Ten years and counting: moving leucine-rich repeat kinase 2 inhibitors to the clinic

Abstract

The burden that Parkinson's disease (PD) exacts on the population continues to increase year after year. Though refinement of symptomatic treatments continues at a reasonable pace, no accepted therapies are available to slow or prevent disease progression. The leucine-rich repeat kinase 2 (LRRK2) gene was identified in PD genetic studies and offers new hope for novel therapeutic approaches. The evidence linking LRRK2 kinase activity to PD susceptibility is presented, as well as seminal discoveries relevant to the prosecution of LRRK2 kinase inhibition. Finally, suggestions are made for predictive preclinical modeling and successful first-in-human trials.

Keywords: PARK8; kinase inhibition; neurodegeneration; neuroprotection.

Figure 1

Timeline of key events for the development of LRRK2 therapies. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 2

Selected variants and features in LRRK2 useful for the development of LRRK2-targeting therapies. Arrows reflect approximate position relative to conserved LRRK2 domains. (A) Pathogenic variants, proven by familial segregation, that cause late-onset PD. (B) Variants >1% frequency that are protective or disease-associated, * are variants in Asian populations. R1398H may be the functional variant in a protective haplotype with N551K. (C) Sensitive and specific commercial monoclonal Abs that can detect human and rodent LRRK2. Positions of binding are shown. (D) LRRK2 autophosphorylation sites proven with phospho-specific Abs. (E) Phosphorylation sites on the LRRK2 protein that are not autophosphorylation sites and do not measure LRRK2 activity, but effectively track LRRK2 kinase inhibition, and binding to 14-3-3 proteins. (F) Epitope tags and fluorescent proteins that can be appended to the N- or C-terminus of LRRK2 that have been shown, in biochemical assays, to retain LRRK2 kinase and/or GTPase activity. FLAG (acidic) and bulky proteins such as eGFP have not been compatible with active LRRK2 when attached to the C-terminus. ^$eGFP, and many other fluorescent proteins, have been appended successfully to the N-terminus. Abbreviations for the LRRK2 protein domains include “LRRK2-repeats” that encode armadillo-like and ankryin-like repeats, “LRR” that is leucine-rich repeats, “ROC” that is ras-of-complex (i.e., GTPase), “COR” that is c-terminal of ras-of-complex, “kinase” that is the kinase domain, and “WD-40” that is WD-40-like repeats. eGFP, enhanced green fluorescent protein. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 3

Summary of a kinase-activation hypothesis for the mechanism of action of LRRK2 pathogenic mutations. GTP, guanosine triphosphate. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]