ABSTRACT
Initial work in Drosophila and mice demonstrated that the transcription factor cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) is a master control gene for memory formation. The relationship between CREB and memory has also been found to be true in other species, including aplysia and rats. It is thus well-established that CREB activation plays a central role in memory enhancement and that CREB is activated during memory formation. On the basis of these findings, a phenotypic high-throughput screening campaign utilizing a CRE-luciferase (CRE-Luci) SK-N-MC cell line was performed to identify compounds that enhance transcriptional activation of the CRE promoter with a suboptimal dose of forskolin. A number of small-molecule hits of unknown mechanisms of action were identified in the screening campaign, including HT-0411. Follow-up studies suggested that the CREB activation by HT-0411 is attributed to its specific and selective inhibition of monoamine oxidase B (MAO-B). Further, HT-0411 was shown to improve 24 h memory in rodents in a contextual fear conditioning model. This report describes the lead optimization of a series of 5-(1-methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl) thiophene-2-carboxamides that were identified as novel, potent, and selective inhibitors of MAO-B. Extensive SAR studies and in vivo behavioral evaluations of this and other related analogue series identified a number of potential clinical development candidates; ultimately, compound 8f was identified as a candidate molecule with high selectivity toward MAO-B (29-56 nM) over MAO-A (19% inhibition at a screening concentration of 50 µM), an excellent profile against a panel of other enzymes and receptors, good pharmacokinetic properties in rodents and dogs, and efficacy in multiple rodent memory models.
Subject(s)
Carboxylic Acids/administration & dosage , Carboxylic Acids/chemistry , Cognition/drug effects , Memory/drug effects , Monoamine Oxidase/metabolism , Nootropic Agents/administration & dosage , Nootropic Agents/chemistry , Amides/administration & dosage , Amides/chemistry , Animals , Cognition/physiology , Dose-Response Relationship, Drug , Male , Memory/physiology , Mice, Inbred C57BL , Monoamine Oxidase Inhibitors/administration & dosage , Monoamine Oxidase Inhibitors/chemistry , Rats , Treatment OutcomeABSTRACT
Aging is associated with declines in memory and cognitive function. Here, we evaluate the effects of HT-0712 on memory formation and on cAMP response element-binding protein (CREB)-regulated genes in aged mice. HT-0712 enhanced long-term memory formation in normal young mice at brain concentrations similar to those found to increase CRE-mediated gene expression in hippocampal neurons. Aged mice showed significantly poorer contextual and trace conditioning compared with young-adult mice. In aged mice, a single injection of HT-0712 significantly boosted contextual and trace long-term memory. Additional effects of HT-0712 were seen in a spatial memory task. Our parallel biochemical experiments revealed that inductions of the CREB-regulated genes, cFos, Zif268, and Bdnf, after fear conditioning were diminished in aged mice. HT-0712 facilitated expression of these CREB-regulated genes in aged hippocampus, indicating that the drug engages a CREB-regulated mechanism in vivo. These findings corroborate and extend our previous results on the mechanism of action of HT-0712 and its efficacy to enhance memory formation. Our data also indicate that HT-0712 may be effective to treat age-associated memory impairment in humans.
