Integrative Multimodal Metabolomics to Early Predict Cognitive Decline Among Amyloid Positive Community-Dwelling Older Adults

Alzheimer's disease is strongly linked to metabolic abnormalities. We aimed to distinguish amyloid-positive people who progressed to cognitive decline from those who remained cognitively intact. We performed untargeted metabolomics of blood samples from amyloid-positive individuals, before any sign of cognitive decline, to distinguish individuals who progressed to cognitive decline from those who remained cognitively intact. A plasma-derived metabolite signature was developed from Supercritical Fluid chromatography coupled with high-resolution mass spectrometry (SFC-HRMS) and nuclear magnetic resonance (NMR) metabolomics. The 2 metabolomics data sets were analyzed by Data Integration Analysis for Biomarker discovery using Latent approaches for Omics studies (DIABLO), to identify a minimum set of metabolites that could describe cognitive decline status. NMR or SFC-HRMS data alone cannot predict cognitive decline. However, among the 320 metabolites identified, a statistical method that integrated the 2 data sets enabled the identification of a minimal signature of 9 metabolites (3-hydroxybutyrate, citrate, succinate, acetone, methionine, glucose, serine, sphingomyelin d18:1/C26:0 and triglyceride C48:3) with a statistically significant ability to predict cognitive decline more than 3 years before decline. This metabolic fingerprint obtained during this exploratory study may help to predict amyloid-positive individuals who will develop cognitive decline. Due to the high prevalence of brain amyloid-positivity in older adults, identifying adults who will have cognitive decline will enable the development of personalized and early interventions.

A locally optimised machine learning approach to early prognostication of long-term neurological outcomes after out-of-hospital cardiac arrest

Background

Out-of-hospital cardiac arrest (OHCA) represents a major burden for society and health care, with an average incidence in adults of 67 to 170 cases per 100,000 person-years in Europe and in-hospital survival rates of less than 10%. Patients and practitioners would benefit from a prognostication tool for long-term good neurological outcomes.

Objective

We aim to develop a machine learning (ML) pipeline on a local database to classify patients according to their neurological outcomes and identify prognostic features.

Methods

We collected clinical and biological data consecutively from 595 patients who presented OHCA and were routed to a single regional cardiac arrest centre in the south of France. We applied recursive feature elimination and ML analyses to identify the main features associated with a good neurological outcome, defined as a Cerebral Performance Category score less than or equal to 2 at six months post-OHCA.

Results

We identified 12 variables 24 h after admission, capable of predicting a six-month good neurological outcome. The best model (extreme gradient boosting) achieved an AUC of 0.96 and an accuracy of 0.92 in the test cohort.

Conclusion

We demonstrated that it is possible to build accurate, locally optimised prediction and prognostication scores using datasets of limited size and breadth. We proposed and shared a generic machine-learning pipeline which allows external teams to replicate the approach locally.

CD36 Drives Metastasis and Relapse in Acute Myeloid Leukemia

Identifying mechanisms underlying relapse is a major clinical issue for effective cancer treatment. The emerging understanding of the importance of metastasis in hematologic malignancies suggests that it could also play a role in drug resistance and relapse in acute myeloid leukemia (AML). In a cohort of 1,273 AML patients, we uncovered that the multifunctional scavenger receptor CD36 was positively associated with extramedullary dissemination of leukemic blasts, increased risk of relapse after intensive chemotherapy, and reduced event-free and overall survival. CD36 was dispensable for lipid uptake but fostered blast migration through its binding with thrombospondin-1. CD36-expressing blasts, which were largely enriched after chemotherapy, exhibited a senescent-like phenotype while maintaining their migratory ability. In xenograft mouse models, CD36 inhibition reduced metastasis of blasts and prolonged survival of chemotherapy-treated mice. These results pave the way for the development of CD36 as an independent marker of poor prognosis in AML patients and a promising actionable target to improve the outcome of patients.

SIGNIFICANCE

CD36 promotes blast migration and extramedullary disease in acute myeloid leukemia and represents a critical target that can be exploited for clinical prognosis and patient treatment.

Explainable machine learning framework to predict personalized physiological aging

Attaining personalized healthy aging requires accurate monitoring of physiological changes and identifying subclinical markers that predict accelerated or delayed aging. Classic biostatistical methods most rely on supervised variables to estimate physiological aging and do not capture the full complexity of inter-parameter interactions. Machine learning (ML) is promising, but its black box nature eludes direct understanding, substantially limiting physician confidence and clinical usage. Using a broad population dataset from the National Health and Nutrition Examination Survey (NHANES) study including routine biological variables and after selection of XGBoost as the most appropriate algorithm, we created an innovative explainable ML framework to determine a Personalized physiological age (PPA). PPA predicted both chronic disease and mortality independently of chronological age. Twenty-six variables were sufficient to predict PPA. Using SHapley Additive exPlanations (SHAP), we implemented a precise quantitative associated metric for each variable explaining physiological (i.e., accelerated or delayed) deviations from age-specific normative data. Among the variables, glycated hemoglobin (HbA1c) displays a major relative weight in the estimation of PPA. Finally, clustering profiles of identical contextualized explanations reveal different aging trajectories opening opportunities to specific clinical follow-up. These data show that PPA is a robust, quantitative and explainable ML-based metric that monitors personalized health status. Our approach also provides a complete framework applicable to different datasets or variables, allowing precision physiological age estimation.

Periostin Plasma Levels and Changes on Physical and Cognitive Capacities in Community-Dwelling Older Adults

Periostin, involved in extracellular matrix development and support, has been shown to be elevated in senescent tissues and fibrotic states, transversal signatures of aging. We aimed to explore associations between plasma periostin and physical and cognitive capacity evolution among older adults. Our hypothesis was that higher levels of plasma periostin will be associated with worse physical and mental capacities along time. Analyses included 1 096 participants (mean age = 75.3 years ± 4.4; 63.9% women) from the Multidomain Alzheimer Preventive Trial. Periostin levels (pg/mL) were measured in plasma collected at year 1. Periostin was used in continuous variable, and as a dichotomous variable highest quartile (POSTN+) versus lowest 3 quartiles (POSTN-) were used. Outcomes were measured annually over 4 years and included: gait speed (GS), short physical performance battery (SPPB) score, 5-times sit-to-stand test (5-STS), and handgrip strength (HS) as physical and cognitive composite z-score (CCS) and the Mini-Mental State Examination (MMSE) as cognitive endpoints. Plasma periostin as a continuous variable was associated with the worsening of physical and cognitive capacities over 4 years of follow-up, specifically the SPPB score, the 5-STS, and CCS in full-adjusted models. POSTN+ was associated with worse evolution in the physical (GS: [β = -0.057, 95% confidence interval (CI) = -0.101, -0.013], SPPB score [β = -0.736, 95% CI = -1.091, -0.381], 5-STS [β = 1.681, 95% CI = 0.801, 2.561]) as well as cognitive (CCS [β = -0.215, 95% CI = -0.335, -0.094]) domains compared to POSTN- group. No association was found with HS or the MMSE score. Our study showed for the first time that increased plasma periostin levels were associated with declines in both physical and cognitive capacities in older adults over a 4-year follow-up. Further research is needed to evaluate whether periostin might be used as a predictive biomarker of functional decline at an older age.

A gerophysiology perspective on healthy ageing

Improvements in public health and health care have resulted in significant increases in lifespan globally, but also in a significant increase in chronic disease prevalence. This has led to a focus on healthy ageing bringing a shift from a pathology-centered to an intrinsic capacity and function-centered view. In parallel, the emerging field of geroscience has promoted the exploration of the biomolecular drivers of ageing towards a transverse vision by proposing an integrated set of molecular hallmarks. In this review, we propose to take a step further in this direction, highlighting a gerophysiological perspective that considers the notion of homeostasis/allostasis relating to robustness/fragility respectively. While robustness is associated with homeostasis achieved by an optimal structure/function relationship in all organs, successive repair processes occurring after daily injuries and infections result in accumulation of scar healing leading to progressive tissue degeneration, allostasis and frailty. Considering biological ageing as the accumulation of scarring at the level of the whole organism emphasizes three transverse and shared elements in the body - mesenchymal stroma cells/immunity/metabolism (SIM). This SIM tryptich drives tissue and organ fate to regulate the age-related evolution of body functions. It provides the basis of a gerophysiology perspective, possibly representing a better way to decipher healthy ageing, not only by defining a composite biomarker(s) but also by developing new preventive/curative strategies.

Long non-coding RNA Neat1 and paraspeckle components are translational regulators in hypoxia

Internal ribosome entry sites (IRESs) drive translation initiation during stress. In response to hypoxia, (lymph)angiogenic factors responsible for tissue revascularization in ischemic diseases are induced by the IRES-dependent mechanism. Here, we searched for IRES trans-acting factors (ITAFs) active in early hypoxia in mouse cardiomyocytes. Using knock-down and proteomics approaches, we show a link between a stressed-induced nuclear body, the paraspeckle, and IRES-dependent translation. Furthermore, smiFISH experiments demonstrate the recruitment of IRES-containing mRNA into paraspeckle during hypoxia. Our data reveal that the long non-coding RNA Neat1, an essential paraspeckle component, is a key translational regulator, active on IRESs of (lymph)angiogenic and cardioprotective factor mRNAs. In addition, paraspeckle proteins p54^nrb and PSPC1 as well as nucleolin and RPS2, two p54^nrb-interacting proteins identified by mass spectrometry, are ITAFs for IRES subgroups. Paraspeckle thus appears as a platform to recruit IRES-containing mRNAs and possibly host IRESome assembly. Polysome PCR array shows that Neat1 isoforms regulate IRES-dependent translation and, more widely, translation of mRNAs involved in stress response.

Healthy Aging Biomarkers: The INSPIRE's Contribution

The find solutions for optimizing healthy aging and increase health span is one of the main challenges for our society. A novel healthcare model based on integration and a shift on research and care towards the maintenance of optimal functional levels are now seen as priorities by the WHO. To address this issue, an integrative global strategy mixing longitudinal and experimental cohorts with an innovative transverse understanding of physiological functioning is missing. While the current approach to the biology of aging is mainly focused on parenchymal cells, we propose that age-related loss of function is largely determined by three elements which constitute the general ground supporting the different specific parenchyma: i.e. the stroma, the immune system and metabolism. Such strategy that is implemented in INSPIRE projects can strongly help to find a composite biomarker capable of predicting changes in capacity across the life course with thresholds signalling frailty and care dependence.

Lactate Fluxes and Plasticity of Adipose Tissues: A Redox Perspective

Lactate, a metabolite produced when the glycolytic flux exceeds mitochondrial oxidative capacities, is now viewed as a critical regulator of metabolism by acting as both a carbon and electron carrier and a signaling molecule between cells and tissues. In recent years, increasing evidence report its key role in white, beige, and brown adipose tissue biology, and highlights new mechanisms by which lactate participates in the maintenance of whole-body energy homeostasis. Lactate displays a wide range of biological effects in adipose cells not only through its binding to the membrane receptor but also through its transport and the subsequent effect on intracellular metabolism notably on redox balance. This study explores how lactate regulates adipocyte metabolism and plasticity by balancing intracellular redox state and by regulating specific signaling pathways. We also emphasized the contribution of adipose tissues to the regulation of systemic lactate metabolism, their roles in redox homeostasis, and related putative physiopathological repercussions associated with their decline in metabolic diseases and aging.

Revisiting the Hallmarks of Aging to Identify Markers of Biological Age

The Geroscience aims at a better understanding of the biological processes of aging, to prevent and/or delay the onset of chronic diseases and disability as well as to reduce the severity of these adverse clinical outcomes. Geroscience thus open up new perspectives of care to live a healthy aging, that is to say without dependency. To date, life expectancy in healthy aging is not increasing as fast as lifespan. The identification of biomarkers of aging is critical to predict adverse outcomes during aging, to implement interventions to reduce them, and to monitor the response to these interventions. In this narrative review, we gathered information about biomarkers of aging under the perspective of Geroscience. Based on the current literature, for each hallmark of biological aging, we proposed a putative biomarker of healthy aging, chosen for their association with mortality, age-related chronic diseases, frailty and/or functional loss. We also discussed how they could be validated as useful predictive biomarkers.

The INSPIRE Bio-Resource Research Platform for Healthy Aging and Geroscience: Focus on the Human Translational Research Cohort (The INSPIRE-T Cohort)

BACKGROUND

The Geroscience field focuses on the core biological mechanisms of aging, which are involved in the onset of age-related diseases, as well as declines in intrinsic capacity (IC) (body functions) leading to dependency. A better understanding on how to measure the true age of an individual or biological aging is an essential step that may lead to the definition of putative markers capable of predicting healthy aging.

OBJECTIVES

The main objective of the INStitute for Prevention healthy agIng and medicine Rejuvenative (INSPIRE) Platform initiative is to build a program for Geroscience and healthy aging research going from animal models to humans and the health care system. The specific aim of the INSPIRE human translational cohort (INSPIRE-T cohort) is to gather clinical, digital and imaging data, and perform relevant and extensive biobanking to allow basic and translational research on humans.

METHODS

The INSPIRE-T cohort consists in a population study comprising 1000 individuals in Toulouse and surrounding areas (France) of different ages (20 years or over - no upper limit for age) and functional capacity levels (from robustness to frailty, and even dependency) with follow-up over 10 years. Diversified data are collected annually in research facilities or at home according to standardized procedures. Between two annual visits, IC domains are monitored every 4-month by using the ICOPE Monitor app developed in collaboration with WHO. Once IC decline is confirmed, participants will have a clinical assessment and blood sampling to investigate markers of aging at the time IC declines are detected. Biospecimens include blood, urine, saliva, and dental plaque that are collected from all subjects at baseline and then, annually. Nasopharyngeal swabs and cutaneous surface samples are collected in a large subgroup of subjects every two years. Feces, hair bulb and skin biopsy are collected optionally at the baseline visit and will be performed again during the longitudinal follow up.

EXPECTED RESULTS

Recruitment started on October 2019 and is expected to last for two years. Bio-resources collected and explored in the INSPIRE-T cohort will be available for academic and industry partners aiming to identify robust (set of) markers of aging, age-related diseases and IC evolution that could be pharmacologically or non-pharmacologically targetable. The INSPIRE-T will also aim to develop an integrative approach to explore the use of innovative technologies and a new, function and person-centered health care pathway that will promote a healthy aging.

Lactate fluxes mediated by the monocarboxylate transporter-1 are key determinants of the metabolic activity of beige adipocytes

Activation of energy-dissipating brown/beige adipocytes represents an attractive therapeutic strategy against metabolic disorders. While lactate is known to induce beiging through the regulation of Ucp1 gene expression, the role of lactate transporters on beige adipocytes' ongoing metabolic activity remains poorly understood. To explore the function of the lactate-transporting monocarboxylate transporters (MCTs), we used a combination of primary cell culture studies, 13C isotopic tracing, laser microdissection experiments, and in situ immunofluorescence of murine adipose fat pads. Dissecting white adipose tissue heterogeneity revealed that the MCT1 is expressed in inducible beige adipocytes as the emergence of uncoupling protein 1 after cold exposure was restricted to a subpopulation of MCT1-expressing adipocytes suggesting MCT1 as a marker of inducible beige adipocytes. We also observed that MCT1 mediates bidirectional and simultaneous inward and outward lactate fluxes, which were required for efficient utilization of glucose by beige adipocytes activated by the canonical β3-adrenergic signaling pathway. Finally, we demonstrated that significant lactate import through MCT1 occurs even when glucose is not limiting, which feeds the oxidative metabolism of beige adipocytes. These data highlight the key role of lactate fluxes in finely tuning the metabolic activity of beige adipocytes according to extracellular metabolic conditions and reinforce the emerging role of lactate metabolism in the control of energy homeostasis.

Towards a large-scale assessment of the relationship between biological and chronological aging: The INSPIRE Mouse Cohort

Aging is the major risk factor for the development of chronic diseases. After decades of research focused on extending lifespan, current efforts seek primarily to promote healthy aging. Recent advances suggest that biological processes linked to aging are more reliable than chronological age to account for an individual’s functional status, i.e. frail or robust. It is becoming increasingly apparent that biological aging may be detectable as a progressive loss of resilience much earlier than the appearance of clinical signs of frailty. In this context, the INSPIRE program was built to identify the mechanisms of accelerated aging and the early biological signs predicting frailty and pathological aging. To address this issue, we designed a cohort of outbred Swiss mice (1576 male and female mice) in which we will continuously monitor spontaneous and voluntary physical activity from 6 to 24 months of age under either normal or high fat/high sucrose diet. At different age points (6, 12, 18, 24 months), multiorgan functional phenotyping will be carried out to identify early signs of organ dysfunction and generate a large biological fluids/feces/organs biobank (100,000 samples). A comprehensive correlation between functional and biological phenotypes will be assessed to determine: 1) the early signs of biological aging and their relationship with chronological age; 2) the role of dietary and exercise interventions on accelerating or decelerating the rate of biological aging; and 3) novel targets for the promotion of healthy aging. All the functional and omics data, as well as the biobank generated in the framework of the INSPIRE cohort will be available to the aging scientific community. The present article describes the scientific background and the strategies employed for the design of the INSPIRE Mouse cohort.

The INSPIRE research initiative: a program for GeroScience and healthy aging research going from animal models to humans and the healthcare system

Aging is the most important risk factor for the onset of several chronic diseases and functional decline. Understanding the interplays between biological aging and the biology of diseases and functional loss as well as integrating a function-centered approach to the care pathway of older adults are crucial steps towards the elaboration of preventive strategies (both pharmacological and non-pharmacological) against the onset and severity of burdensome chronic conditions during aging. In order to tackle these two crucial challenges, ie, how both the manipulation of biological aging and the implementation of a function-centered care pathway (the Integrated Care for Older People (ICOPE) model of the World Health Organization) may contribute to the trajectories of healthy aging, a new initiative on Gerosciences was built: the INSPIRE research program. The present article describes the scientific background on which the foundations of the INSPIRE program have been constructed and provides the general lines of this initiative that involves researchers from basic and translational science, clinical gerontology, geriatrics and primary care, and public health.

Vasohibin1, a new mouse cardiomyocyte IRES trans-acting factor that regulates translation in early hypoxia

Hypoxia, a major inducer of angiogenesis, triggers major changes in gene expression at the transcriptional level. Furthermore, under hypoxia, global protein synthesis is blocked while internal ribosome entry sites (IRES) allow specific mRNAs to be translated. Here, we report the transcriptome and translatome signatures of (lymph)angiogenic genes in hypoxic HL-1 mouse cardiomyocytes: most genes are induced at the translatome level, including all IRES-containing mRNAs. Our data reveal activation of (lymph)angiogenic factor mRNA IRESs in early hypoxia. We identify vasohibin1 (VASH1) as an IRES trans-acting factor (ITAF) that is able to bind RNA and to activate the FGF1 IRES in hypoxia, but which tends to inhibit several IRESs in normoxia. VASH1 depletion has a wide impact on the translatome of (lymph)angiogenesis genes, suggesting that this protein can regulate translation positively or negatively in early hypoxia. Translational control thus appears as a pivotal process triggering new vessel formation in ischemic heart.

Human adipose stromal-vascular fraction self-organizes to form vascularized adipose tissue in 3D cultures

Native human subcutaneous adipose tissue (AT) is well organized into unilocular adipocytes interspersed within dense vascularization. This structure is completely lost under standard culture conditions and may impair the comparison with native tissue. Here, we developed a 3-D model of human white AT reminiscent of the cellular architecture found in vivo. Starting with adipose progenitors derived from the stromal-vascular fraction of human subcutaneous white AT, we generated spheroids in which endogenous endothelial cells self-assembled to form highly organized endothelial networks among stromal cells. Using an optimized adipogenic differentiation medium to preserve endothelial cells, we obtained densely vascularized spheroids containing mature adipocytes with unilocular lipid vacuoles. In vivo study showed that when differentiated spheroids were transplanted in immune-deficient mice, endothelial cells within the spheroids connected to the recipient circulatory system, forming chimeric vessels. In addition, adipocytes of human origin were still observed in transplanted mice. We therefore have developed an in vitro model of vascularized human AT-like organoids that constitute an excellent tool and model for any study of human AT.

Mass Spectrometry-based Absolute Quantification of 20S Proteasome Status for Controlled Ex-vivo Expansion of Human Adipose-derived Mesenchymal Stromal/Stem Cells

The proteasome controls a multitude of cellular processes through protein degradation and has been identified as a therapeutic target in oncology. However, our understanding of its function and the development of specific modulators are hampered by the lack of a straightforward method to determine the overall proteasome status in biological samples. Here, we present a method to determine the absolute quantity and stoichiometry of ubiquitous and tissue-specific human 20S proteasome subtypes based on a robust, absolute SILAC-based multiplexed LC-Selected Reaction Monitoring (SRM) quantitative mass spectrometry assay with high precision, accuracy, and sensitivity. The method was initially optimized and validated by comparison with a reference ELISA assay and by analyzing the dynamics of catalytic subunits in HeLa cells following IFNγ-treatment and in range of human tissues. It was then successfully applied to reveal IFNγ- and O2-dependent variations of proteasome status during primary culture of Adipose-derived-mesenchymal Stromal/Stem Cells (ADSCs). The results show the critical importance of controlling the culture conditions during cell expansion for future therapeutic use in humans. We hypothesize that a shift from the standard proteasome to the immunoproteasome could serve as a predictor of immunosuppressive and differentiation capacities of ADSCs and, consequently, that quality control should include proteasomal quantification in addition to examining other essential cell parameters. The method presented also provides a new powerful tool to conduct more individualized protocols in cancer or inflammatory diseases where selective inhibition of the immunoproteasome has been shown to reduce side effects.

FTY720 (Fingolimod) Inhibits HIF1 and HIF2 Signaling, Promotes Vascular Remodeling, and Chemosensitizes in Renal Cell Carcinoma Animal Model

Clear cell renal cell carcinoma (ccRCC) is characterized by intratumoral hypoxia and chemoresistance. The hypoxia-inducible factors HIF1α and HIF2α play a crucial role in ccRCC initiation and progression. We previously identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway as a new modulator of HIF1α and HIF2α under hypoxia in various cancer cell models. Here, we report that FTY720, an inhibitor of the S1P signaling pathway, inhibits both HIF1α and HIF2α accumulation in several human cancer cell lines. In a ccRCC heterotopic xenograft model, we show that FTY720 transiently decreases HIF1α and HIF2α intratumoral level and modifies tumor vessel architecture within 5 days of treatment, suggesting a vascular normalization. In mice bearing subcutaneous ccRCC tumor, FTY720 and a gemcitabine-based chemotherapy alone display a limited effect, whereas, in combination, there is a significant effect on tumor size without toxicity. Noteworthy, administration of FTY720 for 5 days before chemotherapy is not associated with a more effective tumor control, suggesting a mode of action mainly independent of the vascular remodeling. In conclusion, these findings demonstrate that FTY720 could successfully sensitize ccRCC to chemotherapy and establish this molecule as a potent therapeutic agent for ccRCC treatment, independently of drug scheduling. Mol Cancer Ther; 15(10); 2465-74. ©2016 AACR.

Neutralizing S1P inhibits intratumoral hypoxia, induces vascular remodelling and sensitizes to chemotherapy in prostate cancer

Hypoxia promotes neovascularization, increased tumor growth, and therapeutic resistance. The transcription factor, hypoxia-inducible factor 1α (HIF-1α), has been reported as the master driver of adaptation to hypoxia. We previously identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway as a new modulator of HIF-1α under hypoxia. Taking advantage of a monoclonal antibody neutralizing extracellular S1P (sphingomab), we report that inhibition of S1P extracellular signaling blocks HIF-1α accumulation and activity in several cancer cell models exposed to hypoxia. In an orthotopic xenograft model of prostate cancer, we show that sphingomab reduces hypoxia and modifies vessel architecture within 5 days of treatment, leading to increased intratumoral blood perfusion. Supporting the notion that a transient vascular normalization of tumor vessels is the mechanism by which sphingomab exerts its effects, we demonstrate that administration of the antibody for 5 days before chemotherapy is more effective at local tumor control and metastatic dissemination than any other treatment scheduling. These findings validate sphingomab as a potential new normalization agent that could contribute to successful sensitization of hypoxic tumors to chemotherapy.

Essential role for SphK1/S1P signaling to regulate hypoxia-inducible factor 2α expression and activity in cancer

The sphingosine kinase-1/sphingosine 1-phosphate (SphK1/S1P) signaling pathway has been reported to modulate the expression of the canonical transcription factor hypoxia-inducible HIF-1α in multiple cell lineages. HIF-2α is also frequently overexpressed in solid tumors but its role has been mostly studied in clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, where HIF-2α has been established as a driver of a more aggressive disease. In this study, the role of SphK1/S1P signaling with regard to HIF-2α was investigated in various cancer cell models including ccRCC cells. Under hypoxic conditions or in ccRCC lacking a functional von Hippel-Lindau (VHL) gene and expressing high levels of HIF-2α, SphK1 activity controls HIF-2α expression and transcriptional activity through a phospholipase D (PLD)-driven mechanism. SphK1 silencing promotes a VHL-independent HIF-2α loss of expression and activity and reduces cell proliferation in ccRCC. Importantly, downregulation of SphK1 is associated with impaired Akt and mTOR signaling in ccRCC. Taking advantage of a monoclonal antibody neutralizing extracellular S1P, we show that inhibition of S1P extracellular signaling blocks HIF-2α accumulation in ccRCC cell lines, an effect mimicked when the S1P transporter Spns2 or the S1P receptor 1 (S1P₁) is silenced. Here, we report the first evidence that the SphK1/S1P signaling pathway regulates the transcription factor hypoxia-inducible HIF-2α in diverse cancer cell lineages notably ccRCC, where HIF-2α has been established as a driver of a more aggressive disease. These findings demonstrate that SphK1/S1P signaling may act as a canonical regulator of HIF-2α expression in ccRCC, giving support to its inhibition as a therapeutic strategy that could contribute to reduce HIF-2 activity in ccRCC.

Inhibition of the GTPase Rac1 mediates the antimigratory effects of metformin in prostate cancer cells

Cell migration is a critical step in the progression of prostate cancer to the metastatic state, the lethal form of the disease. The antidiabetic drug metformin has been shown to display antitumoral properties in prostate cancer cell and animal models; however, its role in the formation of metastases remains poorly documented. Here, we show that metformin reduces the formation of metastases to fewer solid organs in an orthotopic metastatic prostate cancer cell model established in nude mice. As predicted, metformin hampers cell motility in PC3 and DU145 prostate cancer cells and triggers a radical reorganization of the cell cytoskeleton. The small GTPase Rac1 is a master regulator of cytoskeleton organization and cell migration. We report that metformin leads to a major inhibition of Rac1 GTPase activity by interfering with some of its multiple upstream signaling pathways, namely P-Rex1 (a Guanine nucleotide exchange factor and activator of Rac1), cAMP, and CXCL12/CXCR4, resulting in decreased migration of prostate cancer cells. Importantly, overexpression of a constitutively active form of Rac1, or P-Rex, as well as the inhibition of the adenylate cyclase, was able to reverse the antimigratory effects of metformin. These results establish a novel mechanism of action for metformin and highlight its potential antimetastatic properties in prostate cancer.

Synthesis, structures, and selective toxicity to cancer cells of gold(I) complexes involving N-heterocyclic carbene ligands

New gold(I) complexes containing two 1-[2-(diethylamino)ethyl]imidazolydene ligands have been synthesized and characterized. The X-ray structures of two key compounds are presented. All complexes have been tested for their antiproliferative activities in prostate cancer cell line PC-3. Lipophilicity (Log P) has been determined for these complexes. The most active complex has been tested for the cytotoxic activities in five human cancer cell lines and primary endothelial cells. The most active complex demonstrated a potent selectivity for cancer cells.

Preclinical evidence that SSR128129E--a novel small-molecule multi-fibroblast growth factor receptor blocker--radiosensitises human glioblastoma

Resistance of glioblastoma to radiotherapy is mainly due to tumour cell radioresistance, which is partially controlled by growth factors such as fibroblast growth factor (FGF). Because we have previously demonstrated the role of FGF-2 in tumour cell radioresistance, we investigate here whether inhibiting FGF-2 pathways by targeting fibroblast growth factor receptor (FGFR) may represent a new strategy to optimise the efficiency of radiotherapy in glioblastoma. Treating radioresistant U87 and SF763 glioblastoma cells with the FGFR inhibitor, SSR12819E, radiosensitises these cells while the survival after irradiation of the more radiosensitive U251 and SF767 cells was not affected. SSR128129E administration to U87 cells increases the radiation-induced mitotic cell death. It also decreased cell membrane availability of the FGFR-1 mainly expressed in these cells, increased this receptor's ubiquitylation, inhibited radiation-induced RhoB activation and modulated the level of hypoxia inducible factor, HIF-1α, a master regulator of hypoxia, thus suggesting a role of FGFR in the regulation of hypoxia pathways. Moreover, treating orthotopically U87 xenografted mice with SSR128129E before two subsequent local 2.5Gy irradiations significantly increased the animals neurological sign free survival (NSFS) compared to the other groups of treatment. These results strongly suggest that targeting FGFR with the FGFR blocker SSR128129E might represent an interesting strategy to improve the efficiency of radiotherapy in glioblastoma.

Osteoblast-derived sphingosine 1-phosphate to induce proliferation and confer resistance to therapeutics to bone metastasis-derived prostate cancer cells

Sphingosine 1-phosphate (S1P) plays important roles in cell proliferation, differentiation or survival mainly through its surface G-protein-coupled receptors S1P1-5. Bone represents the major site of metastasis for prostate cancer (CaP) cells, which rely on bone-derived factors to support their proliferation and resistance to therapeutics. In the present work we have found that conditioned medium (CM) from the MC3T3 osteoblastic cell line or primary murine and human osteoblast-like cells, as well as co-culture with MC3T3 stimulate proliferation of CaP lines in S1P-dependent manner. In addition, osteoblastic-derived S1P induces resistance of CaP cells to therapeutics including chemotherapy and radiotherapy. When S1P release from osteoblastic cells is decreased (inhibition of SphK1, knock-down of SphK1 or the S1P transporter, Spns2 by siRNA) or secreted S1P neutralized with anti-S1P antibody, the proliferative and survival effects of osteoblasts on CaP cells are abolished. Because of the paracrine nature of the signaling, we studied the role of the S1P receptors expressed on CaP cells in the communication with S1P secreted by osteoblasts. Strategies aimed at down-regulating S1P1, S1P2 or S1P3 (siRNA, antagonists), established the exclusive role of the S1P/S1P1 signaling between osteoblasts and CaP cells. Bone metastases from CaP are associated with osteoblastic differentiation resulting in abnormal bone formation. We show that the autocrine S1P/S1P3 signaling is central during differentiation to mature osteoblasts by regulating Runx2 level, a key transcription factor involved in osteoblastic maturation. Importantly, differentiated osteoblasts exhibited enhanced secretion of S1P and further stimulated CaP cell proliferation in a S1P-dependent manner. By establishing the dual role of osteoblast-borne S1P on both osteoblastic differentiation and CaP cell proliferation and survival, we uncover the importance of S1P in the bone metastatic microenvironment, which may open a novel area of study for the treatment of CaP bone metastasis by targeting S1P.

Hypoxia, therapeutic resistance, and sphingosine 1-phosphate

Hypoxia, defined as a poor oxygenation, has been long recognized as a hallmark of solid tumors and a negative prognostic factor for response to therapeutics and survival of patients. Cancer cells have evolved biochemical mechanisms that allow them to react and adapt to hypoxia. At the cellular level, this adaptation is under the control of two related transcription factors, HIF-1 and HIF-2 (hypoxia-inducible factor), that respond rapidly to decreased oxygen levels to activate the expression of a broad range of genes promoting neoangiogenesis, glycolysis, metastasis, increased tumor growth, and resistance to treatments. Recent studies have identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) signaling pathway-which elicits various cellular processes including cell proliferation, cell survival, or angiogenesis-as a new regulator of HIF-1 or HIF-2 activity. In this review, we will focus on how the inhibition/neutralization of the SphK1/S1P signaling could be exploited for cancer therapy.

First evidence of sphingosine 1-phosphate lyase protein expression and activity downregulation in human neoplasm: implication for resistance to therapeutics in prostate cancer

This is the first report of sphingosine 1-phosphate lyase (SPL) protein expression and enzymatic activity in human neoplasm. This enzyme drives irreversible degradation of sphingosine 1-phosphate (S1P), a bioactive lipid associated with resistance to therapeutics in various cancers, including prostate adenocarcinoma. In fresh human prostatectomy specimens, a remarkable decrease in SPL enzymatic activity was found in tumor samples, as compared with normal adjacent tissues. A significant relationship between loss of SPL expression and higher Gleason score was confirmed in tissue microarray (TMA) analysis. Moreover, SPL protein expression and activity were inversely correlated with those of sphingosine kinase-1 (SphK1), the enzyme producing S1P. SPL and SphK1 expressions were independently predictive of aggressive cancer on TMA, supporting the relevance of S1P in prostate cancer. In human C4-2B and PC-3 cell lines, silencing SPL enhanced survival after irradiation or chemotherapy by decreasing expression of proteins involved in sensing and repairing DNA damage or apoptosis, respectively. In contrast, enforced expression of SPL sensitized cancer cells to irradiation or docetaxel by tilting the ceramide/S1P balance toward cell death. Interestingly, the S1P degradation products failed to sensitize to chemo- and radiotherapy, supporting the crucial role of ceramide/S1P balance in cancer. Of note, the combination of SPL enforced expression with a SphK1 silencing strategy by further decreasing S1P content made prostate cancer cells even more sensitive to anticancer therapies, suggesting that a dual strategy aimed at stimulating SPL, and inhibiting SphK1 could represent a future approach to sensitize cancer cells to cancer treatments.

Hypoxia-inducible factors and sphingosine 1-phosphate signaling

Hypoxia, defined as reduced tissue oxygen concentration, is a characteristic of solid tumors and is an indicator of unfavorable diagnosis in patients. At the cellular level, the adaptation to hypoxia is under the control of two related transcription factors, HIF-1α and HIF-2α (Hypoxia-Inducible Factor), which activate expression of genes promoting angiogenesis, metastasis, increased tumor growth and resistance to treatments. A role for HIF-1α and HIF-2α is also emerging in hematologic malignancies such as lymphoma and l eukemia. Recent studies have identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) signaling pathway - which elicits various cellular processes including cell proliferation, cell survival or angiogenesis - as a new regulator of HIF-1α or HIF-2α activity. This review will consider how targeting the SphK1/S1P signaling could represent an attractive strategy for therapeutic intervention in cancer.

Abstract 4826: A therapeutic sphingosine 1-phosphate antibody improves intratumoral oxygenation and sensitizes to chemotherapy in prostate cancer animal model

Hypoxia promotes neovascularization, metastasis, and resistance to treatments. The activation of the transcription factor HIF-1α has been identified as the master mechanism of adaptation to hypoxia. We recently identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway as a new modulator of HIF-1α activity under hypoxia in multiple cancer cell models including prostate cancer (Ader et al, Cancer Res, 2008). S1P elicits proliferation, survival, or angiogenesis, and is believed to exert most of its actions as a ligand for a family of specific GPCRs to elicit paracrine or autocrine signaling. We have suggested that inhibiting SphK1/S1P signaling, which is upregulated under hypoxia, may normalize the microenvironment and increase sensitivity to chemotherapy, in the broader concept of “normalization of tumor vessels” as tumor oxygenation is known to enhance response to chemotherapy (Ader et al., Cancer Res, 2009). Methods: Quantification of intratumoral hypoxia and angiogenesis, and treatment efficacy (primary tumor, metatasis dissemination) using an orthotopic (o.t) xenograft model of fluorescent hormone refractory prostate cancer cells. Results: We first provide in vitro evidence that inhibition of the S1P exogenous signaling, through pharmacological inhibition of its receptors or by taking advantage of a monoclonal antibody neutralizing S1P, blocks HIF-1α accumulation and its activity in prostate cancer cells under to hypoxia. Second, using an o.t model of prostate cancer, we show that an anti-S1P antibody inhibits intratumoral hypoxia and modifies vessel architecture and improves tumor perfusion within 5 days of treatment. Third, we show for the first time that an anti-S1P strategy sensitizes to docetaxel, the ‘gold standard’ treatment for hormone-refractory prostate cancer. A 5-day anti-S1P antibody pretreatment markedly sensitizes to docetaxel in an o.t. PC-3/GFP model established in nude mice. The combination anti-S1P antibody together with docetaxel was not only accompanied by a smaller primary tumor volume compared to docetaxel treatment, but also significantly reduced the occurrence and number of metastases. Conclusion: These preclinical data establish the proof-of-concept that blocking the exogenous action of S1P induces vascular normalization, improves intratumoral oxygenation and sensitizes to chemotherapy in prostate cancer animal model.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4826. doi:1538-7445.AM2012-4826

Effect of a therapeutic sphingosine 1-phosphate antibody on intratumoral hypoxia and standard chemotherapy in a preclinical model of prostate cancer

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Background: Hypoxia promotes vascularization, metastasis and resistance to treatments. The activation of HIF-1α is identified as the master mechanism of adaptation to hypoxia. We recently identified the sphingosine kinase 1/sphingosine 1- phosphate (SphK1/S1P) pathway as a new modulator of HIF-1α activity under hypoxia in multiple cancer cell models (Ader et al, Cancer Res, 2008). S1P elicits proliferation, survival, or angiogenesis, and is believed to exert most of its actions as a ligand for a family of specific GPCRs to elicit paracrine or autocrine signaling. We have suggested that inhibiting SphK1/S1P signaling, which is upregulated under hypoxia, may normalize the microenvironment and increase sensitivity to chemotherapy, in the broader concept of «normalization of tumor vessels» as tumor oxygenation is known to enhance response to chemotherapy (Ader et al., Cancer Res, 2009).

Methods: Quantitation of hypoxia and angiogenesis, and treatment efficacy using an orthotopic (o.t) xenograft model of fluorescent HRPC cells.

Results: We provide in vitro evidence that inhibiting the S1P exogenous signaling, through pharmacological inhibition of its receptors or by taking advantage of a monoclonal antibody neutralizing S1P, blocks HIF-1α accumulation and its activity in prostate cancer cells under hypoxia. Second, using an o.t model of prostate cancer, we show that an anti-S1P antibody inhibits intratumoral hypoxia, modifies vessel architecture and improves tumor perfusion within 5 days of treatment. Third, we demonstrate that an anti-S1P strategy sensitizes to docetaxel, the ’gold standard’ treatment for HRPC. A 5-day anti-S1P antibody pretreatment markedly sensitizes to docetaxel in an o.t. PC-3/GFP model established in nude mice. The combination anti-S1P antibody together with docetaxel was not only accompanied by a smaller primary tumor volume compared to docetaxel alone, but also significantly reduced the occurrence and number of metastases.

Conclusions: These data establish the proof-of-concept that blocking the exogenous action of S1P reduces intratumoral hypoxia and sensitizes to chemotherapy in prostate cancer animal model.

Effect of a therapeutic sphingosine 1-phosphate antibody on intratumoral hypoxia and sensitivity to standard chemotherapy in prostate cancer animal model

24

Background: Hypoxia promotes neovascularization, metastasis, growth and resistance to treatments. The activation of HIF-1α has been identified as the master mechanism of adaptation to hypoxia. We recently identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway as a new modulator of HIF-1α activity under hypoxia in multiple cancer cell models (Ader et al, Cancer Res, 2008). S1P elicits proliferation, survival, or angiogenesis, and is believed to exert most of its actions as a ligand for a family of specific GPCRs to elicit paracrine or autocrine signaling. We have suggested that inhibiting SphK1/S1P signaling, which is up-regulated under hypoxia, may help normalizing the tumor microenvironment and increase sensitivity to chemotherapy, in the broader concept of normalization of tumor vessels as tumor oxygenation is known to enhance response to chemotherapy (Ader et al., Cancer Res, 2009).

Methods: Quantitation of hypoxia and angiogenesis, and treatment efficacy using an orthotopic (o.t) xenograft model of fluorescent HRPC cells.

Results: We provide in vitro evidence that inhibiting the S1P exogenous signaling, through pharmacological inhibition of its receptors or by taking advantage of a monoclonal antibody neutralizing S1P, blocks HIF-1α accumulation and its activity in prostate cancer cells under hypoxia. Second, using an o.t model of prostate cancer, we show that an anti-S1P antibody inhibits intratumoral hypoxia and modifies vessel architecture within 5 days of treatment. Third, we demonstrate that an anti-S1P strategy sensitizes to docetaxel, the “gold standard” treatment for HRPC. A 5-day anti-S1P antibody pretreatment markedly sensitizes to docetaxel in an o.t. PC-3/GFP model established in nude mice. The combination anti-S1P antibodytogether withdocetaxel was not only accompanied by a smaller primary tumor volume compared to docetaxel alone, but also significantly reduced the occurrence and number of metastases.

Conclusions: These data establish the proof-of-concept that blocking the exogenous action of S1P reduces intratumoral hypoxia and sensitizes to chemotherapy in prostate cancer animal model.

[Table: see text]

Activation of sphingosine kinase-1 in cancer: implications for therapeutic targeting

Sphingolipid metabolites are critical to the regulation of a number of fundamental biological processes including cancer. Whereas ceramide and sphingosine mediate and trigger apoptosis or cell growth arrest, sphingosine 1-phosphate promotes proliferation, cell survival and angiogenesis. The delicate equilibrium between the intracellular levels of each of these sphingolipids is controlled by the enzymes that either produce or degrade these metabolites. Sphingosine kinase-1 is a crucial regulator of this two-pan balance, because its produces the pro-survival and pro-angiogenic sphingosine 1-phosphate and decreases the amount of both ceramide and sphingosine, the pro-apoptotic sphingolipids. Moreover, its gene is oncogenic, its mRNA is overproduced in several solid tumors, its overexpression protects cells from apoptosis, and its activity is down-regulated by anti-cancer treatments. Therefore, the sphingosine kinase-1/sphingosine 1-phosphate signaling pathway appears to be a target of interest for therapeutic manipulation.

The sphingosine kinase-1 survival pathway is a molecular target for the tumor-suppressive tea and wine polyphenols in prostate cancer

The sphingosine kinase-1/sphingosine 1-phosphate (SphK1/S1P) pathway has been associated with cancer promotion and progression and resistance to treatments in a number of cancers, including prostate adenocarcinoma. Here we provide the first evidence that dietary agents, namely, epigallocatechin gallate (EGCg, IC(50)≈75 μM), resveratrol (IC(50)≈40 μM), or a mixture of polyphenols from green tea [polyphenon E (PPE), IC(50)≈70 μM] or grapevine extract (vineatrol, IC(50)≈30 μM), impede prostate cancer cell growth in vitro and in vivo by inhibiting the SphK1/S1P pathway. We establish that SphK1 is a downstream effector of the ERK/phospholipase D (PLD) pathway, which is inhibited by green tea and wine polyphenols. Enforced expression of SphK1 impaired the ability of green tea and wine polyphenols, as well as pharmacological inhibitors of PLD and ERK activities, to induce apoptosis in PC-3 and C4-2B cells. The therapeutic efficacy of these polyphenols on tumor growth and the SphK1/S1P pathway were confirmed in animals using a heterotopic PC-3 tumor in place model. PC-3/SphK1 cells implanted in animals developed larger tumors and resistance to treatment with polyphenols. Furthermore, using an orthotopic PC-3/GFP model, the chemopreventive effect of an EGCg or PPE diet was associated with SphK1 inhibition, a decrease in primary tumor volume, and occurrence and number of metastases. These results provide the first demonstration that the prosurvival, antiapoptotic SphK1/S1P pathway represents a target of dietary green tea and wine polyphenols in cancer.

Abstract LB-35: A monoclonal sphingosine 1-phosphate antibody inhibits intratumoral hypoxia and sensitizes to docetaxel in prostate cancer animal model

The reduction in the normal level of tissue oxygen tension or hypoxia is a characteristic of solid tumors that triggers the activation of signaling pathways promoting neovascularization, metastasis, increased tumor growth, and resistance to treatments. The activation of the transcription factor hypoxia-inducible factor 1α (HIF-1α) has been identified as the master mechanism of adaptation to hypoxia. In a recent study (Ader et al, Cancer Res, 2008), we identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway, which elicits various cellular processes including cell proliferation, cell survival, or angiogenesis, as a new modulator of HIF-1α activity under hypoxic conditions Indeed, we have shown that SphK1 activity (which generates S1P) was rapidly stimulated under low oxygen conditions. The pharmacological inhibition and RNA silencing of SphK1 activity could prevent the accumulation of HIF-1α and its transcriptional activity in multiple cancer cell lineages - including prostate - suggesting a canonical pathway.

We have suggested that inhibiting the SphK1/S1P signaling, that is up-regulated under low oxygen tension, might help normalizing the tumor microenvironment and increase tumor sensitivity to radiation and chemotherapy, in the broader concept of « normalization of tumor vessels » as tumor oxygenation is known to enhance response to chemotherapy and radiation (reviewed in Ader et al., Cancer Res, 2009).

S1P is believed to exert most of its actions as a specific ligand for a family of five cognate G protein-coupled receptors to elicit paracrine or autocrine signaling cascades. We now provide evidence that inhibition of the S1P exogenous signaling, through pharmacological inhibition of its receptors or by taking advantage of a monoclonal antibody neutralizing S1P, blocks HIF-1α accumulation and its transcriptional activity in prostate cancer cells exposed to hypoxia. More importantly, in an orthotopic (o.t) xenograft model of prostate cancer, we show that a monoclonal antibody directed against S1P markedly reduces intratumoral hypoxia and modifies vessel architecture within 5 days of treatment. Finally, we demonstrate for the first time that a monoclonal antibody directed against S1P could sensitize to the antitumoral effects of docetaxel, the ‘gold standard’ treatment for hormone-refractory prostate cancer. Indeed, a 5-day anti-S1P antibody pretreatment markedly sensitizes to docetaxel in an o.t. PC-3/green fluorescent protein model established in nude mice. The combination anti-S1P antibody together with docetaxel was not only accompanied by a smaller primary tumor volume compared to docetaxel treatment but also markedly reduced the occurrence and number of metastases.

In conclusion, these data establish the proof-of-concept that blocking the exogenous action of S1P, by reducing intratumoral hypoxia, can sensitize to docetaxel-based chemotherapy in prostate cancer animal model.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-35.

When the sphingosine kinase 1/sphingosine 1-phosphate pathway meets hypoxia signaling: new targets for cancer therapy

The reduction in the normal level of tissue oxygen tension or hypoxia is a characteristic of solid tumors that triggers the activation of signaling pathways promoting neovascularization, metastasis, increased tumor growth, and resistance to treatments. The activation of the transcription factor hypoxia-inducible factor 1alpha (HIF-1alpha) has been identified as the master mechanism of adaptation to hypoxia. In a recent study, we identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway, which elicits various cellular processes including cell proliferation, cell survival, or angiogenesis, as a new modulator of HIF-1alpha activity under hypoxic conditions. Here, we consider how the SphK1/S1P signaling pathway could represent a very important target for therapeutic intervention in cancer.

Sphingosine kinase 1: a new modulator of hypoxia inducible factor 1alpha during hypoxia in human cancer cells

Here, we provide the first evidence that sphingosine kinase 1 (SphK1), an oncogenic lipid kinase balancing the intracellular level of key signaling sphingolipids, modulates the transcription factor hypoxia inducible factor 1alpha (HIF-1alpha), master regulator of hypoxia. SphK1 activity is stimulated under low oxygen conditions and regulated by reactive oxygen species. The SphK1-dependent stabilization of HIF-1alpha levels is mediated by the Akt/glycogen synthase kinase-3beta signaling pathway that prevents its von Hippel-Lindau protein-mediated degradation by the proteasome. The pharmacologic and RNA silencing inhibition of SphK1 activity prevents the accumulation of HIF-1alpha and its transcriptional activity in several human cancer cell lineages (prostate, brain, breast, kidney, and lung), suggesting a canonical pathway. Therefore, we propose that SphK1 can act as a master regulator for hypoxia, giving support to its inhibition as a valid strategy to control tumor hypoxia and its molecular consequences.

Gem associates with Ezrin and acts via the Rho-GAP protein Gmip to down-regulate the Rho pathway

Gem is a protein of the Ras superfamily that plays a role in regulating voltage-gated Ca2+ channels and cytoskeletal reorganization. We now report that GTP-bound Gem interacts with the membrane-cytoskeleton linker protein Ezrin in its active state, and that Gem binds to active Ezrin in cells. The coexpression of Gem and Ezrin induces cell elongation accompanied by the disappearance of actin stress fibers and collapse of most focal adhesions. The same morphological effect is elicited when cells expressing Gem alone are stimulated with serum and requires the expression of ERM proteins. We show that endogenous Gem down-regulates the level of active RhoA and actin stress fibers. The effects of Gem downstream of Rho, i.e., ERM phosphorylation as well as disappearance of actin stress fibers and most focal adhesions, require the Rho-GAP partner of Gem, Gmip, a protein that is enriched in membranes under conditions in which Gem induced cell elongation. Our results suggest that Gem binds active Ezrin at the plasma membrane-cytoskeleton interface and acts via the Rho-GAP protein Gmip to down-regulate the processes dependent on the Rho pathway.

Farnesylated RhoB inhibits radiation-induced mitotic cell death and controls radiation-induced centrosome overduplication

Our previous results demonstrated that expressing the GTPase ras homolog gene family, member B (RhoB) in radiosensitive NIH3T3 cells increases their survival following 2 Gy irradiation (SF2). We have first demonstrated here that RhoB expression inhibits radiation-induced mitotic cell death. RhoB is present in both a farnesylated and a geranylgeranylated form in vivo. By expressing RhoB mutants encoding for farnesylated (RhoB-F cells), geranylgeranylated or the CAAX deleted form of RhoB, we have then shown that only RhoB-F expression was able to increase the SF2 value by reducing the sensitivity of these cells to radiation-induced mitotic cell death. Moreover, RhoB-F cells showed an increased G2 arrest and an inhibition of centrosome overduplication following irradiation mediated by the Rho-kinase, strongly suggesting that RhoB-F may control centrosome overduplication during the G2 arrest after irradiation. Overall, our results for the first time clearly implicate farnesylated RhoB as a crucial protein in mediating cellular resistance to radiation-induced nonapoptotic cell death.

Inhibition of Rho pathways induces radiosensitization and oxygenation in human glioblastoma xenografts

We previously demonstrated in vitro that inhibiting the biological pathways of the small GTPase Rho radiosensitizes the human glioma U87 cell line. The aim of this study was to determine if Rho might be involved in the control of in vivo radiosensitivity altogether by controlling cellular radioresistance and by modifying tumor microenvironment. We demonstrate here that the in vivo induction of the dominant negative of Rho, RhoBN19, in U87 xenografts induces a significant decrease of tumor cell survival after irradiation more important than the one we previously observed in vitro. This in vivo increased effect of RhoBN19 expression is due to the improvement of the tumor oxygenation associated with a significant decrease of the vessel density and of the metalloproteinase 2 (MMP2) expression. Moreover, in vitro RhoBN19 expression in U87 cells leads to the inhibition of MMP2 activity. Our results demonstrate for the first time that inhibiting Rho pathways modifies the in vivo radiosensitivity of human glioma cells by controlling intrinsic radioresistance, hypoxia and angiogenesis. These data strongly suggest that Rho should be a major determinant of cellular resistance to ionizing radiation.

The radioprotective effect of the 24 kDa FGF-2 isoform in HeLa cells is related to an increased expression and activity of the DNA dependent protein kinase (DNA-PK) catalytic subunit

We previously reported that overexpression of the 24 kDa basic fibroblast factor (or FGF-2) isoform provides protection from the cytotoxic effect of ionizing radiation (IR). DNA double-strand breaks (DSB), the IR-induced lethal lesions, are mainly repaired in human cells by non-homologous end joining system (NHEJ). NHEJ reaction is dependent on the DNA-PK holoenzyme (composed of a regulatory sub-unit, Ku, and a catalytic sub-unit, DNA-PKcs) that assembles at sites of DNA damage. We demonstrated here that the activity of DNA-PK was increased by twofold in two independent radioresistant cell lines, HeLa 3A and CAPAN A3, over expressing the 24 kDa FGF-2. This increase was associated with an overexpression of the DNA-PKcs without modification of Ku expression or activity. This overexpression was due to an up-regulation of the DNA-PKcs gene transcription by the 24 kDa FGF-2 isoform. Finally, HeLa 3A cells exhibited the hallmarks of phenotypic changes associated with the overexpression of an active DNA-PKcs. Indeed, a faster repair rate of DSB and sensitization to IR by wortmannin was observed in these cells. Our results represent the characterization of a new mechanism of control of DNA repair and radioresistance in human tumor cells dependent on the overproduction of the 24 kDa FGF-2 isoform.

RhoB controls the 24 kDa FGF-2-induced radioresistance in HeLa cells by preventing post-mitotic cell death

Farnesylated Ras oncoprotein induces a cellular resistance to ionizing radiation that can be reversed by farnesyltransferase inhibitors (FTI). We previously demonstrated that, expression of the 24 kDa FGF2 isoform in wild type ras bearing HeLa cells, induced radioresistance which was also reversed by FTI. We tested the hypothesis that wild type Ras or RhoB, which has been proposed as a potential FTI target, could control the FGF-2-induced radioresistance mechanisms. For this, we expressed inducible dominant negative forms of Ras (RasN17) and Rho (RhoBN19) in 24 kDa FGF2 transfected HeLa cells and analysed their survival after irradiation. While no cell survival modification was observed after RasN17 induction, the expression of RhoBN19 induced a radiosensitization of FGF2 radioresistant HeLa cells in the same range as the one observed after a 48 h treatment with the specific FTI, R115777. Moreover, we showed that activated RhoB but not RhoA induced radioresistance in NIH3T3 cells. The radiosensitizer effect of RhoBN19 expression was due to the induction of the radiation induced post-mitotic cell death. Taken together, these data demonstrate that 24 kDa FGF-2-induced radioresistance is controlled by Rho pathways and suggest that RhoB should be a major determinant in cellular resistance to ionizing radiation.

Increased expression of a COOH-truncated nucleophosmin resulting from alternative splicing is associated with cellular resistance to ionizing radiation in HeLa cells

We previously demonstrated that transfecting HeLa cells with the 24 kDa basic fibroblast growth factor-2 (FGF-2) isoform dramatically increased cell survival after irradiation. To investigate genes implicated in this radioresistance acquisition, we compared mRNA expression between radioresistant 24 kDa FGF-2-expressing cells (HeLa 3A) and radiosensitive control HeLa PINA cells using the differential display technique. Of the 32 differentially expressed mRNAs, 1 presented a significant homology with a known gene. This 378 bp fragment presented 100% identity with exon 11 and 12 of human nucleophosmin (NPM) but differed by including a part of intron 9 in its 5' end. The differential expression of this fragment was confirmed using an RNase protection assay. We then cloned the entire corresponding mRNA and showed that it contained all the exons of NPM plus intron 9, suggesting that it was a splicing product of the NPM gene. This variant encoded for a 35-amino acid truncated NPM (NPM2). NPM2 expression was increased in HeLa 3A. To investigate NPM2's role in radioresistance acquisition, we transfected HeLa cells with NPM2 cDNA and analyzed survival after irradiation of the clones obtained. After transfection with NPM2, radiosensitive HeLa cells exhibited a dramatic increase in cell survival after irradiation. Taken together, our results demonstrate that expression of a COOH-truncated NPM form resulting from the alternative splicing of NPM mRNA is able to increase cell survival after irradiation and suggests that it might be involved in cellular response to ionizing radiation.

Inhibition of human tumor cell growth in vivo by an orally bioavailable inhibitor of human farnesyltransferase, BIM-46228

Oncogenic mutations of the ras gene leading to constitutive activation of downstream effectors have been detected in a wide spectrum of human cancers (pancreas, thyroid, colon, non-small-cell lung cancer). Membrane anchorage of Ras, required for functional activity in signal transduction, is facilitated by post-translational modifications resulting in covalent attachment of a farnesyl group to the cysteine in the C-terminal CAAX motif. This attachment is mediated by farnesyltransferase (FTase). Here, we report a novel FTase inhibitor, BIM-46228, which showed (i) specific inhibition of purified human FTase enzyme, (ii) inhibition of proliferation in vitro in a large spectrum of human tumor cell lines, (iii) inhibition of growth of human tumor xenografts in athymic nude mice treated by per os administration and (iv) the benefits of in vitro combination of its activity with chemotherapy or radiotherapy.

The farnesyltransferase inhibitor FTI-277 suppresses the 24-kDa FGF2-induced radioresistance in HeLa cells expressing wild-type RAS

In this paper, we describe the effect of the inhibitor of farnesyltransferase (FTI-277) on radioresistance induced by the 24-kDa isoform of FGF2 in human cells expressing wild-type RAS. Treatment with FTI-277 (20 microM) for 48 h prior to irradiation led to a significant decrease in survival of radioresistant cells expressing the 24-kDa isoform (HeLa 3A) but had no effect on the survival of control cells (HeLa PINA). The radiosensitizing effect of FTI-277 is accompanied by a stimulation of postmitotic cell death in HeLa 3A cells and by a reduction in G(2)/M-phase arrest in both cell types. These results clearly demonstrate that at least one farnesylated protein is involved in the regulation of the radioresistance induced by the 24-kDa isoform of FGF2. Furthermore, the radiation-induced G(2)/M-phase arrest is also under the control of farnesylated protein. This work also demonstrates that FTase inhibitors may be effective radiosensitizers of certain human tumors with wild-type RAS.