A phase 1/2 clinical trial of enzyme replacement in fabry disease: pharmacokinetic, substrate clearance, and safety studies

Abstract

Fabry disease results from deficient alpha-galactosidase A (alpha-Gal A) activity and the pathologic accumulation of the globotriaosylceramide (GL-3) and related glycosphingolipids, primarily in vascular endothelial lysosomes. Treatment is currently palliative, and affected patients generally die in their 40s or 50s. Preclinical studies of recombinant human alpha-Gal A (r-halphaGalA) infusions in knockout mice demonstrated reduction of GL-3 in tissues and plasma, providing rationale for a phase 1/2 clinical trial. Here, we report a single-center, open-label, dose-ranging study of r-halphaGalA treatment in 15 patients, each of whom received five infusions at one of five dose regimens. Intravenously administered r-halphaGalA was cleared from the circulation in a dose-dependent manner, via both saturable and non-saturable pathways. Rapid and marked reductions in plasma and tissue GL-3 were observed biochemically, histologically, and/or ultrastructurally. Clearance of plasma GL-3 was dose-dependent. In patients with pre- and posttreatment biopsies, mean GL-3 content decreased 84% in liver (n=13), was markedly reduced in kidney in four of five patients, and after five doses was modestly lowered in the endomyocardium of four of seven patients. GL-3 deposits were cleared to near normal or were markedly reduced in the vascular endothelium of liver, skin, heart, and kidney, on the basis of light- and electron-microscopic evaluation. In addition, patients reported less pain, increased ability to sweat, and improved quality-of-life measures. Infusions were well tolerated; four patients experienced mild-to-moderate reactions, suggestive of hypersensitivity, that were managed conservatively. Of 15 patients, 8 (53%) developed IgG antibodies to r-halphaGalA; however, the antibodies were not neutralizing, as indicated by unchanged pharmacokinetic values for infusions 1 and 5. This study provides the basis for a phase 3 trial of enzyme-replacement therapy for Fabry disease.

Figure 1

Pharmacokinetics of r-hαGalA infusions. Semilog plots of mean concentration-time data for r-hαGalA infusions at doses of 0.3 (♦), 1.0 (●), or 3.0 (▴) mg/kg (groups A–C), demonstrating the dose-dependent (nonlinear) profile consistent with enzyme cleared from the circulation via both saturable and nonsaturable (concentration independent) pathways. R-hαGalA was infused over 120 min. See text for details.

Figure 2

Effect of r-hαGalA dose on plasma GL-3 clearance. Individual patient plasma GL-3 concentrations determined just prior to infusions 1–5 for the 0.3 (A), 1.0 (B), and 3.0 (C) mg/kg biweekly dosing groups.

Figure 3

Light-microscopic assessment of the vascular endothelial GL-3 deposits in skin (A), heart (B), and kidney (C), before and after r-hαGalA treatment by expert pathologists blinded to time of biopsy and patient. A, Pre- and posttreatment GL-3 scores (ranging from 0, normal or near normal, to 4, severe) of skin capillary endothelium for 14 patients. Note that the seven with paired pre- and posttreatment biopsies all cleared their capillary endothelial GL-3 deposits (“0” scores). B, Pre- and posttreatment endomyocardial vascular endothelium GL-3 scores (ranging from 0, normal or near normal, to 3, severe) for seven patients: three in group C, three in group D, and one in group E. Note that the seven patients with paired pre- and posttreatment biopsies all had reduced GL-3 scores and four had cleared their capillary endothelium (“0” scores). C, Pre- and posttreatment GL-3 scores (ranging from 0, normal or near normal, to 3, severe) for kidney vascular endothelium for seven patients: three in group C, two in group D, and two in group E. Note that the two with paired pre- and posttreatment biopsies had cleared their capillary endothelial GL-3 deposits (“0” scores). See text for details.

Figure 4

A and B, Immunohistochemistry for GL-3 in skin with verotoxin subunit B. Comparison of pretreatment (A) and posttreatment (B) photomicrographs shows that r-hαGalA treatment resulted in marked clearance of GL-3 inclusions, particularly from the superficial vasculature of the papillary dermis. C and D, Electron micrographs of single superficial capillaries of the skin. Before treatment (C), the capillary endothelium was heavily laden with lamellar glycosphingolipid inclusions (arrows). After treatment (D), the endothelium of superficial capillaries was cleared of GL-3 inclusions (arrow). See text for details.

Figure 5

Photomicrographs of interstitial capillaries of the myocardium before (A) and after (B) treatment (methylene blue/azure II stain). Pretreatment (A), small-to-medium–sized glycosphingolipid inclusions were seen in the endothelium of small interstitial capillaries (arrows; score 2). After treatment (B), glycosphingolipid inclusions were cleared from the endothelium of small capillaries (arrows). The GL-3 inclusions in the cardiomyocytes (arrowheads) were less responsive to treatment. See text for details.

Figure 6

Light and electron micrographs of kidney pre- and posttreatment (methylene blue/azure II stain). A and B, Light microscopy of capillaries in the intertubular interstitium. Before treatment (A), the capillary endothelium (arrows) is heavily laden with glycosphingolipid inclusions, some impinging on the lumen (score 3). After treatment (B), most of the capillaries (arrows) have been cleared of glycosphingolipid inclusions (score 0). C and D, Electron micrographs of kidney cortex with examples of an intertubular capillary (arrow) and neighboring distal convoluted tubule (arrowhead). Before treatment (C), numerous electron-dense glycosphingolipid inclusions are seen in the capillary endothelium (small arrow). In the adjacent distal convoluted tubule, the epithelium is heavily packed with numerous electron-dense lamellar lysosomal inclusions (small arrowhead). After treatment (D), the endothelium of a small capillary (arrow) has no evidence of glycosphingolipid inclusions. In the adjacent distal convoluted tubule (arrowhead), the number and distribution of lysosomal inclusions appear similar; however, the lamellar architecture of the individual lysosomes appears less tightly organized (small arrowhead), suggesting enzymatic hydrolysis of the accumulated GL-3.

Figure 7

Comparison of the pharmacokinetics of r-hαGalA for infusions 1 and 5. Comparison of mean concentration-time data for groups A and B. R-hαGalA was infused over 120 min. Infusion 1: group A (●), group B (▴); infusion 5: group A (♦), group B (×). See text for details.