Drug discovery targeting non-amyloid pathways in Alzheimer’s disease

Abstract: Alzheimer’s disease (AD) is the most common form of dementia with almost 50 million people affected and unfortunately, no cure or treatment to halt the disease progression is available. In the hereditary forms of AD, an overproduction of amyloid β (Aβ) and the Aβ plaque formation are the basis for the amyloid hypothesis of AD, while several additional factors seem to influence the likelihood to develop sporadic forms of AD. Inflammation, mitochondrial dysfunction, neurotransmitter alterations, defective autophagy processes, the ApoE4 gene variant, oxidative stress and lack of neurotrophic support, are other established alterations associated with sporadic forms of AD. The main aim of this thesis was to advance non-amyloidogenic drug discovery projects to improve the treatment options in AD. The first target for drug discovery research in this thesis was the 15-lipoxygenase-1 (15-LO-1) enzyme, which oxidizes polyunsaturated fatty acids and forms both reactive oxygen intermediates and pro- as well as anti-inflammatory metabolites. The 15-LO-1 activity has been found upregulated in the brain of AD patients. Inhibitors of 15-lipoxygenase have therefore been suggested as potential therapeutic substances for AD. In Study I, we developed a high- throughput screening assay with the aim to identify 15-LO-1 inhibitors. An automated assay in 384-well format using fluorescent analysis amenable for high-throughput screening was established. Potent 15-LO-1 inhibitors were identified, which may be a useful tool to evaluate the inflammatory component of AD. The second target for drug discovery approaches in this thesis was the altered neurotrophin signaling observed in AD. Basal forebrain cholinergic neuronal degeneration is one of the earliest signs of AD leading to cognitive impairment, described as the cholinergic hypothesis of AD. Associated with this impairment in the brains of patients with AD is the reduced nerve growth factor (NGF) signaling. The cognitive dysfunction seen in AD is also linked to the memory formation process in the hippocampus and the brain derived neurotrophic factor (BDNF) signaling. To modulate neurotrophin signaling, we investigated three NGF mutants in Study II and identified two small molecular compounds in Study III and IV that improve NGF and BDNF signaling. In Study II we showed that the hereditary sensory and autonomic neuropathy type V (HSAN V)-like mutant (NGF-R100E), displayed more potent activation of the neurotrophin receptor TrkA and could promote cell survival and neurite outgrowth to a higher degree than wild-type NGF itself in human fetal dorsal root ganglion (DRG) neurons. In Study III we identified a class of steroid derivatives which potently enhanced both the TrkA and the neurotrophin receptor TrkB signaling. Compound AC-25793, a soluble cardenolide was investigated further, which attenuated cognitive dysfunction and decreased depressive-like symptoms in vivo in mice. In Study IV we discovered a registered drug that enhanced NGF and BDNF signaling, increased long-term potentiation in rat hippocampal slices, increased acetylcholine levels after microdialysis in rats, improved cognitive functions and reduced depression-like symptoms in both mice and rats. The results using this compound, named ACD855 by us, suggest a compound with promising potential for treating cognitive deficiency and depression in AD. In summary, these findings have contributed to further knowledge in drug discovery projects aiming for a non-amyloid treatment in AD.