Augmentation of antitumor activity of an antibody-interleukin 2 immunocytokine with chemotherapeutic agents.

PURPOSE Immune-based therapies, such as the immunocytokine huKS-IL2, exert potent antitumor responses in some animal models by targeting cytokine activity to the tumor microenvironment. We found that certain chemotherapy agents in the appropriate dose and schedule can augment the antitumor activity of huKS-IL2. EXPERIMENTAL DESIGN Chemotherapy agents were given in a single dose followed 1 day (paclitaxel) or 3 days (cyclophosphamide) later with five daily doses of huKS-IL2 in mice bearing established s.c. tumors, liver metastases, or lung metastases. Tumor models used were CT26/KSA colon, 4T1/KSA mammary, or LLCKSA Lewis lung carcinomas. To measure huKS-IL2 distribution, radiolabeled protein was given to CT26/KSA tumor-bearing mice 1 or 24 h after paclitaxel. huKS-IL2 levels in the tumors were evaluated. RESULTS Both paclitaxel and cyclophosphamide followed by huKS-IL2 resulted in enhanced antitumor responses compared with either of the treatments alone in the three different tumor models. Results from studies to determine whether the role of the cytotoxic agents in antitumor activity enhancement was related to tumor uptake indicated that a larger fraction of the radiolabeled huKS-IL2 penetrated the tumors when it was administered 24 h after cytotoxic drug "sensitization." CONCLUSION These data support the idea that prior drug therapy serves to decompress the tumor and lower the diffusion barrier for macromolecules, thus allowing for increased uptake of the huKS-IL2 immunocytokine into the tumor microenvironment. Because the toxicity of the immunocytokine is relatively low at optimal doses, the therapeutic index would likely be greater with the combination treatments.