A Phase II Study Repurposing Atomoxetine for Neuroprotection in Mild Cognitive Impairment

Allan I. Levey; Deqiang Qiu; Liping Zhao; William T. Hu; Duc M. Duong; Lenora Higginbotham; Eric B. Dammer; Nicholas T. Seyfried; Thomas S. Wingo; Chadwick M. Hales; Malú Gámez Tansey; David S. Goldstein; Anees Abrol; Vince D. Calhoun; Felicia C. Goldstein; Ihab Hajjar; Anne M. Fagan; Doug Galasko; Steven D. Edland; John Hanfelt; James J. Lah; David Weinshenker

Disclosures

Brain. 2022;145(6):1924-1938. 

In This Article

Abstract and Introduction

Abstract

The locus coeruleus is the initial site of Alzheimer's disease neuropathology, with hyperphosphorylated Tau appearing in early adulthood followed by neurodegeneration in dementia. Locus coeruleus dysfunction contributes to Alzheimer's pathobiology in experimental models, which can be rescued by increasing norepinephrine transmission. To test norepinephrine augmentation as a potential disease-modifying therapy, we performed a biomarker-driven phase II trial of atomoxetine, a clinically-approved norepinephrine transporter inhibitor, in subjects with mild cognitive impairment due to Alzheimer's disease.

The design was a single-centre, 12-month double-blind crossover trial. Thirty-nine participants with mild cognitive impairment and biomarker evidence of Alzheimer's disease were randomized to atomoxetine or placebo treatment. Assessments were collected at baseline, 6- (crossover) and 12-months (completer). Target engagement was assessed by CSF and plasma measures of norepinephrine and metabolites. Prespecified primary outcomes were CSF levels of IL1α and TECK. Secondary/exploratory outcomes included clinical measures, CSF analyses of amyloid-β42, Tau, and pTau181, mass spectrometry proteomics and immune-based targeted inflammation-related cytokines, as well as brain imaging with MRI and fluorodeoxyglucose-PET.

Baseline demographic and clinical measures were similar across trial arms. Dropout rates were 5.1% for atomoxetine and 2.7% for placebo, with no significant differences in adverse events. Atomoxetine robustly increased plasma and CSF norepinephrine levels. IL-1α and TECK were not measurable in most samples. There were no significant treatment effects on cognition and clinical outcomes, as expected given the short trial duration. Atomoxetine was associated with a significant reduction in CSF Tau and pTau181 compared to placebo, but not associated with change in amyloid-β42. Atomoxetine treatment also significantly altered CSF abundances of protein panels linked to brain pathophysiologies, including synaptic, metabolism and glial immunity, as well as inflammation-related CDCP1, CD244, TWEAK and osteoprotegerin proteins. Treatment was also associated with significantly increased brain-derived neurotrophic factor and reduced triglycerides in plasma. Resting state functional MRI showed significantly increased inter-network connectivity due to atomoxetine between the insula and the hippocampus. Fluorodeoxyglucose-PET showed atomoxetine-associated increased uptake in hippocampus, parahippocampal gyrus, middle temporal pole, inferior temporal gyrus and fusiform gyrus, with carry-over effects 6 months after treatment.

In summary, atomoxetine treatment was safe, well tolerated and achieved target engagement in prodromal Alzheimer's disease. Atomoxetine significantly reduced CSF Tau and pTau, normalized CSF protein biomarker panels linked to synaptic function, brain metabolism and glial immunity, and increased brain activity and metabolism in key temporal lobe circuits. Further study of atomoxetine is warranted for repurposing the drug to slow Alzheimer's disease progression.

Introduction

Alzheimer's disease is a devastating progressive dementia with tremendous societal burden, yet no disease-modifying treatments exist. With the projected dramatic age-related increasing prevalence in the next few decades, and growing numbers of failed clinical trials targeting amyloid, there is an urgent need to expand the scope of potential therapeutic targets. Genetic, epidemiological, and experimental studies have identified a multitude of risk factors that appear to converge on several biological pathways downstream of amyloid-β such as neurofibrillary tangle formation and neuroinflammation that damage neural circuits and synaptic transmission involved in memory, cognition, and behaviour, and relentlessly drive progressive neurodegeneration.[1] Given that amyloid-β deposition begins two or more decades prior to symptom onset, these downstream pathways provide new treatment targets for disease modification if initiated prior to significant neurodegeneration and dementia.

The locus coeruleus (LC), the major brainstem noradrenergic nucleus that innervates and supplies norepinephrine (NE) to the forebrain to regulate arousal, cognition, and behaviour, has garnered interest in its potential as a disease-modifying therapeutic target for Alzheimer's disease.[2] While degeneration of the LC has long been known as a ubiquitous feature of Alzheimer's disease,[3–7] studies provide several lines of compelling evidence that impaired LC function in Alzheimer's disease contributes to not only the clinical symptoms, but also triggers underlying pathophysiological mechanisms involved in progressive neurodegeneration.[2,8–20] Both imaging and post-mortem studies indicate that volumetric reduction, neuronal loss, and neuropathology in LC predict the rate of cognitive decline, attentional and executive function deficits, and Tau burden in humans, suggesting an important role in cognitive resilience and abnormal protein aggregation.[16,21–25] Hyperphosphorylated Tau, a 'pretangle' form of the protein prone to aggregation, appears in the LC before any other area of the brain, and is now considered the earliest detectable Alzheimer's disease-like neuropathology, evident even in young and middle-aged adults.[14,26–32] The connectivity of the LC provides a neuroanatomical substrate that may mediate the spread of pathological Tau seeds to the forebrain.[20,33] The appearance of Tau pathology in the LC is also associated with depression and sleep disturbances, important risk factors for Alzheimer's disease,[7,34] and cognitive impairment becomes evident as LC neurons start to degenerate.[19] Causal relationships between the LC and disease-modifying processes are implicated using genetic and neurotoxin-induced lesions of the LC, which exacerbate neuropathology and cognitive deficits in both amyloid- and Tau-based transgenic mouse models of Alzheimer's disease, at least in part mediated by the critical role of LC in regulation of neuroinflammation.[2,7,8,35,36] NE has potent effects on inflammation in the brain, where it suppresses the production and release of pro-inflammatory molecules in favor of anti-inflammatory cascades[2,8,10,11,18,37,38] and stimulates microglial clearance of amyloid.[38] Moreover, lesions of the LC in Alzheimer's disease mouse model systems recapitulate several other features of the human disease, including regional hypometabolism, neurotrophin deficiency, blood–brain barrier permeability, and neurodegeneration.[11,15,39–41] Finally, cutting-edge technologies that directly manipulate LC activity, such as DREADD (Designer receptors exclusively activated by designer drugs) chemogenetics or more traditional pharmacological augmentation of NE neurotransmission, reverse the pro-inflammatory and other pathophysiological features of Alzheimer's disease, increase microglial phagocytosis and amyloid clearance, and rescue cognitive and behavioural deficits.[9,13,38,42,43] Compared to other therapeutic strategies, one advantage of targeting the LC-NE system is the abundance of available drugs that regulate various steps in NE transmission, from synthesis to release/reuptake and downstream receptor signalling, which have shown efficacy in cell culture and animal models of Alzheimer's disease.[9,13,38,41,42,44–48]

To test proof of concept for NE augmentation as a potential disease-modifying therapy in humans, we initiated a biomarker-driven phase II trial of atomoxetine in mild cognitive impairment (MCI). We chose atomoxetine, a selective NE reuptake inhibitor for several reasons. The drug blocks the plasma membrane NE transporter, but not other monoamine transporters,[49] resulting in increased extracellular NE in the periphery and brain.[50,51] Atomoxetine (in combination with the synthetic NE precursor L-3,4-dihydroxyphenylserine, L-DOPS) ameliorates glial activation and amyloid-β deposition, increases neurotrophin expression, and reverses cognitive deficits in a mouse model of Alzheimer's disease.[42] Atomoxetine also improves the phasic-to-tonic ratio of LC firing, which is associated with focused attention important for some aspects of learning and memory.[52] It is possible to quantitatively demonstrate target engagement by measuring levels of NE and its primary metabolite 3,4-dihydroxyphenylglycol (DHPG) in blood and CSF.[53] In addition, as an FDA-approved drug widely used for treating attention disorders,[54–56] atomoxetine is safe for chronic use in children and adults, including geriatric populations,[57,58] and improves cognitive function in Parkinson's disease patients with lower LC volume,[59] providing an excellent opportunity to repurpose this medication for Alzheimer's disease.

Here we report the results of a single-centre, phase II randomized, double-blind, placebo-controlled, 6-month crossover trial. Thirty-nine subjects with MCI and biomarker results consistent with Alzheimer's disease were randomized to atomoxetine or placebo treatment for 6 months, and then crossed over to receive the alternative intervention for 6 months. The primary outcomes of the study were safety and tolerability, CSF biomarkers of target engagement (NE metabolites), and neuroinflammation. IL1-α and TECK (aka C-C Motif Chemokine Ligand 25 or CCL25) were preselected as primary CSF outcome markers of neuroinflammation because they best predicted subsequent cognitive decline in a preliminary study.[60] Since neither marker was detectable in the majority of subjects in the current study, we assessed if there was a difference in non-detection between the treatment groups. Given the diversity of mechanisms by which NE augmentation can modify the neurobiology of disease in preclinical studies, a key goal of this study was to investigate the effects of atomoxetine treatment on a wide range of pathophysiological processes in addition to clinical outcomes. As such, our secondary and exploratory outcomes broadly explored a range of biomarkers using advanced proteomics and imaging methods to inform both disease biology and future clinical trial design. In addition to clinical findings and biomarkers of Alzheimer's disease progression with CSF amyloid-β42, total Tau and phospho-Tau (pTau181), we used recently developed mass spectrometry methods to assess five panels of neuropathology-based protein biomarkers linked to synaptic dysfunction, glial immunity, metabolism, myelin injury, and vascular biology.[61,62] We also used immunoassays to explore the effects of atomoxetine on cytokines and a panel of inflammation analytes,[63,64] CSF brain-derived neurotrophic factor (BDNF), and brain imaging using volumetric MRI, resting-state functional MRI, and fluorodeoxyglucose (FDG)-PET.

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