Approximately 10% of cases of amyotrophic lateral sclerosis (ALS), a progressive and fatal degeneration that targets motor neurons (MNs), are inherited, and Ϸ20% of these cases of familial ALS (FALS) are caused by mutations of copper͞zinc superoxide dismutase type 1. Glutamate excitotoxicity has been implicated as a mechanism of MN death in both ALS and FALS. In this study, we tested whether a neuroprotective strategy involving potent and selective inhibitors of glutamate carboxypeptidase II (GCPII), which converts the abundant neuropeptide N-acetylaspartylglutamate to glutamate, could protect MNs in an in vitro and animal model of FALS. Data suggest that the GCPII inhibitors prevented MN cell death in both of these systems because of the resultant decrease in glutamate levels. GCPII inhibition may represent a new therapeutic target for the treatment of ALS.A myotrophic lateral sclerosis (ALS) is a progressive and fatal degeneration of motor neurons (MNs) in the spinal cord and cerebral cortex. About 10% of ALS cases are inherited in an autosomal dominant fashion, and Ϸ20% of these cases of familial ALS (FALS) are caused by a mutation in copper͞zinc superoxide dismutase type 1 (SOD1) (1). Mice and rats that carry mutant (MT) SOD1 as a transgene manifest a progressive MN degeneration similar to that in patients with ALS (2-4). Several lines of evidence suggest that glutamate excitotoxicity is a pathogenic mechanism in both sporadic .N-acetylaspartylglutamate (NAAG) is one of the most abundant peptides in the mammalian central and peripheral nervous system (14), is present in neuronal vesicles, is released from neurons in a calcium-dependent manner, and functions as a high-affinity agonist at the group II metabotropic glutamate receptor subtype 3 (mGluR3). Activation of mGluR3 by NAAG has been shown to inhibit glutamate release (15), increase release of transforming growth factor ␤ (TGF␤) from glial cells, and provide neuroprotection (16). NAAG is hydrolyzed to N-acetylaspartate and glutamate by glutamate carboxypeptidase II (GCPII) (EC 3.4.17.21; also termed N-acetylated-␣-linked acidic dipeptidase or NAALADase; ref. 17), an enzyme localized on the plasma membrane of glial cells with its catalytic region facing the synapse (18). Therefore, inhibition of GCPII would be expected to provide neuroprotection by means of both decreasing glutamate and increasing NAAG (19).We hypothesized that GCPII inhibition would protect MNs expressing MT SOD1 from cell death, as well as ameliorate the MN degeneration seen in FALS transgenic mouse. For in vitro studies, we used 2-(phosphonomethyl)pentanedioic acid (2-PMPA), a potent and selective GCPII inhibitor (K i ϭ 0.2 nM; ref. 20) that has been shown to selectively reduce ischemic glutamate and provide neuroprotection in cell culture and animal models of ischemia (19), diabetic neuropathy (21), and drug abuse (22, 23). For the animal studies, we used a recently discovered thiol-based GCP II inhibitor, 2-(3-mercaptopropyl)pentanedioic acid (2-MPPA) (24). Unlike 2-PMPA, 2-MPPA is o...

Various compounds active in promoting in vitro differentiation of certain murine leukemia cell lines (Friend erythroleukemia cells and mouse myeloid leukemia cells) were tested for their capacity to induce differentiation of HL-60 cells, a human promyelocytic leukemia cell line capable of terminally differentiating in vitro to functionally mature granulocytes. Polar planar compounds including hexamethylene bisacetamide (HMBA), certain purines (particularly hypoxanthine), and actinomycin-D induced morphological and functional (as assessed by the capacity to reduce NBT dye) differentiation of HL-60. In contrast, hemin, ouabain, prostaglandin E1, X-irradiation, dexamethasone and some other anti-leukemic chemotherapeutic agents induced little if any significant differentiation of HL-60 cells. These results, together with previous observations with murine leukemia cells, suggest that the human HL-60 cells share common cellular target sites for the inducing action of polar planar compounds, hypoxanthine and actinomycin-D with some murine leukemic cells. In contrast, hemin, ouabain and prostaglandin E1 may be specific for mouse erythroleukemia cells, while X-irradiation and chemotherapeutic agents induce differentiation of both types (erythroid and myeloid) of mouse leukemic cells, but have little effect on HL-60 cells.

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Overexpression of gp120, the major coat protein of the HIV-1 virus, in central glial cells, or treatment of neurons with gp120 in culture, produces apoptotic neuronal death. Here we demonstrate that CEP-1347 (KT7515), an inhibitor of mixed lineage kinase 3 (MLK3), an upstream activator of JNK, inhibits gp120IIIB-induced apoptosis of hippocampal neurons. Furthermore, expression of wild type MLK3 in hippocampal pyramidal neurons enhanced gp120IIIB-induced neurotoxicity, whereas expression of a dominant negative MLK3 protected neurons from the toxic effects of the glycoprotein. These results indicate a role for MLK3 signaling in gp120IIIB-induced neuronal death, and suggest potential clinical utility of CEP-1347 in inhibiting the progression of AIDS dementia.