Development of Prodrugs for Treatment of Parkinson's Disease: New Inorganic Scaffolds for Blood-Brain Barrier Permeation

The treatment of Parkinson's disease (PD) has not been consistently modified for more than 60 years. L-DOPA, the blood-brain barrier permeable precursor prodrug of dopamine, is to date the only effective therapy on the market. However, it is well known that prolonged treatment with L-DOPA leads to several side effects, which may affect the patient's life expectancy (i.e., the wearing-off phenomenon, on-off fluctuations, and dyskinesia). For this reason, modifications, and supplements to L-DOPA treatment have been and are being studied, which, however, have not yet resulted in a valid alternative to the cornerstone drug. This review aims to summarize the main formulations currently in use for PD treatment, explaining advantages and disadvantages for each class. The attention will be focused on the promising prodrug concept, aimed at finding a suitable L-DOPA substitute with improved pharmacokinetic behavior. In this respect, new potential candidates which show interesting properties for the intended scope, the so-called dicarba-closo-dodecaboranes(12) (carboranes), will be discussed. Carboranes are inorganic molecular icosahedral boron-carbon clusters with 12 vertices and 20 deltahedral faces. They have been extensively studied for applications in medicine as potential pharmacophores, reagents in boron neutron capture therapy (BNCT) and radiotherapy. Here, we discuss them as inorganic scaffolds for dopamine delivery at the central nervous system (CNS) level.

Zonisamide improves axial symptoms in dementia with Lewy bodies with parkinsonism: Post hoc analysis of clinical trials

Patients with dementia with Lewy bodies (DLB) experience worsening axial symptoms with disease progression, which can negatively affect quality of life. Previous phase 2 and 3 clinical trials conducted in Japan showed that zonisamide improved parkinsonism in patients with DLB. In the present study, we performed a post hoc analysis of pooled data from the previous phase 2 and 3 trials to examine the effect of zonisamide on axial symptoms in this patient group. In our pooled analysis, the primary outcome was the change from baseline to 12 weeks in axial symptom score, measured as the sum of Unified Parkinson's Disease Rating Scale Part III items relevant to gait/balance/midline function. A total of 498 patients were included in this analysis. Zonisamide 25 mg and 50 mg significantly reduced the axial symptom score at week 12 compared with placebo (p < 0.01 and p < 0.001, respectively, by mixed model of repeated measures). Our findings indicate that zonisamide may improve axial symptoms in DLB with parkinsonism and, thus, may potentially reduce the risk of falls and improve quality of life in this vulnerable patient population.

Cognitive Correlates of Instrumental Activities of Daily Living Performance in Parkinson Disease Without Dementia

OBJECTIVE

To investigate cognitive correlates of instrumental activities of daily living (IADL) performance among people with Parkinson disease (PD) without dementia.

DESIGN

Cross-sectional.

SETTING

Academic medical center.

PARTICIPANTS

Volunteer sample (N=161) comprising participants with PD without dementia (n=102) and healthy comparison (HC) participants (n=59).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Performance-based assessment of cognitively-demanding IADL (meal preparation, bill paying, shopping, medication management, small home repair), neuropsychological tests (attentional control/flexibility, planning, working memory, memory, crystallized intelligence), and measures of motor function and other characteristics (eg, depressive symptoms).

RESULTS

There were no group differences in neuropsychological test performance (P>.06). The PD group performed more poorly than the HC group on a number of cognitive IADL tasks (P<.04). After accounting for the effects of motor impairment and other disease-related characteristics, neuropsychological test performance accounted for a small but unique portion of the variance in performance of all cognitive IADL combined, meal preparation, shopping, and medication management in the PD group (R 2=4%-13%; P≤.01).

CONCLUSIONS

The PD group had cognitive IADL performance limitations despite being unimpaired on neuropsychological tests. Within PD, neuropsychological test performance accounted for a small but significant portion of the variance in cognitive IADL performance over and above the effects of motor and other impairments. These results support the added value of using performance-based IADL assessments in functional evaluations of individuals with early and mild PD without dementia.

Pharmacokinetics and safety/efficacy of levodopa pro-drug ONO-2160/carbidopa for Parkinson's disease

We conducted a phase I study investigating the efficacy, safety, and tolerability of ONO-2160, a newly developed levodopa pro-drug, and carbidopa compared with levodopa and carbidopa to stabilize levodopa plasma concentration fluctuations in Japanese patients with Parkinson's disease. In an open-label two-period design, patients (n = 12) with Parkinson's disease received levodopa and carbidopa for 3 days before 7 days of treatment with ONO-2160 and carbidopa. Patients were primarily evaluated using the Unified Parkinson's Disease Rating Scale Part III, a Parkinson's disease symptom diary, and analysis of adverse events. Pharmacokinetic analysis of plasma levodopa concentration was also performed.

ONO-2160 and carbidopa therapy stabilized effective plasma levodopa concentration. No adverse events with safety concerns were observed. The combination of ONO-2160 and carbidopa produced a prolonged and stable plasma levodopa concentration with a reduction in Unified Parkinson's Disease Rating Scale Part III total scores. The combination was well tolerated, with no safety concerns, when administered to Japanese patients with Parkinson's disease.

Chronic exposure to dopamine agonists affects the integrity of striatal D2 receptors in Parkinson's patients

We aimed to investigate the integrity and clinical relevance of striatal dopamine receptor type-2 (D₂R) availability in Parkinson's disease (PD) patients. We studied 68 PD patients, spanning from early to advanced disease stages, and 12 healthy controls. All participants received one [¹¹C]raclopride PET scan in an OFF medication condition for quantification of striatal D₂R availability in vivo. Parametric images of [¹¹C]raclopride non-displaceable binding potential were generated from the dynamic [¹¹C]raclopride scans using implementation of the simplified reference tissue model with cerebellum as the reference tissue. PET data were interrogated for correlations with clinical data related to disease burden and dopaminergic treatment. PD patients showed a mean 16.7% decrease in caudate D₂R and a mean 3.5% increase in putaminal D₂R availability compared to healthy controls. Lower caudate [¹¹C]raclopride BP_ND correlated with longer PD duration. PD patients on dopamine agonist treatment had 9.2% reduced D₂R availability in the caudate and 12.8% in the putamen compared to PD patients who never received treatment with dopamine agonists. Higher amounts of lifetime dopamine agonist therapy correlated with reduced D₂Rs availability in both caudate and putamen. No associations between striatal D₂R availability and levodopa treatment and dyskinesias were found. In advancing PD the caudate and putamen D₂R availability are differentially affected. Chronic exposure to treatment with dopamine agonists, but no levodopa, suppresses striatal D₂R availability, which may have relevance to output signaling to frontal lobes and the occurrence of executive deficits, but not dyskinesias.

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D₂R in caudate and putamen are differentially affected in PD.

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Loss of D₂R in caudate correlates with longer disease duration.

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Dopamine agonists treatment, but not levodopa, suppresses caudate and putamen D₂Rs.

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No association between striatal D₂R availability, levodopa treatment and dyskinesia.

Putamen-midbrain functional connectivity is related to striatal dopamine transporter availability in patients with Lewy body diseases

Prior work has shown that functional connectivity between the midbrain and putamen is altered in patients with impairments in the dopamine system. This study examines whether individual differences in midbrain-striatal connectivity are proportional to the integrity of the dopamine system in patients with nigrostriatal dopamine loss (Parkinson's disease and dementia with Lewy bodies). We assessed functional connectivity of the putamen during resting state fMRI and dopamine transporter (DAT) availability in the striatum using 11C-Altropane PET in twenty patients. In line with the hypothesis that functional connectivity between the midbrain and the putamen reflects the integrity of the dopaminergic neurotransmitter system, putamen-midbrain functional connectivity was significantly correlated with striatal DAT availability even after stringent control for effects of head motion. DAT availability did not relate to functional connectivity between the caudate and thalamus/prefrontal areas. As such, resting state functional connectivity in the midbrain-striatal pathway may provide a useful indicator of underlying pathology in patients with nigrostriatal dopamine loss.

Pathomechanisms and compensatory efforts related to Parkinsonian speech

Voice and speech in Parkinson's disease (PD) patients are classically affected by a hypophonia, dysprosody, and dysarthria. The underlying pathomechanisms of these disabling symptoms are not well understood. To identify functional anomalies related to pathophysiology and compensation we compared speech-related brain activity and effective connectivity in early PD patients who did not yet develop voice or speech symptoms and matched controls. During fMRI 20 PD patients ON and OFF levodopa and 20 control participants read 75 sentences covertly, overtly with neutral, or with happy intonation. A cue-target reading paradigm allowed for dissociating task preparation from execution. We found pathologically reduced striato-prefrontal preparatory effective connectivity in early PD patients associated with subcortical (OFF state) or cortical (ON state) compensatory networks. While speaking, PD patients showed signs of diminished monitoring of external auditory feedback. During generation of affective prosody, a reduced functional coupling between the ventral and dorsal striatum was observed. Our results suggest three pathomechanisms affecting speech in PD: While diminished energization on the basis of striato-prefrontal hypo-connectivity together with dysfunctional self-monitoring mechanisms could underlie hypophonia, dysarthria may result from fading speech motor representations given that they are not sufficiently well updated by external auditory feedback. A pathological interplay between the limbic and sensorimotor striatum could interfere with affective modulation of speech routines, which affects emotional prosody generation. However, early PD patients show compensatory mechanisms that could help improve future speech therapies.