Background: Monitoring L-asparagine (L-ASN) plasma levels could provide information useful for determining whether the dosage or schedule of L-asparaginase (L-ASE) administration is adequate. Very few data are available on depletion caused by the Erwinia chrysanthemi (E. chrysanthemi) product. Since it has been suggested that L-ASN depletion may have been overestimated in the past due to residual L-ASE activity, samples in this study have been analyzed after deproteinization with sulphosalicylic acid. Patients undergoing subsequent exposures to L-ASE derived from E. chrysanthemi have been investigated.
Patients and methods: Fifty-four children with newly diagnosed acute lymphoblastic leukemia (ALL) at our institution entered this study. L-ASE was given at conventional doses (10,000 IU/sqm) every three days during the induction phase (8 doses, first exposure) or twice a week (4 doses, second exposure) during the reinduction phase. High-dose L-ASE (i.e., HD-L-ASE 25,000 IU/sqm) was given weekly, for a total of 20 doses, as a second or third exposure during the reinduction and/or maintenance phases. To determine the plasma levels of L-ASN, samples were deproteinized with sulphosalicylic acid, stored at -80 degrees C and then analyzed by HPLC after precolumn derivatization with o-phthaldialdehyde. The CSF samples were analyzed by the same procedure. An experiment was carried out to detect in vitro L-ASE deactivation in patients' plasma.
Results: L-ASN plasma depletion was observed in 80% of the cases during the first exposure to conventional doses of L-ASE and only in 25% of the cases during the second or third exposures to either conventional or high doses of L-ASE. A correlation was found between plasma and CSF L-ASN levels. Activity inhibitory to L-ASE was found in the plasma of patients not depleted during L-ASE treatment and was not found in the plasma of those in whom L-ASN plasma depletion was obtained.
Conclusions: L-ASN plasma depletion is regularly obtained in the majority of patients during the first exposure to conventional doses of E. chrysanthemi L-ASE. Conversely, in most cases depletion does not occur during subsequent exposures. Studies should be performed to evaluate whether L-ASE derived from different species or conjugated with polyethylene-glycole are effective in obtaining L-ASN plasma depletion in patients previously treated with Erwinia C. L-ASE. The clinical impact of L-ASN depletion should also be investigated in large cohorts of patients.