Radiolabeled Aminopyrazoles as Novel Isoform Selective Probes for pJNK3 Quantification

Abstract

The c-Jun N-terminal kinase 3 (JNK3) is a stress-activated kinase primarily expressed in the brain and implicated as an early mediator of neuronal apoptosis. We sought to develop a PET tracer to visualize pathological JNK3 activation. Because regional JNK3 activation precedes apoptosis, such an imaging agent might enable the detection of “at risk” brain regions prior to neuronal death. We prepared a set of 19F-containing compounds on the basis of the reported aminopyrazoles. The candidate, F3, was tritiated and used in autoradiography experiments to demonstrate regional and temporal changes in JNK3 activation in a mouse model of Parkinson’s disease. A significant increase in pJNK3 B max versus control animals in multiple brain regions was observed at 8 months, including the ventral midbrain. Pathological activation of JNK3 in these regions preceded statistically significant neuron loss. Analyses of brain concentrations of [18F]-F3 in naïve rats following intravenous injection revealed a small but detectable signal over the background, but was likely not sufficient to support PET imaging.

Physiological JNK3 Concentrations Are Higher in Motor-related and Disease-implicated Brain Regions of C57BL6/J Mice

“…As mentioned, earlier Jnk3 -/- mice exhibit some behavioral deficits in the elevated plus maze and potentially in the Morris water maze compared to wild-type mice, and these tests require processes affiliated with the cortical and hippocampal regions suggesting that JNK3 activities may be crucial to basal neurological function [46]. Our current study finds that pJNK3 levels are elevated in the hippocampus and cortex of healthy male and female mice (Figure 7) indicating that there is basal JNK3 activities are contributing to neurophysiology in these regions, which is consistent with recent pJNK3 radioligand labeling studies [49]. The higher levels of JNK3 activity in the hippocampal region could also represent a “double-edged sword” to explain why these regions are vulnerable to neuron loss in AD and other neurodegenerative disorders, as elevated and sustained levels of pJNK3 have been implicated in these conditions.…”

“…Alternatively, the diminished presence of JNK3 in the striatum (Figure 1, Figure 4, and Table 2), a site of Parkinson’s disease pathology (the loss of dopaminergic terminals [59]), is interesting given not only the involvement of JNK3 in synapse dysfunction and dendritic pruning [15, 60], but also many data indicating that JNK3-selective inhibitors protect in part against the loss of striatal dopamine in preclinical models [11, 26, 49, 61]. The lower levels of JNK3 in the striatum may speak to a reduced capacity for neuritogenesis.…”

“…In the hippocampus, high JNK3 expression was reported predominantly within neuron-like cell bodies in CA1, CA3, the subiculum, and the dentate gyrus, while moderate staining was observed in the habenula [48]. Most recently, radiolabeled-aminopyrazoles were developed as isoform-selective probes for activated JNK3 (pJNK3), which were tested for selectivity in a Parkinson’s disease mouse model (Mutator/Park2 -/- mice) [49]. These probes found more pJNK3 in the hippocampus and the cortex of the C57BL6/J mice with other regions exhibiting relatively low levels.…”

Discovery of Novel Indazole Chemotypes as Isoform-Selective JNK3 Inhibitors for the Treatment of Parkinson’s Disease

“…Recently, Brian et al discovered a 19 F-containing probe F3, which could selectively target JNK3. F3 determined a significant pJNK3 increase in the ventral midbrain region of the PD progressive genetic model . Encouraged by early evidence that JNK3 has brain-specific expression, inhibition or knockout of JNK3 has been validated to improve neurodegeneration in PD models.…”

“…F3 determined a significant pJNK3 increase in the ventral midbrain region of the PD progressive genetic model. 17 Encouraged by early evidence that JNK3 has brain-specific expression, inhibition or knockout of JNK3 has been validated to improve neurodegeneration in PD models. Therefore, JNK3 was well recognized as a promising therapeutic target of PD.…”