Improved pharmacodynamics of L-asparaginase-loaded in human red blood cells

To evaluate the modification of pharmacodynamic parameters induced by the administration of L-asparaginase loaded into red blood cells, 13 patients received a single dose of L-asparaginase internalised into the carrier. The enzyme was loaded using a reversible lysis-resealing process. The dose per patient ranged from 30 to 200 i.u. kg-1. Considerable heterogeneity occurred between patients. the level of L-asparaginase circulating after 24 h represented 47% of the total injected dose as compared to 74.8% for red blood cells (RBCs). However, the half-life of the enzyme remaining in the circulation was very similar to that of the RBC carrier, i.e. 29 days and 27 days, respectively, compared with 8-24 h for the free enzyme. Sustained elimination of plasma L-asparagine occurred, the duration of which was dependent on the injected dose. A single injection of 30.i.u.kg-1 was sufficient to eliminate plasma L-asparagine over 10 days. With 150-200 IU.kg-1 the elimination period was extended to 50 days. These data show that the use of RBCs as carriers of L-asparaginase greatly improves the pharmacodynamic parameters of the drug.