Dual Identity of Senescence: From Tumor Barrier to Plastic States
Tumor Suppressive Functions of Senescence: Mechanisms of the Classical Defensive Barrier
Figure 1. Mechanism of senescence-associated secretory phenotype (SASP)[1].
Cellular senescence suppresses tumorigenesis primarily through two complementary mechanisms: irreversible
cell-cycle arrest and immune-mediated clearance of damaged cells.
The Cell-Cycle Arrest Barrier
Senescence is commonly triggered by persistent cellular stress, particularly DNA damage induced by from
oncogene activation,
replication stress, or genotoxic insults. In response, the
p53/p21 and
p16INK4a/RB signaling pathways cooperatively
establish a stable cell-cycle arrest, thereby preventing the expansion of premalignant cells.
Importantly, senescence-associated markers such as p16INK4a are frequently detected in premalignant lesions
but are often absent in fully developed malignancies, suggesting that bypassing senescence is a prerequisite
for malignant transformation.
Immune Surveillance and Clearance
Beyond intrinsic growth arrest, senescent cells actively communicate with the immune system through the
secretion of
SASP factors. In tumor-suppressive contexts, SASP components—often regulated by pathways such as
cGAS-
STING—facilitate the recruitment and activation of immune cells
including macrophages,
natural killer (NK) cells and CD4⁺ T cells.
This process, termed "senescence surveillance", promotes the immune-mediated elimination of senescent
premalignant cells and serves as an essential extrinsic defense mechanism against tumor initiation.
Collectively, cellular senescence functions as a potent anticancer barrier by coupling durable proliferative
arrest with immune-mediated clearance mechanisms during the early stages of tumorigenesis.
"Non-Terminal" Nature of Senescence: Redefining Cellular Plasticity
The traditional view of senescence describes it as an irreversible endpoint of cellular proliferation.
However, accumulating evidence now indicates that senescence represents a dynamic and potentially reversible
cellular state characterized by substantial phenotypic and functional plasticity[2].
Reversibility and Senescence Escape
Recent studies challenge the long-standing assumption that senescence is strictly irreversible. Under
specific conditions, therapy-induced senescent cells may re-enter the cell cycle and regain proliferative
capacity. For example, in B-cell lymphoma models, activation of
WNT signaling has been shown to promote
senescence escape and tumor recurrence.
These findings suggest that senescence should be viewed as a regulated cellular program rather than a
definitive terminal fate[3].
Functional Plasticity of SASP
The biological effects of senescent cells are largely determined by the composition of the SASP, which
itself is highly heterogeneous
and dynamically regulated. Pharmacological interventions, including combinations such as Docetaxel (
HY-B0011) and Adapalene (
HY-B0091)
or inhibition of the
JAK-
STAT3 pathway, have
been shown to reprogram a protumorigenic SASP into a more immunostimulatory phenotype.
Such observations highlight the context-dependent nature of senescent cells function and underscore the
therapeutic potential of SASP modulation[4].
Senescence as a Transitional State Toward Stemness
Emerging evidence further suggests that senescence-associated epigenetic remodeling and metabolic
reprogramming may facilitate the acquisition of stem cell-like properties. Senescent cells, particularly
those that undergo senescence escape, can exhibit enhanced cellular plasticity, tumor-initiating capacity,
and therapy resistance.
Therefore, senescence may function not only as a barrier to tumorigenesis but also as a transitional state
that contributes to tumor evolution under certain pathological conditions.
SASP-Driven Tumor Progression: Microenvironmental and Immune Reprogramming
The Biphasic Effects of SASP
Figure 2. The positive and negative effects of aging on tumors and the tumor microenvironment[5].
Senescent cells exert complex and context-dependent effects within the TME, largely through the secretion
of SASP factors. Consequently, cellular senescence is increasingly recognized as a "double-edged sword" in
cancer biology.
On one hand, senescence can suppress tumor progression by inducing stable growth arrest, promoting immune
surveillance and transiently remodeling the microenvironment in a manner that facilitates antitumor
immunity and therapeutic delivery. On the other hand, the persistent accumulation of senescent cells may
ultimately promote tumor progression. Chronic SASP signaling can educate cancer-associated fibroblasts
(CAFs), stimulate angiogenesis and epithelial-mesenchymal transition (EMT), and recruit myeloid-derived
suppressor cells (MDSC), thereby establishing a pro-tumorigenic microenvironment that supports tumor
growth, metastasis and therapy resistance.
Importantly, the biological effects of SASP are highly time-dependent. During the early stages of
tumorigenesis, SASP predominantly facilitates immune-mediated clearance of damaged cells. However,
prolonged SASP exposure gradually shifts the microenvironment toward chronic inflammation and immune
suppression, ultimately promoting tumor progression and immune evasion.
Although the underlying mechanisms remain incompletely understood, accumulating evidence suggests that
SASP-mediated remodeling of the immune microenvironment represents a critical driver of the shift from
immune surveillance to immune escape[6].
Recruitment and Activation of T cells
SASP factors activate and recruit CD4⁺ T cells by stimulating endothelial cells through the
NF‑κB signaling pathway and modulating STAT1 cascades. Together, these mechanisms
drive effective immune surveillance and the subsequent clearance of senescent cells. For instance,
drug‑induced senescence profoundly enhances T cell infiltration in pancreatic cancer models.
Activation of Innate Immune Clearance
Senescent cells also activate innate immune responses by recruiting macrophages, neutrophils, and NK
cells. In models of liver fibrosis and hepatocellular carcinoma, p53‑induced senescent cells promote the
immune-mediated clearance of damaged or transformed cells through phagocytosis and direct cytotoxicity.
Adaptive Immunity Is not Absolutely Required
Notably, p53‑mediated tumor regression has been observed even in animal models lacking functional B and T
cells, suggesting that immune responses alone can mediate efficient clearance of senescent tumor cells
under certain conditions.
Enhancement of Antigen Presentation
Recent studies further demonstrate that
IFN‑γ synergizes with SASP to
enhance antigen presentation in senescent tumor cells. This process increases immune recognition and
facilitates the elimination of senescent cells by cytotoxic immune system.
SASP is composed of a broad spectrum of bioactive molecules, including
IL‑6, IL‑8,
TGF‑β,
VEGF and
MMPs, and its composition dynamically
evolves over time and across tissue contexts.
Three Major Functional Axes Driven by SASP
SASP represents the central mediator through which senescent cells reshape the TME. Its multifaceted
effects can be categorized into three interconnected functional axes[6,7].
Immune Regulatory Axis
The impact of SASP on immune responses exhibits pronounced temporal duality. During the early phase, SASP
promotes immune surveillance by recruiting and activating NK cells, macrophages, and cytotoxic T cells
through the secretion of inflammatory cytokines and chemokines. Senescent cells may also enhance immune
recognition by upregulating surface molecules such as MHC-I.
However, chronic SASP exposure progressively remodels the immune microenvironment toward an
immunosuppressive state. Persistent inflammatory signaling promotes the accumulation of MDSCs, regulatory
T cells (Tregs), and M2-type macrophages, while simultaneously driving effector T cell exhaustion.
Collectively, these changes establish a permissive niche for tumor immune evasion.
Inflammatory Tumor-Promoting Axis
SASP constitutes a sustained source of inflammatory signaling that directly contributes to malignant
progression. Senescent stromal cells, including fibroblasts and M2-type macrophages, secrete high levels
of IL-6, IL-8, MMPs, and extracellular vesicles enriched with oncogenic miRNAs.
These factors cooperatively activate major oncogenic pathways such as STAT3,
MAPK, and
PI3K/
AKT in
neighboring tumor cells, thereby promoting proliferation, invasion, epithelial-mesenchymal transition,
stemness acquisition, and therapeutic resistance.
This inflammatory axis represents one of the principal mechanisms through which senescence transitions
from a tumor-suppressive process to a tumor-promoting program.
Stroma and TME Remodeling Axis
Beyond immune regulation, SASP profoundly alters the structural and biochemical properties of the TME.
Through the secretion of VEGF and related angiogenic factors, senescent cells promote aberrant
neovascularization. Simultaneously, MMP-mediated extracellular matrix (ECM) degradation and remodeling
facilitate tumor invasion and dissemination.
SASP also activates CAFs, leading to ECM fibrosis, tissue stiffening, and the sustained production of
additional tumor-promoting factors. These processes generate a self-reinforcing feedback loop that
continuously supports tumor growth and metastatic progression.
Taken together, SASP acts as a dynamic "architect" of the TME by coordinating immune remodeling, chronic
inflammation, and stromal reorganization.
Senescence-Targeted Therapies: From Clearance to Precision Modulation
Targeting Senescent Cancer Cells with Senolytics
Selective elimination of senescent cells within the TME has emerged as a promising therapeutic strategy in
cancer treatment. Senolytic therapies primarily function by disrupting the anti-apoptotic or pro-survival
pathways upon which senescent cells depend.
Among the most extensively studied senolytic agents are inhibitors of the
BCL-2 family. For example, Navitoclax (
HY-10087)
effectively induces
apoptosis in senescent cells by inhibiting
BCL-XL-mediated survival signaling. However,
its clinical application is limited by significant severe off-target toxicities, particularly
thrombocytopenia.
To improve specificity and reduce systemic toxicity, several next-generation approaches have been
developed,
including SA-β-galactosidase-activated prodrugs such as Nav-Gal and
PROTAC-based strategies designed to selectively
degrade BCL-XL (e.g.,
ARV-825).
Additional senolytic approaches—including Dasatinib (
HY-10181) plus
Quercetin (
HY-18085), FOXO4-DRI peptides (
HY-P4157),
cardiotonic agents exploiting membrane depolarization vulnerability and
mTOR inhibitors suppressing SASP—have also
demonstrated substantial senescence-clearing activity in preclinical studies.
Figure 3. Targeting senescent cells with senolytic agents[8].
Importantly, senolytics frequently exhibit synergistic anti-tumor potential when combined with
conventional radiotherapy or chemotherapy. Nevertheless, their clinical translation remains challenging
due to issues including narrow therapeutic windows, genotype-dependent efficacy, and the broad biological
functions of many targeted pathways.
Immune-Mediated Clearance of Senescent Cells
Figure 4. Regulation of the immune system by aging[9].
The immune system plays a central role in regulating the accumulation and clearance of senescent cells. In
anti-tumor contexts,
SASP factors such as
CCL2, CCL5, CXCL1 and IL-6 recruit and activate NK
cells and CD8⁺ T cells. Senescent cells may further
enhance their immunogenicity through upregulation of
MHC-I molecules or the
expression of neoantigens generated by aberrant
splicing events.
In addition, SASP-mediated vascular remodeling can increase vascular permeability and improve the
intratumoral delivery of
chemotherapeutic agents, thereby enhancing the efficacy of immune checkpoint blockade therapies such as
anti-PD-1 treatment.
Conversely, persistent SASP signaling can also drive immunosuppression. For example, IL-6-mediated
recruitment of MDSCs suppresses lymphocyte activity, while MMPs may facilitate immune escape by cleaving
activating ligands from the surface of NK cells.
To overcome these limitations, emerging immunotherapeutic strategies increasingly focus on targeting
senescence-associated surface antigens. Examples include uPAR-directed CAR-T cells and B2M-targeting
antibody-drug conjugates (
ADC), both of which have demonstrated encouraging
potential for selectively eliminating senescent cancer cells and overcoming therapy resistance.
One-Two Punch Strategy: A Mainstream Combination Framework for Tumor Therapy
Figure 5. The relationship between tumor therapy and cell aging[9].
While effectively eliminating tumor cells, cancer therapies often carry the side effect of inducing
senescence in normal cells, leading to various treatment-related complications. The above figure
systematically outlines the core mechanisms by which three major cancer therapies-chemotherapy,
radiotherapy, and immunotherapy-induce cellular senescence, along with corresponding intervention
strategies, offering critical insights into understanding therapy-induced senescence and developing
mitigation approaches.
Induction of Senescence
The first step involves inducing senescence in tumor cells using chemotherapy, radiotherapy,
CDK4/6 inhibitors, or oncogene activation. These interventions trigger persistent
DNA damage responses that activate the p53-p21 and p16INK4a-RB pathways, ultimately establishing stable
proliferative arrest.
This phase exploits the intrinsic tumor-suppressive function of senescence by directly limiting tumor cell
proliferation.
Elimination or Suppression of Senescence-Associated Effects
Because long-term persistence of senescent cells may promote inflammation, immunosuppression, and therapy
resistance through SASP secretion, the second step aims to selectively eliminate senescent cells or
suppress detrimental SASP signaling.
Current strategies include the use of senolytic agents as well as SASP inhibitors targeting key pathways
such as cGAS-STING,
ASK1-p38 signaling.
The major advantage of this strategy lies in its ability to preserve the initial antitumor growth-arrest
effect while simultaneously minimizing the pro-tumorigenic consequences of chronic senescence.
Furthermore, by alleviating immunosuppressive remodeling and reversing T-cell exhaustion, this strategy
may improve responsiveness to immune checkpoint blockade therapies[2,9].
Frontier Trends: Precision Senotherapy
The Senescence Identification Tool (SIT), which integrates senescence-associated and cell cycle‑related
gene signatures, enables the detection of heterogeneous intratumoral senescent cells (SnCs) in
vivo. Importantly, SIT has revealed substantial diversity in SASP composition and survival
mechanisms among SnC subsets, thereby supporting the development of more targeted senotherapy.
Additional computational tools, including SENCAN, SenMayo, and DeepScence, further facilitate the
identification and characterization of senescent cells across multiple tissue contexts and sequencing
platforms. Collectively, these approaches are beginning to clarify the context-specific roles of
senescence in tumor progression and therapeutic resistance[2].
Artificial Intelligence for Identifying Cellular Senescence in Tumors
Artificial intelligence (AI) recognizes senescent cells through morphological, chromatin and
microenvironmental features. Combined with biomarkers and computational modeling, these technologies
provide scalable and potentially noninvasive approaches for senescence detection.
Figure 6. Machine learning and artificial intelligence in senescence research[2].
High-content imaging platforms integrated with machine learning algorithms—including SAMPs, cascaded R-CNN
and Deep-SeSMo—have substantially improved the automation and quantitative analysis of conventional
senescence assays such as SA-β-Gal staining.
Deep learning models can additionally evaluate senescence-associated nuclear traits to predict cancer risk
with superior accuracy over traditional models. Meanwhile, bioinformatic tools like SenPred and DNAmSen
identify senescent cells based on transcriptomic and DNA methylation signatures across multiple tissue
types[2].
Together, these advances provide powerful tools for studying senescence heterogeneity, tumor
microenvironment remodeling, and therapeutic responses.
Summary
Cell senescence is increasingly recognized as a dynamic and context-dependent process in cancer biology.
While senescence
initially suppresses tumorigenesis by enforcing stable cell-cycle arrest and promoting immune clearance, the
persistent accumulation of senescent cells can subsequently drive chronic inflammation, immune suppression,
and tumor microenvironment remodeling through SASP signaling.
Importantly, the heterogeneity and plasticity of senescent cells further contribute to tumor progression,
therapeutic resistance, and disease recurrence under certain conditions. Therefore, future therapeutic
strategies should move beyond simply inducing or eliminating senescence and instead focus on precisely
modulating senescent states and their downstream effects.
With the continued development of senolytics, senomorphics, and senescence-targeted immunotherapies, precise
senotherapy holds considerable promise for improving cancer treatment and reshaping the tumor
microenvironment.
Recommended Products targeting SASP components in senescence
| Product Name |
Cat. No. |
Category |
Mechanism of action |
| Tocilizumab |
HY-P9917 |
Monoclonal antibody |
Blocks IL-6 binding to IL-6R, inhibiting JAK/STAT3 signaling and SASP amplification |
| Ruxolitinib |
HY-50856 |
JAK inhibitor |
Inhibits JAK/STAT signaling, reducing SASP cytokine transcription |
| Etanercept |
HY-108847 |
TNF-α inhibitor |
Soluble receptor decoy for TNF-α, blocks TNF-induced NF-κB activation |
| Anakinra |
HY-108841 |
IL-1 receptor antagonist |
Competitive inhibition of IL-1R signaling, reducing inflammation and senescence signals |
| Maraviroc |
HY-13004 |
CCR5 antagonist |
Blocks CCR5-mediated recruitment of immune cells, limiting paracrine senescence |
| Navitoclax |
HY-10087 |
Senolytic (Bcl-2 inhibitor) |
Induces apoptosis in senescent cells, reducing SASP-producing cell burden |
| Rapamycin |
HY-10219 |
mTOR inhibitor |
Inhibits mTORC1, a key regulator of SASP production and translation |
| Metformin |
HY-B0627 |
AMPK activator |
Activates AMPK,
suppresses NF-κB
signaling, indirectly
reducing SASP |
Note: MCE can provide products for research use only. We do not sell to patients.
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Dual Identity of Senescence: From Tumor Barrier to Plastic States
SASP-Driven Tumor Progression: Microenvironmental and Immune
Reprogramming
Senescence-Targeted Therapies: From Clearance to Precision
Modulation
