Asparaginase

L-asparaginase Assay for Leukemia Patients

The L-asparaginase assays are laboratory developed tests (LDT) to determine the enzyme activity of L-asparaginase or the presence of anti-asparaginase antibodies in patients who have been treated with Asparlas®, Erwinaze®, Oncaspar® or Rylaze®. These assays have been validated and are performed in a CLIA certified high complexity laboratory.

L-asparaginase activity test can help physicians identify patients experiencing “silent inactivation” as well as to ensure that adequate asparaginase activity is present during asparaginase treatment. The assay is performed using a serum sample obtained from the patient after treatment. A minimal volume of sample (0.2 mL) is required, and the results are returned within one business day.

The ELISA antibody assay determines the presence or absence of antibodies to Asparaginase. This test allows clinicians to monitor their patient’s antibody levels in a manner similar to therapeutic drug monitoring as done with the asparaginase activity assay currently in place at Granger Genetics. This assay reports the presence or absence of antibodies to asparaginase in the sample, but it does not distinguish between general antibodies towards asparaginase and neutralizing antibodies.

Problem

Testing

What is L-asparaginase?

Acute lymphoblastic leukemia (ALL) is a blood cell cancer characterized by an over accumulation of immature white blood cells called lymphoblasts. These immature cells inhibit the production of normal blood cells and infiltrate to other organs. ALL has an annual incidence of 6000 persons per year and peaks in early childhood. Asparginase, an enzyme produced by bacteria, is used as an anti-neoplastic agent to treat ALL. The mechanism of action is inhibition of asparagine in cancer cells. Asparagine is a non-essential amino acid, meaning that normal cells can produce asparagine through its innate biochemical pathways.

Asparagine is needed by all cells as an important part of its protein structures. Cells without asparagine will die. The immature white blood cell does not have the capacity to manufacture asparagine. In the cancer cells, asparaginase breaks down asparagine and ultimately kills the cells. Asparaginase treatment has been incorporated into many ALL protocols for kids and adults. Like all chemotherapeutic and anti-neoplastic agents, asparaginase is not without side effects. The most common adverse reactions are hypersensitivity and sub-clinical hypersensitivity (silent inactivation). Silent inactivation occurs when patients develop anti-asparaginase antibodies without clinical signs of hypersensitivity. These patients suffer greater incidence of cancer relapse. Therapeutic drug monitoring through measurement of asparaginase enzyme activity can identify patients at risk for silent inactivation. Antibody screening can also identify patients who are developing antibodies against asparaginase prior to seeing effects of silent in activation.

The Testing

The primary goal of Asparaginase therapy is to maintain adequate asparagine depletion. The Asparaginase activity assay developed by scientists at Granger Genetics is a therapeutic drug monitoring test that accurately measures the activity level of Asparaginase in a patient’s blood. The activity assay quantitatively measures the activity level of the drug and allows physicians to optimize treatment. The antibody assay is a qualitative assay that reports the presence or absence of antibodies towards asparaginase. The antibody assay allows physicians to see if patients are producing antibodies against asparaginase even prior to seeing potential effects of silent inactivation. Results are reported within one day of sample receipt for either (or both) of these assays.

How Does It Work?

Activity Assay

A minimum of 0.200mL of serum is needed to run the assay. Activity levels are determined using a coupled enzymatic assay that ultimately results in decreased absorbance at 340nm. The rate of reaction at 37°C is a linear function of enzyme activity.

Samples with activities exceeding the upper range of the calibration curve are re-assayed after diluting with blank human serum. Assay performance: accuracy was 94.0% of the target activity and the precision was 9.7%CV.

Antibody Assay

A minimum of 0.100mL of serum is needed to run the assay. The presence or absence of absence of antibodies is determined though a traditional antigen-capture ELISA assay. Asparaginase is used as the antigen for coating the plate in which the asparaginase antibodies are then immobilized. Bound antibodies are detected with an HRP-conjugated detection antibody and TMB enzyme substrate.