Antitumor effect of α-galactosylceramide (KRN7000) on spontaneous hepatic metastases requires endogenous interleukin 12 in the liver

Hepatic metastasis is a major clinical problem in cancer treatment. We examined antitumor activity of alpha-galactosylceramide (KRN7000) on mice with spontaneous liver metastases of reticulum cell sarcoma M5076 tumor cells (spontaneous metastasis model). In this model, all mice that were s.c. challenged with one million tumor cells developed a solid s.c. mass by day 7 and died of hepatic metastases, In the current study, we administered 100 mu g/kg of KRN7000 to the model mice on days 7, 11, and 15, This treatment suppressed the growth of established Liver metastases and resulted in the prolongation of survival time. Fluorescence-activated cell sorter analysis of phenotypes of spleen cells, hepatic lymphocytes, and regional lymph node cells around the s.c. tumor revealed that CD3(+)NK1.1(+) (NKT) cells increased in hepatic lymphocytes of the KRN7000-treated mice. Cytotoxic activity and IFN-gamma production of hepatic lymphocytes were augmented in comparison with those of spleen cells and regional LN cells. At the same time, interleukin (TL)-12 production of hepatic lymphocytes was markedly enhanced. Neutralization of IL-12 using a blocking monoclonal antibody diminished the prolonged survival time. These results showed that the in vivo antitumor effects of KRN7000 on spontaneous liver metastases were dependent on the endogenous IL-12 production, where NKT cells in the liver are suggested to be involved, Adjuvant immunotherapy using KRN7000 could be a promising modality for the prevention of postoperative liver metastases.