New Small Molecule Alleviates Alzheimer’s in Mouse Model

Scientists have developed a custom-made molecule that targets a post-translationally modified kinase linked to Alzheimer’s, improving symptoms in a murine model of the disease [1].

A novel approach to neutralizing proteins

MAPK is a family of kinases involved in numerous cellular processes. One member of this family, p38 MAPK, is known to be activated by pro-inflammatory cytokines and environmental stresses. Its activated form, phosphorylated p38 MAPK (p-p38 MAPK) is upregulated in various pathological conditions, including neurodegeneration [2]. Scientists suspect that p-p38 MAPK plays an important role in the pathogenesis of Alzheimer’s disease [3] and have been after it for quite some time.

However, since phosphorylation is a posttranslational modification, blocking transcription or translation of p38 MAPK would not be an ideal solution. One of the very few effective ways to neutralize post-translationally modified proteins is a novel technique called targeted protein degradation (TPD).

TPD selectively eliminates disease-causing proteins by delivering them to the cell’s natural protein degradation machinery [4]. TPD involves the use of small molecules that bind to specific disease-causing proteins and bring them close to a ubiquitin ligase, which then tags the protein with ubiquitin, marking it for destruction by the cell’s proteasome.

This approach is superior to traditional small molecule inhibitors, which neutralize proteins by binding to them but do not eliminate them from the cell. TPD can degrade proteins that are impervious to traditional approaches and thus lead to better target inhibition.

Custom-designed TPD drug

In this new paper, the researchers describe creating the novel TPD molecule PRZ-18002. When tested on two types of human cell lines, PRZ-18002 proved to be highly selective. It effectively decreased p-p38 MAPK levels but did not significantly affect the levels of inactive p38 MAPK, other MAPKs, or other kinases with analogous structures.

The researchers then applied PRZ-18002 to multiple types of murine brain cells: microglia, astrocytes, neuroblasts, and hippocampal neurons. In all cases, the drug caused a significant reduction in p-p38 MAPK levels, but not in the inactive form. The treatment also led to marked downregulation of the pro-inflammatory cytokines IL-6, IL-1β, IL-12, and TNF-α, which are all thought to be mediated by p-p38 MAPK.

Less Aβ and tau, better cognition

For their in vivo experiments, the researchers used 5xFAD mice, a popular murine model of Alzheimer’s disease. TPD drugs such as PRZ-18002 are generally too large to pass the blood-brain barrier, but recent research suggests that intranasal delivery, especially in a specific position, can help [5]. The researchers used a chair-like mechanism to put anesthetized mice in the required position, which enabled successful intranasal delivery.

Monthlong treatment with PRZ-18002 reduced the level of p-p38 MAPK in the cortex and hippocampus and significantly improved the mice’s water maze performance, indicating better memory and cognition. PRZ-18002 also effectively decreased the levels of amyloid-beta (Aβ) in the cortex and hippocampus along with the deposition of Aβ plaques. Several markers of neuroinflammation were decreased as well.

Along with amyloid-beta, hyperphosporylated tau protein is considered one of the hallmarks of Alzheimer’s disease. PRZ-18002 treatment significantly decreased accumulation of several versions of mutated tau, both in vitro and in vivo. The treated mice spent more time in the lit part of the light-dark box, indicating an increased propensity for exploration, which the researchers interpreted as a sign of better cognition.

Targeted protein degradation (TPD) provides unique advantages over gene knockdown in that it can induce selective degradation of disease-associated proteins attributed to pathological mutations or aberrant post-translational modifications (PTMs). Herein, we report a protein degrader, PRZ-18002, that selectively binds to an active form of p38 MAPK. PRZ-18002 induces degradation of phosphorylated p38 MAPK (p-p38) and a phosphomimetic mutant of p38 MAPK in a proteasome-dependent manner. Given that the activation of p38 MAPK plays pivotal roles in the pathophysiology of Alzheimer’s disease (AD), selective degradation of p-p38 may provide an attractive therapeutic option for the treatment of AD. In the 5xFAD transgenic mice model of AD, intranasal treatment of PRZ-18002 reduces p-p38 levels and alleviates microglia activation and amyloid beta (Aβ) deposition, leading to subsequent improvement of spatial learning and memory.

Conclusion

Alzheimer’s research needs new approaches. This paper describes a promising molecule built using a technique that can be expanded to numerous other proteins with post-translational modifications. The researchers were also able to deliver the rather large molecule intranasally across the blood-brain barrier, alleviating symptoms of Alzheimer’s. It should be noted, however, that murine models of Alzheimer’s are not completely adequate.

Literature

[2] McLaughlin, B., Pal, S., Tran, M. P., Parsons, A. A., Barone, F. C., Erhardt, J. A., & Aizenman, E. (2001). p38 activation is required upstream of potassium current enhancement and caspase cleavage in thiol oxidant-induced neuronal apoptosis. Journal of Neuroscience, 21(10), 3303-3311.

[3] Gee, M. S., Son, S. H., Jeon, S. H., Do, J., Kim, N., Ju, Y. J., … & Lee, J. K. (2020). A selective p38α/β MAPK inhibitor alleviates neuropathology and cognitive impairment, and modulates microglia function in 5XFAD mouse. Alzheimer’s Research & Therapy, 12, 1-18.

[4] Schapira, M., Calabrese, M. F., Bullock, A. N., & Crews, C. M. (2019). Targeted protein degradation: expanding the toolbox. Nature reviews Drug discovery, 18(12), 949-963.

[5] Merkus, P., Ebbens, F. A., Muller, B., & Fokkens, W. J. (2006). Influence of anatomy and head position on intranasal drug deposition. European Archives of Oto-Rhino-Laryngology and Head & Neck, 263, 827-832.