Alzheimer’s disease and neuroinflammation: will new drugs in clinical trials pave the way to a multi-target therapy?

Despite extensive research, no disease-modifying therapeutic option, able to prevent, cure or halt the progression of Alzheimer’s disease [AD], is currently available. AD, a devastating neurodegenerative pathology leading to dementia and death, is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of neurofibrillary tangles (NFTs) consisting of altered hyperphosphorylated tau protein. Both have been widely studied and pharmacologically targeted for many years, without significant therapeutic results. In 2022, positive data on two monoclonal antibodies targeting Aβ, donanemab and lecanemab, followed by the 2023 FDA accelerated approval of lecanemab and the publication of the final results of the phase III Clarity AD study, have strengthened the hypothesis of a causal role of Aβ in the pathogenesis of AD. However, the magnitude of the clinical effect elicited by the two drugs is limited, suggesting that additional pathological mechanisms may contribute to the disease. Cumulative studies have shown inflammation as one of the main contributors to the pathogenesis of AD, leading to the recognition of a specific role of neuroinflammation synergic with the Aβ and NFTs cascades. The present review provides an overview of the investigational drugs targeting neuroinflammation that are currently in clinical trials. Moreover, their mechanisms of action, their positioning in the pathological cascade of events that occur in the brain throughout AD disease and their potential benefit/limitation in the therapeutic strategy in AD are discussed and highlighted as well. In addition, the latest patent requests for inflammation-targeting therapeutics to be developed in AD will also be discussed.

Single dose, Randomized, Sequential Assignment doseescalation study to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of TB006 in Healthy Subjects.

Agents inhibiting the action or the production of pro-inflammatory cytokines or eicosanoids (N = 6)
Active Substance (Category)  Recently, icariside II was also shown to rescue impaired Icariside II represents a promising candidate drug for targeting inflammation in AD, given the evidence of a direct effect on glial cells and thanks to the potential cognitive benefits linked to its PDE5 inhibitor activity. A drawback to the potential use of icariside II as a therapeutic agent is its low oral bioavailability due to its poor aqueous solubility (Hou et al., 2016), which urges for the development of an improved formulation. Furthermore, given the broad biological actions resulting from PDE5 inhibition, potential side effects must be carefully taken into account. .

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Artemisin B appears promising as a modulating agent able to interfere with chronicization of inflammation, the most distinctive feature in AD progression, acting on multiple targets at once. However, the safety profile of this class of drugs may be an issue, particularly with long-term use needed for AD therapy. Artemisinin drugs are currently approved only for the acute treatment of malaria. Adverse events observed in this indication include very frequent gastrointestinal side effects, headache and dizziness, but also less frequent palpitation, QT prolongation, haemoglobinuria and acute renal failure. In vivo, DL0410-3 is said to display low toxicity and good BBB-permeability; additional data reported a reduction of IL-1 and IL-6 and an improvement in cognitive functions when administered to AD animal models (Liu et al., 2018b).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Notably, a previously developed compound (DL0410) with a similar mechanism of action as a dual AchE/BchE inhibitor, has also been shown to exert neuroprotective and antiinflammatory activity in AD models (Lian et al., 2017;Zhang et al., 2021c).
Based on its recognized benefits, genistein has attracted attention for the development of a number of derivatives with improved pharmacokinetics and target selectivity, along with potentiated protective features, including DL0410-3 (Fang et al., 2014). Preliminary data suggest that DL0410-3 combines an antiinflammatory action with the beneficial effects on cholinergic transmission typical of cholinesterase inhibitors, with good inhibition of both AchE and BuChE, setting the ground for future developments of the molecule in AD therapy. The compounds were also able to contrast the A-induced activation of SAPK/JNK and pERK pathways in neuronal cells (Telerman et al, 2017).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
The data of the two compounds effects as anti-inflammatory agents in AD are encouraging but still preliminary. More research needs to be done to better dissect the mechanisms of action, the cellular targets involved and the in vivo effects, in order to depict a clearer picture of their true potential. Telmisartan is an antihypertensive drug that belongs to the class of angiotensin type 1 receptor (AT1R) antagonists. As other drugs in this class, telmisartan is a candidate for repositioning in the treatment of neurological conditions, due to its Telmisartan inhibited PPARγ-, NF-kB-and IL1β-mediated inflammation in vitro and in different in vivo models of neuropathologies, including AD (Garrido-Gil et al., 2012;Pang et al., 2012;Xu et al., 2015;Torika et al., 2016;Wang et al., 2020b).
In agreement with telmisartan's This patent includes an association of the two compounds into a new drug, also including a new method for its synthesis. The butylphthalidetelmisartan heterocomplex was designed on the principle of prodrug combination, using the ring-opening derivative of butylphthalide, i.e. potassium 2-(1-hydroxypentyl)- 3-N-Butylphthalide (NBP), initially isolated from the seeds of celery (Apium graveolens Linn.), is a drug used in the management of stroke, with established neuroprotective effects. NBP was shown to be protective in a number of in vivo models of neurodegeneration (Abdoulaye and Guo, 2016). In stroke models, NBP promoted a better post-stroke outcome in vivo, with a multitargeted action on several mechanisms, from oxidative stress to mitochondrial dysfunction to apoptosis and inflammation (Liu et al, 2021;Liu et al., 2022b;Zhang et al., 2023).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
postulated beneficial role, cortical AT1Rs were shown to be increased in brain areas with ongoing inflammation in AD models (Torika et al., 2016). Efficacy of intranasal administration of the drug in the long term was analysed in 5XFAD mice, where improvements in brain pathology, glial reactivity and cognitive abilities were confirmed (Torika et al., 2017).
NBP was shown to inhibit key inflammatory pathways, such as benzoate (PHPB). The preparation was shown to possess an improved water-solubility and a doubled oral bioavailability compared to NBP. The repurposing of the two drugs with improved qualities and combinatorial effects directed at key players in inflammation, appears as a valuable approach to pursue. Dapansutrile is an orally active βsulfonyl nitrile molecule, previously shown to selectively inhibit the activation of the NLRP3 inflammasome, thereby reducing downstream release of the inflammatory mediators IL-1β and IL-18. Its safety has been assessed in healthy humans (Marchetti et al., 2018a). The efficacy of The oral administration of depansutrile to transgenic AD mice for 3 months reduced plaque pathology, preserved synaptic plasticity, reduced microglial reactivity and rescued the animals from cognitive impairment, compared to WT mice. In addition, plasma metabolic markers of AD were normalized The evidence on the safety of depansutrile, together with its ability to selectively block one of the main inflammatory pathways especially relevant in glial cells' activation, are in support of its therapeutic potential. Validation from other laboratories will be required to further strengthen the current evidence. This patent includes three hematopoietic serine proteases found in the azurophilic granules of neutrophils: i) cationic antimicrobial protein of 37 kDa (CAP37), ii) cathepsin G (CG), and iii) neutrophil elastase (NE).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
(Peptide < 40 amino acids) In addition to their degrading action inside phagolysosomes, these proteases are released during neutrophil activation and contribute to the regulation of inflammatory and immune responses (Korkmaz et al., 2010).
All three peptides have been shown to exert anti-inflammatory activity in AD by targeting two key players of neuroinflammation, i.e. Aβ and the receptor for advanced glycation end-products (RAGE) (Stock et al, 2018). RAGE expression is up-regulated in the brain of patients with AD, where it mediates the toxic effects of Aβ through a direct interaction with the peptide. In microglial cells, RAGE mediates proinflammatory activation by interaction different ligands (Yan et al., 2009). Finally, at the BBB, RAGE mediates the influx of circulating Aβ into the brain, and may contribute to endothelial damage (Wan et al., 2014). Upon Despite the evidence on their beneficial effect against Aβ-triggered inflammation, the peptides have also been implicated in a detrimental role in AD, in connection with their function as mediators of neutrophil activation and would even be responsible for BBB damage and ensuing inflammation (Stock et al, 2018). In agreement, CAP37 has been shown to be upregulated in the brain of AD patients and to recruit and activate microglial cells to release pro-inflammatory mediators (Pereira et al., 1996;Pereira et al., 2003). This critical issue has been reviewed and discussed in a very recent publication (Aries and Hensley-McBain, 2023).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Data from preclinical AD models Comments/Perspectives binding to Aβ, CAP37, CG and NE can operate its cleavage at different sites and with different catalytic activities, resulting in reduced accumulation and fibrillation (Kasus-Jacobi et al., 2021). Furthermore, the peptides can disrupt the Aβ-RAGE interaction both inhibiting downstream inflammatory signalling and preventing Aβ entrance in the brain parenchyma.
In conclusion, the peptide therapeutics presented in this patent are interesting for they combine an anti-amyloid and an antiinflammatory strategy. This approach is in line with the therapeutical attempts in AD research. The patent describes different administration routes, including intranasal delivery, and suggest the possibility to use appropriate nanocarriers, although no data on the concentration reached in the brain are available. However, central distribution of these peptides could in part mimic the effects of peripheral immune cells infiltration through a BBB, an occurrence that is typical of chronic neuroinflammatory conditions and whose ultimate outcome is still under debate. This surely represents an important issue that will need to be taken into account in future developments.

Combination of acyclovir and dexamethasone
Acyclovir is a guanosine analogue approved in the clinics as an antiviral for the treatment of infections caused by the herpes simplex virus (HSV) (Taylor and Gerriets, 2022). Its potential benefit in AD lays its foundations on the evidence of a link between infections and the risk for AD development. In fact, pathogens can promote the seeding of Aβ by prompting its aggregation to form a barrier around them (Soscia et al., 2010;Piekut et al., 2022). An in The association of acyclovir and DXMT was investigated on the bases of a potential synergy of anti-amyloidogenic effects by acyclovir and anti-inflammatory effects by DMTX. Results showed significantly increased neuroprotective effect of the combination of drugs, compared to single use, against cognitive impairment in mice subjected to intraventricular injection of Aβ oligomers, and 13 days of treatment. The combination This patent describes an association of acyclovir and dexamethasone and includes successful preclinical data on its effectiveness against cognitive deficits in transgenic AD models.
Evidence of neuroprotection by GC against dementia appears scarce in the literature (Nerius et al., 2020). Interestingly, it has been recently proposed that the stress-related risk for neurodegeneration is influenced by genetic factors, and that interindividual differences could impact The acyclovir can directly inhibit the activities of indoleamine 2,3dioxygenase 1 (IDO-1) and tryptophan 2,3-dioxygenase 2 (TDO-2); these two key enzymes are responsible for tryptophan metabolism to prevent quinolinic acid-induced neurotoxicity.

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Dexamethasone (DXMT) is a synthetic glucocorticoid (GC) approved for the treatment of pathologies with allergic, inflammatory or autoimmune components (Johnson et al., 2022). While the anti-inflammatory action of GC would be expected to prove protective against dementia, several in vitro and in vivo studies have correlated increased levels of GC, such as in chronic stress, to an increased risk of dementia (Green et al., 2006;Vyas et al., 2016;Bisht et al., 2018;Sharma and Singh, 2020;Canet et al., 2022).
Increased levels of cortisol have been found in AD patients (Ouanes and Popp, 2019;Zheng et al., decreased Aβ oligomer-induced microglial and astrocyte activation, pro-inflammatory cytokines upregulation, post synaptic density-95 (PSD95) protein reduction, phospho-Tau expression and spatial cognitive impairment. Notably, DXMT was also shown to contrast mice weight loss that resulted as a side effect of acyclovir treatment (Hui et al., 2020).
the sensitivity to GC stress response and trigger microglia to become proinflammatory (Milligan Armstrong et al., 2021).
The successful results obtained in this preliminary study need to be considered with great caution, in view of the still open debate regarding the true role of GC exposure in AD onset/progression.

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Data from preclinical AD models Comments/Perspectives 2020b). Targeting of glucocorticoid receptors with selective modulators reduced Aβ levels and rescued the cognitive deficits in transgenic AD mice exposed to early life stress (Lesuis et al., 2018), and chronic exposure to DMTX, to simulate stress responses in AD animal models, negatively affected Aβ and tau pathology, leading to memory deficits (Joshi et al., 2012;Canet et al., 2018). According to the patent, J37941 was shown to be BBB permeable, and it displayed relatively low toxicity in vivo. Furthermore, J37941-induced cognitive improvement has been reported in a mouse model of dementia caused by scopolamine (Wang et al., 2017b).

Agents targeting key enzymes/receptors involved in potentially detrimental biochemical pathways when deregulated (N=4)
The mechanism of action of this drug is not innovative, but its dual action on both esterases and the improved pharmacokinetics might make it a candidate worth further investigation. The α7 acetylcholine nicotine receptor (A7R) is widely expressed in neuronal, glial and endothelial cells, where its activation has been shown to regulate both physiological and pathological processes, likely depending on the cell type and microenvironmental context (extensively reviewed in Xu et al., 2021b).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Aβ(1-42) has been shown to bind to neuronal A7R with high affinity. The resulting complex is internalized by the cell, with the involvement of p38 signalling (Ma et al., 2018), and can ultimately lead to synaptic impairment and cell death, accounting for selective Aβvulnerability of A7R-expressing cholinergic neurons in AD brains (Wang et al., 2000;Nagele et al., 2002;Farhat and Ahmed, 2017;Ma et al., 2018). At the surface of endothelial cells, the A7R-Aβ complex has been proposed to disrupt BBB integrity and to contribute to abnormal circulating Aβ entry in the brain (Liu et al., 2017). The targeting of the alpha 7 nicotinic acetylcholine receptor has been described to reduce amyloid accumulation in Alzheimer's disease pyramidal neurons by D'Andrea and Nagele (D'Andrea and Nagele, 2006).
Varenicicline, an A7R agonist used for smoke cessation, has The patent holder's primary target is reported to be the prevention of A7R-Aβ complex-mediated BBB disruption by administration of A7R binding agents. Treatment is proposed to prevent the excessive accumulation of bloodstream-derived Aβ in the CNS and the detrimental consequences on neuronal cells. The specific A7R binding agents can be either novel or re-purposed, and include agonists, antagonists, inhibitors and allosteric modulators and are meant as an adjunctive therapy together with other therapeutical approaches, with a selection of the potential target population by analysis of appropriate biomarkers, especially those indicative of a BBB impairment (D'Andrea, 2021).

Mechanism of Action (Neuroinflammation)/grounds for activity in neuroinflammation
Data from preclinical AD models Comments/Perspectives recently entered a phase II crossover study in Korea, but results showed no improvement in cognitive and behavioural outcomes in the analysed population (Kim et al., 2014). Selective studies on the exact mechanism of action and targeted pathways of the patented furanone derivatives in AD are not currently available.

Compounds still in need of clarification (N=1)
This patent includes a number of furanone derivatives, developed as claimed anti-inflammatory protective agents, and potentially useful for the treatment of neurodegenerative disorders, including Alzheimer's disease, stroke, cerebral ischemia, and other oxidative stress−related conditions (Wang et al., 2004). The lack of available information from pre-clinical studies prevents at present any evaluation.