Cancer therapy with chemically modified enzymes. II. The therapeutic effectiveness of arginase, and arginase modified by the covalent attachment of polyethylene glycol, on the taper liver tumor and the L5178Y murine leukemia.

Monomethoxypolyethylene glycol (PEG) was attached covalently to arginase. PEG-arginase was effective in prolonging the survival times of mice injected with the Taper liver tumor, whereas unmodified arginase was ineffective. PEG-arginase was more effective than arginase in the in vitro destruction of L5178Y mouse leukemia. However, neither PEG-arginase nor arginase inhibited the in vivo growth of this tumor.