| dc.description.abstract |
The p38α mitogen-activated protein (MAP) Kinase signaling pathway is known to be
triggered by stress stimuli and to contribute to chronic inflammatory responses. A
number of recent studies have identified this signaling pathway as a central player in
different neurodegenerative diseases such as multiple sclerosis (MS) and Alzheimer
Disease (AD) and their principal animal models: experimental allergic encephalomyelitis
(EAE) and neuronal amyloidosis (APP/PS1 transgenic mice), respectively. This study set
out to investigate the effect of inhibiting p38α MAP Kinase on the induction and
development of EAE and amyloidosis and the potential of modulating this pathway as a
disease-modifying therapy in both MS and AD respectively.
Thirteen novel “Skepinone-based” p38α MAP Kinase inhibitors were characterized in vitro
and in vivo to select potent and metabolically stable Skepinone-based inhibitors of p38α
MAP Kinase with the ability to cross the blood-brain barrier (BBB). Out of the 13 inhibitor
compounds, 11 and 13 had the highest in vitro potency in human whole blood but differed
in central neuro system (CNS) partition (11 non-BBB-penetrant while 13 had a brain to
plasma ratio of ca. 0.3). Certainly, continuing with thus, 11 and 13 were used as in detailed
studies in EAE and Amyloidosis.
In earlier studies in CNS inflammation, there were indications that diet and diabetic status
played a role in the overall inflammatory stress in the brain and in the regulation of the
immune response in host mice. Given that these factors may play a role in human disease,
the models were conducted with modified diets to potentially reflect the clinical situation
for patients in developed countries.
The myelin oligodendrocyte peptide (MOG) EAE model in C57B6J mice was first optimized
by taking into account effects of diet and antigen preparation. The goal was to reduce
variation in incidence while maintaining severity at a moderate level (High Incidence, Low
Variation Moderate Score: HILVMS). Briefly, the results suggest that allowing mice to
mature for 4 weeks or more on a low fiber diet leads to a more uniform EAE response.
Similarly, sonication of Complete Freund´s Adjuvant/Myelin oligodendrocyte peptide
(CFA/MOG) emulsion made the response more uniform.
Compounds 11 and 13, previously characterized in vitro and in vivo in Chapter 1, were
evaluated in the optimized EAE model. Given that previous generations of p38 inhibitors
were reported to exert untoward effects on the liver, detailed analysis of liver effects
were included in the assessment of the model. Compound 11, which had high levels in
liver and spleen but not in the CNS, increased the survival of the EAE CFA/MOG induced
animals while decreasing the severity of the signs of EAE. At a dose of 12 µmol/kg/day
p.o., compound 11 could be considered moderately anti-inflammatory but highly
protective of both liver morphology and of myelin levels in the brain.
Given its apparent protective effects in the acute inflammatory CNS model EAE, the next
question was “would this compound also have a protective effect in a chronic
degenerative model driven by amyloidosis, in which inflammation plays a significant
role?”.
Compounds 11 (peripherally active) and 13 (BBB-penetrant) were applied p.o. in two
different amyloidosis studies (long and short-term). Behavioral tests and histological
findings showed pronounced treatment effects in both, long and short-term treatment
studies. Both candidates improved cognitive and affective parameters in the long-term
study: memory, activity and anxiety were maintained at WT levels in age-matched mice.
Further histological analysis in brain showed that both compounds mediated the removal
of Amyloid aggregates both over 10.5 months treatment (long-term study) or 2 weeks
(short term study).
The short-term study was based on published data for VX 745 which depleted amyloid in
a Tg2576 amyloid mouse model over 3 weeks of treatment. In the APP/PS1 model, VX
745 at 10 mg/kg p.o. was inactive over a 2-week application period and indeed was
associated with a moderate increase in amyloid. It is not clear whether this difference is
due to differences in the model, or to matters of dose. VX 745, despite promising data in
animal models, failed in phase II clinical trials. The absence of activity in the APP/PS1
model is, at least, consistent with the clinical data.
In summary, these data suggest that the highly selective p38α MAP Kinase inhibitors were
active in a range of systems from cellular to in vivo neurodegenerative settings. The
effects in the animal models suggest that the substances are potentially useful as
treatments for both, MS and AD. |
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