Alglucerase. A review of its therapeutic use in Gaucher's disease

Alglucerase is a mannose-terminated form of human placental glucocerebrosidase, developed to treat patients with Gaucher's disease. Functional glucocerebrosidase is deficient in Gaucher's disease, an autosomal recessive lipid storage disorder that affects people of all ethnic backgrounds, but has a higher incidence among East European Jews (Ashkenazim). Gaucher's disease manifests with hepatosplenomegaly, bleeding disorders and bone disease, with the more rare subtypes (types 2 and 3) featuring neurological dysfunction. Prior to the development of enzyme replacement therapy, treatment for Gaucher's disease was mainly symptomatic relief. Primary treatment with glucocerebrosidase focuses on removal of the lipid metabolite that causes the pathology. Because of the rarity of Gaucher's disease clinical trials are small, and much of the data investigating alglucerase therapy have been obtained from studies of patients with type 1 disease, the prevalent subtype. Nonetheless, after intravenous administration of alglucerase, improvements are evident within 6 months of therapy. Patients have increased haemoglobin levels and platelet counts, and decreased incidences of epistaxis and bruising. Spleen and liver size are reduced, and skeletal parameters improve. Children gain height and most patients receiving alglucerase therapy are able to resume work and daily activities. Alglucerase is well tolerated, with few mild adverse reactions reported. Although the pharmacokinetic and pharmacodynamic information for alglucerase is limited, its unequivocal efficacy justifies enzyme replacement therapy with this compound as first-line treatment for patients with Gaucher's disease, for whom treatment options are limited.

Enzyme augmentation in moderate to life-threatening Gaucher disease

Gaucher disease type 1 (GD type 1) is the most prevalent lysosomal storage disease and has its highest frequency in the Ashkenazi Jewish population. Deficiency of the enzyme, acid beta-glucosidase, results in the deposition of glucocerebroside primarily in macrophages. The accumulation of such "Gaucher cells" leads to visceromegaly, hepatic and bone marrow dysfunction, hypersplenism, and bony disease. Eleven GD type 1 patients, ages 4-52 y, with moderate to life-threatening manifestations, received 6-12 mo of enzyme augmentation with a macrophage-targeted acid beta-glucosidase preparation. Within 6 mo, substantial increases in Hb levels (mean = +30%) and platelet counts (mean = +39%) were observed. Hepatic and splenic volumes decreased by approximately 20% (range = 3-35%) and approximately 35% (20-52%), respectively. Hematologic and hepatic volume improvements were similar in the splenectomized (n = 4) and nonsplenectomized (n = 7) patient groups. In this patient population, no major differences were observed in the hematologic and visceral improvements with enzyme doses of 30, 50, or 60 IU/kg administered every 2 wk. Normal levels of acid beta-glucosidase activity were present in hepatic autopsy samples from one patient 11 d after enzyme infusion. In comparison, exogenous activity was absent from brain and lung specimens of the same patient. High levels (approximately 10-fold normal) were present in bone marrow samples from two patients obtained at 1 and 11 d after infusions. These studies demonstrate biochemical and clinical improvements by targeted enzyme augmentation in GD type 1, even in far advanced, life-threatening involvement.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-dependent responses to macrophage-targeted glucocerebrosidase in a child with Gaucher disease

Long-term studies of a child with Gaucher disease indicated that the response to treatment with macrophage-targeted glucocerebrosidase (glucosylceramidase) is dose dependent, and that the hematologic response precedes the skeletal response.

Effect of platelet count on the DDAVP-induced shortening of the bleeding time in thrombocytopenic Gaucher's patients

As part of an investigative protocol requiring serial liver biopsies in patients with Type I Gaucher's disease who were receiving enzyme replacement therapy, we gave 11 patients a total of 15 infusions of DDAVP (0.3 micrograms/kg IV) and measured the Simplate bleeding time pre- and postin-fusion. All patients were thrombocytopenic (one patient 100-150,000; seven 66-99,000; and three 50-65,000/microliters). Nine of 15 infusions resulted in at least a 2-min shortening of the bleeding time; in 6/11 infusions in which the platelet count was greater than 65,000, the bleeding time shortened to less than or equal to 10 min, in 1/11 it shortened greater than or equal to 2 min but not to less than or equal to 10 min. In only 2/4 infusions given to patients with platelet counts less than 65,000 did the bleeding time demonstrate any significant shortening. None of the six liver biopsies performed in the patients whose bleeding time shortened to less than or equal to 10 min resulted in any significant bleeding; blood products were not transfused either pre- or postprocedure. These limited data demonstrate that a high percentage of patients with platelet counts of 65-100,000/microliters can manifest a significant shortening of bleeding time following a standard infusion of DDAVP, and that in approximately half of these patients the bleeding time will shorten enough to safely allow the performance of a liver biopsy without the need for prophylactic transfusion of blood products.

Creating the costliest orphan. The Orphan Drug Act in the development of Ceredase

The FDA recently approved Ceredase, a new treatment for Gaucher's disease, under the provisions of the Orphan Drug Act. Ceredase is unusually expensive, but there are no satisfactory alternative therapies. It appears likely that Ceredase would not have become available without the protection of the Orphan Drug Act, but its expense and the lack of information about its long-term effects on health raise questions about whether the ODA provides appropriate incentives to develop cost-effective technologies.

Hematologic improvement in a patient with Gaucher disease on long-term enzyme replacement therapy: evidence for decreased splenic sequestration and improved red blood cell survival

We describe here an investigation of the hematologic response of a child with Gaucher disease to a six-year therapeutic trial of human placental mannose-terminated glucocerebrosidase. While on enzyme replacement therapy, the patient's hemoglobin and platelet count significantly increased (6.9 g/dl to 12.2 g/dl, and 39,000/microliters to 74,000/microliters, respectively). Over the same time interval his absolute reticulocyte count decreased (88.1 x 10(3)/microliters to 31.5 x 10(3)/microliters). The patient's splenic volume decreased by over 60% (2108ml to 797ml) and his bone marrow demonstrated a dramatic clearing of Gaucher cell infiltration. Serum erythropoietin levels were at the lower range of normal at points in time when he was severely anemic and did not change with improvement in hemoglobin. Coincident with the improvement in the patient's hemoglobin, in vivo survival of autologous radiolabeled RBCs increased 34%. The improved hematopoietic profile appeared to result primarily from an increase in the in vivo survival of mature hematopoietic elements secondary to a decrease in splenic sequestration. Improved marrow function secondary to the clearing of Gaucher cell infiltrates may also play a role in his improved hematologic status.

Treatment of type 1 Gaucher's disease affecting bone with aminohydroxypropylidene bisphosphonate (pamidronate)

Two patients with Type 1 (adult) Gaucher's disease and major skeletal involvement with multiple fractures have been treated with the second generation bisphosphonate pamidronate for extensive periods. There was evidence of an immediate reduction in bone resorption, with increased calcium absorption (delayed in Patient 1), improved calcium balance and maintained or improved bone density indices in the axial and peripheral skeleton. There was no evidence of immediate relapse on treatment cessation. No toxic effects of pamidronate treatment were identified and subjective skeletal pain diminished in both patients. Histomorphometry of transiliac bone biopsies obtained before the start of treatment, after double in vivo tetracycline labelling, represents one of the earliest reports of the quantitative findings in iliac bone invaded by Gaucher cells.

Replacement therapy for inherited enzyme deficiency--macrophage-targeted glucocerebrosidase for Gaucher's disease

BACKGROUND AND METHODS

Gaucher's disease, the most prevalent of the sphingolipid storage disorders, is caused by a deficiency of the enzyme glucocerebrosidase (glucosylceramidase). Enzyme replacement was proposed as a therapeutic strategy for this disorder in 1966. To assess the clinical effectiveness of this approach, we infused macrophage-targeted human placental glucocerebrosidase (60 IU per kilogram of body weight every 2 weeks for 9 to 12 months) into 12 patients with type 1 Gaucher's disease who had intact spleens. The frequency of infusions was increased to once a week in two patients (children) during part of the trial because they had clinically aggressive disease.

RESULTS

The hemoglobin concentration increased in all 12 patients, and the platelet count in 7. Serum acid phosphatase activity decreased in 10 patients during the trial, and the plasma glucocerebroside level in 9. Splenic volume decreased in all patients after six months of treatment, and hepatic volume in five. Early signs of skeletal improvements were seen in three patients. The enzyme infusions were well tolerated, and no antibody to the exogenous enzyme developed.

CONCLUSIONS

Intravenous administration of macrophage-targeted glucocerebrosidase produces objective clinical improvement in patients with type 1 Gaucher's disease. The hematologic and visceral responses to enzyme replacement develop more rapidly than the skeletal response.

Gaucher's disease: lack of antibody response in 12 patients following repeated intravenous infusions of mannose terminal glucocerebrosidase

An amplified ELISA has been employed for monitoring the safety of repeated intravenous infusions of modified human placental glucocerebrosidase. The enzyme infusions consisted of biweekly injections of macrophage targeted glucocerebrosidase over a 6 month duration. Serum samples collected throughout the study were assayed by use of an ELISA using alkaline phosphatase coupled to alcohol dehydrogenase for amplification. Using this protocol, 0.2-5 ng affinity purified immunoglobulin specific for glucocerebrosidase can be detected. Occasional false positives necessitate multiple repeat assays over time to accurately assess immunogenic response. Blinded ELISAs were performed on sera from both infused patients with Gaucher's disease and uninfused control patients and compared with apparent immunoglobulin concentration in 54 normal control sera. Although several samples showed apparently elevated immunoglobulin levels, repeat analyses failed to demonstrate high levels reproducibly. Furthermore, these sera were unable to neutralize enzyme or to precipitate radiolabelled enzyme, confirming the absence of antibody. Problems with high sensitivity ELISA formats are discussed.

Therapeutic response to intravenous infusions of glucocerebrosidase in a patient with Gaucher disease

Enzyme replacement has been under consideration as a therapeutic strategy for patients with Gaucher disease for more than two decades. Previous studies indicated that single injections of purified glucocerebrosidase reduced the amount of storage material in the liver. It was important to determine whether administration of exogenous enzyme on a regular basis would be of clinical benefit. We report here that weekly i.v. infusions of a macrophage-targeted preparation of human placental glucocerebrosidase in a child with type 1 Gaucher disease increased hemoglobin from 6.9 +/- 0.8 g/dl (+/- 1 SD) to 10.2 +/- 0.4 g/dl (+/- 1 SD) over a 20-week period. The platelet count also increased from a pretreatment value of 30,000 +/- 7000/mm3 (+/- 1 SD) to 54,000 +/- 11,000/mm3 (+/- 1 SD). Phagocytic activity in the spleen decreased during the period of enzyme administration, and there was radiographic evidence of skeletal improvement. These observations document objective clinical responses to enzyme supplementation in a patient with a sphingolipid storage disorder.

Uptake by neuroblastoma cells of glucosylceramide, glucosylceramide glucosidase, its stimulator protein, and phosphatidylserine

Serum-free cultured neuroblastoma cells (clone NlE-115) have been shown to absorb emulsified glucosylceramide, glucosylceramide glucosidase, an activator protein for the enzyme, and phosphatidylserine from a synthetic medium. Uptake of the enzyme was augmented by phosphatidylserine, and vice versa. Uptake of the enzyme-lipid complex was further augmented by the activator protein. It appears likely that the activator forms a complex only with the enzyme-lipid complex, not with the individual components. Two uptake mechanisms for the enzyme seem to be involved, one of which (the complex with activator proteins and acidic lipid) is sensitive to mannosyl phosphate groups. Hydrolysis of absorbed glucosylceramide was slow unless the medium was supplemented with the acidic phospholipid or glucosidase. The most rapid disappearance of stored glycolipid took place when the ternary mixture was added to the cell medium, enzyme + activator protein + phosphatidylserine. These findings may be relevant to enzyme replacement therapy for Gaucher disease.

Status of enzyme replacement therapy for Gaucher disease

At this point in time, enzyme replacement therapy for Gaucher disease appears both biochemically effective (patients 1-3, and 10) as well as clinically promising (patients 4 and 5), although these salutary responses have not been obtained consistently (patients 6-9). The discrepancy may be due to the method employed for the isolation of the enzyme. One current opinion is that glucocerebrosidase prepared by conventional fractionation and ion exchange chromatographic procedures may have been more effective in vivo than enzyme prepared by butanol extraction and hydrophobic column chromatography, which we developed because of the difficulty in obtaining large quantities of glucocerebrosidase by the conventional method. It should be remembered that the enzyme prepared by the latter procedure was fully active on glucocerebroside in liver biopsy specimens in vitro. Furthermore, glucocerebrosidase prepared by the second method exerted a positive effect in 2 young patients, who received relatively large amounts of enzyme, and in an adult who was treated with corticosteroid prior to infusion of the enzyme. At this moment, a possible explanation is that a necessary associated factor, perhaps a lipid, may have been removed by the large-scale isolation procedure. We are attempting to improve the biochemical and clinical responses to enzyme infusion by investigating the effects of lysosomal modifying agents and by enhancing the uptake and localization of the infused enzyme in lysosomes of cells that contain the stored glucocerebroside.