Introduction: Mucopolysaccharidosis type VII (MPS VII, Sly Syndrome) is a progressive, debilitating, ultra-rare lysosomal storage disorder caused by the deficiency of β-glucuronidase (GUS), an enzyme required for breakdown of glycosaminoglycans (GAGs). Vestronidase alfa, a recombinant human GUS, is an enzyme replacement therapy approved in the US and EU for the treatment of MPS VII.
Methods: The pharmacokinetics (PK) and pharmacodynamics (PD) of vestronidase alfa were evaluated in 23 adult and pediatric subjects with MPS VII enrolled in phase I-III clinical trials to optimize the clinical dosing regimen of vestronidase alfa. The serum concentration-time profiles were adequately described by a two-compartment population PK model incorporating subjects' body weight as the only significant covariate.
Results: Model-based simulations predicted a substantially decreased time duration of serum exposures exceeding the level of Kuptake (the in vitro determined vestronidase alfa concentration corresponding to 50% maximum rate of cellular uptake) for 4 or 8 mg/kg once every 4 weeks dosing, compared with 4 mg/kg once every other week (QOW) dosing by intravenous infusion, suggesting that given the same total monthly dose, the QOW dosing frequency should result in more efficient delivery to the GUS-deficient tissue cells, and therefore superior treatment efficacy. A standard inhibitory maximal effect model reasonably explained the observed pharmacological PD responses of reduction in urinary GAGs from pretreatment baseline, which appeared to have reached the plateau of maximal effect at the 4 mg/kg QOW dose.
Conclusion: The modeling results, together with the clinical evidence of safety and efficacy, supported the recommended 4 mg/kg QOW dosing regimen of vestronidase alfa for pediatric and adult patients with MPS VII.
Clinical trial registration: NCT01856218, NCT02418455, NCT02230566.