Novel Ubiquitin Specific Protease-13 Inhibitors Alleviate Neurodegenerative Pathology

Ubiquitin Specific Protease-13 (USP13) promotes protein de-ubiquitination and is poorly understood in neurodegeneration. USP13 is upregulated in Alzheimer’s disease (AD) and Parkinson’s disease (PD), and USP13 knockdown via shRNA reduces neurotoxic proteins and increases proteasome activity in models of neurodegeneration. We synthesized novel analogues of spautin-1 which is a non-specific USP13 inhibitor but unable to penetrate the brain. Our synthesized small molecule compounds are able to enter the brain, more potently inhibit USP13, and significantly reduce alpha-synuclein levels in vivo and in vitro. USP13 inhibition in transgenic mutant alpha-synuclein (A53T) mice increased the ubiquitination of alpha-synuclein and reduced its protein levels. The data suggest that novel USP13 inhibitors improve neurodegenerative pathology via antagonism of de-ubiquitination, thus alleviating neurotoxic protein burden in neurodegenerative diseases.

Regulatory Role of Ubiquitin Specific Protease-13 (USP13) in Misfolded Protein Clearance in Neurodegenerative Diseases

Ubiquitin Specific Protease (USP)-13 is a de-ubiquitinase member of the cysteine-dependent protease superfamily that cleaves ubiquitin off protein substrates to reverse ubiquitin-mediated protein degradation. Several findings implicate USPs in neurodegeneration. Ubiquitin targets proteins to major degradation pathways, including the proteasome and the lysosome. In melanoma cells, USP13 regulates the degradation of several proteins primarily via ubiquitination and de-ubiquitination. However, the significance of USP13 in regulating protein clearance in neurodegeneration is largely unknown. This mini-review summarizes the most recent evidence pertaining to the role of USP13 in protein clearance via autophagy and the proteasome in neurodegenerative diseases.

Multikinase Abl/DDR/Src Inhibition Produces Optimal Effects for Tyrosine Kinase Inhibition in Neurodegeneration

Background and objectives

Inhibition of Abelson (Abl) tyrosine kinase as a therapeutic target has been gaining attention in neurodegeneration. Post-mortem Alzheimer’s and Parkinson’s disease brains show that the levels of several other tyrosine kinases, including Discoidin Domain Receptors (DDR1/2) are elevated. Knockdown of these tyrosine kinases with shRNA reduces neurotoxic proteins, including alpha-synuclein, beta-amyloid and tau.

Methods

Direct profiling of the pharmacokinetics of multi-kinase inhibitors Nilotinib, Bosutinib, Bafetinib, Radotinib and LCB-03-0110 shows differential levels of brain penetration but the ability of these agents to reduce toxic proteins is independent of brain concentration and selectivity to Abl.

Results

Our results indicate that the effective dose of Nilotinib has the lowest plasma:brain ratio (1%) followed by Bosutinib and Radotinib (5%), Bafetinib (12%) and LCB-03-0110 (12%). However, similar doses of multi-kinase Abl/DDR inhibitor Nilotinib, DDR/Src inhibitor LCB-03-0110 and Abl/Src inhibitor Bosutinib were much more effective than the more selective Abl inhibitors Radotinib and Bafetinib. Taken together, these data suggest that a multi-kinase target that includes Abl and other tyrosine kinases (DDRs, and Src) may offer more advantages alleviating neurodegenerative pathologies than the absolute CNS drug concentration and selectivity to Abl.

Conclusion

DDRs and Src are other potential co-targets with Abl in neurodegeneration.

Electronic supplementary material

The online version of this article (10.1007/s40268-019-0266-z) contains supplementary material, which is available to authorized users.

Pharmacokinetics and pharmacodynamics of a single dose Nilotinib in individuals with Parkinson's disease

Nilotinib is a broad-based tyrosine kinase inhibitor with the highest affinity to inhibit Abelson (c-Abl) and discoidin domain receptors (DDR1/2). Preclinical evidence indicates that Nilotinib reduces the level of brain alpha-synuclein and attenuates inflammation in models of Parkinson's disease (PD). We previously showed that Nilotinib penetrates the blood-brain barrier (BBB) and potentially improves clinical outcomes in individuals with PD and dementia with Lewy bodies (DLB). We performed a physiologically based population pharmacokinetic/pharmacodynamic (popPK/PD) study to determine the effects of Nilotinib in a cohort of 75 PD participants. Participants were randomized (1:1:1:1:1) into five groups (n = 15) and received open-label random single dose (RSD) 150:200:300:400 mg Nilotinib vs placebo. Plasma and cerebrospinal fluid (CSF) were collected at 1, 2, 3, and 4 hours after Nilotinib administration. The results show that Nilotinib enters the brain in a dose-independent manner and 200 mg Nilotinib increases the level of 3,4-Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), suggesting alteration to dopamine metabolism. Nilotinib significantly reduces plasma total alpha-synuclein and appears to reduce CSF oligomeric: total alpha-synuclein ratio. Furthermore, Nilotinib significantly increases the CSF level of triggering receptors on myeloid cells (TREM)-2, suggesting an anti-inflammatory effect. Taken together, 200 mg Nilotinib appears to be an optimal single dose that concurrently reduces inflammation and engages surrogate disease biomarkers, including dopamine metabolism and alpha-synuclein.

Post-translational modifications of Parkinson's disease-related proteins: Phosphorylation, SUMOylation and Ubiquitination

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons in the nigrostriatal pathway. The etiology of PD remains unclear and most cases are sporadic, however genetic mutations in more than 20 proteins have been shown to cause inherited forms of PD. Many of these proteins are linked to mitochondrial function, defects in which are a central characteristic of PD. Post-translational modifications (PTMs) allow rapid and reversible control over protein function. Largely focussing on mitochondrial dysfunction in PD, here we review findings on the PTMs phosphorylation, SUMOylation and ubiquitination that have been shown to affect PD-related proteins.

Activating Autophagy as a Therapeutic Strategy for Parkinson's Disease

Parkinson's disease is a progressive neurodegenerative disease characterized by Lewy body pathology of which the primary constituent is aggregated misfolded alpha-synuclein protein. Currently, there are no clinical therapies for treatment of the underlying alpha-synuclein dysfunction and accumulation, and the standard of care for patients with Parkinson's disease focuses only on symptom management, creating an immense therapeutic gap that needs to be filled. Defects in autophagy have been strongly implicated in Parkinson's disease. Here, we review evidence from human, mouse, and cell culture studies to briefly explain these defects in autophagy in Parkinson's disease and the necessity for autophagy to be carefully and precisely tuned to maintain neuron survival. We summarize recent experimental agents for treating alpha-synuclein accumulation in α-synuclein Parkinson's disease and related synucleinopathies. Most of the efforts for developing experimental agents have focused on immunotherapeutic strategies, but we discuss why those efforts are misplaced. Finally, we emphasize why increasing autophagy flux for alpha-synuclein clearance is the most promising therapeutic strategy. Activating autophagy has been successful in preclinical models of Parkinson's disease and yields promising results in clinical trials.

Discoidin domain receptor inhibition reduces neuropathology and attenuates inflammation in neurodegeneration models

The role of cell surface tyrosine kinase collagen-activated receptors known as discoidin domain receptors (DDRs) is unknown in neurodegenerative diseases. We detect up-regulation in DDRs level in post-mortem Alzheimer and Parkinson brains. Lentiviral shRNA knockdown of DDR1 and DDR2 reduces the levels of α-synuclein, tau, and β-amyloid and prevents cell loss in vivo and in vitro. DDR1 and DDR2 knockdown alters brain immunity and significantly reduces the level of triggering receptor expressed on myeloid cells (TREM)-2 and microglia. These studies suggest that DDR1 and DDR2 inhibition is a potential target to clear neurotoxic proteins and reduce inflammation in neurodegeneration.

Mitochondria Initiate and Regulate Sarcopenia

We present the hypothesis that an accumulation of dysfunctional mitochondria initiates a signaling cascade leading to motor neuron and muscle fiber death and culminating in sarcopenia. Interactions between neural and muscle cells that contain dysfunctional mitochondria exacerbate sarcopenia. Preventing sarcopenia will require identifying mitochondrial sources of dysfunction that are reversible.