L-Asparaginase Loaded Inside Red Cells Has An Acceptable Tolerability Profile On Bilirubin Value

L-asparaginase has been a major drug in the treatment of acute lymphoblastic leukemia (ALL) over the past decades, its efficacy has been demonstrated in a broad range of patient clinical profiles. However frequence and severity of toxicities, of which allergic reactions, have been a major drawback. L-asparaginase loaded inside homologous red cells, suspended in SAG-mannitol preservative solution, (GRASPA) is a new available formulation for administering L-asparaginase in combination with standard chemotherapy in different ALL populations, including frail patients older than 55years. Tolerability and efficacy of GRASPA in patients with ALL have been investigated in successive clinical trials (GRASPALL 2005-01 and GRASPALL/GRAALL-SA2-2008). The global toxicity of this new L-asparaginase formulation is decreased, in all age groups, with fewer hypersensitive reactions. A significant reduction of the coagulation disorders in patients <55 years old has also been reported. The pharmacokinetics is improved, with a half-life of about 30 days compared to 1 day for the free formulation. GRASPA has been proposed as a new approach to maintain the complete activity of L-asparaginase while reducing its antibody mediated toxicity. The red blood cells (RBC) act as a micro bioreactor and protect the enzyme against circulating antibodies. Plasma asparagine diffuses through the RBC membrane to the intra cellular compartment where it is cleaved by the entrapped L-asparaginase. In addition, encapsulation into RBC has been shown to extend the duration of drug action, allowing a reduction in the number of injections.

Hepatic toxicity has often been reported with regular L-aparaginase associated with chemotherapy in ALL patients. Therefore this, and more specifically the occurrence of hyperbilirubinemia, with GRASPA, need to be studied. Indeed, bilirubin is a major breakdown product of hemoglobin. Hemoglobin is derived from red cells that have outlived their natural life and subsequently have been trapped inside the spleen. During splenic degradation of RBC, hemoglobin is separated from iron and cell membrane components. Hemoglobin is then transferred to the liver where it undergoes its further metabolic transformations in a process called conjugation. As the liver becomes irritated, the total bilirubin may rise and this lead to hyperbilirubinemia. GRASPA is containing a weak fraction of extracellular hemoglobin (2 g/dl maximum the day of injection), and the red cell half-life has been shown similar to that of non-processed red cells (about 30 days).

We investigated in our clinical studies, whether there is any relationship between GRASPA administration and the occurrence of hyperbilirubinemia. In a first study in 12 relapsed-ALL patients <55 years old, at the dosages of 100 and 150IU/kg, we observed 1/6 case of transient hyperbilirubinemia (due to cytolysis) in the adult population and 0/6 case in the children stratum. In the same study, 1/3 adults (due to cytolysis) and 2/3 children, from the control group receiving the native E.Coli L-asparaginase, developped hyperbilirubinemia. In a non-randomised study, 27 newly diagnosed ALL patients over 55 year-old were investigated. At the same dosages, 4/27 experienced hyperbilirubinemia (including 1 with increasing bilirubinemia before treatment). These results are in accordance with data from the literature (W. Stock, 2011, leuk. & lymph.). Interestingly, GRASPA was also administrated in monotherapy in 12 patients with pancreatic carcinoma. Results showed that up to the highest dose tested (150IU/kg) all patients had normal bilirubinemia values.

In conclusion, using red cells to vehicle L-asparaginase does not increase the risk of hyperbilirubimenia, and has an acceptable tolerability profile for fragile patients.