Phase Ib Study of Unesbulin (PTC596) Plus Dacarbazine for the Treatment of Locally Recurrent, Unresectable or Metastatic, Relapsed or Refractory Leiomyosarcoma.

PURPOSE: This multicenter, single-arm, open-label, phase Ib study was designed to determine the recommended phase II dose (RP2D) and to evaluate the safety and preliminary efficacy of unesbulin plus dacarbazine (DTIC) in patients with advanced leiomyosarcoma (LMS). PATIENTS AND METHODS: Adult subjects with locally advanced, unresectable or metastatic, relapsed or refractory LMS were treated with escalating doses of unesbulin orally twice per week in combination with DTIC 1,000 mg/m2 intravenously (IV) once every 21 days. The time-to-event continual reassessment method was used to determine the RP2D on the basis of dose-limiting toxicities (DLTs) assessed during the first two 21-day treatment cycles. All explored doses of unesbulin (200 mg up to 400 mg) were in combination with DTIC. An expansion cohort was enrolled to evaluate the safety and efficacy of unesbulin at the RP2D. RESULTS: Unesbulin 300 mg administered orally twice per week in combination with DTIC 1,000 mg/m2 IV once every 21 days was identified as the RP2D. On the basis of data from 27 subjects who were deemed DLT-evaluable, toxicity was higher in the unesbulin 400 mg group, with three of four subjects (75%) experiencing DLTs versus one of four subjects (25%) in the 200 mg group and three of 19 subjects (15.8%) in the 300 mg group. The most commonly reported DLTs and treatment-related grade 3 and 4 adverse events were thrombocytopenia and neutropenia. At the RP2D, seven subjects who were efficacy evaluable achieved partial response for an objective response rate of 24.1%. CONCLUSION: Unesbulin 300 mg twice per week plus DTIC 1,000 mg/m2 once every 21 days was identified as the RP2D, demonstrating a favorable benefit-risk profile in a heavily pretreated population of adults with advanced LMS.

Quantitative Systems Toxicology Modeling Informed Safe Dose Selection of Emvododstat in Acute Myeloid Leukemia Patients.

Clinical investigation of emvododstat for the treatment of solid tumors was halted after two patients who were heavily treated with other anticancer therapies experienced drug-induced liver failure. However, preclinical investigations supported that emvododstat at lower doses might be effective in treating acute myeloid leukemia (AML) and against severe acute respiratory syndrome-coronavirus 2 as a dihydroorotate dehydrogenase inhibitor. Therefore, a quantitative systems toxicology model, DILIsym, was used to predict liver safety of the proposed dosing of emvododstat in AML clinical trials. In vitro mechanistic toxicity data of emvododstat and its desmethyl metabolite were integrated with in vivo exposure within DILIsym to predict hepatotoxicity responses in a simulated human population. DILIsym simulations predicted alanine aminotransferase elevations observed in prior emvododstat clinical trials in patients with solid tumors, but not in the prospective AML clinical trial with the proposed dosing regimens. Exposure predictions based on physiologically-based pharmacokinetic modeling suggested that reduced doses of emvododstat would produce clinical exposures that would be efficacious to treat AML. In the AML clinical trial, only eight patients experienced aminotransferase elevations, all of which were mild (grade 1), all resolving within a short period of time, and no patient showed symptoms of hepatotoxicity, confirming the prospective prediction of liver safety. Overall, retrospective DILIsym simulations adequately predicted the liver safety liabilities of emvododstat in solid tumor trials and prospective simulations predicted the liver safety of reduced doses in an AML clinical trial. The modeling was critical to enabling regulatory approval to proceed with the AML clinical trial wherein the predicted liver safety was confirmed.

LC-MS/MS methods for direct measurement of sepiapterin and tetrahydrobiopterin in human plasma and clinical applications.

Aim: Tetrahydrobiopterin (BH4), a natural cofactor of aromatic amino acid hydroxylases, and sepiapterin, a natural precursor of BH4, are endogenously present in human plasma. This is the first report on methods for direct quantification of sepiapterin and BH4 in human plasma by LC-MS/MS for pharmacokinetic assessment. Materials & methods: The analytes in plasma were harvested from blood that were treated with 10% ascorbic acid (AA) to a final concentration of 1% AA. Results & conclusion: The quantification methods were validated for calibration ranges of 0.75-500 ng/ml and 0.5-500 ng/ml for sepiapterin and BH4, respectively. Quantification of analytes was challenging due to their susceptibility to redox reactions. The validated methods were utilized successfully to support clinical development of sepiapterin.

Relative Oral Bioavailability and Food Effects of Two Sepiapterin Formulations in Healthy Participants.

Sepiapterin is an orally administered drug in development for the treatment of phenylketonuria, an inborn error of metabolism characterized by the deficiency of the phenylalanine-metabolizing enzyme phenylalanine hydroxylase. This study characterized the pharmacokinetics, safety, and tolerability of 2 clinical sepiapterin formulations (Phase 1/2, Phase 3) and the effects of food on the pharmacokinetics of the Phase 3 formulation in healthy participants. In Part A, 18 participants were randomized to one of 2 treatment sequences, each with 4 dosing periods comprising a single dose (20 or 60 mg/kg) of the Phase 1/2 or the Phase 3 formulation with a low-fat diet. In Part B, 14 participants were randomized to one of 2 sequences, each comprising 4 dosing periods of a single dose (20 or 60 mg/kg) of the Phase 3 formulation under fed (high-fat) or fasted conditions. Following oral administration, sepiapterin was quickly absorbed and rapidly and extensively converted to tetrahydrobiopterin (BH4). BH4 was the major circulating active moiety. Under low-fat conditions, the Phase 3 formulation was bioequivalent to the Phase 1/2 formulation at 20 mg/kg, while slightly lower BH4 exposure (approximately 0.81×) for the Phase 3 formulation was observed at 60 mg/kg. BH4 exposure increased to approximately 1.7× under the low-fat condition and approximately 2.8× under the high-fat condition at a dose of either 20 or 60 mg/kg for the Phase 3 formulation, compared with the fasted condition. Both sepiapterin formulations were well tolerated, with no serious or severe adverse events reported. All treatment-emergent adverse events were mild or moderate in severity.

Pharmacokinetics of Dacarbazine and Unesbulin and CYP1A2-Mediated Drug Interactions in Patients With Leiomyosarcoma.

Unesbulin is being investigated in combination with dacarbazine (DTIC) as a potential therapeutic agent in patients with advanced leiomyosarcoma (LMS). This paper reports the pharmacokinetics (PK) of unesbulin, DTIC, and its unreactive surrogate metabolite 5-aminoimidazole-4-carboxamide (AIC) in 29 patients with advanced LMS. Drug interactions between DTIC (and AIC) and unesbulin were evaluated. DTIC (1000 mg/m2 ) was administered to patients with LMS via 1-hour intravenous (IV) infusion on Day 1 of every 21-day (q21d) cycle. Unesbulin dispersible tablets were administered orally twice weekly (BIW), starting on Day 2 of every cycle, except for Cycle 2 (C2), where unesbulin was dosed either on Day 1 together with DTIC or on Day 2, 1 day after DTIC administration. The PK of DTIC, AIC, and unesbulin in Cycle 1 (C1) and C2 were estimated using noncompartmental analysis. DTIC and AIC were measurable immediately after the start of infusion and reached Cmax immediately or shortly after end of infusion at 1.0 and 1.4 hours (Tmax ), respectively. Coadministration of unesbulin orally at 200 mg or above with DTIC inhibited cytochrome P450 (CYP)1A2-mediated DTIC metabolism, resulting in 66.7% reduction of AIC exposures. Such inhibition could be mitigated when unesbulin was dosed the day following DTIC infusion. Repeated unesbulin dosing demonstrated evidence of clinical CYP1A2 induction and increased AIC Cmax by 69.4% and AUCinf by 57.9%. No meaningful difference in unesbulin PK was observed between C2 and C1. The combination therapy of 1000 mg/m2 IV DTIC q21d and 300 mg unesbulin BIW in a staggered regimen is well tolerated in patients with LMS.

Absorption, metabolism and excretion of 14C-emvododstat following repeat daily oral dose administration in human volunteers using a combination of microtracer radioactivity and high radioactivity doses.

Emvododstat is a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of COVID-19 and acute myeloid leukemia. Since the metabolism and pharmacokinetics of emvododstat in humans is time­dependent, a repeat dose study design using a combination of microtracer radioactivity and high radioactivity doses was employed to evaluate the metabolism and excretion of emvododstat near steady state. Seven healthy male subjects each received 16 mg/0.3 µCi 14C-emvododstat daily oral doses for 6 days followed by a 16 mg/100 µCi high radioactivity oral dose on Day 7. Following the last 16 mg/0.3 µCi 14C­emvododstat dose on Day 6, total radioactivity in plasma peaked at 6 h post-dose. Following a high radioactivity oral dose (16 mg/100 µCi) of 14C-emvododstat on Day 7, both whole blood and plasma radioactivity peaked at 6 h, rapidly declined from 6 h to 36 h post-dose, and decreased slowly thereafter with measurable radioactivity at 240 h post-dose. The mean cumulative recovery of the administered dose was 6.0% in urine and 19.9% in feces by 240 h post-dose, and the mean extrapolated recovery to infinity was 37.3% in urine and 56.6% in feces. Similar metabolite profiles were observed after repeat daily microtracer radioactivity oral dosing on Day 6 and after a high radioactivity oral dose on Day 7. Emvododstat was the most abundant circulating component, M443 and O-desmethyl emvododstat glucuronide were the major circulating metabolites; M474 was the most abundant metabolite in urine, while O­desmethyl emvododstat was the most abundant metabolite in feces. Significance Statement This study provides a complete set of the absorption, metabolism and excretion data of emvododstat, a potent inhibitor of dihydroorotate dehydrogenase, at close to steady state in healthy human subjects. Resolution of challenges due to slow metabolism and elimination of a lipophilic compound highlighted in this study can be achieved by repeat daily microtracer radioactivity oral dosing followed by a high radioactivity oral dosing at therapeutically relevant doses.

Absorption, distribution, metabolism and excretion of 14C-vatiquinone in rats, dogs, and human subjects.

Vatiquinone is a potent inhibitor of 15-lipoxygenase and is in clinical development for the treatment of mitochondrial diseases and other disorders characterised by high levels of oxidative stress and dysregulation of energy metabolism.In rats, 14C-vatiquinone-derived radioactivity was quickly and widely distributed throughout the body and cleared from most tissues by 24 h post-dose following a single oral dose of 14C-vatiquinone.Following oral administration, 94% of dose was recovered within seven days in rats, approximately 61% of dose was recovered within seven days in dogs and approximately 93% of dose was recovered within nine days in human subjects (IND 119220). Faecal excretion was the major route (>56% dose) in all species; urinary excretion was minimal in rats and dogs (<3% dose) but was higher in humans (∼ 22% dose).Following oral administration, vatiquinone was the dominant circulating component in rats and dogs but was minor in human subjects. There were no plasma metabolites that were more than 10% of total drug related exposures in all species.Following oral administration, vatiquinone was not detectable in urine but was the most prominent component in faeces in rats, dogs, and humans.

A clinical pharmacokinetic drug-drug interaction study between dextromethorphan and emvododstat, a potent anti-SARS-CoV-2 dihydroorotate dehydrogenase inhibitor.

PURPOSE: A therapeutic agent that targets both viral replication and the hyper-reactive immune response would offer a highly desirable treatment for severe acute respiratory syndrome corona virus 2 (SARS-CoV-2, coronavirus disease 2019, COVID-19) management. Emvododstat (PTC299; 4-chlorophenyl 6-chloro-1-[4-methoxyphenyl]-1,3, 4,9-tetrahydro-2H-pyrido[3,4-b]indole-2-carboxylate) was found to be a potent inhibitor of immunomodulatory and inflammation-related processes by inhibition of dihydroorotate dehydrogenase to reduce the severity of SARS-CoV-2 infections This drug interaction study was performed to determine if emvododstat was an inhibitor of CYP2D6. METHODS: Potential drug-drug interactions between emvododstat and a CYP2D6 probe substrate (dextromethorphan) were investigated by measuring plasma dextromethorphan and metabolite (dextrorphan) concentrations before and after emvododstat administration. On day 1, 18 healthy subjects received an oral dose of 30 mg dextromethorphan followed by a 4-day washout period. On day 5, subjects received an oral dose of 250 mg emvododstat with food. Two hours later, 30 mg dextromethorphan was administered. RESULTS: When given with emvododstat, plasma dextromethorphan concentrations increased substantially, while metabolite levels (dextrorphan) remained essentially the same. Maximum plasma dextromethorphan concentration (Cmax) increased from 2006 to 5847 pg/mL. Dextromethorphan exposure (AUC) increased from 18,829 to 157,400 h·pg/mL for AUC0-last and from 21,585 to 362,107 h·pg/mL for AUC0-inf following administration of emvododstat. When dextromethorphan parameters were compared before and after emvododstat, least squares mean ratios (90% confidence interval) were found to be 2.9 (2.2, 3.8), 8.4 (6.1, 11.5), and 14.9 (10.0, 22.1) for Cmax, AUC0-last, and AUC0-inf, respectively. CONCLUSION: Emvododstat appears to be a strong CYP2D6 inhibitor. No drug-related treatment emergent adverse effects (TEAEs) were considered to be severe or serious. TRIAL REGISTRATION: EudraCT 2021-004626-29, 11 May 2021.

A pharmacokinetic drug-drug interaction study between rosuvastatin and emvododstat, a potent anti-SARS-CoV-2 (COVID-19) DHODH (dihydroorotate dehydrogenase) inhibitor.

A therapeutic agent that targets both viral replication and the hyper-reactive immune response would offer a highly desirable treatment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; COVID-19) management. Emvododstat (PTC299) was found to be a potent inhibitor of immunomodulatory and inflammation-related processes by the inhibition of dihydroorotate dehydrogenase (DHODH) to reduce SARS-CoV-2 replication. DHODH is the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. This drug interaction study was performed to determine whether emvododstat was an inhibitor of breast cancer resistance protein (BCRP) transporters in humans. Potential drug-drug interactions (DDIs) between emvododstat and a BCRP transporter substrate (rosuvastatin) were investigated by measuring plasma rosuvastatin concentrations before and after emvododstat administration. There was no apparent difference in rosuvastatin plasma exposure. The geometric means of maximum plasma rosuvastatin concentrations (Cmax ) were 4369 (rosuvastatin) and 5141 pg/mL (rosuvastatin + emvododstat) at 4 h postdose. Geometric mean rosuvastatin area under the concentration-time curve (AUC) from time 0 to the last measurable plasma concentration was 45 616 and 48 975 h·pg/mL when administered alone and after 7 days of b.i.d. emvododstat dosing, respectively. Geometric least squares mean ratios for Cmax and AUC were approximately equal to 1. Overall, administration of multiple doses of 100 mg emvododstat b.i.d. for 7 days in combination with a single dose of rosuvastatin was safe and well tolerated. Emvododstat can be safely administered with other BCRP substrate drugs. Hence, pharmacokinetic DDI mediated via BCRP inhibition is not expected when emvododstat and BCRP substrates are coadministered.

Validation and application of volumetric absorptive microsampling (VAMS) dried blood method for phenylalanine measurement in patients with phenylketonuria.

BACKGROUND: Frequent blood phenylalanine (Phe) measurement is required for phenylketonuria (PKU) patients for diagnosis and disease status monitoring. Though various methods are available for blood Phe measurement, there is a lack of validated quantitative methods for measuring Phe with less than 15% variability. A method to allow at home blood sample collection for the PKU community is in high demand. METHODS: A volumetric absorptive microsampling (VAMS) dried blood collection high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed and fully validated for blood Phe measurement in compliance with regulatory guidances. The method accuracy, precision, stability, selectivity, matrix and hematocrit effects were assessed. A venous plasma collection HPLC-MS/MS method was developed and validated as a reference method. 311 matching VAMS and plasma samples were collected from 24 PKU subjects in a Phase 2 clinical study. Phe measurements using the two methods were compared. RESULTS: Both VAMS and the plasma sample collection methods met the acceptance criteria for Good Laboratory Practice (GLP) bioanalytical analysis. Comparisons showed a high Pearson's correlation of 0.9813. The Passing-Bablok analysis showed that the difference was estimated to be less than 5% and Bland Altman analysis indicated that the difference was proportional with Phe concentration and for the majority of samples (88.85%) the measurement was within ±20% difference. Following 7 days treatment with 60 or 20 mg/kg/day PTC923 (Sepiapterin) or 20 mg/kg/day sapropterin, PKU patients exhibited respectively -206.4, -146.9, and -91.5 µmol/L reductions of blood Phe as measured by the VAMS method. CONCLUSIONS: Concordant results were obtained using VAMS and plasma methods, which demonstrated that VAMS is a reliable method for clinical applications to monitor blood Phe for PKU patients.

First-in-Human Studies of Pharmacokinetics and Safety of Utreloxastat (PTC857), a Novel 15-Lipooxygenase Inhibitor for the Treatment of Amyotrophic Lateral Sclerosis.

Utreloxastat (PTC857) is a 15-lipoxygenase inhibitor being developed to treat amyotrophic lateral sclerosis. This first-in-human study investigated the safety and pharmacokinetics of utreloxastat in healthy volunteers (N = 82) in a double-blind, placebo-controlled trial. The effects of a single ascending dose (100-1000 mg), multiple ascending doses (150-500 mg), and food (500 mg) on the pharmacokinetics and safety of utreloxastat were evaluated. Following single doses, the time to maximum plasma concentration (Cmax ) was observed ≈4 hours after dosing and the terminal half-life ranged from 20 to 25.3 hours. The Cmax and area under the concentration-time curve (AUC) increased slightly over dose proportionally. Following multiple doses (once daily/twice daily), the apparent clearance reduced and terminal half-life was ≥33 hours. There was no apparent difference of exposure following morning or evening doses. Varying diets increased the Cmax and AUCs of utreloxastat but did not alter time to Cmax . There were no gender-based differences in exposure. Utreloxastat showed no marked safety signal following single doses up to 1000 mg and multiple doses over 14 days of 500 mg once daily or 250 mg twice daily. The results support further development of utreloxastat for the treatment of patients with amyotrophic lateral sclerosis at a 250-mg twice-daily dose administered with food.

Emvododstat, a Potent Dihydroorotate Dehydrogenase Inhibitor, Is Effective in Preclinical Models of Acute Myeloid Leukemia.

Blocking the pyrimidine nucleotide de novo synthesis pathway by inhibiting dihydroorotate dehydrogenase (DHODH) results in the cell cycle arrest and/or differentiation of rapidly proliferating cells including activated lymphocytes, cancer cells, or virally infected cells. Emvododstat (PTC299) is an orally bioavailable small molecule that inhibits DHODH. We evaluated the potential for emvododstat to inhibit the progression of acute myeloid leukemia (AML) using several in vitro and in vivo models of the disease. Broad potent activity was demonstrated against multiple AML cell lines, AML blasts cultured ex vivo from patient blood samples, and AML tumor models including patient-derived xenograft models. Emvododstat induced differentiation, cytotoxicity, or both in primary AML patient blasts cultured ex vivo with 8 of 10 samples showing sensitivity. AML cells with diverse driver mutations were sensitive, suggesting the potential of emvododstat for broad therapeutic application. AML cell lines that are not sensitive to emvododstat are likely to be more reliant on the salvage pathway than on de novo synthesis of pyrimidine nucleotides. Pharmacokinetic experiments in rhesus monkeys demonstrated that emvododstat levels rose rapidly after oral administration, peaking about 2 hours post-dosing. This was associated with an increase in the levels of dihydroorotate (DHO), the substrate for DHODH, within 2 hours of dosing indicating that DHODH inhibition is rapid. DHO levels declined as drug levels declined, consistent with the reversibility of DHODH inhibition by emvododstat. These preclinical findings provide a rationale for clinical evaluation of emvododstat in an ongoing Phase 1 study of patients with relapsed/refractory acute leukemias.

In vitro metabolism, pharmacokinetics and drug interaction potentials of emvododstat, a DHODH inhibitor.

Emvododstat was identified as a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of acute myeloid leukaemia and COVID-19. The objective of this paper is to evaluate the metabolism, pharmacokinetics, and drug interaction potentials of emvododstat.Emvododstat showed high binding to plasma protein with minimal distribution into blood cells in mouse, rat, dog, monkey, and human whole blood.O-Demethylation followed by glucuronidation appeared to be the major metabolic pathway in rat, dog, monkey, and human hepatocytes. CYP2C8, 2C19, 2D6, and 3A4 were involved in O-desmethyl emvododstat metabolite formation. Both emvododstat and O-desmethyl emvododstat inhibited CYP2D6 activity and induced CYP expression to different extents in vitro.Emvododstat and O-desmethyl emvododstat inhibited BCRP transporter activity but did not inhibit bile salt transporters and other efflux or uptake transporters. Neither emvododstat nor O-desmethyl emvododstat was a substrate for common efflux or uptake transporters investigated.Emvododstat is bioavailable in mice, rats, dogs, and monkeys following a single oral dose. The absorption was generally slow with the mean plasma Tmax ranging from 2 to 5 h; plasma exposure of O-desmethyl emvododstat was lower in rodents, but relatively higher in dogs and monkeys.

Absorption, distribution, metabolism and excretion of 14C-Emvododstat following a single oral dose in rats and dogs.

Emvododstat is a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of acute myeloid leukaemia and COVID-19.Following an oral dose administration in Long-Evans rats, 14C-emvododstat-derived radioactivity was widely distributed throughout the body, with the highest distribution in the endocrine, fatty, and secretory tissues and the lowest in central nervous system.Following a single oral dose of 14C-emvododstat in rats, 54.7% of the dose was recovered in faeces while less than 0.4% of dose was recovered in urine 7 days post-dose. Emvododstat was the dominant radioactive component in plasma and faeces.Following a single oral dose of 14C-emvododstat in dogs, 75.2% of the dose was recovered in faeces while 0.5% of dose was recovered in urine 8 days post-dose. Emvododstat was the dominant radioactive component in faeces, while emvododstat and its two metabolites (O-desmethyl emvododstat and emvododstat amide bond hydrolysis product) were the major circulating radioactivity in dog plasma.

Preclinical and Early Clinical Development of PTC596, a Novel Small-Molecule Tubulin-Binding Agent.

PTC596 is an investigational small-molecule tubulin-binding agent. Unlike other tubulin-binding agents, PTC596 is orally bioavailable and is not a P-glycoprotein substrate. So as to characterize PTC596 to position the molecule for optimal clinical development, the interactions of PTC596 with tubulin using crystallography, its spectrum of preclinical in vitro anticancer activity, and its pharmacokinetic-pharmacodynamic relationship were investigated for efficacy in multiple preclinical mouse models of leiomyosarcomas and glioblastoma. Using X-ray crystallography, it was determined that PTC596 binds to the colchicine site of tubulin with unique key interactions. PTC596 exhibited broad-spectrum anticancer activity. PTC596 showed efficacy as monotherapy and additive or synergistic efficacy in combinations in mouse models of leiomyosarcomas and glioblastoma. PTC596 demonstrated efficacy in an orthotopic model of glioblastoma under conditions where temozolomide was inactive. In a first-in-human phase I clinical trial in patients with cancer, PTC596 monotherapy drug exposures were compared with those predicted to be efficacious based on mouse models. PTC596 is currently being tested in combination with dacarbazine in a clinical trial in adults with leiomyosarcoma and in combination with radiation in a clinical trial in children with diffuse intrinsic pontine glioma.

Ataluren metabolism: Ataluren-O-1ß-acyl glucuronide is a stable circulating metabolite in mouse, rat, dog and human.

Ataluren is an aromatic acid derivative with a 1,2,4-oxodiazole moiety. Ataluren-O-1ß-acyl glucuronide is a prominent circulatory metabolite in mice, rats, dogs, and humans following oral administration of ataluren. The objective of this paper was to evaluate the stability in vitro and in vivo of ataluren-O-1ß-acyl glucuronide metabolite. Ultrahigh performance liquid chromatography-mass spectrometry methods were developed to separate and monitor ataluren-O-1ß-acyl glucuronide and its possible migration isomers. In vitro stability was assessed in phosphate buffered saline as well as in control rat and human plasma. The disappearance of ataluren-O-1ß-acyl glucuronide and the formation of migration isomers were monitored by the ultrahigh performance liquid chromatography-mass spectrometry methods. In vitro, ataluren-O-1ß-acyl glucuronide underwent isomerization with an estimated half-life of approximately 1 h. However, ataluren-O-1ß-acyl glucuronide was stable and was the only detectable acyl glucuronide following oral administration of ataluren in mice, rats, dogs, and humans using the same analytical methods. Ataluren acyl glucuronide in mouse, rat, dog, and human plasma could be hydrolyzed by ß-glucuronidase, further confirming the structure of O-1ß-acyl glucuronide. These results demonstrated that ataluren-O-1ß-acyl glucuronide did not undergo migration in vivo. No clinical safety concern related to ataluren-O-1ß-acyl glucuronide migration has been detected.

In vitro cytochrome P450- and transporter-mediated drug interaction potential of 6ß-hydroxy-21-desacetyl deflazacort-A major human metabolite of deflazacort.

6ß-Hydroxy-21-desacetyl deflazacort (6ß-OH-21-desDFZ) is a major circulating but not biologically active metabolite of deflazacort (DFZ). In vitro studies were performed to evaluate cytochrome P450 (CYP)- and transporter-mediated drug interaction potentials of 6ß-OH-21-desDFZ. Up to 50 µM, the highest soluble concentration in the test system, 6ß-OH-21-desDFZ weakly inhibited (IC50  > 50 µM) the enzyme activity of CYPs 1A2, 2B6, 2C8, 2C9, and 2D6, while moderately inhibiting CYP2C19 and CYP3A4 with IC50 values of approximately 50 and 35 µM, respectively. The inhibition was neither time-dependent nor metabolism-based. Incubation of up to 50 µM 6ß-OH-21-desDFZ with plated cryopreserved human hepatocytes for 48 h resulted in no meaningful concentration-dependent induction of either mRNA levels or enzyme activity of CYP1A2, CYP2B6, or CYP3A4. In transporter inhibition assays, 6ß-OH-21-desDFZ, up to 50 µM, did not show interaction with human OAT1, OAT3, and OCT2 transporters. It weakly inhibited (IC50  > 50 µM) human MATE1, MATE2-K, and OCT1 transporter activity, and moderately inhibited human MDR1, OATP1B1, and OATP1B3 transporter activity with IC50 values of 19.81 µM, 37.62 µM, and 42.22 µM, respectively. 14 C-6ß-OH-21-desDFZ was biosynthesized using bacterial biotransformation and the subsequent study showed that 6ß-OH-21-desDFZ was not a substrate for human BCRP, MDR1, MATE1, MATE2-K, OAT1, OATP1B1, OATP1B3, and OCT2 transporters, but appeared to be an in vitro substrate for the human OAT3 uptake transporter. At plasma concentrations of 6ß-OH-21-desDFZ seen in the clinic, CYP- and transporter-mediated drug-drug interactions are not expected following administration of a therapeutic dose of DFZ in Duchenne muscular dystrophy (DMD) patients.

Pharmacokinetics and Safety of PTC596, a Novel Tubulin-Binding Agent, in Subjects With Advanced Solid Tumors.

PTC596 is a novel, orally bioavailable, small-molecule tubulin-binding agent that reduces B-cell-specific Moloney murine leukemia virus insertion site 1 activity and is being developed for the treatment of solid tumors. A phase 1, open-label, multiple-ascending-dose study was conducted to evaluate the pharmacokinetics and safety of the drug in subjects with advanced solid tumors. PTC596 was administered orally biweekly based on body weight. Dose escalation followed a modified 3 + 3 scheme using doses of 0.65, 1.3, 2.6, 5.2, 7.0, and 10.4 mg/kg. Following oral administration, PTC596 was rapidly absorbed, and between 0.65 and 7.0 mg/kg reached a maximum plasma concentration 2 to 4 hours after dosing. Area under the plasma concentration-time curve increased proportionally with body weight-adjusted doses. Maximum plasma concentration increased with dose, although the increase was less than dose proportional at dose levels >2.6 mg/kg. No accumulation occurred after multiple administrations up to 7.0 mg/kg. PTC596 had a terminal half-life ranging 12 to 15 hours at all doses except for the highest dose of 10.4 mg/kg, where the half-life was approximately 20 hours. Overall, PTC596 was well tolerated. The most frequently reported PTC596-related treatment-emergent adverse events were mild to moderate gastrointestinal symptoms, including diarrhea (54.8%), nausea (45.2%), vomiting (35.5%), and fatigue (35.5%). Only 1 patient treated with 10.4 mg/kg experienced dose-limiting toxicity of neutropenia and thrombocytopenia, both of which were reversible. Stable disease as best overall response was observed among 7 patients, with 2 patients receiving the study drug up to 16 weeks. These results support the further development of PTC596 for the treatment of solid tumors.

The DHODH inhibitor PTC299 arrests SARS-CoV-2 replication and suppresses induction of inflammatory cytokines.

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for therapeutics that inhibit the SARS-COV-2 virus and suppress the fulminant inflammation characteristic of advanced illness. Here, we describe the anti-COVID-19 potential of PTC299, an orally bioavailable compound that is a potent inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. In tissue culture, PTC299 manifests robust, dose-dependent, and DHODH-dependent inhibition of SARS-COV-2 replication (EC50 range, 2.0-31.6 nM) with a selectivity index >3,800. PTC299 also blocked replication of other RNA viruses, including Ebola virus. Consistent with known DHODH requirements for immunomodulatory cytokine production, PTC299 inhibited the production of interleukin (IL)-6, IL-17A (also called IL-17), IL-17 F, and vascular endothelial growth factor (VEGF) in tissue culture models. The combination of anti-SARS-CoV-2 activity, cytokine inhibitory activity, and previously established favorable pharmacokinetic and human safety profiles render PTC299 a promising therapeutic for COVID-19.

LC-MS/MS quantification of ataluren and ataluren acyl glucuronide in human plasma/urine: application in clinical studies.

Background: This paper describes for the first-time analytical procedures established to resolve the challenges associated with simultaneous and direct quantification of ataluren and ataluren-O-1ß-acyl glucuronide (AAG) by LC-MS/MS in human plasma and urine matrices. Methodology/results: The plasma quantification method was validated for calibration range of 12.5-12500 ng/ml for ataluren and 6.25-2500 ng/ml for AAG. The urine quantification method was validated for calibration range of 0.01-10 and 1-1000 µg/ml for ataluren and AAG, respectively. Plasma and urine samples were stabilized upon collection and through storage to prevent hydrolysis and acyl migration of AAG. Conclusion: Methods described in this paper enabled successful completion of ataluren clinical pharmacology studies for simultaneous pharmacokinetic assessment of ataluren and AAG.