Clinical Pharmacology for Vyondys 53
Mechanism Of Action
Golodirsen is designed to bind to exon 53 of dystrophin pre-mRNA resulting in exclusion of this exon during mRNA processing in patients with genetic mutations that are amenable to exon 53 skipping. Exon 53 skipping is intended to allow for production of an internally truncated dystrophin protein in patients with genetic mutations that are amenable to exon 53 skipping [see Clinical Studies].
Pharmacodynamics
After treatment with VYONDYS 53, all patients evaluated (n=25) in Study 1 Part 2 [see Clinical Studies] had an increase in skipping of exon 53 demonstrated by reverse transcription polymerase chain reaction (RT-PCR), compared to baseline.
In Study 1 Part 2 [see Clinical Studies], dystrophin levels as assessed by the Sarepta western blot assay increased from 0.10% (SD 0.07) of normal at baseline to 1.02% (SD 1.03) of normal after 48 weeks of treatment with VYONDYS 53. The mean change from baseline in dystrophin after 48 weeks of treatment with VYONDYS 53 was 0.92% (SD 1.01) of normal levels (p<0.001); the median change from baseline was 0.88%. This increase in dystrophin protein expression positively correlated with the level of exon skipping. Dystrophin levels assessed by western blot can be meaningfully influenced by differences in sample processing, analytical technique, reference materials, and quantitation methodologies. Therefore, comparing dystrophin results from different assay protocols will require a standardized reference material and additional bridging studies.
Correct localization of truncated dystrophin to the sarcolemma in muscle fibers of patients treated with golodirsen was demonstrated by immunofluorescence staining.
Pharmacokinetics
The pharmacokinetics of golodirsen was evaluated in DMD patients following administration of intravenous doses ranging from 4 mg/kg/week to 30 mg/kg/week (i.e., recommended dosage). Golodirsen exposure increased proportionally with dose, with minimal accumulation with once-weekly dosing. Inter-subject variability (as %CV) for Cmax and AUC ranged from 38% to 72%, and 34% to 44%, respectively.
Distribution
Steady-state volume of distribution was similar between DMD patients and healthy subjects. The mean golodirsen steady-state volume of distribution was 668 mL/kg (%CV=32.3) at a dose of 30 mg/kg. Golodirsen plasma protein binding ranged from 33% to 39% and is not concentration dependent.
Elimination
Golodirsen elimination half-life (SD) was 3.4 (0.6) hours, and plasma clearance was 346 mL/hr/kg at the 30 mg/kg dose.
Metabolism
Golodirsen is metabolically stable. No metabolites were detected in plasma or urine.
Excretion
Golodirsen is mostly excreted unchanged in the urine. The elimination half-life (t½) was 3.4 hours.
Specific Populations
Age
The pharmacokinetics of golodirsen have been evaluated in male pediatric DMD patients. There is no experience with the use of VYONDYS 53 in DMD patients 65 years of age or older.
Sex
Sex effects have not been evaluated; VYONDYS 53 has not been studied in female patients.
Race
The potential impact of race is not known because 92% of the patients in studies were Caucasians.
Patients With Renal Impairment
The effect of renal impairment on the pharmacokinetics of golodirsen was evaluated in non-DMD subjects aged 41 to 65 years with Stage 2 chronic kidney disease (CKD) (n=8, estimated glomerular filtration rate (eGFR) ≥60 and <90 mL/min/1.73 m²) or Stage 3 CKD (n=8, eGFR ≥30 and <60 mL/min/1.73 m²) and matched healthy subjects (n=8, eGFR ≥90 mL/min/1.73 m²). Subjects received a single 30 mg/kg IV dose of golodirsen.
In subjects with Stage 2 or Stage 3 CKD, exposure (AUC) increased approximately 1.2-fold and 1.9-fold, respectively. There was no change in the Cmax in subjects with Stage 2 CKD; in subjects with Stage 3 CKD, there was a 1.2-fold increase in Cmax compared with subjects with normal renal function. The effect of Stage 4 or Stage 5 CKD on golodirsen pharmacokinetics and safety has not been studied.
Estimated GFR values derived from MDRD equations and the threshold definitions for various CKD stages in otherwise healthy adults would not be generalizable to pediatric patients with DMD. Therefore, no specific dosage adjustment can be recommended for patients with renal impairment [see Use In Specific Populations].
Patients With Hepatic Impairment:
VYONDYS 53 has not been studied in patients with hepatic impairment.
Drug Interaction Studies
Golodirsen did not inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5 in vitro. Golodirsen was a weak inducer of CYP1A2 and did not induce CYP2B6 or CYP3A4. Golodirsen was not metabolized by human hepatic microsomes and was not a substrate or strong inhibitor of any of the key human drug transporters tested (OAT1, OAT3, OCT2, OATP1B1, MATE1, P-gp, BCRP, and MRP2, OATP1B3 and MATE2-K). Based on in vitro data, golodirsen has a low potential for drug-drug interactions in humans.
Animal Toxicology And/Or Pharmacology
Kidney toxicity was observed in studies in male mice and rats; findings in urinary bladder were observed in male mice.
In male mice, golodirsen was administered weekly for 12 weeks by intravenous injection (0, 12, 120, or 960 mg/kg) or for 26 weeks by subcutaneous injection (0, 120, 300, or 600 mg/kg). In the 12-week study, microscopic findings in kidney (tubular dilatation, basophilic or eosinophilic casts, vacuolation), correlated with increases in serum markers of renal function (e.g., urea nitrogen, creatinine), were observed primarily at the highest dose tested; hypertrophy of the transitional epithelium of the ureter or urinary bladder was observed at all doses. In the 26-week study, renal tubular degeneration and degeneration of the transitional epithelium of the urinary bladder were observed at all doses.
In male rats, intravenous administration of golodirsen (0, 60, 100, 300, or 600 mg/kg) weekly for 13 weeks resulted in tubular degeneration at all but the lowest dose tested; at the high dose, the microscopic changes were accompanied by increases in serum urea nitrogen.
In male monkeys, intravenous administration of golodirsen (0, 80, 200, or 400 mg/kg) weekly for 39 weeks resulted in microscopic changes in kidney (basophilia, dilatation, or mononuclear cell infiltration) at all doses, which correlated with increases in serum markers of renal function (urea nitrogen, creatinine) at the highest dose tested.
Clinical Studies
The effect of VYONDYS 53 on dystrophin production was evaluated in one study in DMD patients with a confirmed mutation of the DMD gene that is amenable to exon 53 skipping (Study 1; NCT02310906).
Study 1 Part 1 was a double-blind, placebo-controlled, dose-titration study in 12 DMD patients. Patients were randomized 2:1 to receive VYONDYS 53 or matching placebo. VYONDYS 53Âtreated patients received four escalating dose levels, ranging from 4 mg/kg/week (less than the recommended dosage) to 30 mg/kg/week, by intravenous infusion for 2 weeks at each dose level.
Study 1 Part 2 was a 168-week, open-label study assessing the efficacy and safety of VYONDYS 53 at a dose of 30 mg/kg/week in the 12 patients enrolled in Part 1, plus 13 additional treatment-naive patients with DMD amenable to exon 53 skipping. At study entry (either in Part 1 or Part 2), patients had a median age of 8 years and were on a stable dose of corticosteroids for at least 6 months. Efficacy was assessed based on change from baseline in the dystrophin protein level (measured as % of the dystrophin level in healthy subjects, i.e., % of normal) at Week 48 of Part 2. Muscle biopsies were obtained at baseline prior to treatment and at Week 48 of Part 2 in all VYONDYS 53-treated patients (n=25), and were analyzed for dystrophin protein level by Sarepta western blot. Mean dystrophin levels increased from 0.10% (SD 0.07) of normal at baseline to 1.02% (SD 1.03) of normal by Week 48 of Study 1 Part 2, with a mean change in dystrophin of 0.92% (SD 1.01) of normal levels (p<0.001); the median change from baseline was 0.88%.
Individual patient dystrophin levels from Study 1 are shown in Table 2 .
Table 2: Dystrophin Expression Sarepta Western Blot by Individual Patient From Study 1
| Patient Number |
Sarepta Western Blot % Normal Dystrophin |
Patient number |
Sarepta Western Blot % Normal Dystrophin |
| Baseline |
Part 2 Week 48 |
Change from baseline |
Baseline |
Part 2 Week 48 |
Change from baseline |
| 1 |
0.08 |
0.09 |
0.01 |
14 |
0.22 |
0.28 |
0.06 |
| 2 |
0.11 |
0.11 |
0.01 |
15 |
0.14 |
0.21 |
0.07 |
| 3 |
0.21 |
0.22 |
0.01 |
16 |
0.05 |
0.42 |
0.37 |
| 4 |
0.05 |
0.12 |
0.08 |
17 |
0.07 |
1.03 |
0.97 |
| 5 |
0.03 |
0.12 |
0.09 |
18 |
0.02 |
1.57 |
1.55 |
| 6 |
0.06 |
0.14 |
0.09 |
19 |
0.12 |
1.17 |
1.05 |
| 7 |
0.12 |
0.37 |
0.25 |
20 |
0.03 |
1.72 |
1.69 |
| 8 |
0.11 |
1.06 |
0.95 |
21 |
0.11 |
1.77 |
1.66 |
| 9 |
0.06 |
0.54 |
0.48 |
22 |
0.31 |
4.30 |
3.99 |
| 10 |
0.05 |
0.97 |
0.92 |
23 |
0.11 |
0.36 |
0.25 |
| 11 |
0.06 |
1.55 |
1.49 |
24 |
0.03 |
0.91 |
0.88 |
| 12 |
0.07 |
1.91 |
1.84 |
25 |
0.07 |
1.29 |
1.22 |
| 13 |
0.10 |
3.25 |
3.15 |
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