JUPITER, Fla.—In their ongoing research on a classof enzymes called c-jun-N-terminal kinases (JNK, pronounced "junk"),researchers from the Florida campus of The Scripps Research Institute (TSRI)have found a compound that could counter Parkinson's disease by attacking JNKand another protein closely associated with the neurodegenerative disorder.
JNKs are members of the mitogen activated protein kinases (MAPKs), acting asprimary mediators of the stress response to regulate insulin signaling, cellfate, DNA repair and T cell differentiation. Differences in the timing andduration of JNK activation can determine whether cells proliferate or undergoprogrammed cell death, highlighting the critical importance of tight regulationof this pathway.
JNKs are members of the mitogen activated protein kinases (MAPKs), acting asprimary mediators of the stress response to regulate insulin signaling, cellfate, DNA repair and T cell differentiation. Differences in the timing andduration of JNK activation can determine whether cells proliferate or undergoprogrammed cell death, highlighting the critical importance of tight regulationof this pathway.
As reported in the Nov. 27, 2012 issue of DDNEWS Online, the laboratory of Dr.Philip LoGrasso, the TSRI's scientific director, has shown JNK to be prevalentin not just Parkinson's, but also Alzheimer's disease and amyotrophic lateralsclerosis (ALS). In our previous interview with LoGrasso, he discussed a studypublished Nov. 8 by the Cell Press journal Structurein which he and his colleagues described how the structure of JNK, when boundto three peptides from different protein families, play a critical role instress-induced apoptosis.
In their latest study, published recently onlineahead of print by the journal ACSChemical Biology, the TSRI team describes how a new dual inhibitor (labeledin the study as "compound 6") attacks JNK and another enzyme, the leucine-richrepeat kinase 2 (LRRK2), both of which are associated with Parkinson's.
Development of brain-penetrant, small-moleculeinhibitors for JNK and LRRK2 has been a major focus in the development ofpotential efficacious therapeutics for Parkinson's and other neurodegenerativediseases. TSRI and Elan, in particular, have successfully developed selective,brain-penetrant and orally bioavailable small-molecule JNK inhibitors that showgood efficacy for the treatment of Parkinson's animal models as well as inother neurodegeneration models. LRRK2 inhibitors have also been discovered inseveral labs, but selectivity, cell potency and brain-penetration capabilityfor these initial compounds still need improvement.
"In general, these two enzymes amplify the effect ofeach other," says LoGrasso. "What we were looking for is a high-affinity,high-selectivity treatment that is additive or synergistic in its effect—aone-two punch."
The TSRI team set out to discover unique JNKinhibitors from diversified scaffolds, with the goal of developing compoundscapable of inhibiting both JNK3 and LRRK2 simultaneously, with greater efficacythan compounds that inhibit only JNK or LRRK2 individually. Dual inhibitors canbe used as in-vitro or in-vivo probes to test the hypothesisthat dual inhibition of JNK and LRRK2 may be additive or synergistic in thetreatment of both familial and idiopathic Parkinson's. A dual inhibitor ispreferred over combined, individual JNK and LRRK2 inhibitors because iteliminates complications of drug-drug interactions and the need to optimizeindividual inhibitor doses for efficacy.
LoGrasso's strategy for identifying small-moleculekinase inhibitors that combine these advantages was to design bidentate-bindinginhibitors that can simultaneously bind to the kinase hinge and to a surfacepocket that was close to but outside of the hinge region and/or the ATP pocket.This surface pocket could be a substrate binding site or an allosteric bindingpocket.
Compound 6 was a potent JNK3 and modest LRRK2 dualinhibitor with an enzyme IC50 value of 12 nM and 99 nM, respectively. Compound6 also exhibited good cell potency, inhibited LRRK2's induced mitochondrialdysfunction in cells and was demonstrated to be reasonably selective against apanel of 116 kinases from representative kinase families.
According to LoGrasso and his colleagues, this bidentate-bindingdesign strategy could find wide applications in the development of highlyselective and potent kinase inhibitors as probe molecules, since surfacepockets close to the hinge area exist in almost all kinases.
"In addition, in the design of a bidentate kinaseinhibitor, there may be no need to use a strong hinge binder and/or astrong-binding fragment for the protein surface pockets. The synergy effectsresulting from the simultaneous binding to multiple pockets should produce astrong protein modulator composed of weaker–binding structural fragments,provided the fragments are covalently connected with an appropriate linkingmoiety," the researchers concluded.
More bidentate-binding kinase inhibitors and SARstudies are underway in LoGrasso's labs, and subsequent studies will bepublished, he says.
"Both enzymes be able to treat the disease in anadditive or synergistic matter," he says. "A LRRK2 inhibitor may be effective,JNK may be and together they throw the knockout blow. Now these compounds haveto be optimized for potency, broad selectivity, bioavailability and brainpenetration so they can be tested in animal models of the disease."
The study, "A Small-Molecule Bidentate-Binding DualInhibitor Probe of the LRRK2 and JNK Kinases," was funded in part by a grantfrom the U.S. National Institutes of Health.
