Systemic alterations in ornithine decarboxylase activity caused by colon cancer in mice

Tumors are known to cause profound changes in host biology, but the mechanisms responsible for these changes remain unclear. Ornithine decarboxylase (ODC) is a ratelimiting enzyme that catalyzes the biosynthesis of polyamines. The purpose of this study was to examine the effects of MC-26 tumor burden on ODC activity in the gastrointestinal tract, kidney and liver of mice. Forty-four Balb/c mice were randomly divided into 2 groups and the test group was pair-fed (to control). Group 1 was the tumor-free control. Group 2 was inoculated subcutaneously with 5 × 10⁵ MC-26 cells. The ODC activity in the kidney and liver of tumor-bearing mice was significantly lower compared to tumor-free controls at sacrifice. ODC activity in the colon increased almost 4-fold. These results suggest that the presence of MC-26 tumor causes systemic effects that alter ODC activity. The tumor may elaborate a substance that suppresses ODC activity in some normal tissues while stimulating ODC activity in the tissue from which the tumor was derived.