α-Difluoromethylornithine inhibits liver metastasis produced by intrasplenic injection of human tumor cells into nude mice

The purpose of these studies was to examine metastatic potentials of a human colon tumor xenograft (T6) and three different human tumor cell lines (LS174T, HT29 and A549) using the intrasplenic-nude mouse model system (ISMS model system). A further objective was to study the activity of-difluoromethylornithine (DFMO) against primary and metastatic growth of the xenograft and the three cell lines. DFMO is an irreversible inhibitor of ornithine decarboxylase, a rate-limiting step in polyamine biosynthesis. Tumor burdens in the liver of nude mice were observed 6 weeks after the intrasplenic injection with LS174T and 12–14 weeks after intrasplenic injections with T6, HT29 and A549. Most of the mice developed primary tumor growth in the spleens. DFMO showed significant activity against liver metastases but had little or no activity against primary tumor growth in the spleens of the ISMS model and against s.c. growth of the xenograft. The studies demonstrated that the ISMS model system is an excellent system for studying metastatic behavior of human tumors and for studying the antimetastatic activity of experimental drugs.