The Role of Sirt1 in Epileptogenesis.

The mechanisms by which brain insults lead to subsequent epilepsy remain unclear. Insults, including trauma, stroke, tumors, infections, and long seizures [status epilepticus (SE)], create a neuronal state of increased metabolic demand or decreased energy supply. Neurons express molecules that monitor their metabolic state, including sirtuins (Sirts). Sirtuins deacetylate cytoplasmic proteins and nuclear histones, and their epigenetic modulation of the chromatin governs the expression of many genes, influencing neuronal properties. Thus, sirtuins are poised to enduringly modulate neuronal properties following SE, potentially contributing to epileptogenesis, a hypothesis supported by the epilepsy-attenuating effects of blocking a downstream target of Sirt1, Neuron-Restrictive Silencer Factor (NRSF) also know as REST (RE1-Silencing Transcription factor). Here we used an adult male rat model of epileptogenesis provoked by kainic acid-induced SE (KA-SE). We assessed KA-SE-provoked Sirt1 activity, infused a Sirt1 inhibitor (EX-527) after KA-SE, and examined for epileptogenesis using continuous digital video-EEG. Sirt1 activity, measured using chromatin immunoprecipitation for Sirt1 binding at a target gene, increased rapidly after SE. Post hoc infusion of the Sirt1 inhibitor prevented Sirt1-mediated repression of a target gene. Blocking Sirt1 activity transiently after KA-SE did not significantly influence the time- course and all of the parameters of epilepsy development. Specifically, latency to first seizure and seizure number, duration, and severity (using the Racine scale and EEG measures) as well as the frequency and duration of interictal spike series, were all unchanged. KA-SE provoked a robust inflammatory response and modest cell loss, yet neither was altered by blocking Sirt1. In conclusion, blocking Sirt1 activity after KA-SE does not abrogate epilepsy development, suggesting that the mechanisms of such acquired epileptogenesis are independent of Sirt1 function.

Targeting cancer metabolism by simultaneously disrupting parallel nutrient access pathways.

Oncogenic mutations drive anabolic metabolism, creating a dependency on nutrient influx through transporters, receptors, and macropinocytosis. While sphingolipids suppress tumor growth by downregulating nutrient transporters, macropinocytosis and autophagy still provide cancer cells with fuel. Therapeutics that simultaneously disrupt these parallel nutrient access pathways have potential as powerful starvation agents. Here, we describe a water-soluble, orally bioavailable synthetic sphingolipid, SH-BC-893, that triggers nutrient transporter internalization and also blocks lysosome-dependent nutrient generation pathways. SH-BC-893 activated protein phosphatase 2A (PP2A), leading to mislocalization of the lipid kinase PIKfyve. The concomitant mislocalization of the PIKfyve product PI(3,5)P2 triggered cytosolic vacuolation and blocked lysosomal fusion reactions essential for LDL, autophagosome, and macropinosome degradation. By simultaneously limiting access to both extracellular and intracellular nutrients, SH-BC-893 selectively killed cells expressing an activated form of the anabolic oncogene Ras in vitro and in vivo. However, slower-growing, autochthonous PTEN-deficient prostate tumors that did not exhibit a classic Warburg phenotype were equally sensitive. Remarkably, normal proliferative tissues were unaffected by doses of SH-BC-893 that profoundly inhibited tumor growth. These studies demonstrate that simultaneously blocking parallel nutrient access pathways with sphingolipid-based drugs is broadly effective and cancer selective, suggesting a potential strategy for overcoming the resistance conferred by tumor heterogeneity.