Abstract: AIM: To study the antitumor effects of chemical modification enzyme which recombinant L-asparaginase (rL-ASP)modified by monomethoxy-polyethylene glycol (mPEG). METHODS: PEG modification of rLASP formed rL-ASP-PEG and compared molecular weight of rL-ASP and rL-ASP-PEG with sodium dodecyl sulfaete polyacrylamide gel electrophoresis (SDS-PAGE).Anti-tumor activity was tested by (3-(4, 4-dimcthylthioazol-2-yl)-2, 5-diphenyl tetrazolium bromide analysis(MTT)and apoptosis was valued by flow cytometry (FCM)in vivo.The effect of Anti-tumor activity was evaluated by weights of solid tumor of P₃₃₈ on DBA/2 mice in vitro.Transmission electron microscopy (TEM)observed the effects of rLASP-PEG inhibiting P₃₈₈ solid tumor on DBA/2 mice. RESULTS: rL-ASP-PEG had significant antitumor effects on P₃₈₈ cells, and the inhibitory concentration 50 %(IC₅₀)of rL-ASP-PEG was 2.056 IU·ml^-1 .FCM data showed that the ultramicro pathological picture of transplant tumor in TEM that L-ASP-PEG reacting showed the tumor cells necrosis. CONCLUSION: rL-ASP-PEG shows a significant effect of antitumor.

Key words: recombinant L-asparaginase (rL-ASP), polyethyethylene glycol(PEG), antitumor, chemical modification, inhibitory concentration 50%(IC50), leukemia, sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE)