EEG Biomarker for Alzheimer's Disease

*Demet Ilhan Algin, Demet Ozbabalık Adapinar and Oguz Osman Erdinc*

#### **Abstract**

Alzheimer's disease (AD) is a neurodegenerative disorder that accounts for nearly 70% of the more than 50 million dementia cases estimated worldwide. There is no cure for AD. Currently, AD diagnosis is carried out using neuropsychological tests, neuroimaging scans, and laboratory tests. In the early stages of AD, brain computed tomography (CT) and magnetic resonance imaging (MRI) findings may be normal, but in late periods, diffuse cortical atrophy can be detected more prominently in the temporal and frontal regions. Electroencephalogram (EEG) is a test that records the electrical signals of the brain by using electrodes that directly reflects cortical neuronal functioning. In addition, EEG is noninvasive and widely available at low cost, has high resolution, and provides access to neuronal signals, unlike functional MR or PET which indirectly detects metabolic signals. Accurate, specific, and cost-effective biomarkers are needed to track the early diagnosis, progression, and treatment response of AD. The findings of EEG in AD are now identified as biomarkers. In this chapter, we reviewed studies that used EEG or event-related potential (ERP) indices as a biomarker of AD.

**Keywords:** Alzheimer's disease, biomarker, EEG, quantitative EEG, neurodegeneration

#### **1. Introduction**

Alzheimer's disease (AD) is a neurodegenerative disease that accounts for about 70% of the estimated 46 million dementia cases worldwide. Although there is no definitive treatment for AD, early diagnosis and correct follow-up to stop disease progression can improve the quality of life for the AD patients and caregivers [1].

Amnesia, aphasia, apraxia, and agnosia are the leading clinical signs of AD. The first symptom in AD is often the loss of the ability to learn new information (amnesia). Loss of episodic memory is the main symptom of AD. Episodic memory is particularly concerned with the hippocampus. In the beginning, the patient becomes forgetful, repeats the same things, and loses his things. Semantic memory is about social events and general knowledge. It is not destroyed as markedly as episodic memory in the early stages of AD. As the disease progresses, destruction starts in semantic memory [2–4].

According to the symptomatology, AD is divided into three stages: (1) preclinical, (2) mild cognitive impairment (MCI), and (3) AD-related dementia. (1) Preclinical AD: changes in brain, blood, and cerebrospinal fluid associated with AD begin to occur, but the patient does not show any symptoms. This stage may start years

or decades before the first clinical symptoms of dementia [5]. (2) Mild cognitive impairment (MCI): MCI describes the clinical situation between normal aging and Alzheimer's disease. In 1999, the information that memory impairment differs according to age, as well as educational level, was added to the definition made on MCI. MCI usually manifests itself with subjective complaints such as forgetting the names and not being able to remember where the items were placed. However, it has been observed that 30% of cases diagnosed with MCI do not progress to AD soon [6]. (3) Alzheimer's dementia: Typically, the symptoms of the disease begin with mild memory difficulties and cognitive impairment develops into dysfunctions in complex daily activities and some other aspects of cognition. When AD is diagnosed clinically, neuron loss and neuropathological lesions occur in many brain regions [7]. However, there is no ideal biomarker to identify AD, and a definitive diagnosis can only be made by autopsy or biopsy. Therefore, the diagnosis of AD can be made by medical history, laboratory tests, neuroimaging, and neuropsychological methods. These clinical assessments are not specific and costly. As a result, an accurate, universal, specific, and cost-effective biomarker is needed for early diagnosis and to monitor disease progression and treatment response [8].

The National Institute on Aging-Alzheimer's Association (NIA-AA) has developed new study criteria to use a panel of prognostic fluids and imaging biomarkers to determine the probability of AD pathology and preclinical AD staging and prodromal and later progression to clinical AD. These are cerebrospinal fluid (CSF) amyloid-β (Aβ) 42, amyloid positron emission tomography (PET), CSF total tau, threonine 181 (T181) phospho-tau, magnetic resonance imaging (MRI) mesial temporal lobe (MTL) atrophy, 18F-fluorodeoxyglucose (FDG)-PET temporoparietal/precuneus hypometabolism, or hypoperfusion [9]. Today, standard neuropsychological tests are used to diagnose AD and are widely supported by expensive neuroimaging methods and invasive laboratory tests. In recent years, electroencephalography (EEG) has emerged as an alternative noninvasive technique compared to more expensive neuroimaging methods such as MRI and PET [10, 11].

#### **2. Alzheimer's disease and its pathophysiology**

Data obtained with AD have shown the presence of amyloid plaques and neurofibrillary tangles in the pathology of the disease and that these pathological aggregates have a specific distribution pattern and density [12, 13].

Molecular studies have shown that the main component of amyloid plaques is amyloid beta (Aβ), and neurofibrillary tangles are tau protein. In AD patients, the pathway that forms the Aβ peptide is more active or is thought to be a defect in the mechanism of Aβ clearance. There are mature fibrils in the structure of amyloid plaques. In pathology studies in AD patients, amyloid plaques are indispensable pathological findings and Aβ formation in the pathogenesis of the disease is thought to initiate the pathogenesis of the disease. This hypothesis is defined as the "amyloid cascade hypothesis" [14]. In the pathogenesis of AD, tau hyperphosphorylation is known to impair microtubule stability and function, as well as to gain toxic function, for instance, tau aggregates induce apoptosis. However, like Aβ, it is thought that the tau oligomers they form are associated with neurodegeneration and memory impairment rather than the aggregates formed by the tau protein [15].

#### **3. Alzheimer's disease and EEG**

The source of routine EEG activity recorded from the scalp is the postsynaptic potentials of cortical pyramidal cells. According to the synaptic activity being

**71**

**Table 1.** *EEG waves.*

*EEG Biomarker for Alzheimer's Disease DOI: http://dx.doi.org/10.5772/intechopen.93711*

potential markers in Alzheimer's disease.

in real time [16, 17].

cholinergic therapy [25].

excitatory and inhibitory, the postsynaptic membrane becomes depolarized or hyperpolarized. The total electrical current generated by these excitatory and inhibitory postsynaptic potentials from millions of neurons creates superficial EEG activity. Adeli and Ghosh-Dastidar developed the wavelet-chaos method for the analysis of delta, theta, alpha, and beta (**Table 1**) subbands of EEG to identify

To evaluate the effect of visual warning and attention, evaluation is done with eyes open and eyes closed. EEGs from different loci in the brain are used to explore the responsible areas of the brain and directly measure the functioning of synapses

In AD, a significant decrease in cortical alpha frequency (8–10.5 Hz) was observed, especially in the limbic, temporal, parietal, and central areas [6].

alpha activity was found to decrease during or after the disease [18].

State Examination (MMSE) showed negative correlations [21, 22].

However, it has been reported that the age of onset of AD can change this criterion, and that focal and diffuse EEG abnormalities are more common in early onset AD patients than in late-age AD patients. In the first studies, an increase in theta activity in EEG was considered as one of the earliest changes in Alzheimer's dementia, while

EEG markers showing the progression of the disease in MCI cases include an increase in delta and theta power and a decrease in beta or alpha power in the temporal and occipital regions [19]. Osipova et al. showed that alpha rhythm shifts from the parieto-occipital region to temporal regions in AD [20]. In other spontaneous EEG studies, it was found that frontal delta and occipital theta sources were higher in MCI patients than healthy ones, and frontal delta sources and the Mini-Mental

The cortical cholinergic system has an important role in controlling many different functions such as cerebral blood flow, cortical activity, sleep/wake cycle, modulation of cortical plasticity, and cognitive performance and learningmemory processes. The presence of cholinergic neurons in the basal forebrain was first reported by Shute and Lewis in 1967. ACh deficiency is observed in the brains of individuals with AD in the entire cortex, especially the temporoparietal cortex [23, 24]. Also, one of the possible mechanisms underlying the observed relationship between Aβ42 and increased slow EEG activity is Aβ and cholinergic deficiencies in the brain in AD. Cholinergic therapy has different effects on delta and theta oscillation responses. Theta oscillations were similar in controls to those receiving cholinergic therapy in the AD patients, regardless of treatment. In other words, theta oscillation responses are affected by cholinergic therapy in AD patients, while the amplitudes of delta oscillation responses are not affected by

Moreover, in studies evaluating the relationship between AD neuropathology, EEG frequencies, and CSF markers, amyloid β42 (Aβ42) showed a significant relationship with slow frequency (delta and theta) activity, while phospho-tau (p-tau) and total tau (t-tau) are associated with activity at only fast frequencies (alpha and beta) (26). Smailovic et al. demonstrated the correlation of qEEG and

**Type of wave Frequency** Beta >13 Hz Alpha 8–13 Hz Theta 4–7 Hz Delta 1–4 Hz

#### *EEG Biomarker for Alzheimer's Disease DOI: http://dx.doi.org/10.5772/intechopen.93711*

*Neurodegenerative Diseases - Molecular Mechanisms and Current Therapeutic Approaches*

monitor disease progression and treatment response [8].

**2. Alzheimer's disease and its pathophysiology**

have a specific distribution pattern and density [12, 13].

**3. Alzheimer's disease and EEG**

or decades before the first clinical symptoms of dementia [5]. (2) Mild cognitive impairment (MCI): MCI describes the clinical situation between normal aging and Alzheimer's disease. In 1999, the information that memory impairment differs according to age, as well as educational level, was added to the definition made on MCI. MCI usually manifests itself with subjective complaints such as forgetting the names and not being able to remember where the items were placed. However, it has been observed that 30% of cases diagnosed with MCI do not progress to AD soon [6]. (3) Alzheimer's dementia: Typically, the symptoms of the disease begin with mild memory difficulties and cognitive impairment develops into dysfunctions in complex daily activities and some other aspects of cognition. When AD is diagnosed clinically, neuron loss and neuropathological lesions occur in many brain regions [7]. However, there is no ideal biomarker to identify AD, and a definitive diagnosis can only be made by autopsy or biopsy. Therefore, the diagnosis of AD can be made by medical history, laboratory tests, neuroimaging, and neuropsychological methods. These clinical assessments are not specific and costly. As a result, an accurate, universal, specific, and cost-effective biomarker is needed for early diagnosis and to

The National Institute on Aging-Alzheimer's Association (NIA-AA) has developed new study criteria to use a panel of prognostic fluids and imaging biomarkers to determine the probability of AD pathology and preclinical AD staging and prodromal and later progression to clinical AD. These are cerebrospinal fluid (CSF) amyloid-β (Aβ) 42, amyloid positron emission tomography (PET), CSF total tau, threonine 181 (T181) phospho-tau, magnetic resonance imaging (MRI) mesial temporal lobe (MTL) atrophy, 18F-fluorodeoxyglucose (FDG)-PET temporoparietal/precuneus hypometabolism, or hypoperfusion [9]. Today, standard neuropsychological tests are used to diagnose AD and are widely supported by expensive neuroimaging methods and invasive laboratory tests. In recent years, electroencephalography (EEG) has emerged as an alternative noninvasive technique compared to more expensive neuroimaging methods such as MRI and PET [10, 11].

Data obtained with AD have shown the presence of amyloid plaques and neurofibrillary tangles in the pathology of the disease and that these pathological aggregates

Molecular studies have shown that the main component of amyloid plaques is amyloid beta (Aβ), and neurofibrillary tangles are tau protein. In AD patients, the pathway that forms the Aβ peptide is more active or is thought to be a defect in the mechanism of Aβ clearance. There are mature fibrils in the structure of amyloid plaques. In pathology studies in AD patients, amyloid plaques are indispensable pathological findings and Aβ formation in the pathogenesis of the disease is thought to initiate the pathogenesis of the disease. This hypothesis is defined as the "amyloid cascade hypothesis" [14]. In the pathogenesis of AD, tau hyperphosphorylation is known to impair microtubule stability and function, as well as to gain toxic function, for instance, tau aggregates induce apoptosis. However, like Aβ, it is thought that the tau oligomers they form are associated with neurodegeneration and memory impairment rather than the aggregates formed by the tau protein [15].

The source of routine EEG activity recorded from the scalp is the postsynaptic potentials of cortical pyramidal cells. According to the synaptic activity being

**70**

excitatory and inhibitory, the postsynaptic membrane becomes depolarized or hyperpolarized. The total electrical current generated by these excitatory and inhibitory postsynaptic potentials from millions of neurons creates superficial EEG activity. Adeli and Ghosh-Dastidar developed the wavelet-chaos method for the analysis of delta, theta, alpha, and beta (**Table 1**) subbands of EEG to identify potential markers in Alzheimer's disease.

To evaluate the effect of visual warning and attention, evaluation is done with eyes open and eyes closed. EEGs from different loci in the brain are used to explore the responsible areas of the brain and directly measure the functioning of synapses in real time [16, 17].

In AD, a significant decrease in cortical alpha frequency (8–10.5 Hz) was observed, especially in the limbic, temporal, parietal, and central areas [6]. However, it has been reported that the age of onset of AD can change this criterion, and that focal and diffuse EEG abnormalities are more common in early onset AD patients than in late-age AD patients. In the first studies, an increase in theta activity in EEG was considered as one of the earliest changes in Alzheimer's dementia, while alpha activity was found to decrease during or after the disease [18].

EEG markers showing the progression of the disease in MCI cases include an increase in delta and theta power and a decrease in beta or alpha power in the temporal and occipital regions [19]. Osipova et al. showed that alpha rhythm shifts from the parieto-occipital region to temporal regions in AD [20]. In other spontaneous EEG studies, it was found that frontal delta and occipital theta sources were higher in MCI patients than healthy ones, and frontal delta sources and the Mini-Mental State Examination (MMSE) showed negative correlations [21, 22].

The cortical cholinergic system has an important role in controlling many different functions such as cerebral blood flow, cortical activity, sleep/wake cycle, modulation of cortical plasticity, and cognitive performance and learningmemory processes. The presence of cholinergic neurons in the basal forebrain was first reported by Shute and Lewis in 1967. ACh deficiency is observed in the brains of individuals with AD in the entire cortex, especially the temporoparietal cortex [23, 24]. Also, one of the possible mechanisms underlying the observed relationship between Aβ42 and increased slow EEG activity is Aβ and cholinergic deficiencies in the brain in AD. Cholinergic therapy has different effects on delta and theta oscillation responses. Theta oscillations were similar in controls to those receiving cholinergic therapy in the AD patients, regardless of treatment. In other words, theta oscillation responses are affected by cholinergic therapy in AD patients, while the amplitudes of delta oscillation responses are not affected by cholinergic therapy [25].

Moreover, in studies evaluating the relationship between AD neuropathology, EEG frequencies, and CSF markers, amyloid β42 (Aβ42) showed a significant relationship with slow frequency (delta and theta) activity, while phospho-tau (p-tau) and total tau (t-tau) are associated with activity at only fast frequencies (alpha and beta) (26). Smailovic et al. demonstrated the correlation of qEEG and


CSF abnormalities with the AD profile at different stages of cognitive impairment, which revealed that qEEG can demonstrate neurodegeneration-induced synaptic dysfunction [26].

#### **4. Sensory-stimulated oscillations**

Sensory-evoked oscillatory responses are obtained by digital filtering of the frequency bands such as delta, theta, alpha, beta, and gamma of the "evoked potential" that appears with the delivery of the sensory stimulus. Haupt et al. showed that gamma and beta2 bands showed a different distribution compared to both patient groups in the visual-evoked oscillatory responses that they examined in Alzheimer's, MCI and healthy group controls, and the current density distribution followed a movement from the right hemisphere to the left hemisphere in these patient groups. In a visual sensory-evoked oscillatory study, the difference between AD patients and the healthy group was shown to disappear when the stimulus did not contain the cognitive load. Besides, when controlled, the parieto-occipital theta-stimulated oscillatory responses of the untreated Alzheimer's patient group were found to be higher than those of the treated Alzheimer's patient group and the healthy group [27].

#### **5. Sensory-evoked coherencies and event-related coherences**

Coherence or phase-locking statistics are the most common methods used to evaluate relationships between neural communities [28, 29]. Hogan et al. investigated memory-related EEG strength and coherence in the temporal and central areas in early stage AD patients and the normal control group and the behavioral performances of mild Alzheimer patients did not differ significantly from the healthy ones while they found a decrease in high alpha coherence between central and right temporal cortex of Alzheimer patients [30]. Rossini et al. measured the spontaneous EEG coherence of healthy control and MCI patients (progressive and constant) and found that the course of disease in patients with high coherence in the delta and gamma frequency bands progressed faster [31]. In another study examining the coherencies related to the event in patients with mild AD using visual sparse stimuli, the authors found higher OI coherence in the "delta," "theta," and "alpha" bands compared to the controls in the AD group that did not receive drug treatment. Alpha OI coherence values are higher in the medicated group compared to the drug-free AD group [32].

#### **6. Conclusion**

AD is a progressive neurocognitive disease in the elderly population. This disease is characterized by behavioral problems, cognitive impairment, delirium, and memory loss.

Most studies in AD have been done on frequency changes with EEG reactivity. When eyes are open, theta and alpha reactivity index and alpha/theta index were integrated into this study and were found as a useful approach to evaluate quantitative EEG (qEEG). EEG is advantageous compared to functional MRI or PET, which indirectly detects metabolic signals due to its noninvasive, wide availability, low cost, and direct access to neuronal signaling. Studies reveal that neuritic plaques, nodes, tangles, granulovacuolar degeneration, and the formation of amyloid

**73**

**Author details**

Demet Ilhan Algin1

Eskisehir, Turkey

\*, Demet Ozbabalık Adapinar2

\*Address all correspondence to: demetozbabalik@gmail.com

provided the original work is properly cited.

1 Neurology Department, Eskisehir Osmangazi University, Medical Faculty,

angiopathy are some of the pathological variations that cause AD. Neuroprotective and symptomatic approaches such as antioxidants and neurotransmitters are effective in treating AD symptoms and delay their development. No cure can treat AD, but medications that can treat disease symptoms and delay its progression have been developed and will continue to be developed. Therefore, early diagnosis is the key in treating the disease. Advances in neuroimaging technology, cognitive neuroscience, psychopathology, neuropathology, and neurobiology lead to the discovery

Researchers are also working on improving the accuracy of EEG-based AD diagnosis. New studies are needed to develop an algorithm in the early onset

We would like to thank Grifolscompany for its support in publishing this section.

diagnosis of AD, and this will happen sometime in the future.

The authors proclaim that they have no competing interests.

2 Neurology Department, Atlas University Medical Faculty, Istanbul, Turkey

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Oguz Osman Erdinc1

*EEG Biomarker for Alzheimer's Disease DOI: http://dx.doi.org/10.5772/intechopen.93711*

of AD biomarkers for early detection.

**Acknowledgements**

**Conflict of interest**

#### *EEG Biomarker for Alzheimer's Disease DOI: http://dx.doi.org/10.5772/intechopen.93711*

*Neurodegenerative Diseases - Molecular Mechanisms and Current Therapeutic Approaches*

dysfunction [26].

healthy group [27].

**6. Conclusion**

memory loss.

**4. Sensory-stimulated oscillations**

compared to the drug-free AD group [32].

CSF abnormalities with the AD profile at different stages of cognitive impairment, which revealed that qEEG can demonstrate neurodegeneration-induced synaptic

Sensory-evoked oscillatory responses are obtained by digital filtering of the frequency bands such as delta, theta, alpha, beta, and gamma of the "evoked potential" that appears with the delivery of the sensory stimulus. Haupt et al. showed that gamma and beta2 bands showed a different distribution compared to both patient groups in the visual-evoked oscillatory responses that they examined in Alzheimer's, MCI and healthy group controls, and the current density distribution followed a movement from the right hemisphere to the left hemisphere in these patient groups. In a visual sensory-evoked oscillatory study, the difference between AD patients and the healthy group was shown to disappear when the stimulus did not contain the cognitive load. Besides, when controlled, the parieto-occipital theta-stimulated oscillatory responses of the untreated Alzheimer's patient group were found to be higher than those of the treated Alzheimer's patient group and the

**5. Sensory-evoked coherencies and event-related coherences**

Coherence or phase-locking statistics are the most common methods used to evaluate relationships between neural communities [28, 29]. Hogan et al. investigated memory-related EEG strength and coherence in the temporal and central areas in early stage AD patients and the normal control group and the behavioral performances of mild Alzheimer patients did not differ significantly from the healthy ones while they found a decrease in high alpha coherence between central and right temporal cortex of Alzheimer patients [30]. Rossini et al. measured the spontaneous EEG coherence of healthy control and MCI patients (progressive and constant) and found that the course of disease in patients with high coherence in the delta and gamma frequency bands progressed faster [31]. In another study examining the coherencies related to the event in patients with mild AD using visual sparse stimuli, the authors found higher OI coherence in the "delta," "theta," and "alpha" bands compared to the controls in the AD group that did not receive drug treatment. Alpha OI coherence values are higher in the medicated group

AD is a progressive neurocognitive disease in the elderly population. This disease

Most studies in AD have been done on frequency changes with EEG reactivity. When eyes are open, theta and alpha reactivity index and alpha/theta index were integrated into this study and were found as a useful approach to evaluate quantitative EEG (qEEG). EEG is advantageous compared to functional MRI or PET, which indirectly detects metabolic signals due to its noninvasive, wide availability, low cost, and direct access to neuronal signaling. Studies reveal that neuritic plaques, nodes, tangles, granulovacuolar degeneration, and the formation of amyloid

is characterized by behavioral problems, cognitive impairment, delirium, and

**72**

angiopathy are some of the pathological variations that cause AD. Neuroprotective and symptomatic approaches such as antioxidants and neurotransmitters are effective in treating AD symptoms and delay their development. No cure can treat AD, but medications that can treat disease symptoms and delay its progression have been developed and will continue to be developed. Therefore, early diagnosis is the key in treating the disease. Advances in neuroimaging technology, cognitive neuroscience, psychopathology, neuropathology, and neurobiology lead to the discovery of AD biomarkers for early detection.

Researchers are also working on improving the accuracy of EEG-based AD diagnosis. New studies are needed to develop an algorithm in the early onset diagnosis of AD, and this will happen sometime in the future.

### **Acknowledgements**

We would like to thank Grifolscompany for its support in publishing this section.

### **Conflict of interest**

The authors proclaim that they have no competing interests.

### **Author details**

Demet Ilhan Algin1 \*, Demet Ozbabalık Adapinar2 and Oguz Osman Erdinc1

1 Neurology Department, Eskisehir Osmangazi University, Medical Faculty, Eskisehir, Turkey

2 Neurology Department, Atlas University Medical Faculty, Istanbul, Turkey

\*Address all correspondence to: demetozbabalik@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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*EEG Biomarker for Alzheimer's Disease DOI: http://dx.doi.org/10.5772/intechopen.93711*

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[25] Yener GG, Güntekin B, Öniz A, Başar E. Increased frontal phase-locking of event-related theta oscillations in Alzheimer patients treated with cholinesterase inhibitors. International Journal of Psychophysiology. 2007;**64**(1):46-52

[26] Smailovic U, Koenig T, Kareholt I, Andersson T, Kramberger MG, Winblad B, et al. Quantitative EEG power and synchronization correlate with Alzheimer's disease CSF biomarkers. Neurobiology of Aging. 2018;**63**:88-95

[27] Yener GG, Güntekin B, Tülay E, Başar E. A comparative analysis of sensory visual evoked oscillations with visual cognitive event related oscillations in Alzheimer's disease. Neuroscience Letters. 2009;**462**(3):193-197

[28] Gardner WA. Unifying view of coherence in signal processing. Signal Processing. 1993;**29**:113-140

[29] Lachaux JP, Lutz A, Rudrauf D, Cosmelli D, Quyen MLV, Martinerie J, et al. Estimating the time course of coherence between single-trial brain signals, an introduction to wavelet coherence. Neurophysiologie Clinique. 2002;**32**(3):157-174

[30] Hogan MJ, Swanwick GR, Kaiser J, Rowan M, Lawlor B. Memory-related EEG power and coherence reductions in mild Alzheimer's disease. International Journal of Psychophysiology. 2003;**49**(2):147-163

[31] Rossini PM, Del Percio C, Pasqualetti P, Cassetta E, Binetti G, Dal Forno G, et al. Conversion from mild cognitive impairment to

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recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease. Alzheimers Dement. 2011;**7**(3):280-292

[10] Weiner MW, Veitch DP, Aisen PS, et al. 2014 Update of the Alzheimer's Disease Neuroimaging Initiative: A review of papers published since its inception. Alzheimers Dement.

[11] McKhann GM, Knopman DS, Chertkow H, Hyman BT, Jack CR Jr, Kawas CH, et al. The diagnosis of dementia due to Alzheimer's disease: Recommendations from the National Institute on Aging and the Alzheimer's Association Workgroup. Alzheimers

Dement. 2011;**7**(3):263-269

[12] Blennow K, de Leon MJ, Zetterberg H. Alzheimer's disease. Lancet. 2006;**368**(9533):387-403

[13] Counts ES, Ikonomovic DM, Mercado N, Vega EI, Mufson JE. Biomarkers for the early detection and progression of Alzheimer's disease. Neurotherapeutics. 2017;**14**(1):35-53

[14] Buerger K, Ewers M, Pirttila T, et al. CSF phosphorylated tau protein correlates with neocortical neurofibrillary pathology in Alzheimer's disease. Brain. 2006;**129**(11):3035-3041

[15] Seppala TT, Nerg O, Koivisto AM, et al. CSF biomarkers for Alzheimer disease correlate with cortical brain biopsy findings. Neurology.

2012;**78**(20):1568-1575

2008;**444**(2):190-194

[16] Adeli H, Ghosh-Dastidar S, Dadmehr N. A spatiotemporal wavelet-chaos methodology for EEG-based diagnosis of Alzheimer's disease. Neuroscience Letters.

2015;**11**(6):1-120

[1] Cassani R, Estarellas M, San-Martin R, Fraga JF, Falk HT. Systematic Review on Resting EEG for Alzheimer's Diseases Diagnosis. 2018.

WHO; 2012. p. 112

[2] World Health Organization and Alzheimer's Disease International. Dementia: A Public Health Priority.

[3] Duthey B. "Background paper 6.11: Alzheimer disease and other dementias," A Public Health Approach

Disease International; 2015. p. 84

[5] Dubois B, Hampel H, Feldman HH, et al. Preclinical Alzheimer's disease: Definition, natural history, and diagnostic criteria. Alzheimer's & Dementia. 2016;**12**(3):292-323

[6] Albert MS, DeKosky ST, Dickson D, Dubois B, Feldman HH, Fox NC, et al. The diagnosis of mild cognitive impairment due to Alzheimer's disease: Recommendations from the National Institute on Aging and Alzheimer's Association Workgroup. Alzheimers

[7] Terry RD. Neuropathological changes in Alzheimer disease. Progress in Brain

[8] Sarazin M, de Souza LC, Lehéricy S,

[9] Sperling RA, Aisen PS, Beckett LA, et al. Toward defining the preclinical

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Research. 1994;**101**:383-390

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stages of Alzheimer's disease:

Dubois B. Clinical and research diagnostic criteria for Alzheimer's disease. Neuroimaging Clinics of North

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to Innovation. 2013. pp. 1-74

p. 26

**References**

**77**

**Chapter 6**

**Abstract**

ladostigil, ANAVEX 2-73

tic strategies of Alzheimer's disease.

**1. Introduction**

Multi-Target-Directed Ligands in

So far, the only clinically approved drugs that are effective in Alzheimer's disease

(AD) are those neurotransmitters oriented in their mode of action and focus, in particular, on the functional significance of acetylcholine or glutamate in the brain. Current AD drugs can, therefore, reduce the severity of cognitive symptoms, improve the quality of life, and stabilize the symptoms for some years, but they are not able to significantly modify the course of the disease. Complex disorders such as neurodegenerative diseases tend to result from multiple molecular abnormalities, not from a single defect. Moreover, a single target is unlikely to help in such cases because the cells can often find ways to compensate for a protein whose activity is affected by a drug. Thus, these limitations of the conventional "one-target, onemolecule" paradigm have triggered a recent shift in efforts to create drugs that hit more than one target simultaneously. The term multi-target-directed ligands (MTDLs) have been proposed to describe these hybrid molecules that are effective in treating complex diseases. Within our contribution, we would like to present general overview of MTDL design strategy in AD therapy, its positives and negatives, and finally summary of such multipotent compounds evaluated in clinical trials.

**Keywords:** Alzheimer's disease, therapy, multi-target-directed ligands, drug design,

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with unknown etiology. Currently, no causal treatment is available, probably due to multiple factors involved in pathophysiology of the disease. Recently, it has become clear that "one-target, one-molecule" therapy is not effective to complex diseases with multifactorial pathogenesis. Thus, novel approach, called multi-target-

directed ligand (MTDL) strategy, has been developed. Hybrid compounds resulting from this drug design strategy have to be capable to act at diverse biological targets simultaneously. Discovery and subsequent launch of such multipotent drug candidates on the pharmaceutical market would greatly facilitate and improve therapeu-

**2. Drug design history leading to multi-target-directed ligand strategy**

The "one-target, one-molecule" philosophy has resulted in many approved drugs and will likely continue to be the benchmark in the time to come [1]. This paradigm

Alzheimer's Disease Therapy

*Eugenie Nepovimova and Kamil Kuca*

Alzheimer's disease is predicted by sources and coherence of brain electroencephalography rhythms. Neuroscience. 2006;**143**(3):793-803

[32] Güntekin B, Saatçi E, Yener G. Decrease of evoked delta, theta and alpha coherence in Alzheimer patients during a visual oddball paradigm. Brain Research. 2008;**1235**:109-116

#### **Chapter 6**

*Neurodegenerative Diseases - Molecular Mechanisms and Current Therapeutic Approaches*

Alzheimer's disease is predicted by sources and coherence of brain electroencephalography rhythms. Neuroscience. 2006;**143**(3):793-803

[32] Güntekin B, Saatçi E, Yener G. Decrease of evoked delta, theta and alpha coherence in Alzheimer patients during a visual oddball paradigm. Brain

Research. 2008;**1235**:109-116

**76**

## Multi-Target-Directed Ligands in Alzheimer's Disease Therapy

*Eugenie Nepovimova and Kamil Kuca*

#### **Abstract**

So far, the only clinically approved drugs that are effective in Alzheimer's disease (AD) are those neurotransmitters oriented in their mode of action and focus, in particular, on the functional significance of acetylcholine or glutamate in the brain. Current AD drugs can, therefore, reduce the severity of cognitive symptoms, improve the quality of life, and stabilize the symptoms for some years, but they are not able to significantly modify the course of the disease. Complex disorders such as neurodegenerative diseases tend to result from multiple molecular abnormalities, not from a single defect. Moreover, a single target is unlikely to help in such cases because the cells can often find ways to compensate for a protein whose activity is affected by a drug. Thus, these limitations of the conventional "one-target, onemolecule" paradigm have triggered a recent shift in efforts to create drugs that hit more than one target simultaneously. The term multi-target-directed ligands (MTDLs) have been proposed to describe these hybrid molecules that are effective in treating complex diseases. Within our contribution, we would like to present general overview of MTDL design strategy in AD therapy, its positives and negatives, and finally summary of such multipotent compounds evaluated in clinical trials.

**Keywords:** Alzheimer's disease, therapy, multi-target-directed ligands, drug design, ladostigil, ANAVEX 2-73

#### **1. Introduction**

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with unknown etiology. Currently, no causal treatment is available, probably due to multiple factors involved in pathophysiology of the disease. Recently, it has become clear that "one-target, one-molecule" therapy is not effective to complex diseases with multifactorial pathogenesis. Thus, novel approach, called multi-targetdirected ligand (MTDL) strategy, has been developed. Hybrid compounds resulting from this drug design strategy have to be capable to act at diverse biological targets simultaneously. Discovery and subsequent launch of such multipotent drug candidates on the pharmaceutical market would greatly facilitate and improve therapeutic strategies of Alzheimer's disease.

#### **2. Drug design history leading to multi-target-directed ligand strategy**

The "one-target, one-molecule" philosophy has resulted in many approved drugs and will likely continue to be the benchmark in the time to come [1]. This paradigm

has been driven by the notion that a single target's selective modulation can help create the needed extend of efficiency while simultaneously bringing down the risk of off-target side effects. On the other hand, current research has shown that the failure of such compounds is largely owed to poor safety and poor efficiency, observed in the last 10 years. It has therefore been put forward that the biology networks' intrinsic robustness and redundancy are the main culprits when it comes to highly selective drugs failing to ensure that the needed impact or result is present [2]. Furthermore, substances that focus on one target likely prove to be ineffective or insufficient when the treatment is being focused on complex illnesses, including diabetes mellitus, neurodegenerative disorders, cardiovascular diseases, and cancer that come laced with several pathogenic aspects [1].

After three decades, it seems that this approach is not effective in terms of possible success. Some of these substances only prove to be helpful to a specific set of the population [3]. When a "one-target, one-molecule" drug is not effective enough to address an illness, the next route involves several drugs administered together. Such approach is sometimes denoted as "cocktail of drugs," where multiple substances are mixed together to tackle the illness [1]. These mixtures typically contain two or more substances that come together to produce a more holistic impact [4]. This approach helps not only to increase the efficiency of the therapy but also to address and bring down the side effects – such a situation is not possible when only a single drug is being used to provide therapy. This positive situation has been observed within the treatment of several maladies, including hypertension, HIV, and cancer. However, the benefits of taking several drugs can become shaky if the patient does not comply with the regime properly. This is especially typical for situations when the illness is asymptomatic [2].

In recent times, multicomponent drugs have become more popular, where two agents or more are mixed into a single tablet, so that patient's compliance can be improved alongside the dosing schedules [2, 4]. Such combinations are called "fixed drug combinations" (FDCs). On the other hand, the problems that stem from highly complicated pharmacodynamics/pharmacokinetics necessitate formulations that have the right kind of sophistication due to the occurrence of possible drugdrug interactions, which could have a considerable impact on the costs and risks of designed FDCs [2].

Two independent scientific groups of Inestrosa and Brimijoin found out that the active site of enzyme acetylcholinesterase (AChE; E.C. 3.1.1.7) is close enough to its allosteric peripheral site and that these two sites can be spanned by one molecule at the same time. This discovery has launched rational design of novel class of therapeutic agents – dual-binding site acetylcholinesterase inhibitors (AChEIs) [5]. Inestrosa and Brimijoin in their studies demonstrated that AChE interacts through its allosteric site with amyloid peptide (Aβ) and acts thus like a pathological chaperone inducing a conformational change favoring Aβ aggregation [6, 7]. In this respect, ligands that can simultaneously interact with both sites could produce many merits comparing to active site inhibitors. Namely, such dual-binding site inhibitors considerably increase the inhibitory potential toward AChE, thus providing symptomatic relief, facilitating memory process, and, at the same time, exerting neuroprotective preventive effect [8]. Positive effects of dual-binding site inhibitors, AD's multifactorial aspect, and the routine of use of combination therapy in clinical practice prompted drug designers to pay more attention to development of more complex medicaments that in turn use dual-binding site inhibitors as an appropriate starting point [9].

Cancer, depression, neurodegenerative maladies, cardiovascular diseases, and other complex disorders typically result from several abnormalities at the molecular level, not because of a single issue. Moreover, modulation of one single target would

**79**

*Multi-Target-Directed Ligands in Alzheimer's Disease Therapy*

could be effective in treating complex diseases [1].

**3. Advantages and disadvantages of MTDLs**

**4. Classification of MTDLs**

of the starting compounds [2].

will prove to be inherently better than FDCs or cocktails of drugs.

probably not show any significance in such cases since the cells will likely find routes through which the protein can be compensated after its activity is affected by the medicine. Thus, these limitations of the conventional "one-target, one-molecule" paradigm have induced a shift in pharmaceutical companies' research to develop therapeutics that can address more than one problem. Many research groups and pharma companies now look for compounds that can address multiple issues and are even attempting to develop the so-called promiscuous drugs [3, 10]. With this new drug design strategy, two or more compounds, binding with a very high selectivity to their respective targets, are used as the starting blocks, and their structural elements are combined into a single molecule to incorporate activity at both targets. Hence, this approach normally involves the use of two or more different pharmacophoric moieties (in most cases, at least one is directly related to AChEI being a pillar of standard AD therapy) to include into a single framework [4, 10]. The term multitarget-directed ligand has been proposed to describe these hybrid molecules that

The use of such promiscuous drugs may provide some advantages: (i) in terms of the disease, various pathways can be effectively targeted via a single multipotent molecule, thus increasing its efficiency; (ii) drugs of a promiscuous nature do not always overactivate or suppress a network or pathway; (iii) single molecular species, although consisting of several pharmacophores, show a complex ADMET profile; (iv) drug-drug interactions' risk should be reduced; and (v) the drug regimen of the patients taking MTDLs should be greatly simplified [1, 11]. However, beside the advantages, there are also several drawbacks. A key problem linked to the use of promiscuous drugs has to do with how hard it is to optimize potencies for two different targets while using one medicine. Taking into account all the advantages and disadvantages, therapy that uses one medicine with several biological activities

Depending on the extent to which the frameworks of selective pharmacophores have been integrated, three different classes of MTDLs can be distinguished (**Figure 1**). The first class is represented by linked MTDLs, whose molecular frameworks have not been integrated but have been connected via a specific linker not found in either of the starting selective pharmacophores. Sometimes, pharmacophores in linked MTDLs contain a metabolically cleavable linker, purposely designed to exude *in vivo* two ligands that can independently interact with related targets. Such scenario could be considered as a half-way between real MTDLs and FDCs. However, in most cases, the linker is designed to be metabolically stable, yielding a single compound capable of interacting with two targets simultaneously. In particular, dual-binding site inhibitors are the best representatives of linked subclass. Fused MTDLs constitute the second class. In fused MTDLs, the frameworks are linked directly. However, medicinal chemists generally aspire to maximize the degree of framework overlap in order to design as simplest and smallest molecules as possible with favorable physicochemical properties. Therefore, it would probably not be surprising that the most common and sought after are merged MTDLs, where the frameworks are integrated by the use of commonalities in the structures

*DOI: http://dx.doi.org/10.5772/intechopen.93269*

*Multi-Target-Directed Ligands in Alzheimer's Disease Therapy DOI: http://dx.doi.org/10.5772/intechopen.93269*

*Neurodegenerative Diseases - Molecular Mechanisms and Current Therapeutic Approaches*

that come laced with several pathogenic aspects [1].

the illness is asymptomatic [2].

appropriate starting point [9].

designed FDCs [2].

has been driven by the notion that a single target's selective modulation can help create the needed extend of efficiency while simultaneously bringing down the risk of off-target side effects. On the other hand, current research has shown that the failure of such compounds is largely owed to poor safety and poor efficiency, observed in the last 10 years. It has therefore been put forward that the biology networks' intrinsic robustness and redundancy are the main culprits when it comes to highly selective drugs failing to ensure that the needed impact or result is present [2]. Furthermore, substances that focus on one target likely prove to be ineffective or insufficient when the treatment is being focused on complex illnesses, including diabetes mellitus, neurodegenerative disorders, cardiovascular diseases, and cancer

After three decades, it seems that this approach is not effective in terms of possible success. Some of these substances only prove to be helpful to a specific set of the population [3]. When a "one-target, one-molecule" drug is not effective enough to address an illness, the next route involves several drugs administered together. Such approach is sometimes denoted as "cocktail of drugs," where multiple substances are mixed together to tackle the illness [1]. These mixtures typically contain two or more substances that come together to produce a more holistic impact [4]. This approach helps not only to increase the efficiency of the therapy but also to address and bring down the side effects – such a situation is not possible when only a single drug is being used to provide therapy. This positive situation has been observed within the treatment of several maladies, including hypertension, HIV, and cancer. However, the benefits of taking several drugs can become shaky if the patient does not comply with the regime properly. This is especially typical for situations when

In recent times, multicomponent drugs have become more popular, where two agents or more are mixed into a single tablet, so that patient's compliance can be improved alongside the dosing schedules [2, 4]. Such combinations are called "fixed drug combinations" (FDCs). On the other hand, the problems that stem from highly complicated pharmacodynamics/pharmacokinetics necessitate formulations that have the right kind of sophistication due to the occurrence of possible drugdrug interactions, which could have a considerable impact on the costs and risks of

Two independent scientific groups of Inestrosa and Brimijoin found out that the active site of enzyme acetylcholinesterase (AChE; E.C. 3.1.1.7) is close enough to its allosteric peripheral site and that these two sites can be spanned by one molecule at the same time. This discovery has launched rational design of novel class of therapeutic agents – dual-binding site acetylcholinesterase inhibitors (AChEIs) [5]. Inestrosa and Brimijoin in their studies demonstrated that AChE interacts through its allosteric site with amyloid peptide (Aβ) and acts thus like a pathological chaperone inducing a conformational change favoring Aβ aggregation [6, 7]. In this respect, ligands that can simultaneously interact with both sites could produce many merits comparing to active site inhibitors. Namely, such dual-binding site inhibitors considerably increase the inhibitory potential toward AChE, thus providing symptomatic relief, facilitating memory process, and, at the same time, exerting neuroprotective preventive effect [8]. Positive effects of dual-binding site inhibitors, AD's multifactorial aspect, and the routine of use of combination therapy in clinical practice prompted drug designers to pay more attention to development of more complex medicaments that in turn use dual-binding site inhibitors as an

Cancer, depression, neurodegenerative maladies, cardiovascular diseases, and other complex disorders typically result from several abnormalities at the molecular level, not because of a single issue. Moreover, modulation of one single target would

**78**

probably not show any significance in such cases since the cells will likely find routes through which the protein can be compensated after its activity is affected by the medicine. Thus, these limitations of the conventional "one-target, one-molecule" paradigm have induced a shift in pharmaceutical companies' research to develop therapeutics that can address more than one problem. Many research groups and pharma companies now look for compounds that can address multiple issues and are even attempting to develop the so-called promiscuous drugs [3, 10]. With this new drug design strategy, two or more compounds, binding with a very high selectivity to their respective targets, are used as the starting blocks, and their structural elements are combined into a single molecule to incorporate activity at both targets. Hence, this approach normally involves the use of two or more different pharmacophoric moieties (in most cases, at least one is directly related to AChEI being a pillar of standard AD therapy) to include into a single framework [4, 10]. The term multitarget-directed ligand has been proposed to describe these hybrid molecules that could be effective in treating complex diseases [1].

#### **3. Advantages and disadvantages of MTDLs**

The use of such promiscuous drugs may provide some advantages: (i) in terms of the disease, various pathways can be effectively targeted via a single multipotent molecule, thus increasing its efficiency; (ii) drugs of a promiscuous nature do not always overactivate or suppress a network or pathway; (iii) single molecular species, although consisting of several pharmacophores, show a complex ADMET profile; (iv) drug-drug interactions' risk should be reduced; and (v) the drug regimen of the patients taking MTDLs should be greatly simplified [1, 11]. However, beside the advantages, there are also several drawbacks. A key problem linked to the use of promiscuous drugs has to do with how hard it is to optimize potencies for two different targets while using one medicine. Taking into account all the advantages and disadvantages, therapy that uses one medicine with several biological activities will prove to be inherently better than FDCs or cocktails of drugs.

#### **4. Classification of MTDLs**

Depending on the extent to which the frameworks of selective pharmacophores have been integrated, three different classes of MTDLs can be distinguished (**Figure 1**). The first class is represented by linked MTDLs, whose molecular frameworks have not been integrated but have been connected via a specific linker not found in either of the starting selective pharmacophores. Sometimes, pharmacophores in linked MTDLs contain a metabolically cleavable linker, purposely designed to exude *in vivo* two ligands that can independently interact with related targets. Such scenario could be considered as a half-way between real MTDLs and FDCs. However, in most cases, the linker is designed to be metabolically stable, yielding a single compound capable of interacting with two targets simultaneously. In particular, dual-binding site inhibitors are the best representatives of linked subclass. Fused MTDLs constitute the second class. In fused MTDLs, the frameworks are linked directly. However, medicinal chemists generally aspire to maximize the degree of framework overlap in order to design as simplest and smallest molecules as possible with favorable physicochemical properties. Therefore, it would probably not be surprising that the most common and sought after are merged MTDLs, where the frameworks are integrated by the use of commonalities in the structures of the starting compounds [2].

**Figure 1.** *Classification of MTDLs.*

#### **5. MTDLs in clinical trials**

In Alzheimer's disease drug development pipeline for year 2019 issued annually by Alzheimer's and Dementia, there was no MTDL currently assessed in AD clinical trials [12]. The only drug candidate with multimodal action found within the mentioned list was ANAVEX 2-73. However, for completeness of the subchapter, we have decided to include also ladostigil as the only real representative of MTDLs ever evaluated in clinics.

Ladostigil (TV3326; **Figure 2**) is a dual cholinesterase (ChE) and brain-selective monoaminooxidase-A (MAO-A) and monoaminooxidase-B (MAO-B) inhibitor indicated for the treatment of dementia comorbid with extrapyramidal disorders and depression [13]. The design of this MTDL is based on the combination of carbamate rivastigmine and *N*-propargyl scaffold of anti-Parkinsonian drug and irreversible selective MAO-B inhibitor, rasagiline [14, 15].

Rasagiline is an irreversible inhibitor of MAO-B used as a monotherapy to treat symptoms of early Parkinson's disease (PD) or as an adjunct therapy in more advanced cases of PD [16]. Rivastigmine is a nonselective AChE and butyrylcholinesterase (BChE; E.C. 3.1.1.8) inhibitor [17]. It could be also classified as pseudo-irreversible

**81**

**Figure 3.**

*Chemical structure of ANAVEX 2-73.*

well [22, 24].

*Multi-Target-Directed Ligands in Alzheimer's Disease Therapy*

withdrawal indicated disease-modifying effect [20].

rinic receptor agonist and activator of sigma-1 receptors.

and Aβ accumulation in AD model [25].

ChE inhibitor since the duration of inhibition is longer than its elimination half-life [18]. It is indicated for the treatment of mild-to-moderate dementia associated with Alzheimer's disease type and PD [18]. Rivastigmine has also proven efficacy in decreasing psychiatric symptoms and cognitive deficits [19]. This fact together with the continued beneficial effect observed in rivastigmine-treated patients after drug

In rodents, oral administration of ladostigil was shown to antagonize scopolamine-induced spatial memory impairments, pointing out that it is able to sufficiently penetrate the blood-brain barrier [21]. Apart from MAO and ChE inhibition, ladostigil has shown to possess a broad scale of neuroprotective activities against a variety of neurotoxins and neuronal cell culture models of neurodegeneration [20]. All these perspective preclinical results forwarded ladostigil to clinical evaluation. In 2011, Avraham Pharmaceuticals evaluated a 6-month trial of ladostigil in Phase II in 201 people with mild-to-moderate Alzheimer's disease. However, this trial missed its primary endpoint on the ADAS-cog11, and thus, development for Alzheimer's disease was terminated [22, 23]. In January 2012, the same company started the second Phase II study, in this case evaluating a lower dose of ladostigil for its ability to delay progression from mild cognitive impairment (MCI) to AD. This study enrolled 210 people with a clinical diagnosis of MCI. In September 2016, the company disclosed that ladostigil missed its primary endpoint in this trial as

ANAVEX 2-73 (blarcamesine; **Figure 3**) is an experimental drug in Phase II clinical trial for Alzheimer's disease, Phase I for epilepsy, and preclinical trials for amyotrophic lateral sclerosis, Parkinson's disease, Rett syndrome, and stroke [25, 26]. From the pharmacological point of view, this small molecule acts as a musca-

Within preclinical trials, ANAVEX 2-73 alleviated scopolamine- and dizocilpineinduced learning impairments, pointing out to its antimuscarinic and neuroprotective effect mediated by NMDA receptors [27, 28]. The sigma-1 receptors are small transmembrane stress-reducing survival proteins, mainly located on the endoplasmic reticulum membrane of cells. Moreover, these receptors are known to modulate cellular processes relevant to neurodegeneration. In particular, ANAVEX 2-73 is thought to help to restore cellular balance by targeting protein misfolding, oxidative stress, mitochondrial dysfunction, inflammation, and cellular stress [29]. More recently, the effect of ANAVEX 2-73 on the main hallmarks, that is, Aβ1–42 seeding and tau hyperphosphorylation, of Alzheimer's disease has been studied. The results of such experiment revealed that ANAVEX 2-73 significantly blocked an increase in Aβ1–42 levels in hippocampus, suggesting that it may alleviate amyloid load in AD model. In addition, the data presented within the same study suggested that modulation of both receptors, that is, muscarinic and sigma-1, targets GSK-3β activity and that inhibiting of this kinase efficiently decreases tau hyperphosphorylation

Phase I clinical trial, assessing safety and pharmacokinetics, with ANAVEX 2-73 was successfully completed in healthy volunteers in Germany. The maximum

*DOI: http://dx.doi.org/10.5772/intechopen.93269*

**Figure 2.** *Chemical structure of ladostigil.*

#### *Multi-Target-Directed Ligands in Alzheimer's Disease Therapy DOI: http://dx.doi.org/10.5772/intechopen.93269*

*Neurodegenerative Diseases - Molecular Mechanisms and Current Therapeutic Approaches*

In Alzheimer's disease drug development pipeline for year 2019 issued annually by Alzheimer's and Dementia, there was no MTDL currently assessed in AD clinical trials [12]. The only drug candidate with multimodal action found within the mentioned list was ANAVEX 2-73. However, for completeness of the subchapter, we have decided to include also ladostigil as the only real representative of MTDLs ever

Ladostigil (TV3326; **Figure 2**) is a dual cholinesterase (ChE) and brain-selective monoaminooxidase-A (MAO-A) and monoaminooxidase-B (MAO-B) inhibitor indicated for the treatment of dementia comorbid with extrapyramidal disorders and depression [13]. The design of this MTDL is based on the combination of carbamate rivastigmine and *N*-propargyl scaffold of anti-Parkinsonian drug and

Rasagiline is an irreversible inhibitor of MAO-B used as a monotherapy to treat symptoms of early Parkinson's disease (PD) or as an adjunct therapy in more advanced cases of PD [16]. Rivastigmine is a nonselective AChE and butyrylcholinesterase (BChE; E.C. 3.1.1.8) inhibitor [17]. It could be also classified as pseudo-irreversible

irreversible selective MAO-B inhibitor, rasagiline [14, 15].

**80**

**Figure 2.**

*Chemical structure of ladostigil.*

**5. MTDLs in clinical trials**

evaluated in clinics.

*Classification of MTDLs.*

**Figure 1.**

ChE inhibitor since the duration of inhibition is longer than its elimination half-life [18]. It is indicated for the treatment of mild-to-moderate dementia associated with Alzheimer's disease type and PD [18]. Rivastigmine has also proven efficacy in decreasing psychiatric symptoms and cognitive deficits [19]. This fact together with the continued beneficial effect observed in rivastigmine-treated patients after drug withdrawal indicated disease-modifying effect [20].

In rodents, oral administration of ladostigil was shown to antagonize scopolamine-induced spatial memory impairments, pointing out that it is able to sufficiently penetrate the blood-brain barrier [21]. Apart from MAO and ChE inhibition, ladostigil has shown to possess a broad scale of neuroprotective activities against a variety of neurotoxins and neuronal cell culture models of neurodegeneration [20].

All these perspective preclinical results forwarded ladostigil to clinical evaluation. In 2011, Avraham Pharmaceuticals evaluated a 6-month trial of ladostigil in Phase II in 201 people with mild-to-moderate Alzheimer's disease. However, this trial missed its primary endpoint on the ADAS-cog11, and thus, development for Alzheimer's disease was terminated [22, 23]. In January 2012, the same company started the second Phase II study, in this case evaluating a lower dose of ladostigil for its ability to delay progression from mild cognitive impairment (MCI) to AD. This study enrolled 210 people with a clinical diagnosis of MCI. In September 2016, the company disclosed that ladostigil missed its primary endpoint in this trial as well [22, 24].

ANAVEX 2-73 (blarcamesine; **Figure 3**) is an experimental drug in Phase II clinical trial for Alzheimer's disease, Phase I for epilepsy, and preclinical trials for amyotrophic lateral sclerosis, Parkinson's disease, Rett syndrome, and stroke [25, 26]. From the pharmacological point of view, this small molecule acts as a muscarinic receptor agonist and activator of sigma-1 receptors.

Within preclinical trials, ANAVEX 2-73 alleviated scopolamine- and dizocilpineinduced learning impairments, pointing out to its antimuscarinic and neuroprotective effect mediated by NMDA receptors [27, 28]. The sigma-1 receptors are small transmembrane stress-reducing survival proteins, mainly located on the endoplasmic reticulum membrane of cells. Moreover, these receptors are known to modulate cellular processes relevant to neurodegeneration. In particular, ANAVEX 2-73 is thought to help to restore cellular balance by targeting protein misfolding, oxidative stress, mitochondrial dysfunction, inflammation, and cellular stress [29]. More recently, the effect of ANAVEX 2-73 on the main hallmarks, that is, Aβ1–42 seeding and tau hyperphosphorylation, of Alzheimer's disease has been studied. The results of such experiment revealed that ANAVEX 2-73 significantly blocked an increase in Aβ1–42 levels in hippocampus, suggesting that it may alleviate amyloid load in AD model. In addition, the data presented within the same study suggested that modulation of both receptors, that is, muscarinic and sigma-1, targets GSK-3β activity and that inhibiting of this kinase efficiently decreases tau hyperphosphorylation and Aβ accumulation in AD model [25].

Phase I clinical trial, assessing safety and pharmacokinetics, with ANAVEX 2-73 was successfully completed in healthy volunteers in Germany. The maximum

**Figure 3.** *Chemical structure of ANAVEX 2-73.* tolerated dose in men was determined to be 55 mg. The results of Phase II clinical trial on patients with mild-to-moderate Alzheimer's disease showed a significant association between the dosage of ANAVEX2-73 and the cognitive and function improvements [29].

#### **6. Conclusion**

While AChEI itself is an ever evolving branch of AD research, the rationale for MTDL design strategy clearly stems from the AD's multifactorial etiological basis. In a meanwhile, novel therapeutic targets continually emerge. Optimization of the therapeutic potential of dual-binding site AChEIs by adding biological activities, such as one from the arsenal against neurodegeneration, is an ongoing process for medicinal chemists. Several approaches are being deployed to design MTDLs; however, all of them use the combination of different smaller fragments of a given specific activity in a single molecule. Future work on such design strategy will involve fine tuning of pharmacokinetic and activity profiles of novel drug candidates for the purpose of modulating the selected molecular targets at the similar levels. Additionally, more clinical trials are required to prove the MTDL concept. The way ahead is not a short one; however, it is extremely possible that MTDLs could become the future treatment against AD and other similar complex multifactorial diseases, including infectious disorders, cancer, cardiovascular maladies, and so on.

#### **Acknowledgements**

This work was supported by the University of Hradec Kralove (Faculty of Science, VT2019-2021).

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Eugenie Nepovimova and Kamil Kuca\* Department of Chemistry, Faculty of Science, University of Hradec Kralove, Hradec Kralove, Czech Republic

\*Address all correspondence to: kamil.kuca@uhk.cz

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**83**

*Multi-Target-Directed Ligands in Alzheimer's Disease Therapy*

inhibitors to multi-target-directed ligands (MTDLs): A step forward in the treatment of Alzheimer's disease. Mini Reviews in Medicinal Chemistry.

2008;**8**(10):960-967

[10] Bolognesi ML, Rosini M,

[11] Espinoza-Fonseca LM. The benefits of the multi-target approach

in drug design and discovery. Bioorganic & Medicinal Chemistry.

[12] Cummings J, Lee G, Ritter A, Sabbagh M, Zhong K. Alzheimer's disease drug development pipeline. Alzheimers & Dementia (NY). 2019;**5**:

[13] Weinreb O, Amit T, Bar-Am O, Youdim MBH. Ladostigil: A novel multimodal neuroprotective drug with cholinesterase and brain-selective monoamine oxidase inhibitory activities for Alzheimer's disease treatment. Current Drug Targets.

[14] Weinstock M, Bejar C, Wang RH, Poltyrev T, Gross A, Finberg JP, et al. TV3326, a novel neuroprotective drug with cholinesterase and monoamine oxidase inhibitory activities for the treatment of Alzheimer's disease. Journal of Neural Transmission. Supplementum. 2000;**60**:157-169

[15] Korábečný J, Nepovimová E, Cikánková T, Špilovská K, Vašková L, Mezeiová E, et al. Newly developed drugs for Alzheimer's disease in relation to energy metabolism, cholinergic and monoaminergic neurotransmission. Neuroscience. 2018;**370**:191-206

2006;**14**(4):896-897

2012;**13**(4):483-494

272-293

Andrisano V, Bartolini M, Minarini A, Tumiatti V, et al. MTDL design strategy in the context of Alzheimer's disease: From lipocrine to memoquin and beyond. Current Pharmaceutical Design. 2009;**15**(6):601-613

*DOI: http://dx.doi.org/10.5772/intechopen.93269*

[1] Cavalli A, Bolognesi ML, Minarini A, Rosini M, Tumiatti V, Recanatini M, et al. Multi-target-directed ligands to combat neurodegenerative diseases. Journal of Medicinal Chemistry.

[2] Morphy R, Rankovic Z. Designing

[3] Frantz S. Drug discovery: Playing dirty. Nature. 2005;**437**(7061):942-943

[4] Rampa A, Belluti F, Gobbi S, Bisi A. Hybrid-based multi-target ligands for the treatment of Alzheimer's disease. Current Topics in Medicinal Chemistry.

[6] Inestrosa NC, Alvarez A, Pérez CA, Moreno RD, Vicente M, Linker C, et al. Acetylcholinesterase accelerates assembly of amyloid-beta-peptides into Alzheimer's fibrils: Possible role of the peripheral site of the enzyme. Neuron.

[7] Rees T, Hammond PI, Soreq H,

promotes beta-amyloid plaques in cerebral cortex. Neurobiology of Aging.

Younkin S, Brimijoin S. Acetylcholinesterase

[8] Castro A, Martinez A. Peripheral and dual binding site acetylcholinesterase inhibitors: Implications in treatment of Alzheimer's disease. Mini Reviews in Medicinal Chemistry. 2001;**1**(3):267-272

[9] Bolognesi ML, Minarini A, Rosini M, Tumiatti V, Melchiorre C. From dual binding site acetylcholinesterase

multiple ligands—Medicinal chemistry strategies and challenges. Current Pharmaceutical Design.

2008;**51**(3):347-372

**References**

2009;**15**(6):587-600

2011;**11**(22):2716-2730

2008;**15**(24):2433-2455

1996;**16**(4):881-891

2003;**24**(6):777-787

[5] Muñoz-Torrero D. Acetylcholinesterase inhibitors as diseasemodifying therapies for Alzheimer's disease. Current Medicinal Chemistry. *Multi-Target-Directed Ligands in Alzheimer's Disease Therapy DOI: http://dx.doi.org/10.5772/intechopen.93269*

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*Neurodegenerative Diseases - Molecular Mechanisms and Current Therapeutic Approaches*

tolerated dose in men was determined to be 55 mg. The results of Phase II clinical trial on patients with mild-to-moderate Alzheimer's disease showed a significant association between the dosage of ANAVEX2-73 and the cognitive and function

While AChEI itself is an ever evolving branch of AD research, the rationale for MTDL design strategy clearly stems from the AD's multifactorial etiological basis. In a meanwhile, novel therapeutic targets continually emerge. Optimization of the therapeutic potential of dual-binding site AChEIs by adding biological activities, such as one from the arsenal against neurodegeneration, is an ongoing process for medicinal chemists. Several approaches are being deployed to design MTDLs; however, all of them use the combination of different smaller fragments of a given specific activity in a single molecule. Future work on such design strategy will involve fine tuning of pharmacokinetic and activity profiles of novel drug candidates for the purpose of modulating the selected molecular targets at the similar levels. Additionally, more clinical trials are required to prove the MTDL concept. The way ahead is not a short one; however, it is extremely possible that MTDLs could become the future treatment against AD and other similar complex multifactorial diseases,

including infectious disorders, cancer, cardiovascular maladies, and so on.

This work was supported by the University of Hradec Kralove (Faculty of

**82**

**Author details**

**Acknowledgements**

Science, VT2019-2021).

**Conflict of interest**

improvements [29].

**6. Conclusion**

Eugenie Nepovimova and Kamil Kuca\*

provided the original work is properly cited.

\*Address all correspondence to: kamil.kuca@uhk.cz

The authors declare no conflict of interest.

Hradec Kralove, Czech Republic

Department of Chemistry, Faculty of Science, University of Hradec Kralove,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

[1] Cavalli A, Bolognesi ML, Minarini A, Rosini M, Tumiatti V, Recanatini M, et al. Multi-target-directed ligands to combat neurodegenerative diseases. Journal of Medicinal Chemistry. 2008;**51**(3):347-372

[2] Morphy R, Rankovic Z. Designing multiple ligands—Medicinal chemistry strategies and challenges. Current Pharmaceutical Design. 2009;**15**(6):587-600

[3] Frantz S. Drug discovery: Playing dirty. Nature. 2005;**437**(7061):942-943

[4] Rampa A, Belluti F, Gobbi S, Bisi A. Hybrid-based multi-target ligands for the treatment of Alzheimer's disease. Current Topics in Medicinal Chemistry. 2011;**11**(22):2716-2730

[5] Muñoz-Torrero D. Acetylcholinesterase inhibitors as diseasemodifying therapies for Alzheimer's disease. Current Medicinal Chemistry. 2008;**15**(24):2433-2455

[6] Inestrosa NC, Alvarez A, Pérez CA, Moreno RD, Vicente M, Linker C, et al. Acetylcholinesterase accelerates assembly of amyloid-beta-peptides into Alzheimer's fibrils: Possible role of the peripheral site of the enzyme. Neuron. 1996;**16**(4):881-891

[7] Rees T, Hammond PI, Soreq H, Younkin S, Brimijoin S. Acetylcholinesterase promotes beta-amyloid plaques in cerebral cortex. Neurobiology of Aging. 2003;**24**(6):777-787

[8] Castro A, Martinez A. Peripheral and dual binding site acetylcholinesterase inhibitors: Implications in treatment of Alzheimer's disease. Mini Reviews in Medicinal Chemistry. 2001;**1**(3):267-272

[9] Bolognesi ML, Minarini A, Rosini M, Tumiatti V, Melchiorre C. From dual binding site acetylcholinesterase

inhibitors to multi-target-directed ligands (MTDLs): A step forward in the treatment of Alzheimer's disease. Mini Reviews in Medicinal Chemistry. 2008;**8**(10):960-967

[10] Bolognesi ML, Rosini M, Andrisano V, Bartolini M, Minarini A, Tumiatti V, et al. MTDL design strategy in the context of Alzheimer's disease: From lipocrine to memoquin and beyond. Current Pharmaceutical Design. 2009;**15**(6):601-613

[11] Espinoza-Fonseca LM. The benefits of the multi-target approach in drug design and discovery. Bioorganic & Medicinal Chemistry. 2006;**14**(4):896-897

[12] Cummings J, Lee G, Ritter A, Sabbagh M, Zhong K. Alzheimer's disease drug development pipeline. Alzheimers & Dementia (NY). 2019;**5**: 272-293

[13] Weinreb O, Amit T, Bar-Am O, Youdim MBH. Ladostigil: A novel multimodal neuroprotective drug with cholinesterase and brain-selective monoamine oxidase inhibitory activities for Alzheimer's disease treatment. Current Drug Targets. 2012;**13**(4):483-494

[14] Weinstock M, Bejar C, Wang RH, Poltyrev T, Gross A, Finberg JP, et al. TV3326, a novel neuroprotective drug with cholinesterase and monoamine oxidase inhibitory activities for the treatment of Alzheimer's disease. Journal of Neural Transmission. Supplementum. 2000;**60**:157-169

[15] Korábečný J, Nepovimová E, Cikánková T, Špilovská K, Vašková L, Mezeiová E, et al. Newly developed drugs for Alzheimer's disease in relation to energy metabolism, cholinergic and monoaminergic neurotransmission. Neuroscience. 2018;**370**:191-206

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[17] Zemek F, Drtinova L, Nepovimova E, Sepsova V, Korabecny J, Klimes J, et al. Outcomes of Alzheimer's disease therapy with acetylcholinesterase inhibitors and memantine. Expert Opinion on Drug Safety. 2014;**13**(6): 759-774

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[21] Weinstock M, Gorodetsky E, Poltyrev T, Gross A, Sagi Y, Youdim M. A novel cholinesterase and brainselective monoamine oxidase inhibitor for the treatment of dementia comorbid with depression and Parkinson's disease. Progress in Neuro-Psychopharmacology & Biological Psychiatry. 2003;**27**(4):555-561

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**85**

Section 3

Polyglutamine Pathology,

Huntington's Disease and

Stem Cell Approach in

Therapy

### Section 3
