Clinical Pharmacology for Nulibry
Mechanism Of Action
Patients with MoCD Type A have mutations in the MOCS1 gene leading to deficient MOCS1A/B dependent synthesis of the intermediate substrate, cPMP. Substrate replacement therapy with NULIBRY provides an exogenous source of cPMP, which is converted to molybdopterin. Molybdopterin is then converted to molybdenum cofactor, which is needed for the activation of molybdenum-dependent enzymes, including sulfite oxidase (SOX), an enzyme that reduces levels of neurotoxic sulfites.
Pharmacodynamics
In MoCD Type A, the lack of effective SOX leads to elevated levels of the neurotoxic sulfite, S-sulfocysteine (SSC). Treatment with NULIBRY resulted in a reduction in the level of urinary SSC normalized to creatinine and the reduction was sustained with long-term treatment with NULIBRY [see Clinical Studies].
Cardiac Electrophysiology
At the maximum approved recommended dose, Nulibry did not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics
The pharmacokinetics of fosdenopterin in healthy adult subjects following a single intravenous NULIBRY infusion are summarized in Table 3. The area under the plasma concentration-time curve (AUC) and the maximum plasma concentration (Cmax) of fosdenopterin increased in an approximately proportional manner with increasing doses.
Table 3 : Mean (SD) Pharmacokinetic Parameters Following A Single Intravenous Dose of Fosdenopterin in Healthy Subjects
| Parameter |
0.075 mg/kg1 |
0.24 mg/kg1 |
0.68 mg/kg1 |
| Cmax (ng/mL) |
285 (57) |
873 (99) |
2800 (567) |
| AUC0-inf (ng*h/mL) |
523 (75) |
1790 (213) |
5960 (1820) |
| 1 0.075 mg/kg, 0.24 mg/kg, and 0.68 mg/kg doses are 0.08, 0.27, and 0.76 times the recommended maximum dose, respectively. |
Distribution
The volume of distribution (Vd) of fosdenopterin was approximately 300 mL/kg. The plasma protein binding of fosdenopterin ranged from 6 to 12%.
Elimination
The mean total body clearance (CL) of fosdenopterin ranged from 167 to 195 mL/h/kg. The mean half-life of fosdenopterin ranged from 1.2 to 1.7 hours.
Metabolism
Fosdenopterin is predominantly metabolized through nonenzymatic degradation processes to Compound Z, an inactive oxidation product of endogenous cPMP.
Excretion
Renal clearance of fosdenopterin accounts for approximately 40% of total body clearance.
Specific Populations
The effect of renal and hepatic impairment on the pharmacokinetics of fosdenopterin is unknown.
Pediatric Patients
Pharmacokinetic properties of fosdenopterin in pediatric MoCD Type A patients are similar to healthy adult subjects.
Drug Interaction Studies
In Vitro Studies
Cytochrome P450 (CYP) Enzymes
Fosdenopterin does not inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5. Fosdenopterin does not induce CYP1A2, CYP2B6, or CYP3A4.
Transporter Systems
Fosdenopterin is a weak inhibitor of MATE2-K and OAT1, but does not inhibit P-gp, BCRP, OATP1B1, OATP1B3, OCT2, OAT3, and MATE1. Fosdenopterin is a weak substrate for MATE1, but is not a substrate of P-gp, BCRP, OATP1B1, OATP1B3, OCT2, OAT1, OAT3, or MATE2-K.
Animal Toxicology And/Or Pharmacology
Fosdenopterin has demonstrated phototoxic potential in an animal study at doses equal to and greater than 4.5 times the maximum recommended human dose (based on human equivalent dose comparison). In this study, which was conducted in pigmented rats, intravenous (bolus) administration of fosdenopterin for three consecutive days followed by ultraviolet radiation (UVR) exposure resulted in dose-dependent cutaneous skin reactions (erythema, edema, flaking, and eschar) and ophthalmic and histopathologic changes indicative of phototoxicity [see WARNINGS AND PRECAUTIONS].
Clinical Studies
The efficacy of NULIBRY for the treatment of patients with MoCD Type A was established based on data from three clinical studies (Studies 1, 2, and 3) that were compared to data from a natural history study.
Study 1
Study 1 (NCT02047461) was a prospective, open-label, single-arm, dose escalation study in patients with MoCD Type A who were receiving treatment with rcPMP prior to treatment with NULIBRY. Study 1 included 8 patients, 6 of whom previously participated in Study 3. The initial NULIBRY dosage was matched to the patient’s rcPMP dosage upon entering the study. The NULIBRY dosage was then titrated over a period of 5 months to a maximum dosage of 0.9 mg/kg administered once daily as an intravenous infusion.
Study 2
Study 2 (NCT02629393) was a prospective, open-label, single-arm, dose escalation study in one patient with MoCD Type A who had not been previously treated with rcPMP. The initial dosage of NULIBRY in Study 2 was based on the gestational age of the patient (i.e., 36 weeks). The initial dosage was then incrementally escalated up to a maximum dosage of 0.98 mg/kg administered once daily as an intravenous infusion (1.1 times the maximum approved recommended dosage) [see DOSAGE AND ADMINISTRATION].
Study 3
Study 3 was a retrospective, observational study that included 10 patients with a confirmed diagnosis of MoCD Type A who received rcPMP. Six of these 10 patients were later enrolled in Study 1 to receive treatment with NULIBRY.
Efficacy Results
The efficacy of NULIBRY and rcPMP were assessed in a combined analysis of the 13 patients with genetically confirmed MoCD Type A from Study 1 (n=8), Study 2 (n=1), and Study 3 (n=4) who received substrate replacement therapy with NULIBRY or rcPMP.
Of the 13 treated patients included in the combined analysis, 54% were male, 77% were White and 23% were Asian; the median gestational age was 39 weeks (range 35 to 41 weeks). Of these 13 treated patients, the age at first dose was ≤ 14 days for 10 patients (with 5 patients initiating treatment at 1 day of age) and ≥ 32 days and < 69 days for the remaining 3 patients.
Overall Survival
Efficacy was assessed by comparing overall survival in pediatric patients treated with NULIBRY or rcPMP (n=13) with an untreated natural history cohort of pediatric patients with genetically confirmed MoCD Type A who were genotype-matched to the treated patients (n=18). Patients treated with NULIBRY or rcPMP had an improvement in overall survival compared to the untreated, genotype-matched, historical control group (Table 4 and Figure 1). Results were similar when comparing treated patients with all patients in the untreated natural history cohort with genetically confirmed MoCD Type A (n=37, includes the 18 genotype-matched untreated patients as well as 19 additional untreated patients who were not genotype-matched).
Table 4 : Overall Survival in Patients with MoCD Type A Treated with NULIBRY or rcPMP Versus Genotype-Matched Untreated Patients in Historical Control
|
NULIBRY (or rcPMP)
(n=13) |
Untreated Genotype-Matched Historical Control
(n=18) |
Treatment Difference (95% CI) |
| Number of Deaths (%) |
2 (15%) |
12 (67%) |
|
| 50th Percentile (Median) |
| Survival Time in Months (95% CI)a |
NE (16, NE) months |
48 (10, 99) months |
|
| Kaplan Meier Survival Probability (95% CI) |
| 1 year |
92%
(57%, 99%) |
67%
(40%, 83%) |
|
| 3 years |
84%
(49%, 96%) |
55%
(30%, 74%) |
|
| Mean Survival Time (Months) |
| At 1 yearb (95% CI) |
11 (9, 13) months |
10 (8, 12) months |
1 (-1, 4) months |
| At 3 yearsc (95% CI) |
32 (26, 37) months |
24 (17, 31) months |
8 (-1, 16) months |
| Hazard Ratio for Risk of Death (95% CI)d |
0.18 (0. |
04, 0.72) |
|
Abbreviations: CI=confidence interval; NE=not estimable; rcPMP=recombinant Escherichia coli-derived cPMP.
a Quartile estimates from product-limit (Kaplan-Meier) method, with associated log-log confidence intervals.
b Based on the area under the survival curves up to 1 year of follow-up.
c Based on the area under the survival curves up to 3 years of follow-up.
d Based on Cox proportional hazards model regressing survival status on an indicator variable denoting treatment status. The 95% CIs are based on the modified score test statistic under the Cox model. The hazard ratio represents the risk of death in the treated patients compared to the untreated historical control patients. |
Figure 1 : Kaplan Meier Curve for Overall Survival in Patients with MoCD Type A Treated with NULIBRY or rcPMP Versus Genotype-Matched Untreated Patients in Historical Control
MoCD Biomarker Results
Treatment with NULIBRY resulted in a reduction in urine concentrations of SSC in patients with MoCD Type A and the reduction was sustained with long-term treatment over 48 months. The baseline level of urinary SSC normalized to creatinine was characterized in one patient (Study 2) with a value of 89.8 μmol/mmol. Following treatment with NULIBRY in Studies 1 and 2 (n=9), the mean ± SD levels of urinary SSC normalized to creatinine ranged from 11 (±8.5) to 7 (±2.4) μmol/mmol from Month 3 to Month 48.