ALZHEIMERS RESEARCH PROJECT: Alzheimer's disease drug development

National Institute On Aging

Investigators

Linked publications & trials

Abstract

Overview: Evidence from clinical and preclinical studies indicates that basal inflammatory status increases as a function of normal aging, and progressive development of a mild pro-inflammatory state closely associates with the major degenerative diseases of the elderly (Holmes et al., Neurology 73:768-74, 2009; Heneka et al., Lancet Neurol 14:388-405, 2015). Hallmarks of aging include increased oxidative stress, lipid peroxidation and mitochondrial and DNA damage, particularly in brain. Microarray studies indicate a rise in inflammatory and pro-oxidant genes with a decline in growth, anti-inflammatory and anti-oxidant genes in the brain of older vs. adult rodents (Cribbs et al., J Neuroinflammation 9:179, 2012). In line with this, levels of brain pro-inflammatory cytokines are elevated with age in rodents and humans, and several regulatory molecules and anti-inflammatory cytokines reduced (Deleidi et al., Front Neurosci 9:172, 2015). Microglia are implicated as the major culprit of this ensuing neuroinflammation. Correcting the overproduction of pro-inflammatory cytokines by microglia may mitigate a broad number of neurodegenerative disorders prevalent in the elderly, and, in particular Alzheimer’s disease (AD). However, finding an appropriate drug target to safely and effectively achieve this has thus far proved difficult, and likely accounts for many of the numerous failures of clinical trials of anti-inflammatory agents in AD and associated disorders. Tumor necrosis factor-alpha (TNF) is a key pro-inflammatory cytokine generated by microglia. On release, TNF may initiate a self-propagating cycle of unchecked inflammation (Jung et al., Front Cell Dev Biol 7:313, 2019). Pharmacologic intervention to interrupt this cycle may be beneficial in the setting of neuroinflammation-mediated diseases. In 1993, Moreira et al. (J Exp Med 177:1675-80, 1993) described studies showing that the drug thalidomide (THAL) was able to lower TNF protein levels post-transcriptionally by accelerating degradation of its mRNA. Unfortunately, THAL is not a particularly potent TNF lowering agent and is associated with serious teratogenic adverse effects to embryos in utero, sedation and peripheral neuropathy at clinical doses (Calabrese & Fleischer, Am J Med 108:487-95, 2000; DeCourt et al., Curr Alzheimer Res 14:403-411, 2017). Nevertheless, the observation of THALs TNF lowering activity supported studies to differentiate these actions, understand THALs TNF structure/activity relationship and develop more potent analogs. In principle, the identification of analogs with enhanced anti-TNF activity and reduced teratogenic and neurotoxic effects may provide a viable treatment for neuroinflammatory and other inflammatory diseases. Our chemistry modifications to the backbone of THAL and newer analogs (namely pomalidomide (POM)) have generated a library of novel agents (US patents: 7,973,057 and 8,927,725, and Application No. 62/235,105, 63/397,235 and 63/664,442). Our focus is to identify well-tolerated drug-like compounds with more potent anti-TNF activity from our generated libraies, and develop these as experimental drugs to characterize the role of the neuroinflammatory component in and to treat AD and associated disorders. Problem/Focused Aims: AD is a complex disorder that manifests as progressive dementia with few other symptoms. With a long meandering course, AD is associated with deposits of amyloid-beta protein (A) of 40 and 42 amino acids as much as 20 years prior to development of dementia. It also induces intracellular accumulation of the microtubule-associated protein Tau (MAPT) as neurofibrillary tangles (NFTs) that correlate more closely with the extent of dementia (Sambamurti et al. Curr Alzheimer Res 3:81-90, 2006; Baranello et al. Curr Alzheimer Res 12:32-46, 2015). NFTs arise some 10 years after A, and brain atrophy follows after approximately 5 more years. However, the resilience and redundancy of the nervous system protects affected subjects from dementia for approx. 5 further years after the detection of atrophy by brain image analysis. The discovery that familial AD (FAD) mutations in A precursor protein (APP) and presenilins (PSEN1) and 2 (PSEN2) increase A42, have placed amyloid at the Occams razor of AD. The finding that the E4 variant of apolipoprotein E (APOE), detected in almost half the AD population, also fosters A deposition further boosts the amyloid hypothesis. Despite the consistency of this finding, the time-dependent A-triggered mechanisms of neuronal dysfunction and degeneration remain unclear; thereby making therapeutic intervention difficult. As A oligomers and aggregates are tolerated over an extended time, their toxicity may not be the direct cause of neurodegeneration but, instead, an initiator of a cascade of events that become self-propagating and then drive AD progression. This premise may account for the failure of anti-amyloid therapies in clinical trials when administered late in the disease course (Becker et al., Nature Rev Drug Discov 13:156, 2014). The presence of soluble and insoluble A and MAPT can induce microglia activation (McGeer Acta Neuropathol 126:479-97, 2013), and direct evidence of neuroinflammation in AD brain has been shown by in vivo PET imaging (Schuitemaker et al., Neurobiol Aging 34:12836, 2013). Notably, levels of pro-inflammatory cytokines are elevated in serum and CSF from AD patients, for TNF by as much as 25-fold (Tarkowski et al., J Clin Immunol 19:223-30, 1999). In MCI subjects that progress to develop AD, a rise in CSF TNF correlates with disease progression (Tarkowski et al., J Neurol Neurosurg Psychiatry 74:1200-5, 2003). Paralleling this, elevated expression of TNF is reported in the entorhinal cortex of 3xTg-AD mice prior to amyloid and tau pathology, and this increase associates with the onset of cognitive deficits in these mice and to later neuronal loss (Janelsins et al. J Neuroinflamm 2:23, 2005). We postulate that failure of protein homeostasis leads to accumulation of proteins (e.g., A, APOE, MAPT) that induce microglial activation and a proinflammatory M1 response to instigate their removal. A continuing generation of protein (A, APOE, MAPT) leads to maintenance of a chronic M1 response, impairment of transition to an anti-inflammatory M2 response (particularly in aging brain already vulnerable to inflammation) with ensuing neuronal impairment observed in animal models and in preclinical AD, which ultimately leads to cell death. Proinflammatory cytokines, like TNF, induce vascular changes to allow lymphocyte infiltration that may underpin reported cerebral vasculature leakiness of AD patients and related Tg mouse models. Moreover, TNF induces A production in cellular and animal AD models, further increasing its accumulation and the entire cascade. Our focus is to elucidate the time course of development of neuropathology accumulation of inflammatory cytokines and behavioral deficits in unique mouse models that may reflect the disease pathology more than the currently available ones. We also evaluate the treatment of these deficits with a clinically approved immunomodulator, POM, which lowers TNF generation as well as with the new more potent small molecule TNF synthesis inhibitors generated and patented for NIH by our research collaborative group within the Intramural Research Program of NIA. Our research has highlighted thionated analogs of POM as new AD therapeutic candidates that mitigate neuroinflammation, neuronal loss and behavioral impairments in AD cellular/animal models (Jung et al., Front Cell Dev Biol. 7:313, 2019; Jung et al., Front Neurosci. 15:656921, 2021; Kopp et al. Biomolecules. 13:747, 2023). Using the same models, the drug Phenserine, likewise, appears highly promising in mitigating programmed neuronal cell death/inflammation. We have extended our studies to evaluate these same compounds in models associated with neuroinflammation, as a 'cytokine storm' appears across such disorders.