Cellular Senescence and Senolytic Agents: Recent Updates on Their Role and Applications.

Cellular senescence, an eternal condition of cell cycle arrest due to cellular stressors, is a sign of aging. Senescent cells (SCs) build up in tissues as they age, impairing their ability to repair themselves by causing the cell cycle to seize in progenitor cells and producing proinflammatory and the senescence-associated secretory phenotype (SASP) or matrix-degrading molecules. SASP aids in the emergence of several age-related diseases. Genetic studies have shown that removing SCs can delay aging and prolong life. Senolytics are small molecules designed to treat numerous age-related disorders can selectively kill SCs. A detailed discussion on senolytics and their potential as therapeutics to treat neuro-disorder and slow down aging is described herein. Emerging natural products, such as quercetin, dasatinib, fisetin, piperlongumine, and curcumin, have recently been reported to be effective senolytic agents, and some structurally modified analogue of these have also been explored for better selectivity and efficacy in animal models. These showed significant potential in clinical studies and could be developed as senolytic drugs in the future.

Use of the senolytics dasatinib and quercetin for prevention of pelvic organ prolapse in a mouse animal model.

OBJECTIVE: Senolytic agents have the potential to target age-related pathology associated with cellular senescence and reduce senescent cell activity in several disease processes. We utilized a mouse model of pelvic organ prolapse, Fibulin-5 knockout (Fbln-5-/-) mice, to assess the ability of dasatinib and quercetin (D+Q) to prevent development of prolapse. METHODS: Four-week-old female Fbln-5-/- (n=63) and wild-type (WT) mice (n=54) were assigned to control (vehicle injection) or treatment (D = 5 mg/kg, Q = 50 mg/kg) groups. Weekly oral gavage injections were administered from weeks 4-8 of life. Pelvic organ prolapse quantification system measurements were obtained weekly. Vaginal tissue was harvested at 10, 12 and 20 weeks. Tissue analysis included immunostaining for cell cycle inhibitors, multiplex cytokine analysis, senescence-associated-ß-galactosidase (SA-ß-Gal) and histologic analysis of extracellular matrix proteins. RESULTS: Perineal body length was significantly longer in Fbln-5-/- treatment mice at 20 weeks. Expression of p16 and p53 was decreased in Fbln-5-/- treatment mice compared to controls (4.0% vs. 26.7%, p=0.0124 and 2.9% vs. 16.8%, p=0.272) at 20 weeks. Expression of SA-ß-Gal and senescence-associated cytokines did not vary significantly between groups. At 20 weeks, vaginal tissue elastin content in Fbln-5-/- treatment mice increased compared to controls (1.04% vs. 0.84%, p=0.999). CONCLUSIONS: D+Q injections did not result in clinically significant differences in prolapse development but did demonstrate decreased expression of cellular senescence markers in Fbln-5-/- mice. This suggests senolytic agents may mitigate contributions of cellular senescence to tissue dysfunction associated with prolapse. Further studies are needed to confirm ideal timing, dosage, and route of senolytics in prevention of prolapse.

Chemo-Senolytic Therapeutic Potential against Angiosarcoma.

Angiosarcoma is an aggressive soft-tissue sarcoma with a poor prognosis. Chemotherapy for this cancer typically employs paclitaxel, a taxane (genotoxic drug), although it has a limited effect owing to chemoresistance to prolonged treatment. In this study, we examine an alternative angiosarcoma treatment approach that combines chemotherapeutic and senolytic agents. We find that the chemotherapeutic drugs cisplatin and paclitaxel efficiently induce senescence in angiosarcoma cells. Subsequent treatment with the senolytic agent ABT-263 eliminates senescent cells by activating the apoptotic pathway. In addition, expression analysis indicates that senescence-associated secretory phenotype genes are activated in senescent angiosarcoma cells and that ABT-263 treatment downregulates IFN-I pathway genes in senescent cells. Moreover, we show that cisplatin treatment alone requires high doses to remove angiosarcoma cells. In contrast, lower doses of cisplatin are sufficient to induce senescence, followed by the elimination of senescent cells by the senolytic treatment. This study sheds light on a potential therapeutic strategy against angiosarcoma by combining a relatively low dose of cisplatin with the ABT-263 senolytic agent, which can help ease the deleterious side effects of chemotherapy.

Radiotherapy-Induced Astrocyte Senescence Promotes an Immunosuppressive Microenvironment in Glioblastoma to Facilitate Tumor Regrowth.

Accumulating evidence suggests that changes in the tumor microenvironment caused by radiotherapy are closely related to the recurrence of glioma. However, the mechanisms by which such radiation-induced changes are involved in tumor regrowth have not yet been fully investigated. In the present study, how cranial irradiation-induced senescence in non-neoplastic brain cells contributes to glioma progression is explored. It is observed that senescent brain cells facilitated tumor regrowth by enhancing the peripheral recruitment of myeloid inflammatory cells in glioblastoma. Further, it is identified that astrocytes are one of the most susceptible senescent populations and that they promoted chemokine secretion in glioma cells via the senescence-associated secretory phenotype. By using senolytic agents after radiotherapy to eliminate these senescent cells substantially prolonged survival time in preclinical models. The findings suggest the tumor-promoting role of senescent astrocytes in the irradiated glioma microenvironment and emphasize the translational relevance of senolytic agents for enhancing the efficacy of radiotherapy in gliomas.

Therapeutic strategies targeting cellular senescence for cancer and other diseases.

Cellular senescence occurs in response to endogenous or exogenous stresses and is characterized by stable cell cycle arrest, alterations in nuclear morphology and secretion of proinflammatory factors, referred to as the senescence-associated secretory phenotype (SASP). An increase of senescent cells is associated with the development of several types of cancer and aging-related diseases. Therefore, senolytic agents that selectively remove senescent cells may offer opportunities for developing new therapeutic strategies against such cancers and aging-related diseases. This review outlines senescence inducers and the general characteristics of senescent cells. We also discuss the involvement of senescent cells in certain cancers and diseases. Finally, we describe a series of senolytic agents and their utilization in therapeutic strategies.

Cellular senescence in skin-related research: Targeted signaling pathways and naturally occurring therapeutic agents.

Despite the growing interest by researchers into cellular senescence, a hallmark of cellular aging, its role in human skin remains equivocal. The skin is the largest and most accessible human organ, reacting to the external and internal environment. Hence, it is an organ of choice to investigate cellular senescence and to target root-cause aging processes using senolytic and senomorphic agents, including naturally occurring plant-based derivatives. This review presents different aspects of skin cellular senescence, from physiology to pathology and signaling pathways. Cellular senescence can have both beneficial and detrimental effects on the skin, indicating that both prosenescent and antisenescent therapies may be desirable, based on the context. Knowledge of molecular mechanisms involved in skin cellular senescence may provide meaningful insights for developing effective therapeutics for senescence-related skin disorders, such as wound healing and cosmetic skin aging changes.

Exploring the role of senescence inducers and senotherapeutics as targets for anticancer natural products.

During the last few decades, cancer has remained one of the deadliest diseases that endanger human health, emphasizing urgent drug discovery. Cellular senescence has gained a great deal of attention in recent years because of its link to the development of cancer therapy. Senescent cells are incapable of proliferating due to irreversibly inhibition of the initiation of the cell cycle pathways. However, senescent cells aggregate in tissues and produce a pro-inflammatory secretome called senescence-associated secretory phenotype (SASP) that can cause serious harmful effects if not managed properly. There is mounting evidence that senescent cells lead to various phases of tumorigenesis in various anatomical sites, owing mostly to the paracrine activities of the SASP. Therefore, a new treatment field called senotherapeutics has been established. Senotherapeutics are newly developed anticancer agents that have been demonstrated to inhibit cancer efficiently. In light of recent findings, several promising natural products have been identified as senescence inducers and senotherapeutics, including, miliusanes, epigallocatechin gallate, phloretin, silybin, resveratrol, genistein, sulforaphane, quercetin, allicin, fisetin, piperlongumine, berberine, triptolide, tocotrienols and curcumin analogs. Some of them have already been validated through preclinical trials and exert an enormous potential for clinical trials. This review article focuses on and summarizes the latest advances made on cellular senescence and its potential as a target for cancer treatment and highlights the well-known natural products as senescence inducers and senotherapeutics for cancer treatment.

Renal Delivery of Pharmacologic Agents During Machine Perfusion to Prevent Ischaemia-Reperfusion Injury: From Murine Model to Clinical Trials.

Donor organ shortage still remains a serious obstacle for the access of wait-list patients to kidney transplantation, the best treatment for End-Stage Kidney Disease (ESKD). To expand the number of transplants, the use of lower quality organs from older ECD or DCD donors has become an established routine but at the price of increased incidence of Primary Non-Function, Delay Graft Function and lower-long term graft survival. In the last years, several improvements have been made in the field of renal transplantation from surgical procedure to preservation strategies. To improve renal outcomes, research has focused on development of innovative and dynamic preservation techniques, in order to assess graft function and promote regeneration by pharmacological intervention before transplantation. This review provides an overview of the current knowledge of these new preservation strategies by machine perfusions and pharmacological interventions at different timing possibilities: in the organ donor, ex-vivo during perfusion machine reconditioning or after implementation in the recipient. We will report therapies as anti-oxidant and anti-inflammatory agents, senolytics agents, complement inhibitors, HDL, siRNA and H2S supplementation. Renal delivery of pharmacologic agents during preservation state provides a window of opportunity to treat the organ in an isolated manner and a crucial route of administration. Even if few studies have been reported of transplantation after ex-vivo drugs administration, targeting the biological pathway associated to kidney failure (i.e. oxidative stress, complement system, fibrosis) might be a promising therapeutic strategy to improve the quality of various donor organs and expand organ availability.

Senolytic Cocktail Dasatinib+Quercetin (D+Q) Does Not Enhance the Efficacy of Senescence-Inducing Chemotherapy in Liver Cancer.

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death, which develops in the context of fibrosis and cirrhosis caused by chronic inflammation, in turn due to non-alcoholic fatty liver disease (NAFLD), alcohol consumption and/or hepatitis viral infection. An increased number of senescent cells are associated with age-related tissue degeneration during NAFLD-induced HCC, or during chemotherapeutic treatment. Senolytic agents target selectively senescent cells. A combination of the senolytic drugs dasatinib and quercetin (D+Q) reduced hepatic lipid accumulation and alleviated age-associated physical dysfunction in mice. However, whether D+Q can impact the treatment of HCC, at the end-stage of the NAFLD inflammatory spectrum, is unknown. Here, using two well-established HCC cell lines (HepG2, Huh-7), we demonstrate that the maximal cytostatic doses for D and/or Q (1 + 1 µM) lacked efficacy in removing doxorubicin-induced ß-gal-positive senescent cells. Moreover, D+Q did not affect doxorubicin-dependent induction of flattened morphology, activation of p16, expression of SASP-associated genes or formation of γH2AX foci. We then investigated the antitumor efficacy of doxorubicin, D+Q, or the combination, in xenograft studies conducted with HCC cells inoculated in athymic nude mice. Doxorubicin reduced tumor growth by 30% compared to control mice, while D+Q was ineffective in synergizing with doxorubicin and in clearing doxorubicin-induced HCC senescent cells. Unexpectedly, D+Q alone appeared to have acute pro-tumorigenic effects in control mice. While our data need to be confirmed in animal models that fully recapitulate NAFLD, we demonstrate that these compounds are ineffective, alone or in synergy with senescence-inducing chemotherapy, against experimental HCC.

Discovery of piperlongumine as a potential novel lead for the development of senolytic agents.

Accumulating evidence indicates that senescent cells play an important role in many age-associated diseases. The pharmacological depletion of senescent cells (SCs) with a "senolytic agent", a small molecule that selectively kills SCs, is a potential novel therapeutic approach for these diseases. Recently, we discovered ABT-263, a potent and highly selective senolytic agent, by screening a library of rationally-selected compounds. With this screening approach, we also identified a second senolytic agent called piperlongumine (PL). PL is a natural product that is reported to have many pharmacological effects, including anti-tumor activity. We show here that PL preferentially killed senescent human WI-38 fibroblasts when senescence was induced by ionizing radiation, replicative exhaustion, or ectopic expression of the oncogene Ras. PL killed SCs by inducing apoptosis, and this process did not require the induction of reactive oxygen species. In addition, we found that PL synergistically killed SCs in combination with ABT-263, and initial structural modifications to PL identified analogs with improved potency and/or selectivity in inducing SC death. Overall, our studies demonstrate that PL is a novel lead for developing senolytic agents.