R-Trihexyphenidyl for the treatment of movement disorders

Abstract

Compositions and methods for selectively targeting M1 and / or M4 muscarinic receptors, and compositions and methods for treating movement disorders such as dystonia with improved formulations of trihexyphenidyl, particularly compositions comprising high chiral purity R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 407,219, filed September 16, 2022, entitled R-Trihexyphenidyl for the Treatment of Movement Disorders, which is incorporated herein by reference in its entirety.

[0002] Federally sponsored research or development This invention was made with government support under Grant No. T32 HD069038 awarded by the National Institutes of Health. The government has certain rights in this invention.

[0003] FIELD OF THE INVENTION The present invention relates to the treatment of movement disorders by selectively targeting M1 and / or M4 muscarinic receptors, which are preferentially expressed in the central nervous system (CNS), with enantiomerically enriched R-trihexyphenidyl. [Background technology]

[0004] 2. Description of Related Art Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions, resulting in abnormal, often repetitive, movements or postures, or both. Dystonic movements are typically stereotyped, twisting, and may be tremulous. Dystonia is often precipitated or exacerbated by voluntary movements and is accompanied by overflow muscle activity. One of the most common causes of childhood dystonia is neonatal brain injury resulting in cerebral palsy, which affects 3 in 10,000 live births. Dystonia is an underrecognized but major determinant of functional disability in cerebral palsy. There is a significant unmet need for symptomatic treatment options in children with dystonia, particularly those with dystonia secondary to structural brain lesions or metabolic disorders.

[0005] Trihexyphenidyl (THP) is an antispasmodic used to treat stiffness, tremors, spasms, and poor muscle control. THP is an antimuscarinic agent often used to manage Parkinson's disease, among other movement disorders. A racemic mixture of THP (containing both the R- and S-enantiomers in a 50:50 ratio) is currently approved for patients as a generic medication, including for the treatment of dystonia (first approved in 1949). However, its effectiveness for the treatment of dystonia in children with cerebral palsy has been well documented. Furthermore, current treatment protocols are clinically ineffective because trihexyphenidyl's disposition is poorly understood and there are no standardized dosing guidelines, resulting in a wide range of initial dosages. Consequently, clinicians and patients may need considerable trial and error to find an effective dosage for each individual patient. Furthermore, the drug is often associated with intolerable, treatment-limiting side effects, causing patients to discontinue use of the drug even when it otherwise effectively alleviates dystonia. Given the limitations of using the current racemic formulation of THP and the lack of other effective agents for these conditions, there remains a need for improved therapeutic compositions and protocols for treating dystonia in cerebral palsy, Parkinson's disease, and other movement disorders. Summary of the Invention

[0006] Thus, embodiments of the present invention provide a clinically important alternative for the treatment of dystonia and other movement disorders associated with abnormal excitability of striatal cholinergic interneurons. In particular, agents that selectively target M1 and / or M4 receptors, which are preferentially expressed in the CNS, may offer improved efficacy while reducing side effects due to binding to other receptor subtypes (M2, M3, and M5) that are primarily expressed peripherally (outside the CNS). These agents selectively target muscarinic receptors involved in movement disorders, including dystonia, Parkinson's disease, cerebral palsy, and the like, but do not target peripheral muscarinic receptors, which are responsible for many of the side effects of current agents. This could aid in the treatment of people with dystonia or Parkinson's disease, or other conditions that may benefit from inhibiting M1 and / or M4, by providing agents with a more targeted site of action, increased efficacy, and reduced side effects.

[0007] Thus, contemplated herein is a method for treating a movement disorder by administering a therapeutically effective amount of enantiomerically enriched R-trihexyphenidyl (FIG. 1) or a pharmaceutically acceptable salt thereof to a subject in need of such treatment (i.e., a subject suffering from a movement disorder). Preferably, the administered composition contains purified R-trihexyphenidyl, and more preferably is substantially free of S-trihexyphenidyl enantiomers. Enantiomerically enriched or purified R-trihexyphenidyl pharmaceuticals can be used as selective / specific inhibitors of M1 and M4 receptors, allowing for more effective treatment of movement disorders.

[0008] Also described herein is a method for selectively targeting M1 and / or M4 muscarinic receptors in a subject suffering from a movement disorder. The method comprises administering to the subject a therapeutically effective amount of enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof. Preferably, the administered composition comprises purified R-trihexyphenidyl, more preferably substantially free of S-trihexyphenidyl enantiomer.

[0009] Also described herein is a therapeutic composition comprising (consisting essentially of, or consisting of) enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof dispersed in a pharmaceutically acceptable carrier.In one or more embodiments, the therapeutic composition can be in the form of a pharmaceutical dosage form or unit dosage form, such as a tablet, a powder, a gelatin capsule, or a 3-D printed individualized dosage form.

[0010] Advantageously, administering R-trihexyphenidyl as a single enantiomer may be safer and more effective because R-trihexyphenidyl is a more selective / specific inhibitor of M1 and M4 receptors, avoiding the potential side effects caused by S-trihexyphenidyl's indiscriminate interaction with M1-M5 receptors expressed outside the CNS. This is supported by the results and data shown herein that R-trihexyphenidyl enantiomers and S-trihexyphenidyl enantiomers have different inhibitory activities at various muscarinic receptor subtypes, have different clearance pathways, and are metabolized by different drug-metabolizing enzymes, such as cytochrome P450 (CYP). In summary, the embodiments described herein have important pharmacogenomic applications for individualizing drug therapy.

[0011] Also described herein are improved therapeutic methods for treating and managing movement disorders by utilizing factors unique to individual patients to facilitate precision therapy. For example, embodiments described herein include obtaining or identifying a subject's cytochrome P450 genotype (diplotype) or genotype-predicted phenotype for drug metabolism (and drug-drug interactions) to inform treatment and dosing decisions. For example, subjects with reduced CYP2D6 or CYP3A4 / CYP3A5 activity due to genetic mutations (poor metabolizers) or drug-drug interactions are likely candidates for accumulating S-trihexyphenidyl levels and increasing the incidence of side effects. Such subjects are candidates for the recommended use of enantiomer-enriched R-trihexyphenidyl formulations. The method includes obtaining an individual's genotype-predicted CYP450 metabolic phenotype and administering a therapeutically effective amount of enantiomer-enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof to a subject who is a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer. The disclosed embodiments also relate to methods of initiating R-trihexyphenidyl treatment in patients who are CYP2D6 or CYP3A4 / CYP3A5 poor metabolizers.

[0012] Similarly, subjects identified as CYP2C19 fast (or ultrarapid) metabolizers are likely candidates for rapid depletion of R-trihexyphenidyl levels and may be able to tolerate or even require higher initial doses, particularly when treated with an enantiomer-enriched R-trihexyphenidyl formulation. If the subject is also a CYP2D6 or CYP3A4 / CYP3A5 normal or rapid metabolizer, the subject is also likely to be able to tolerate higher doses of the racemic mixture without suffering from side effects due to the S-enantiomer. The method includes obtaining an individual's genotype-predicted CYP450 metabolic phenotype and administering a therapeutically effective amount of enantiomer-enriched R-trihexyphenidyl or the racemic mixture, or a pharmaceutically acceptable salt thereof, to a subject who is a CYP2C19 rapid metabolizer.

[0013] Similarly, this method can be used to treat movement disorders in subjects who are CYP2C19 poor metabolizers.This method includes obtaining the genotype prediction CYP450 metabolic phenotype of individual, and administering a therapeutically effective amount of enantiomer-enriched R-trihexyphenidyl or its pharmaceutically acceptable salt to the subject who is CYP2C19 poor metabolizers, where this therapeutically effective amount is a lower dose of R-trihexyphenidyl compared with standard clinically recommended dose.For example, the effective amount in such individual can be half of standard recommended dose, and preferably this lower dose is 3mg / day to 15mg / day.

[0014] The method disclosed herein can also be used to treat movement disorders in subjects who are CYP2D6 or CYP3A4 / CYP3A5 poor metabolizers, so as to minimize side effects.The method includes obtaining an individual's genotype-predicted CYP450 metabolic phenotype, and administering the initial dose of the racemic mixture of trihexyphenidyl or its pharmaceutically acceptable salt to the subject who is CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer to a reduced amount of less than 1 mg / day, or administering the initial dose of the racemic mixture of trihexyphenidyl or its pharmaceutically acceptable salt to the subject who is CYP2D6 or CYP3A4 / CYP3A5 normal or very rapid metabolizer to a increased amount of more than 6 mg / day, wherein the initial dose is based on the initial dose recommended in the clinical guidelines for trihexyphenidyl.

[0015] The present disclosure also relates to methods of administering to a subject in need thereof an initial dose of an M1 and / or M4 muscarinic receptor inhibitor, wherein the initial dose is based on the initial dose recommended in clinical guidelines for the inhibitor, and the inhibitor is selected from the group consisting of a racemic mixture of trihexyphenidyl, enantiomerically enriched R-trihexyphenidyl, and pharmaceutically acceptable salts thereof. The methods generally involve obtaining the subject's genotype for a panel of cytochrome P450 enzymes, including at least CYP2D6 and / or CYP2C19 alleles, wherein the subject is assigned a metabolic phenotype selected from poor metabolizer, intermediate metabolizer, or very rapid metabolizer for each enzyme based on the number of functional alleles for each cytochrome P450 gene. The method includes administering to the patient an initial dose of the inhibitor, wherein the initial dose is (a) half the initial dose recommended in clinical guidelines when the metabolic phenotype is one or more of CYP2D6 poor metabolizer, CYP2D6 intermediate metabolizer, or CYP2C19 poor metabolizer; or (b) equal to or greater than the initial dose recommended in clinical guidelines when the metabolic phenotype is one or more of CYP2D6 very rapid metabolizer or CYP2C19 very rapid metabolizer.

[0016] Also described herein is a method for reducing side effects from an initial dose of an M1 and / or M4 muscarinic receptor inhibitor in a subject in need thereof, wherein the initial dose is based on an initial dose recommended in clinical guidelines for the inhibitor, and the inhibitor is a racemic mixture of trihexyphenidyl or a pharmaceutically acceptable salt thereof.

[0017] The method includes obtaining a subject's genotype for a panel of cytochrome P450CYP2D6 alleles, wherein the subject is assigned a metabolic phenotype selected from poor metabolizer, intermediate metabolizer, or very rapid metabolizer for CYP2D6 based on the number of functional alleles for CYP2D6.The method includes administering to the patient an initial dose of the inhibitor, wherein (a) if the metabolic phenotype is one or more of CYP2D6 poor metabolizer or CYP2D6 intermediate metabolizer, the initial dose is half the initial dose recommended in clinical guidelines; or (b) if the metabolic phenotype is CYP2D6 very rapid metabolizer, the initial dose is equal to or greater than the initial dose recommended in clinical guidelines.

[0018] Also described herein are medicaments for selectively targeting M1 and / or M4 muscarinic receptors or for treating dystonia in a subject in need thereof, which generally comprise a therapeutic composition comprising enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof according to any one of the embodiments disclosed herein, or a pharmaceutical dosage form according to any one of the embodiments disclosed herein. [Brief explanation of the drawings]

[0019] [Figure 1] Figure 1 shows the molecular structure of trihexyphenidyl, showing a) the location of the chiral center (chiral carbon) and the resulting b) R-enantiomer and c) S-enantiomer, which have the same chemical structure but differ in three-dimensional space. [Figure 2] FIG. 2 presents data identifying the CYP metabolic pathways involved in the biotransformation (metabolism) of R-trihexyphenidyl and S-trihexyphenidyl. [Figure 3]Figure 3 shows the results of in vitro incubations in which R-trihexyphenidyl (1,000 ng / ml) and S-trihexyphenidyl (1,000 ng / ml) were incubated with heterologously expressed CYP2C19, CYP2D6, and CYP3A4, and the metabolites produced indicate that R-THP-M1 is formed almost exclusively by CYP2C19, whereas S-THP-M2 is formed mainly by CYP2D6. [Figure 4-1] Figures 4A-B, 4C-D, and 4E-F illustrate the interindividual variability of CYP2C19- and CYP2D6-dependent metabolite plasma concentrations in three patients with different CYP2C19 and CYP2D6 genotypes when administered prescribed racemic trihexyphenidyl and coadministered an inhibitor of CYP2C19 activity. Figures 4A-B show graphs of the plasma concentration-time profiles of (A) R-trihexyphenidyl and (B) S-trihexyphenidyl for Patient 1, who has an intermediate metabolizer (IM) genotype for CYP2C19 (CYP2C19*1 / *2) and a normal metabolizer (NM) genotype for CYP2D6 (CYP2D6*1 / *2), and who is concurrently receiving esomeprazole 40 mg / day, an inhibitor of CYP2C19. [Figure 4-2] Figures 4C-D show graphs of the plasma concentration-time profiles of (C) R-trihexyphenidyl and (D) S-trihexyphenidyl for Patient 2, who has the intermediate metabolizer (IM) genotype for CYP2C19 (CYP2C19*2 / *17), the intermediate metabolizer (IM) genotype for CYP2D6 (CYP2D6*1 / *4), and who is concurrently receiving 20 mg / day of omeprazole, an inhibitor of CYP2C19. [Figure 4-3] Figures 4E-F show graphs of the plasma concentration-time profiles of (E)R-trihexyphenidyl and (F)S-trihexyphenidyl for Patient 3, who had the normal metabolizer (NM) genotype for CYP2C19 (CYP2C19*1 / *1), the poor metabolizer (PM) genotype for CYP2D6 (CYP2D6*4 / *4), and was not receiving an inhibitor of CYP2C19. [Figure 5-1]Figures 5A-B show the results of inter-individual variability in CYP2C19-dependent and CYP2D6-dependent trihexyphenidyl metabolism for patient 1 from Figures 4A-B on the plasma concentrations of racemic trihexyphenidyl, R-trihexyphenidyl, and S-trihexyphenidyl after (A) a prescribed dose of 0.05 mg / kg racemic trihexyphenidyl and (B) a standardized dose of 0.1 mg / kg. [Figure 5-2] Figures 5C-D show the results of inter-individual variability in CYP2C19-dependent and CYP2D6-dependent trihexyphenidyl metabolism for patient 2 from Figures 4C-D on the plasma concentrations of racemic trihexyphenidyl, R-trihexyphenidyl, and S-trihexyphenidyl after (C) a prescribed dose of 0.025 mg / kg racemic trihexyphenidyl and (D) a standardized dose of 0.1 mg / kg. [Figure 5-3] Figures 5E-F show the results of inter-individual variability in CYP2C19-dependent and CYP2D6-dependent trihexyphenidyl metabolism for patient 3 from Figures 4E-F on the plasma concentrations of racemic trihexyphenidyl, R-trihexyphenidyl, and S-trihexyphenidyl after (E) a prescribed dose of 0.13 mg / kg racemic trihexyphenidyl and (F) a standardized dose of 0.1 mg / kg (Figure 5F). DETAILED DESCRIPTION OF THE INVENTION

[0020] Detailed Description The present invention relates to a method for treating movement disorders using an improved trihexyphenidyl formulation, in particular a composition comprising high chiral purity R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl. Thus, herein, therapeutic compositions are described, comprising (consisting essentially of, or consisting of) high chiral purity R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl dispersed in a pharmaceutically acceptable carrier, or a pharmaceutically acceptable salt thereof. As used herein, "high chiral purity" or "enantiomerically enriched" means that the compound is predominantly the enantiomer described, preferably at least 75% of the compound present is the R-enantiomer, more preferably at least 85%, even more preferably at least 95%, even more preferably at least 99% (compared to conventional racemic mixtures of trihexyphenidyl, which typically contain a 50:50 mixture of R-enantiomer and S-enantiomer). Therefore, the compound is preferably purified to remove substantially all of the S-enantiomer from the racemic mixture.

[0021] Pharmaceutically acceptable salts include hydrochlorides, hydrobromides, acetates, benzoates, carbonates, mesylates, bitartrates, etc. References herein to therapeutic doses of enantiomers are intended to encompass the salt forms unless otherwise specified.

[0022] Thus, various embodiments of the present invention are directed to multi-component systems, pharmaceutical compositions, and methods comprising highly chirally pure R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl at dosages and chiral purities different from those achievable with conventional racemic mixtures without causing adverse effects. For therapeutic applications, highly chirally pure R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl is administered as part of a composition comprising a therapeutically effective amount of highly chirally pure R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl dispersed in a pharmaceutically acceptable carrier.

[0023] As used herein, the term "carrier" refers to a diluent, excipient, vehicle, etc., in which the R-enantiomer can be suspended or dispersed for administration. Suitable carriers are pharmaceutically acceptable. As used herein, the term "pharmaceutically acceptable" means that the carrier can be administered to a subject without undue toxicity, irritation, or allergic reaction, and is not biologically or otherwise undesirable in that it does not cause unacceptable biological effects or interact in a deleterious manner with the R-enantiomer or other components of the composition containing it. Pharmaceutically acceptable carriers are selected to minimize degradation of the R-enantiomer or other drugs and to minimize adverse side effects in the subject. Trihexyphenidyl is typically provided in tablet form or as a liquid elixir or oral solution. Pharmaceutically acceptable ingredients include those acceptable for veterinary use as well as human pharmaceutical use, and vary depending on the route of administration. Other ingredients, including preservatives, buffers, salts, and other pharmaceutically acceptable ingredients, may be included in the composition. For example, R-enantiomer compositions suitable for oral administration include binders or bulk excipients for compressed tablet or gelcap dosage forms, such as colloidal silicon dioxide, calcium hydrogen phosphate, lactose monohydrate, magnesium stearate, microcrystalline cellulose, sodium starch glycolate, starch, etc., while liquid elixirs or oral suspensions include alcohol 5%, citric acid, parabens, sodium chloride, sugar alcohol (e.g., sorbitol), flavorings, etc.

[0024] The composition may comprise a therapeutically effective amount of the R-enantiomer dispersed in a carrier. As used herein, a "therapeutically effective" amount refers to an amount that induces the biological or medical response of a tissue, system, or subject that a researcher or clinician is seeking, particularly an amount that induces some desired alleviation of dystonia or other movement disorders, such as by selectively blocking M1 and / or M4 muscarinic receptors. Thus, the R-enantiomer is preferably provided in an amount sufficient to selectively bind to these receptors. Those skilled in the art will recognize that an amount may be considered therapeutically "effective" even if the condition is not completely eradicated or halted, but the condition or its symptoms and / or effects are only partially improved or alleviated in a subject, such as, for example, a reduction in the number, frequency, or severity of uncontrollable movements, spasms, or other indicators of dystonia, or an improvement in measurements on gross or fine motor function tasks or recognized scales for assessing dystonia (e.g., the Burke-Fahn-Marsden Dystonia Scale, the Barry-Albright Dystonia Scale, the Melbourne Assessment of Unilateral Upper Limb Function, etc.). It is also contemplated that the improved enantiomerically enriched R-trihexyphenidyl may be used as part of a multifaceted treatment plan.

[0025] It is also contemplated that patients may achieve a therapeutically effective dose of the enantiomer at a lower initial dose compared to the conventional racemic mixture. Generally, the therapeutically effective dose may be half the dose required for the racemic mixture. It is also contemplated that because the harmful side effects typically caused by the S-enantiomer are avoided by the new treatment modality, subjects may be able to tolerate higher doses that achieve even greater therapeutic effects. In one or more embodiments, potential doses of R-trihexyphenidyl may range from 3 mg / day to 30 mg / day or more. That is, without wishing to be bound by theory, it is proposed that the current recommended effective dose of the racemic mixture, 6 mg / day to 60 mg / day, may be halved when using only the R-enantiomer. However, it has also been proposed that, if the treatment-limiting side effects of S-trihexyphenidyl were eliminated, subjects might actually be able to tolerate even higher doses of enantiomerically enriched R-trihexyphenidyl (i.e., greater than 60 mg / day) with correspondingly greater therapeutic efficacy (while also lacking the side effects typically encountered when using the racemic mixture at the same dose).

[0026] The method comprises administering a therapeutically effective amount of R-trihexyphenidyl or a pharmaceutically acceptable salt thereof to a subject in need thereof (i.e., a subject suffering from a movement disorder). Preferably, the administered composition comprises purified R-trihexyphenidyl, more preferably substantially free of S-trihexyphenidyl enantiomer. As used herein, "substantially free" means that the composition (racemic mixture) has been purified to remove all or substantially all of the S-enantiomer of trihexyphenidyl, and in particular, means that the composition contains less than 1% w / w, preferably less than 0.5% w / w, and even more preferably less than 0.1% w / w of the S-enantiomer. That is, at least 99% w / w, preferably at least 99.5% w / w, and more preferably 99.9% w / w of the trihexyphenidyl present in the composition is R-trihexyphenidyl. The composition can be administered once a day, twice a day, or three times a day depending on the dosage form to achieve the total daily dosage described herein. That is, the "effective" amount or "initial" amount refers to the total daily dosage, which can be divided into one, two, or three separate administrations per day to achieve the total recommended daily dosage. Extended-release dosage forms may require fewer administrations. As mentioned above, trihexyphenidyl is typically administered orally as a tablet, liquid elixir, or oral suspension.

[0027] Advantageously, R-trihexyphenidyl is a selective / specific inhibitor of M1 and M4 receptors, with activity 525 times greater than S-trihexyphenidyl, which promiscuously interacts with all five receptors (M1-M5) with comparable inhibitory potency. Therefore, R-trihexyphenidyl is a much more potent antimuscarinic agent. By using highly chirally pure R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl, improved therapeutic efficacy can be achieved while avoiding the side effects associated with the S-enantiomer. Furthermore, the stereoselective metabolism of trihexyphenidyl means that clinicians can use pharmacogenetic testing and precision medicine to identify subjects who may be intolerant to the conventional trihexyphenidyl racemic mixture.

[0028] Metabolic phenotypes can be determined using standard approaches, including determining phenotypes based on test probe substances such as dextromethorphan (DXM). However, more commonly, pharmacogenetic testing of a patient's body fluid samples (blood, serum, urine, saliva, etc.) can be used to assign a predicted metabolizer phenotype or status, according to established guidelines, such as those published by the Clinical Pharmacogenetic Implementation Consortium (CPIC). Currently, genetic assays are available that predict metabolic phenotypes based on the presence or absence of genetic variants of various CYP450 enzymes, which result in altered metabolic clearance of specific drugs for that individual. The results of the genetic assays are converted into predicted metabolic phenotypes based on an understanding of the functional effects of specific pharmacogenetic variants, or "alleles," on enzyme activity. This conversion process is facilitated by utilizing publicly accessible resources. The Pharmacogene Variation (PharmVar) Consortium evaluates, catalogs, and curates reports available on pharmvar.org on allelic variation in genes affecting drug metabolism, drug disposition, and drug response, and provides a uniform nomenclature system (nomenclature) for use by the global pharmacogenetics / genomics community, including academia, medicine, industry, and regulatory agencies. The standardized nomenclature (core allele definitions) developed by PharmVar are incorporated into the Pharmacogenomics Knowledge Base ( P harmaco g economic K knowledge BThe PharmGKB is utilized by the Clinical Pharmacogenetics Implementation Consortium (CPIC). PharmGKB is an NIH-funded resource dedicated to providing information on how human genetic variation influences drug response and collecting, curating, and disseminating knowledge on clinically actionable gene-drug associations and genotype-phenotype relationships. CPIC develops, curates, and posts freely available, peer-reviewed, evidence-based, updatable, detailed gene / drug clinical practice guidelines that follow a standardized format, including standardized terminology and systematic classification of peer-reviewed evidence and clinical recommendations. CPIC guidelines are posted at cpicpgx.org, published in leading clinical pharmacology journals, indexed in PubMed, and referenced by ClinGen and PharmGKB. Coordination of activities by PharmVar, PharmGKB, and CPIC will ensure consistency in the evaluation of new allele data submitted to PharmVar for assessment and curation, as well as in the evaluation of evidence assessing the association between pharmacogenetic variants and drug clearance / systemic drug exposure and the resulting clinical impact (i.e., related to drug efficacy or risk of adverse reactions) for the clinical application of pharmacogenetic variant data in the form of guidelines for translating genetic clinical test results into actionable prescribing decisions for affected drugs.

[0029] Genetic mutations or polymorphisms in these enzymes can affect enzyme activity, ranging from a complete loss of catalytic activity in poor metabolizers to increased enzyme activity accompanied by rapid clearance in ultra-rapid metabolizers. Generally, the presence of fully functional alleles on each chromosome assigns "normal metabolizer" status, while the presence of non-functional variants on each chromosome assigns "poor metabolizer" status. Intermediate metabolizer status generally includes diplotypes, which are combinations of non-functional alleles with reduced or partially functional alleles. Depending on the pharmacogenetic gene involved, ultra-rapid metabolizer status is assigned when two or more functional copies of a gene are present on the same chromosome (e.g., due to duplication or amplification events) or when alleles associated with increased activity are present. Assigning predicted function to specific alleles is specific to the gene of interest. For example, the CYP2D6*2 allele is associated with fully functional enzyme activity, while the CYP2C19*2 allele is associated with a complete loss of activity. Information about variants and associated phenotypes for each CYP450 enzyme is continuously updated and available on the PharmVar website. Other primary sources of PGx guidance include institutional clinical practice guidelines, the Pharmacogenomics Knowledge Base (PharmGKB), and the US Food and Drug Administration's (FDA) Drug Labeling and Table of Pharmacogenetic Associations.

[0030] Once isoforms are identified, they can be converted into activity scores that reflect the relative activity of the enzyme in a particular patient (see, e.g., Gaedigk, A., Simon, S., Pearce, R., Bradford, L., Kennedy, M. and Leeder, J. (2008), The CYP2D6 Activity Score: Translating Genotype Information into a Qualitative Measure of Phenotype. Clinical Pharmacology & Therapeutics, 83: 234-242. doi:10.1038 / sj.clpt.6100406). Activity scores and associated genotype-predicted phenotypes are continually reviewed by PharmVar, PharmGKB, and CPIC.

[0031] Genetically predicted metabolic phenotypes are categorized and expressed relative to the average individual, who is considered a normal metabolizer. Common nomenclature refers to these functional phenotypes as "poor metabolizers" on the one hand and "very rapid metabolizers" on the other. Poor metabolizers are typically individuals in which both copies of a gene (alleles) are low in activity or nonfunctional. Ultra-rapid metabolizers are typically individuals with at least one allele with a normal functioning allele multiplied (thus increasing overall function), while other alleles may be hypofunctional but still functional, usually with multiple copies of the hypofunctional allele present. "Normal" metabolizers are typically individuals with two normal functioning alleles or one normal functioning allele and one hypofunctional allele multiplied. "Intermediate" metabolizers fall between poor and normal metabolizers, typically individuals with one normal functioning allele, or two reduced-function alleles and one non-functional allele, or two reduced-function alleles, or one reduced-function allele and a multiplication of reduced-function alleles, resulting in at least some overall activity level (above that of poor metabolizers, but still below that of normal metabolizers).

[0032] Based on published methods, an enzyme "activity score" can be calculated based on the individual activity values ​​of each allele and can be used to assign a predicted individual functional phenotype (Gaedigk et al., 2008). Generally, an overall activity score of 0 (or less than 0.5) indicates a poor metabolizer, while an activity score of 2.5 or greater indicates an ultrarapid metabolizer. Normal metabolizers have activity scores between 1.5 and 2.0, while activity scores between 0.5 and 1 indicate intermediate metabolizers. Information about activity scores for individual enzymes can be found on PharmVar sites, e.g., pharmvar.org / gene / CYP2D6 or pharmvar.org / gene / CYP2C19. CYP isoforms can also be measured using various commercially available kits. Beyond genotype, drug-drug interactions must also be considered to account for other xenobiotics taken by the subject that may act as CYP450 inhibitors.

[0033] Therefore, in one or more embodiments, clinicians can first identify the subject in need of treatment who has a functional phenotype that predicts that he or she is a poor metabolizer of CYP2D6 or CYP3A4 / CYP3A5, and is the ideal candidate for precision therapy.Clinicians can use any suitable approach for metabolic phenotyping (including genotype-predicted phenotype and drug-induced phenotype) to obtain the CYP450 metabolic phenotype (or preferably at least the CYP2D6 or CYP3A4 / CYP3A5 phenotype) of an individual.For example, pharmacogenomic testing or metabolic phenotyping can be carried out according to a known protocol using test probe substances to evaluate the metabolites produced by an individual, or according to standard genotyping.However, various CYP450 assays are available, and new approaches are routinely developed.Pharmacogenomic testing of CYP450 enzyme activity is also routinely available, including the interpretation of results and the assignment of functional phenotypes.

[0034] If a subject is identified as having reduced CYP2D6 or CYP3A4 / CYP3A5 enzyme activity, the subject is labeled as a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer. In this case, by using precision medicine or personalized medicine, clinicians are now informed that if a subject is treated with conventional trihexyphenidyl racemic mixture, the risk of adverse side effects may be increased (due to the accumulation of S-trihexyphenidyl). In such cases, clinicians can adjust the initial dose of racemic trihexyphenidyl based on the subject's metabolic phenotype to minimize side effects. In contrast, subjects identified as "normal" metabolizers can be started with a higher initial dose of racemic trihexyphenidyl, potentially reducing the risk of adverse side effects. Nevertheless, the dose will be determined by dose titration consistent with typical clinical treatment, as will be understood by those skilled in the art. In one or more embodiments, the methods described herein comprise administering a therapeutically effective amount of enantiomer-enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof to a subject who is a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer. Disclosed embodiments also relate to methods of initiating enantiomer-enriched R-trihexyphenidyl therapy in patients who are CYP2D6 or CYP3A4 / CYP3A5 poor metabolizers.

[0035] Similarly, clinicians can use an individual's CYP2C19 metabolic phenotype (as predicted by CYP2C19 genotype) to prescribe conventional trihexyphenidyl racemic mixture or enantiomer-enriched R-trihexyphenidyl formulations for the treatment of movement disorders. If a patient is identified as having reduced CYP2C19 enzyme activity, they are assigned CYP2C19 poor metabolizer status and can be effectively managed with lower doses of either conventional trihexyphenidyl racemic mixture or highly enriched R-trihexyphenidyl formulations. Similarly, patients with CYP2C19 genotypes associated with increased activity, such as CYP2C19*17 / *17, are assigned an ultrarapid metabolizer phenotype and may require higher-than-normal doses to achieve therapeutic concentrations of R-trihexyphenidyl in the body. It will be appreciated that a particular advantage of using enantiomerically enriched R-trihexyphenidyl is that by substantially removing S-trihexyphenidyl from the formulation, concerns associated with additional genetic variation from CYP2D6 isoforms are reduced or eliminated. Thus, by using precision or personalized medicine, clinicians are now better informed about individual-specific factors that may affect the therapeutic benefit and risk of toxicity associated with different treatment protocols.

[0036] In this manner, the embodiments described herein can be used to inform clinicians' treatment protocols in a more precise and personalized manner to improve patient outcomes. One skilled in the art can develop an appropriate treatment plan based on the patient's age and condition, the patient's tolerance to side effects, and the severity of the condition.

[0037] In some embodiments, high chiral purity R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl or composition can be provided in a unit dosage form in a suitable container.The term "unit dosage form" refers to a physically discrete unit suitable for use as a unit dose for humans or animals.Each unit dosage form can contain a predetermined amount of high chiral purity R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl (and / or other active agent) in a carrier calculated to produce a desired effect.In one or more embodiments, high chiral purity R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl can be provided separately from the carrier (e.g., in its own vial, ampoule, sachet, or other suitable container) for on-site mixing (e.g., at a pharmacy or at home) before administration to a subject. In one or more embodiments, the chirally pure R-trihexyphenidyl or enantiomerically enriched R-trihexyphenidyl is provided in individual tablets, pills, gelcaps, 3D printed personalized dosage forms, and the like.

[0038] Also disclosed herein is a kit comprising high chiral purity R-trihexyphenidyl or enantiomer-enriched R-trihexyphenidyl.The kit further comprises instructions for administering high chiral purity R-trihexyphenidyl or enantiomer-enriched R-trihexyphenidyl to a subject.High chiral purity R-trihexyphenidyl or enantiomer-enriched R-trihexyphenidyl can be provided as part of a dosage unit already dispersed in a pharmaceutically acceptable carrier, or can be provided separately from the carrier.The kit can further comprise instructions for preparing high chiral purity R-trihexyphenidyl or enantiomer-enriched R-trihexyphenidyl for administration to a subject, such as instructions for dispersing high chiral purity R-trihexyphenidyl or enantiomer-enriched R-trihexyphenidyl in a suitable vehicle to form an elixir or oral suspension.

[0039] It will be understood that the methods of treatment described herein are applicable not only to humans, but also to veterinary use on suitable animals, including, but not limited to, dogs, cats and other companion animals, as well as rodents, primates, horses, cattle, pigs, etc. The methods are also applicable to clinical research and / or testing.

[0040] The embodiments described herein are suitable for treating subjects in whom selective inhibition of M1 and / or M4 muscarinic receptors produces a beneficial effect in the subject. For example, the embodiments described herein are suitable for treating subjects suffering from a variety of movement disorders, including dystonia or dystonia secondary to other conditions, such as Parkinson's disease, cerebral palsy, Angelman syndrome, or other genetically mediated movement disorders.

[0041] Further advantages of various embodiments of the present invention will be apparent to those skilled in the art upon review of the disclosure herein and the following examples. It will be understood that the various embodiments described herein are not necessarily mutually exclusive, unless otherwise indicated herein. For example, features described or depicted in one embodiment may, but are not necessarily, included in other embodiments. Thus, the present invention encompasses various combinations and / or integrations of the specific embodiments described herein.

[0042] As used herein, the term "and / or," when used in a list of two or more items, means that any one of the listed items can be used alone, or any combination of two or more of the listed items can be used. For example, if a composition is described as including or excluding components A, B, and / or C, the composition can include or exclude A alone; B alone; C alone; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0043] "Enantiomer" refers to an asymmetric molecule that can exist in two different isomeric forms with different spatial configurations. Other terms used to designate or refer to enantiomers include "stereoisomers" (all enantiomers are stereoisomers, but not all stereoisomers are enantiomers, due to different configurations or stereochemistry around the chiral center). Molecules that exist in two enantiomeric forms are chiral, meaning they can be considered to exist in "counterclockwise" and "clockwise" forms. The most common source of chirality in organic molecules is the presence of a tetrahedral carbon bonded to four different substituents or groups. Such a carbon is referred to as a chiral center, as shown in Figure 1. Enantiomers have the same empirical chemical formula and are generally considered chemically identical in reactivity, physical properties, and spectroscopic properties. However, there is growing appreciation for the different pharmacokinetic profiles of enantiomers, or isomers, of the same compound. The designations "R" and "S" are used according to their conventional meaning to denote the absolute configuration of a molecule around its chiral center.

[0044] This description also uses numerical ranges to quantify certain parameters related to various embodiments of the present invention. It should be understood that when numerical ranges are provided, such ranges should be construed as providing literal support for claim limitations that recite only the lower value of the range, and for claim limitations that recite only the upper value of the range. For example, a disclosed numerical range of about 10 to about 100 provides literal support for claims recited as "greater than about 10" (without an upper limit) and claims recited as "less than about 100" (without a lower limit). [Example]

[0045] The following examples describe methods according to the present invention, however, it should be understood that these examples are provided by way of illustration and not as limiting the overall scope of the invention.

[0046] Example 1 Biotransformation study of trihexyphenidyl and its application to dystonic cerebral palsy Objective: Trihexyphenidyl (THP) is an anticholinergic drug commonly used to treat dystonia and other movement disorders in children with cerebral palsy or certain genetic conditions, such as Angelman syndrome. The pathophysiology of dystonia involves an increase in the number of striatal cholinergic interneurons and their abnormal excitability. Therefore, anticholinergic drugs such as THP are potential treatments, and rodent models demonstrate normalization of striatal activity after THP exposure. For example, studies in mouse models have shown that trihexyphenidyl acts on M4 muscarinic receptors in the striatum, normalizing dopamine release associated with dystonia. However, in clinical practice, patients treated with THP exhibit inconsistent efficacy and adverse effects (nausea, constipation, and urinary retention) that may be due to a variable dose-exposure relationship. Patients often require dose reduction or treatment discontinuation due to adverse events. These mixed results have led to current recommendations concluding that there is insufficient evidence regarding the efficacy of trihexyphenidyl for patients with cerebral palsy.

[0047] Trihexyphenidyl may be used to treat dystonia, myoclonus, and other movement disorders in Angelman syndrome. Rodent models of Angelman syndrome demonstrate impaired dopamine release, with increased dopamine in the nucleus accumbens and decreased dopamine in the striatum, leading to movement disorders and behavioral changes. Muscarinic receptor modulation with M4-selective antimuscarinics (such as trihexyphenidyl) may have the advantage of increasing dopamine release in the striatum, while antagonism of M1 and M5 muscarinic receptors in the nucleus accumbens decreases dopamine release. Because trihexyphenidyl is a selective M1 and M4 muscarinic antagonist, it may be useful for both dopamine deficiency and excess in patients with Angelman syndrome, making it a promising therapeutic option for treating movement disorders and behavioral changes.

[0048] Many drugs are metabolized in the liver by one or more (usually a combination) of the cytochrome P450 (CYP) family of enzymes. For example, CYP2D6 is a key xenobiotic-metabolizing enzyme involved in the clearance of many drugs. Genetic polymorphisms in CYP2D6 or other enzymes, such as CYP3A4 / CYP3A5 or CYP2C19, contribute to large interindividual variability in drug metabolism and, therefore, drug clearance from the body. Similarly, how quickly or slowly a drug is metabolized and / or excreted from the body affects how that drug functions in the body, both in terms of the extent of therapeutic effect and side effects.

[0049] Most patients are characterized as having "normal" enzyme function for various CYP450 enzymes and readily metabolize certain drugs. However, some patients have little or no enzyme function for certain enzymes and may be considered or assigned the status of "poor metabolizer" for these enzymes, i.e., have a significantly reduced ability to metabolize certain drugs metabolized via these specific enzymes. Therefore, an individual's pharmacogenomic profile, along with information on which CYP450 metabolic pathway a particular drug follows, can help predict dose-response. Reduced enzyme activity due to pharmacogenetic variation or drug-drug inhibition results in accumulation of the affected drug and an increased risk of concentration-dependent side effects. Conversely, pharmacogenetic variations that result in increased activity, such as functional CYP2D6 variant duplication / multiplication or the CYP2C19*17 / *17 genotype, can result in insufficient concentrations in the body and increased drug clearance from the body, leading to treatment failure. Furthermore, some drugs or foods act as inhibitors of the enzyme function of CYP2D6, CYP3A4 / CYP3A5, or CYP2C19, and therefore may inhibit or reduce the metabolism of these drugs when taken concomitantly or within the same time frame as these drugs. This consideration also applies to other enzymes in the CYP450 family.

[0050] For example, in the context of the present disclosure, as shown herein, patients who are CYP2D6 poor metabolizers are predicted to have a reduced ability to metabolize and eliminate S-trihexyphenidyl (the enantiomer that causes side effects), and therefore are predicted to be more likely to experience side effects when treated with a racemic mixture.In this case, these individuals are potential candidates for recommending treatment with enantiomer-enriched R-trihexyphenidyl.Similarly, in the context of the present disclosure, as shown herein, patients who are CYP2C19 fast metabolizers are predicted to have a faster clearance of R-trihexyphenidyl (the enantiomer that causes therapeutic effects), and therefore can benefit from a higher initial dose to ensure sufficient (therapeutically effective) plasma levels of R-trihexyphenidyl (for binding to M1 and / or M4 receptors). Additionally, the individual's CYP2D6 status may also be considered depending on whether the clinician is treating with the racemic mixture or enantiomer-enriched R-trihexyphenidyl CYP2D6 metabolizer status (if S-trihexyphenidyl metabolism is a concern)

[0051] Current treatment protocols for the racemic mixture of THP recommend starting with a low dose of 0.5–1 mg daily, titrated by 1 mg every 3–5 days until benefit or adverse effects occur. While typical effective doses vary widely, ranging from 6–60 mg / day, some patients require higher doses. Consequently, little is known about the biotransformation of THP, which could inform individualized dosing strategies to provide optimal systemic exposure for each patient. We investigated the biotransformation of THP using in vivo and in vitro analyses to determine whether new protocols could improve dosing response while reducing side effects of this promising agent.

[0052] Method: THP and deuterated THP (D11-THP, a racemic form in which all 11 available hydrogens on the cyclohexane ring are deuterated) 11"D-trihexyphenidyl" and "5D-trihexyphenidyl" (in which all five available hydrogens on the phenyl ring are deuterated) were incubated with recombinant CYP2D6, CYP2C19, and CYP3A4 / CYP3A5 enzymes and human liver microsomes. The resulting metabolites were identified and quantified using mass spectrometry. Urine samples from patients taking THP were also obtained, and metabolites were identified and quantified using mass spectrometry.

[0053] Initial results: Incubation of THP with recombinant CYP450 enzymes revealed predominant CYP2D6 metabolism at low THP concentrations (0.2 μg / ml), shifting to predominant CYP3A4 metabolism at high (supraphysiological) concentrations (6 μg / ml). Incubation of D11-THP confirmed hydroxylation of the cyclohexane ring by both CYP2D6 and CYP3A4, resulting in the formation of two or three distinct metabolites (two major and one minor), the major being MW238. Patient urine samples revealed mixed CYP2D6 and CYP3A4 metabolite formation, with the CYP3A4-predominant metabolite present in all patient urine, confirming the in vitro results.

[0054] Further results: Subsequent analysis using a larger panel of CYP450 enzymes provided more insight. Racemic trihexyphenidyl (20 ng / ml) was incubated with a panel of heterologously expressed human CYPs (XenoTech LLC). Metabolites with molecular weights equivalent to that of trihexyphenidyl plus an additional 16 Da, consistent with the formation of a hydroxylated metabolite, were separated by liquid chromatography using a chiral column (Restek Raptor® Biphenyl, 1.8 μm, 100 × 2.1 mm) that cannot resolve individual enantiomers. The abundance of each metabolite was measured by tandem mass spectrometry (LC / MS / MS). Because their structures (positions on the cyclohexane ring) have not yet been determined, these metabolites are referred to as "Metabolite 1," "Metabolite 2," and "Metabolite 3." The amounts of metabolites formed were determined by integrating the areas of their elution peaks in arbitrary area units. Under these experimental conditions, incubation of racemic THP with a larger panel of 12 recombinant CYPs revealed two major metabolites and one minor metabolite formed by the three major CYPs, CYP2C19, CYP2D6, and CYP3A4, with minor contributions from CYP3A5 and CYP2C9 (Figure 2). The contributions of the three major CYPs to metabolite formation in vitro were 51% for CYP2C19, 43% for CYP2D6, and 6% for CYP3A4. Incubation of D11-THP with human liver microsomes confirmed that both metabolites were formed by hydroxylation of the cyclohexane ring. Similar metabolites were also present in the patient's urine and plasma samples, with metabolite 1 predominating.

[0055] Conclusions: Biotransformation of THP occurs primarily through hydroxylation of the cyclohexane ring via combined metabolism of CYP2C19, CYP2D6, and CYP3A4, and metabolites were confirmed to be present in the plasma and urine of all patients taking THP.

[0056] Example 2 Further enantiomeric analysis Further analysis of THP identified differences between the enantiomers of THP. The R-enantiomer has up to 525-fold higher binding affinity than the S-enantiomer and has selective affinity for human M1 and M4 muscarinic receptors, whereas the S-enantiomer has equal affinity for all receptor subtypes. Furthermore, our data reveal stereoselective metabolism of THP.

[0057] We incubated R-trihexyphenidyl (1,000 ng / ml) and S-trihexyphenidyl (1,000 ng / ml) with heterologously expressed CYP2C19, CYP2D6, and CYP3A4. The metabolites produced during the incubation were separated as described in Figure 2. However, a chiral column (Supelco Astec CHIROBIOTIC® V 25 cm × 4.6 mm, 5 μm) was used to separate R-trihexyphenidyl and S-trihexyphenidyl and the metabolites formed from each enantiomer. Under the chromatographic conditions used, the CYP-generated hydroxylated metabolites eluted from the column in two pairs or peaks. One pair had elution times of 10.8 and 11.2 minutes, and the other pair had retention times of 12.0 and 12.9 minutes. The first-eluting pair of metabolites is designated M1; the peak at 10.8 min is formed from R-trihexyphenidyl (R-THP-M1), and the metabolite eluting at 11.2 min is formed from S-trihexyphenidyl (S-THP-M1). Similarly, the peak at 12.0 min is designated R-THP-M2, and the peak at 12.9 min is designated S-THP-M2.

[0058] The presented data indicate that R-THP-M1 and S-THP-M2 are the most abundant metabolites formed under these experimental conditions, with R-THP-M1 formed almost exclusively by CYP2C19, whereas S-THP-M2 is formed primarily by CYP2D6 (Figure 3). Therefore, in patients who are CYP2D6 poor metabolizers, S-trihexyphenidyl may accumulate to high concentrations, potentially increasing the risk of side effects, while in patients who are CYP2C19 rapid metabolizers, R-THP concentrations may be low, potentially reducing drug efficacy. Based on this new understanding, we propose that the development of formulations enriched in R-trihexyphenidyl or containing only R-trihexyphenidyl may reduce or eliminate potential toxicities associated with S-trihexyphenidyl and CYP2D6 genetic variations.

[0059] We investigated this by determining the impact of CYP2D6 and CYP2C19 metabolizer genotype predictors on the concentrations of S-trihexyphenidyl and R-trihexyphenidyl metabolites present in patient plasma. In addition to interindividual variability in CYP2C19 and CYP2D6 genotypes, the results in graphs A–F in ​​Figure 4 demonstrate that the metabolite patterns in three patients differed with respect to their CYP2C19 and CYP2D6 genotypes, the prescribed dose of racemic trihexyphenidyl, and the coadministration of inhibitors of CYP2C19 activity. In each graph, the pharmacokinetics of S-trihexyphenidyl or R-trihexyphenidyl is shown by black circles, the concentrations of the M1 metabolite are shown by gray circles, and the concentrations of the M2 metabolite are shown by white circles. Note that CYP2D6-dependent S-THP-M2 concentrations were not detected in Patient 2, a CYP2D6 intermediate metabolizer predicted to have reduced CYP2D6 activity, or in Patient 3, a CYP2D6 poor metabolizer with no activity. Concentrations of the CYP3A4-dependent S-THP-M1 metabolite were present in all three patients and exceeded S-trihexyphenidyl concentrations in Patients 1 and 2. Regarding R-THP, the CYP2C19-dependent R-THP-M1 concentration was highest compared with R-trihexyphenidyl plasma concentrations in Patient 3, who had the normal metabolizer CYP2C19*1 / *1 genotype, and lowest compared with R-trihexyphenidyl plasma concentrations in Patient 1, who had the intermediate CYP2C19*1 / *2 genotype and was receiving a maximum dose of 40 mg / day of the CYP2C19 inhibitor esomeprazole.

[0060] The interindividual variability in CYP2C19- and CYP2D6-dependent trihexyphenidyl metabolism described in Figure 4 is shown in Figure 5 for the same three patients. Steady-state concentrations of racemic trihexyphenidyl (black circles) and the two individual enantiomers, S-trihexyphenidyl (white circles) and R-trihexyphenidyl (gray circles), were measured over the entire 6-hour dosing interval. Each patient was unique with respect to CYP2C19 and CYP2D6 genotype, prescribed dose of racemic trihexyphenidyl, and coadministration of inhibitors of CYP2C19 activity; each pair represents the results of a single patient, with the respective genotype, racemic trihexyphenidyl dose, and inhibitor dose indicated at the top of each column. In each pair, the graph on the left represents plasma concentrations relative to the actual prescribed dose, and the graph on the right represents the concentration-time profile corrected for a usual dose of 0.1 mg / kg racemic trihexyphenidyl. In other words, assuming linear kinetics, the graph on the right shows the expected concentrations after administration of 0.1 mg / kg to each patient. Although the shape of the curves is the same, the curves are shifted upward by two and four times in patient 1 and patient 2, respectively. The curve for patient 3 is shifted downward because the actual dose was higher than 0.1 mg / kg. The similarity of the racemate (black) and R-trihexyphenidyl (gray) kinetics in patient 1 (a CYP2D6 normal metabolizer; NM) and patient 2 (a CYP2D6 intermediate metabolizer; IM) indicates that the majority of trihexyphenidyl present in the plasma of these patients exists as R-trihexyphenidyl. In patient 3 (a CYP2D6 poor metabolizer; PM), the S-trihexyphenidyl (white circles) concentration is approximately 32% of the total trihexyphenidyl present, compared to 5–6% in the other two patients. Expressed another way, in patient 3, the S-trihexyphenidyl concentration is approximately 50% of the R-trihexyphenidyl concentration.In all patients, R-trihexyphenidyl concentrations were higher than S-trihexyphenidyl concentrations and tended to decline more slowly in patients 1 and 2 due to the intermediate metabolizer CYP2C19 genotype and the presence of esomeprazole and omeprazole, respectively, which are inhibitors of CYP2C19 activity.

[0061] These data indicate that in vitro, THP is metabolized stereoselectively via hydroxylation of the cyclohexane ring, with R-THP primarily metabolized by CYP2C19 and S-THP primarily metabolized by CYP2D6. Collectively, these observations are consistent with the formation of R-THP-M1 by CYP2C19, the primary pathway involved in R-trihexyphenidyl clearance (reduced enzyme activity due to genetic mutations and coadministration of inhibitors affect residual enzyme activity), and the CYP2D6-dependent formation of S-THP-M2, which contributes to reduced clearance of S-trihexyphenidyl and thus accumulation of high concentrations of S-trihexyphenidyl (increasing the potential for adverse drug reactions).

[0062] Based on these preliminary results, we propose that R-trihexyphenidyl is superior to the racemic mixture because it is more selective for M1 and M4 muscarinic receptors, which are involved in movement disorders including dystonia, more specifically Parkinson's disease, cerebral palsy, and Angelman syndrome. It has been suggested that the S-enantiomer is not selective for muscarinic subtypes and may actually be associated with side effects due to interactions with M1-M5 and activation of peripheral muscarinic receptors, particularly in poor CYP2D6 metabolizers. Administering R-THP as a single enantiomer may be safer and more effective. Data also indicate that the R- and S-enantiomers have different metabolic and clearance pathways (metabolized by different ADMERs); this observation may have important pharmacogenomic applications for individualizing drug therapy, including by adjusting recommended doses based on an individual's CYP2D6 and CYP2C19 metabolizer status.

Claims

1. A therapeutic composition comprising enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof dispersed in a pharmaceutically acceptable carrier.

2. 10. The composition of claim 1, wherein the composition comprises R-trihexyphenidyl in an enantiomeric excess of at least about 75%.

3. 10. The composition of claim 1, wherein the composition comprises R-trihexyphenidyl in an enantiomeric excess of at least about 85%.

4. 10. The composition of claim 1, wherein the composition comprises R-trihexyphenidyl in an enantiomeric excess of at least about 95%.

5. 10. The composition of claim 1, wherein the composition comprises R-trihexyphenidyl in an enantiomeric excess of at least about 99%.

6. 10. The composition of claim 1, wherein the composition comprises less than 25% S-trihexyphenidyl.

7. 10. The composition of claim 1, wherein the R-trihexyphenidyl is at least 95% enantiomerically pure.

8. 2. The composition of claim 1, wherein R-trihexyphenidyl is in the form of a pharmaceutically acceptable salt selected from the group consisting of hydrochloride, hydrobromide, acetate, benzoate, carbonate, mesylate, and bitartrate.

9. A pharmaceutical dosage form comprising a therapeutically effective amount of the composition of claim 1.

10. 10. The dosage form of claim 9, wherein the dosage form is a tablet, capsule, or oral liquid.

11. 10. The dosage form of claim 9, wherein the therapeutically effective amount is a dose of 3 mg / day to 30 mg / day.

12. 1. A method for selectively targeting M1 and / or M4 muscarinic receptors in a subject in need thereof, comprising administering to the subject a therapeutically effective amount of enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof, wherein R-trihexyphenidyl selectively binds to M1 and / or M4 receptors in the subject.

13. 13. The method of claim 12, comprising orally administering a dosage form containing R-trihexyphenidyl, wherein the dosage form contains R-trihexyphenidyl in an enantiomeric excess of at least about 75%.

14. 14. The method of claim 13, wherein the dosage form contains purified R-trihexyphenidyl, more preferably substantially free of S-trihexyphenidyl enantiomer.

15. 14. The method of claim 13, wherein the dosage form is a tablet, capsule, or oral liquid.

16. 14. The method of claim 13, wherein the method comprises administering R-trihexyphenidyl at a dose of 3 mg / day to 30 mg / day.

17. 13. The method of claim 12, wherein the subject exhibits a decrease in the number, frequency, or severity of uncontrollable movements and convulsions, or an improvement in a measure of gross motor function or fine motor function after administration of the R-trihexyphenidyl.

18. 12. Use of a medicament for selectively targeting M1 and / or M4 muscarinic receptors or for treating dystonia in a subject in need thereof, the medicament comprising a therapeutic composition comprising enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof according to any one of claims 1 to 8, or a pharmaceutical dosage form according to any one of claims 9 to 11.

19. 1. An improved method for treating a movement disorder in a subject in need thereof who is a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer, the method comprising: obtaining a CYP450 metabolic phenotype of said subject; and administering to said subject who is a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer a therapeutically effective amount of enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof. A method comprising:

20. 1. An improved method for treating a movement disorder in a subject in need thereof who is a CYP2C19 poor metabolizer, the method comprising: obtaining a CYP450 metabolic phenotype of said subject; and administering to the subject who is a CYP2C19 poor metabolizer a therapeutically effective amount of enantiomerically enriched R-trihexyphenidyl or a pharmaceutically acceptable salt thereof, wherein the therapeutically effective amount is a lower dose of R-trihexyphenidyl compared to the dose recommended in clinical guidelines for trihexyphenidyl. A method comprising:

21. 21. The method of claim 20, wherein the low dose is half of the standard recommended dose, preferably the low dose is 3 mg / day to 15 mg / day.

22. 1. An improved method for treating movement disorders in a subject who is a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer to minimize side effects, the method comprising: obtaining a CYP450 metabolic phenotype of said subject; and reducing the initial dose of a racemic mixture of trihexyphenidyl or a pharmaceutically acceptable salt thereof to less than 1 mg / day and administering to said subject who is a CYP2D6 or CYP3A4 / CYP3A5 poor metabolizer; or Increasing the initial dose of a racemic mixture of trihexyphenidyl or a pharmaceutically acceptable salt thereof to greater than 6 mg / day and administering to said subject who is a CYP2D6 or CYP3A4 / CYP3A5 normal or ultrarapid metabolizer. a method comprising: The initial dose is based on the initial dose recommended in clinical guidelines for trihexyphenidyl. method.

23. 1. A method of administering to a subject in need thereof an initial dose of an M1 and / or M4 muscarinic receptor inhibitor, wherein the initial dose is based on an initial dose recommended in clinical guidelines for the inhibitor, the method comprising: obtaining the subject's genotype for a panel of cytochrome P450 enzymes including at least CYP2D6 and / or CYP2C19 alleles, wherein the subject is assigned a metabolic phenotype selected from poor metabolizer, intermediate metabolizer, or very rapid metabolizer for each enzyme based on the number of functional alleles for each cytochrome P450 gene; administering to said patient an initial dose of said inhibitor, wherein said initial dose comprises (a) an initial dose that is half the initial dose recommended in clinical guidelines if the metabolic phenotype is one or more of CYP2D6 poor metabolizer, CYP2D6 intermediate metabolizer, or CYP2C19 poor metabolizer; or (b) an initial dose that is equal to or greater than the initial dose recommended in clinical guidelines if the metabolic phenotype is one or more of CYP2D6 very rapid metabolizer or CYP2C19 very rapid metabolizer; is) wherein the inhibitor is selected from the group consisting of a racemic mixture of trihexyphenidyl, enantiomerically enriched R-trihexyphenidyl, and pharmaceutically acceptable salts thereof.

24. 1. A method of reducing a side effect of an initial dose of an M1 and / or M4 muscarinic receptor inhibitor in a subject in need thereof, wherein the initial dose is based on an initial dose recommended in clinical guidelines for the inhibitor, the method comprising: obtaining the subject's genotype for a panel of cytochrome P450s including at least CYP2D6 alleles, wherein the subject is assigned a metabolic phenotype selected from poor metabolizer, intermediate metabolizer, or very rapid metabolizer for each enzyme based on the number of functional alleles for CYP2D6; administering to said patient an initial dose of said inhibitor, wherein said initial dose comprises (a) an initial dose that is half the initial dose recommended in clinical guidelines if the metabolic phenotype is a CYP2D6 poor metabolizer or a CYP2D6 intermediate metabolizer; or (b) if the metabolic phenotype is a CYP2D6 ultrarapid metabolizer, an initial dose that is equal to or greater than the initial dose recommended in clinical guidelines; is) wherein the inhibitor is a racemic mixture of trihexyphenidyl or a pharmaceutically acceptable salt thereof.

25. 25. The method according to any one of claims 19 to 24, wherein the therapeutically effective amount or the initial amount is per day, and the trihexyphenidyl or a pharmaceutically acceptable salt thereof is administered once, twice, or three times per day to reach the therapeutically effective amount or the initial amount per day.

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