A selective neurotoxin takes many forms: as an antibody to a neurotrophin, as an alkylator, as an excitotoxin, as a blocker of requisite neuronal excitation during ontogenetic development, as a generator of oxidative stress, as an inhibitor of vital intraneuronal processes, and as an agent adversely affecting a host of multiple sites in neurons. Neurotoxins have been invaluable for elucidating cellular mechanisms attending or preventing neuronal necrosis and apoptosis, and for modeling and thereby discerning mechanisms invoked in neurological and psychiatric disorders. Neuroprotectants, endogenous and exogenous, are being explored as potentially useful agents to ward off diseases. Finally, hypothesized as posing a risk to humans as environmental constituents, neurotoxins are now being remodeled as adjuncts for therapeutic intervention in a variety of human medical disorders.

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Le sarcome de Ewing est la seconde tumeur pédiatrique de l’os la plus fréquente. Elle est caractérisée par une translocation chromosomique résultant à la fusion de EWSR1 avec un membre de la famille ETS. Chez 85% des patients, cette fusion conduit à l’expression de la protéine chimérique EWS-FLI1 qui est l’oncogène majeur de ce sarcome. Ce dernier agit principalement par son action transcriptionelle sur des cibles qui lui sont propres. Au niveau thérapeutique, le sarcome d’Ewing est traité par chimiothérapie, chirurgie locale et par radiothérapie. La survie à long terme des patients est de l’ordre de 70%, mais beaucoup plus basse pour les patients métastatiques et quasi nulle lors d’une récidive. Parmi maintes caractéristiques, certains cancers présentent une dérégulation énergétique. L’influence d’EWS-FLI1 sur cet aspect n’a fait l’objet d’aucune étude dans le contexte du sarcome d’Ewing. Nous avons donc étudié par profilage métabolomique des cellules de sarcome d’Ewing en présence ou en absence d’EWS-FLI1. En comparant ces deux conditions, des modulations du profil énergétique relatif au cycle de Krebs, des précurseurs de le glycosylation ainsi que des métabolites de la voie de la méthionine et du tryptophane ont été observés. En parallèle, grâce à un crible de banque de shRNAs réalisé dans des conditions expérimentales similaires à l’étude métabolomique (lignée d’Ewing avec ou sans EWS-FLI1), nous avons pu identifier des gènes présentant des caractéristiques « synthétique létales », c'est-à-dire tuant uniquement les cellules du sarcome d’Ewing en présence de son oncogène. / Ewing sarcoma, the second most commonly occurring pediatric bone tumor, is most often characterized by a chromosomal translocation between EWSR1 and FLI1. The gene fusion EWS-FLI1 accounts for 85% of all Ewing sarcoma and is considered the major oncogene and master regulator of Ewing sarcoma. EWS-FLI1 is a transcriptional modulator of targets, both directly and indirectly. Ewing sarcoma is aggressively treated with chemotherapy, localized surgery and radiation and has an overall survival of about 70%, however, survival for metastasis or relapsed cases remains low. One of the cancer hallmarks, metabolic deregulation, is most likely partly dependent on EWS-FLI1 in Ewing sarcoma cells. In order to get a better understanding of Ewing sarcoma biology and oncogenesis, it might be of high interest to investigate the influence of EWS-FLI1 in Ewing sarcoma cells. We therefore performed a global metabolic profiling of Ewing sarcoma cells with or without inhibition of EWS-FLI1. Several changes in the energy metabolism were observed throughout this study; the observed changes were consistent with an energy profile that moved from a cancer cell energy metabolism towards the energy metabolism of a more normal cell upon EWS-FLI1 inhibition, primarily based on the TCA cycle. Levels of TCA intermediates, glycosylation precursors, methionine pathway metabolites and amino acids, especially changes in the tryptophan metabolic pathway, were altered upon EWS-FLI1 inhibition. Parallel to this study, we performed a high-throughput synthetic lethality screen, in order to not only identify essential genes for cell survival and proliferation, but also to identify new synthetic lethal targets that could specifically target Ewing sarcoma cells carrying the EWS-FLI1 fusion gene.

Introduction: Coronary artery disease (CAD) has been associated with depressive symptoms and deficits in cognitive performance, both of which have been associated with poorer medical prognoses and poorer psychosocial outcomes. Physical activity can improve cognitive and depressive symptoms, and, for those with CAD, improve medical prognoses. It was hypothesized that depressive symptoms and poorer cognitive performance would be associated with poorer cardiopulmonary fitness in patients with CAD, and that these sequelae would be associated prospectively with noncompletion of cardiac rehabilitation (CR). The benefits of physical activity are thought to result, in part, from decreased inflammatory activity and increased adaptive neural plasticity, to which the ratio of kynurenine to tryptophan (K/T) and brain derived neurotrophic factor (BDNF), respectively, in peripheral blood may pertain. Methods and Results: In a cohort study of patients entering CR, depressive symptoms (Center for Epidemiological Studies Depression scale; CES-D scores) were associated with cardiopulmonary fitness (peak volume of oxygen uptake; VO2Peak) during an exercise stress test (B=-.404, p=.001, n=366). The VO2Peak was also associated with performance across multiple cognitive domains, but most strongly with performance on tests involving executive function, attention and psychomotor processing speed (β=.322, p=.002 for composite score, n=81) in a cohort of patients entering CR. In prospective cohort studies, Major Depressive Disorder (adjusted hazard ratio [HR] 2.5, 95% confidence interval [CI] 1.3–4.7, n=195) and poorer performance on a verbal memory test (HR 0.86, 95% CI 0.77-0.96, p=.009, n=131) predicted non-completion of CR. In patients undertaking CR, higher serum K/T ratios were associated with CES-D scores (β=.322, p=.002, n=95) and with VO2Peak (β=-.391, p<.001, n=95), and in a cohort of patients entering CR (n=88), serum concentrations of BDNF were associated with psychomotor processing speed (F1,87=9.620, p=.003), overall cognitive status (Mini Mental Status Exam) scores (F1,87=15.406, p<.0005) and VO2Peak (β=.305, p=.013). Conclusions: Depressive symptoms and poorer cognitive performance are clinically important in patients with CAD entering CR and they are both associated with poorer cardiopulmonary fitness. Poorer cardiopulmonary fitness was also associated with higher K/T ratios and with lower BDNF concentrations in serum, which predicted depressive symptoms and poorer cognitive performance, respectively.

Introduction: Coronary artery disease (CAD) has been associated with depressive symptoms and deficits in cognitive performance, both of which have been associated with poorer medical prognoses and poorer psychosocial outcomes. Physical activity can improve cognitive and depressive symptoms, and, for those with CAD, improve medical prognoses. It was hypothesized that depressive symptoms and poorer cognitive performance would be associated with poorer cardiopulmonary fitness in patients with CAD, and that these sequelae would be associated prospectively with noncompletion of cardiac rehabilitation (CR). The benefits of physical activity are thought to result, in part, from decreased inflammatory activity and increased adaptive neural plasticity, to which the ratio of kynurenine to tryptophan (K/T) and brain derived neurotrophic factor (BDNF), respectively, in peripheral blood may pertain. Methods and Results: In a cohort study of patients entering CR, depressive symptoms (Center for Epidemiological Studies Depression scale; CES-D scores) were associated with cardiopulmonary fitness (peak volume of oxygen uptake; VO2Peak) during an exercise stress test (B=-.404, p=.001, n=366). The VO2Peak was also associated with performance across multiple cognitive domains, but most strongly with performance on tests involving executive function, attention and psychomotor processing speed (β=.322, p=.002 for composite score, n=81) in a cohort of patients entering CR. In prospective cohort studies, Major Depressive Disorder (adjusted hazard ratio [HR] 2.5, 95% confidence interval [CI] 1.3–4.7, n=195) and poorer performance on a verbal memory test (HR 0.86, 95% CI 0.77-0.96, p=.009, n=131) predicted non-completion of CR. In patients undertaking CR, higher serum K/T ratios were associated with CES-D scores (β=.322, p=.002, n=95) and with VO2Peak (β=-.391, p<.001, n=95), and in a cohort of patients entering CR (n=88), serum concentrations of BDNF were associated with psychomotor processing speed (F1,87=9.620, p=.003), overall cognitive status (Mini Mental Status Exam) scores (F1,87=15.406, p<.0005) and VO2Peak (β=.305, p=.013). Conclusions: Depressive symptoms and poorer cognitive performance are clinically important in patients with CAD entering CR and they are both associated with poorer cardiopulmonary fitness. Poorer cardiopulmonary fitness was also associated with higher K/T ratios and with lower BDNF concentrations in serum, which predicted depressive symptoms and poorer cognitive performance, respectively.

There has been an awareness of nerve poisons from ancient times. At the dawn of the twentieth century, the actions and mechanisms of these poisons were uncovered by modern physiological and biochemical experimentation. However, the era of selective neurotoxins began with the pioneering studies of R. Levi-Montalcini through her studies of the neurotrophin "nerve growth factor" (NGF), a protein promoting growth and development of sensory and sympathetic noradrenergic nerves. An antibody to NGF, namely, anti-NGF - developed in the 1950s in a collaboration with S. Cohen - was shown to produce an "immunosympathectomy" and virtual lifelong sympathetic denervation. These Nobel Laureates thus developed and characterized the first identifiable selective neurotoxin. Other selective neurotoxins were soon discovered, and the compendium of selective neurotoxins continues to grow, so that today there are numerous selective neurotoxins, with the potential to destroy or produce dysfunction of a variety of phenotypic nerves. Selective neurotoxins are of value because of their ability to selectively destroy or disable a common group of nerves possessing (1) a particular neural transporter, (2) a unique set of enzymes or vesicular transporter, (3) a specific type of receptor or (4) membranous protein, or (5) other uniqueness. The era of selective neurotoxins has developed to such an extent that the very definition of a "selective" neurotoxin has warped. For example, (1) N-methyl-D- aspartate receptor (NMDA-R) antagonists, considered to be neuroprotectants by virtue of their prevention of excitotoxicity from glutamate receptor agonists, actually lead to the demise of populations of neurons with NMDA receptors, when administered during ontogenetic development. The mere lack of natural excitation of this nerve population, consequent to NMDA-R block, sends a message that these nerves are redundant - and an apoptotic cascade is set in motion to eliminate these nerves. (2) The rodenticide rotenone, a global cytotoxin that acts mainly to inhibit complex I in the respiratory transport chain, is now used in low dose over a period of weeks to months to produce relatively selective destruction of substantia nigra dopaminergic nerves and promote alpha-synuclein deposition in brain to thus model Parkinson's disease. Similarly, (3) glial toxins, affecting oligodendrocytes or other satellite cells, can lead to the damage or dysfunction of identifiable groups of neurons. Consequently, these toxins might also be considered as "selective neurotoxins," despite the fact that the targeted cell is nonneuronal. Likewise, (4) the dopamine D2-receptor agonist quinpirole, administered daily for a week or more, leads to development of D2-receptor supersensitivity - exaggerated responses to the D2-receptor agonist, an effect persisting lifelong. Thus, neuroprotectants can become "selective" neurotoxins; nonspecific cytotoxins can become classified as "selective" neurotoxins; and receptor agonists, under defined dosing conditions, can supersensitize and thus be classified as "selective" neurotoxins. More examples will be uncovered as the area of selective neurotoxins expands. The description and characterization of selective neurotoxins, with unmasking of their mechanisms of action, have led to a level of understanding of neuronal activity and reactivity that could not be understood by conventional physiological observations. This chapter will be useful as an introduction to the scope of the field of selective neurotoxins and provide insight for in-depth analysis in later chapters with full descriptions of selective neurotoxins.