Ceredase (Alglucerase) - Description and Clinical Pharmacology

DESCRIPTION

Ceredase^® (alglucerase injection) is a modified form of the enzyme,ß-glucocerebrosidase (ß-D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45). Alglucerase is a monomeric glycoprotein of 497 amino acids with carbohydrates making up approximately 6% of the molecule (M_r=59,300 as determined by SDS-PAGE). The unmodified enzyme (ß-glucocerebrosidase) also contains 497 amino acids and contains approximately 12% carbohydrate (M_r=67,000). The carbohydrates on the unmodified enzyme consist of N-linked carbohydrate chains of the complex and high mannose type. Glucocerebrosidase and alglucerase catalyze the hydrolysis of the glycolipid, glucocerebrosidase, within the lysosomes of the reticuloendothelial system.

Alglucerase is prepared by modification of the oligosaccharide chains of human ß-glucocerebrosidase. The modification alters the sugar residues at the non-reducing ends of the oligosaccharide chains of the glycoprotein so that they are predominantly terminated with mannose residues which are specifically recognized by carbohydrate receptors on macrophage cells.

Ceredase^® is supplied as a clear sterile non-pyrogenic solution of alglucerase in a citrate buffered solution (53 mM citrate, 143 mM sodium) containing 1% albumin human USP. The enzyme is supplied in one concentration, 400 units per bottle (80 units/mL) with a fill volume of 5 mL per bottle. An enzyme unit (U) is defined as the amount of enzyme required to hydrolyze in one minute one micromole of the synthetic substrate, p-nitrophenyl-ß-D-glucopyranoside.

Ceredase^® is purified from a large pool of human placental tissue collected from selected donors. Steps have been introduced into the manufacturing process to reduce further the risk of viral contamination. However, no procedure has been shown to be totally effective in removing viral infectivity (see PRECAUTIONS ). Each lot of product has been tested and found negative for hepatitis B surface antigen (HBsAg) and for human immunodeficiency virus antigen (HIV-1) and antibody (HIV-1/2).

Human chorionic gonadotropin (hCG) is a naturally occurring hormone in human placenta. It is likely the hCG is partially deglycosylated. In vitro studies have previously demonstrated biological activity of approximately 3 units of hCG activity per unit Ceredase^® , as determined by an in vitro cell based assay. New process steps have since been introduced into the manufacturing process that significantly reduce the amount of hCG present in the Ceredase^® product. Initial manufacturing data indicate that the resulting level of hCG in the product is less than 1 μg hCG per mg Ceredase^® protein, as determined by the ELISA assay. These data indicate that the level of hCG in the product has been reduced about 15 fold as a result of the new process steps.

CLINICAL PHARMACOLOGY

Ceredase^® (alglucerase injection) catalyzes the hydrolysis of the glycolipid, glucocerebroside, to glucose and ceramide as part of the normal degradation pathway for membrane lipids. Glucocerebroside is primarily derived from hematologic cell turnover. Gaucher disease is characterized by a functional deficiency inß-glucocerebrosidase enzymatic activity and the resultant accumulation of lipid glucocerebroside in tissue macrophages which become engorged and are termed Gaucher cells. Gaucher cells are typically found in liver, spleen and bone marrow and occasionally, as well, in lung, kidney and intestine. Secondary hematologic sequelae include severe anemia and thrombocytopenia in addition to the characteristic progressive hepatosplenomegaly. Skeletal complications, including osteonecrosis and osteopenia with secondary pathological fractures, are a common feature of Gaucher disease.

Pharmacokinetics

Following an intravenous infusion of different doses (between 0.6 and 234 units/kg) of Ceredase^® (alglucerase injection) over a 4-hour period, steady-state enzymatic activity was achieved by 60 minutes. Individual steady-state enzymatic activity and area under the curve of the activity increased linearly with the infused dose (0.6 and 121 units/kg). Following infusion termination, plasma enzymatic activity declined rapidly with elimination half-life ranging between 3.6 and 10.4 minutes. Plasma clearance of Ceredase^® , calculated from its plasma enzymatic activity, was variable and ranged between 6.34 and 25.39 mL/min/kg, whereas the volume of distribution ranged from 49.4 to 282.1 mL/kg. Within the dosage range of 0.6 and 121 units/kg, elimination half-life, plasma clearance, and volume of distribution values appear to be independent of the infused dose.

Pharmacologic Actions

Chronic administration of Ceredase^® (alglucerase injection) in 13 patients with Type I Gaucher disease from initial studies induced the following effects:

1. Splenomegaly and hepatomegaly were significantly reduced, presumably by disruption of the lysosomal storage sites and metabolism of glucocerebroside in Gaucher cells. This effect was demonstrated within 6 months of initiation of therapy.
2. Hematologic deficiencies in hemoglobin, hematocrit, erythrocyte and platelet counts were significantly improved. In most patients a change in hemoglobin was the first observable effect. In some patients hemoglobin levels were normalized after 6 months of therapy.
3. Improved mineralization of bone, as revealed by plain radiographs of long bones, occurred in three patients after prolonged treatment as a result of a reduction in the osteolytic actions of lipid-laden Gaucher cells in the marrow.
4. Cachexia and wasting in children were reduced.