Patent
`79532.8004.US01
`
`To:
`
`Commissioner for Patents
`P.O. Box 1450
`Alexandria, VA 22313-1450
`
`NEW APPLICATION TRANSMITTAL- UTILITY
`
`Sir:
`
`Transmitted herewith for filing is a utility patent application:
`
`lnventor(s): Bruce SCHARSCHMIDT
`Masoud MOKHTARAN I
`
`I.
`
`II.
`
`Title:
`
`METHODS OF THERAPEUTIC MONITORING OF PHENYLACETIC
`ACID PRODRUGS
`
`PAPERS ENCLOSED HEREWITH FOR FILING UNDER 37 CFR § 1.53(b):
`41
`Page(s) of Written Description
`Page(s) Claims
`~
`1
`Page(s) Abstract
`Sheets of Drawings
`7
`Sheets of Sequence Listing
`
`ADDITIONAL PAPERS ENCLOSED IN CONNECTION WITH THIS FILING:
`D
`Declaration
`D
`Power of Attorney D SeparateD Combined with Declaration
`D
`Assignment to and assignment cover sheet
`D
`Certified Copy of Priority Document No(s): __
`D
`Information Disclosure Statement w/PTO 1449 D Copy of Citations
`D
`Preliminary Amendment
`D
`Sequence Listing Diskette and Declaration
`D
`Request and Certification under 35 U.S.C. § 122(b)(2)(B)(i). Applicant must
`attach form PTO/SB/35
`Return Postcard
`
`D
`
`Ill.
`
`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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`IV.
`
`V.
`
`FEES:
`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.
`~
`
`Patent
`79532.8004.US01
`
`CORRESPONDENCE ADDRESS
`Please send all correspondence to Customer Number 34055.
`Perkins Coie LLP
`Patent- LA
`P.O. Box 1208
`Seattle, WA 98111-1208
`Phone: (31 0) 788-9900
`Fax: (206) 332-7198
`Please direct all inquiries to Patrick Morris, at the above customer number.
`
`Dated: September 11. 2012
`
`Respectfully submitted,
`
`PERKINS COlE LLP
`
`By: /Patrick D. Morris/
`Patrick D. Morris, Ph.D.
`Reg. No. 53,351
`
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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 U.S. Provisional Application No. 61/636,256,
`
`filed April20, 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,
`
`often referred to as end-stage renal disease (ESRD).
`
`[0003]
`
`UCDs include several inherited deficiencies of enzymes or transporters necessary for the
`
`synthesis of urea from ammonia, including enzymes involved in the urea cycle. The urea cycle is
`
`depicted in Figure 1, which also illustrates how certain ammonia-scavenging drugs act to assist in
`
`elimination of excessive ammonia. With reference to Figure 1, 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 tum,
`
`carbamyl phosphate reacts with ornithine to produce citrulline in a reaction mediated by ornithine
`
`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 ornithine 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 function 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
`
`ammonia is the cornerstone of treatment.
`
`[0004]
`
`HE refers to a spectrum of neurologic signs and symptoms believed to result from
`
`hyperammonemia, which frequently occur in subjects with cirrhosis or certain other types of liver
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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
`
`ammonia due to dysfunctional liver in detoxifying dietary protein is the main pathophysiology
`
`associated with HE (Ong 2003).
`[0005]
`
`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 ofESRD, 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 (P AA) 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/or 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 -1 00), which is described in U.S. 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 ofPAA. The difference between HPN-100 and NaPBA with respect to
`
`metabolism is that HPN-100 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]
`
`HPN -100 and N aPBA share the same general mechanism of action: PBA is converted to
`
`P AA via beta oxidation, and P AA is conjugated enzymatically with glutamine to form
`
`phenylacetylglutamine (P AGN), which is excreted in the urine. The structures of PBA, P AA, and
`
`PAGN are set forth below:
`
`[0008]
`
`The clinical benefit ofNaPBA and HPN-100 with regard to nitrogen retention disorders
`
`derives from the ability of P AGN 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 P AGN excreted in the urine. Therefore, two equivalents of nitrogen are
`
`removed for each mole ofPAA 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, P AA 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
`
`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 ofNaPBA in
`
`lowering plasma levels of branched chain amino acids is reported to be mediated by PBA-induced
`
`inhibition of the kinase that regulates activity ofbranched 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 ofPAA 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/or post-translational effects on protein function via PBA and/or PAA.
`
`[0010]
`
`Numerous publications reports adverse events following administration ofPBA and/or
`
`PAA (Mokhtarani 2012), and PAA is reported to cause reversible toxicity when present in high
`
`levels in circulation. While many of these publications have not recorded P AA blood levels and/or
`
`temporally correlated adverse events with P AA levels, toxicities such as nausea, headache, emesis,
`
`fatigue, weakness, lethargy, somnolence, dizziness, slurred speech, memory loss, confusion, and
`
`disorientation have been shown to be temporally associated with P AA levels ranging from 499-
`
`1285 j..tg/mL in cancer patients receiving P AA intravenously, and these toxicities have been shown
`
`to resolve with discontinuation of P AA administration (Thiebault 1994; Thiebault 1995).
`
`Therefore, when administering P AA pro drugs for treatment of nitrogen retention disorders and other
`
`conditions, it is important to optimize dosing so as to achieve the desired therapeutic effect while
`
`minimizing the risk ofPAA associated toxicity.
`
`SUMMARY
`
`[0011]
`
`Provided herein is a clinically practical approach for utilizing and interpreting blood
`
`levels of P AA and P AGN to adjust the dose of a P AA pro drug in order to minimize the risk of
`
`toxicities and maximize drug effectiveness.
`
`[0012]
`
`Provided herein in certain embodiments are methods of treating a nitrogen retention
`
`disorder or a condition for which P AA prodrug administration is expected to be beneficial in a
`
`subject comprising the steps of administering a first dosage of a P AA prodrug, measuring plasma
`
`P AA and PAGN levels, calculating a plasma P AA:P AGN ratio, and determining whether the P AA
`
`prodrug dosage needs to be adjusted based on whether the P AA: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
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`certain embodiments, a P AA:PAGN ratio above the target range indicates that the dosage of the
`
`P AA 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 P AA:PAGN
`
`ratio below the target range indicates that the dosage of the P AA pro drug needs to be increased. In
`
`other embodiments, a P AA:P AGN 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 P AA: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 further 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 P AA prodrug administration is expected to be beneficial is cancer, a
`
`neurodegenerative diseases, a metabolic disorder, or sickle cell disease. In certain embodiments, the
`
`P AA pro drug is HPN -100 or N aPBA. In certain embodiments, measurement of plasma P AA and
`
`P AGN levels takes place after the first dosage of the P AA pro drug 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 P AA prodrug administration is expected to be beneficial in a
`
`subject who has previously received a first dosage ofPAA prodrug comprising the steps of
`
`measuring plasma P AA and PAGN levels, calculating a plasma P AA:PAGN ratio, and determining
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`whether the P AA prodrug dosage needs to be adjusted based on whether the P AA: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 P AA prodrug needs to be decreased. In other embodiments, a P AA:P AGN 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 P AA:P AGN ratio below the target range indicates that the dosage of the P AA
`
`prodrug needs to be increased. In other embodiments, a P AA:P AGN 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 P AA: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 P AA prodrug does not need to be
`
`adjusted, but that the subject needs to be subjected to more frequent monitoring. In certain
`
`embodiments, the methods further comprise a step of administering an adjusted second dosage if
`
`such an adjustment is determined to be necessary based on the P AA: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, measurement of plasma P AA and P AGN
`
`levels takes place after the first dosage of the P AA pro drug 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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`Attorney Docket No. 79532.8004.US01
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`P AA prodrug, measuring plasma P AA and P AGN levels, calculating a plasma P AA:PAGN ratio,
`
`and determining whether the P AA pro drug 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 P AA pro drug needs to be decreased. In other embodiments, a
`
`P AA: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 P AA:PAGN ratio below the target range indicates that the dosage of the P AA
`
`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 P AA: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 P AA prodrug does not need to be
`
`adjusted, but that the subject needs to be subjected to more frequent monitoring. In certain
`
`embodiments, the methods further comprise a step of administering an adjusted second dosage if
`
`such an adjustment is determined to be necessary based on the P AA: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, measurement of plasma
`
`P AA and PAGN levels takes place after the first dosage of the P AA 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 P AA prodrug can be safely administered to a subject comprising the steps of
`
`administering the first dosage of a P AA prodrug, measuring plasma P AA and PAGN levels,
`
`calculating a plasma P AA:P AGN 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 P AA:P AGN ratio above the target range indicates that the first dosage is unsafe and
`
`needs to be decreased. In other embodiments, a P AA:P AGN 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
`
`P AA: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 further 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 P AA and P AGN levels takes place after the first dosage of
`the P AA pro drug 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 P AA pro drug is likely to be effective for treating a nitrogen retention disorder or
`
`another disorder for which P AA pro drug administration is expected to be beneficial comprising the
`
`steps of administering the first dosage of a P AA prodrug, measuring plasma P AA and P AGN levels,
`
`calculating a plasma P AA:PAGN ratio, and determining whether the first dosage is likely to be
`
`effective based on whether the P AA:P AGN 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 P AA:P AGN ratio below the target range indicates that the first dosage is unlikely to
`
`be effective needs to be increased. In other embodiments, a P AA:P AGN 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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`Attorney Docket No. 79532.8004.US01
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`embodiments, a P AA:P AGN ratio that is within the target range but within a particular subrange
`
`(e.g., 1 to 1.5 where the target range is 1 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 further comprise a step of administering an adjusted second dosage if such an adjustment is
`
`determined to be necessary based on the P AA:PAGN ratio and, optionally, other characteristics of
`
`the subject. In certain embodiments, measurement of plasma PAA and PAGN levels takes place
`
`after the first dosage of the P AA pro drug 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 pro drug in a subject who has previously been adminsitered a first dosage of P AA pro drug
`
`comprising the steps of measuring plasma P AA and PAGN levels, calculating a plasma P AA:PAGN
`
`ratio, and determining whether the P AA pro drug 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 P AA pro drug needs to be decreased. In other embodiments, a
`
`P AA: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 P AA:P AGN ratio below the target range indicates that the dosage of the P AA
`
`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 P AA: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 P AA 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 further 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 P AA:PAGN ratio and, optionally,
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`other characteristics of the subject. In other embodiments, the methods further 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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`P AA and P AGN levels takes place after the first dosage of the P AA 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 P AA:P AGN ratio
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`within a target range in a subject comprising the steps of administering a first dosage of a P AA
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`prodrug, measuring plasma P AA and PAGN levels, calculating a plasma P AA:PAGN ratio, and
`
`determining whether the P AA:P AGN ratio falls within the target range. If the P AA:P AGN ratio
`
`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 P AA:PAGN ratio falling within the target range is achieved. In certain
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`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 ofthe PAA
`
`prodrug needs to be decreased and a P AA:P AGN ratio below the target range indicates that the
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`dosage of the P AA pro drug needs to be increased. In certain embodiments, measurement of plasma
`
`P AA and PAGN levels takes place after the first dosage of the P AA 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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`[0020]
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`Figure 1: Urea cycle.
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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
`
`elevated plasma P AA:PAGN ratio (2:2.0) 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
`
`(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 (~-tg/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
`
`embodiments of the invention. As such, the specific modifications discussed are not to be construed
`
`as limitations on the scope of the invention. It will be apparent to one skilled in the art that various
`
`equivalents, changes, and modifications may be made without departing from the scope of the
`
`invention, and it is understood that such equivalent embodiments are to be included herein.
`
`[0025]
`
`The enzymes responsible for beta oxidation of PBA to P AA are present in most cell
`
`types capable of utilizing fatty acids as energy substrates, and the widespread distribution of these
`
`enzymes presumably accounts for the rapid and essentially complete conversion of PBA to P AA.
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`However, the enzymes that conjugate P AA with glutamine to form P AGN are found primarily in
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`the liver and to a lesser extend in kidneys (Moldave 1957). Therefore, the conversion ofPAA to
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`PAGN may be affected under several circumstances, including the following: a) if conjugation
`
`capacity is saturated (e.g., by high doses ofP AA prodrug); b) if conjugation capacity is
`
`compromised (e.g., by severe hepatic and/or renal dysfunction); c) if the substrate (glutamine) for
`P AA to P AGN conjugation is rate limiting; d) genetically determined variability (i.e.,
`
`polymorphisms) in the enzymes responsible for PAA to PAGN conversion, or e) in young children,
`
`since the capacity to convert P AA to P AGN varies with body size measured as body surface area
`
`(Monteleone 2012). The presence of any one of these conditions may lead to accumulation ofPAA
`
`in the body, which causes reversible toxicity.
`
`[0026]
`
`The goal of P AA pro drug 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 ofPAA. The goal ofPAA 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
`
`produce a clinical benefit by alteration of gene expression and/or protein folding or function.
`
`However, there are several difficulties associated with determining the proper dosage in patients
`
`with nitrogen retention disorders.
`
`[0027]
`
`Plasma PAA and PAGN levels are affected by various factors, including timing of the
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`blood draw in relation to drug administration, hepatic function, availability of metabolizing
`
`enzymes, and availability of substrates required for metabolism. A random P AA level drawn during
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`an outpatient visit to determine if levels are in the toxicity range without considering co