Abstract
In the tumor model ER 15-P, a chemically induced pleomorphic myofibrosarcoma of the C57/Bl6J mouse, cell lines with liver-preferential metastatic tumor spread were selected in vivo. In order to describe cell-surface molecules relevant for hepatic metastasis, monoclonal antibodies were raised against the liver-preferential variants. In a syngeneic immunization with viable tumor cells cyclophosphamide was used for augmentation of the humoral antitumor immunity. The monoclonal antibody mAb 3H4, an IgG2b isotype, reacted with a cell-surface epitope exclusively detected on the liver-preferential metastatic phenotype (Me) of the tumor model ER 15-P; no reactivity with the non-organ-specific metastatic phenotype (P) was observed. Regarding the morphological heterogeneity of different Me and P tumor cell populations, mAb 3H4 antigen expression was consistently associated with liver-preferential metastasis, not with different morphological stages of differentiation. It showed no cross-reaction with other tumor cell lines tested except MethA murine fibrosarcoma. The antibody was unreactive with normal tissue cells in C57/Bl6J mice. mAb 3H4 antigen expression was not dependent on the cell cycle. In an experimental assay of hematogenous metastasis, preincubation with mAb 3H4 significantly reduced the number of liver metastases of the liver-preferential tumor cells. Although no crossreaction of the primary ER 15-P with mAb 3H4 was observed, the antibody also significantly reduced the number of renal metastases of the P tumor cell population. The syngeneic IgG2b monoclonal antibody mAb 3H4 identified a new tumor-associated cell-surface antigen correlating with liver-preferential metastasis. mAb 3H4 antigen expression was a stable property of the liver-preferential tumor cells regardless of morphological diversity or functional cell status. In an in vivo blocking assay mAb 3H4 reduced liver colonization in vivo.