Inhibition of CT-26 Murine Adenocarcinoma Growth in the Rectum of Mice Treated with Recombinant Human Interleukin-6

In the present study we evaluated the antitumor effects of recombinant human interleukin-6 (rhIL-6), expressed in Chinese hamster ovary cells, in a murine primary tumor model. We showed that treatment with rhIL-6 substantially inhibited the implantation and growth rates of CT-26 adenocar-cinoma tumor cells in the rectal submucosa of syngeneic mice. This effect was achieved by injecting rhIL-6 for 7 consecutive days starting 1 day prior to tumor inoculation. No obvious antitumor effect was noted when rhIL-6 injections started 5 days after tumor inoculation. Analysis of the mechanisms by which rhIL-6 exerts its antitumor effects did not reveal a direct antitumor effect on CT-26 tumor cells or the up-regulation of major histocompatibility complex antigens on these cells. However, infiltration of lymphocytes at the tumor site was observed. Increase of carcinoembryonic antigen by IL-6 was clearly seen in human HT-29 colon carcinoma cells. The possible application of these results for adjuvant immunotherapy of selected colorectal patients and prevention of reimplantation of tumor cells disseminated during surgery is discussed.