In vitro proliferation and in vivo malignancy of cell lines simultaneouslyderived from a chemically-induced heterogeneous rat mammary tumor

Identification of clones in primary tumors responsible for proliferation, i nvasion, and metastasis was carried out. Four different aneuploid establish ed cell lines derived from a ductal infiltrating mammary rat tumor induced by 7,12-dimethylbenz[a]anthracene were studied for proliferative and growth features in vitro and for tumorigenic and metastatic potential in vivo in nude mice. Clones, named RM1, RM2, RM3, and RM4, were characterized by diff erent proliferative activity, Clone RM1 showed the highest proliferative ac tivity by both tritiated thymidine incorporation and S-phase flow cytometry , followed by clone RM4. Conversely, clones RM2 and RM3 showed a lower prol iferation rate. Growth-promoting activity, tested on 3T3 Sw-iss cells, was high in all clones, although RM1 showed significantly lower growth factors- releasing activity. Nude mice tumorigenesis demonstrated a strong tumor ind uction of line RM1 (100% of the mice after 47 +/- 7 d) and a slightly lower tumor induction of line RM4 (70% of the mice after 69 +/- 9 d). Line RM3 s howed tumor induction in 40% of the mice after 186 +/- 16 d. Lines RM2 show ed no tumor induction. Metastasis occurred in mice treated with line RM1 on ly. Therefore, tumorigenesis and metastasis correlate with proliferation bu t not with the release of growth factors. In conclusion, flow cytometry mon itoring of clones from heterogeneous primary tumors proved to be a suitable model for the study of in vivo malignancy and in vitro proliferation.