differentially with their microenvironment depending on the type of cyclin D they express. We established several clones that constitutively express cyclin D1 from the parental RPMI8226 MM cell line and analyzed the impact of cyclin D1 expression on cell behavior. We performed a gene expression profiling study on cyclin D1-expressing vs. control cells and validated the results by semi-quantitative RT-PCR. The expression of cyclin D1 altered the transcription of genes that control adhesion and migration. We confirmed that cyclin D1 increases cell adhesion to stromal cells and fibronectin, stabilizes F-actin fibers, and enhances chemotaxis and inflammatory chemokine secretion. Both control and cyclin D1-expressing cells were more resistant to acute carfilzomib treatment when cultured on stromal cells than in suspension. However, this resistance was specifically reduced in cyclin D1-expressing cells after pomalidomide pre-treatment that modifies tumor cell/microenvironment interactions. Transcriptomic analysis revealed that cyclin D1 expression was also associated with changes in the expression of genes controlling metabolism. We also found that cyclin D1 expression disrupted the redox balance by producing reactive oxygen species. The resulting oxidative stress activated the p44/42 mitogen-activated protein kinase (or ERK1/2) signaling pathway, increased cell adhesion to fibronectin or stromal cells, and controlled drug sensitivity.

Our results have uncovered a new function for cyclin D1 in the control of redox metabolism and interactions of cyclin D1-expressing MM cells with their bone marrow microenvironment.

Telomere Length Dynamics and the Evolution of Cancer Genome Architecture

Telomeres are progressively eroded during repeated rounds of cell division due to the end replication problem but also undergo additional more substantial stochastic shortening events. In most cases, shortened telomeres induce a cell-cycle arrest or trigger apoptosis, although for those cells that bypass such signals during tumour progression, a critical length threshold is reached at which telomere dysfunction may ensue. Dysfunction of the telomere nucleoprotein complex can expose free chromosome ends to the DNA double-strand break (DSB) repair machinery, leading to telomere fusion with both telomeric and non-telomeric loci. The consequences of telomere fusions in promoting genome instability have long been appreciated through the breakage-fusion-bridge (BFB) cycle mechanism, although recent studies using high-throughput sequencing technologies have uncovered evidence of involvement in a wider spectrum of genomic rearrangements including chromothripsis. A critical step in cancer progression is the transition of a clone to immortality, through the stabilisation of the telomere repeat array. This can be achieved via the reactivation of telomerase, or the induction of the alternative lengthening of telomeres (ALT) pathway. Whilst telomere dysfunction may promote genome instability and tumour progression, by limiting the replicative potential of a cell and enforcing senescence, telomere shortening can act as a tumour suppressor mechanism. However, the burden of senescent cells has also been implicated as a driver of ageing and age-related pathology, and in the promotion of cancer through inflammatory signalling. Considering the critical role of telomere length in governing cancer biology, we review questions related to the prognostic value of studying the dynamics of telomere shortening and fusion, and discuss mechanisms and consequences of telomere-induced genome rearrangements.

Senescent fibroblast-derived Chemerin promotes squamous cell carcinoma migration

Aging is associated with a rising incidence of cutaneous squamous cell carcinoma (cSCC), an aggressive skin cancer with the potential for local invasion and metastasis. Acquisition of a senescence-associated secretory phenotype (SASP) in dermal fibroblasts has been postulated to promote skin cancer progression in elderly individuals. The underlying molecular mechanisms are largely unexplored. We show that Chemerin, a previously unreported SASP factor released from senescent human dermal fibroblasts, promotes cSCC cell migration, a key feature driving tumor progression. Whereas the Chemerin abundance is downregulated in malignant cSCC cells, increased Chemerin transcripts and protein concentrations are detected in replicative senescent fibroblasts in vitro and in the fibroblast of skin sections from old donors, indicating that a Chemerin gradient is built up in the dermis of elderly. Using Transwell^® migration assays, we show that Chemerin enhances the chemotaxis of different cSCC cell lines. Notably, the Chemerin receptor CCRL2 is remarkably upregulated in cSCC cell lines and human patient biopsies. Silencing Chemerin in senescent fibroblasts or the CCRL2 and GPR1 receptors in the SCL-1 cSCC cell line abrogates the Chemerin-mediated chemotaxis. Chemerin triggers the MAPK cascade via JNK and ERK1 activation, whereby the inhibition impairs the SASP- or Chemerin-mediated cSCC cell migration.

Taken together, we uncover a key role for Chemerin, as a major factor in the secretome of senescent fibroblasts, promoting cSCC cell migration and possibly progression, relaying its signals through CCRL2 and GPR1 receptors with subsequent MAPK activation. These findings might have implications for targeted therapeutic interventions in elderly patients.

Inhibition of the colony-stimulating-factor-1 receptor affects the resistance of lung cancer cells to cisplatin

In the present work we show that multiple lung cancer cell lines contain cisplatin resistant cell subpopulations expressing the Colony-Stimulating-Factor-Receptor-1 (CSF-1R) and surviving chemotherapy-induced stress. By exploiting siRNA-mediated knock down in vitro and the use of an investigational CSF-1R TKI (JNJ-40346527) in vitro and in vivo, we show that expression and function of the receptor are required for the clonogenicity and chemoresistance of the cell lines. Thus, inhibition of the kinase activity of the receptor reduced the levels of EMT-associated genes, stem cell markers and chemoresistance genes. Additionally, the number of high aldehyde dehydrogenase (ALDH) expressing cells was reduced, consequent to the lack of cisplatin-induced increase of ALDH isoforms. This affected the collective chemoresistance of the treated cultures. Treatment of tumor bearing mice with JNJ-40346527, at pharmacologically relevant doses, produced strong chemo-sensitizing effects in vivo. These anticancer effects correlated with a reduced number of CSF-1Rpos cells, in tumors excised from the treated mice. Depletion of the CD45pos cells within the treated tumors did not, apparently, play a major role in mediating the therapeutic response to the TKI. Thus, lung cancer cells express a functional CSF-1 and CSF-1R duo which mediates pro-tumorigenic effects in vivo and in vitro and can be targeted in a therapeutically relevant way. These observations complement the already known role for the CSF-1R at mediating the pro-tumorigenic properties of tumor-infiltrating immune components.

HSP90 inhibition alters the chemotherapy-driven rearrangement of the oncogenic secretome

Adaptive resistance to therapy is a hallmark of cancer progression. To date, it is not entirely clear how microenvironmental stimuli would mediate emergence of therapy-resistant cell subpopulations, although a rearrangement of the cancer cell secretome following therapy-induced stress can be pivotal for such a process. Here, by using the highly chemoresistant malignant pleural mesothelioma (MPM) as an experimental model, we unveiled a key contribution of the chaperone HSP90 at assisting a chemotherapy-instigated Senescence-Associated-Secretory-Phenotype (SASP). Thus, administration of a clinical trial grade, HSP90, inhibitor blunted the release of several cytokines by the chemotherapy-treated MPM cells, including interleukin (IL)-8. Reduction of IL-8 levels hampered the FAK-AKT signaling and inhibited 3D growth and migration. This correlated with downregulation of key EMT and chemoresistance genes and affected the survival of chemoresistant ALDH^bright cell subpopulations. Altogether, inhibition of HSP90 provoked a switch from a pro-tumorigenic SASP to a pro-apoptotic senescence status, thus resulting in chemosensitizing effects. In mouse xenografts treated with first-line agents, inhibiting HSP90 blunted FAK activation and reduced the expression of ALDH1A3 and the levels of circulating human IL-8, these latter strongly correlating with the effect on tumor growth. We validated the above findings in primary mesothelioma cultures, a more clinically relevant model. We unveiled here a key contribution of the chaperone HSP90 at assisting the secretory stress in chemotherapy-treated cells, which may warrant further investigation in combinatorial therapeutic settings.

"Social Life" of Senescent Cells: What Is SASP and Why Study It?

Cellular senescence was first described as a failure of normal human cells to divide indefinitely in culture. Until recently, the emphasis in the study of cell senescence has been focused on the accompanying intracellular processes. The focus of the attention has been on the irreversible growth arrest and two important physiological functions that rely on it: suppression of carcinogenesis due to the proliferation loss of damaged cells, and the acceleration of organism aging due to the deterioration of the tissue repair mechanism with age. However, the advances of the past years have revealed that senescent cells can impact the surrounding tissue microenvironment, and, thus, that the main consequences of senescence are not solely mediated by intracellular alterations. Recent studies have provided evidence that a pool of molecules secreted by senescent cells, including cytokines, chemokines, proteases and growth factors, termed the senescence-associated secretory phenotype (SASP), via autocrine/paracrine pathways can affect neighboring cells. Today it is clear that SASP functionally links cell senescence to various biological processes, such as tissue regeneration and remodeling, embryonic development, inflammation, and tumorigenesis. The present article aims to describe the "social" life of senescent cells: basically, SASP constitution, molecular mechanisms of its regulation, and its functional role.

Identification of new genes associated to senescent and tumorigenic phenotypes in mesenchymal stem cells

Although human mesenchymal stem cells (hMSCs) are a powerful tool for cell therapy, prolonged culture times result in replicative senescence or acquisition of tumorigenic features. To identify a molecular signature for senescence, we compared the transcriptome of senescent and young hMSCs with normal karyotype (hMSCs/n) and with a constitutional inversion of chromosome 3 (hMSC/inv). Senescent and young cells from both lineages showed differentially expressed genes (DEGs), with higher levels in senescent hMSCs/inv. Among the 30 DEGs in senescent hMSC/inv, 11 are new candidates for biomarkers of cellular senescence. The functional categories most represented in senescent hMSCs were related to cellular development, cell growth/proliferation, cell death, cell signaling/interaction, and cell movement. Mapping of DEGs onto biological networks revealed matrix metalloproteinase-1, thrombospondin 1, and epidermal growth factor acting as topological bottlenecks. In the comparison between senescent hMSCs/n and senescent hMSCs/inv, other functional annotations such as segregation of chromosomes, mitotic spindle formation, and mitosis and proliferation of tumor lines were most represented. We found that many genes categorized into functional annotations related to tumors in both comparisons, with relation to tumors being highest in senescent hMSCs/inv. The data presented here improves our understanding of the molecular mechanisms underlying the onset of cellular senescence as well as tumorigenesis.

Stem cell senescence drives age-attenuated induction of pituitary tumours in mouse models of paediatric craniopharyngioma

Senescent cells may promote tumour progression through the activation of a senescence-associated secretory phenotype (SASP), whether these cells are capable of initiating tumourigenesis in vivo is not known. Expression of oncogenic β-catenin in Sox2+ young adult pituitary stem cells leads to formation of clusters of stem cells and induction of tumours resembling human adamantinomatous craniopharyngioma (ACP), derived from Sox2- cells in a paracrine manner. Here, we uncover the mechanisms underlying this paracrine tumourigenesis. We show that expression of oncogenic β-catenin in Hesx1+ embryonic precursors also results in stem cell clusters and paracrine tumours. We reveal that human and mouse clusters are analogous and share a common signature of senescence and SASP. Finally, we show that mice with reduced senescence and SASP responses exhibit decreased tumour-inducing potential. Together, we provide evidence that senescence and a stem cell-associated SASP drive cell transformation and tumour initiation in vivo in an age-dependent fashion.

Blocking the utilization of glucose induces the switch from senescence to apoptosis in pseudolaric acid B-treated human lung cancer cells in vitro

Pseudolaric acid B (PAB), a diterpene acid isolated from the root bark of Pseudolarix kaempferi Gordon, exerts anti-tumor effects in several cancer cell lines. Our previous study showed that PAB mainly induced senescence via p53-p21 activation rather than apoptosis in suppression of the growth of human lung cancer A549 cells (p53 wild-type). In p53-null human lung cancer H1299 cells, however, PAB caused apoptosis without senescence. In this study we investigated what mechanism was responsible for the switch from senescence to apoptosis in PAB-treated human lung cancer cell lines. Senescent cells were examined by SA-β-gal staining. Glucose uptake and the apoptosis ratio were assessed using a FACScan flow cytometer. Commercial assay kits were used to measure the levels of ATP and lactate. Transfection of siRNA was used to knockdown the expression of p53 or p21. Western blot analysis was applied to measure the protein expression levels. In p53 wild-type A549 cells, PAB (20 μmol/L) caused senescence, and time-dependently increased glucose utilization; knockdown of p53 or p21 significantly decreased the uptake and metabolism of glucose but elevated PAB-induced apoptosis. Inhibition of glucose utilization using a glycolytic inhibitor 2-DG (1 mmol/L) significantly enhanced apoptosis induction. Similar results were observed in another p53 wild-type H460 cells treated with PAB. Opposite results were found in p53-null H1299 cells, where PAB time-dependently decreased glucose utilization, and induced only apoptosis. Our results demonstrate that PAB-induced senescence is associated with enhanced glucose utilization, and lower glucose utilization might contribute to apoptosis induction. Thus, blocking glucose utilization contributes to the switch from senescence to apoptosis, and p53 plays an important role in this process.

The Role of Kinase Modulators in Cellular Senescence for Use in Cancer Treatment

Recently, more than 30 small molecules and eight monoclonal antibodies that modulate kinase signaling have been approved for the treatment of several pathological conditions, including cancer, idiopathic pulmonary fibrosis, and rheumatoid arthritis. Among them, kinase modulators have been a primary focus for use in cancer treatment. Cellular senescence is believed to protect cells from tumorigenesis by irreversibly halting cell cycle progression and avoiding the growth of damaged cells and tissues. Senescence can also contribute to tumor suppression and be utilized as a mechanism by anti-cancer agents. Although the role of kinase modulators in cancer treatment and their effects on senescence in tumor development have been extensively studied, the relationship between kinase modulators for cancer treatment and senescence has not been fully discussed. In this review, we discuss the pro- and anti-tumorigenesis functions of senescence and summarize the key roles of kinase modulators in the regulation of senescence against tumors.

Iscador Qu inhibits doxorubicin-induced senescence of MCF7 cells

Chemotherapy in patients with inoperable or advanced breast cancer inevitably results in low-dose exposure of tumor-cell subset and senescence. Metabolically active senescent cells secrete multiple tumor promoting factors making their elimination a therapeutic priority. Viscum album is one of the most widely used alternative anti-cancer medicines facilitating chemotherapy tolerance of breast cancer patients. The aim of this study was to model and investigate how Viscum album extracts execute additive anti-tumor activity with low-dose Dox using ER + MCF7 breast cancer cells. We report that cotreatment of MCF7 with Viscum album and Dox abrogates G2/M cycle arrest replacing senescence with intrinsic apoptotic program. Mechanistically, this switch was associated with down-regulation of p21, p53/p73 as well as Erk1/2 and p38 activation. Our findings, therefore, identify a novel mechanistic axis of additive antitumor activity of Viscum album and low dose-Dox. In conclusion, ER + breast cancer patients may benefit from addition of Viscum album to low-dose Dox chemotherapy due to suppression of cancer cell senescence and induction of apoptosis.

Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging

The accumulation of irreparable cellular damage restricts healthspan after acute stress or natural aging. Senescent cells are thought to impair tissue function, and their genetic clearance can delay features of aging. Identifying how senescent cells avoid apoptosis allows for the prospective design of anti-senescence compounds to address whether homeostasis can also be restored. Here, we identify FOXO4 as a pivot in senescent cell viability. We designed a FOXO4 peptide that perturbs the FOXO4 interaction with p53. In senescent cells, this selectively causes p53 nuclear exclusion and cell-intrinsic apoptosis. Under conditions where it was well tolerated in vivo, this FOXO4 peptide neutralized doxorubicin-induced chemotoxicity. Moreover, it restored fitness, fur density, and renal function in both fast aging Xpd^TTD/TTD and naturally aged mice. Thus, therapeutic targeting of senescent cells is feasible under conditions where loss of health has already occurred, and in doing so tissue homeostasis can effectively be restored.

Senescence-Inflammatory Regulation of Reparative Cellular Reprogramming in Aging and Cancer

The inability of adult tissues to transitorily generate cells with functional stem cell-like properties is a major obstacle to tissue self-repair. Nuclear reprogramming-like phenomena that induce a transient acquisition of epigenetic plasticity and phenotype malleability may constitute a reparative route through which human tissues respond to injury, stress, and disease. However, tissue rejuvenation should involve not only the transient epigenetic reprogramming of differentiated cells, but also the committed re-acquisition of the original or alternative committed cell fate. Chronic or unrestrained epigenetic plasticity would drive aging phenotypes by impairing the repair or the replacement of damaged cells; such uncontrolled phenomena of in vivo reprogramming might also generate cancer-like cellular states. We herein propose that the ability of senescence-associated inflammatory signaling to regulate in vivo reprogramming cycles of tissue repair outlines a threshold model of aging and cancer. The degree of senescence/inflammation-associated deviation from the homeostatic state may delineate a type of thresholding algorithm distinguishing beneficial from deleterious effects of in vivo reprogramming. First, transient activation of NF-κB-related innate immunity and senescence-associated inflammatory components (e.g., IL-6) might facilitate reparative cellular reprogramming in response to acute inflammatory events. Second, para-inflammation switches might promote long-lasting but reversible refractoriness to reparative cellular reprogramming. Third, chronic senescence-associated inflammatory signaling might lock cells in highly plastic epigenetic states disabled for reparative differentiation. The consideration of a cellular reprogramming-centered view of epigenetic plasticity as a fundamental element of a tissue's capacity to undergo successful repair, aging degeneration or malignant transformation should provide challenging stochastic insights into the current deterministic genetic paradigm for most chronic diseases, thereby increasing the spectrum of therapeutic approaches for physiological aging and cancer.

Clonal cooperativity in heterogenous cancers

Tumor heterogeneity is a major obstacle to the development of effective therapies and is thus an important focus of cancer research. Genetic and epigenetic alterations, as well as altered tumor microenvironments, result in tumors made up of diverse subclones with different genetic and phenotypic characteristics. Intratumor heterogeneity enables competition, but also supports clonal cooperation via cell-cell contact or secretion of factors, resulting in enhanced tumor progression. Here, we summarize recent findings related to interclonal interactions within a tumor and the therapeutic implications of such interactions, with an emphasis on how different subclones collaborate with each other to promote proliferation, metastasis and therapy-resistance. Furthermore, we propose that disruption of clonal cooperation by targeting key factors (such as Wnt and Hedgehog, amongst others) can be an alternative approach to improving clinical outcomes.

The Regulation of Cellular Functions by the p53 Protein: Cellular Senescence

Transformed cells have properties that allow them to survive and proliferate inappropriately. These characteristics often arise as a result of mutations caused by DNA damage. p53 suppresses transformation by removing the proliferative or survival capacity of cells with DNA damage or inappropriate cell-cycle progression. Cellular senescence, marked by morphological and gene expression changes, is a critical component of p53-mediated tumor suppression. In response to stress, p53 can facilitate an arrest and senescence program in cells exposed to stresses such as DNA damage and oncogene activation, preventing transformation. Senescent cells are evident in precancerous adenoma-type lesions, whereas proliferating, malignant tumors have bypassed senescence, either by p53 mutation or inactivation of the p53 pathway by other means. Tumors that have retained wild-type p53 often show a p53-mediated senescence response to chemotherapy. This response is actually detrimental in some tumor types, as senescent cells can drive relapse by persisting and producing cytokines and chemokines through an acquired secretory phenotype.

Induction of metastasis, cancer stem cell phenotype, and oncogenic metabolism in cancer cells by ionizing radiation

Radiation therapy is one of the major tools of cancer treatment, and is widely used for a variety of malignant tumours. Radiotherapy causes DNA damage directly by ionization or indirectly via the generation of reactive oxygen species (ROS), thereby destroying cancer cells. However, ionizing radiation (IR) paradoxically promotes metastasis and invasion of cancer cells by inducing the epithelial-mesenchymal transition (EMT). Metastasis is a major obstacle to successful cancer therapy, and is closely linked to the rates of morbidity and mortality of many cancers. ROS have been shown to play important roles in mediating the biological effects of IR. ROS have been implicated in IR-induced EMT, via activation of several EMT transcription factors—including Snail, HIF-1, ZEB1, and STAT3—that are activated by signalling pathways, including those of TGF-β, Wnt, Hedgehog, Notch, G-CSF, EGFR/PI3K/Akt, and MAPK. Cancer cells that undergo EMT have been shown to acquire stemness and undergo metabolic changes, although these points are debated. IR is known to induce cancer stem cell (CSC) properties, including dedifferentiation and self-renewal, and to promote oncogenic metabolism by activating these EMT-inducing pathways. Much accumulated evidence has shown that metabolic alterations in cancer cells are closely associated with the EMT and CSC phenotypes; specifically, the IR-induced oncogenic metabolism seems to be required for acquisition of the EMT and CSC phenotypes. IR can also elicit various changes in the tumour microenvironment (TME) that may affect invasion and metastasis. EMT, CSC, and oncogenic metabolism are involved in radioresistance; targeting them may improve the efficacy of radiotherapy, preventing tumour recurrence and metastasis. This study focuses on the molecular mechanisms of IR-induced EMT, CSCs, oncogenic metabolism, and alterations in the TME. We discuss how IR-induced EMT/CSC/oncogenic metabolism may promote resistance to radiotherapy; we also review efforts to develop therapeutic approaches to eliminate these IR-induced adverse effects.

SASP: Tumor Suppressor or Promoter? Yes!

Cellular senescence is a permanent growth arrest in cells with damage or stress that could lead to transformation. Some tumor cells also undergo senescence in response to chemotherapy. Senescent cells secrete cytokines and other factors of the senescence-associated secretory phenotype (SASP) that contribute to tumor suppression by enforcing arrest and recruiting immune cells that remove these damaged or oncogene-expressing cells from organisms. However, some cells can develop a SASP comprising factors that are immunosuppressive and protumorigenic by paracrine mechanisms. Likewise, the SASP in treated cancers can either contribute to durable responses or drive relapse. Here, we discuss the studies that have demonstrated a complex and often conflicting role for the SASP in tumorigenesis and treatment response.

Whole Chromosome Instability induces senescence and promotes SASP

Age-related accumulation of ploidy changes is associated with decreased expression of genes controlling chromosome segregation and cohesin functions. To determine the consequences of whole chromosome instability (W-CIN) we down-regulated the spindle assembly checkpoint component BUB1 and the mitotic cohesin SMC1A, and used four-color-interphase-FISH coupled with BrdU incorporation and analyses of senescence features to reveal the fate of W-CIN cells. We observed significant correlations between levels of not-diploid cells and senescence-associated features (SAFs). W-CIN induced DNA double strand breaks and elevated oxidative stress, but caused low apoptosis. SAFs of W-CIN cells were remarkably similar to those induced by replicative senescence but occurred in only 13 days versus 4 months. Cultures enriched with not-diploid cells acquired a senescence-associated secretory phenotype (SASP) characterized by IL1B, CXCL8, CCL2, TNF, CCL27 and other pro-inflammatory factors including a novel SASP component CLEC11A. These findings suggest that W-CIN triggers premature senescence, presumably to prevent the propagation of cells with an abnormal DNA content. Cells deviating from diploidy have the ability to communicate with their microenvironment by secretion of an array of signaling factors. Our results suggest that aneuploid cells that accumulate during aging in some mammalian tissues potentially contribute to age-related pathologies and inflammation through SASP secretion.

HIF-1α and rapamycin act as gerosuppressant in multiple myeloma cells upon genotoxic stress

Multiple myeloma (MM) is still an incurable hematological malignancy. Despite recent progress due to new anti-myeloma agents, the pathology is characterized by a high frequency of de novo or acquired resistance. Delineating the mechanisms of MM resistance is essential for therapeutic advances. We previously showed that long-term genotoxic stress induces the establishment of a senescence-associated secretory phenotype, a pro-inflammatory response that favors the emergence of cells with cancer stem-like properties. Here, we studied the short-term response of MM cells following treatment with various DNA damaging agents such as the energetic C-ion irradiation. MM cells are highly resistant to all treatments and do not enter apoptosis after they arrest cycling at the G2 phase. Although the DNA damage response pathway was activated, DNA breaks remained chronically in damaged MM cells. We found, using a transcriptomic approach that RAD50, a major DNA repair gene was downregulated early after genotoxic stress. In two gerosuppression situations: induction of hypoxia and inhibition of the mammalian target of rapamycin (mTOR) pathway, we observed, after the treatment with a DNA damaging agent, a normalization of RAD50 expression concomitant with the absence of cell cycle arrest. We propose that combining inhibitors of mTOR with genotoxic agents could avoid MM cells to senesce and secrete pro-inflammatory factors responsible for cancer stem-like cell emergence and, in turn, relapse of MM patients.