Journal of Neurochemistry, 2001, 77, 220±228 A synthetic inhibitor of p53 protects neurons against death induced by ischemic and excitotoxic insults, and amyloid b-peptide Carsten Culmsee,* , ² Xiaoxiang Zhu,* Qian-Sheng Yu,* Sic L. Chan,* Simonetta Camandola,* Zhihong Guo,* Nigel H. Greig* and Mark P. Mattson* , ³ *Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center, Baltimore, USA ²Institut fu Èr Pharmakologie und Toxikologie, Philipps-Universita Èt Marburg, Marburg, Germany ³Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, USA Abstract The tumor suppressor protein p53 is essential for neuronal death in several experimental settings and may participate in human neurodegenerative disorders. Based upon recent studies characterizing chemical inhibitors of p53 in preclinical studies in the cancer therapy ®eld, we synthesized the compound pi®thrin-a and evaluated its potential neuroprotec- tive properties in experimental models relevant to the pathogenesis of stroke and neurodegenerative disorders. Pi®thrin-a protected neurons against apoptosis induced by DNA-damaging agents, amyloid b-peptide and glutamate. Protection by pi®thrin-a was correlated with decreased p53 DNA-binding activity, decreased expression of the p53 target gene Bax and suppression of mitochondrial dysfunction and caspase activation. Mice given pi®thrin-a exhibited increased resistance of cortical and striatal neurons to focal ischemic injury and of hippocampal neurons to excitotoxic damage. These preclinical studies demonstrate the ef®cacy of a p53 inhibitor in models of stroke and neurodegenerative disorders, and suggest that drugs that inhibit p53 may reduce the extent of brain damage in related human neurodegenerative conditions. Keywords: Alzheimer's disease, apoptosis, glutamate, hippocampus, ischemic stroke, mitochondria. J. Neurochem. (2001) 77, 220±228. Several prominent neurological disorders manifest symp- toms that result from degeneration and death of speci®c populations of neurons; hippocampal and cortical neurons involved in cognition degenerate in Alzheimer's disease (Mattson 2000), midbrain dopaminergic neurons that control motor functions die in Parkinson's disease (Jenner and Olanow 1998), and cortical and striatal neurons controlling various behaviors are often killed as the result of a stroke (Dirnagl et al. 1999). Although the genetic and environ- mental factors that initiate the neuronal death process differ among diseases, a shared biochemical cascade of events appears to carry out the cell death process. The cascade involves increased oxidative stress, activation of glutamate receptors, disruption of cellular calcium homeostasis and activation of a death program called apoptosis (Green and Reed 1998; Mattson, 2000). Neuronal apoptosis involves mitochondrial ion permeability changes, cytochrome c release and activation of cysteine proteases called caspases (Chan and Mattson 1999; Lipton 1999; Marks and Berg 1999; Lee et al. 2000). An important regulatory step in apoptosis occurs at mitochondrial membranes where members of the Bcl-2 family of proteins either promote (Bax and Bad) or prevent (Bcl-2 and Bcl-XL) membrane permeability transition. Signaling events that act upstream of mitochondrial changes in neuronal apoptosis are not fully established, but may include production of prostate apoptosis response-4 (Guo et al. 1998) and the tumor suppressor protein p53 (Hughes et al. 1997; Sakhi et al. 1997; Uberti et al. 1998; Cregan et al. 1999). 220 q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 77, 220±228 Received November 20, 2000; revised manuscript received December 21, 2000; accepted December 22, 2000. Address correspondence and reprint requests to Mark P. Mattson, Laboratory of Neurosciences, National Institute on Aging, GRC 4F01, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA. E-mail: mattsonm@grc.nia.nih.gov Abbreviations used: ABP, amyloid b-peptide; PBS, phosphate- buffered saline.