Actively Transported Levodopa Prodrug XP21279: A Study in Patients With Parkinson Disease Who Experience Motor Fluctuations

Levodopa-Induced Dyskinesias in Parkinson's Disease: An Overview on Pathophysiology, Clinical Manifestations, Therapy Management Strategies and Future Directions

Since its first introduction, levodopa has become the cornerstone for the treatment of Parkinson's disease and remains the leading therapeutic choice for motor control therapy so far. Unfortunately, the subsequent appearance of abnormal involuntary movements, known as dyskinesias, is a frequent drawback. Despite the deep knowledge of this complication, in terms of clinical phenomenology and the temporal relationship during a levodopa regimen, less is clear about the pathophysiological mechanisms underpinning it. As the disease progresses, specific oscillatory activities of both motor cortical and basal ganglia neurons and variation in levodopa metabolism, in terms of the dopamine receptor stimulation pattern and turnover rate, underlie dyskinesia onset. This review aims to provide a global overview on levodopa-induced dyskinesias, focusing on pathophysiology, clinical manifestations, therapy management strategies and future directions.

The Management of Parkinson's Disease: An Overview of the Current Advancements in Drug Delivery Systems

Parkinson's disease (PD) has significantly affected a large proportion of the elderly population worldwide. According to the World Health Organization, approximately 8.5 million people worldwide are living with PD. In the United States, an estimated one million people are living with PD, with approximately 60,000 new cases diagnosed every year. Conventional therapies available for Parkinson's disease are associated with limitations such as the wearing-off effect, on-off period, episodes of motor freezing, and dyskinesia. In this review, a comprehensive overview of the latest advances in DDSs used to reduce the limitations of current therapies will be presented, and both their promising features and drawbacks will be discussed. We are also particularly interested in the technical properties, mechanism, and release patterns of incorporated drugs, as well as nanoscale delivery strategies to overcome the blood-brain barrier.

Improving the Delivery of Levodopa in Parkinson's Disease: A Review of Approved and Emerging Therapies

Levodopa is the most effective drug for the treatment of Parkinson's disease, but its use as an oral medication is complicated by its erratic absorption, extensive metabolism and short plasma half-life. On long-term use and with disease progression, there is a high incidence of motor and non-motor complications, which remain a major clinical and research challenge. It is widely accepted that levodopa needs to be administered using formulations that result in good and consistent bioavailability and the physiologically relevant and continuous formation of dopamine in the brain to maximise its efficacy while avoiding and reversing 'wearing off' and dyskinesia. However, the physicochemical properties of levodopa along with its pharmacokinetic and pharmacodynamic profile make it difficult to deliver the drug in a manner that fulfils these criteria. In this review, we examine the problems associated with the administration of levodopa in Parkinson's disease and how the use of novel technologies and delivery devices is leading to a more consistent and sustained levodopa delivery with the aim of controlling motor function as well as non-motor symptoms.

Onset and duration of effect of extended-release carbidopa-levodopa in advanced Parkinson's disease

BACKGROUND

In patients with Parkinson's disease (PD), oral dosing of extended-release carbidopa-levodopa (Rytary, IPX066 [ER CD-LD]) achieves peak levodopa plasma concentrations within 1 hour and maintains them for 4-6 hours.

AIMS

To compare the onset and duration of ER CD-LD benefit with those of immediate-release carbidopa-levodopa (IR CD-LD) in PD patients with motor fluctuations, using crossover data, and to evaluate which threshold values of improvement in finger-tapping and Unified Parkinson's Disease Rating Scale (UPDRS) motor scores yield results most similar to those for trained raters' "on"/"off" assessments.

METHODS

Patients underwent serial "on"/"off" rating and provided serial finger-tapping and UPDRS motor scores after receiving, in an "off" state, their usual morning IR dose or an ER dose designed to produce a similar levodopa peak concentration. Predefined improvement thresholds for analysis were 10%, 15%, and 20% increases in finger-tapping score and 2.5, 5, 7, and 11-point decreases in UPDRS motor score. Serial plasma samples were assayed for levodopa.

RESULTS

Among 27 patients, mean time to onset of an "on" state was similar for ER compared with IR CD-LD (0.83 vs 0.81 hour), but mean duration was significantly longer for ER CD-LD than for IR CD-LD (5.56 vs 2.69 hours; P<0.0001). Duration was best matched by a $20% improvement in finger-tapping, a $11-point improvement in UPDRS motor score, and a levodopa plasma concentration $1,000 ng/mL.

CONCLUSION

For ER CD-LD, observer assessments of "on" state were corroborated by sustained treatment effects. Correlations among "on"-state duration, finger-tapping score, and UPDRS motor score may suggest clinically relevant thresholds for acute assessment of treatment benefit.

Levodopa in Parkinson's Disease: Current Status and Future Developments

BACKGROUND

Ever since the pioneering reports in the 60s, L-3,4-Dioxyphenylalanine (levodopa) has represented the gold standard for the treatment of Parkinson's Disease (PD). However, long-term levodopa (LD) treatment is frequently associated with fluctuations in motor response with serious impact on patient quality of life. The pharmacokinetic and pharmacodynamic properties of LD are pivotal to such motor fluctuations: discontinuous drug delivery, short half-life, poor bioavailability, and narrow therapeutic window are all crucial for such fluctuations. During the last 60 years, several attempts have been made to improve LD treatment and avoid long-term complications.

METHODS

Research and trials to improve the LD pharmacokinetic since 1960s are reviewed, summarizing the progressive improvements of LD treatment.

RESULTS

Inhibitors of peripheral amino acid decarboxylase (AADC) have been introduced to achieve proper LD concentration in the central nervous system reducing systemic adverse events. Inhibitors of catechol-O-methyltransferase (COMT) increased LD half-life and bioavailability. Efforts are still being made to achieve a continuous dopaminergic stimulation, with the combination of oral LD with an AADC inhibitor and a COMT inhibitor, or the intra-duodenal water-based LD/ carbidopa gel. Further approaches to enhance LD efficacy are focused on new non-oral administration routes, including nasal, intra-duodenal, intrapulmonary (CVT-301) and subcutaneous (ND0612), as well as on novel ER formulations, including IPX066, which recently concluded phase III trial.

CONCLUSION

New LD formulations, oral compounds as well as routes have been tested in the last years, with two main targets: achieve continuous dopaminergic stimulation and find an instant deliver route for LD.

The Design and Evaluation of an l-Dopa-Lazabemide Prodrug for the Treatment of Parkinson's Disease

l-Dopa, the metabolic precursor of dopamine, is the treatment of choice for the symptomatic relief of the advanced stages of Parkinson’s disease. The oral bioavailability of l-dopa, however, is only about 10% to 30%, and less than 1% of the oral dose is estimated to reach the brain unchanged. l-Dopa’s physicochemical properties are responsible for its poor bioavailability, short half-life and the wide range of inter- and intrapatient variations of plasma levels. An l-dopa–lazabemide prodrug is proposed to overcome the problems associated with l-dopa absorption. Lazabemide is a monoamine oxidase (MAO)-B inhibitor, a class of compounds that slows the depletion of dopamine stores in Parkinson’s disease and elevates dopamine levels produced by exogenously administered l-dopa. l-Dopa was linked at the carboxylate with the primary aminyl functional group of lazabemide via an amide, a strategy which is anticipated to protect l-dopa against peripheral decarboxylation and possibly also enhance the membrane permeability of the prodrug. Selected physicochemical and biochemical properties of the prodrug were determined and included lipophilicity (logD), solubility, passive diffusion permeability, pK_a, chemical and metabolic stability as well as cytotoxicity. Although oral and i.p. treatment of mice with the prodrug did not result in enhanced striatal dopamine levels, 3,4-dihydroxyphenylacetic acid (DOPAC) levels were significantly depressed compared to saline, l-dopa and carbidopa/l-dopa treatment. Based on the results, further preclinical evaluation of the l-dopa–lazabemide prodrug should be undertaken with the aim of discovering prodrugs that may be advanced to the clinical stages of development.

Novel Levodopa Formulations for Parkinson's Disease

Levodopa remains the most effective treatment for Parkinson's disease and is considered the gold standard therapy. However, disease progression and changes in the gastrointestinal tract result in a declining window of treatment response in a majority of patients. Efforts have been made recently to improve levodopa bioavailability either by developing more effective oral formulations or by innovating routes of administration (intestinal infusion, transcutaneous or inhaled levodopa). IPX066 is a novel levodopa-carbidopa (LD/CD) oral formulation combining immediate-release (IR) and extended-release (ER) LD/CD recently approved in the USA and the EU. Levodopa-carbidopa intestinal gel (LCIG) is an approved therapy consisting of a suspension of levodopa and carbidopa infused directly into the proximal jejunum via a percutaneous endoscopic gastrojejunostomy (PEG-J) tube through a portable infusion pump. Ongoing studies are evaluating the 'accordion pill' (AP09004), an ER LD/CD formulation with gastroretentive properties. ND0612 is a proprietary liquid formulation of LD/CD that enables subcutaneous administration via a small patch-pump device, and CVT-301 is a levodopa inhalation powder with rapid onset of action; both are currently in active studies. Other novel formulations have been discontinued, including DM-1992, which is a bilayer formulation containing an IR LD/CD layer and an ER LD/CD layer with gastroretentive properties, and XP21279, a novel oral levodopa prodrug that is absorbed from the small and large intestine by high-capacity nutrient transporters expressed throughout the gastrointestinal system. ODM-101 is a new oral formulation of levodopa/carbidopa/entacapone that contains a higher amount of carbidopa (65 or 105 mg), but no active studies are underway. The current review aims to summarize the pharmacokinetic aspects, clinical efficacy, and potential adverse events of novel levodopa formulations currently available or under development.

A review of current and novel levodopa formulations for the treatment of Parkinson's disease

Parkinson's disease treatment is characterized by the nearly inevitable development of motor complications, including fluctuations and dyskinesias, in which the duration of benefit of a dose of medication is offset by involuntary movements that can be more disabling than the Parkinsonian features themselves. While levodopa remains the gold standard of therapy, it is the most likely to be associated with these complications. The concept of continuous dopaminergic stimulation has gained increasing acceptance as a potential mechanism by which to avoid or delay the development of motor complications, or to minimize their impact once they have already occurred. This article will explore existing and novel formulations of levodopa to identify their role in the spectrum of Parkinson's disease therapeutics.

New and emerging medical therapies in Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is one of the most challenging neurodegenerative disorders to treat as it manifests with a large variety of troublesome, and often disabling, motor and non-motor symptoms. Despite limitations, such as motor and other complications, levodopa remains the most effective drug in the treatment of PD.

AREAS COVERED

In this review, we focus on phase 2 and 3 studies describing new and emerging medical therapies in PD. We discuss new formulations of levodopa, medications that prolong levodopa response and ameliorate levodopa-induced dyskinesias, and innovative delivery methods that are currently being evaluated in clinical trials or are in development with the promise of better efficacy and tolerability. We also describe novel non-dopaminergic drugs that have been identified for treatment of motor and non-motor symptoms. A specific section is designated for potential disease modifying therapies.

EXPERT OPINION

Alternative formulations of levodopa appear to be promising especially to help with the motor fluctuations either by providing sustained benefits with controlled released formulations or ameliorate sudden OFF by formulations such as inhaled levodopa. Several different medications affecting non-dopaminergic pathways are being evaluated which may aide levodopa. As the understanding of the disease grows further, numerous novel neuroprotective or disease modifying therapies have been suggested. This along with development of medications to treat various non-motor symptoms will help improve quality of life of patients with PD.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

New treatments for the motor symptoms of Parkinson's disease

Levodopa remains the most potent drug to treat motor symptoms in Parkinson's disease (PD); however, motor fluctuations and levodopa-induced dyskinesia that occur with long-term use restrict some of its therapeutic value. Despite these limitations, the medical treatment of PD strives for continuous relief of symptoms using different strategies throughout the course of the illness: increasing the half-life of levodopa, using 'levodopa-sparing agents' and adding non-dopaminergic drugs. New options to 'improve' delivery of levodopa are under investigation, including long-acting levodopa, nasal inhalation and continuous subcutaneous or intrajejunal administration of levodopa. Long-acting dopamine agonists were recently developed and are undergoing further comparative studies to investigate potential superiority over the immediate-release formulations. Non-dopaminergic drugs acting on adenosine receptors, cholinergic, adrenergic, serotoninergic and glutamatergic pathways are newly developed and many are being evaluated in Phase II and Phase III trials. This article focuses on promising novel therapeutic approaches for the management of PD motor symptoms and motor complications. We will provide an update since 2011 on new formulations of current drugs, new drugs with promising results in Phase II and Phase III clinical trials, old drugs with new possibilities and some new potential strategies that are currently in Phase I and II of development (study start date may precede 2011 but are included as study is still ongoing or full data have not yet been published). Negative Phase II and Phase III clinical trials published since 2011 will also be briefly mentioned.

Novel formulations and modes of delivery of levodopa

Ever since its early clinical use in the 1960s, levodopa has remained the gold standard of symptomatic efficacy in the drug treatment of Parkinson's disease (PD). Motor response fluctuations and drug-induced dyskinesias seriously compromise the unparalleled symptomatic efficacy of l-dopa during long-term treatment. Discontinuous drug delivery resulting from the short half-life of l-dopa and erratic gastrointestinal absorption plays a major role in the pathophysiology of these motor complications. Several approaches to improve the pharmacokinetics and ways of administration of l-dopa are in different stages of clinical development and include novel formulations as well as nonoral routes of drug delivery. IPX066 is a novel extended-release l-dopa capsule that has successfully completed phase III clinical trials while the l-dopa prodrug XP21279 and a gastric retention formulation ("accordion pill") are in earlier phases of clinical development. Novel enzyme inhibitors enhancing l-dopa efficacy and half-life are also still being developed, including a novel catechol-O-methyltransferase inhibitor with once-daily pharmacokinetics, and there are studies testing the effects of increasing the dose of amino acid decarboxylase inhibitors given concomitantly with l-dopa. Intrajejunal infusion of a gel formulation of l-dopa/carbidopa is in clinical use in Europe, and its efficacy to smooth out motor fluctuations has recently been shown in a randomized, controlled trial. Subcutaneous and intrapulmonal delivery routes of l-dopa have reached phase III of clinical development. After more than 50 years of clinical use, l-dopa not only remains the gold standard of symptomatic efficacy, but it also remains a drug in active clinical development.

IPX066 , a mixed immediate/sustained-release levodopa preparation for Parkinson's disease

INTRODUCTION

L-DOPA has long been the 'gold standard' treatment for Parkinson's disease (PD), but suffers from poor oral bioavailability and rapid pharmacokinetic elimination. A longer acting preparation has long been sought.

AREAS COVERED

We conducted PubMed search for IPX066 and reviewed abstracts from meetings that included the topic of PD. IPX066 is a novel mixed immediate release (IR) and sustained-release levodopa preparation designed to prolong the clinical effect of a single dose. Pharmacokinetic studies demonstrate similar time to peak dose as regular IR L-DOPA, but a longer duration of time with > 50% of peak dose. This contrasts with available controlled release preparations that have a delay to onset. Clinic trials in fluctuating PD patients show that IPX066 provided more 'on' time despite fewer daily doses, compared to IR L-DOPA. As expected, it was also superior to placebo in early PD. However, it is not known whether it can achieve l-DOPA levels that are continuous enough to delay the onset of fluctuations when given early in the disease.

EXPERT OPINION

Although not a radical advance in L-DOPA therapy, the drug will clearly have a role in more advanced patients taking multiple L-DOPA doses and may have a role as first-line therapy when starting l-DOPA.

Continuous drug delivery in Parkinson's disease

Development of motor and non-motor complications during the course of Parkinson's disease (PD) is a major challenge for therapeutic management. At advanced disease stages, patients frequently fluctuate between PD symptoms-such as bradykinesia-and dyskinesias, in response to fluctuations in drug concentrations. Continuous subcutaneous infusion of the dopamine agonist apomorphine or intestinal infusion of levodopa reduce such fluctuations in both pharmacokinetics and motor function. This is the basis for the concept of continuous drug delivery in PD, and the more theoretical concept of continuous dopaminergic stimulation. These expressions are sometimes used to describe a treatment that is more continuous in its pharmacokinetic profile or that produces more sustained effects, compared with immediate-release levodopa, i.e. not only pump treatments. For example, sustained-release formulations of levodopa or dopamine agonists, transdermal delivery of rotigotine, and addition of catechol-O-methyltransferase inhibitors or monoamine oxidase-B inhibitors have been developed with the aim to provide more continuous drug concentrations, sustained benefits and minimized side effects. Progress has been made, but there are still knowledge gaps regarding how these treatment alternatives can be optimally used. New treatments are currently being developed to provide the continuous drug delivery that is known to successfully alleviate motor and non-motor complications. Hopefully, although not yet proven, these new methods may also prevent or postpone some of the late-stage complications.

Therapy for Parkinson's disease: what is in the pipeline?

Despite advances in the treatment of Parkinson's disease there are still many unmet needs, including neuroprotection, treatment of motor complications, treatment of dyskinesia, treatment of psychosis, and treatment of nondopaminergic symptoms. In this review, I highlight the obstacles to develop a neuroprotective drug and some of the treatment strategies recently approved or still in clinical trials designed to meet these unmet needs.

Therapeutic prospects for Parkinson disease

Dopaminergic therapies such as levodopa have provided benefit for millions of patients with Parkinson's disease (PD) and revolutionized the treatment of this disorder. However patients continue to experience disability despite the best of modern treatment. Dopaminergic and surgical therapies are associated with potentially serious side effects. Non-motor and non-dopaminergic features such as freezing, falling, and dementia are not adequately controlled with available medications and represent the major source of disability for advanced patients. And, the disease continues to relentlessly progress. Major therapeutic unmet needs include a dopaminergic therapy that is not associated with serious side effects, a therapy that addresses the non-motor and non-dopaminergic features of the disease, and a disease-modifying therapy that slows or stops disease progression. This review will consider current attempts to address these issues and the obstacles that must be overcome in order to develop more effective therapies for PD.