Neuroprotective Activity and Evaluation of Hsp90 Inhibitors in an Immortalized Neuronal Cell Line

Alzheimer's disease (AD) neuropathology is characterized by loss of synapses and neurons, neuritic plaques consisting of beta-amyloid (Abeta) peptides, and neurofibrillary tangles consisting of intracellular aggregates of hyperphosphorylated tau protein in susceptible brain regions. Abeta oligomers trigger a cascade of pathogenic events including tau hyperphosphorylation and aggregation, inflammatory reactions, and excitotoxicity that contribute to the progression of AD. The molecular chaperone Hsp90 facilitates the folding of newly synthesized and denatured proteins and is believed to play a role in neurodegenerative disorders in which the defining pathology results in misfolded proteins and the accumulation of protein aggregates. Some agents that inhibit Hsp90 protect neurons against Abeta toxicity and tau aggregation, and assays for rapidly screening potential Hsp90 inhibitors are of interest. We used the release of the soluble cytosolic enzyme lactate dehydrogenase (LDH) as an indicator of the loss of cell membrane integrity and cytotoxicity resulting from exposure to Abeta peptides to evaluate the neuroprotective properties of novel novobiocin analogues and established Hsp90 inhibitors. Compounds were assessed for potency in protecting proliferating and differentiated SH-SY5Y neuronal cells against Abeta-induced cell death; the potential toxicity of each agent alone was also determined. The data indicated that several of the compounds decreased Abeta toxicity even at low nanomolar concentrations and, unexpectedly, were more potent in protecting the undifferentiated cells against Abeta. The novobiocin analogues alone were not toxic even up to 10 microM concentrations whereas GDA and the parent compound, novobiocin, were toxic at 1 and 10 microM, respectively. The results suggest that novobiocin analogues may provide novel leads for the development of neuroprotective drugs.