The main symptoms of Parkinson’s disease are tremor, rigidity and involuntary movement, caused by loss of dopaminergic neurons in the brain. Leucine-rich repeat protein kinase-2 (LRRK2) is mutated in a significant number of Parkinson’s disease cases, both familial and sporadic late-onset. A common mutation in which a glycine residue in the active site is altered to serine enhances catalytic activity of the kinase, suggesting that LRRK2 inhibitors might be useful for the treatment of Parkinson’s disease, although it is not entirely clear why enhanced LRRK2 activity causes loss of dopamine-producing neurons. Scientists led by a team at the Johns Hopkins University School of Medicine have now shown that inhibitors of the G2019S variant of LRRK2 can protect the nerve cells of mice genetically modified to produce the mutated kinase. Three weeks twice daily injections of GW5074 provided almost complete protection against loss of dopaminergic neurons compared with placebo treatment.
Although GW5074 is not an especially potent inhibitor of wild type or G2019S LRRK2 (IC50 0.2µM – 1.0µM depending on substrate) and is not selective (IC50 vs cRaf ca 10nM), the study, which is published in Nature Medicine, provides encouragement that a more potent and selective inhibitor could lead to a new disease-modifying treatment for Parkinson’s disease. The John Hopkins team are collaborating with researchers at Southern Methodist University to design more selective inhibitors and many other groups in both industry and academia are engaged in the search for potent and selective LRRK2 inhibitors.