WO2017070293A1 - Phosphodiesterase 9 inhibitor and levodopa therapy - Google Patents

Abstract

The present disclosure relates to pharmaceutical compositions comprising an effective amount of L-dopa and an effective amount of a phosphodiesterase 9 inhibitor, and methods for treating Parkinson's disease or Parkinsonism, comprising administering to a patient in need thereof an effective amount of L-dopa and an effective amount of a phosphodiesterase 9 inhibitor.

Description

PHOSPHODIESTERASE 9 INHIBITOR AND LEVODOPA THERAPY

1. FIELD

[0000] This application claims priority to U.S. Provisional Application Serial No.

62/243,968, filed October 20, 2015 and to U.S. Provisional Application Serial No.

62/247,882, filed October 29, 2015, the contents of each of which are herein incorporated by reference in their entirety.

[0001] This disclosure relates generally to the treatment of a central nervous system disorders, and more specifically, to the use of a combination of levodopa and a

phosphodiesterase 9 inhibitor for the treatment of Parkinson's disease or Parkinsonism.

2. BACKGROUND

[0002] The phosphodiesterases (PDEs) are a superfamily of enzymes with eleven members encoded by 21 genes that regulate intracellular cyclic nucleotide signaling (i.e., cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)). The phosphodiesterase 9 enzyme (PDE9) selectively hydrolyzes cGMP over cAMP and has the highest affinity of any PDE for cGMP, Km -170 nM (Fisher et al, J. Biol. Chem. 1998, 273 (25), 15559-15564). PDE9 is found to be present in a variety of human tissues including prostate, colon, small intestine, spleen, kidney, brain and skeletal muscle.

[0003] Parkinson's disease is a degenerative disorder of the central nervous system. The core motor features of Parkinson's disease result from the death of dopamine-containing cells in the substantia nigra, a region of the midbrain, and the degeneration of the nigrostriatal dopaminergic pathway. The cause of cell-death is unknown. The diagnosis of Parkinson's disease is generally made when motor symptoms become apparent. Motor symptoms of Parkinson's disease include shaking, rigidity, slowness of movement and difficulty with walking and gait. As the symptomatic period advances, the severity of symptoms increase, there is an onset of motor complications of therapy, and core motor features are progressively overshadowed by non-motor symptoms. Motor complications of levodopa-therapy include motor fluctuations and dyskinesia. A correlation has been found between the severity of the motor symptoms and the loss of dopamine. Therefore, treatment of Parkinson's disease has largely focused on the replacement of dopamine. [0004] Parkinsonism is a clinical syndrome characterized by bradykinesia, resting tremor, rigidity, and postural instability. The defining feature of Parkinsonism is bradykinesia, or slowness with decrement and degradation of repetitive movements. Subtle bradykinesia can occur in the "normal elderly" population, but this may reflect a non-specific slowness rather than bradykinesia as defined above. Parkinson's disease is the most common

neurodegenerative cause of parkinsonism. Other causes of Parkinsonism include, but are not limited to, multiple system atrophy, progressive supranuclear palsy and corticobasal degeneration. These other neurodegenerative conditions are sometimes referred to as "atypical parkinsonism" or "parkinson-plus syndromes." They do not respond as well to dopaminergic treatments and generally have a worse prognosis compared to typical

Parkinson's disease. Degenerative causes of Parkinsonism may be difficult to diagnose in the earliest stages.

[0005] Parkinsonism can also be symptomatic, as a result of various vascular, drug- related, infectious, toxic, structural and other known secondary causes. Of these, drug- induced Parkinsonism is probably the most frequent and includes agents that block postsynaptic dopamine D2 receptors with high affinity (such as antipsychotic and anti-emetic medications) and sodium valproate. Vascular parkinsonism (arteriosclerotic

pseudoparkinsonism) usually has a lower body emphasis with gait disturbance and concomitant cognitive impairment.

[0006] Levodopa (L-dopa), a precursor to dopamine, is presently considered the most effective and well tolerated dopamine replacing agent and is the gold standard for

symptomatic treatment of Parkinson's disease or Parkinsonism (Salat et al., J. Parkinson ' s Dis. 2013, 3, 255-269). The long-term treatment of Parkinson's disease or Parkinsonism with L-dopa is complicated by the development of motor complications, including response fluctuations, dyskinesia, and psychiatric abnormalities. The response fluctuations result from a wearing off effect of L-dopa at the end of dosing periods and may develop into a more complex phenomenon wherein the patient fluctuates between being relatively free of symptoms of Parkinson's disease or Parkinsonism and having symptoms of Parkinson's disease or Parkinsonism re-emerge before the following scheduled treatment. Generally, when motor complications develop, an additional drug to the L-dopa regimen is added from one of three other classes of treatments: dopamine agonists, catechol-O-methyl transferase inhibitors (COMTIs), or monoamine oxidase type B inhibitors (MAOBIs). Although trials have shown that these drugs are beneficial compared to placebo, it remains unclear as to the best way to treat patients experiencing motor complications and whether one class of drug is more effective than another (Stowe et al., The Cochrane Library, 2010, 7, 1). Thus there is a strong need for improved treatment of Parkinson's disease or Parkinsonism.

3. SUMMARY

[0007] The invention described is based, in part, on the surprising discovery that administration of L-dopa and a phosphodiesterase 9 inhibitor increases the period of time during which the patient is relatively free of symptoms of Parkinson's disease or

Parkinsonism, which allows administration of L-dopa at a sub-optimal dose.

[0008] It is understood that any of the embodiments described below can be combined in any desired way, and that any embodiment or combination of embodiments can be applied to each of the aspects described below, unless the context indicates otherwise.

[0009] In one aspect, the invention provides a method for treating a central nervous system disorder in a patient in need thereof, the method comprising administering to the patient: (a) an effective amount of L-dopa and (b) an effective amount of a phosphodiesterase

9 inhibitor.

[0010] In some embodiments, the central nervous system disorder is Parkinson's disease or Parkinsonism.

[0011] In some embodiments, the invention further comprises administering an effective amount of a dopa-decarboxylase (DDC) inhibitor. In some embodiments, the dopa- decarboxylase (DDC) inhibitor is benserazide or carbidopa.

[0012] In some embodiments, the method further comprises administering an effective amount of a monoamine oxidase (MAO-B) inhibitor.

[0013] In some embodiments, the method further comprises administering an effective amount of a catechol-O-methyltransferase (COMT) inhibitor.

[0014] In some embodiments, the phosphodiesterase 9 inhibitor is (+)-2-((3S,4S)-4- methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

[0015] In some embodiments, the phosphodiesterase 9 inhibitor is BAY 73-6691, 28s,

PF-04447943, PF-4181366, BI 409306, or a pharmaceutically acceptable salt thereof. [0016] In some embodiments, th

-5 -

(R = substituted phenyl

or pyridyl), (R = alkyl, cycloalkyl, aryl, heteroaryl; R = heterocycloalkyl),

(R = alkyl, cycloalkyl, aryl, heteroaryl),

thereof. In some embodiments, the phosphodiesterase 9 inhibitor does not interact substantially with L-dopa pharmacokinetic parameters. Examples of such parameters are Cmax and AUClast.

[0017] In some embodiments, the effective amount of L-dopa is a suboptimal dose. In some embodiments, the sub-optimal dose is determined by titration in the patient.

[0018] In some embodiments, L-dopa and the phosphodiesterase 9 inhibitor are administered simultaneously. In some embodiments, L-dopa and the phosphodiesterase 9 inhibitor are administered sequentially.

[0019] In some embodiments, L-dopa is administered prior to administration of the phosphodiesterase 9 inhibitor. In some embodiments, the phosphodiesterase 9 inhibitor is administered prior to administration of L-dopa.

[0020] In some embodiments, Parkinson's disease is early onset Parkinson's disease.

[0021] In some embodiments, the effective amount of the phosphodiesterase 9 inhibitor is about 1 to about 100 mg. In some embodiments, the effective amount of the

phosphodiesterase 9 inhibitor is about 5 to about 50 mg. In some embodiments, the effective amount of the phosphodiesterase 9 inhibitor is about 10 to about 25 mg. In some embodiments, the effective amount of the phosphodiesterase 9 inhibitor is about 15 to about 20 mg.

[0022] In another aspect, the invention provides a method for treating Parkinson's disease or Parkinsonism in a patient in need thereof, the method comprising administering to the human: (a) an effective amount of L-dopa and (b) an effective amount of a phosphodiesterase 9 inhibitor.

[0023] In some embodiments, the method further comprises administering an effective amount of a dopa-decarboxylase (DDC) inhibitor. In some embodiments, the dopa- decarboxylase (DDC) inhibitor is benserazide or carbidopa.

[0024] In some embodiments, the phosphodiesterase 9 inhibitor is (+)-2-((3S,4S)-4- methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

[0025] In some embodiments, the effective amount of the phosphodiesterase 9 inhibitor is about 1 to about 100 mg.

[0026] In some embodiments, the effective amount of L-dopa is about 25 to about 600 mg.

[0027] In another aspect, the invention provides a pharmaceutical composition comprising L-dopa, a phosphodiesterase 9 inhibitor and a pharmaceutically acceptable carrier or vehicle.

[0028] In some embodiments, the composition further comprises benserazide or carbidopa.

[0029] In some embodiments, the composition further comprises a monoamine oxidase (MAO-B) inhibitor.

[0030] In some embodiments, the composition further comprises a catechol-O- methyltransferase (COMT) inhibitor.

[0031] In some embodiments, the phosphodiesterase 9 inhibitor is (+)-2-((3,4-trans)-4- methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

[0032] In some embodiments, the phosphodiesterase 9 inhibitor is BAY 73-6691, 28s,

PF-04447943, PF-4181366, BI 409306, or a pharmaceutically acceptable salt thereof.

[0033] In some embodiments, the composition is suitable for oral administration.

[0034] In some embodiments, the composition is in a solid oral dosage form. [0035] In some embodiments, the solid oral dosage form is a tablet, a capsule, or a softgel.

[0036] In another aspect, the invention provides a kit comprising: (a) L-dopa and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a phosphodiesterase 9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container; and (c) instructions for use.

[0037] In some embodiments, the kit further comprises dopa-decarboxylase (DDC) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container.

[0038] In some embodiments, the dopa-decarboxylase (DDC) inhibitor is carbidopa or benserazide.

[0039] The details of the invention are set forth in the accompanying description below.

[0040] All patents and publications cited in this specification are hereby incorporated by reference in their entirety.

4. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1A is a plot of the motor disability scores (MDS) for parkinsonian monkeys when treated with a threshold dose of L-dopa in combination with varying doses of Compound A, a PDE9 inhibitor. Compound A significantly attenuated MDS at all doses tested in the threshold (Fp<0.01) L-dopa conditions compared to saline treatment.

[0042] Figure IB is a bar graph of the on time duration as a percent of the control for each of the three doses of Compound A (2.5 mg/kg, 5 mg/kg, 7.5 mg/kg) in threshold conditions. At all doses tested, Compound A significantly prolonged on time duration in the threshold (p<0.01) conditions compared to saline treatment.

[0043] Figure 2A is a plot of the motor disability scores (MDS) for parkinsonian monkeys when treated with a sub-optimal dose of L-dopa in combination with varying doses of Compound A. Compound A significantly attenuated MDS at all doses tested in the suboptimal (p<0.01) L-dopa conditions compared to saline treatment.

[0044] Figure 2B is a bar graph of the on time duration as a percent of the control for each of the three doses of Compound A (2.5 mg/kg, 5 mg/kg, 7.5 mg/kg) in sub-optimal conditions. At all doses tested, Compound A significantly prolonged on time duration in the sub-optimal (Figure 2B; p<0.01) conditions compared to saline treatment. 5. DETAILED DESCRIPTION

5.1 Definitions and Abbreviations

[0045] The following are definitions of terms used in the present specification. The initial definition provided for a group or term herein applies to that group or term throughout the present specification individually or as part of another group, unless otherwise indicated. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0046] The term "Compound A" as used herein refers to "(+)-2-((3S,4S)-4-methyl- 1- (pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f] [ 1 ,2,4] triazin-4(3H)-one."

[0047] The term "on time" as used herein refers to the period of time after a dose has been administered to a patient during which the patient is relatively free of symptoms of Parkinson's disease or Parkinsonism.

[0048] The term "on response" as used herein refers to a response after administration that is >50% improvement over the saline baseline.

[0049] The term "wearing off as used herein refers to the re-emergence of symptoms of Parkinson's disease or Parkinsonism before the following scheduled treatment dose.

[0050] The term "off time" as used herein refers to the period of time during which symptoms of Parkinson's disease or Parkinsonism re-emerge before the following scheduled treatment.

[0051] The term "off as used herein refers to a state of decreased mobility or a state in which symptoms of Parkinson's disease or Parkinsonism have re-emerged.

[0052] The term "optimal dose" as used herein refers to the dose that induces the best "on response", which is usually associated with prominent L-dopa-induced dyskinesia (LID) in advanced parkinsonian primates and may only reduce the Motor Disability Score (MDS) by 70-75% in some animals.

[0053] The term "sub-optimal dose" as used herein refers to the dose that produces half of the optimal dose response with significantly reduced, but still ratable, L-dopa-induced dyskinesia. [0054] The term "threshold dose" as used herein refers to the dose that induces a reproducible small improvement of mobility (e.g., 25-30% reduction of Motor Disability Score) without L-dopa-induced dyskinesia. These doses are determined individually according to the particular motor response of each animal.

[0055] The term "pharmaceutically acceptable carrier or vehicle" as used herein, refers to a pharmaceutically acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, excipient, solvent or encapsulating material, involved in carrying or transporting the PDE9 inhibitor and/or levodopa from one organ, or portion of the body, to another organ, or portion of the body. Each carrier or vehicle must be "acceptable" in the sense of being compatible with the other ingredients of the formulation and not injurious to the subject. Some examples of materials which can serve as pharmaceutically acceptable carriers or vehicles include: sugars, such as lactose, glucose and sucrose; starches, such as corn starch and potato starch; cellulose, and its derivatives, such as sodium carboxymethyl cellulose, ethyl cellulose and cellulose acetate; powdered tragacanth; malt; gelatin; talc; excipients, such as cocoa butter and suppository waxes; oils, such as peanut oil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil and soybean oil; glycols, such as butylene glycol; polyols, such as glycerin, sorbitol, mannitol and polyethylene glycol; esters, such as ethyl oleate and ethyl laurate; agar; buffering agents, such as magnesium hydroxide and aluminum hydroxide; alginic acid; pyrogen-free water; isotonic saline; Ringer' s solution; ethyl alcohol; phosphate buffer solutions; and other non-toxic compatible substances employed in pharmaceutical formulations.

[0056] Reference to a compound described herein is understood to include reference to salts thereof, unless otherwise indicated. The term "salt(s)", as employed herein, denotes acidic and/or basic salts formed with inorganic and/or organic acids and bases. In addition, when a compound described herein contains both a basic moiety, such as, but not limited to, amine, pyridine or imidazole and an acidic moiety, such as, but not limited to, a carboxylic acid, zwitterions ("inner salts") may be formed and are included within the term "salt(s)" as used herein. Pharmaceutically acceptable (i.e. , non-toxic, physiologically acceptable) salts are preferred, although other salts are also useful, e.g. , in isolation or purification steps which may be employed during preparation. Salts of compounds described herein may be formed, for example, by reacting a compound with an amount of acid or base, such as an equivalent amount, in a medium, such as one in which the salt precipitates or in an aqueous medium followed by lyophilization. [0057] As used herein, "effective amount" refers to any amount that is necessary or sufficient for achieving or promoting a desired outcome, e.g., for treating, preventing, or ameliorating a symptom of Parkinson's disease or Parkinsonism. In some instances an effective amount is a therapeutically effective amount. A therapeutically effective amount is any amount that is necessary or sufficient for promoting or achieving a desired biological response in a subject. The effective amount for any particular application can vary depending on such factors as the disease or condition being treated, the particular agent being administered, the size of the subject, or the severity of the disease or condition.

[0058] As used herein, "treat" or "treating" includes stopping the progression, reversing the progression, preventing and/or reducing or ameliorating a symptom a central nervous system disorder (such as Parkinson's disease or Parkinsonism), for example, improving motor function.

[0059] Abbreviations

Abbreviations used herein include:

cAMP cyclic adenosine monophosphate

cGMP cyclic guanosine monophosphate

CNS central nervous system

COMTI catechol-O-methyl transferase inhibitor

DDC dopa-decarboxylase

L-dopa levodopa

LID L-dopa-induced dyskinesia

LTP long term potentiation

MAOBI monoamine oxidase type B inhibitor

MDS Motor Disability Score

PD Parkinson's disease or Parkinsonism

PDE phosphodiesterase

PDE9 phosphodiesterase 9

s.c. subcutaneous

5.2 Phosphodiesterase 9 (PDE9) Inhibitors

[0060] A number of PDE9 inhibitors and methods for making them have been described in the art, including, but not limited to, US 2009/0030003, WO 2004/113306, DE 10238722, DE 10238724, WO 2004/018474, WO 2004/099210, WO 2004/099211, WO 2004/096811, WO/2003/037432, US 2008/139293, WO 2012/040230, WO 2013/142269, WO 2013/110768, US. Pat. No. 7,737,156, and WO 2009/121919, each of which is hereby incorporated by reference in its entirety.

[0061] Specific examples of PDE9 inhibitors include

(BAY 73-

),

- 17-

substituted phenyl or pyridyl), (R 1 = alkyl, cycloalkyl, aryl, heteroaryl; R 2 : heterocycloalkyl),

(R¹ = alkyl, cycloalkyl, aryl, heteroaryl),

-21 -

thereof. [0062] In some embodiments, the PDE9 inhibitor is (+)-2-((3S,4S)-4-methyl- 1-

(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof. The synthesis of (+)-

2-((3S,4S)-4-methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4- yl)imidazo[5,l-f][l,2,4]triazin-4(3H)-one is described in WO 2012/040230.

[0063] In some embodiments, the PDE9 inhibitor is BAY 73-6691. BAY 73-6691 is described in DE 10238722, DE 10238724, WO 2004/018474, WO 2004/099210, and WO

2004/099211.

[0064] In some embodiments, the PDE9 inhibitor is PF-04447943. PF-04447943 is described in WO 2008/139293.

[0065] In some embodiments, the PDE9 inhibitor is 28s or PF-4181366.

In some embodiments, the PDE9 inhibitor is BI 409306. In some embodiments, the PDE9 inhibitor is described in WO 2013/110768.

[0066] Additional PDE9 inhibitors are described in Tuttle et al., Top. Med. Chem. , 2015, 13, 255-316.

5.3 Levodopa

[0067] Levodopa (L-dopa), a precursor to dopamine, is presently considered an effective and well tolerated dopamine replacing agent. It is considered the gold standard for symptomatic treatment of Parkinson's disease and contributes significantly to improvements in the quality of life of patients with Parkinson's disease (Salat et al., J. Parkinson ' s Dis. 2013, 3, 255-269). When L-dopa is administered orally, it is quickly decarboxylated and only a small proportion reaches the central nervous system. To counter this, L-dopa is routinely administered in combination with a dopa-decarboxylase (DDC) inhibitor, such as carbidopa or benserazide. This co-administration of L-dopa with a dopa-decarboxylase inhibitor extends the half-life of L-dopa and increases its availability to the brain, thereby prolonging the duration of its symptomatic effect.

[0068] L-dopa is effective in the early stages of Parkinson's disease or Parkinsonism and remains effective as the disease progresses. Intolerance of L-dopa does not develop with the passage of time. The main drawbacks of L-dopa are dyskinesias and response fluctuations, which are partly related to its short half-life (Salat et al., J. Parkinson 's Dis. 2013, 3, 255- 269). The long-term treatment of Parkinson's disease or Parkinsonism with L-dopa is complicated by the development of motor complications, including response fluctuations, dyskinesia, and psychiatric abnormalities. L-dopa induced dyskinesia is particularly troubling as the abnormal, involuntary movements can be disabling and interfere with activities of daily living.

[0069] Generally, when motor complications develop, an additional drug to the L-dopa regimen is added from one of three other classes of treatments: dopamine agonists, catechol- O-methyl transferase inhibitors (COMTIs), or monoamine oxidase type B inhibitors

(MAOBIs). Although trials have shown that these drugs are beneficial compared to placebo, it remains unclear as to the best way to treat patients experiencing motor complications and whether one class of drug is more effective than another (Stowe et al., The Cochrane Library, 2010, 7, 1). Examples of combination therapy include ropinirole with L-dopa (WO

1997/048394).

5.4 Methods for Treating Central Nervous System Disorders and Other Disorders

[0070] Described below are methods for treating central nervous system disorders (such as Parkinson's disease or Parkinsonism), the methods comprising administering L-dopa and a PDE9 inhibitor. Surprisingly, the co-administration of L-dopa and a PDE9 inhibitor increases the "on time," or the period of time during which the patient is relatively free of symptoms of Parkinson's disease or Parkinsonism, which allows administration of L-dopa at a sub-optimal dose.

[0071] The long-term treatment of Parkinson's disease or Parkinsonism with L-dopa is complicated by the development of motor complications, including response fluctuations, dyskinesia, and psychiatric abnormalities. The response fluctuations result from a wearing off effect of L-dopa at the end of dosing periods and may develop into a more complex phenomenon wherein the patient fluctuates between periods of being relatively free of symptoms of Parkinson's disease or Parkinsonism ("on time") and periods of having symptoms of Parkinson's disease or Parkinsonism re-emerge before the following scheduled treatment ("off time"). These fluctuations, referred to as the on-off effect, can occur many times a day and often with startling rapidity. The fluctuations are a major problem in the long-term treatment of Parkinson's disease or Parkinsonism with L-dopa. A method of treatment that can increase the "on time" or decrease the "off time" would provide significant benefit to Parkinson's disease or Parkinsonism patients suffering from motor complications of L-dopa treatment. [0072] The driving factor for the development of motor complications appears to be L- dopa dose. In one trial, the incidence of wearing-off in those receiving smaller doses of levodopa (150 or 300 mg/day) was considerably lower than those receiving 600 mg/day of L- dopa (Salat et al., J. Parkinson ' s Dis. 2013, 3, 255-269). Thus, a method of treatment that can decrease the dose of L-dopa while still effectively treating the symptoms of Parkinson's disease or Parkinsonism would also provide significant benefit to Parkinson's disease or Parkinsonism patients suffering from motor complications of L-dopa treatment.

[0073] In one aspect, the present disclosure provides a method for treating a central nervous system disorder such as Parkinson's disease or Parkinsonism, the method comprising administering an effective amount of L-dopa and an effective amount of a PDE9 inhibitor to a patient in need thereof.

[0074] In some embodiments, the method further comprises administering an effective amount of a dopa-decarboxylase (DDC) inhibitor, e.g., benserazide or carbidopa. A levodopa/carbidopa formulation is available commercially as SINEMET® (Merck & Co.). Benserazide and levodopa/benserazide formulations are available commercially from multiple sources (e.g., TEVA Pharmaceuticals).

[0075] In some embodiments, the method further comprises administering an effective amount of a monoamine oxidase (MAO-B) inhibitor. Examples of monoamine oxidase (MAO-B) inhibitors include rasagiline (Azilect®, TEVA Pharmaceuticals) and selegiline (Eldepryl®, Somerset Pharmaceuticals Inc.; Zelapar®, Valeant Pharmaceuticals).

[0076] In some embodiments, the method further comprises administering an effective amount of a catechol-O-methyltransferase (COMT) inhibitor. Examples of catechol-O- methyltransferase (COMT) inhibitors include tolcapone (Tasmar®, available from Valeant Pharmaceuticals) and entacapone (Comtan®, available from Novartis).

[0077] In some embodiments, the method for treating Parkinson's disease or

Parkinsonism further comprises administering effective amounts of benserazide and a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the method for treating Parkinson's disease or Parkinsonism further comprises administering effective amounts of benserazide and a catechol-O-methyltransferase (COMT) inhibitor.

[0078] In some embodiments, the method further comprises administering an effective amount of a dopamine agonist. Examples of dopamine agonists include pramipexole (Mirapex®, available from Boehringer Ingelheim), ropinirole (Requip®, available from GlaxoSmithLine), and rotigotine (Neupro® patch, available from UCB). [0079] In some embodiments, the method further comprises administering an effective amount of an A₂A antagonist. An example of an A₂A antagonist is istradefylline (KW-6002®, available from Kyowa Pharmaceutical).

[0080] In some embodiments, L-dopa is administered in an amount that is lower than a therapeutically effective amount of L-dopa when administered as a sole therapeutic agent for the treatment of Parkinson's disease or Parkinsonism, or when administered in combination with benserazide for the treatment of Parkinson's disease or Parkinsonism, or when administered in combination with carbidopa for the treatment of Parkinson's disease or Parkinsonism.

[0081] In another aspect, the invention provides a method for treating Parkinson's disease or Parkinsonism in a patient in need thereof, the method comprising administering to the human: (a) an effective amount of L-dopa and (b) an effective amount of a phosphodiesterase 9 inhibitor.

[0082] In some embodiments, the method further comprises administering an effective amount of a dopa-decarboxylase (DDC) inhibitor. In some embodiments, the dopa- decarboxylase (DDC) inhibitor is benserazide or carbidopa.

[0083] In some embodiments, the phosphodiesterase 9 inhibitor is (+)-2-((3S,4S)-4- methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

[0084] Ameliorating or reducing the symptoms can be manifested in a variety of ways, for example, by improvement in motor function. Such improvement can be assessed relative to the motor function of the subject prior to being treated or being administered a

combination of a PDE9 inhibitor and L-dopa or being administered a pharmaceutical composition comprising an effective amount of a PDE9 inhibitor and L-dopa. Improvement in motor function can be also be assessed by using motor disability scores (MDS) wherein motor evaluations are performed live by trained examiners using a standardized primate motor scale for MPTP treated monkeys (Papa et al., Ann. Neurol. 1996, 39, 574-578). Motor disability scores (MDS) can be obtained prior to being administered a combination of a PDE9 inhibitor and L-dopa or being administered a pharmaceutical composition comprising an effective amount of a PDE9 inhibitor and L-dopa, at a fixed time after administration, and at regular intervals thereafter or until symptoms are no longer present. Examiners are blinded to the treatment and the PDE9 inhibitor dose during testing.

[0085] Exemplary symptoms of Parkinson's disease or Parkinsonism include, but are not limited to, shaking, rigidity, slowness of movement, and difficulty with walking and gait. As the symptomatic period advances, the severity of symptoms increase, there is an onset of motor complications of L-dopa therapy, and core motor features are progressively

overshadowed by non-motor symptoms. Motor complications of L-dopa therapy include motor fluctuations and dyskinesia. Thus, symptoms of Parkinson's disease or Parkinsonism also include motor fluctuations and dyskinesia. Exemplary symptoms of Parkisonism include bradykinesia, resting tremor, rigidity, and postural instability, bradykinesia, resting tremor, rigidity, and postural instability. Administration of a PDE9 inhibitor and L-dopa, optionally in combination with a DDC inhibitor, can reduce or improve one or more of these symptoms.

[0086] Parkinsonism includes atypical parkinsonism and parkinson-plus syndromes, drug-induced Parkinsonism and vascular parkinsonism (arteriosclerotic pseudoparkinsonism).

[0087] Additional central nervous system disorders that can be treated with the methods and compositions described herein include, but are not limited to, Angelman syndrome (AS), restless leg syndrome (RLS), dopamine -responsive dystonia (DRD), and periodic limb movement disorder (PLMD).

5.5 Administration, Dosing, and Pharmaceutical Compositions Comprising L-dopa and a PDE9 inhibitor

[0088] In accordance with the methods described herein, the compositions described herein are administered to the patient in an amount effective for treating Parkinson's disease or Parkinsonism, which include ameliorating one or more symptoms of Parkinson's disease or Parkinsonism. The precise dose to be employed can be determined by standard clinical techniques. In addition, in vivo assays can optionally be employed to help identify optimal dosage ranges. The skilled practitioner can adjust the amount and timing of administration on the basis of observations of one or more symptoms. The precise dose to be employed can also depend on the route of administration, and the seriousness of the condition being treated and can be decided according to the judgment of a health-care practitioner and each patient's circumstances. In some embodiments, the composition is suitable for oral administration. In some embodiments, the composition is suitable for intravenous administration.

[0089] Several formulations of levodopa (L-dopa) are available for oral administration: levodopa in combination with a dopa decarboxylase inhibitor, levodopa in combination with a dopa decarboxylase inhibitor and a catechol-O-methyltransferase inhibitor, slow-release levodopa in combination with a dopa decarboxylase inhibitor, and levodopa/dopa

decarboxylase inhibitor dispersible tablets. L-dopa is commonly administered as a combination of carbidopa and levodopa. The combination is available as "25-100", containing 25 mg of carbidopa and 100 mg of levodopa, "10-100", containing 10 mg of carbidopa and 100 mg of levodopa, or "25-250", containing 25 mg of carbidopa and 250 mg of levodopa. The optimum daily dosage of carbidopa-levodopa is determined by careful titration in each patient.

[0090] In some embodiments, the effective amount of L-dopa is a suboptimal dose. In some embodiments, the sub-optimal dose is determined by titration in the patient.

[0091] In some embodiments, L-dopa is administered in an amount that is lower than a therapeutically effective amount of L-dopa when administered as a sole therapeutic agent for the treatment of Parkinson's disease or Parkinsonism. In some embodiments, L-dopa is administered in an amount that is lower than a therapeutically effective amount of L-dopa when administered with benserazide for the treatment of Parkinson's disease or

Parkinsonism. In some embodiments, L-dopa is administered in an amount that is lower than a therapeutically effective amount of L-dopa when administered with carbidopa for the treatment of Parkinson's disease or Parkinsonism.

[0092] The amount of L-dopa that is effective for treating Parkinson's disease or

Parkinsonism is in the range of about 300-600 mg/day. Suitable lower doses of L-dopa are in the range of about 25-200 mg/day. In some embodiments, suitable lower doses of L-dopa are in the range of about 25-200 mg/day, about 25-150 mg/day or about 50-100 mg/day.

[0093] In some embodiments, the effective amount of the PDE9 inhibitor is in the range of about 0.1 mg to about 10 mg/kg, about 0.1 mg to about 6 mg/kg, about 0.1 mg to about 4 mg /kg, or about 0.1 mg to about 2 mg/kg of the patient's body weight. In some

embodiments, the effective amount of the PDE9 inhibitor is 0.1 mg/kg, 0.2 mg/kg, 0.25 mg/kg, 0.5 mg/kg, 0.75 mg/kg, 1 mg/kg, 1.25 mg/kg, 1.5 mg/kg, 1.75 mg/kg, 2 mg/kg, 3 mg/kg, 4 mg/kg, 5 mg/kg, 6 mg/kg, 7 mg/kg, 8 mg/kg, 9 mg/kg, 10 mg/kg, 11 mg/kg, 12 mg/kg, 13 mg/kg, 14 mg/kg, 15 mg/kg, 16 mg/kg, 17 mg/kg, 18 mg/kg, 19 mg/kg or 20 mg/kg of the patient's body weight.

[0094] In some embodiments the effective amount of the PDE9 inhibitor is in the range of about 1 to 500 mg, about 2 to 150 mg, about 2 to 120 mg, about 2 to 80 mg, about 2 to 40 mg, about 5 to 150 mg, about 5 to 120 mg, about 5 to 80 mg, about 10 to 150 mg, about 10 to 120 mg, about 10 to 80 mg, about 10 to 40 mg, about 20 to 150 mg, about 20 to 120 mg, about 20 to 80 mg, about 20 to 40 mg, about 40 to 150 mg, about 40 to 120 mg or about 40 to 80 mg. In some embodiments the effective amount of the PDE9 inhibitor is 0.25 mg, 0.5 mg, 0.75 mg, 1 mg, 1.5 mg, 2 mg, 4 mg, 4 mg, 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, 30 mg, 35 mg, 40 mg, 50 mg, 60 mg, 70 mg, 75 mg, 80 mg, 90 mg, 100 mg, 125 mg, 150 mg, 175 mg, 200 mg, 250 mg, 300 mg, 400 mg, 500 mg, 750 mg or 1,000 mg.

[0095] The effective amount of the PDE9 inhibitor is any amount that is necessary or sufficient for treating Parkinson's disease or Parkinsonism. In some instances an effective amount is a therapeutically effective amount. A therapeutically effective amount is any amount that is necessary or sufficient for treating Parkinson's disease or Parkinsonism in a subject. The effective amount for any particular application can vary depending on such factors as the disease or condition being treated, the particular agent being administered, the size of the subject, or the severity of the disease or condition. The effective amount of the PDE9 inhibitor can also vary depending on whether the PDE9 inhibitor is administered with L-dopa in combination with benserazide, whether the PDE9 inhibitor is administered with L- dopa in combination with carbidopa, whether the PDE9 inhibitor is administered with L-dopa in combination with a monoamine oxidase type B inhibitor, or whether the PDE9 inhibitor is administered with L-dopa in combination with a catechol-O-methyl transferase inhibitor. The effective amount of the PDE9 inhibitor can further vary depending on whether the PDE9 inhibitor is administered with L-dopa in combination with carbidopa and a monoamine oxidase type B inhibitor, with L-dopa in combination with carbidopa and a catechol-O- methyl transferase inhibitor, with L-dopa in combination with benserazide and a monoamine oxidase type B inhibitor, or with L-dopa in combination with benserazide and a catechol-O- methyl transferase inhibitor.

[0096] The amount of a dopa-decarboxylase (DDC) inhibitor, e.g., benserazide or carbidopa, that is effective for treating Parkinson's Disease or Parkinsonism is in the range of about 1-500 mg/day. In some embodiments the effective amount of a dopa-decarboxylase (DDC) inhibitor is in the range of about 1 to 500 mg, about 2 to 150 mg, about 2 to 120 mg, about 2 to 80 mg, about 2 to 40 mg, about 5 to 150 mg, about 5 to 120 mg, about 5 to 80 mg, about 10 to 150 mg, about 10 to 120 mg, about 10 to 80 mg, about 10 to 40 mg, about 20 to 150 mg, about 20 to 120 mg, about 20 to 80 mg, about 20 to 40 mg, about 40 to 150 mg, about 40 to 120 mg or about 40 to 80 mg. Exemplary effective doses of carbidopa include, but are not limited to, 10 mg, 15 mg, 20 mg, and 25 mg. Exemplary effective doses of benserazide include, but are not limited to, 1 mg, 2 mg, 3 mg, 4 mg, 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, 50 mg, 60 mg, 70 mg, 80 mg and 100 mg.

[0097] In some embodiments the effective amount of a monoamine oxidase (MAO-B) inhibitor, e.g., rasagiline or selegiline, is in the range of about 1 to 500 mg, about 2 to 150 mg, about 2 to 120 mg, about 2 to 80 mg, about 2 to 40 mg, about 5 to 150 mg, about 5 to 120 mg, about 5 to 80 mg, about 10 to 150 mg, about 10 to 120 mg, about 10 to 80 mg, about 10 to 40 mg, about 20 to 150 mg, about 20 to 120 mg, about 20 to 80 mg, about 20 to 40 mg, about 40 to 150 mg, about 40 to 120 mg or about 40 to 80 mg. In some embodiments the effective amount of the monoamine oxidase (MAO-B) inhibitor is 0.25 mg, 0.5 mg, 0.75 mg,

1 mg, 1.5 mg, 2 mg, 4 mg, 4 mg, 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, 30 mg, 35 mg, 40 mg, 50 mg, 60 mg, 70 mg, 75 mg, 80 mg, 90 mg, 100 mg, 125 mg, 150 mg, 175 mg, 200 mg, 250 mg, 300 mg, 400 mg, 500 mg, 750 mg or 1,000 mg.

[0098] In some embodiments the effective amount of a catechol-O-methyltransferase (COMT) inhibitor, e.g., tolcapone or entacapone, is in the range of about 1 to 500 mg, about

2 to 150 mg, about 2 to 120 mg, about 2 to 80 mg, about 2 to 40 mg, about 5 to 150 mg, about 5 to 120 mg, about 5 to 80 mg, about 10 to 150 mg, about 10 to 120 mg, about 10 to 80 mg, about 10 to 40 mg, about 20 to 150 mg, about 20 to 120 mg, about 20 to 80 mg, about 20 to 40 mg, about 40 to 150 mg, about 40 to 120 mg or about 40 to 80 mg. In some

embodiments the effective amount of the catechol-O-methyltransferase (COMT) inhibitor is 0.25 mg, 0.5 mg, 0.75 mg, 1 mg, 1.5 mg, 2 mg, 4 mg, 4 mg, 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, 30 mg, 35 mg, 40 mg, 50 mg, 60 mg, 70 mg, 75 mg, 80 mg, 90 mg, 100 mg, 125 mg, 150 mg, 175 mg, 200 mg, 250 mg, 300 mg, 400 mg, 500 mg, 750 mg or 1,000 mg.

[0099] The PDE9 inhibitor or pharmaceutically acceptable salts thereof and L-dopa can be administered at different times or at the same time. In some embodiments, L-dopa and the PDE9 inhibitor are administered simultaneously. In some embodiments, L-dopa and the PDE9 inhibitor are administered sequentially. In some embodiments, L-dopa is administered prior to administration of the PDE9 inhibitor. In some embodiments, the PDE9 inhibitor is administered prior to administration of L-dopa. When a dopa-decarboxylase (DDC) inhibitor is administered in addition to the PDE9 inhibitor and L-dopa, it can be administered before, after or concurrently with either the PDE9 inhibitor and/or L-dopa.

[0100] L-dopa, PDE9 inhibitor and/or dopa-decarboxylase (DDC) inhibitor can each independently be administered to the patient once, twice, three times, four times, five times, six times, 8 times or 12 times a day.

[0101] The methods described herein can further comprise administering an effective amount of another therapeutic agent, that is, the pharmaceutical compositions described herein can be administered concurrently with, prior to, or subsequent to, one or more other desired therapeutics or medical procedures. The particular combination of therapies

(therapeutics or procedures) to employ in a combination regimen will take into account compatibility of the desired therapeutics and/or procedures and the desired therapeutic effect to be achieved. In some embodiments, the methods described herein can further comprise administering an effective amount of a dopa-decarboxylase (DDC) inhibitor such as benserazide or carbidopa. In some embodiments, the methods described herein further comprise administering an effective amount of a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the methods described herein further comprise administering an effective amount of a catechol-O-methyltransferase (COMT) inhibitor. In some embodiments, the methods described herein further comprise administering effective amounts of benserazide and a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the methods described herein further comprise administering effective amounts of benserazide and a catechol-O- methyltransferase (COMT) inhibitor. In some embodiments, the methods described herein further comprise administering effective amounts of carbidopa and a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the methods described herein further comprise administering effective amounts of carbidopa and a catechol-O-methyltransferase (COMT) inhibitor.

[0102] When a monoamine oxidase (MAO-B) inhibitor or a catechol-O- methyltransferase (COMT) inhibitor is administered in addition to the PDE9 inhibitor and L- dopa, it can be administered before, after or concurrently with either the PDE9 inhibitor and/or L-dopa. When a monoamine oxidase (MAO-B) inhibitor or a catechol-O- methyltransferase (COMT) inhibitor is administered in addition to the PDE9 inhibitor, L- dopa and a dopa-decarboxylase (DDC) inhibitor, it can be administered before, after or concurrently with the PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor.

[0103] Details on techniques for formulation and administration are well described in the scientific and patent literature, see, e.g., Remington: The Science and Practice of Pharmacy (2 Volumes), (22nd Edition, 2012), Pharmaceutical Press ("Remington's").

[0104] After a pharmaceutical composition has been formulated in an acceptable carrier, it can be placed in an appropriate container and labeled for treatment of an indicated condition. Such labeling would include, e.g., instructions concerning the amount, frequency, and method of administration.

[0105] In another aspect, the present disclosure provides pharmaceutical compositions useful in treating central nervous disorders, such as Parkinson's disease or Parkinsonism. Such compositions comprise L-dopa, a PDE9 inhibitor, and a pharmaceutically acceptable carrier or vehicle. [0106] Pharmaceutical compositions may conveniently be presented in unit dosage form and may be prepared by any methods well known in the art of pharmacy. The amount of active ingredient which can be combined with a carrier material to produce a single dosage form will vary depending upon the subject being treated, the particular mode of

administration. The amount of active ingredient, which can be combined with a carrier or vehicle material to produce a single dosage form will generally be that amount of the compound which produces a therapeutic effect. Generally, out of 100%, this amount will range from about 1% to about 99% of active ingredient, preferably from about 5% to about 70%, most preferably from about 10% to about 30%.

[0107] The pharmaceutical compositions described herein can be employed in combination with other therapies, that is, the pharmaceutical compositions can be

administered concurrently with, prior to, or subsequent to, one or more other desired therapeutics or medical procedures. The particular combination of therapies (therapeutics or procedures) to employ in a combination regimen will take into account compatibility of the desired therapeutics and/or procedures and the desired therapeutic effect to be achieved.

[0108] In some embodiments, the pharmaceutical composition described herein further comprises a dopa-decarboxylase (DDC) inhibitor such as benserazide or carbidopa. In some embodiments, the composition further comprises a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the compositions further comprises a catechol-O-methyltransferase (COMT) inhibitor. In some embodiments, the composition further comprises benserazide and a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the composition further comprises benserazide and a catechol-O-methyltransferase (COMT) inhibitor. In some embodiments, the composition further comprises carbidopa and a monoamine oxidase (MAO-B) inhibitor. In some embodiments, the composition further comprises carbidopa and a catechol-O-methyltransferase (COMT) inhibitor.

[0109] In some embodiments, the PDE9 inhibitor of the composition is (+)-2-((3S,4S)-4- methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof. In some

embodiments, the PDE9 inhibitor of the composition is BAY 73-6691, 28s, PF-4181366, BI 409306, or PF-04447943.

[0110] Methods of preparing these compositions include the step of bringing into association a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor a with the carrier and, optionally, one or more accessory ingredients. In general, the compositions are prepared by uniformly and intimately bringing into association a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor with liquid carriers, or finely divided solid carriers, or both, and then, if necessary, shaping the product.

[0111] When a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor are administered as pharmaceuticals to humans, they can independently be given per se or as a pharmaceutical composition containing, for example, 0.1% to 99.5% (more preferably, 0.5% to 90%) of active ingredient in combination with a pharmaceutically acceptable carrier or vehicle.

[0112] The pharmaceutical compositions described herein can be administered in a variety of dosage forms including, but not limited to, a solid dosage form, a liquid dosage form, an oral dosage form, a parenteral dosage form, an intranasal dosage form, a suppository, a lozenge, a troche, a buccal dosage form, a controlled release dosage form, a pulsed release dosage form, an immediate release dosage form, an intravenous solution, a suspension or combinations thereof. In some embodiments, the composition is a solid oral dosage form. In some embodiments, the solid oral dosage form is a tablet, a capsule, or a softgel.

Oral Formulations and Administration

[0113] Pharmaceutical compositions described herein suitable for oral administration can be in the form of capsules, cachets, pills, tablets, caplet, lozenges (using a flavored basis, usually sucrose and acacia or tragacanth), powders, granules, or as a solution or a suspension in an aqueous or non-aqueous liquid, or as an oil-in-water or water-in-oil liquid emulsion, or as an elixir or syrup, or as pastilles (using an inert base, such as gelatin and glycerin, or sucrose and acacia) and/or as mouthwashes and the like, each containing a predetermined amount of a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor described herein as an active ingredient. The dosage can be an oral dosage form that is a controlled release dosage form.

[0114] In some embodiments, the solid dosage form comprises both the PDE9 inhibitor and L-dopa, optionally with a dopa-decarboxylase (DDC) inhibitor. In some embodiments, the solid dosage form comprises the PDE9 inhibitor and a separate solid dosage form comprises L-dopa. An example of a separate solid dosage form that comprises L-dopa is the commercially available L-dopa/carbidopa formulation such as SINEMET® (Merck & Co.).

[0115] In solid dosage forms described herein for oral administration (capsules, tablets, pills, dragees, powders, granules and the like), the active ingredient is mixed with one or more pharmaceutically acceptable carriers and/or any of the following: fillers or extenders, such as starches, lactose, sucrose, glucose, mannitol, and/or silicic acid; binders, such as, for example, carboxymethylcellulose, alginates, gelatin, polyvinyl pyrrolidone, sucrose and/or acacia; humectants, such as glycerol; disintegrating agents, such as agar-agar, calcium carbonate, potato or tapioca starch, alginic acid, certain silicates, sodium carbonate, and sodium starch glycolate; solution retarding agents, such as paraffin; absorption accelerators, such as quaternary ammonium compounds; wetting agents, such as, for example, cetyl alcohol, glycerol monostearate, and polyethylene oxide-polybutylene oxide copolymer; absorbents, such as kaolin and bentonite clay; lubricants, such a talc, calcium stearate, magnesium stearate, solid polyethylene glycols, sodium lauryl sulfate, and mixtures thereof; and coloring agents. In the case of capsules, tablets and pills, the pharmaceutical compositions can also comprise buffering agents. Solid compositions of a similar type can also be employed as fillers in soft and hard-filled gelatin capsules using such excipients as lactose or milk sugars, as well as high molecular weight polyethylene glycols and the like.

[0116] A tablet can be made by compression or molding, optionally with one or more accessory ingredients. Compressed tablets can be prepared using a binder (for example, gelatin or hydroxybutylmethyl cellulose), lubricant, inert diluent, preservative, disintegrant (for example, sodium starch glycolate or cross-linked sodium carboxymethyl cellulose), surface-active or dispersing agent. Molded tablets can be made by molding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent.

[0117] Tablets, and other solid dosage forms of the pharmaceutical compositions described herein, such as dragees, capsules, pills and granules, can optionally be scored or prepared with coatings and shells, such as enteric coatings and other coatings well known in the pharmaceutical-formulating art. They can also be formulated so as to provide slow or controlled release of the active ingredient therein using, for example, hydroxybutylmethyl cellulose in varying proportions to provide the desired release profile, other polymer matrices, liposomes and/or microspheres. They can be sterilized by, for example, filtration through a bacteria-retaining filter, or by incorporating sterilizing agents in the form of sterile solid compositions, which can be dissolved in sterile water, or some other sterile injectable medium immediately before use. These compositions can also optionally contain opacifying agents and may be of a composition that they release the active ingredient(s) only, or preferentially, in a certain portion of the gastrointestinal tract, optionally, in a delayed manner. Examples of embedding compositions which can be used include polymeric substances and waxes. The active ingredient can also be in micro-encapsulated form, if appropriate, with one or more of the above-described excipients. [0118] Capsules for oral use include hard gelatin capsules in which the active ingredient is mixed with a solid diluent, and soft gelatin capsules, wherein the active ingredients is mixed with water or an oil, such as peanut oil, liquid paraffin or olive oil.

[0119] Dragee cores are provided with suitable coatings. For this purpose, concentrated sugar solutions may be used, which may optionally contain gum arabic, talc, polyvinyl pyrrolidone, carbopol gel, polyethylene glycol, and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. Dyestuffs or pigments can be added to the tablets or dragee coatings for identification or to characterize different combinations of active compound doses.

[0120] Liquid dosage forms for oral administration of the pharmaceutical compositions described herein include pharmaceutically acceptable emulsions, microemulsions, solutions, suspensions, syrups and elixirs. In addition to the active ingredient, the liquid dosage forms may contain inert diluents commonly used in the art, such as, for example, water or other solvents, solubilizing agents and emulsifiers, such as ethyl alcohol, isobutyl alcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzyl benzoate, butylene glycol, 1,3-butylene glycol, oils (in particular, cottonseed, groundnut, corn, germ, olive, castor and sesame oils), glycerol, tetrahydrofuryl alcohol, polyethylene glycols and fatty acid esters of sorbitan, and mixtures thereof. Additionally, cyclodextrins, e.g., hydroxybutyl- -cyclodextrin, may be used to solubilize compounds.

[0121] Suspensions, in addition to the active compounds, can contain suspending agents as, for example, ethoxylated isostearyl alcohols, polyoxyethylene sorbitol and sorbitan esters, microcrystalline cellulose, aluminum metahydroxide, bentonite, agar and tragacanth, and mixtures thereof.

[0122] Besides inert diluents, the oral compositions can also include adjuvants, such as wetting agents, emulsifying and suspending agents, sweetening, flavoring, coloring, perfuming and preservative agents.

[0123] Pharmaceutical preparations for oral use can be obtained through combination of a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor with a solid excipient, optionally grinding a resultant mixture, and processing the mixture of granules, after adding suitable additional compounds, if desired, to obtain tablets or dragee cores. Suitable solid excipients in addition to those previously mentioned are carbohydrate or protein fillers that include, but are not limited to, sugars, including lactose, sucrose, mannitol, or sorbitol; starch from corn, wheat, rice, potato, or other plants; cellulose, such as methyl cellulose, hydroxypropylmethyl-cellulose or sodium carboxymethylcellulose; and gums including arabic and tragacanth; as well as proteins, such as gelatin and collagen. If desired, disintegrating or solubilizing agents can be added, such as the cross-linked polyvinyl pyrrolidone, agar, alginic acid, or a salt thereof, such as sodium alginate.

[0124] Pharmaceutical preparations for oral use can be presented as aqueous or liposome formulations. Aqueous suspensions can contain a PDE9 inhibitor, L-dopa and/or dopa- decarboxylase (DDC) inhibitor in admixture with excipients suitable for the manufacture of aqueous suspensions. Such excipients include a suspending agent, such as sodium carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia, and dispersing or wetting agents, such as a naturally occurring phosphatide (e.g., lecithin), a condensation product of an alkylene oxide with a fatty acid (e.g., polyoxyethylene stearate), a condensation product of ethylene oxide with a long chain aliphatic alcohol (e.g., heptadecaethylene oxycetanol), a

condensation product of ethylene oxide with a partial ester derived from a fatty acid and a hexitol (e.g., polyoxyethylene sorbitol mono-oleate), or a condensation product of ethylene oxide with a partial ester derived from fatty acid and a hexitol anhydride (e.g.,

polyoxyethylene sorbitan mono-oleate). The aqueous suspension can also contain one or more preservatives, such as ethyl or n-propyl p-hydroxybenzoate, one or more coloring agents, one or more flavoring agents and one or more sweetening agents, such as sucrose, aspartame or saccharin. Formulations can be adjusted for osmolarity.

[0125] Oil suspensions can be formulated by suspending a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor in a vegetable oil, such as arachis oil, olive oil, sesame oil or coconut oil, or in a mineral oil, such as liquid paraffin; or a mixture of these. The oil suspensions can contain a thickening agent, such as beeswax, hard paraffin or cetyl alcohol. Sweetening agents can be added to provide a palatable oral preparation, such as glycerol, sorbitol or sucrose. These formulations can be preserved by the addition of an antioxidant, such as ascorbic acid. As an example of an injectable oil vehicle, see Minto, J. Pharmacol. Exp. Ther. 281:93-102, 1997. The pharmaceutical formulations can also be in the form of oil-in- water emulsions. The oily phase can be a vegetable oil or a mineral oil, described above, or a mixture of these. Suitable emulsifying agents include naturally- occurring gums, such as gum acacia and gum tragacanth, naturally occurring phosphatides, such as soybean lecithin, esters or partial esters derived from fatty acids and hexitol anhydrides, such as sorbitan mono-oleate, and condensation products of these partial esters with ethylene oxide, such as polyoxyethylene sorbitan mono-oleate. The emulsion can also contain sweetening agents and flavoring agents, as in the formulation of syrups and elixirs. Such formulations can also contain a demulcent, a preservative, or a coloring agent.

Parenteral Formulations and Administration

[0126] The PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor can independently or jointly be administered parenterally, such as by intravenous (IV) or intramuscular (IM) administration. The formulations for administration will commonly comprise a solution of a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor dissolved in a pharmaceutically acceptable carrier. Administration of a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor to any of the above mentioned sites can be achieved by direct injection of the pharmaceutical composition comprising the PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor or by the use of infusion pumps. The pharmaceutical compositions can be formulated in solid form and re-dissolved or suspended immediately prior to use. Lyophilized forms are also included. The injection can be, for example, in the form of a bolus injection or continuous infusion (e.g., using infusion pumps) of pharmaceutical composition.

[0127] Pharmaceutical compositions suitable for parenteral administration can comprise a PDE9 inhibitor, L-dopa and/or a dopa-decarboxylase (DDC) inhibitor in combination with one or more pharmaceutically acceptable sterile isotonic aqueous or nonaqueous solutions, dispersions, suspensions or emulsions, or sterile powders which may be reconstituted into sterile injectable solutions or dispersions just prior to use, which may contain antioxidants, buffers, bacteriostats, solutes which render the formulation isotonic with the blood of the intended recipient or suspending or thickening agents.

[0128] Among the acceptable vehicles and solvents that can be employed for formulation and/or reconstitution are water (e.g., water for injection) and Ringer's solution, an isotonic sodium chloride. In addition, sterile fixed oils can conventionally be employed as a solvent or suspending medium. For this purpose, any bland fixed oil can be employed including synthetic mono- or diglycerides. In addition, fatty acids, such as oleic acid can likewise be used in the preparation of injectables. These solutions are sterile and generally free of undesirable matter. These formulations may be sterilized by conventional, well known sterilization techniques such as gamma-radiation or electron beam sterilization. The formulations can contain pharmaceutically acceptable auxiliary substances as required to approximate physiological conditions, such as pH adjusting and buffering agents, toxicity adjusting agents, e.g., sodium acetate, sodium chloride, potassium chloride, calcium chloride, sodium lactate and the like. The concentration of a PDE9 inhibitor, L-dopa and/or a dopa- decarboxylase (DDC) inhibitor in these formulations can vary widely, and will be selected primarily based on fluid volumes, viscosities, body weight, and the like, in accordance with the particular mode of administration selected and the subject's needs. For IV administration, the formulation can be a sterile injectable preparation, such as a sterile injectable aqueous or oleaginous suspension. This suspension can be formulated according to the known art using those suitable dispersing or wetting agents and suspending agents. The sterile injectable preparation can also be a sterile injectable solution or suspension in a nontoxic parenterally- acceptable diluent or solvent, such as a solution of 1,3-butanediol.

5.6 Kits

[0129] Described herein are kits that can simplify the administration of a PDE9 inhibitor and L-dopa to a patient. The kit can comprise one or more containers filled with one or more of the ingredients of the pharmaceutical compositions described herein. Optionally associated with such container(s) can be a notice in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals or biological products, which notice reflects approval by the agency of manufacture, use or sale for human administration.

[0130] An exemplary kit comprises a unit dosage form of a PDE9 inhibitor and a unit dosage form of L-dopa. In one embodiment, the kit comprises: (a) L-dopa and a

pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container. In one embodiment, the kit comprises: (a) L-dopa, carbidopa, and a pharmaceutically acceptable carrier or vehicle in a first container; and (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container. In one embodiment, the kit comprises: (a) L-dopa,

benserazide, and a pharmaceutically acceptable carrier or vehicle in a first container; and (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container. The kit can further comprise a label or printed instructions instructing the use of the PDE9 inhibitor and L-dopa to treat Parkinson's disease. The kit can further comprise a label or printed instructions instructing the use of the PDE9 inhibitor, L-dopa to treat Parkinson's disease or Parkinsonism.

[0131] The kit can also further comprise a unit dosage form of a dopa-decarboxylase (DDC) inhibitor. Such a dopa-decarboxylase (DDC) inhibitor can be present in a third container. Thus, in one embodiment, the kit comprises: (a) L-dopa and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) a dopa-decarboxylase (DDC) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container. Example of a dopa-decarboxylase (DDC) inhibitor include, but are not limited to, benserazide and carbidopa.

[0132] In another embodiment, the kit comprises: (a) L-dopa and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) monoamine oxidase (MAO-B) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container. In another embodiment, the kit comprises: (a) L-dopa and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) catechol-O-methyltransferase (COMT) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container.

[0133] In another embodiment, the kit comprises: (a) L-dopa, benserazide, and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) monoamine oxidase (MAO-B) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container. In another embodiment, the kit comprises: (a) L-dopa, benserazide, and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) catechol-O- methyltransferase (COMT) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container. In another embodiment, the kit comprises: (a) L-dopa, carbidopa, and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) monoamine oxidase (MAO-B) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container. In another embodiment, the kit comprises: (a) L-dopa, carbidopa, and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a PDE9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container, and (c) catechol-O- methyltransferase (COMT) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container.

[0134] The kit can also comprise a unit dosage form of a PDE9 inhibitor and L-dopa. In one embodiment, the kit comprises L-dopa, a PDE9 inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container. The kit can further comprise a label or printed instructions instructing the use of the PDE9 inhibitor and L-dopa to treat Parkinson's disease or Parkinsonism. In one embodiment, the kit comprises L-dopa, a PDE9 inhibitor, a dopa-decarboxylase (DDC) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container.

[0135] In another embodiment, the kit comprises L-dopa, a PDE9 inhibitor, a monoamine oxidase (MAO-B) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container. In another embodiment, the kit comprises L-dopa, a PDE9 inhibitor, a catechol-O- methyltransferase (COMT) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container. In another embodiment, the kit comprises L-dopa, a PDE9 inhibitor, benserazide, a monoamine oxidase (MAO-B) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container. In another embodiment, the kit comprises L-dopa, a PDE9 inhibitor, benserazide, a catechol-O-methyltransferase (COMT) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container. In another embodiment, the kit comprises L-dopa, a PDE9 inhibitor, carbidopa, a monoamine oxidase (MAO-B) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container. In another embodiment, the kit comprises L-dopa, a PDE9 inhibitor, carbidopa, a catechol-O- methyltransferase (COMT) inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container.

[0136] In some embodiments, the kit further comprises a monoamine oxidase (MAO-B) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container.

[0137] In some embodiments, the kit further comprises a catechol-O-methyltransferase (COMT) inhibitor and a pharmaceutically acceptable carrier or vehicle in a third container.

[0138] In another aspect, the invention provides a kit comprising: (a) L-dopa, a phosphodiesterase 9 inhibitor, and a pharmaceutically acceptable carrier or vehicle in a single container; and (b) instructions for use.

[0139] In some embodiments, the kit further comprises a dopa-decarboxylase (DDC) inhibitor in the single container.

[0140] In some embodiments, the dopa-decarboxylase (DDC) inhibitor is carbidopa or benserazide.

[0141] In some embodiments, the kit further comprises a monoamine oxidase (MAO-B) inhibitor in the single container.

[0142] In some embodiments, the kit further comprises a catechol-O-methyltransferase (COMT) inhibitor in the single container. [0143] The representative examples which follow are intended to help illustrate the invention, and are not intended to, nor should they be construed to, limit the scope of the invention. Indeed, various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including the examples which follow and the references to the scientific and patent literature cited herein. It should further be appreciated that the contents of those cited references are incorporated herein by reference to help illustrate the state of the art. The following examples contain additional information, exemplification and guidance which can be adapted to the practice of this invention in its various embodiments and equivalents thereof. The examples do not limit the scope of the invention described in the claims.

6. EXAMPLES Example 1

[0144] Non-Human Primate Model. The l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP) primate models of Parkinson's disease reproduce most, but not all, of the clinical and pathological hallmarks of Parkinson's disease and is the model of choice in translational research for Parkinson's disease (Porras et al., Cold Spring Harb. Perspect. Med. 2012, 2:a009308). Six adult monkeys (Macaca fascicularis, 2 female and 4 male) were rendered parkinsonian by repeated systemic l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP) administration (Cao et al. /. Pharmacol. Exp. Ther. 2007, 323, 318-326). After stabilization of parkinsonian motor disability, all monkeys received oral L-dopa/carbidopa SINEMET® 25/100, Merck & Co.) 1 to 4 times daily as maintenance treatment and gradually developed dyskinesia. Oral L-dopa doses were determined individually according to the animal's sensitivity to produce an acceptable "on" state regarding mobility and function. After L- dopa-induced dyskinesia (LID) was fully developed and stabilized with chronic oral SINEMET® administration, optimal subcutaneous (s.c.) dose of L-dopa methyl ester plus benserazide (one quarter of L-dopa dose; both from Sigma- Aldrich, St Louis, MO) was determined for each animal based on their response to repeated tests of various doses. This optimal injectable L-dopa dose, which was defined as the lowest dose that induced a satisfactory "on response" (> 50% improvement) with clear dyskinesias. Based on this the threshold and sub-optimal L-dopa doses were determined for each animal. [0145] PDE9 Inhibitor Tests. All tests were performed after overnight fast and at least 48 hours apart to ensure adequate washout of Compound A ((+)-2-((3S,4S)-4-methyl-l- (pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4-yl)imidazo[5,l- f][l,2,4]triazin-4(3H)-one). SINEMET® maintenance treatment was withheld on all test days. During co-administration tests, Compound A was injected immediately before L-dopa methyl ester. Compound A doses were tested in random order, and each dose was repeated at least 3 times. Data were averaged to yield a mean of at least 3 values for each dose in each monkey.

[0146] On test days, Compound A alone at 0 (control saline injection) or 2.5 - 7.5 mg/kg s.c. (Compound A, dissolved in saline) in combination with either of two s.c. doses of L-dopa methyl ester plus benserazide (threshold and sub-optimal doses). Behavioral assessments were done to evaluate the effects of Compound A on the antiparkinsonian action of L-dopa.

[0147] Behavioral Evaluations. Motor evaluations were performed live by trained examiners using a standardized primate motor scale for MPTP treated monkeys (Papa et al., Ann. Neurol.1996, 39, 574-578). Motor disability scores (MDS) were obtained prior to drug treatment (time 0,"off ' state), 30 minutes after injection(s), and again every 20 minutes thereafter for 180 minutes or until dyskinesias were no longer present. Examiners were blinded to the treatment and dose of Compound A during testing.

[0148] Statistical Analysis. Behavioral effects of Compound A were analyzed with 1- or 2- way analysis of variance (ANOVA) for repeated measures with Dunnett post hoc tests. All data were normalized to control values for analysis. Data are presented as means + standard error of the mean. Significance was determined at p<0.05.

[0149] Results. The therapeutic anti-Parkinson's disease action of L-dopa was potentiated by Compound A at all of the doses tested for both threshold and sub-optimal L- dopa conditions (Figures 1A-1B and Figures 2A-2B; p<0.001, respectively). Specifically, Compound A significantly attenuated MDS at all doses tested in both the threshold (Figure 1A; p<0.01) and sub-optimal (Figures 2A; p<0.01) L-dopa conditions compared to saline treatment. Figure 1A is a plot of the motor disability scores (MDS) for parkinsonian monkeys when treated with a threshold dose of L-dopa in combination with varying doses of Compound A, a PDE9 inhibitor. Figure 2A is a plot of the motor disability scores (MDS) for parkinsonian monkeys when treated with a sub-optimal dose of L-dopa in combination with varying doses of Compound A.

[0150] Additionally, Compound A at all doses tested significantly prolonged on time duration in both the threshold (Figure IB; p<0.01) and sub-optimal (Figure 2B; p<0.01) L- dopa conditions compared to saline treatment. Figure IB is a bar graph of the on time duration as a percent of the control for each of the three doses of Compound A (2.5 mg/kg, 5 mg/kg, 7.5 mg/kg) in threshold L-dopa conditions. Figure 2B is a bar graph of the on time duration as a percent of the control for each of the three doses of Compound A (2.5 mg/kg, 5 mg/kg, 7.5 mg/kg) in sub-optimal L-dopa conditions. Overall, these data suggest that PDE9 inhibition with Compound A synergized with the anti-Parkinson's disease action of L-dopa and that PDE9 inhibition may be a therapeutic strategy to extend and smooth responses to L- dopa facilitating the use of lower doses and reducing motor complications.

Example 2

[0151] In separate and repeated tests, blood samples were collected at multiple time points after drug injections for measurement of plasma levels of Compound A and L-dopa. The results in Table I show that Compound A does not interact substantially with L-dopa pharmacokinetics, e.g., as measured by pharmacokinetic parameters Cmax and/or AUClast.

TABLE I

Claims

We claim:

1. A method for treating a central nervous system disorder in a patient in need thereof, the method comprising administering to the patient: (a) an effective amount of L-dopa and (b) an effective amount of a phosphodiesterase 9 inhibitor.

2. The method of claim 1, wherein the central nervous system disorder is Parkinson's

disease or Parkinsonism.

3. The method of any one of claims 1-2, further comprising administering an effective amount of a dopa-decarboxylase (DDC) inhibitor.

4. The method of claim 3, wherein the dopa-decarboxylase (DDC) inhibitor is benserazide or carbidopa.

5. The method of any one of claims 1-4, further comprising administering an effective amount of a monoamine oxidase (MAO-B) inhibitor.

6. The method of any one of claims 1-4, further comprising administering an effective amount of a catechol-O-methyltransferase (COMT) inhibitor.

7. The method of any one of claims 1-6, wherein the phosphodiesterase 9 inhibitor is (+)-2- ((3S,4S)-4-methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4- yl)imidazo[5,l-f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

8. The method of any one of claims 1-6, wherein the phosphodiesterase 9 inhibitor is

-46-

-47-

r pyridyl),

(R 1 = alkyl, cycloalkyl, aryl, heteroaryl; R 2 = heterocycloalkyl),

9. The method of any one of claims 1-8, wherein the effective amount of L-dopa is a suboptimal dose.

10. The method of claim 9, wherein the sub-optimal dose is determined by titration in the patient.

11. The method of any one of claims 1-9, wherein L-dopa and the phosphodiesterase 9

inhibitor are administered simultaneously.

12. The method of any one of claims 1-9, wherein L-dopa and the phosphodiesterase 9

inhibitor are administered sequentially.

13. The method of claim 11, wherein L-dopa is administered prior to administration of the phosphodiesterase 9 inhibitor.

14. The method of claim 11, wherein the phosphodiesterase 9 inhibitor is administered prior to administration of L-dopa.

15. The method of claim 1 or 2, wherein Parkinson's disease is early onset Parkinson's

disease.

16. The method of any one of claims 1-14, wherein the effective amount of the

phosphodiesterase 9 inhibitor is about 1 to about 100 mg.

17. The method of any of claims 1-14, wherein the effective amount of the phosphodiesterase 9 inhibitor is about 5 to about 50 mg.

18. The method of any one of claims 1-14, wherein the effective amount of the

phosphodiesterase 9 inhibitor is about 10 to about 25 mg.

19. The method of any one of claims 1-14, wherein the effective amount of the

phosphodiesterase 9 inhibitor is about 15 to about 20 mg.

20. A method for treating Parkinson's disease or Parkinsonism in a patient in need thereof, the method comprising administering to the human: (a) an effective amount of L-dopa and (b) an effective amount of a phosphodiesterase 9 inhibitor.

21. The method of claim 20, further comprising administering an effective amount of a dopa- decarboxylase (DDC) inhibitor.

22. The method of claim 21, wherein the dopa-decarboxylase (DDC) inhibitor is benserazide or carbidopa.

23. The method of any one of claims 20-22, wherein the phosphodiesterase 9 inhibitor is (+)- 2-((3S,4S)-4-methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H-pyran-4- yl)imidazo[5,l-f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

24. The method of any one of claims 20-23, wherein the effective amount of the

phosphodiesterase 9 inhibitor is about 1 to about 100 mg.

25. The method of any one of claims 20-23, wherein the effective amount of L-dopa is about 25 to about 600 mg.

26. A pharmaceutical composition comprising L-dopa, a phosphodiesterase 9 inhibitor and a pharmaceutically acceptable carrier or vehicle.

27. The composition of claim 19, further comprising benserazide or carbidopa.

28. The composition of claim 19 or 20, further comprising a monoamine oxidase (MAO-B) inhibitor.

29. The composition of claim 19 or 20, further comprising a catechol-O-methyltransferase (COMT) inhibitor.

30. The composition of any one of claims 19-22, wherein the phosphodiesterase 9 inhibitor is (+)-2-((3,4-trans)-4-methyl-l-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl)-7-(tetrahydro-2H- pyran-4-yl)imidazo[5,l-f][l,2,4]triazin-4(3H)-one or a pharmaceutically acceptable salt thereof.

31. The composition of any one of claims 19-22, wherein the phosphodiesterase 9 inhibitor is BAY 73-6691, 28s, PF-04447943, PF-4181366, BI 409306, or a pharmaceutically acceptable salt thereof.

32. The composition any one of claims 19-24, wherein the composition is suitable for oral administration.

33. The composition of claim 25, wherein the composition is in a solid oral dosage form.

34. The composition of claim 26, wherein the solid oral dosage form is a tablet, a capsule, or a softgel.

35. A kit comprising: (a) L-dopa and a pharmaceutically acceptable carrier or vehicle in a first container; (b) a phosphodiesterase 9 inhibitor and a pharmaceutically acceptable carrier or vehicle in a second container; and (c) instructions for use.

36. The kit of claim 28, further comprising dopa-decarboxylase (DDC) inhibitor and a

pharmaceutically acceptable carrier or vehicle in a third container.

37. The kit of claim 29, wherein the dopa-decarboxylase (DDC) inhibitor is carbidopa or benserazide.