A laboratory test using blood samples could help identify Gaucher disease (GD) patients likely to respond to experimental chaperone therapies, a study reports.
The assay is based on macrophages, white blood cells particularly affected in GD, and could help optimize the effectiveness of chaperone therapies regardless of which mutation a patient carries.
The study, “Functional Assessment Of Glucocerebrosidase Modulator Efficacy In Primary Patient-Derived Macrophages Is Essential For Drug Development And Patient Stratification,” was published in the journal Haematologica.
Gaucher is caused by mutations in the GBA gene, which provides instructions for making beta-glucocerebrosidase (GCase). Normally, this enzyme breaks down a fat molecule called glucocerebroside into smaller molecules. But when faulty, GCase adopts an abnormal conformation, becoming unstable and quickly destroyed, resulting in the accumulation of glucocerebroside to toxic levels inside cells.
Enzyme replacement therapy (ERT) — injections of a working version of GCase — has been found effective for treating the systemic manifestations of the disease, including blood disorders and enlargement of the liver and spleen.
However, because of its inability to enter the brain, ERT cannot reduce or reverse certain neurological symptoms associated with Gaucher disease types 2 and 3, the two forms that typically affect the brain and spinal cord.
To find a way to treat all GD types, scientists have turned to a different class of compounds — small-molecule chaperones that are able to cross the blood-brain barrier (a semi-permeable protective barrier that controls which substances reach the brain).
Chaperones work by stabilizing faulty GCase. When correctly folded, these enzymes escape degradation and are shuttled to lysosomes, the cell compartments where they break down glucocerebroside. The goal of this approach is to decrease glucocerebroside levels and ease GD symptoms.
Several treatment chaperones are being investigated for Gaucher, but one important concern is that, because they directly bind to GCase, they may also block their activity — which would limit their therapeutic application.
Researchers in the U.K. developed a potential assay that can be used to evaluate the effectiveness and side effects of these compounds directly on patients’ cells.
The team derived macrophages in the lab from white blood cells collected from 10 patients with GD type 1. Macrophages are particularly important in Gaucher disease, as they are responsible for recycling old cells, and part of this process requires GCase.
The assay was used to assess isofagomine, a chaperone under development by Amicus Therapeutics, in patients with diverse GBA mutations.
First, researchers noted that GCase activity was increased, but glucocerebroside levels inside lysosomes did not go down, suggesting that isofagomine was causing unwanted inhibitory effects.
This is an important difference because BGL tests to diagnose GD measure the total activity of GCase in blood samples, which would not detect these unwanted effects.
Then, the team used the model to find a better approach to overcome this problem. They saw that, rather than giving isofagomine continuously, using a washout period after its administration to macrophages helped boost the beneficial effects and greatly reduced glucocerebroside levels.
This indicates “a therapeutic value of such compounds [chaperones] under the right treatment regimen,” the researchers wrote.
“It also underscores the need to perform such in vitro [in cells cultured in the lab] biomarker testing to first understand how individual patients may respond to treatment,” and ensures that the right population of patients will benefit from well-designed clinical trials, they added.
