Dual mTORC1/C2 inhibitors suppress cellular geroconversion (a senescence program)

Too big not to fail: emerging evidence for size-induced senescence

Cellular senescence refers to a permanent and stable state of cell cycle exit. This process plays an important role in many cellular functions, including tumor suppression. It was first noted that senescence is associated with increased cell size in the early 1960s; however, how this contributes to permanent cell cycle exit was poorly understood until recently. In this review, we discuss new findings that identify increased cell size as not only a consequence but also a cause of permanent cell cycle exit. We highlight recent insights into how increased cell size alters normal cellular physiology and creates homeostatic imbalances that contribute to senescence induction. Finally, we focus on the potential clinical implications of these findings in the context of cell cycle arrest-causing cancer therapeutics and speculate on how tumor cell size changes may impact outcomes in patients treated with these drugs.

Emerging Therapeutic Approaches to Target the Dark Side of Senescent Cells: New Hopes to Treat Aging as a Disease and to Delay Age-Related Pathologies

Life expectancy has drastically increased over the last few decades worldwide, with important social and medical burdens and costs. To stay healthy longer and to avoid chronic disease have become essential issues. Organismal aging is a complex process that involves progressive destruction of tissue functionality and loss of regenerative capacity. One of the most important aging hallmarks is cellular senescence, which is a stable state of cell cycle arrest that occurs in response to cumulated cell stresses and damages. Cellular senescence is a physiological mechanism that has both beneficial and detrimental consequences. Senescence limits tumorigenesis, lifelong tissue damage, and is involved in different biological processes, such as morphogenesis, regeneration, and wound healing. However, in the elderly, senescent cells increasingly accumulate in several organs and secrete a combination of senescence associated factors, contributing to the development of various age-related diseases, including cancer. Several studies have revealed major molecular pathways controlling the senescent phenotype, as well as the ones regulating its interactions with the immune system. Attenuating the senescence-associated secretory phenotype (SASP) or eliminating senescent cells have emerged as attractive strategies aiming to reverse or delay the onset of aging diseases. Here, we review current senotherapies designed to suppress the deleterious effect of SASP by senomorphics or to selectively kill senescent cells by "senolytics" or by immune system-based approaches. These recent investigations are promising as radical new controls of aging pathologies and associated multimorbidities.

Senescence-associated tumor growth is promoted by 12-Lipoxygenase

Radiation therapy is a commonly used treatment modality for cancer. Although effective in providing local tumor control, radiation causes oxidative stress, inflammation, immunomodulatory and mitogenic cytokine production, extracellular matrix production, and premature senescence in lung parenchyma. The senescence associated secretory phenotype (SASP) can promote inflammation and stimulate alterations in the surrounding tissue. Therefore, we hypothesized that radiation-induced senescent parenchymal cells in irradiated lung would enhance tumor growth. Using a murine syngeneic tumor model of melanoma and non-small cell lung cancer lung metastasis, we demonstrate that radiation causes a significant increase in markers of premature senescence in lung parenchyma within 4 to 8 weeks. Further, injection of B16F0 (melanoma) or Lewis Lung carcinoma (epidermoid lung cancer) cells at these time points after radiation results in an increase in the number and size of pulmonary tumor nodules relative to unirradiated mice. Treatment of irradiated mice with a senolytic agent (ABT-737) or agents that prevent senescence (rapamycin, INK-128) was sufficient to reduce radiation-induced lung parenchymal senescence and to mitigate radiation-enhanced tumor growth. These agents abrogated radiation-induced expression of 12-Lipoxygenase (12-LOX), a molecule implicated in several deleterious effects of senescence. Deficiency of 12-LOX prevented radiation-enhanced tumor growth. Together, these data demonstrate the pro-tumorigenic role of radiation-induced senescence, introduces the dual TORC inhibitor INK-128 as an effective agent for prevention of radiation-induced normal tissue senescence, and identifies senescence-associated 12-LOX activity as an important component of the pro-tumorigenic irradiated tissue microenvironment. These studies suggest that combining senotherapeutic agents with radiotherapy may decrease post-therapy tumor growth.

The hyperfunction theory: An emerging paradigm for the biology of aging

The process of senescence (aging) is predominantly determined by the action of wild-type genes. For most organisms, this does not reflect any adaptive function that senescence serves, but rather evolutionary effects of declining selection against genes with deleterious effects later in life. To understand aging requires an account of how evolutionary mechanisms give rise to pathogenic gene action and late-life disease, that integrates evolutionary (ultimate) and mechanistic (proximate) causes into a single explanation. A well-supported evolutionary explanation by G.C. Williams argues that senescence can evolve due to pleiotropic effects of alleles with antagonistic effects on fitness and late-life health (antagonistic pleiotropy, AP). What has remained unclear is how gene action gives rise to late-life disease pathophysiology. One ultimate-proximate account is T.B.L. Kirkwood's disposable soma theory. Based on the hypothesis that stochastic molecular damage causes senescence, this reasons that aging is coupled to reproductive fitness due to preferential investment of resources into reproduction, rather than somatic maintenance. An alternative and more recent ultimate-proximate theory argues that aging is largely caused by programmatic, developmental-type mechanisms. Here ideas about AP and programmatic aging are reviewed, particularly those of M.V. Blagosklonny (the hyperfunction theory) and J.P. de Magalhães (the developmental theory), and their capacity to make sense of diverse experimental findings is assessed.

mTOR Activity and Autophagy in Senescent Cells, a Complex Partnership

Cellular senescence is a form of proliferative arrest triggered in response to a wide variety of stimuli and characterized by unique changes in cell morphology and function. Although unable to divide, senescent cells remain metabolically active and acquire the ability to produce and secrete bioactive molecules, some of which have recognized pro-inflammatory and/or pro-tumorigenic actions. As expected, this “senescence-associated secretory phenotype (SASP)” accounts for most of the non-cell-autonomous effects of senescent cells, which can be beneficial or detrimental for tissue homeostasis, depending on the context. It is now evident that many features linked to cellular senescence, including the SASP, reflect complex changes in the activities of mTOR and other metabolic pathways. Indeed, the available evidence indicates that mTOR-dependent signaling is required for the maintenance or implementation of different aspects of cellular senescence. Thus, depending on the cell type and biological context, inhibiting mTOR in cells undergoing senescence can reverse senescence, induce quiescence or cell death, or exacerbate some features of senescent cells while inhibiting others. Interestingly, autophagy—a highly regulated catabolic process—is also commonly upregulated in senescent cells. As mTOR activation leads to repression of autophagy in non-senescent cells (mTOR as an upstream regulator of autophagy), the upregulation of autophagy observed in senescent cells must take place in an mTOR-independent manner. Notably, there is evidence that autophagy provides free amino acids that feed the mTOR complex 1 (mTORC1), which in turn is required to initiate the synthesis of SASP components. Therefore, mTOR activation can follow the induction of autophagy in senescent cells (mTOR as a downstream effector of autophagy). These functional connections suggest the existence of autophagy regulatory pathways in senescent cells that differ from those activated in non-senescence contexts. We envision that untangling these functional connections will be key for the generation of combinatorial anti-cancer therapies involving pro-senescence drugs, mTOR inhibitors, and/or autophagy inhibitors.

Gene expression in human mesenchymal stem cell aging cultures: modulation by short peptides

Effects of the short peptides Ala-Glu-Asp (AED), Lys-Glu-Asp (KED) and Lys-Glu (KE) on the expression of IGF1, FOXO1, TERT, TNKS2, and NFκB genes were studied in human embryo bone marrow mesenchymal stem cells (line FetMSCs) variously aged in "passages" or "stationary" cultures. Both cell aging models were similar in gene expression. The main difference was in the TERT gene expression level, which showed an eightfold increase at the "stationary" aging. IGF1 gene expression levels were very similar in both cell culture aging models, being enhanced by 3.5-5.6 fold upon the addition of the peptides. The FOXO1 gene was expressed twice more actively in the "stationary" than in the "passages" aging model. KED peptide inhibited FOXO1 gene expression by 1.6-2.3 fold. KE peptide increased FOXO1 gene expression by about two-fold in the "stationary" aging model but did not affect it in the "passage" aging model. The most striking difference in the peptide effect on cell aging between "passages" and "stationary" aging models was in the KED effects on TNKS2 gene expression; this expression was inhibited by KED in the "passages" model, while stimulation was observed in the "stationary" model. AED, KED, and KE stimulated expression of the NFκB gene in both models. Thus, the peptides studied at nanomolar concentrations modulate the expression of some genes known to be involved in cell aging.

The roles of MTOR and miRNAs in endothelial cell senescence

Accumulation of senescent cells in vascular endothelium is known to contribute to vascular aging and increases the risk of developing cardiovascular diseases. The involvement of classical pathways such as p53/p21 and p16/pRB in cellular senescence are well described but there are emerging evidence supporting the increasingly important role of mammalian target of rapamycin (MTOR) as driver of cellular senescence via these pathways or other effector molecules. MicroRNAs (miRNAs) are a highly conserved group of small non-coding RNAs (18-25 nucleotides), instrumental in modulating the expression of target genes associated with various biological and cellular processes including cellular senescence. The inhibition of MTOR activity is predominantly linked to cellular senescence blunting and prolonged lifespan in model organisms. To date, known miRNAs regulating MTOR in endothelial cell senescence remain limited. Herein, this review discusses the roles of MTOR and MTOR-associated miRNAs in regulating endothelial cell senescence, including the crosstalk between MTOR Complex 1 (MTORC1) and cell cycle pathways and the emerging role of MTORC2 in cellular senescence. New insights on how MTOR and miRNAs coordinate underlying molecular mechanisms of endothelial senescence will provide deeper understanding and clarity to the complexity of the regulation of cellular senescence.

Geroprotective and senoremediative strategies to reduce the comorbidity, infection rates, severity, and lethality in gerophilic and gerolavic infections

The recently identified SARS-CoV-2 betacoronavirus responsible for the COVID-19 pandemic has uncovered the age-associated vulnerability in the burden of disease and put aging research in the spotlight. The limited data available indicates that COVID-19 should be referred to as a gerolavic (from Greek, géros "old man" and epilavís, "harmful") infection because the infection rates, severity, and lethality are substantially higher in the population aged 60 and older. This is primarily due to comorbidity but may be partially due to immunosenescence, decreased immune function in the elderly, and general loss of function, fitness, and increased frailty associated with aging. Immunosenescence is a major factor affecting vaccination response, as well as the severity and lethality of infectious diseases. While vaccination reduces infection rates, and therapeutic interventions reduce the severity and lethality of infections, these interventions have limitations. Previous studies showed that postulated geroprotectors, such as sirolimus (rapamycin) and its close derivative rapalog everolimus (RAD001), decreased infection rates in a small sample of elderly patients. This article presents a review of the limited literature available on geroprotective and senoremediative interventions that may be investigated to decrease the disease burden of gerolavic infections. This article also highlights a need for rigorous clinical validation of deep aging clocks as surrogate markers of biological age. These could be used to assess the need for, and efficacy of, geroprotective and senoremediative interventions and provide better protection for elderly populations from gerolavic infections. This article does not represent medical advice and the medications described are not yet licensed or recommended as immune system boosters, as they have not undergone clinical evaluation for this purpose.

Suppression of mTORC1 activity in senescent Ras-transformed cells neither restores autophagy nor abrogates apoptotic death caused by inhibition of MEK/ERK kinases

Autophagy is conservative catabolic process that degrades organelles, in particular, mitochondria, and misfolded proteins within the lysosomes, thus maintaining cellular viability. Despite the close relationship between mitochondrial dysfunction and cellular senescence, it is unclear how mitochondria damage can induce autophagy in senescent cells. We show that MEK/ERK suppression induces mitochondria damage followed by apoptosis of senescent Ras-expressing cells. To understand the role of persistent mTORC1 signaling in breaking the cAMPK-induced autophagy caused by mitochondrial damage, we inhibited mTORС1 with low concentrations of pp242. mTORC1 suppression neither restores the AMPK-induced autophagy nor decreases the level of apoptosis upon MEK/ERK inhibition. We discovered the existence of an alternative autophagy-like way that partially increases the viability of senescent cells under suppressed mTORC1. The pp242-treated cells survive due to formation of the non-autophagous LC3-negative vacuoles, which contain the damaged mitochondria and lysosomes with the following excretion the content from the cell. MEK/ERK activity is required to implement this process in senescent cells. Senescent cells exhibit distinctive spatial distribution of organelles and proteins that provides uncoupling of final participants of autophagy. We show that this feature stops the process of cytoprotective autophagy in response to MEK/ERK suppression, thus allowing selective elimination of senescent Ras-expressing cells.

Targeting senescent cells in translational medicine

Organismal ageing is a complex process driving progressive impairment of functionality and regenerative potential of tissues. Cellular senescence is a state of stable cell cycle arrest occurring in response to damage and stress and is considered a hallmark of ageing. Senescent cells accumulate in multiple organs during ageing, contribute to tissue dysfunction and give rise to pathological manifestations. Senescence is therefore a defining feature of a variety of human age-related disorders, including cancer, and targeted elimination of these cells has recently emerged as a promising therapeutic approach to ameliorate tissue damage and promote repair and regeneration. In addition, in vivo identification of senescent cells has significant potential for early diagnosis of multiple pathologies. Here, we review existing senolytics, small molecules and drug delivery tools used in preclinical therapeutic strategies involving cellular senescence, as well as probes to trace senescent cells. We also review the clinical research landscape in senescence and discuss how identifying and targeting cellular senescence might positively affect pathological and ageing processes.

Dissecting Aging and Senescence-Current Concepts and Open Lessons

In contrast to the programmed nature of development, it is still a matter of debate whether aging is an adaptive and regulated process, or merely a consequence arising from a stochastic accumulation of harmful events that culminate in a global state of reduced fitness, risk for disease acquisition, and death. Similarly unanswered are the questions of whether aging is reversible and can be turned into rejuvenation as well as how aging is distinguishable from and influenced by cellular senescence. With the discovery of beneficial aspects of cellular senescence and evidence of senescence being not limited to replicative cellular states, a redefinition of our comprehension of aging and senescence appears scientifically overdue. Here, we provide a factor-based comparison of current knowledge on aging and senescence, which we converge on four suggested concepts, thereby implementing the newly emerging cellular and molecular aspects of geroconversion and amitosenescence, and the signatures of a genetic state termed genosenium. We also address the possibility of an aging-associated secretory phenotype in analogy to the well-characterized senescence-associated secretory phenotype and delineate the impact of epigenetic regulation in aging and senescence. Future advances will elucidate the biological and molecular fingerprints intrinsic to either process.

Rapamycin retards epigenetic ageing of keratinocytes independently of its effects on replicative senescence, proliferation and differentiation

The advent of epigenetic clocks has prompted questions about the place of epigenetic ageing within the current understanding of ageing biology. It was hitherto unclear whether epigenetic ageing represents a distinct mode of ageing or a manifestation of a known characteristic of ageing. We report here that epigenetic ageing is not affected by replicative senescence, telomere length, somatic cell differentiation, cellular proliferation rate or frequency. It is instead retarded by rapamycin, the potent inhibitor of the mTOR complex which governs many pathways relating to cellular metabolism. Rapamycin, however, is also an effective inhibitor of cellular senescence. Hence cellular metabolism underlies two independent arms of ageing - cellular senescence and epigenetic ageing. The demonstration that a compound that targets metabolism can slow epigenetic ageing provides a long-awaited point-of-entry into elucidating the molecular pathways that underpin the latter. Lastly, we report here an in vitro assay, validated in humans, that recapitulates human epigenetic ageing that can be used to investigate and identify potential interventions that can inhibit or retard it.

Lysosomal trapping of palbociclib and its functional implications

Palbociclib is a selective inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6) approved for the treatment of some cancers. The main mechanism of action of palbociclib is to induce cell cycle arrest and senescence on responsive cells. Here, we report that palbociclib concentrates in intracellular acidic vesicles, where it can be readily observed due to its intrinsic fluorescence, and it is released from these vesicles upon dilution or washing out of the extracellular medium. This reversible storage of drugs into acidic vesicles is generally known as lysosomal trapping and, based on this, we uncover novel properties of palbociclib. In particular, a short exposure of cells to palbociclib is sufficient to produce a stable cell-cycle arrest and long-term senescence. Moreover, after washing out the drug, palbociclib-treated cells release the drug to the medium and this conditioned medium is active on susceptible cells. Interestingly, cancer cells resistant to palbociclib also accumulate and release the drug producing paracrine senescence on susceptible cells. Finally, other lysosomotropic drugs, such as chloroquine, interfere with the accumulation of palbociclib into lysosomes, thereby reducing the minimal dose of palbociclib required for cell-cycle arrest and senescence. In summary, lysosomal trapping explains the prolonged temporal activity of palbociclib, the paracrine activity of exposed cells, and the cooperation with lysosomotropic drugs. These are important features that may help to improve the therapeutic dosing and efficacy of palbociclib. Finally, two other clinically approved CDK4/6 inhibitors, ribociclib and abemaciclib, present a similar behavior as palbociclib, suggesting that lysosomal trapping is a property common to all three clinically-approved CDK4/6 inhibitors.

Toxin-induced hormesis may restrain aging

Mild environmental stress might have beneficial effects in aging by activating maintenance and repair processes in cells and organs. These beneficial stress effects fit to the concept of hormesis. Prominent stressors acting in a hormetic way are physical exercises, fasting, cold and heat. This review will introduce some toxins, which have been found to induce hormetic responses in animal models of aging research. To highlight the molecular signature of these hormetic effects we will depict signaling pathways affected by low doses of toxins on cellular and organismic level. As prominent examples for signaling pathways involved in both aging processes as well as toxin responses, PI3K/Akt/mTOR- and AMPK-signal transduction will be described in more detail. Due to the striking overlap of signaling pathways mediating toxin induced responses and aging processes we propose considering the ability of low doses of toxins to slow down the rate of aging.

Prospects of Pharmacological Interventions to Organismal Aging

Intense research in the areas of cellular and organismal aging using diverse laboratory model systems has enriched our knowledge in the processes and the signalling pathways involved in normal and pathological conditions. The field finds itself in a position to take decisive steps towards clinical applications and interventions not only for targeted age-related diseases such as cardiovascular conditions and neurodegeneration but also for the modulation of health span and lifespan of a whole organism. Beyond nutritional interventions such as dietary restriction without malnutrition and various regimes of intermittent fasting, accumulating evidence provides promise for pharmacological interventions. The latter, mimic caloric or dietary restriction, tune cellular and organismal stress responses, affect the metabolism of microbiome with subsequent effects on the host or modulate repair pathways, among others. In this mini review, we summarise some of the evidence on drugs that can alter organismal lifespan and the prospects they might offer for promoting healthspan and delaying age-related diseases.

Rapamycin, proliferation and geroconversion to senescence

Rapamycin inhibits cell proliferation, yet preserves (re)-proliferative potential (RPP). RPP is a potential of quiescent cells that is lost in senescent cells. mTOR drives conversion from quiescence to senescence (geroconversion). By suppressing geroconversion, rapamycin preserves RPP. Geroconversion is characterized by proliferation-like levels of phospho-S6K/S6/4E-BP1 in nonproliferating cells arrested by p16 and/or p21. mTOR-driven geroconversion is associated with cellular hyperfunction, which in turn leads to organismal aging manifested by age-related diseases.

Altered modulation of lamin A/C-HDAC2 interaction and p21 expression during oxidative stress response in HGPS

Defects in stress response are main determinants of cellular senescence and organism aging. In fibroblasts from patients affected by Hutchinson-Gilford progeria, a severe LMNA-linked syndrome associated with bone resorption, cardiovascular disorders, and premature aging, we found altered modulation of CDKN1A, encoding p21, upon oxidative stress induction, and accumulation of senescence markers during stress recovery. In this context, we unraveled a dynamic interaction of lamin A/C with HDAC2, an histone deacetylase that regulates CDKN1A expression. In control skin fibroblasts, lamin A/C is part of a protein complex including HDAC2 and its histone substrates; protein interaction is reduced at the onset of DNA damage response and recovered after completion of DNA repair. This interplay parallels modulation of p21 expression and global histone acetylation, and it is disrupted by LMNAmutations leading to progeroid phenotypes. In fact, HGPS cells show impaired lamin A/C-HDAC2 interplay and accumulation of p21 upon stress recovery. Collectively, these results link altered physical interaction between lamin A/C and HDAC2 to cellular and organism aging. The lamin A/C-HDAC2 complex may be a novel therapeutic target to slow down progression of progeria symptoms.

Dual mTORC1/mTORC2 blocker as a possible therapy for tauopathy in cellular model

Tauopathy comprises a group of disorders caused by abnormal aggregates of tau protein. In these disorders phosphorylated tau protein tends to accumulate inside neuronal cells (soma) instead of the normal axonal distribution of tau. A suggested therapeutic strategy for tauopathy is to induce autophagy to increase the ability to get rid of the unwanted tau aggregates. One of the key controllers of autophagy is mTOR. Blocking mTOR leads to stimulation of autophagy. Recently, unravelling molecular structure of mTOR showed that it is formed of two subunits: mTORC1/C2. So, blocking both subunits of mTOR seems more attractive as it will explore all abilities of mTOR molecule. In the present study, we report using pp242 which is a dual mTORC1/C2 blocker in cellular model of tauopathy using LUHMES cell line. Adding fenazaquin to LUHMES cells induced tauopathy in the form of increased phospho tau aggregates. Moreover, fenazaquin treated cells showed the characteristic somatic redistribution of tau. PP242 use in the present tauopathy model reversed the pathology significantly without observable cellular toxicity for the used dosage of 1000 nM. The present study suggests the possible use of pp242 as a dual mTOR blocker to treat tauopathy.

From rapalogs to anti-aging formula

Inhibitors of mTOR, including clinically available rapalogs such as rapamycin (Sirolimus) and Everolimus, are gerosuppressants, which suppress cellular senescence. Rapamycin slows aging and extends life span in a variety of species from worm to mammals. Rapalogs can prevent age-related diseases, including cancer, atherosclerosis, obesity, neurodegeneration and retinopathy and potentially rejuvenate stem cells, immunity and metabolism. Here, I further suggest how rapamycin can be combined with metformin, inhibitors of angiotensin II signaling (Losartan, Lisinopril), statins (simvastatin, atorvastatin), propranolol, aspirin and a PDE5 inhibitor. Rational combinations of these drugs with physical exercise and an anti-aging diet (Koschei formula) can maximize their anti-aging effects and decrease side effects.

Of Cytometry, Stem Cells and Fountain of Youth

Outlined are advances of cytometry applications to identify and sort stem cells, of laser scanning cytometry and ImageStream imaging instrumentation to further analyze morphometry of these cells, and of mass cytometry to classify a multitude of cellular markers in large cell populations. Reviewed are different types of stem cells, including potential candidates for cancer stem cells, with respect to their "stemness", and other characteristics. Appraised is further progress in identification and isolation of the "very small embryonic-like stem cells" (VSELs) and their autogenous transplantation for tissue repair and geroprotection. Also assessed is a function of hyaluronic acid, the major stem cells niche component, as a guardian and controller of stem cells. Briefly appraised are recent advances and challenges in the application of stem cells in regenerative medicine and oncology and their future role in different disciplines of medicine, including geriatrics.

Molecular regulation of apoptotic machinery and lipid metabolism by mTORC1/mTORC2 dual inhibitors in preclinical models of HER2+/PIK3CAmut breast cancer

The mechanistic target of rapamycin (mTOR) is a rational target for cancer treatment. While the mTORC1-selective rapalogs have shown significant benefits in the clinic, antitumor response may be further improved by inhibiting both mTORC1 and mTORC2. Herein, we established target profile of a novel mTOR kinase inhibitor (mTOR-KI) MTI-31 and employed it to study new therapeutic mechanism in breast cancer. MTI-31 demonstrated a potent mTOR binding affinity with >5000 fold selectivity over the related PI3K family isoforms. MTI-31 inhibited mTORC1- and mTORC2 function at ≤120 nM in cellular assays or 5 mg/kg orally in tumor-bearing mice. In a panel of breast cancer lines, the antitumor efficacy of MTI-31 was dependent on HER2+ and/or PIK3CAmut (HER2+/PIK3CAmut) status of the tumors and required mTORC2-specific modulation of Bim, MCL-1 and GSK3. Inactivation of Bim or GSK3 each attenuated apoptotic death resulting in mTOR-KI resistance. The antitumor response also required a suppression of lipid metabolism in therapy-sensitive tumors. Treatment with MTI-31 or AZD8055 substantially reduced lipogenesis and acetyl-CoA homeostasis, which was mechanistically linked to a blockade of mTORC2-dependent glucose-to-lipid conversion rate. We also found that the basal levels of carnitine palmitoyltransferase 1A and lipid catabolism were elevated in HER2+/PIK3CAmut breast cells and were inhibited upon mTOR-KI treatment. A CPT1A inhibitor etomoxir mimicked MTI-31 action in selective downregulation of cellular lipid catabolism. Co-treatments with MTI-31 and etomoxir enhanced the suppression of cyclin D1, c-Myc and cell growth in HER2+/PIK3CAmut tumors. These new mechanistic findings provide a rationale for targeting mTORC1 and mTORC2 in HER2+/PIK3CAmut breast cancer.

Suppression of PC-1/PrLZ sensitizes prostate cancer cells to ionizing radiation by attenuating DNA damage repair and inducing autophagic cell death

Radiotherapy is promising and effective for treating prostate cancer but the addition of a tumor cell radiosensitizer would improve therapeutic outcomes. PC-1/PrLZ, a TPD52 protein family member is frequently upregulated in advanced prostate cancer cells and may be a biomarker of aggressive prostate cancer. Therefore, we investigated the potential role of PC-1/PrLZ for increasing radioresistance in human prostate cancer cell lines. Growth curves and survival assays after g-ray irradiation confirmed that depletion of endogenous PC-1/PrLZ significantly increased prostate cancer cell radiosensitivity. Irradiation (IR) increased PC-1/PrLZ expression in a dose- and time-dependent manner and increased radiosensitivity in PC-1/PrLZ-suppressed cells was partially due to decreased DNA double strand break (DBS) repair which was measured with comet and gH2AX foci assays. Furthermore, depletion of PC-1/PrLZ impaired the IR-induced G2/M checkpoint, which has been reported to be correlate with radioresistance in cancer cells. PC-1/PrLZ-deficient cells exhibited higher level of autophagy when compared with control cells. Thus, specific inhibition of PC-1/PrLZ might provide a novel therapeutic strategy for radiosensitizing prostate cancer cells.

Targeted elimination of senescent Ras-transformed cells by suppression of MEK/ERK pathway

The Ras-Raf-MEK-ERK pathway plays a central role in tumorigenesis and is a target for anticancer therapy. The successful strategy based on the activation of cell death in Ras-expressing cells is associated with the suppression of kinases involved in Ras pathway. However, activation of cytoprotective autophagy overcomes antiproliferative effect of the inhibitors and develops drug resistance. We studied whether cellular senescence induced by HDAC inhibitor sodium butyrate in E1a+cHa-Ras-transformed rat embryo fibroblasts (ERas) and A549 human Ki-Ras mutated lung adenocarcinoma cells would enhance the tumor suppressor effect of MEK/ERK inhibition. Treatment of control ERas cells with PD0325901 for 24 h results in mitochondria damage and apoptotic death of a part of cellular population. However, the activation of AMPK-dependent autophagy overcomes pro-apoptotic effects of MEK/ERK inhibitor and results in restoration of the mitochondria and rescue of viability. Senescent ERas cells do not develop cytoprotective autophagy upon inhibition of MEK/ERK pathway due to spatial dissociation of lysosomes and autophagosomes in the senescent cells. Senescent cells are unable to form the autophagolysosomes and to remove the damaged mitochondria resulting in apoptotic death. Our data show that suppression of MEK/ERK pathway in senescent cells provides a new strategy for elimination of Ras-expressing cells.

Endothelin-1-induced hypertrophic alterations and heme oxygenase-1 expression in cardiomyoblasts are counteracted by beta estradiol: in vitro and in vivo studies

Endothelin-1 (ET-1), a potent vasoconstrictor normally active in maintaining vascular tone, may mediate significant pathogenic effects, contributing to several serious diseases when aberrantly expressed or regulated. The present study evaluates the capacity of ET-1 to affect endothelin-1-associated hypertrophic activity and decreased expression of heme oxygenase-1 by H9c2 rat cardiomyoblasts in vitro, corresponding to in vivo processes underlying cardiovascular diseases (CVDs). Beta estradiol (β-E) is tested for its capacity to alter the effects of ET-1. H9c2 cells, cultured 48 h, were stimulated with 100-10,000 nM of ET-1 and evaluated for changes in cell size, cell viability, and expression of the cytoprotective heat shock protein heme oxygenase-1 (HO-1), with 200 nM of β-E included in selected cultures to evaluate its effect on ET-1-mediated changes. The application of 100 to 10,000 nM of ET-1 resulted in a significant increase in average cell size and decreases in both cell viability and HO-1 protein content (p < 0.05). Moreover, 200 nM of β-E was observed to significantly counteract these effects by cardiomyoblasts stimulated with 1000 nM of ET-1 (p < 0.05). Sprague-Dawley rats treated intravenously with 1000 ng/kg of ET-1 demonstrated reduced HO-1 expression in peripheral blood and left ventricular tissue, which was counteracted by injection of 200 ng/kg β-E-demonstrating a possible correspondence between in vitro and in vivo effects. An outcome of particular value for clinical use of β-E, in the management of cardiac hypertrophy, is the observed capacity of the drug to abate ET-1-mediated suppression of HO-1 expression. It has been previously demonstrated that HO-1 inducers exhibit potent cardioprotective properties, thus offering the promise of combining them with β-E, allowing lower effective dosage of the drug and concomitantly lower adverse side effects associated with its clinical use. Major findings of this investigation are that pretreatment of cardiomyoblasts with β-E inhibited their hypertrophic response to ET-1 and counteracts the decrease of cell viability. These effects were associated with a restoration of HO-1 protein expression in both under in vitro and in vivo conditions.

mTOR complex-2 stimulates acetyl-CoA and de novo lipogenesis through ATP citrate lyase in HER2/PIK3CA-hyperactive breast cancer

The mechanistic target of rapamycin (mTOR) is a major regulator of cell growth and is frequently dysregulated in cancer. While mTOR complex-1 (mTORC1) is a validated cancer target, the role of mTOR complex-2 (mTORC2) remains less defined. Here, we reveal mTORC2 as a critical regulator of breast cancer metabolism. We showed that hyperphosphorylation in ATP citrate lyase (ACL) occurs frequently in human breast tumors and correlates well with HER2+ and/or PIK3CA-mutant (HER2+/PIK3CAmut) status in breast tumor cell lines. In HER2+/PIK3CAmut cells, mTORC2 controls Ser-455 phosphorylation of ACL thereby promoting acetyl-CoA production, de novo lipogenesis and mitochondrial physiology, all of which were inhibited by an mTORC1/mTORC2 kinase inhibitor (mTOR-KI) or cellular depletion of mTORC2 or ACL. mTOR-KI but not rapamycin blocked the IGF-1-induced ACL phosphorylation and glucose to lipid conversion. Depletion of mTORC2 but not mTORC1 specifically inhibited the ACL-dependent acetyl-CoA production. In the HER2+/PIK3CAmut MDA361, MDA453, BT-474 and T47D cells, depletion of mTORC2 or ACL led to growth inhibition and mitochondrial hyperpolarization, which were partially rescued by an alternate source of acetyl-CoA. These same changes were not apparent in mTORC2- or ACL-depleted HER2-/PIK3CAwt MDA231 and HCC1806 cells, highlighting a differential dependence of mTORC2-ACL for survival in these two cell types. Moreover, ACL Ser-455 mutants S455E (phosphomimetic) and S455A (non-phosphorylatable) each increased or decreased, respectively, the acetyl-CoA production, mitochondrial homeostasis and survival in ACL-depleted MDA453 cells. These studies define a new and rapamycin-resistant mechanism of mTORC2-ACL in lipogenesis and acetyl-CoA biology and provide a rationale for targeting of mTORC1 and mTORC2 in HER2+/PIK3CAmut breast cancer.

Evidence that hematopoietic stem cell function is preserved during aging in long-lived S6K1 mutant mice

The mechanistic target of rapamycin (mTOR) signalling pathway plays a highly conserved role in aging; mice lacking ribosomal protein S6 kinase 1 (S6K1^−/−) have extended lifespan and healthspan relative to wild type (WT) controls. Exactly how reduced mTOR signalling induces such effects is unclear, although preservation of stem cell function may be important. We show, using gene expression analyses, that there was a reduction in expression of cell cycle genes in young (12 week) and aged (80 week) S6K1^−/− BM-derived c-Kit⁺ cells when compared to age-matched WT mice, suggesting that these cells are more quiescent in S6K1^−/− mice. In addition, we investigated hematopoietic stem cell (HSC) frequency and function in young and aged S6K1^−/− and WT mice. Young, but not aged, S6K1^−/− mice had more LSK (lineage⁻, c-Kit⁺, Sca-1⁺) cells (% of bone marrow (BM)), including the most primitive long-term repopulating HSCs (LT-HSC) relative to WT controls. Donor-derived engraftment of LT-HSCs in recipient mice was unaffected by genotype in young mice, but was enhanced in transplants using LT-HSCs derived from aged S6K1^−/− mice. Our results are the first to provide evidence that age-associated HSC functional decline is ameliorated in a long-lived mTOR mutant mouse.

Accelerated geroncogenesis in hereditary breast-ovarian cancer syndrome

The geroncogenesis hypothesis postulates that the decline in metabolic cellular health that occurs naturally with aging drives a "field effect" predisposing normal tissues for cancer development. We propose that mutations in the cancer susceptibility genes BRCA1/2 might trigger "accelerated geroncogenesis" in breast and ovarian epithelia. By speeding up the rate at which the metabolic threshold becomes "permissive" with survival and expansion of genomically unstable pre-tumoral epithelial cells, BRCA haploinsufficiency-driven metabolic reprogramming would operate as a bona fide oncogenic event enabling malignant transformation and tumor formation in BRCA carriers. The metabolic facet of BRCA1 one-hit might involve tissue-specific alterations in acetyl-CoA, α-ketoglutarate, NAD+, FAD, or S-adenosylmethionine, critical factors for de/methylation or de/acetylation dynamics in the nuclear epigenome. This in turn might induce faulty epigenetic reprogramming at the "install phase" that directs cell-specific differentiation of breast/ovarian epithelial cells, which can ultimately determine the penetrance of BRCA defects during developmental windows of susceptibility. This model offers a framework to study whether metabolic drugs that prevent or revert metabolic reprogramming induced by BRCA haploinsufficiency might displace the "geroncogenic risk" of BRCA carriers to the age typical for those without the mutation. The identification of the key nodes that directly communicate changes in cellular metabolism to the chromatin in BRCA haploinsufficient cells may allow the epigenetic targeting of genomic instability using exclusively metabolic means. The validation of accelerated geroncogenesis as an inherited "one-hit" metabolic "field effect" might offer new strategies to therapeutically revisit the apparently irreversible genetic-hereditary fate of women with hereditary breast-ovarian cancer syndrome.

Inverse correlation between longevity and developmental rate among wild C. elegans strains

Genetic studies using model organisms have shown that many long-lived mutants display impaired fitness, such as reduced fecundity and delayed development. However, in several wild animals, the association between longevity and fitness does not seem to be inevitable. Thus, the relationship between longevity and fitness in wild organisms remains inconclusive. Here, we determined the correlation between lifespan and fitness, developmental rate and brood size, by using 16 wild-derived C. elegans strains originated from various geographic areas. We found a negative correlation between lifespan and developmental rate. In contrast, we did not find such negative correlation between longevity and developmental rate among the individuals of C. elegans strains. These data imply that polymorphic genetic variants among wild isolates determine resource allocation to longevity and developmental rate.

Preclinical validation of a novel compound targeting p70S6 kinase in breast cancer

Breast cancer is a frequent and treatable disease. However, when recurrent, breast cancer often becomes refractory to therapy and progresses into metastatic forms that are typically incurable. Thus, understanding and targeting the critical pathways underlying breast cancer recurrence is urgently needed to eradicate primary disease and achieve better prognosis. Recently, we have demonstrated that the ribosomal protein p70S6K is activated in residual breast cancer cells as a result of post-surgical inflammation and that interfering with its activity in the peri-operative setting strongly suppresses recurrence in a mouse model. In order to develop clinically-exploitable treatments targeting p70S6K, we have tested a newly generated compound, called FS-115. FS-115 potently inhibited p70S6K1 (IC50 35nM) with high selectivity over other AGC kinases or PI3K pathway kinases. In vitro, treatment with FS-115 efficiently blocked p70S6K activity in breast cancer cell lines and impaired colony formation and anchorage independent growth. Pharmacokinetic profiling showed that FS-115 exhibited high oral bioavailability, optimal plasma distribution and high brain penetrance. In nude mice, FS-115 strongly suppressed tumor take-rate and primary tumor growth. Oral dosing with FS-115 in a peri-operative schedule was effective in decreasing local recurrence of breast cancer and a long-term treatment schedule was well tolerated and efficiently suppressed distant metastasis formation. Altogether, we propose that FS-115 might be a good candidate for the treatment of breast cancer patients at high risk to relapse.

SUMMARY STATEMENT

Our results confirm that inhibition of p70S6K represents a valuable opportunity for restraining loco-regional relapse and metastasis in breast cancer and identify in FS-115 a promising candidate-inhibitor to move from preclinical to clinical treatments.

Gerosuppression by pan-mTOR inhibitors

Rapamycin slows organismal aging and delays age-related diseases, extending lifespan in numerous species. In cells, rapamycin and other rapalogs such as everolimus suppress geroconversion from quiescence to senescence. Rapamycin inhibits some, but not all, activities of mTOR. Recently we and others demonstrated that pan-mTOR inhibitors, known also as dual mTORC1/C2 inhibitors, suppress senescent phenotype. As a continuation of these studies, here we investigated in detail a panel of pan-mTOR inhibitors, to determine their optimal gerosuppressive concentrations. During geroconversion, cells become hypertrophic and flat, accumulate lysosomes (SA-beta-Gal staining) and lipids (Oil Red staining) and lose their re-proliferative potential (RPP). We determined optimal gerosuppressive concentrations: Torin1 (30 nM), Torin 2 (30 nM), AZD8055 (100 nM), PP242 (300 nM), both KU-006379 and GSK1059615 (1000 nM). These agents decreased senescence-associated hypertrophy with IC50s: 20, 18, 15, 200 and 400 nM, respectively. Preservation of RPP by pan-mTOR inhibitors was associated with inhibition of the pS6K/pS6 axis. Inhibition of rapamycin-insensitive functions of mTOR further contributed to anti-hypertrophic and cytostatic effects. Torin 1 and PP242 were more "rapamycin-like" than Torin 2 and AZD8055. Pan-mTOR inhibitors were superior to rapamycin in suppressing hypertrophy, senescent morphology, Oil Red O staining and in increasing so-called "chronological life span (CLS)". We suggest that, at doses lower than anti-cancer concentrations, pan-mTOR inhibitors can be developed as anti-aging drugs.

Towards natural mimetics of metformin and rapamycin

Aging is now at the forefront of major challenges faced globally, creating an immediate need for safe, widescale interventions to reduce the burden of chronic disease and extend human healthspan. Metformin and rapamycin are two FDA-approved mTOR inhibitors proposed for this purpose, exhibiting significant anti-cancer and anti-aging properties beyond their current clinical applications. However, each faces issues with approval for off-label, prophylactic use due to adverse effects. Here, we initiate an effort to identify nutraceuticals-safer, naturally-occurring compounds-that mimic the anti-aging effects of metformin and rapamycin without adverse effects. We applied several bioinformatic approaches and deep learning methods to the Library of Integrated Network-based Cellular Signatures (LINCS) dataset to map the gene- and pathway-level signatures of metformin and rapamycin and screen for matches among over 800 natural compounds. We then predicted the safety of each compound with an ensemble of deep neural network classifiers. The analysis revealed many novel candidate metformin and rapamycin mimetics, including allantoin and ginsenoside (metformin), epigallocatechin gallate and isoliquiritigenin (rapamycin), and withaferin A (both). Four relatively unexplored compounds also scored well with rapamycin. This work revealed promising candidates for future experimental validation while demonstrating the applications of powerful screening methods for this and similar endeavors.

Rethinking modern theories of ageing and their classification: the proximate mechanisms and the ultimate explanations

For a very long time, ageing has been an insurmountable problem in biology. The collection of age-dependent changes that render ageing individuals progressively more likely to die seemed to be an intractable labyrinth of alterations and associations whose direct mechanisms and ultimate explanations were too complex and difficult to understand. The science of ageing has always been fraught with insuperable problems and obstacles. In 1990, Zhores Medvedev presented a list of roughly 300 different hypotheses to illustrate this remarkable complexity of the ageing process and various approaches to understanding its mechanisms, though none of these hypotheses or aspect theories could be the general theory of senescence. Moreover, in the light of current data some of these ideas are obsolete and inapplicable. Nonetheless, the misconception that there are hundreds of valid theories of ageing persists among many researchers and authors. In addition, some of these obsolete and discarded hypotheses, such as the rate of living theory, the wear and tear theory, the poisoning theory, or the entropy theory still can be found in today’s medical textbooks, scientific publications aimed at the general public, and even in scientific writing. In fact, there are only several modern theories of ageing supported by compelling evidence that attempt to explain most of the data in current gerontology. These theories are competing to be a general and integrated model of ageing, making it unlikely that all of them could be true. This review summarises briefly several selected modern theories of senescence in the light of the contemporary knowledge of the biological basis for ageing and current data.

Association of mSin1 with mTORC2 Ras and Akt reveals a crucial domain on mSin1 involved in Akt phosphorylation

mSin1 is a unique component within the mammalian target of rapamycin (mTOR) complex 2 (mTORC2), which is responsible for cellular morphology and glucose metabolism. The association between mSin1 and other mTORC2 components, as well as their functions, has been explored previously; nevertheless, the mapping of the various binding domains of the components is lacking. Based on an evolutionary analysis of the gene, we constructed various fragments and truncated-forms of mSin1. We characterized the individual binding sites of mSin1 with its various partners, including mTOR, Rictor, Ras, and Akt. mTOR and Rictor bind to the amino acid (aa) 100-240 region of mSin1, which is different to the Ras binding site, the aa 260-460 region. A reciprocal examination found that mSin1 associated with the aa 2148-2300 region of mTOR, which is within the kinase domain, and with the carboxyl terminus of Rictor. Interestingly, Akt was found to associate with mSin1 in a region that slightly overlapped with the mTOR/Rictor complex binding site, namely aa 220-260. When only the Akt binding site was deleted from mSin1, phosphorylation of Akt S473 was greatly reduced. Furthermore, the association between Akt and mTOR can be regulated by serum, insulin and LY294002, but not by rapamycin or MAPK kinase inhibitors. Taken together, mSin1 would seem to act as a hub that allows mTORC2 to phosphorylate Akt S473. Our findings should facilitate future proteomic and crystallographic studies, help the development of dominant inhibitors and promote the identification of new drug targets.

While reinforcing cell cycle arrest, rapamycin and Torins suppress senescence in UVA-irradiated fibroblasts

Sunlight predisposes to skin cancer and melanomas. Ultraviolet A (UVA), a long wave component of sunlight, can reach dermal fibroblasts. Here we studied UVA-induced senescence in human fibroblasts in vitro. It is known that senescence occurs, when cell cycle is arrested, but mTOR is still active, thus converting arrest to senescence (geroconversion). We showed that, while arresting cell cycle, UVA did not inhibit mTOR, enabling geroconversion. In UVA-treated cells, mTOR remained fully active. Rapamycin and Torins 1/ 2 prevented UVA-induced senescent phenotype, although they further re-enforced cell cycle arrest. Given that senescent stromal fibroblasts support tumorigenesis, we envision that mTOR inhibitors may potentially be used to prevent sunlight-caused tumors as well as skin photo-aging.

Impact on Autophagy and Ultraviolet B Induced Responses of Treatment with the MTOR Inhibitors Rapamycin, Everolimus, Torin 1, and pp242 in Human Keratinocytes

The mechanistic target of Rapamycin (MTOR) protein is a crucial signaling regulator in mammalian cells that is extensively involved in cellular biology. The function of MTOR signaling in keratinocytes remains unclear. In this study, we detected the MTOR signaling and autophagy response in the human keratinocyte cell line HaCaT and human epidermal keratinocytes treated with MTOR inhibitors. Moreover, we detected the impact of MTOR inhibitors on keratinocytes exposed to the common carcinogenic stressors ultraviolet B (UVB) and UVA radiation. As a result, keratinocytes were sensitive to the MTOR inhibitors Rapamycin, everolimus, Torin 1, and pp242, but the regulation of MTOR downstream signaling was distinct. Next, autophagy induction only was observed in HaCaT cells treated with Rapamycin. Furthermore, we found that MTOR signaling was insensitive to UVB but sensitive to UVA radiation. UVB treatment also had no impact on the inhibition of MTOR signaling by MTOR inhibitors. Finally, MTOR inhibition by Rapamycin, everolimus, or pp242 did not affect the series of biological events in keratinocytes exposed to UVB, including the downregulation of BiP and PERK, activation of Histone H2A and JNK, and cleavage of caspase-3 and PARP. Our study demonstrated that MTOR inhibition in keratinocytes cannot always induce autophagy, and the MTOR pathway does not play a central role in the UVB triggered cellular response.

Therapeutic interventions for aging: the case of cellular senescence

Organismal aging is a multifactorial process characterized by the onset of degenerative conditions and cancer. One of the key drivers of aging is cellular senescence, a state of irreversible growth arrest induced by many pro-tumorigenic stresses. Senescent cells accumulate late in life and at sites of age-related pathologies, where they contribute to disease onset and progression through complex cell and non-cell autonomous effects. Here, we summarize the mechanisms by which cellular senescence can promote aging, and we offer an extensive description of current potential pharmacological interventions for senescent cells, highlighting limitations and suggesting alternatives.

Oncogenic KRAS activates an embryonic stem cell-like program in human colon cancer initiation

Colorectal cancer is the third most frequently diagnosed cancer worldwide. Prevention of colorectal cancer initiation represents the most effective overall strategy to reduce its associated morbidity and mortality. Activating KRAS mutation (KRASmut) is the most prevalent oncogenic driver in colorectal cancer development, and KRASmut inhibition represents an unmet clinical need. We apply a systems-level approach to study the impact of KRASmut on stem cell signaling during human colon cancer initiation by performing gene set enrichment analysis on gene expression from human colon tissues. We find that KRASmut imposes the embryonic stem cell-like program during human colon cancer initiation from colon adenoma to stage I carcinoma. Expression of miR145, an embryonic SC program inhibitor, promotes cell lineage differentiation marker expression in KRASmut colon cancer cells and significantly suppresses their tumorigenicity. Our data support an in vivo plasticity model of human colon cancer initiation that merges the intrinsic stem cell properties of aberrant colon stem cells with the embryonic stem cell-like program induced by KRASmut to optimize malignant transformation. Inhibition of the embryonic SC-like program in KRASmut colon cancer cells reveals a novel therapeutic strategy to programmatically inhibit KRASmut tumors and prevent colon cancer.

mTOR kinase inhibitor pp242 causes mitophagy terminated by apoptotic cell death in E1A-Ras transformed cells

mTOR is a critical target for controlling cell cycle progression, senescence and cell death in mammalian cancer cells. Here we studied the role of mTOR-dependent autophagy in implementating the antiprolifrative effect of mTORC1-specific inhibitor rapamycin and ATP-competitive mTOR kinase inhibitor pp242. We carried out a comprehensive analysis of pp242- and rapamycin-induced autophagy in ERas tumor cells. Rapamycin exerts cytostatic effect on ERas tumor cells, thus causing a temporary and reversible cell cycle arrest, activation of non-selective autophagy not accompanied by cell death. The rapamycin-treated cells are able to continue proliferation after drug removal. The ATP-competitive mTORC1/mTORC2 kinase inhibitor pp242 is highly cytotoxic by suppressing the function of mTORC1-4EBP1 axis and mTORC1-dependent phosphorylation of mTORC1 target--ULK1-Ser757 (Atg1). In contrast to rapamycin, pp242 activates the selective autophagy targeting mitochondria (mitophagy). The pp242-induced mitophagy is accompanied by accumulation of LC3 and conversion of LC3-I form to LC3-II. However reduced degradation of p62/SQSTM indicates abnormal flux of autophagic process. According to transmission electron microscopy data, short-term pp242-treated ERas cells exhibit numerous heavily damaged mitochondria, which are included in single membrane-bound autophagic/autolysophagic vacuoles (mitophagy). Despite the lack of typical for apoptosis features, ERas-treated cells with induced mitophagy revealed the activation of caspase 3, 9 and nucleosomal DNA fragmentation. Thus, pp242 activates autophagy with suppressed later stages, leading to impaired recycling and accumulation of dysfunctional mitochondria and cell death. Better understanding of how autophagy determines the fate of a cell--survival or cell death, can help to development of new strategy for cancer therapy.

Targeting mTOR signaling by polyphenols: A new therapeutic target for ageing

Current ageing research is aimed not only at the promotion of longevity, but also at improving ‎health span‎ through the‎ discovery and development‎ of new therapeutic strategies‎‏‎ by investigating ‎molecular and ‎cellular ‎pathways involved in cellular senescence.‎ Understanding the mechanism of action ‎of ‎polyphenolic compounds targeting mTOR (mechanistic target of rapamycin) and related pathways opens up new directions ‎‎to revolutionize ways to slow down the ‎onset and development of age-dependent degeneration. Herein, we will ‎discuss the mechanisms by which polyphenols can delay the‎ molecular ‎pathogenesis of ageing via manipulation or more specifically inhibition of mTOR-signaling pathways. We will also discuss the implications of polyphenols in targeting mTOR and its related ‎pathways‎‎ on ‎health life span extension and longevity.‎.

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.

Dual mTORC1/C2 inhibitors: gerosuppressors with potential anti-aging effect

Over the past decade, our understanding of the molecular and cellular mechanisms presiding over cellular and tissue decline with aging has greatly advanced. Classical hallmarks of aging cell include increasing levels of reactive oxygen species, DNA damage and senescence entry, which disrupt tissue architecture and function. Tissue dysfunction with aging has been shown to correlate with a cellular switch from a G0 reversible quiescence state into a G0 irreversible senescence state (geroconversion), causing a permanent proliferative block. The TOR (target of rapamycin) kinase has been shown to promote geroconversion. Rapamycin and other rapalogs specifically suppress activity of the mammalian TOR (mTOR) complex 1 (mTORC1) -but not mTOR complex 2 (mTORC2)- and decrease senescence entry, thus preserving proliferative potential. In this perspective, we briefly comment recent progress of Leontieva and colleagues showing a new class of non-rapalog drugs that target simultaneously mTORC1 and mTORC2 and prevent geroconversion in a more efficient way than rapamycin. Its potential future use as rejuvenating, anti-aging therapeutics is therefore proposed.

How ageing increases cancer susceptibility: A tale of two opposing yet synergistic views

It is well known that with increasing age, the risk of acquiring certain age-related diseases - such as diabetes, cancer, cardiovascular disease and neurodegenerative diseases, increases. Several theories have been proposed to explain the reason why ageing leads to higher susceptibility to disease. Over time, many of these theories have been proven wrong. Currently, the two theories holding the interest of researchers in this field are the oxidative damage theory and hyperfunction theory of ageing. The former is an old theory which explains that ageing is as a result of oxidative damage (to macromolecular components of the cell) by reactive oxygen species produced as a normal part of metabolism. The hyperfunction theory is a much newer theory which explains that ageing is as a result of the unnecessary and unwanted continuation of certain metabolic processes at old age. In this review, we discuss the mechanisms which underlie the development of age-related cancer. We also discuss the aforementioned theories of ageing. We conclude by explaining the opposing views of proponents of both theories and provide a new viewpoint by revealing a point of synergy in the two theories.

How Diet Intervention via Modulation of DNA Damage Response through MicroRNAs May Have an Effect on Cancer Prevention and Aging, an in Silico Study

The DNA damage response (DDR) is a molecular mechanism that cells have evolved to sense DNA damage (DD) to promote DNA repair, or to lead to apoptosis, or cellular senescence if the damage is too extensive. Recent evidence indicates that microRNAs (miRs) play a critical role in the regulation of DDR. Dietary bioactive compounds through miRs may affect activity of numerous genes. Among the most studied bioactive compounds modulating expression of miRs are epi-gallocatechin-3-gallate, curcumin, resveratrol and n3-polyunsaturated fatty acids. To compare the impact of these dietary compounds on DD/DDR network modulation, we performed a literature search and an in silico analysis by the DIANA-mirPathv3 software. The in silico analysis allowed us to identify pathways shared by different miRs involved in DD/DDR vis-à-vis the specific compounds. The results demonstrate that certain miRs (e.g., -146, -21) play a central role in the interplay among DD/DDR and the bioactive compounds. Furthermore, some specific pathways, such as "fatty acids biosynthesis/metabolism", "extracellular matrix-receptor interaction" and "signaling regulating the pluripotency of stem cells", appear to be targeted by most miRs affected by the studied compounds. Since DD/DDR and these pathways are strongly related to aging and carcinogenesis, the present in silico results of our study suggest that monitoring the induction of specific miRs may provide the means to assess the antiaging and chemopreventive properties of particular dietary compounds.

Potential therapeutic effects of the MTOR inhibitors for preventing ageing and progeria-related disorders

The mammalian target of rapamycin (mTOR) pathway is an highly conserved signal transduction axis involved in many cellular processes, such as cell growth, survival, transcription, translation, apoptosis, metabolism, motility and autophagy. Recently, this signalling pathway has come to the attention of the scientific community owing to the unexpected finding that inhibition of mTOR by rapamycin, an antibiotic with immunosuppressant and chemotherapeutic properties, extends lifespan in diverse animal models. Moreover, rapamycin has been reported to rescue the cellular phenotype in a progeroid syndrome [Hutchinson–Gilford Progeria syndrome (HGPS)] that recapitulates most of the traits of physiological ageing. The promising perspectives raised by these results warrant a better understanding of mTOR signalling and the potential applications of mTOR inhibitors to counteract ageing‐associated diseases and increase longevity. This review is focused on these issues.

Reflections on the role of senescence during development and aging

New and stimulating results have challenged the concept that cellular senescence might not be synonymous with aging. It is indisputable that during aging, senescent cell accumulation has an impact on organismal health. Nevertheless, senescent cells are now known to display physiological roles during embryonic development, during wound healing repair and as a cellular response to stress. The fact that senescence has been found in cells that did not attain their maximal round of replications, nor have metabolic alterations or DNA damage, also challenges the paradigm that senescence is cellular aging, and it is in favor of the idea that cellular senescence is a phenomenon that has a function by itself. Therefore, in order to understand this phenomenon it is important to analyze the relationship between senescence and other cellular responses that have many features in common, such as apoptosis, cancer and autophagy, particularly highlighting their role during development and adulthood.