Robert C. Rosenthal

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‐aspnraginase 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 dogs with spontaneously occurring malignant lymphoma.