A preliminary study on the evaluation of asparaginase. Polyethylene glycol conjugate against canine malignant lymphoma.

Thirty-seven dogs with malignant lymphoma were treated with either polyethylene glycol conjugated (PEG) asparaginase alone (10-30 IU/kg intraperitoneally [IP] weekly--20 dogs) or PEG-asparaginase combined with one cycle of chemotherapy (vincristine, cyclophosphamide, methotrexate, and prednisone), followed by maintenance PEG-asparaginase (30 IU/kg, IP weekly--17 dogs). In the 20 dogs (eight were chemotherapy resistant) treated with PEG-asparaginase alone, seven had a complete response (CR), seven had a partial response (PR), five had no response (NR), and one was not evaluable (NE). The duration of response (CR + PR) ranged from 14 to 102 days (median, 48 days). In the eight chemotherapy-resistant dogs (seven were previously resistant to L-asparaginase) four had responses (one CR and three PR). In the 17 dogs treated with combined PEG-asparaginase and chemotherapy, 13 had a CR, two had a PR, and two had NR. None of the dogs had had prior chemotherapy, and the duration of response (CR + PR) ranged from 7 to 840+ days, with a median of 126+ days. Four dogs are still on maintenance PEG-asparaginase at 16+, 21+, 26+, and 28+ months. Toxicity consisted of death due to massive tumor breakdown (two dogs), disseminated intravascular coagulation (DIC--one dog), hypersensitivity reaction (one dog), vomiting (three dogs) and soft stools (three dogs). Four normal dogs were given very high doses of PEG-asparaginase (200 IU/kg and 1200 IU/kg) once weekly for two treatments without any significant toxicity. These results indicate that PEG-asparaginase has antitumor activity in dog with spontaneously occurring malignant lymphoma.