Single-dose, subcutaneous recombinant phenylalanine ammonia lyase conjugated with polyethylene glycol in adult patients with phenylketonuria: an open-label, multicentre, phase 1 dose-escalation trial

Abstract

Background: Phenylketonuria is an inherited disease caused by impaired activity of phenylalanine hydroxylase, the enzyme that converts phenylalanine to tyrosine, leading to accumulation of phenylalanine and subsequent neurocognitive dysfunction. Phenylalanine ammonia lyase is a prokaryotic enzyme that converts phenylalanine to ammonia and trans-cinnamic acid. We aimed to assess the safety, tolerability, pharmacokinetic characteristics, and efficacy of recombinant Anabaena variabilis phenylalanine ammonia lyase (produced in Escherichia coli) conjugated with polyethylene glycol (rAvPAL-PEG) in reducing phenylalanine concentrations in adult patients with phenylketonuria.

Methods: In this open-label, phase 1, multicentre trial, single subcutaneous injections of rAvPAL-PEG were given in escalating doses (0·001, 0·003, 0·010, 0·030, and 0·100 mg/kg) to adults with phenylketonuria. Participants aged 18 years or older with blood phenylalanine concentrations of 600 μmol/L or higher were recruited from among patients attending metabolic disease clinics in the USA. The primary endpoints were safety and tolerability of rAvPAL-PEG. Secondary endpoints were the pharmacokinetic characteristics of the drug and its effect on concentrations of phenylalanine. Participants and investigators were not masked to assigned dose group. This study is registered with ClinicalTrials.gov, number NCT00925054.

Findings: 25 participants were recruited from seven centres between May 6, 2008, and April 15, 2009, with five participants assigned to each escalating dose group. All participants were included in the safety population. The most frequently reported adverse events were injection-site reactions and dizziness, which were self-limited and without sequelae. Two participants had serious adverse reactions to intramuscular medroxyprogesterone acetate, a drug that contains polyethylene glycol as an excipient. Three of five participants given the highest dose of rAvPAL-PEG (0·100 mg/kg) developed a generalised skin rash. By the end of the study, all participants had developed antibodies against polyethylene glycol, and some against phenylalanine ammonia lyase as well. Drug concentrations peaked about 89-106 h after administration of the highest dose. Treatment seemed to be effective at reducing blood phenylalanine in all five participants who received the highest dose (mean reduction of 54·2% from baseline), with a nadir about 6 days after injection and an inverse correlation between drug and phenylalanine concentrations in plasma. Phenylalanine returned to near-baseline concentrations about 21 days after the injection.

Interpretation: Subcutaneous administration of rAvPAL-PEG in a single dose of up to 0·100 mg/kg was fairly safe and well tolerated in adult patients with phenylketonuria. At the highest dose tested, rAvPAL-PEG reduced blood phenylalanine concentrations. In view of the development of antibodies against polyethylene glycol (and in some cases against phenylalanine ammonia lyase), future studies are needed to assess the effect of repeat dosing.

Funding: BioMarin Pharmaceutical.

Conflict of interest statement

Conflict of interest: Drs. Sile, Gu, and Musson work for BioMarin Pharmaceutical Inc. NL, COH, and BKB receive grant support for clinical research and are advisors for BioMarin Pharmaceutical Inc. All other authors received research support from BioMarin Pharmaceutical Inc. as Investigators in this study.

Copyright © 2014 Elsevier Ltd. All rights reserved.

Figures

Figure 1. Appearance of anti-PEG (panel A) and anti-PAL (panel B) antibodies in subjects with phenylketonuria after a single injection of rAvPAL-PEG in subjects with phenylketonuria

All subjects developed antibodies to PEG, whereas less than 50% had a response to PAL. No differences in the rate of antibody formation were seen across different doses. Anti-PEG: percent of subjects who developed either IgG or IgM against PEG; Anti-PAL: percent of subjects who developed either IgG or IgM against PAL.

Figure 2. Effect of increasing doses (0·001–0·1 mg/kg) of rAvPAL-PEG on plasma phenylalanine concentrations in subjects with phenylketonuria

Subjects received a single dose of the drug on Day 1. Points are averages ± standard deviation (SD) of five determinations. *p

Figure 3. Panel A: Concentrations of plasma phenylalanine (filled circle) and rAvPAL-PEG (open squares) in subjects with phenylketonuria after one dose (time zero) of 0·1 mg/kg of rAvPAL-PEG

Points are averages with the SD indicated in one direction. Panel B: Correlation between plasma concentrations of rAvPAL-PEG and phenylalanine. Note the significant inverse correlation between plasma rAvPAL-PEG and phenylalanine concentrations in subjects with phenylketonuria who received a single dose of 0·1 mg/kg of rAvPAL-PEG. The thick line represents the regression using all points with the parameters indicated. The lines are regression to individual subjects. These were all highly significant (p<0·01) except in Subject 5 where the regression was statistically significant (p<0·05).