In a rat study, giving the chemotherapy drug 5‑fluorouracil together with low‑dose thymosin‑alpha‑1 and interleukin‑2 shrank liver tumors from colon cancer, stopped them from spreading, improved survival, and boosted natural‑killer cell activity.

We studied the effect of combined chemo-immunotherapy, 5-FU followed by thymosin alpha 1 (T alpha 1) and interleukin-2 (IL-2) at low doses, on liver metastases from colorectal cancer, induced by splenic injection of DHD/K12 cells (1,2-dimethylhydrazine-induced colon adenocarcinoma) in syngeneic BDIX rats. The presence of liver metastases was checked by laparotomy 14 days after tumor-cell injection. Evaluable rats were assigned randomly to 5 experimental groups designated as control, 5-FU, IL-2, 5-FU/IL-2 and 5-FU/T alpha 1/IL-2. 5-FU was administered i.v. as a continuous infusion for 7 days by an osmotic device implanted surgically. T alpha 1 and IL-2 were administered for 4 days and repeated after 11 days. Combined chemo-immunotherapy was shown both to significantly reduce the growth of liver metastases and to prevent extra-hepatic spread. 5-FU/T alpha 1/IL-2 also improved survival rate. Combined immunotherapy after 5-FU restored NK activity of the peripheral-blood-mononuclear-cell (PBMC) in tumor and/or 5-FU immunodepressed rats and enhanced PBMC cytotoxic activity against the DHD/K12 autologous cell line. This model was devised to mimic the clinical situation of unresectable liver metastases.