High efficacy of monomethoxypolyethylene glycol-conjugated L-asparaginase (PEG2-ASP) in two patients with hematological malignancies.

Two patients with hematological malignancies were successfully treated with monomethoxypolyethylene glycol-conjugated Escherichia coli L-asparaginase (PEG2-ASP), which reportedly lacks both antigenicity and immunogenicity but retains catalytic activity as well as slow clearance in an experimental animal model. A 20-year-old male patient with leukemic lymphoma was refractory to conventional chemotherapy but responsive to L-asparaginase (L-ASP) followed, however, by severe adverse effects. On relapse, an intravenous infusion of 100-200 IU/day dose of PEG2-ASP alone led to a complete remission 2 months later without hypersensitivity or other significant adverse reactions. Surprisingly, he remained in a complete remission for over one year with a regular weekly infusion of PEG2-ASP, combined with a weekly small dose of Ara-C. During this period, blood asparagine was not detectable. The other patient, a 64-year-old woman with chronic myelogenous leukemia in blast crisis achieved, within 6 weeks, a complete remission with twice-weekly infusions of PEG2-ASP. Thus, PEG2-ASP is a highly effective antitumor agent overcoming the limitations in therapeutic use of L-ASP.