Content uploaded by Delphine Charvin
Author content
All content in this area was uploaded by Delphine Charvin on Jun 03, 2020
Content may be subject to copyright.
RESEARCH ARTICLE
An mGlu4-Positive Allosteric Modulator Alleviates Parkinsonism in
Primates
Delphine Charvin, PhD ,
1
*Therese Di Paolo, PhD,
2
Erwan Bezard, PhD,
3
Laurent Gregoire,
2
Akihiro Takano, PhD,
4
Guillaume Duvey, PhD,
1
Elsa Pioli, PhD,
3
Christer Halldin, PhD,
4
Rossella Medori, MD, PhD
1
and François Conquet, PhD
1
1
Prexton Therapeutics SA, 1228 Plan-les-Ouates, Geneva, Switzerland
2
Neuroscience Research Unit CHU de Québec, CHUL Pavillon and Faculty of Pharmacy, Laval University, Quebec City, Quebec, Canada
3
Motac Neuroscience Ltd, Manchester, United Kingdom
4
Karolinska Institutet, Centre for Psychiatry Research, Department of Clinical Neuroscience, Stockholm, Sweden
ABSTRACT: Background: Levodopa remains the
gold-standard treatment for PD. However, it becomes
less effective as the disease progresses and produces
debilitating side effects, such as motor fluctuations and
L-dopa-induced dyskinesia. Modulation of metabotropic
glutamate receptor 4 represents a promising antiparkin-
sonian approach in combination with L-dopa, but it has
not been demonstrated in primates.
Objective: We studied whether a novel positive allosteric mod-
ulator of the metabotropic glutamate receptor 4, PXT002331
(foliglurax), could reduce parkinsonism in primate models.
Methods: We assessed the therapeutic potential of
PXT002331 in three models of MPTP-induced parkinson-
ism in macaques. These models represent three different
stages of disease evolution: early stage and advanced
stage with and without L-dopa-induced dyskinesia.
Results: As an adjunct to L-dopa, PXT002331 induced a
robust and dose-dependent reversal of parkinsonian
motor symptoms in macaques, including bradykinesia,
tremor, posture, and mobility. Moreover, PXT002331
strongly decreased dyskinesia severity, thus having thera-
peutic efficacy on both parkinsonian motor impairment
and L-dopa-induced dyskinesia. PXT002331 brain pene-
tration was also assessed using PET imaging in
macaques, and pharmacodynamic analyses support tar-
get engagement in the therapeutic effects of PXT002331.
Conclusions: This work provides a demonstration that a
positive allosteric modulator of metabotropic glutamate
receptor 4 can alleviate the motor symptoms of PD and
the motor complications induced by L-dopa in primates.
PXT002331 is the first compound of its class to enter
phase IIa clinical trials. © 2018 International Parkinson
and Movement Disorder Society
Key Words: mGlu4; foliglurax; Parkinson’s disease;
levodopa-induced dyskinesia; MPTP
Dopamine replacement therapy, notably using the
dopamine precursor L-3,4-dihydroxyphenylalanine
(levodopa), is the gold-standard treatment for the
symptomatic management of Parkinson’s disease (PD).
1
However, as the disease progresses, patient quality of
life (QoL) is plagued by emergence of debilitating side
effects of L-dopa,
2,3
such as motor fluctuations
4
and
dyskinesia.
5–7
Physicians have little in the armamentar-
ium to counter these side effects, and so there is an
unmet need to discover novel therapies that target the
management of these motor complications in PD
patients.
The successful alleviation of PD motor symptoms by
DBS of the STN has demonstrated that PD symptoms
can be managed with nondopaminergic therapies acting
outside the striatum, provided that it dampens the patho-
logical activity of the cortico-basal ganglia-thalamo-
cortical loop that is dysfunctional in PD. Therefore, act-
ing at key relays that will normalize the pathological
activity of the basal ganglia motor circuit, be it at
---------------------------------------------------------
*Correspondence to: Dr. Delphine Charvin, Prexton Therapeutics,
14 Chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland;
E-mail: Delphine.Charvin@prextontherapeutics.com
Funding agencies: This study was funded by Prexton Therapeutics.
Part of this work was supported by a grant from the Michael J. Fox
Foundation for Parkinson’s Research (grant ID-9243).
Relevant conflicts of interest/financial disclosures: D.C., G.D.,
R.M., and F.C. are employees of Prexton Therapeutics.
Full financial disclosures and author roles may be found in the
online version of this article.
Received: 7 December 2017; Revised: 23 March 2018; Accepted: 19
April 2018
Published online 14 September 2018 in Wiley Online Library
(wileyonlinelibrary.com). DOI: 10.1002/mds.27462
Movement Disorders, Vol. 33, No. 10, 2018 1619
corticostriatal, striatopallidal, and/or subthalamopallidal
synapses, represents a tantalizing approach. In that
respect, metabotropic glutamate receptor 4 (mGlu4) has
received much interest as a therapeutic target for a L-
dopa-sparing strategy in PD,
8–10
given that it is presynap-
tically expressed in these key relays.
8,11–13
At the striato-
pallidal and subthalamopallidal synapses, mGlu4
activation reduces gamma-aminobutyric acid (GABA)
and glutamate release in both pallidal segments and is
predicted to restrain the overall activity of the overactive
indirect pathway in PD.
14–17
At the corticostriatal synap-
ses, mGlu4 decreases excitatory transmission from the
cortex.
15,18,19
The strong rationale for using mGlu4 as a
therapeutic target in PD is further supported by preclini-
cal evidence that shows that positive allosteric modula-
tors (PAM) of mGlu4 reduce motor disability in rodent
models of PD.
16,20–26
Successful transition to clinical tri-
als in PD requires a safe, brain-penetrant, target-specific
drug with proven therapeutic efficacy in the MPTP-
lesioned macaque model.
27–42
In this study, we evaluated the brain penetrance and
clinically-relevant effects of PXT002331 (INN:
foliglurax) on parkinsonian motor impairment and on
L-dopa-induced dyskinesia in MPTP-macaque models.
The results were used to guide the design of the phase
II clinical trial.
Materials and Methods
The general workflow of experiments and the different
pharmacological treatment regimens are shown in
Figure S1. Three different nonhuman primate models
were used: chronic low dose (CLD) MPTP macaques,
advanced MPTP macaques receiving suboptimal doses of
L-dopa, and advanced MPTP-macaques developing L-
dopa-induced dyskinesia (LID). In each model, all animals
were treated sequentially with vehicle and PXT002331.
All animals were outbred cynomolgus monkeys (Macaca
fascicularis), non-naïve to pharmacological treatments
(i.e., all of them have been included in other previous
studies testing different pharmacological treatments, and
a drug washout of several months was given before start-
ing the present studies). All experiments were blinded.
Animals’spontaneous behavior was video recorded in
their observation cages after treatment administration.
Parkinsonian and dyskinesia scores were measured by
analysis of video recordings by a trained experimenter
blinded to the study treatment. Typically, one individual
randomized the videos, and another would analyze them.
Spontaneous locomotor activity of each animal was also
automatically recorded using computer-based human-
independent devices. To improve statistical power, experi-
ments were performed according to a within-subject
design. Pharmacokinetics (PK) experiments were also
done in cynomolgus monkeys as part of this study.
We also used PET to observe and analyze the target
receptor occupancy (mGlu4) correlated with the anti-
parkinsonian effects of PXT002331.
43
Macaque Model of Early-Stage Parkinsonism
Macaques received chronic low doses of MPTP injec-
tions (dose range: 0.05-0.25 mg/kg; intravenously) two
to three times per week for up to 15 months for induc-
tion of stable cognitive and motor deficits. Initial MPTP
injections for each animal continued until a consistent
15% reduction in baseline cognitive task performances
was observed, as assessed by the variable delay
response (VDR) and continuous performance test
tasks.
44
Such tests assess attentional/spatial short-term
memory components and sustained visual attention,
respectively.
45
Motor deficits exhibited in CLD
macaques are generally observed as mild to moderate
in severity, which was defined as a score >2 and <8 on
the Benazzouz parkinsonian disability scale.
46
This
scale rates seven parkinsonian motor symptoms:
tremor, bradykinesia, changes in posture, vocalization,
freezing, rigidity, and frequency of arm movements.
Minimum and maximum scores are 0 and 25, respec-
tively. A score between 2 and 8 means that parkinso-
nian motor deficits are present, but they do not prevent
animals to feed themselves and are alleviated by L-dopa.
Spontaneous locomotor activity of each animal was
automatically recorded by infrared sensors connected
to computer-based devices (Excalibur; The University
of Manchester, Manchester, UK). A quantitative assess-
ment of the amount of movement of the animal was
obtained every 5 minutes for the duration of the
experiment.
Macaque Models of Advanced-Stage
Parkinsonism
Macaques were rendered parkinsonian by continuous
infusion of MPTP using subcutaneous osmotic mini-
pumps (Alzet; 0.5 mg/24 hours) for around 6 months
until they developed a stable parkinsonian syndrome
(assessed by motor behavior,
36
including posture,
mobility, speed of movements, tremors, and climbing).
Then, they were treated daily with L-dopa for around
1 month or until dyskinesia stabilized as previously
described.
47
Motor deficits exhibited in these macaques
model an advanced stage of motor impairment in PD,
which was defined as a score >5 (maximum being 10)
on the Laval monkey PD Rating Scale (mPDRS).
36
In
this scale, a global score of 5 usually indicates slow
movements, and the maximal score of 10 characterizes
a monkey with total absence of movement. Scores
between 5 and 10 reflect intensity of parkinsonian
motor impairment (flexed posture, reduced mobility,
slowness of movements, presence of tremors, reduced
climbing, reduced grooming, reduced socializing
1620 Movement Disorders, Vol. 33, No. 10, 2018
CHARVIN ET AL
behavior, and reduced voicing). Dyskinesias were
scored with the Laval monkey Dyskinesia Rating Scale
(mDysRS).
36
In this assessment, a score of 0 to 3 is
given for each segment of the body (right and left upper
and lower extremities, neck, trunk, and face), meaning
absence (0), occasional (1), intermittent (2), or continu-
ous (3) presence of dyskinesia in a 15-minute period.
The total “dyskinesia score,”between 0 and 21, thus
reflects the intensity and duration of dyskinesia. Spon-
taneous locomotor activity was quantified using the
Viewpoint electronic monitoring system (VigiePrimates;
Viewpoint, Lyon, France).
In this model, optimal L-dopa was defined as the dose
that produced maximal reversal of PD motor symptoms
(highest decrease of parkinsonian score for the longest
duration, as assessed with the Laval mPDRS scale) and
induced dyskinesia. Suboptimal L-dopa was defined as
a dose that elicited a clear and reproducible antiparkin-
sonian response (same amplitude of decrease of PD
score, but shorter duration of effect when compared to
optimal L-dopa), without inducing dyskinesia.
Statistical Analyses
All analyses were performed using Graphpad Prism
(version 7.0). Parkinsonian and dyskinesia scores were
analyzed using a non-parametric one-way repeated
measure analysis of variance (ANOVA) (Friedman’s
test) followed by Dunn’s multiple comparison. Time
courses and locomotor activity were analyzed using a
one-way repeated measures ANOVA followed by Dun-
nett’s multiple comparison. Statistical significance was
assigned when P<0.05.
Detailed methods are described in the Supporting
Information.
Results
The mGlu4 PAM, PXT002331, Is Brain
Penetrant in Macaques
Previous studies have shown that PXT002331 effec-
tively enters the brain following oral administration.
26
This was confirmed in several animal species, including
mice, rats, and dogs, which showed that the brain (ng/g)/
plasma (ng/mL) ratio for PXT002331 ranged from 4 to
14 depending on the dose and species. This suggested
that oral administration provides direct targeting of
mGlu4 to brain parenchyma. In macaques, PXT002331
concentrations showed a dose-dependent increase in
plasma exposure after oral administration, with a rapid
absorption and median T
max
ranging between 1 and
1.5 hours (Fig. 1A; Table S1). Following twice-daily oral
dosing (BID), steady-state plasma concentrations were
reached by day 4 (2 and 25 mg/kg; Fig. 1A), and plasma
exposure, as assessed by PXT002331 mean C
max
and
AUC
0-12h
values, was dose proportional from 2 to
25 mg/kg on dosing day 8 (Table S1).
In macaques, PET imaging was performed using [
11
C]-
PXT012253, a radioligand that binds to the same allo-
steric site of mGlu4 as PXT002331.
43
Competition studies
revealed that binding of the radioactive tracer was reduced
in the presence of PXT002331 in brain areas where
mGlu4expressionhasbeendescribed(caudate,putamen,
cortex, thalamus, and globus pallidus)
11,12,48,49
(Fig. 1B),
thus confirming that peripherally administered
PXT002331 was able to gain access to the brain of pri-
mates. In vivo binding of [
11
C]-PXT012253 was blocked
by pretreatment with PXT002331 in a dose-dependent
and saturable manner (Fig. 1C).
Lack of Interaction Between PXT002331 and L-
Dopa Metabolism
Before assessing the potential of PXT002331 as an
adjunct therapy in macaque models, we ensured that its
administration did not interfere with L-dopa metabo-
lism. As previously reported, PXT002331 had no effect
on catechol O-methyltransferase (COMT), monoamine
oxidase (MAO)-A, or MAO-B activity in enzymatic
assays.
26
In human liver microsomes, it had no effect
on the metabolism of L-dopa, and L-dopa had no effect
on the metabolism of PXT002331 (Table S2), thus sug-
gesting that there is no interaction between
PXT002331 and L-dopa metabolism in animal models
or in PD patients.
As an Adjunct to L-Dopa, PXT002331 Restores
Motor Function in a Macaque Model of Early-
Stage Parkinsonism (CLD Macaques) Without
Inducing Dyskinesia or Cognitive Impairment
CLD macaques are characterized by reduced locomo-
tor activity, which is partially restored by L-dopa
(Fig. 2A,B). When added to an optimal dose of L-dopa,
a single oral dose of PXT002331 induced a dose-
dependent improvement in motor function of parkinso-
nian macaques, with an increase of the locomotor activ-
ity at the lowest dose tested (25 mg/kg), restoring the
levels of normal nonlesioned animals (Fig. 2A). There
was a loss of effect at higher doses (50-100 mg/kg;
Fig. 2A), which may result from an off-target mecha-
nism, although we have not identified it. PK/PD rela-
tionship showed that amplitude of the maximal effect
of L-dopa on locomotor activity was increased in the
presence of PXT002331 and maintained for 70 minutes
(Fig. 2B). When given alone, in the absence of L-dopa,
PXT002331 did not improve locomotor activity
(25 mg/kg of PXT002331: 458 ± 120 activity counts;
vehicle, 351 ± 107; L-dopa, 1,805 ± 398).
Neither PXT002331 alone nor the combination of
PXT002331 with L-dopa induced any dyskinesia
(Fig. 3B), thus demonstrating that the potentiation of
Movement Disorders, Vol. 33, No. 10, 2018 1621
PXT002331 IN PARKINSONIAN PRIMATE MODELS
FIG. 1. Plasma exposure and brain presence of PXT002331 in macaques. (A) PK of PXT002331 in plasma following oral administration in macaques
(Macaca fascicularis). PXT002331 (in water) was administered at dose levels of 2 and 25 mg/kg, as a single dose on days 1 and 8 and twice-daily on
days 2 through 7. The insert details the first 2 hours after administration of PXT002331 on day 1. Note that plasma levels of PXT002331 at 72 hours
(dosing day 4) are significantly different from baseline levels at time 0 (P= 0.0311 and 0.0135 for the 2- and 25-mg/kg doses, respectively). N = 4.
(B) [
11
C]-PXT012253 PET studies in vehicle- (baseline) or PXT002331 (6 mg/kg intravenously)-injected macaques. Representative results of 1 subject
treated with both molecules. Horizontal (left), sagittal (middle), and coronal (right panel) PET images and corresponding anatomical T1-weighed MRI
images. Note that the color scale on the left corresponds to the radioligand binding, but not to differently colored regions of interest. (C) Relationship
between [
11
C]-PXT012253 binding blockade (as a percentage of baseline) and intravenous dose of PXT002331. Points represent measured data (n = 1
per data point). The relationship between intravenous dose of PXT002331 and [
11
C]-PXT012253 binding blockade was estimated by a binding model
with the following equation: Occupancy (%) = OccuMax*iv dose/(iv dose + Kd), where Kd is the intravenous dose required to achieve 50% of the max-
imum occupancy, and OccuMax is the maximum occupancy. Estimated Kd was 1.14 mg/kg, and estimated OccuMax was 56%. R
2
= 0.99. VT is the
total distribution volume of the PET radiotracer.
1622 Movement Disorders, Vol. 33, No. 10, 2018
CHARVIN ET AL
L-dopa’s effects by PXT002331 was specific to normal
movements, and that not only the quantity, but also the
quality of movements was enhanced.
CLD macaques also present cognitive deficits reminis-
cent of early PD.
44,50
None of the treatments with
PXT002331, alone or in combination with L-dopa,
induced any worsening of animals’cognitive perfor-
mances, as assessed by the VDR computerized task
(Fig. 2C,D), by contrast with L-dopa, which is known
to induce deterioration in cognitive performance in this
model and in PD patients.
44
As an Adjunct to L-Dopa, PXT002331 Improves
Motor Function in a Macaque Model of
Advanced Parkinsonism
In the model of advanced parkinsonism, optimal
L-dopa was defined as the dose that produced maximal
reversal of motor impairment, characterized by the
highest amplitude and the longest duration of efficacy
(Fig. 3A). Suboptimal L-dopa was defined as a dose that
elicited a clear and reproducible antiparkinsonian
response, with the same maximal efficacy as optimal
FIG. 2. PXT002331 as an adjunct to L-dopa restores normal locomotor activity in the macaque model of early parkinsonism without inducing dyskinesia or
worsening cognitive performance. PXT002331 was administered orally in water in CLD macaques 120 minutes before L-dopa was administered orally at
T0. (A) Total locomotor activity values are shown over 4 hours. Data are expressed as mean of group (+SEM) and analyzed using one-way ANOVA
repeated measures followed by the Dunnett multiple comparison (statistical significance assigned when P< 0.05); ****P< 0.0001; *P< 0.05 versus vehi-
cle (Veh);
#
P< 0.05 versus L-dopa alone (L-Dopa). Dotted line represents locomotor activity of non-MPTP macaques. Note the complete restoration of
locomotor activity of CLD macaques in the presence of PXT002331 at 25 mg/kg combined with L-dopa. N = 6. (B) Time course of locomotor activity (Y-
axis on the left) in CLD macaques treated with either L-dopa alone (L-Dopa, gray curve) or with the addition of PXT002331 at 25 mg/kg to L-dopa (L-
Dopa + 25 mg/kg of PXT002331, blue curve). Each time point represents the mean (±SEM) counts for every 5 minutes over a 4-hour period. Orange curve
represents the highest dyskinesia score in the same animals treated with PXT002331 at 25 mg/kg on top of L-dopa (Y-axis on the right). These animals
never developed dyskinesia. Veh, vehicle (baseline); L-dopa (10-16 mg/kg); LMA, locomotor activity. N = 6. (C) Omissions and (D) correct responses in the
global VDR task following administration of PXT002331 alone or in combination with L-dopa (L-Dopa) among CLD macaques. Data are expressed as
means of group (bar) and individual performance (symbol; n = 4; 40 trials each) and analyzed using Friedman tests followed by the Dunnett multiple com-
parison tests versus Vehicle –Vehicle (statistical significance assigned when P< 0.05). The change in performance in the VDR task in presence of
PXT002331 when considered as a group is not statistically significant (P= 0.2250 for omissions; P= 0.6611 for correct responses). Note that in 1 of the
4 animals tested, PXT002331 (25 mg/kg) had a beneficial effect on its cognitive performance in the VDR task. This animal displayed almost 100% of omis-
sions after administration of an optimal dose of L-dopa (worse cognitive performance) (C). The animal’s omission rate decreased by half when PXT002331
was added to the optimal dose of L-dopa treatment (C) and its percentage of correct responses increased accordingly (D). L-dopa (%)/L-dopa dose
expressed as a percentage of optimal L-dopa dose (100%). N = 4.
Movement Disorders, Vol. 33, No. 10, 2018 1623
PXT002331 IN PARKINSONIAN PRIMATE MODELS
FIG. 3. PXT002331 extends duration of efficacy of a suboptimal dose of L-dopa in the macaque model of advanced parkinsonism without inducing dys-
kinesia. PXT002331 was administered orally in water in MPTP macaques 60 minutes before L-dopa administered subcutaneously at T0. Parkinsonian
and dyskinesia scores were rated with Laval mPDRS and mDysRS scales, respectively. (A) Time course of parkinsonian score in MPTP macaques trea-
ted with either a suboptimal (gray curve) or optimal (black curve) dose of L-dopa. Each time point represents the mean (±SEM) parkinsonian score for
every 15-minute observation period. Statistical analyses of the effects of the suboptimal L-dopa dose: two-way RM ANOVA followed by the Dunnett
multiple comparison (statistical significance assigned when P< 0.05). ****P< 0.0001; **P< 0.01 versus optimal L-dopa (optimal L-dopa). N = 7.
(B) Mean parkinsonian score (rated with the Laval mPDRS scale) in MPTP macaques treated with subchronic combined treatments with PXT002331
(BID for 8 days) and suboptimal dose of L-dopa (LD sub-opt) between 60 and 120 minutes after L-dopa administration. Each bar represents the mean
(+SEM) parkinsonian score. **P< 0.01; ***P< 0.001 versus vehicle (Veh);
#
P< 0.05 versus suboptimal L-dopa dose alone (nonparametric one-way
RM ANOVA, statistical significance assigned when P< 0.05). LD opt: optimal dose of L-dopa. N = 7. (C) Time course of parkinsonian score in MPTP
macaques treated with either a suboptimal dose of L-dopa alone (gray curve) or in addition to PXT002331 (BID for 8 days). Each time point represents
the mean (±SEM) parkinsonian score for every 15-minute observation period. L-dopa was administered subcutaneously at T0. N = 7. (D) Mean dyskine-
sia score (rated with the Laval mDysRS scale) in MPTP macaques treated with subchronic combined treatments with PXT002331 (BID for 8 days) and
suboptimal dose of L-dopa (LD sub-opt) for 120 minutes after L-dopa administration. Each bar represents the mean (+SEM) dyskinesia score. Nonpara-
metric one-way RM ANOVA: none of the conditions were significant (statistical significance assigned when P< 0.05). N = 7. (E) Mean parkinsonian
score of each individual MPTP macaque before and after addition of PXT002331 (optimal dose, either 2, 10, or 25 mg/kg, BID for 8 days). N = 7.
1624 Movement Disorders, Vol. 33, No. 10, 2018
L-dopa (i.e., decrease of average PD score from 8.6 at
baseline to 3.8), but a shorter duration. Suboptimal L-
dopa induced a significant improvement in the PD score
for 90 minutes (statistically different from vehicle), with
a maximal response maintained for 60 minutes (statisti-
cally not different from optimal L-dopa), whereas maxi-
mal response of optimal L-dopa was maintained for
120 minutes (Fig. 3A). As a consequence, suboptimal L-
dopa produced a threshold nonsignificant effect on the
mean PD score when measured in the 60- to
120-minute observation period following administra-
tion (Fig. 3B). Therefore, in this model, treatment
effects are measured on the parkinsonian score of the
animals during the 60- to 120-minute time window
(red box in Fig. 3A).
When administered alone, PXT002331 produced a dose-
and time-dependent improvement in parkinsonian disabil-
ity of MPTP macaques, but the efficacy was quite limited
in the absence of any dopaminergic stimulation (Fig. 4).
When administered as an adjunct to suboptimal
L-dopa, PXT002331 prolonged the antiparkinsonian
effect observed with L-dopa alone (Fig. 3C). It produced
asignificant antiparkinsonian effect of high amplitude,
which was maintained during the 60- to 120-minute
observation period and was comparable to the maximal
efficacy obtained with optimal L-dopa (Fig. 3B). Thus,
PXT002331 (2-10-25 mg/kg) was able to correct the re-
emergence of parkinsonian motor symptoms for 1 hour
(Fig. 3B). PXT002331 induced a dose-dependent
improvement in parkinsonian disability. There were
strong reductions in mean parkinsonian score for each
low dose of PXT002331 (2-25 mg/kg) and a progressive
loss of benefit at higher doses (50-100 mg/kg; Fig. 3B).
The combination of any dose of PXT002331 with L-
dopa never induced any dyskinesia (Fig. 3D). Conse-
quently, PXT002331 (2-10-25 mg/kg) extended good
ON-time, producing antiparkinsonian effects without
inducing dyskinesia (Fig. 3B, D). All the macaques in this
study showed an improvement of parkinsonian disability
when PXT002331 (between 2 and 25 mg/kg) was added
to L-dopa, despite their heterogeneity (i.e., with different
basal PD scores; Fig. 3E).
In summary, these results demonstrate that addition
of low doses of PXT002331 to a low suboptimal dose
of L-dopa enhanced and prolonged the antiparkinso-
nian effect of the treatment. Level of efficacy was of
high amplitude (comparable to optimal L-dopa) and
robust, all animals responding to the treatment.
PXT002331 Alleviates LID in a Macaque Model
of Late Parkinsonism
We used amantadine, an N-methyl-D-aspartate
(NMDA) glutamate receptor antagonist,
51,52
as a bench-
mark molecule for antidyskinetic activity.
53–55
Two doses
of amantadine (5-25 mg/kg) were tested acutely, based
on published results in macaques.
29,34,56–58
Amantadine
significantly reduced dyskinesia scores by approximately
25% at each of the tested doses (Fig. 5A; P= 0.0418
and 0.0078 when comparing mean dyskinesia scores
with amantadine 5 or 25 mg/kg to vehicle, respectively
[one-way repeated-measure {RM} analysis of variance
{ANOVA} followed by the Dunnett multiple comparison
test]). Amantadine also induced a dose-dependent
decrease of global locomotor activity compared to L-dopa
FIG. 4. In the absence of L-dopa, PXT002331 induces a modest antiparkinsonian effect in MPTP macaques with advanced parkinsonism. Parkinsonian
and dyskinesia scores were rated with the Laval mPDRS and mDysRS scales, respectively. (A) Time course of parkinsonian score in MPTP macaques
treated with acute stand-alone PXT002331 (oral doses of 2, 10, or 25 mg/kg). Each time point represents the mean (±SEM) PD score for every
15-minute observation period. PXT002331 was administered at T0. N = 7. (B) Mean parkinsonian score in MPTP macaques treated with acute stand-
alone PXT002331 (oral doses of 2, 10, 25, 50, or 100 mg/kg). Each bar represents the mean (+SEM) PD score for a 2-hour period following treatment
administration. Veh, vehicle; LD opt, optimal L-dopa dose. *P< 0.05; ***P< 0.001 versus vehicle (Veh; nonparametric one-way RM ANOVA, statistical
significance assigned when P< 0.05). N = 7.
Movement Disorders, Vol. 33, No. 10, 2018 1625
PXT002331 IN PARKINSONIAN PRIMATE MODELS
1626 Movement Disorders, Vol. 33, No. 10, 2018
CHARVIN ET AL
alone (Fig. 5B). However, the amantadine dose of
25 mg/kg was not well tolerated by animals, inducing a
significant decrease of global motor activity, feeding ces-
sation, and vomiting in the majority of the animals (table
S3). Hallucination-like behavior was also observed in
2 of the 6 animals receiving 25 mg/kg of amantadine
(Table S3). Based on these results, the 5-mg/kg dose was
selected as the tolerated and effective dose of amanta-
dine, which was in accord with previous reports
29
and is
equivalent to the therapeutic dose of 100 mg in humans.
When assessed in the same MPTP macaques,
PXT002331 (oral doses of 1, 2, 10, or 25 mg/kg, acute)
decreased dyskinesia (Fig. 5C). The dose of 0.1 mg/kg was
identified as a noneffective dose of PXT002331, and the
dose of 2 mg/kg induced a higher antidyskinetic effect
than the two doses of amantadine tested (Fig. 5A-C).
While providing antidyskinetic efficacy, PXT002331
maintained the antiparkinsonian maximum effect of opti-
mal L-dopa (Fig. 5D) and did not impair normal locomo-
tor activity of animals (Fig. 5B), thus suggesting that the
effects of PXT002331 are more specificthanthoseof
amantadine, decreasing only the dyskinetic, and not the
general motor activity of the primates. When administered
subchronically over 8 days, PXT002331 (2 mg/kg, twice-
daily) maintained its antidyskinetic efficacy while preserv-
ing maximal antiparkinsonian efficacy of L-dopa (Fig. 5E,
F). By contrast, amantadine (5 mg/kg once-daily) had a
tendency to worsen the parkinsonian score, probably due
to the decrease of global locomotor activity of animals
(Fig. 5F). Contrary to amantadine, PXT002331 did not
induce any adverse effects (Table S3).
The combination of amantadine and PXT002331 did
not add any benefit to antidyskinetic efficacy of
PXT002331 and produced the same worsening of the
parkinsonian score as amantadine alone (Fig. 5E, F).
PK/PD Analyses Support mGlu4 Target
Engagement in the Effects of PXT002331
Combining pharmacodynamics of PXT002331 and
PET imaging of macaque brains, we then confirmed the
in vivo target engagement of PXT002331 in producing
antiparkinsonian and antidyskinetic efficacy. When
PXT002331 plasma concentrations were correlated
with therapeutic efficacy, effective average plasma con-
centrations ranged between approximately 2 and
200 ng/mL (Fig. S3A). In PET measurements, there
were only four occupancy data points. Estimation of
Kd value would be more accurate with more occupancy
data points. However, our PET data set is sufficient to
show that concentrations of PXT002331 that resulted
in consistent antiparkinsonian and antidyskinetic effi-
cacy achieving lower than 50% brain mGlu4 receptor
occupancy (RO; Fig. S2B), indicating that relatively low
levels of occupancy are sufficient to achieve in vivo effi-
cacy. This RO/efficacy relationship correlates well with
a positive effect on the receptor, agonistic-like, or PAM
effect, as previously demonstrated and defined as
“spare receptor capacity.”
59,60
For comparison, typical
antagonists and negative allosteric modulators require
65% to 80% RO for therapeutic efficacy.
61–63
Discussion
We found that the novel mGlu4 PAM, PXT002331,
in combination with L-dopa, shows consistent efficacy
in improving motor function of gold-standard MPTP-
macaque models of parkinsonism. PXT002331 also
counteracts the motor complications induced by L-dopa
(i.e., dyskinesia). These benefits are achieved without
eliciting abnormal behaviors, psychiatric-like signs, or
cognitive impairment.
Overactive glutamate transmission within the basal
ganglia motor circuit has long been implicated in many
aspects of PD, including the cardinal motor symptoms,
loss of dopaminergic neurons, and LID.
3,27,64,65
There-
fore, blocking glutamate transmission may be a thera-
peutic lever to normalize pathological activity of key
relays in the circuit.
65–68
This blockade could be
obtained either by decreasing signaling downstream of
excessive glutamate through inhibition of postsynaptic
FIG. 5. PXT002331 decreases peak dyskinesia in the macaque model of LID while maintaining optimal antiparkinsonian efficacy. Amantadine and
PXT002331 were administered orally 60 and 30 minutes before L-dopa, respectively. L-dopa was administered subcutaneously at T0. Parkinsonian and dys-
kinesia scores were rated with the Laval mPDRS and mDysRS scales, respectively. (A) Time course of dyskinesia score in MPTP macaques treated either
with L-dopa alone (black curve) or in the presence of either amantadine at 5 mg/kg (gray curve with gray triangles), amantadine at 25 mg/kg (gray curve with
white diamonds), or PXT002331 at 2 mg/kg (blue curve). Each time point represents the mean (±SEM) dyskinesia score for every 15-minute observation
period. N = 6. (B) Mean locomotor activity values (+SEM) over 4 hours, analyzed using one-way RM ANOVA followed by the Dunnett multiple comparison
test (statistical significance assigned when P< 0.05); *P< 0.05; **P< 0.01 versu s L-dopa. Dotted line represents the mean locomotor activity of MPTP-
macaques treated with L-dopa alone. L-Dopa post: optimal L-dopa dose administered at the end of the treatment periods for comparison with the pretreat-
ment measures (L-Dopa). Note the dose-dependent decrease of locomotor activity of MPTP macaques in the presence of amantadine at 5 and 25 mg/kg
combined with L-dopa. N = 6. (C) Mean normalized antidyskinetic efficacy (+SEM) of PXT002331 in MPTP macaques, expressed as a percentage of reduc-
tion of the dyskinesia score when compared to L-dopa alone (L-Dopa). Dotted line represents mean normalized antidyskinetic efficacy of the tolerated dose
of amantadine (5 mg/kg). L-Dopa: optimal L-dopa dose alone (0% reduction of dyskinesia score). *P< 0.05; **P< 0.01 versus L-dopa, Friedman test fol-
lowed by the Dunnett test (per study part, statistical significance assigned when P< 0.05). N = 6. (D) Mean parkinsonian score (+SEM) in MPTP macaques
treated with a single oral dose of PXT002331 and an optimal dose of L-dopa, between 0 and 3 hours after L-dopa administration. *P< 0.05 versus L-dopa
(nonparametric one-way RM ANOVA, statistical significance assigned when P< 0.05). N = 6. (E) Median dyskinesia score (+SEM) at the 1-hour peak and
(F) mean parkinsonian score (+SEM) for a 3-hour observation period in MPTP macaques treated with subchronic treatments of either PXT002331 (2 mg/kg
twice-daily), amantadine (5 mg/kg daily), or a combination of PXT002331 (2 mg/kg twice-daily) with amantadine (5 mg/kg daily) for 8 days. Veh: score at
baseline, the day before start of each treatment (L-dopa alone). *P<0.05;**P< 0.01 versus baseline (each corresponding Veh). Two-way RM ANOVA fol-
lowed by the Dunnett test (statistical significance assigned when P< 0.05). N = 7.
Movement Disorders, Vol. 33, No. 10, 2018 1627
PXT002331 IN PARKINSONIAN PRIMATE MODELS
NMDA or mGlu5 or by decreasing glutamate release
itself through activation of presynaptic mGlu4 and
restoring physiological neurotransmitter synaptic levels.
mGlu4 PAMs have the potential to restrain the overac-
tive indirect pathway in PD by decreasing GABA and
glutamate release at the striato- and subthalamopallidal
synapses and decrease corticostriatal glutamate levels
that are in excess in LID.
69–75
Several compounds have
displayed consistent limited activity in rodent models
when given alone, but with the potential for L-dopa
sparing (i.e., ability to preserve maximal antiparkinso-
nian motor benefit with reduction of L-dopa dosage).
76
Despite the validity of these rodent models, considering
the compelling evidence that the function of mGlu
receptors can be context dependent,
19,25,77,78
evidence
of mGlu4 PAM effectiveness in heterogeneous outbred
primates (heterogeneity in genetic backgrounds, disease
stage and history, sexes, and L-dopa dosage), with clini-
cally relevant endpoints, has been eagerly awaited.
27,78
The results of our study provide characterization of an
mGlu4 PAM in primates and a demonstration of fur-
ther potential than L-dopa-sparing not only confirming,
but also extending the results reported in rats. Indeed,
we demonstrate that an mGlu4 PAM as an adjunct to
L-dopa in MPTP primates restores normal locomotor
activity at an early stage of parkinsonism, to extend the
efficacy of L-dopa at a more advanced stage, and
decrease peak dyskinesia in a model of established LID.
We also show that engagement of an mGlu4 PAM was
assessed by PET imaging.
PXT002331 may be the first therapeutic strategy that
could benefit PD patients at all stages of the disease by
addressing all motor symptoms and complications of
PD, including parkinsonian cardinal motor symptoms,
wearing-off, and LID. Indeed, so far, no treatment
option allows correct and long-term management of
motor complications, which strongly impair patient
QoL.
2,79
MAO-B inhibitors provide mild symptomatic
benefit as initial treatment of early disease, but do not
have any antidyskinetic activity.
80
Dopamine agonists
(ropinirole, pramipexole) provide moderate symptom-
atic benefit, but patients must be screened carefully for
adverse events.
81
Current anti-PD medications usually
provide good control of motor signs of PD for 4 to
6years.
1,79
However, after this time, disability often pro-
gresses, and many patients develop long-term motor
complications, including fluctuations and dyskinesia.
Thus, symptomatic therapy for late disease requires dif-
ferent strategies. LID is observed in more than 90% of
PD patients who have received L-dopa treatment for
10 years.
79
Despite decades of clinical research, treat-
ment of LID has remained a major challenge. Enthusi-
asm for prescribing dopamine agonists instead of L-dopa
to prevent development of dyskinesia has waned since it
became clear that they are associated with significant
impairment in patients QoL.
82
Hypothesizing that
minimization of pulsatile stimulation of dopamine recep-
tors would exert positive benefits, COMT inhibitors
were used to slow L-dopa metabolism. However, para-
doxically, the initial clinical trial described an increase
rather than a decrease in dyskinesia.
83
Thereafter, many
studies were launched to assess the effects of novel prep-
arations of L-dopa, but the new therapies are expensive
and may be associated with significant device-related
complications of these invasive methods.
7,84
Among the
available oral medications, amantadine is currently the
drug with the most potent antidyskinetic effect.
52–54
However, cardiovascular
85
and psychiatric adverse
effects like insomnia, confusion, and hallucinations often
limit its use.
86–90
This is of particular importance for PD
patients, who have an increased risk to develop psy-
chotic symptoms.
91
Extended-release amantadine has
been described as another therapeutic alternative to
reduce LID. However, the spectrum of adverse events
was similar to immediate-release forms of amanta-
dine
92,93
and may be attributed to direct inhibition of
NMDA receptors.
51,94
In our study, treatment with PXT002331 brought
more therapeutic benefitthanamantadineoracombina-
tion of amantadine and PXT002331. Indeed,
PXT0023331 had a higher antidyskinetic effect, a better
antiparkinsonian effect, and much improved tolerability
in parkinsonian macaques. The higher efficacy of
PXT002331 may be attributed to its presynaptic mode
of action, which may be a more effective strategy to
decrease glutamate transmission by normalizing gluta-
mate release, than antagonizing postsynaptic NMDA
receptors downstream of excessive glutamate levels at the
synapse. Better tolerability may be attributed to an
absence of a direct effect on NMDA receptors.
51,94
In the
three primate models, PXT002331 showed a very good
tolerability profile, avoiding the psychiatric side effects
observed with dopamine agonists and amantadine. Given
that an 8-day treatment might not be sufficient to assess
development of tolerance or long-term tolerability, it
would be interesting to test the effects of a longer treat-
ment duration in monkeys. The safety and tolerability of
this novel compound has also been demonstrated in a
phase I study (NCT02639221) in healthy volunteers dur-
ing 14 days of exposure.
Although we have evaluated the effects of PXT002331
in three different nonhuman primate models with the
most translational experimental conditions and evalua-
tion of target engagement, efficacy of an mGlu4 PAM
still has not been proven in patients. It will be key to
respond to questions that cannot be answered in animal
models, such as dosing, therapeutic window, and off-
target effects. Given the wide distribution of mGlu4 in
the brain and body, testing the first mGlu4-selective
ligand in humans may also teach us about the potential
mGlu4-mediated effects outside of the targeted brain
1628 Movement Disorders, Vol. 33, No. 10, 2018
CHARVIN ET AL
region. Finally, in this study, monkeys in the CLD group
were all males, whereas monkeys in the advanced PD
group were all females; thus, we could not do a direct
assessment of sex effect at each stage of the disease. This
may be interesting to assess in clinical trials.
Based on the preclinical profile, including this demon-
stration of efficacy in primate models and tolerability of
PXT002331 in phase I, this first-in-class drug is now
being assessed in PD patients in a phase II study
(NCT03162874).
Acknowledgment: We acknowledge financial support from the
Michael J. Fox Foundation for Parkinson’s Research (grant ID-9243). We
thank Hazel Clay and Sandra Robelet and the teams at Covance and
Cynbiose for the PK studies in macaques, and also Kerry Frost at Cypro-
tex for the in vitro metabolism study.
References
1. Olanow CW, Stern MB, Sethi K. The scientific and clinical basis
for the treatment of Parkinson disease. Neurology 2009;72-
(21 Suppl 4):S1-S136.
2. Hechtner MC, Vogt T, Zollner Y, et al. Quality of life in Parkin-
son’s disease patients with motor fluctuations and dyskinesias in
five European countries. Parkinsonism Relat Disord 2014;20:
969-974.
3. Bastide MF, Meissner WG, Picconi B, et al. Pathophysiology of
L-dopa-induced motor and non-motor complications in Parkinson’s
disease. Prog Neurobiol 2015;132:96-168.
4. Shoulson I, Glaubiger GA, Chase TN. On-off response. Clinical
and biochemical correlations during oral and intravenous levodopa
administration in parkinsonian patients. Neurology 1975;25:
1144-1148.
5. Olanow CW, Watts RL, Koller WC. An algorithm (decision tree)
for the management of Parkinson’s disease (2001): treatment guide-
lines. Neurology 2001;56(11 Suppl 5):S1-S88.
6. Prashanth LK, Fox S, Meissner WG. l-Dopa-induced
dyskinesia-clinical presentation, genetics, and treatment. Int Rev
Neurobiol 2011;98:31-54.
7. Rascol O, Perez-Lloret S, Ferreira JJ. New treatments for
levodopa-induced motor complications. Mov Disord 2015;30:
1451-1460.
8. Duty S. Therapeutic potential of targeting group III metabotropic
glutamate receptors in the treatment of Parkinson’s disease. Br J
Pharmacol 2010;161:271-287.
9. Doller D. Metabotropic glutamate receptors at thirty: new insights
from chemical tools enabling mechanistic understanding. Med
Chem Rev 2016;51:37-52.
10. Lindsley CW, Hopkins CR. Metabotropic glutamate receptor
4 (mGlu4)-positive allosteric modulators for the treatment of Par-
kinson’s disease: historical perspective and review of the patent lit-
erature. Expert Opin Ther Pat 2012;22:461-481.
11. Bradley SR, Standaert DG, Rhodes KJ, et al. Immunohistochemical
localization of subtype 4a metabotropic glutamate receptors in the
rat and mouse basal ganglia. J Comp Neurol 1999;407:33-46.
12. Iskhakova L, Smith Y. mGluR4-containing corticostriatal termi-
nals: synaptic interactions with direct and indirect pathway neu-
rons in mice. Brain Struct Funct 2016;221:4589-4599.
13. Bogenpohl J, Galvan A, Hu X, Wichmann T, Smith Y. Metabotro-
pic glutamate receptor 4 in the basal ganglia of parkinsonian mon-
keys: ultrastructural localization and electrophysiological effects of
activation in the striatopallidal complex. Neuropharmacology
2013;66:242-252.
14. Beurrier C, Lopez S, Revy D, et al. Electrophysiological and behav-
ioral evidence that modulation of metabotropic glutamate receptor
4 with a new agonist reverses experimental parkinsonism. FASEB J
2009;23:3619-3628.
15. Cuomo D, Martella G, Barabino E, et al. Metabotropic glutamate
receptor subtype 4 selectively modulates both glutamate and GABA
transmission in the striatum: implications for Parkinson’s disease
treatment. J Neurochem 2009;109:1096-1105.
16. Marino MJ, Williams DL, Jr., O’Brien JA, et al. Allosteric modula-
tion of group III metabotropic glutamate receptor 4: a potential
approach to Parkinson’s disease treatment. Proc Natl Acad Sci U S
A 2003;100:13668-13673.
17. Valenti O, Marino MJ, Conn PJ. Modulation of excitatory trans-
mission onto midbrain dopaminergic neurons of the rat by activa-
tion of group III metabotropic glutamate receptors. Ann N Y Acad
Sci 2003;1003:479-480.
18. Bennouar KE, Uberti MA, Melon C, et al. Synergy between
L-DOPA and a novel positive allosteric modulator of metabotropic
glutamate receptor 4: implications for Parkinson’s disease treat-
ment and dyskinesia. Neuropharmacology 2013;66:158-169.
19. Gubellini P, Melon C, Dale E, Doller D, Kerkerian-Le Goff L. Dis-
tinct effects of mGlu4 receptor positive allosteric modulators at
corticostriatal vs. striatopallidal synapses may differentially con-
tribute to their antiparkinsonian action. Neuropharmacology 2014;
85:166-177.
20. Battaglia G, Busceti CL, Molinaro G, et al. Pharmacological activation of
mGlu4 metabotropic glutamate receptors reduces nigrostriatal degenera-
tion in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.
JNeurosci 2006;26:7222-7229.
21. Broadstock M, Austin PJ, Betts MJ, Duty S. Antiparkinsonian
potential of targeting group III metabotropic glutamate receptor
subtypes in the rodent substantia nigra pars reticulata. Br J Phar-
macol 2012;165:1034-1045.
22. Jones CK, Bubser M, Thompson AD, et al. The metabotropic glu-
tamate receptor 4-positive allosteric modulator VU0364770 pro-
duces efficacy alone and in combination with L-DOPA or an
adenosine 2A antagonist in preclinical rodent models of Parkin-
son’s disease. J Pharmacol Exp Ther 2012;340:404-421.
23. Le Poul E, Bolea C, Girard F, et al. A potent and selective metabo-
tropic glutamate receptor 4 positive allosteric modulator improves
movement in rodent models of Parkinson’s disease. J Pharmacol
Exp Ther 2012;343:167-177.
24. Dube A, Chaudhary S, Mengawade T, Upasani CD. Therapeutic
potential of metabotropic glutamate receptor 4-positive allosteric
modulator TAS-4 in rodent models of movement disorders.
J Neurol Sci 2014 Jul 10. pii: S0022-510X(14)00452-3. doi:
10.1016/j.jns.2014.07.008. [Epub ahead of print]
25. Niswender CM, Jones CK, Lin X, et al. Development and antipar-
kinsonian activity of VU0418506, a selective positive allosteric
modulator of metabotropic glutamate receptor 4 homomers with-
out activity at mGlu2/4 heteromers. ACS Chem Neurosci 2016;7:
1201-1211.
26. Charvin D, Pomel V, Ortiz M, et al. Discovery, structure-activity
relationship and anti-parkinsonian effect of a potent and
brain-penetrant chemical series of positive allosteric modulators of
metabotropic glutamate receptor 4. J Med Chem 2017;60:
8515-8537.
27. Duty S. Targeting glutamate receptors to tackle the pathogenesis,
clinical symptoms and levodopa-induced dyskinesia associated with
Parkinson’s disease. CNS Drugs 2012;26:1017-1032.
28. Close SP, Elliott PJ, Hayes AG, Marriott AS. Effects of classical
and novel agents in a MPTP-induced reversible model of Parkin-
son’s disease. Psychopharmacology (Berl) 1990;102:295-300.
29. Gregoire L, Jourdain VA, Townsend M, Roach A, Di Paolo T. Safi-
namide reduces dyskinesias and prolongs L-DOPA antiparkinso-
nian effect in parkinsonian monkeys. Parkinsonism Relat Disord
2013;19:508-514.
30. Fox SH, Brotchie JM. The MPTP-lesioned non-human primate
models of Parkinson’s disease. Past, present, and future. Prog Brain
Res 2010;184:133-157.
31. Ko WK, Camus SM, Li Q, et al. An evaluation of istradefylline
treatment on Parkinsonian motor and cognitive deficits in
Movement Disorders, Vol. 33, No. 10, 2018 1629
PXT002331 IN PARKINSONIAN PRIMATE MODELS
1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated
macaque models. Neuropharmacology 2016;110(Pt A):48-58.
32. Berg D, Godau J, Trenkwalder C, et al. AFQ056 treatment of
levodopa-induced dyskinesias: results of 2 randomized controlled
trials. Mov Disord 2011;26:1243-1250.
33. Bezard E, Pioli EY, Li Q, et al. The mGluR5 negative allosteric
modulator dipraglurant reduces dyskinesia in the MPTP macaque
model. Mov Disord 2014;29:1074-1079.
34. Blanchet PJ, Konitsiotis S, Chase TN. Amantadine reduces
levodopa-induced dy skinesias in parkinsonian monkeys. Mov Dis-
ord 1998;13:798-802.
35. Duty S, Jenner P. Animal models of Parkinson’s disease: a source
of novel treatments and clues to the cause of the disease. Br J Phar-
macol 2011;164:1357-1391.
36. Morissette M, Di Paolo T. Non-human primate models of PD to
test novel therapies. J Neural Transm (Vienna) 2018;125:291-324.
37. Gregoire L, Morin N, Ouattara B, et al. The acute antiparkinso-
nian and antidyskinetic effect of AFQ056, a novel metabotropic
glutamate receptor type 5 antagonist, in L-Dopa-treated parkinso-
nian monkeys. Parkinsonism Relat Disord 2011;17:270-276.
38. Swanson CR, Joers V, Bondarenko V, et al. The PPAR-gamma
agonist pioglitazone modulates inflammation and induces neuro-
protection in parkinsonian monkeys. J Neuroinflammation 2011;
8:91.
39. Emborg ME, Moirano J, Raschke J, et al. Response of aged parkin-
sonian monkeys to in vivo gene transfer of GDNF. Neurobiol Dis
2009;36:303-311.
40. Jarraya B, Boulet S, Ralph GS, et al. Dopamine gene therapy for
Parkinson’s disease in a nonhuman primate without associated dys-
kinesia. Sci Transl Med 2009;1:2ra4.
41. Hodgson RA, Bedard PJ, Varty GB, et al. Preladenant, a selective
A(2A) receptor antagonist, is active in primate models of move-
ment disorders. Exp Neurol 2010;225:384-390.
42. Michel A, Nicolas JM, Rose S, et al. Antiparkinsonian effects of
the “Radiprodil and Tozadenant”combination in MPTP-treated
marmosets. PLoS One 2017;12:e0182887.
43. Takano A, Nag S, Jia Z, et al. Characterization of [11C]PXT012253
as a PET radioligand for mGlu4 allosteric modulators in nonhuman
primates. Mol Imaging Biol 2018. doi: 10.1007/s11307-018-1257-0.
44. Schneider JS, Pioli EY, Jianzhong Y, Li Q, Bezard E. Levodopa
improves motor deficits but can further disrupt cognition in a
macaque Parkinson model. Mov Disord 2013;28:663-667.
45. Schneider JS, Tinker JP, Van Velson M, Menzaghi F, Lloyd GK.
Nicotinic acetylcholine receptor agonist SIB-1508Y improves cog-
nitive functioning in chronic low-dose MPTP-treated monkeys.
J Pharmacol Exp Ther 1999;290:731-739.
46. Imbert C, Bezard E, Guitraud S, Boraud T, Gross CE. Comparison
of eight clinical rating scales used for the assessment of
MPTP-induced parkinsonism in the Macaque monkey. J Neurosci
Methods 2000;96:71-76.
47. Di Paolo T, Gregoire L, Feuerbach D, Elbast W, Weiss M,
Gomez-Mancilla B. AQW051, a novel and selective nicotinic ace-
tylcholine receptor alpha7 partial agonist, reduces l-Dopa-induced
dyskinesias and extends the duration of l-Dopa effects in parkinso-
nian monkeys. Parkinsonism Relat Disord 2014;20:1119-1123.
48. Makoff A, Lelchuk R, Oxer M, Harrington K, Emson P. Molecular
characterization and localization of human metabotropic glutamate
receptor type 4. Brain Res Mol Brain Res 1996;37:239-248.
49. Corti C, Aldegheri L, Somogyi P, Ferraguti F. Distribution and syn-
aptic localisation of the metabotropic glutamate receptor
4 (mGluR4) in the rodent CNS. Neuroscience 2002;110:403-420.
50. Porras G, Li Q, Bezard E. Modeling Parkinson’s disease in pri-
mates: the MPTP model. Cold Spring Harb Perspect Med 2012;2:
a009308.
51. Hesselink MB, De Boer AG, Breimer DD, Danysz W. Adaptations
of NMDA and dopamine D2, but not of muscarinic receptors fol-
lowing 14 days administration of uncompetitive NMDA receptor
antagonists. J Neural Transm (Vienna) 1999;106:409-421.
52. Blanpied TA, Clarke RJ, Johnson JW. Amantadine inhibits NMDA
receptors by accelerating channel closure during channel block.
J Neurosci 2005;25:3312-3322.
53. Vijayakumar D, Jankovic J. Drug-induced dyskinesia, part 1: treat-
ment of levodopa-induced dyskinesia. Drugs 2016;76:759-777.
54. Ory-Magne F, Corvol JC, Azulay JP, et al. Withdrawing amanta-
dine in dyskinetic patients with Parkinson disease: the AMAN-
DYSK trial. Neurology 2014;82:300-307.
55. Del Dotto P, Pavese N, Gambaccini G, et al. Intravenous amanta-
dine improves levadopa-induced dyskinesias: an acute double-blind
placebo-controlled study. Mov Disord 2001;16:515-520.
56. Hill MP, Ravenscroft P, Bezard E, et al. Levetiracetam potentiates
the antidyskinetic action of amantadine in the 1-methyl-4-phenyl-
1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate model of Par-
kinson’s disease. J Pharmacol Exp Ther 2004;310:386-394.
57. Bibbiani F, Oh JD, Kielaite A, Collins MA, Smith C, Chase TN.
Combined blockade of AMPA and NMDA glutamate receptors
reduces levodopa-induced motor complications in animal models
of PD. Exp Neurol 2005;196:422-429.
58. Aron Badin R, Spinnewyn B, Gaillard MC, et al. IRC-082451, a
novel multitargeting molecule, reduces L-DOPA-induced dyskine-
sias in MPTP Parkinsonian primates. PLoS One 2013;8:e52680.
59. Kenakin T. Pharmacology in Drug Discovery: Understanding Drug
Response. San Diego, CA: Academic; 2012.
60. Rook JM, Tantawy MN, Ansari MS, et al. Relationship between
in vivo receptor occupancy and efficacy of metabotropic glutamate
receptor subtype 5 allosteric modulators with different in vitro
binding profiles. Neuropsychopharmacology 2015;40:755-765.
61. Farde L, Nordstrom AL, Wiesel FA, Pauli S, Halldin C, Sedvall G.
Positron emission tomographic analysis of central D1 and D2
dopamine receptor occupancy in patients treated with classical neu-
roleptics and clozapine. Relation to extrapyramidal side effects.
Arch Gen Psychiatry 1992;49:538-544.
62. Yanai K, Tashiro M. The physiological and pathophysiological
roles of neuronal histamine: an insight from human positron emis-
sion tomography studies. Pharmacol Ther 2007;113:1-15.
63. Le S, Gruner JA, Mathiasen JR, Marino MJ, Schaffhauser H. Cor-
relation between ex vivo receptor occupancy and wake-promoting
activity of selective H3 receptor antagonists. J Pharmacol Exp Ther
2008;325:902-909.
64. Blandini F, Nappi G, Tassorelli C, Martignoni E. Functional
changes of the basal ganglia circuitry in Parkinson’s disease. Prog
Neurobiol 2000;62:63-88.
65. Mellone M, Gardoni F. Glutamatergic mechanisms in L-DOPA-
induced dyskinesia and therapeutic implications. J Neural Transm
(Vienna) 2018 Jan 31. doi: 10.1007/s00702-018-1846-8. [Epub
ahead of print]
66. Litim N, Morissette M, Di Paolo T. Metabotropic glutamate recep-
tors as therapeutic targets in Parkinson's disease: an update from the
last 5 years of research. Neuropharmacology 2017;115:166-179.
67. Picconi B, Calabresi P. Glutamate receptors and levodopa-induced
dyskinesia. In: Levodopa-Induced Dyskinesia in Parkinson’s Dis-
ease. London: Springer-Verlag London Ltd; 2014:229-243.
68. Amalric M. Targeting metabotropic glutamate receptors (mGluRs)
in Parkinson’s disease. Curr Opin Pharmacol 2015;20:29-34.
69. Blandini F, Armentero MT. New pharmacological avenues for the
treatment of L-DOPA-induced dyskinesias in Parkinson’s disease:
targeting glutamate and adenosine receptors. Expert Opin Investig
Drugs 2012;21:153-168.
70. Calabresi P, Di Filippo M, Ghiglieri V, Tambasco N, Picconi B.
Levodopa-induced dyskinesias in patients with Parkinson’s disease:
filling the bench-to-bedside gap. Lancet Neurol 2010;9:1106-1117.
71. Cenci MA, Lundblad M. Post-versus presynaptic plasticity in
L-DOPA-induced dyskinesia. J Neurochem 2006;99:381-392.
72. Garcia BG, Neely MD, Deutch AY. Cortical regulation of striatal
medium spiny neuron dendritic remodeling in parkinsonism: modu-
lation of glutamate release reverses dopamine depletion-induced
dendritic spine loss. Cereb Cortex 2010;20:2423-2432.
1630 Movement Disorders, Vol. 33, No. 10, 2018
CHARVIN ET AL
73. Iravani MM, McCreary AC, Jenner P. Striatal plasticity in Parkin-
son’s disease and L-dopa induced dyskinesia. Parkinsonism Relat
Disord 2012;18(Suppl 1):S123-S125.
74. Jenner P. Molecular mechanisms of L-DOPA-induced dyskinesia.
Nat Rev Neurosci 2008;9:665-677.
75. Sgambato-Faure V, Cenci MA. Glutamatergic mechanisms in the
dyskinesias induced by pharmacological dopamine replacement
and deep brain stimulation for the treatment of Parkinson’s disease.
Prog Neurobiol 2012;96:69-86.
76. Gubellini P, Iskhakova L, Smith Y, Amalric M. Metabotropic gluta-
mate receptors and parkinson’s disease: basic and preclinical neuro-
science. In: Ngomba RT, Di Giovanni G, Battaglia G, Nicoletti F,
eds. mGLU Receptors. Cham, Switzerland: Humana; 2017:33-57.
77. Niswender CM, Johnson KA, Miller NR, et al. Context-dependent
pharmacology exhibited by negative allosteric modulators of meta-
botropic glutamate receptor 7. Mol Pharmacol 2010;77:459-468.
78. Charvin D. mGlu4 allosteric modulation for treating Parkinson’s
disease. Neuropharmacology 2018;135:308-315.
79. Manson A, Stirpe P, Schrag A. Levodopa-induced-dyskinesias clini-
cal features, incidence, risk factors, management and impact on
quality of life. J Parkinsons Dis 2012;2:189-198.
80. Macleod AD, Counsell CE, Ives N, Stowe R. Monoamine oxidase
B inhibitors for early Parkinson’s disease. Cochrane Database Syst
Rev 2005;(3):CD004898.
81. Antonini A, Cilia R. Behavioural adverse effects of dopaminergic
treatments in Parkinson’s disease: incidence, neurobiological basis,
management and prevention. Drug Saf 2009;32:475-488.
82. PD Med Collaborative Group, Gray R, Ives N, et al. Long-term
effectiveness of dopamine agonists and monoamine oxidase B
inhibitors compared with levodopa as initial treatment for Parkin-
son’s disease (PD MED): a large, open-label, pragmatic randomised
trial. Lancet 2014;384:1196-1205.
83. Stocchi F, Rascol O, Kieburtz K, et al. Initiating levodopa/carbi-
dopa therapy with and without entacapone in early Parkinson dis-
ease: the STRIDE-PD study. Ann Neurol 2010;68:18-27.
84. Poewe W, Antonini A. Novel formulations and modes of delivery
of levodopa. Mov Disord 2015;30:114-120.
85. Vale JA, Maclean KS. Amantadine-induced heart-failure. Lancet
1977;1:548.
86. Snoey ER, Bessen HA. Acute psychosis after amantadine overdose.
Ann Emerg Med 1990;19:668-670.
87. Smith EJ. Amantadine-induced psychosis in a young healthy
patient. Am J Psychiatry 2008;165:1613.
88. Flaherty JA, Bellur SN. Mental side effects of amantadine therapy:
its spectrum and characteristics in a normal population. J Clin Psy-
chiatry 1981;42:344-345.
89. Xu WJ, Wei N, Xu Y, Hu SH. Does amantadine induce acute psy-
chosis? A case report and literature review. Neuropsychiatr Dis
Treat 2016;12:781-783.
90. Hayden FG, Gwaltney JM, Jr., Van de Castle RL, Adams KF,
Giordani B. Comparative toxicity of amantadine hydrochloride
and rimantadine hydrochloride in healthy adults. Antimicrob
Agents Chemother 1981;19:226-233.
91. Holroyd S, Currie L, Wooten GF. Prospective study of hallucina-
tions and delusions in Parkinson’s disease. J Neurol Neurosurg Psy-
chiatry 2001;70:734-738.
92. Pahwa R, Tanner CM, Hauser RA, et al. ADS-5102 (Amantadine)
Extended-Release Capsules for Levodopa-Induced Dyskinesia in
Parkinson Disease (EASE LID Study): a randomized clinical trial.
JAMA Neurol. 2017;74:941-949.
93. Pahwa R, Tanner CM, Hauser RA, et al. Amantadine extended
release for levodopa-induced dyskinesia in Parkinson’s disease
(EASED Study). Mov Disord 2015;30:788-795.
94. Krystal JH, Perry EB, Jr., Gueorguieva R, et al. Comparative and
interactive human psychopharmacologic effects of ketamine and
amphetamine: implications for glutamatergic and dopaminergic
model psychoses and cognitive function. Arch Gen Psychiatry
2005;62:985-994.
95. Schneider JS, Kovelowski CJ II. Chronic exposure to low doses of
MPTP. I. Cognitive deficits in motor asymptomatic monkeys. Brain
Res 1990;519:122-128.
96. Schneider JS, Tinker JP, Menzaghi F, Lloyd GK. The subtype-
selective nicotinic acetylcholine receptor agonist SIB-1553A
improves both attention and memory components of a spatial
working memory task in chronic low dose 1-methyl-4-phenyl-
1,2,3,6-tetrahydropyridine-treated monkeys. J Pharmacol Exp Ther
2003;306:401-406.
97. Fox SH, Johnston TH, Li Q, Brotchie J, Bezard E. A critique of
available scales and presentation of the Non-Human Primate Dys-
kinesia Rating Scale. Mov Disord 2012;27:1373-1378.
98. Shen W, Plotkin JL, Francardo V, et al. M4 muscarinic receptor
signaling ameliorates striatal plasticity deficits in models of
L-DOPA-induced dyskinesia. Neuron 2015;88:762-773.
99. Samadi P, Gregoire L, Rouillard C, Bedard PJ, Di Paolo T,
Levesque D. Docosahexaenoic acid reduces levodopa-induced dys-
kinesias in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine monkeys.
Ann Neurol 2006;59:282-288.
100. Bourque M, Gregoire L, Di Paolo T. The plasmalogen precursor
analog PPI-1011 reduces the development of L-DOPA-induced dys-
kinesias in de novo MPTP monkeys. Behav Brain Res 2018;337:
183-185.
101. Naritomi Y, Terashita S, Kimura S, Suzuki A, Kagayama A,
Sugiyama Y. Prediction of human hepatic clearance from in vivo
animal experiments and in vitro metabolic studies with liver micro-
somes from animals and humans. Drug Metab Dispos 2001;29:
1316-1324.
102. Obach RS. Prediction of human clearance of twenty-nine drugs
from hepatic microsomal intrinsic clearance data: an examination
of in vitro half-life approach and nonspecific binding to micro-
somes. Drug Metab Dispos 1999;27:1350-1359.
103. Obeso JA, Olanow CW, Nutt JG. Levodopa motor complica-
tions in Parkinson’s disease. Trends Neurosci 2000;23-
(10 Suppl):S2-7.
104. Morin N, Jourdain VA, Di Paolo T. Modeling dyskinesia in animal
models of Parkinson disease. Exp Neurol 2014;256:105-116.
Supporting Data
Additional Supporting Information may be found in
the online version of this article at the publisher’s
web-site.
Movement Disorders, Vol. 33, No. 10, 2018 1631
PXT002331 IN PARKINSONIAN PRIMATE MODELS
