Effect of interleukin-2 on the biodistribution of technetium-99m-labelled anti-CEA monoclonal antibody in mice bearing human tumour xenografts.

We have evaluated whether interleukin-2 (IL-2) at low doses can enhance delivery of radionuclides to tumour sites by improving the access of the radio-labelled antibody. The effects of 1000 or 2000 units of IL-2 on the biodistribution of technetium-99m-labelled anticarcinoembryonic antigen (CEA) monoclonal antibody, ZCE025, in athymic mice bearing human CEA-positive tumour (MKN45) xenografts were investigated. Treatment with IL-2 resulted in a significantly higher tumour uptake (1.2-1.5-fold) compared with the control group. Some normal organs, such as heart, lung, liver, spleen and kidneys, showed increased 99mTc uptake following the IL-2 treatment. Pretreatment with IL-2 also induced an enhancement of the permeability index for mouse IgG in tumours and in normal organs, whereas the blood flow in both normal organs and tumours remained at control levels. The effects of IL-2 were found to be dose-dependent. The IL-2 treatment increased the plasma CEA levels but not the CEA content in tumour tissues, suggesting that IL-2 enhanced the leakage of CEA from tumour to blood. The enhancement ratios of the tumour 99mTc-ZCE025 uptake following treatment with IL-2 were 1.4 and 1.8 in mice bearing small and large tumours, respectively. Our experimental results indicated that the low dose of IL-2 enhanced the vascular permeability sufficiently to increase the amount of antibody delivered to the tumour target. Administration of IL-2 would render radioimmunotherapy more effective, especially in patients with large tumour burdens.