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Combined effects of local radiotherapy and systemic interleukin-2 on the development of spontaneous lung metastases in Y59 rats

The combined effects of primary tumor irradiation and systemic application of recombinant interleukin-2 (rIL-2) on the development of spontaneous lung metastases were investigated. Y59 inbred rats were injected subcutaneously with syngenic anaplastic carcinoma cells. Subcutaneous injection first led to the development of a locally growing tumor and then to spontaneous lung metastases. Fractionated local irradiation of primary tumor growing in the rat footpad combined with intraperitoneal administration of rIL-2 on irradiation days led to a significant reduction of spontaneous lung metastasis development. The antimetastatic effects of the combined treatment appeared to depend on the primary tumor size. Thus, the antimetastatic effect could be achieved with irradiation delivered to primary tumors of a relatively small size (3 to 4 mm, on day 6 after injection), but not in larger primary tumors (8 mm in diametar, on day 12 after injection). This combined administration of irradiation and rIL-2 also extended the survival rate in tumor injected animals. Moreover, a significant increase of lymphocyte count was detected in spleens of rats treated with irradiation and rIL-2 and the highest lytic activity was also demonstrated in this group of animals. These results suggest that the combined treatment proposed here could play a role in controlling the development of lung metastases.

radiotherapy; lung metastases; rIL-2; rats

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