Background: D-amino acid oxidase (DAO) is an H2O2-generating enzyme, and tumor growth suppression by
selective delivery of porcine DAO in tumors via the cytotoxic action of H2O2 has been reported. DAO isolated from
Fusarium spp. (fDAO) shows much higher enzyme activity than porcine DAO, although the application of fDAO for
antitumor treatment has not yet been determined.
Objective: The purpose of this study was to prepare enzymatically highly active pegylated-fDAO, and to determine whether
it accumulates in tumors and exerts a potent antitumor effect in tumor-bearing mice.
Methods: Polyethylene glycol (PEG; Mw. 2000) was conjugated to fDAO to form PEGylated fDAO (PEG-fDAO). PEGfDAO was intravenously administered into S180 tumor-bearing mice, and the body distribution and antitumor activity of
PEG-fDAO was determined.
Results: The enzyme activity of PEG-fDAO was 26.1 U/mg, which was comparable to that of fDAO. Intravenously
administered PEG-fDAO accumulated in tumors with less distribution in normal tissue except in the plasma. Enzyme
activity in the tumor was 60–120 mU/g-tissue over 7–20 h after i.v. injection of 0.1 mg of PEG-fDAO. To generate the H2O2
in the tumor tissue, PEG-fDAO was intravenously administered, and then, D-phenylalanine was intraperitoneally
administered after a lag time. No remarkable tumor suppression effect was observed under conditions used in this study,
compared to the non-treated group.
Conclusion: The results suggest that PEG-fDAO maintained high enzymatic activity after pegylation. Treatment with PEGfDAO conferred high enzyme activity on tumor tissue; 3–6 fold higher than that of previously reported pDAO; however,
high enzyme activity in the plasma limited repeated treatment owing to lethal toxicity, which seemingly led to poor
therapeutic outcome. Overall, the use of PEG-fDAO is promising for antitumor therapy, although the suppression of DAO
activity in the plasma would also be required rather than only the increase in DAO activity in the tumor for an antitumor