No QT interval prolongation effect of sepiapterin: a concentration-QTc analysis of pooled data from phase 1 and phase 3 studies in healthy volunteers and patients with phenylketonuria

Gao L., Kaushik D., Ingalls K., Smith N., Kong R.

Background: Sepiapterin is a natural precursor of tetrahydrobiopterin (BH4), a key cofactor for phenylalanine hydroxylase. It is being developed for the treatment of patients with phenylketonuria. In this study, the ethnic differences in pharmacokinetics and safety of sepiapterin in Japanese and non-Japanese participants and food effects were evaluated. Methods: Healthy participants (n = 60) received a single oral dose of sepiapterin at either 20, 40, or 60 mg/kg with a low-fat diet. The Japanese participants received two doses at 40 mg/kg, either under fasted conditions or with a low-fat diet with a 3-day washout period in between. Results: Sepiapterin was well tolerated in all participants, with no serious adverse events. Sepiapterin was quickly absorbed (Tmax 1.4–4.5 h) and rapidly and extensively converted to BH4 (Tmax ~4 h). Exposures to sepiapterin were <1% of BH4. BH4 exposures were essentially dose-independent between 20 and 60 mg/kg. A low-fat diet increased BH4 exposures in Japanese participants by 1.7-fold compared with fasted conditions. Conclusions: BH4 exposures (Cmax and AUC0–last) in Japanese participants were 10–30% higher than in non-Japanese participants, which is deemed not clinically relevant; no dose adjustment is warranted. The slightly higher BH4 exposures in Japanese participants are likely due to the higher frequency of ABCG2 c.421C>A mutation in the Japanese population.

Muntau A.C., Longo N., Ezgu F., Schwartz I.V., Lah M., Bratkovic D., Margvelashvili L., Kiykim E., Zori R., Campistol Plana J., Bélanger-Quintana A., Lund A., Guilder L., Chakrapani A., Mungan H.N., et. al.

Phenylketonuria is an inherited condition characterised by neurotoxic accumulation of phenylalanine (Phe). APHENITY assessed the efficacy and safety of orally administered synthetic sepiapterin in children and adults with phenylketonuria.

Gao L., Kaushik D., Ingalls K., Milner S., Smith N., Kong R.

Sepiapterin, also known as PTC923 and CNSA-001, is a synthetic form of endogenous sepiapterin being developed as a novel oral treatment for phenylketonuria. Sepiapterin is a natural precursor of tetrahydrobiopterin (BH4) and, when orally administered, is converted to BH4 via the pterin salvage pathway. In vitro studies have demonstrated that both sepiapterin and BH4 are both substrates and inhibitors of the breast cancer resistance protein (BCRP) transporter. This phase I study investigated BCRP-mediated drug–drug interactions of sepiapterin as a victim and as a perpetrator. An open-label, fixed-sequence, four-period, crossover, single-dose study was conducted in adult male and female healthy volunteers (18–55 years of age). In a given treatment period, subjects received a single oral dose of sepiapterin (20 mg/kg), sepiapterin (20 mg/kg) plus curcumin (2 g), rosuvastatin (10 mg), or rosuvastatin (10 mg) plus sepiapterin (60 mg/kg). The pharmacokinetics of sepiapterin, its metabolite BH4, and rosuvastatin were studied, and geometric mean ratios of exposures in the presence and absence of the BCRP inhibitor curcumin or sepiapterin were estimated. The presence of the BCRP c.421C>A polymorphism was evaluated in all subjects. A total of 29 subjects were enrolled and included in the safety analysis. Among them, 26 subjects were included in the pharmacokinetic and drug–drug interaction analyses. Following oral administration 20 mg/kg sepiapterin, sepiapterin was rapidly and extensively converted to BH4, and BH4 maximum observed concentration (415.0 ng/mL) was observed 4.95 h (time to maximum observed concentration) post-dose. Sepiapterin maximum observed concentration and area under the concentration–time curve from time 0 to time of the last quantifiable measurement or the last sample collection time (AUClast) were <1% of BH4 values. Coadministration of the BCRP inhibitor curcumin (2 g) increased BH4 maximum observed concentration, AUClast, and area under the concentration–time curve from time 0 extrapolated to infinity by 24%, 21%, and 20%, respectively. When sepiapterin was coadministered with the BCRP substrate rosuvastatin, there was no effect on the pharmacokinetics of rosuvastatin. BCRP c.421C/A carriers (n = 4) had higher plasma exposures of BH4 (1.39 × for AUClast) and rosuvastatin (1.61 × for AUClast) than c.421C/C carriers (n = 22). Greater increases in BH4 exposures (1.33 vs 1.18 for AUClast) were observed in c.421C/A carriers compared with c.421C/C carriers when sepiapterin was coadministered with curcumin. All treatments were well tolerated during the study. Oral coadministration of the BCRP inhibitor curcumin slightly increased the plasma exposure of sepiapterin and its metabolite BH4 in healthy volunteers. This modest increase was deemed not clinically meaningful. Sepiapterin did not alter the pharmacokinetics of the BCRP substrate rosuvastatin.

Gao L., Kaushik D., Xia Y., Ingalls K., Milner S., Smith N., Kong R.

AbstractSepiapterin 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.

Gersting S., Barroso M., Etzold S., Smith N.

Rasmussen L., Foulks Z., Wu J., Burton C., Shi H.

Determining the biological significance of pteridines in cancer development and progression remains an important step in understanding the altered levels of urinary pteridines seen in certain cancers. Our companion study revealed that several folate-derived pteridines and lumazines correlated with tumorigenicity in an isogenic, progressive breast cancer cell model, providing direct evidence for the tumorigenic origin of pteridines. This study sought to elucidate the pteridine biosynthetic pathway in a progressive breast cancer model via direct pteridine dosing to determine how pteridine metabolism changes with tumorigenicity. First, MCF10AT breast cancer cells were dosed individually with 15 pteridines to determine which pteridines were being metabolized and what metabolic products were being produced. Second, pteridines that were significantly metabolized were dosed individually across the progressive breast cancer cell model (MCF10A, MCF10AT, and MCF10ACA1a) to determine the relationship between each metabolic reaction and breast cancer tumorigenicity. Several pteridines were found to have altered metabolism in breast cancer cell lines, including pterin, isoxanthopterin, xanthopterin, sepiapterin, 6-biopterin, lumazine, and 7-hydroxylumazine (p < 0.05). In particular, isoxanthopterin and 6-biopterin concentrations were differentially expressed (p < 0.05) with respect to tumorigenicity following dosing with pterin and sepiapterin, respectively. Finally, the pteridine biosynthetic pathway in breast cancer cells was proposed based on these findings. This study, along with its companion study, demonstrates that pteridine metabolism becomes disrupted in breast cancer tumor cells. This work highlights several key metabolic reactions within the pteridine biosynthetic pathway that may be targeted for further investigation and clinical applications.

Bratkovic D., Margvelashvili L., Tchan M.C., Nisbet J., Smith N.

AbstractBackground & aimPTC923 (formerly CNSA-001), an oral formulation of sepiapterin, a natural precursor of intracellular tetrahydrobiopterin (BH4), has been shown in humans to induce larger increases in circulating BH4 vs. sapropterin dihydrochloride. Sapropterin reduces blood phenylalanine (Phe) by ≥20–30% in a minority of subjects with PKU. This was a Phase 2 randomized, multicenter, three-period crossover, open-label, active controlled, all-comers [regardless of phenylalanine hydroxylase (PAH) variants] comparison of PTC923 60 mg/kg, PTC923 20 mg/kg and sapropterin 20 mg/kg in 24 adults with phenylketonuria (PKU) and hyperphenylalaninemia.MethodsEligible subjects were adult men or women (18–60 y) with PKU. Subjects enrolled received 7 days of once-daily oral treatment with PTC923 20 mg/kg/day, PTC923 60 mg/kg/day and sapropterin dihydrochloride 20 mg/kg/day each in a random order. Treatments were separated by a 7-day washout. Subjects maintained their usual pre-study diet, including consumption of amino acid mixtures. Blood Phe was measured on Day 1 (predose baseline), Day 3, Day 5, and Day 7 of each treatment period.ResultsLeast squares mean changes (SE) from baseline in blood Phe were: −206.4 (41.8) μmol/L for PTC923 60 mg/kg (p 

Hillert A., Anikster Y., Belanger-Quintana A., Burlina A., Burton B.K., Carducci C., Chiesa A.E., Christodoulou J., Đorđević M., Desviat L.R., Eliyahu A., Evers R.A., Fajkusova L., Feillet F., Bonfim-Freitas P.E., et. al.

Phenylketonuria (PKU), caused by variants in the phenylalanine hydroxylase (PAH) gene, is the most common autosomal-recessive Mendelian phenotype of amino acid metabolism. We estimated that globally 0.45 million individuals have PKU, with global prevalence 1:23,930 live births (range 1:4,500 [Italy]–1:125,000 [Japan]). Comparing genotypes and metabolic phenotypes from 16,092 affected subjects revealed differences in disease severity in 51 countries from 17 world regions, with the global phenotype distribution of 62% classic PKU, 22% mild PKU, and 16% mild hyperphenylalaninemia. A gradient in genotype and phenotype distribution exists across Europe, from classic PKU in the east to mild PKU in the southwest and mild hyperphenylalaninemia in the south. The c.1241A>G (p.Tyr414Cys)-associated genotype can be traced from Northern to Western Europe, from Sweden via Norway, to Denmark, to the Netherlands. The frequency of classic PKU increases from Europe (56%) via Middle East (71%) to Australia (80%). Of 758 PAH variants, c.1222C>T (p.Arg408Trp) (22.2%), c.1066−11G>A (IVS10−11G>A) (6.4%), and c.782G>A (p.Arg261Gln) (5.5%) were most common and responsible for two prevalent genotypes: p.[Arg408Trp];[Arg408Trp] (11.4%) and c.[1066−11G>A];[1066−11G>A] (2.6%). Most genotypes (73%) were compound heterozygous, 27% were homozygous, and 55% of 3,659 different genotypes occurred in only a single individual. PAH variants were scored using an allelic phenotype value and correlated with pre-treatment blood phenylalanine concentrations (n = 6,115) and tetrahydrobiopterin loading test results (n = 4,381), enabling prediction of both a genotype-based phenotype (88%) and tetrahydrobiopterin responsiveness (83%). This study shows that large genotype databases enable accurate phenotype prediction, allowing appropriate targeting of therapies to optimize clinical outcome.

Smith N., Longo N., Levert K., Hyland K., Blau N.

Tetrahydrobiopterin (BH4) is the natural cofactor of aromatic amino acid hydroxylases and essential for degradation of phenylalanine and synthesis of catecholamines and serotonin. It can be synthesized either de novo from GTP or through the salvage pathway from sepiapterin. Sepiapterin, a natural precursor of BH4, is a more stable molecule and is transported more efficiently across cellular membranes, thus having potentially significant advantage over BH4 as a pharmacological agent for diseases associated with BH4-deficient conditions. We report the results of a first-in-humans, randomized, double-blind, placebo-controlled, dose-ranging, Phase I clinical trial in 83 healthy volunteers of CNSA-001, a novel formulation of sepiapterin. Single oral doses of 2.5-80 mg/kg CNSA-001 caused dose-related increases in plasma sepiapterin (mean Cmax 0.58-2.92 ng/mL) and BH4 (mean Cmax 57-312 ng/mL). Maximum plasma concentrations were achieved in about 1-2 h (sepiapterin) or about 4 h (BH4) after CNSA-001 oral intake. Increases in plasma BH4 were substantially larger in absolute terms and on a dose-for-dose basis following treatment with CNSA-001 vs. sapropterin dihydrochloride, a synthetic form of BH4. The pharmacokinetics of plasma sepiapterin and BH4 were similar before and after seven days of repeat daily dosing with CNSA-001 at 5, 20 or 60 mg/kg indicating little or no drug accumulation. Oral administration of CNSA-001 resulted in higher concentrations of sepiapterin in fasted vs. fed subjects, but overall BH4 plasma exposure following CNSA-001 intake increased by 1.7-1.8-fold in fed subjects. CNSA-001 was well tolerated, with no clear dose-relationship for adverse events (AE), no serious AE and no study discontinuations for AE. These data indicate that CNSA-001 is rapidly and efficiently converted to BH4 in humans supporting further clinical evaluation of CNSA-001 for the management of PKU, primary BH4 deficiencies and other diseases associated with deficient BH4 metabolism.

Garnett C., Bonate P.L., Dang Q., Ferber G., Huang D., Liu J., Mehrotra D., Riley S., Sager P., Tornoe C., Wang Y.

The original version of this article unfortunately contained an error in Equation 1 under the section “Pre-specified linear mixed effects model”. The correct equation has given below.

Garnett C., Bonate P.L., Dang Q., Ferber G., Huang D., Liu J., Mehrotra D., Riley S., Sager P., Tornoe C., Wang Y.

The International Council for Harmonisation revised the E14 guideline through the questions and answers process to allow concentration-QTc (C-QTc) modeling to be used as the primary analysis for assessing the QTc interval prolongation risk of new drugs. A well-designed and conducted QTc assessment based on C-QTc modeling in early phase 1 studies can be an alternative approach to a thorough QT study for some drugs to reliably exclude clinically relevant QTc effects. This white paper provides recommendations on how to plan and conduct a definitive QTc assessment of a drug using C-QTc modeling in early phase clinical pharmacology and thorough QT studies. Topics included are: important study design features in a phase 1 study; modeling objectives and approach; exploratory plots; the pre-specified linear mixed effects model; general principles for model development and evaluation; and expectations for modeling analysis plans and reports. The recommendations are based on current best modeling practices, scientific literature and personal experiences of the authors. These recommendations are expected to evolve as their implementation during drug development provides additional data and with advances in analytical methodology.

Olsson H., Petri N., Erichsen L., Malmberg A., Grundemar L.

Degarelix is a gonadotropin-releasing hormone antagonist registered for the treatment of advanced hormone-dependent prostate cancer. Treatment causing androgen deprivation is associated with QT prolongation and this study investigated whether degarelix at supratherapeutic concentrations has an intrinsic effect per se on cardiac repolarisation and the QT interval. This was a single-centre, randomised, crossover study comparing the effect of degarelix, placebo, and the positive control moxifloxacin on the QT interval. Degarelix and placebo treatments were double-blind, whereas moxifloxacin treatment was open-label. Eighty healthy men, aged 18–45 years, received single intravenous doses of degarelix 2.8 mg, and placebo, as well as a single oral dose of moxifloxacin 400 mg. Electrocardiograms were collected up to 24 h after the start of administration, with the QT interval assessed and plasma concentrations of degarelix concomitantly analysed. Time-matched, one-sided 95% upper confidence boundaries for baseline-corrected average changes from placebo for the QT interval, corrected using the Fridericia method (ΔΔQTcF), did not exceed 10 ms at any timepoint, with maximum degarelix concentrations reaching approximately threefold the concentrations seen in the treatment of prostate cancer. Furthermore, concentration-exposure analysis indicated absence of any QT prolongation effects of degarelix. No significant effect on any other cardiac parameter was observed. The lower bound of the 98.3% confidence interval for moxifloxacin ΔΔQTcF exceeded 5 ms, thus verifying assay sensitivity. The results showed that the study was validated to detect a significant effect on the QT interval, and that degarelix by itself does not have any effect on the QT interval and cardiac repolarisation at supratherapeutic concentrations.

Pollard C.E., Skinner M., Lazic S.E., Prior H.M., Conlon K.M., Valentin J., Dota C.

There has been significant focus on drug-induced QT interval prolongation caused by block of the human ether-a-go-go-related gene (hERG)-encoded potassium channel. Regulatory guidance has been implemented to assess QT interval prolongation risk: preclinical guidance requires a candidate drug's potency as a hERG channel blocker to be defined and also its effect on QT interval in a non-rodent species; clinical guidance requires a "Thorough QT Study" during development, although some QT prolonging compounds are identified earlier via a Phase I study. Clinical, heart rate-corrected QT interval (QTc) data on 24 compounds (13 positives; 11 negatives) were compared with their effect on dog QTc and the concentration of compound causing 50% inhibition (IC50) of hERG current. Concordance was assessed by calculating sensitivity and specificity across a range of decision thresholds, thus yielding receiver operating characteristic curves of sensitivity versus (1-specificity). The area under the curve of ROC curves (for which 0.5 and 1 indicate chance and perfect concordance, respectively) was used to summarize concordance. Three aspects of preclinical data were compared with the clinical outcome (receiver operating characteristic area under the curve values shown in brackets): absolute hERG IC50 (0.78); safety margin between hERG IC50 and clinical peak free plasma exposure (0.80); safety margin between QTc effects in dogs and clinical peak free plasma exposure (0.81). Positive and negative predictive values of absolute hERG IC50 indicated that from an early drug discovery perspective, low potency compounds can be progressed on the basis of a low risk of causing a QTc increase.

Täubel J., Ferber G., Fox G., Fernandes S., Lorch U., Camm A.J.

Aim The D2/D3 antagonist amisulpride has shown promising efficacy against postoperative nausea and vomiting (PONV) at low doses. We investigated whether intravenous amisulpride has an effect on the QTc interval in a formal Thorough QT study (TQT). Methods This was a randomized, double-blind, placebo and positive-controlled, four-way crossover study. Forty healthy Caucasian and Japanese subjects were included to receive a single administration of 5 mg and 40 mg of i.v. amisulpride or a single oral dose of moxifloxacin or placebo per period. Results The therapeutic dose of 5 mg amisulpride was associated with a slight, transient increase in mean ΔΔQTcF, from 2.0 ms prior to dosing to a peak of 5 ms (90% CI: 2.8, 7.1 ms) at 8 min, decreasing to 2.1 ms at 30 min after dosing. The supra-therapeutic dose of 40 mg given at twice the infusion rate was associated with prolongation in ΔΔQTcF peaking at 23.4 ms (90% CI: 21.3, 25.5 ms) at the end of infusion (8 min), returning below 10 ms within 1.5 h. Assay sensitivity was confirmed; ΔΔQTcF had increased by 12.3 ms (90% CI 10.1, 14.6 ms) at 4 h post-dose. The PK-PD relationship revealed no differences between Caucasian and Japanese subjects (p-value > 0.5). Conclusions Amisulpride has a plasma concentration-dependent effect on the QTc interval. The proposed therapeutic dose for management of PONV does not lead to a prolongation of QTcF above the threshold of regulatory concern, while such effect could not be excluded for the supratherapeutic dose.

Täubel J., Ferber G., Lorch U., Wang D., Sust M., Camm A.J.

Background E-52862 is a Sigma-1 receptor antagonist (S1RA) currently under investigation as a potential analgesic medicine. We successfully applied a concentration-effect model retrospectively to a four-way crossover Phase I single ascending dose study and utilized the QTc shortening effects of a meal to demonstrate assay sensitivity by establishing the time course effects from baseline in all four periods, independently from any potential drug effects. Methods Thirty two healthy male and female subjects were included in four treatment periods to receive single ascending doses of 500 mg, 600 mg or 800 mg of E-52862 or placebo. PK was linear over the dose range investigated and doses up to 600 mg were well tolerated. The baseline electrocardiography (ECG) measurements on Day-1 were time-matched with ECG and pharmacokinetic (PK) samples on Day 1 (dosing day). Results In this conventional mean change to time-matched placebo analysis, the largest time-matched difference to placebo QTcI was 1.44 ms (90% CI: -4.04, 6.93 ms) for 500 mg; -0.39 ms (90% CI: -3.91, 3.13 ms) for 600 mg and 1.32 ms (90% CI: -1.89, 4.53 ms) for 800 mg of E-52862, thereby showing the absence of any QTc prolonging effect at the doses tested. In addition concentration-effect models, one based on the placebo corrected change from baseline and one for the change of QTcI from average baseline with time as fixed effect were fitted to the data confirming the results of the time course analysis. Conclusion The sensitivity of this study to detect small changes in the QTc interval was confirmed by demonstrating a shortening of QTcF of -8.1 (90% CI: -10.4, -5.9) one hour and -7.2 (90% CI: -9.4, -5.0) three hours after a standardised meal. Trial Registration EU Clinical Trials Register EudraCT 2010 020343 13