Patent
`79532.8004.USO1
`
`To:
`
`Commissioner for Patents
`
`PO. Box 1450
`
`Alexandria, VA 22313-1450
`
`NEW APPLICATION TRANSMITTAL - UTILITY
`
`Sir:
`
`Transmitted herewith for filing is a utility patent application:
`
`|nventor(s): Bruce SCHARSCHMIDT
`Masoud MOKHTARANI
`
`Title:
`
`METHODS OF THERAPEUTIC MONITORING OF PHENYLACETIC
`
`ACID PRODRUGS
`
`I.
`
`PAPERS ENCLOSED HEREWITH FOR FILING UNDER 37 CFR §1.53(b):
`
`fl
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`Page(s) of Written Description
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`IVI—\I0)
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`Page(s) Claims
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`Page(s) Abstract
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`Sheets of Drawings
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`Sheets of Sequence Listing
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`II.
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`ADDITIONAL PAPERS ENCLOSED IN CONNECTION WITH THIS FILING:
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`Declaration
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`Power of Attorney I:I Separate I:I Combined with Declaration
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`Assignment to and assignment cover sheet
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`Certified Copy of Priority Document No(s): _
`Information Disclosure Statement w/PTO 1449 I:I Copy of Citations
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`Preliminary Amendment
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`Sequence Listing Diskette and Declaration
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`Request and Certification under 35 U.S.C. § 122(b)(2)(B)(i). Applicant must
`attach form PTO/SB/35
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`Return Postcard
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`DDDDDDDD
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`III
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`III.
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`U.S. PRIORITY:
`
`The present application claims priority to U.S. Provisional Application No.
`61/636,256, filed April 20, 2012, the disclosure of which is incorporated by reference
`herein in its entirety, including drawings.
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`Patent
`79532.8004.USO1
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`IV.
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`FEES:
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`IXI
`IXI
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`Applicant claims small entity status pursuant to 37 CFR § 1.27
`This application is being filed without fee or Declaration under 37 CFR § 1.53.
`
`V.
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`CORRESPONDENCE ADDRESS
`
`Please send all correspondence to Customer Number 34055.
`
`Perkins Coie LLP
`
`Patent — LA
`
`PO. Box 1208
`
`Seattle, WA 98111-1208
`
`Phone: (310) 788-9900
`Fax: (206) 332-7198
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`Please direct all inquiries to Patrick Morris, at the above customer number.
`
`Dated: September 11, 2012
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`Respectfully submitted,
`
`PERKINS COIE LLP
`
`By: /Patrick D. Morris/
`Patrick D. Morris, Ph.D.
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`Reg. No. 53,351
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`79532—8004.USOO/LEGAL24638828.1
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`Attorney Docket No. 79532.8004.US01
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`METHODS OF THERAPEUTIC MONITORING OF PHENYLACETIC ACID PRODRUGS
`
`RELATED APPLICATIONS
`
`[0001]
`
`The present application claims priority to US. Provisional Application No. 61/636,256,
`
`filed April 20, 2012, the disclosure of which is incorporated by reference herein in its entirety,
`
`including drawings.
`
`BACKGROUND
`
`[0002]
`
`Nitrogen retention disorders associated with elevated ammonia levels include urea cycle
`
`disorders (UCDs), hepatic encephalopathy (HE), and advanced kidney disease or kidney failure,
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`often referred to as end-stage renal disease (ESRD).
`
`[0003]
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`UCDs include several inherited deficiencies of enzymes or transporters necessary for the
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`synthesis of urea from ammonia, including enzymes involved in the urea cycle. The urea cycle is
`
`depicted in Figure l, which also illustrates how certain ammonia-scavenging drugs act to assist in
`
`elimination of excessive ammonia. With reference to Figure l, N-acetyl glutamine synthetase
`
`(NAGS)—derived N—acetylglutamate binds to carbamyl phosphate synthetase (CPS), which activates
`
`CPS and results in the conversion of ammonia and bicarbonate to carbamyl phosphate. In turn,
`
`carbamyl phosphate reacts with omithine to produce citrulline in a reaction mediated by omithine
`
`transcarbamylase (OTC). A second molecule of waste nitrogen is incorporated into the urea cycle
`
`in the next reaction, mediated by arginosuccinate synthetase (ASS), in which citrulline is condensed
`
`with aspartic acid to form argininosuccinic acid. Argininosuccinic acid is cleaved by
`
`argininosuccinic lyase (ASL) to produce arginine and fumarate. In the final reaction of the urea
`
`cycle, arginase (ARG) cleaves arginine to produce omithine and urea. Of the two atoms of nitrogen
`
`incorporated into urea, one originates from free ammonia (NH4+) and the other from aspartate.
`
`UCD individuals born with no meaningful residual urea synthetic capacity typically present in the
`
`first few days of life (neonatal presentation). Individuals with residual fimction typically present
`
`later in childhood or even in adulthood, and symptoms may be precipitated by increased dietary
`
`protein or physiological stress (e. g., intercurrent illness). For UCD patients, lowering blood
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`ammonia is the cornerstone of treatment.
`
`[0004]
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`HE refers to a spectrum of neurologic signs and symptoms believed to result from
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`hyperammonemia, which frequently occur in subjects with cirrhosis or certain other types of liver
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`Attorney Docket No. 79532.8004.USOl
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`disease. HE is a common manifestation of clinically decompensated liver disease and most
`
`commonly results from liver cirrhosis with diverse etiologies that include excessive alcohol use,
`
`hepatitis B or C virus infection, autoimmune liver disease, or chronic cholestatic disorders such as
`
`primary biliary cirrhosis. Patients with HE typically show altered mental status ranging from subtle
`
`changes to coma, features similar to patients with UCDs. It is believed that an increase in blood
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`ammonia due to dysfunctional liver in detoxifying dietary protein is the main pathophysiology
`
`associated with HE (Ong 2003).
`
`[0005]
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`ESRD results from a variety of causes including diabetes, hypertension, and hereditary
`
`disorders. ESRD is manifested by accumulation in the bloodstream of substances normally excreted
`
`in the urine, including but not limited to urea and creatinine. This accumulation in the bloodstream
`
`of substances, including toxins, normally excreted in the urine is generally believed to result in the
`
`clinical manifestations of ESRD, sometimes referred to also as uremia or uremic syndrome. ESRD
`
`is ordinarily treated by dialysis or kidney transplantation. To the extent that urea, per se, contributes
`
`to these manifestations and that administration of a phenylacetic (PAA) prodrug may decrease
`
`synthesis of urea (see, e. g., Brusilow 1993) and hence lower blood urea concentration, PAA prodrug
`
`administration may be beneficial for patients with ESRD.
`
`[0006]
`
`Subjects with nitrogen retention disorders whose ammonia levels and/or symptoms are
`
`not adequately controlled by dietary restriction of protein and/0r dietary supplements are generally
`
`treated with nitrogen scavenging agents such as sodium phenylbutyrate (NaPBA, approved in the
`
`United States as BUPHENYL® and in Europe as AMMONAPS®), sodium benzoate, or a
`
`combination of sodium phenylacetate and sodium benzoate (AMMONUL®). These are often
`
`referred to as alternate pathway drugs because they provide the body with an alternate pathway to
`
`urea for excretion of waste nitrogen (Brusilow 1980; Brusilow 1991). NaPBA is a PAA prodrug.
`
`Another nitrogen scavenging drug currently in development for the treatment of nitrogen retention
`
`disorders is glyceryl tri-[4-phenylbutyrate] (HPN—100), which is described in US. Patent No.
`
`5,968,979. HPN—100, which is commonly referred to as GT4P or glycerol PBA, is a prodrug of
`
`PBA and a pre-prodrug of PAA. The difference between HPN—lOO and NaPBA with respect to
`
`metabolism is that HPN—lOO is a triglyceride and requires digestion, presumably by pancreatic
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`lipases, to release PBA (McGuire 2010), while NaPBA is a salt and is readily hydrolyzed after
`
`absorption to release PBA.
`
`[0007]
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`HPN—lOO and NaPBA share the same general mechanism of action: PBA is converted to
`
`PAA via beta oxidation, and FAA is conjugated enzymatically with glutamine to form
`
`phenylacetylglutamine (PAGN), which is excreted in the urine. The structures of PBA, FAA, and
`
`PAGN are set forth below:
`
`pfitenyihutgrate
`
`«as
`
`Phemiacam acid
`
`
`
`2Fhangfimiylg-Eutamme
`
`[0008]
`
`The clinical benefit of NaPBA and HPN—lOO with regard to nitrogen retention disorders
`
`derives from the ability of PAGN to effectively replace urea as a vehicle for waste nitrogen
`
`excretion and/or to reduce the need for urea synthesis (Brusilow 1991; Brusilow 1993). Because
`
`each glutamine contains two molecules of nitrogen, the body rids itself of two waste nitrogen atoms
`
`for every molecule of PAGN excreted in the urine. Therefore, two equivalents of nitrogen are
`
`removed for each mole of PAA converted to PAGN. PAGN represents the predominant terminal
`
`metabolite, and one that is stoichiometrically related to waste nitrogen removal, a measure of
`
`efficacy in the case of nitrogen retention states.
`
`[0009]
`
`In addition to nitrogen retention states, PAA prodrugs may be beneficial in a variety of
`
`other disorders for which PBA and/or PAA are believed to modify gene expression and/or exert
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`post-translational effects on protein function. In the case of maple syrup urine disease (MSUD, also
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`known as branched-chain ketoaciduria), for example, the apparently beneficial effect of NaPBA in
`
`lowering plasma levels of branched chain amino acids is reported to be mediated by PBA-induced
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`inhibition of the kinase that regulates activity of branched chain alpha-keto acid dehydrogenase
`
`complex or BCKDC. BCKDC is the enzyme that normally breaks down branched-chain amino
`
`acids and is genetically defective in MSUD patients (Bruneti-Pieri 2011). Similarly, the putative
`
`beneficial effects of PAA prodrugs for the treatment of cancer (Chung 2000), neurodegenerative
`
`diseases (Ryu 2005), and sickle cell disease (Perrine 2008) all involve alteration of gene expression
`
`and/0r post-translational effects on protein function via PBA and/0r PAA.
`
`[0010]
`
`Numerous publications reports adverse events following administration of PBA and/or
`
`PAA (Mokhtarani 2012), and FAA is reported to cause reversible toxicity when present in high
`
`levels in circulation. While many of these publications have not recorded PAA blood levels and/or
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`temporally correlated adverse events with PAA levels, toxicities such as nausea, headache, emesis,
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`fatigue, weakness, lethargy, somnolence, dizziness, slurred speech, memory loss, confiasion, and
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`disorientation have been shown to be temporally associated with PAA levels ranging from 499—
`
`1285 ug/mL in cancer patients receiving PAA intravenously, and these toxicities have been shown
`
`to resolve with discontinuation of PAA administration (Thiebault 1994; Thiebault 1995).
`
`Therefore, when administering PAA prodrugs for treatment of nitrogen retention disorders and other
`
`conditions, it is important to optimize dosing so as to achieve the desired therapeutic effect while
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`minimizing the risk of PAA associated toxicity.
`
`W
`
`[0011]
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`Provided herein is a clinically practical approach for utilizing and interpreting blood
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`levels of FAA and PAGN to adjust the dose of a PAA prodrug in order to minimize the risk of
`
`toxicities and maximize drug effectiveness.
`
`[0012]
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`Provided herein in certain embodiments are methods of treating a nitrogen retention
`
`disorder or a condition for which PAA prodrug administration is expected to be beneficial in a
`
`subject comprising the steps of administering a first dosage of a PAA prodrug, measuring plasma
`
`FAA and PAGN levels, calculating a plasma PAA:PAGN ratio, and determining whether the PAA
`
`prodrug dosage needs to be adjusted based on whether the PAA:PAGN ratio falls within a target
`
`range. In certain embodiments, the target range is l to 2.5, l to 2, l to 1.5, 1.5 to 2, or 1.5 to 2.5. In
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`certain embodiments, a PAA:PAGN ratio above the target range indicates that the dosage of the
`
`PAA prodrug needs to be decreased. In other embodiments, a PAA:PAGN ratio above the target
`
`range indicates that the dosage may need to be decreased, with the final determination of whether to
`
`decrease the dosage taking into account other characteristics of the subject such as biochemical
`
`profile or clinical characteristics such as target nitrogen excretion, actual nitrogen excretion,
`
`symptom severity, disorder duration, age, or overall health. In certain embodiments, a PAA:PAGN
`
`ratio below the target range indicates that the dosage of the PAA prodrug needs to be increased. In
`
`other embodiments, a PAA:PAGN ratio below the target range indicates that the dosage may need
`
`to be increased, with the final determination of whether to increase the dosage taking into account
`
`other characteristics of the subject such as biochemical profile or clinical characteristics such as
`
`target nitrogen excretion, actual nitrogen excretion, symptom severity, disorder duration, age, or
`
`overall health. In certain embodiments, a PAA:PAGN ratio that is within the target range but within
`
`a particular subrange (e.g., l to 1.5 or 2 to 2.5 where the target range is l to 2.5) indicates that the
`
`dosage of the PAA prodrug does not need to be adjusted, but that the subject needs to be subjected
`
`to more frequent monitoring. In certain embodiments, the methods filrther comprise a step of
`
`administering an adjusted second dosage if such an adjustment is determined to be necessary based
`
`on the PAA:PAGN ratio and, optionally, other characteristics of the subject. In other embodiments,
`
`the methods further comprise a step of administering a second dosage that is the same as or nearly
`
`the same as the first dosage if no adjustment in dosage is deemed to be necessary. In certain
`
`embodiments, the nitrogen retention disorder is UCD, HE, or ESRD. In certain embodiments, the
`
`condition for which PAA prodrug administration is expected to be beneficial is cancer, a
`
`neurodegenerative diseases, a metabolic disorder, or sickle cell disease. In certain embodiments, the
`
`PAA prodrug is HPN—lOO or NaPBA. In certain embodiments, measurement of plasma FAA and
`
`PAGN levels takes place after the first dosage of the PAA prodrug has had sufficient time to reach
`
`steady state, such as at 48 hours to 1 week after administration.
`
`[0013]
`
`Provided herein in certain embodiments are methods of treating a nitrogen retention
`
`disorder or a condition for which PAA prodrug administration is expected to be beneficial in a
`
`subject who has previously received a first dosage of PAA prodrug comprising the steps of
`
`measuring plasma FAA and PAGN levels, calculating a plasma PAA:PAGN ratio, and determining
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`whether the PAA prodrug dosage needs to be adjusted based on whether the PAA:PAGN ratio falls
`
`within a target range. In certain embodiments, the target range is 1 to 2.5, 1 to 2, 1 to 1.5, 1.5 to 2,
`
`or 1.5 to 2.5. In certain embodiments, a PAA:PAGN ratio above the target range indicates that the
`
`dosage of the PAA prodrug needs to be decreased. In other embodiments, a PAA:PAGN ratio
`
`above the target range indicates that the dosage may need to be decreased, with the final
`
`determination of whether to decrease the dosage taking into account other characteristics of the
`
`subject such as biochemical profile or clinical characteristics such as target nitrogen excretion,
`
`actual nitrogen excretion, symptom severity, disorder duration, age, or overall health. In certain
`
`embodiments, a PAA:PAGN ratio below the target range indicates that the dosage of the PAA
`
`prodrug needs to be increased. In other embodiments, a PAA:PAGN ratio below the target range
`
`indicates that the dosage may need to be increased, with the final determination of whether to
`
`increase the dosage taking into account other characteristics of the subject such as biochemical
`
`profile or clinical characteristics such as target nitrogen excretion, actual nitrogen excretion,
`
`symptom severity, disorder duration, age, or overall health. In certain embodiments, a PAA:PAGN
`
`ratio that is within the target range but within a particular subrange (e. g., 1 to 1.5 or 2 to 2.5 where
`
`the target range is 1 to 2.5) indicates that the dosage of the PAA prodrug does not need to be
`
`adjusted, but that the subject needs to be subjected to more frequent monitoring. In certain
`
`embodiments, the methods fiarther comprise a step of administering an adjusted second dosage if
`
`such an adjustment is determined to be necessary based on the PAA:PAGN ratio and, optionally,
`
`other characteristics of the subject. In other embodiments, the methods fiarther comprise a step of
`
`administering a second dosage that is the same as or nearly the same as the first dosage if no
`
`adjustment in dosage is deemed to be necessary. In certain embodiments, the nitrogen retention
`
`disorder is UCD, HE, or ESRD. In certain embodiments, the condition for which PAA prodrug
`
`administration is expected to be beneficial is cancer, a neurodegenerative diseases, a metabolic
`
`disorder, or sickle cell disease. In certain embodiments, measurement of plasma FAA and PAGN
`
`levels takes place after the first dosage of the PAA prodrug has had sufficient time to reach steady
`
`state, such as at 48 hours to 1 week after administration.
`
`[0014]
`
`Provided herein in certain embodiments are methods of adjusting the dosage of a PAA
`
`prodrug to be administered to a subject comprising the steps of administering a first dosage of a
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`PAA prodrug, measuring plasma FAA and PAGN levels, calculating a plasma PAA:PAGN ratio,
`
`and determining whether the PAA prodrug dosage needs to be adjusted based on whether the
`
`PAA:PAGN ratio falls within a target range. In certain embodiments, the target range is 1 to 2.5, 1
`
`to 2, 1 to 1.5, 1.5 to 2, or 1.5 to 2.5. In certain embodiments, a PAA:PAGN ratio above the target
`
`range indicates that the dosage of the PAA prodrug needs to be decreased. In other embodiments, a
`
`PAA:PAGN ratio above the target range indicates that the dosage may need to be decreased, with
`
`the final determination of whether to decrease the dosage taking into account other characteristics of
`
`the subject such as biochemical profile or clinical characteristics such as target nitrogen excretion,
`
`actual nitrogen excretion, symptom severity, disorder duration, age, or overall health. In certain
`
`embodiments, a PAA:PAGN ratio below the target range indicates that the dosage of the PAA
`
`prodrug needs to be increased. In other embodiments, a PAA:PAGN ratio below the target range
`
`indicates that the dosage may need to be increased, with the final determination of whether to
`
`increase the dosage taking into account other characteristics of the subject such as biochemical
`
`profile or clinical characteristics such as target nitrogen excretion, actual nitrogen excretion,
`
`symptom severity, disorder duration, age, or overall health. In certain embodiments, a PAA:PAGN
`
`ratio that is within the target range but within a particular subrange (e. g., 1 to 1.5 or 2 to 2.5 where
`
`the target range is 1 to 2.5) indicates that the dosage of the PAA prodrug does not need to be
`
`adjusted, but that the subject needs to be subjected to more frequent monitoring. In certain
`
`embodiments, the methods fiarther comprise a step of administering an adjusted second dosage if
`
`such an adjustment is determined to be necessary based on the PAA:PAGN ratio and, optionally,
`
`other characteristics of the subject. In other embodiments, the methods fiarther comprise a step of
`
`administering a second dosage that is the same as or nearly the same as the first dosage if no
`
`adjustment in dosage is deemed to be necessary. In certain embodiments, measurement of plasma
`
`FAA and PAGN levels takes place after the first dosage of the PAA prodrug has had sufficient time
`
`to reach steady state, such as at 48 hours to 1 week after administration.
`
`[0015]
`
`Provided herein in certain embodiments are methods of determining whether a first
`
`dosage of a PAA prodrug can be safely administered to a subject comprising the steps of
`
`administering the first dosage of a PAA prodrug, measuring plasma FAA and PAGN levels,
`
`calculating a plasma PAA:PAGN ratio, and determining whether the first dosage can be safely
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`administered based on whether the PAA:PAGN ratio falls above a target range. In certain
`
`embodiments, the target range is 1 to 2.5, 1 to 2, 1 to 1.5, 1.5 to 2, or 1.5 to 2.5. In certain
`
`embodiments, a PAA:PAGN ratio above the target range indicates that the first dosage is unsafe and
`
`needs to be decreased. In other embodiments, a PAA:PAGN ratio above the target range indicates
`
`that the first dosage is potentially unsafe and may need to be decreased, with the final determination
`
`of whether to decrease the dosage taking into account other characteristics of the subject such as
`
`biochemical profile or clinical characteristics such as target nitrogen excretion, actual nitrogen
`
`excretion, symptom severity, disorder duration, age, or overall health. In certain embodiments, a
`
`PAA:PAGN ratio that is within the target range but within a particular subrange (e.g., 2 to 2.5 where
`
`the target range is 1 to 2.5) indicates that the first dosage is likely safe, but that the subject needs to
`
`be subjected to more frequent monitoring. In certain embodiments, the methods fiarther comprise a
`
`step of administering an adjusted second dosage if such an adjustment is determined to be necessary
`
`based on the PAA:PAGN ratio and, optionally, other characteristics of the subject. In certain
`
`embodiments, measurement of plasma FAA and PAGN levels takes place after the first dosage of
`
`the PAA prodrug has had sufficient time to reach steady state, such as at 48 hours to 1 week after
`
`administration.
`
`[0016]
`
`Provided herein in certain embodiments are methods of determining whether a first
`
`dosage of a PAA prodrug is likely to be effective for treating a nitrogen retention disorder or
`
`another disorder for which PAA prodrug administration is expected to be beneficial comprising the
`
`steps of administering the first dosage of a PAA prodrug, measuring plasma FAA and PAGN levels,
`
`calculating a plasma PAA:PAGN ratio, and determining whether the first dosage is likely to be
`
`effective based on whether the PAA:PAGN ratio falls below a target range. In certain
`
`embodiments, the target range is 1 to 2.5, 1 to 2, 1 to 1.5, 1.5 to 2, or 1.5 to 2.5. In certain
`
`embodiments, a PAA:PAGN ratio below the target range indicates that the first dosage is unlikely to
`
`be effective needs to be increased. In other embodiments, a PAA:PAGN ratio below the target
`
`range indicates that the first dosage is potentially ineffective and may need to be increased, with the
`
`final determination of whether to increase the dosage taking into account other characteristics of the
`
`subject such as biochemical profile or clinical characteristics such as target nitrogen excretion,
`
`actual nitrogen excretion, symptom severity, disorder duration, age, or overall health. In certain
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`embodiments, a PAA:PAGN ratio that is within the target range but within a particular subrange
`
`(e.g., l to 1.5 where the target range is l to 2.5) indicates that the first dosage is likely effective, but
`
`that the subject needs to be subjected to more frequent monitoring. In certain embodiments, the
`
`methods fiarther comprise a step of administering an adjusted second dosage if such an adjustment is
`
`determined to be necessary based on the PAA:PAGN ratio and, optionally, other characteristics of
`
`the subject. In certain embodiments, measurement of plasma FAA and PAGN levels takes place
`
`after the first dosage of the PAA prodrug has had sufficient time to reach steady state, such as at 48
`
`hours to 1 week after administration.
`
`[0017]
`
`In certain embodiments, methods are provided for optimizing the therapeutic efficacy of
`
`a PAA prodrug in a subject who has previously been adminsitered a first dosage of PAA prodrug
`
`comprising the steps of measuring plasma FAA and PAGN levels, calculating a plasma PAA:PAGN
`
`ratio, and determining whether the PAA prodrug dosage needs to be adjusted based on whether the
`
`PAA:PAGN ratio falls within a target range. In certain embodiments, the target range is l to 2.5, l
`
`to 2, l to 1.5, 1.5 to 2, or 1.5 to 2.5. In certain embodiments, a PAA:PAGN ratio above the target
`
`range indicates that the dosage of the PAA prodrug needs to be decreased. In other embodiments, a
`
`PAA:PAGN ratio above the target range indicates that the dosage may need to be decreased, with
`
`the final determination of whether to decrease the dosage taking into account other characteristics of
`
`the subject such as biochemical profile or clinical characteristics such as target nitrogen excretion,
`
`actual nitrogen excretion, symptom severity, disorder duration, age, or overall health. In certain
`
`embodiments, a PAA:PAGN ratio below the target range indicates that the dosage of the PAA
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`prodrug needs to be increased. In other embodiments, a PAA:PAGN ratio below the target range
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`indicates that the dosage may need to be increased, with the final determination of whether to
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`increase the dosage taking into account other characteristics of the subject such as biochemical
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`profile or clinical characteristics such as target nitrogen excretion, actual nitrogen excretion,
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`symptom severity, disorder duration, age, or overall health. In certain embodiments, a PAA:PAGN
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`ratio that is within the target range but within a particular subrange (e. g., l to 1.5 or 2 to 2.5 where
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`the target range is l to 2.5) indicates that the dosage of the PAA prodrug does not need to be
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`adjusted, but that the subject needs to be subjected to more frequent monitoring. In certain
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`embodiments, the methods fiarther comprise a step of administering an adjusted second dosage if
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`such an adjustment is determined to be necessary based on the PAA:PAGN ratio and, optionally,
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`other characteristics of the subject. In other embodiments, the methods fiarther comprise a step of
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`administering a second dosage that is the same as or nearly the same as the first dosage if no
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`adjustment in dosage is deemed to be necessary. In certain embodiments, measurement of plasma
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`FAA and PAGN levels takes place after the first dosage of the PAA prodrug has had sufficient time
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`to reach steady state, such as at 48 hours to 1 week after administration.
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`[0018]
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`In certain embodiments, methods are provided for obtaining a plasma PAA:PAGN ratio
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`within a target range in a subject comprising the steps of administering a first dosage of a PAA
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`prodrug, measuring plasma FAA and PAGN levels, calculating a plasma PAA:PAGN ratio, and
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`determining whether the PAA:PAGN ratio falls within the target range. If the PAA:PAGN ratio
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`does not fall within the target range, an adjusted second dosage is administered, and these steps are
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`repeated until a plasma PAA:PAGN ratio falling within the target range is achieved. In certain
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`embodiments, the target range is l to 2.5, l to 2, l to 1.5, 1.5 to 2, or 1.5 to 2.5. In certain
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`embodiments, a PAA:PAGN ratio above the target range indicates that the dosage of the PAA
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`prodrug needs to be decreased and a PAA:PAGN ratio below the target range indicates that the
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`dosage of the PAA prodrug needs to be increased. In certain embodiments, measurement of plasma
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`FAA and PAGN levels takes place after the first dosage of the PAA prodrug has had sufficient time
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`to reach steady state, such as at 48 hours to 1 week after administration.
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`BRIEF DESCRIPTION OF DRAWINGS
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`[0019]
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`Figure l: Urea cycle.
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`[0020]
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`Figure 2: Plasma PAA levels versus plasma PAA:PAGN ratio in (A) all subjects
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`combined (healthy adults, patients age 2 months and above with UCDs, and patients with cirrhosis),
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`(B) patients age 2 months and above with UCDs, and (C) patients with cirrhosis.
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`[0021]
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`Figure 3: Estimated probability (95% confidence interval (c.i.)) of correctly detecting
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`elevated plasma PAA:PAGN ratio (22.0) with a single blood sample at a designated time.
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`[0022]
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`Figure 4:Distribution of plasma PAA:PAGN ratio (log scale) by time since dosing
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`(hours) and category of maximum PAA:PAGN ratio in all subjects combined.
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`[0023]
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`Figure 5: Distribution of plasma PAA concentrations (ug/mL) by PAA:PAGN ratio for
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`(A) all subjects and (B) UCD and HE subjects.
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`DETAILED DESCRIPTION
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`[0024]
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`The following description of the invention is merely intended to illustrate various
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`embodiments of the invention. As such, the specific modifications discussed are not to be construed
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`as limitations on the scope of the invention. It will be apparent to one skilled in the art that various
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`equivalents, changes, and modifications may be made without departing from the scope of the
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`invention, and it is understood that such equivalent embodiments are to be included herein.
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`[0025]
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`The enzymes responsible for beta oxidation of PBA to PAA are present in most cell
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`types capable of utilizing fatty acids as energy substrates, and the widespread distribution of these
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`enzymes presumably accounts for the rapid and essentially complete conversion of PBA to PAA.
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`However, the enzymes that conjugate PAA with glutamine to form PAGN are found primarily in
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`the liver and to a lesser extend in kidneys (Moldave 195 7). Therefore, the conversion of PAA to
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`PAGN may be affected under several circumstances, including the following: a) if conjugation
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`capacity is saturated (e.g., by high doses of PAA prodrug); b) if conjugation capacity is
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`compromised (e.g., by severe hepatic and/or renal dysfunction); c) if the substrate (glutamine) for
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`PAA to PAGN conjugation is rate limiting; d) genetically determined variability (i.e.,
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`polymorphisms) in the enzymes responsible for PAA to PAGN conversion, or e) in young children,
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`since the capacity to convert PAA to PAGN varies with body size measured as body surface area
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`(Monteleone 2012). The presence of any one of these conditions may lead to accumulation of PAA
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`in the body, which causes reversible toxicity.
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`[0026]
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`The goal of PAA prodrug administration in subjects with nitrogen retention disorders is
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`to provide a sufficient dosage to obtain a desired level of nitrogen removal while avoiding excess
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`build-up of PAA. The goal of PAA prodrug administration in patients without a nitrogen retention
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`disorder (e.g., a neurodegenerative disease) is to achieve circulating metabolite levels necessary to
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`produce a clinical benefit by alteration of gene expression and/0r protein folding or fimction.
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`However, there are several difficulties associated with determining the proper dosage in patients
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`with nitrogen retention disorders.
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`[0027]
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`Plasma FAA and PAGN levels are affected by various factors, including timing of the
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`blood draw in relation to drug administration, hepatic fimction, availability of metabolizing
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`enzymes, and availability of substrates required for metabolism. A random PAA level drawn during
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`an outpatient visit to determine if levels are in the toxicity range without considering concomitant
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`PAGN level is insufficient to inform dosing. First, PAA levels vary many-fold over the course of
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`the day, fluctuating a great deal between peak and trough levels. For example, in the Hyperion
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`pivotal study evaluating HPN—lOO for use in treating adult UCD (Study ID HPN—100-006, Clinical
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`Trials ID NCT00992459), serial blood samples were obtained for PK studies over a 24 hour period
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`during which subjects were receiving HPN-100 or NaPBA. The fluctuation index for PAA over a
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`24 hour period, which represents the fluctuation between maximum concentration (typically
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`observed after the last daily dose or at approximately 12 hours) and minimum concentration
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`(typically observed in the morning after overnight fasting or at 0 hours), indicated a very high
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`degree of variability (21.50% for NaPBA and 1368% for HPN—lOO). Therefore, a single plasma
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`PAA level may not be representative of the highest PAA level a patient may experience