Senescence as biologic endpoint following pharmacological targeting of receptor tyrosine kinases in cancer

Minimal residual disease in EGFR-mutant non-small-cell lung cancer

Targeted therapy with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) is an effective treatment for EGFR-mutant non-small-cell lung cancer (NSCLC), however most patients invariably relapse after a period of minimal residual disease (MRD). This mini-review explores the mechanistic pathways leading to tumour dormancy, cellular senescence and epigenetic changes involving YAP/TEAD activation. We describe the various approaches of utilising TKIs in combination with agents to intensify initial depth of response, enhance apoptosis and target senescence-like dormancy. This mini-review will also highlight the potential novel therapies under development targeting MRD to improve outcomes for patients with EGFR-mutant NSCLC.

Targeting cellular senescence in cancer by plant secondary metabolites: A systematic review

Senescence suppresses tumor growth, while also developing a tumorigenic state in the nearby cells that is mediated by senescence-associated secretory phenotypes (SASPs). The dual function of cellular senescence stresses the need for identifying multi-targeted agents directed towards the promotion of cell senescence in cancer cells and suppression of the secretion of pro-tumorigenic signaling mediators in neighboring cells. Natural secondary metabolites have shown favorable anticancer responses in recent decades, as some have been found to target the senescence-associated mediators and pathways. Furthermore, phenolic compounds and polyphenols, terpenes and terpenoids, alkaloids, and sulfur-containing compounds have shown to be promising anticancer agents through the regulation of paracrine and autocrine pathways. Plant secondary metabolites are potential regulators of SASPs factors that suppress tumor growth through paracrine mediators, including growth factors, cytokines, extracellular matrix components/enzymes, and proteases. On the other hand, ataxia-telangiectasia mutated, ataxia-telangiectasia and Rad3-related, extracellular signal-regulated kinase/mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin, nuclear factor-κB, Janus kinase/signal transducer and activator of transcription, and receptor tyrosine kinase-associated mediators are main targets of candidate phytochemicals in the autocrine senescence pathway. Such a regulatory role of phytochemicals on senescence-associated pathways are associated with cell cycle arrest and the attenuation of apoptotic/inflammatory/oxidative stress pathways. The current systematic review highlights the critical roles of natural secondary metabolites in the attenuation of autocrine and paracrine cellular senescence pathways, while also elucidating the chemopreventive and chemotherapeutic capabilities of these compounds. Additionally, we discuss current challenges, limitations, and future research indications.

The Paradoxical Role of Cellular Senescence in Cancer

Cellular senescence occurs in proliferating cells as a consequence of various triggers including telomere shortening, DNA damage, and inappropriate expression of oncogenes. The senescent state is accompanied by failure to reenter the cell cycle under mitotic stimulation, resistance to cell death and enhanced secretory phenotype. A growing number of studies have convincingly demonstrated a paradoxical role for spontaneous senescence and therapy-induced senescence (TIS), that senescence may involve both cancer prevention and cancer aggressiveness. Cellular senescence was initially described as a physiological suppressor mechanism of tumor cells, because cancer development requires cell proliferation. However, there is growing evidence that senescent cells may contribute to oncogenesis, partly in a senescence-associated secretory phenotype (SASP)-dependent manner. On the one hand, SASP prevents cell division and promotes immune clearance of damaged cells, thereby avoiding tumor development. On the other hand, SASP contributes to tumor progression and relapse through creating an immunosuppressive environment. In this review, we performed a review to summarize both bright and dark sides of senescence in cancer, and the strategies to handle senescence in cancer therapy were also discussed.

Partial recovery of senescence in circulating follicular helper T cells after Dasatinib treatment

Cellular senescence is an irreversible arrest of cell proliferation triggered by different stimuli, including DNA damage, telomere shortening and oncogenic stress. Senescent cells, by releasing the senescence-associated-secretory-phenotype (SASP), contribute to various diseases pathogenesis. Human atherosclerotic plaque contains cells with multiple markers of senescence that associate with disease severity. We characterized the frequency of senescent cTfh cells and genes expressions before and after treatment with Dasatinib in patients with different degrees of stenosis. Twelve high (≥50%), and twelve low (<50%) stenosis patients and six healthy controls were enrolled. The percentage of senescent CD3⁺CD4⁺CXCR5⁺CD153⁺CD57⁺ cells was significantly decreased in Dasatinib treated cells from individuals with low and high stenosis (P = 0.0007 and P = 0.0002, respectively). However, the frequency of total lymphocytes, CD3⁺ and CD4⁺ T cells were not significantly different between the groups before and after treatment. The expression levels of P53 (P = 0.0003 and P = 0.0001), P16 (P = 0.0005 and P = 0.0002), p21 (P = 0.0002 and P < 0.0001), SENEX (P = 0.0005 and P < 0.0001) and BCL-2 (P = 0.0005 and P = 0.0002) were decreased in PBMCs of low and high stenosis groups after treatment with Dasatinib, respectively. The percentage of senescent cTfh cells positively correlated with cholesterol (P = 0.034; r = 0.671), C-reactive protein (CRP) (P = 0.029; r = 0.707), Erythrocyte sedimentation rate (ESR) levels (P = 0.030; r = 0.598) and neutrophil counts (P = 0.021; r = 0.799) in patients with high stenosis. The decreased frequency of senescent cTfh cells and the expression levels of senescence genes after Dasatinib treatment in patients with atherosclerosis suggest a role for Dasatinib in partial clearance or rejuvenation of senescent cTfh cells, which may decrease inflammatory mediators and attenuate disease progression.

Cancer Response to Therapy-Induced Senescence: A Matter of Dose and Timing

Cellular senescence participates to fundamental processes like tissue remodeling in embryo development, wound healing and inhibition of preneoplastic cell growth. Most senescent cells display common hallmarks, among which the most characteristic is a permanent (or long lasting) arrest of cell division. However, upon senescence, different cell types acquire distinct phenotypes, which also depend on the specific inducing stimuli. Senescent cells are metabolically active and secrete a collection of growth factors, cytokines, proteases, and matrix-remodeling proteins collectively defined as senescence-associated secretory phenotype, SASP. Through SASP, senescent cells modify their microenvironment and engage in a dynamic dialog with neighbor cells. Senescence of neoplastic cells, at least temporarily, reduces tumor expansion, but SASP of senescent cancer cells as well as SASP of senescent stromal cells in the tumor microenvironment may promote the growth of more aggressive cancer subclones. Here, we will review recent data on the mechanisms and the consequences of cancer-therapy induced senescence, enlightening the potentiality and the risk of senescence inducing treatments.

Eco-oncology: Applying ecological principles to understand and manage cancer

Cancer is a disease of single cells that expresses itself at the population level. The striking similarities between initiation and growth of tumors and dynamics of biological populations, and between metastasis and ecological invasion and community dynamics suggest that oncology can benefit from an ecological perspective to improve our understanding of cancer biology. Tumors can be viewed as complex, adaptive, and evolving systems as they are spatially and temporally heterogeneous, continually interacting with each other and with the microenvironment and evolving to increase the fitness of the cancer cells. We argue that an eco-evolutionary perspective is essential to understand cancer biology better. Furthermore, we suggest that ecologically informed therapeutic approaches that combine standard of care treatments with strategies aimed at decreasing the evolutionary potential and fitness of neoplastic cells, such as disrupting cell-to-cell communication and cooperation, and preventing successful colonization of distant organs by migrating cancer cells, may be effective in managing cancer as a chronic condition.

Stem Cell Plasticity and Dormancy in the Development of Cancer Therapy Resistance

Cancer treatment with either standard chemotherapy or targeted agents often results in the emergence of drug-refractory cell populations, ultimately leading to therapy failure. The biological features of drug resistant cells are largely overlapping with those of cancer stem cells and include heterogeneity, plasticity, self-renewal ability, and tumor-initiating capacity. Moreover, drug resistance is usually characterized by a suppression of proliferation that can manifest as quiescence, dormancy, senescence, or proliferative slowdown. Alterations in key cellular pathways such as autophagy, unfolded protein response or redox signaling, as well as metabolic adaptations also contribute to the establishment of drug resistance, thus representing attractive therapeutic targets. Moreover, a complex interplay of drug resistant cells with the micro/macroenvironment and with the immune system plays a key role in dictating and maintaining the resistant phenotype. Recent studies have challenged traditional views of cancer drug resistance providing innovative perspectives, establishing new connections between drug resistant cells and their environment and indicating unexpected therapeutic strategies. In this review we discuss recent advancements in understanding the mechanisms underlying drug resistance and we report novel targeting agents able to overcome the drug resistant status, with particular focus on strategies directed against dormant cells. Research on drug resistant cancer cells will take us one step forward toward the development of novel treatment approaches and the improvement of relapse-free survival in solid and hematological cancer patients.

Early induction of senescence and immortalization in PGC-1α-deficient mouse embryonic fibroblasts

AIMS

Oxidative stress is known to induce early replicative senescence. Senescence has been proposed to work as a barrier to immortalization and tumor development. Here, we aimed to evaluate the impact of the loss of peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α), a master regulator of oxidative metabolism and mitochondrial reactive oxygen species (ROS) generation, on replicative senescence and immortalization in mouse embryonic fibroblasts (MEFs).

RESULTS

We found that primary MEFs lacking PGC-1α showed higher levels of ROS than wild-type MEFs at all cell passages tested. The elevated production of ROS was associated with higher levels of oxidative DNA damage and the increased formation of DNA double-strand breaks. Evaluation of the induction of DNA repair systems in response to γ-radiation indicated that the loss of PGC-1α also resulted in a small but significant reduction in their activity. DNA damage induced the early activation of senescence markers, including an increase in the number of β-galactosidase-positive cells, the induction of p53 phosphorylation, and the increase in p16 and p19 protein. These changes were, however, not sufficient to reduce proliferation rates of PGC-1α-deficient MEFs at any cell passage tested. Moreover, PGC-1α-deficient cells escaped replicative senescence.

INNOVATION & CONCLUSION

PGC-1α plays an important role in the control of cellular senescence and immortalization.