Distinction between Preneoplastic and Neoplastic Mammary Cell Populations in Vitro by Cytochalasin B-induced Multinucleation¹

Epithelial cell cultures of normal mammary gland, preneoplastic hyperplastic nodule outgrowth lines, primary tumors, and transplanted tumors, all derived from BALB/c mice, were examined for their response to cytochalasin B to determine if cells of primary mammary tumors multinucleated and if preneoplastic hyperplastic alveolar nodule cells responded differently than cells of primary tumors. Established tumorigenic and nontumorigenic cell lines were also examined as positive and negative controls. The standard assay conditions were optimized at 1 µg CB per ml for 48 hr. The results, expressed as the mean percentage of cells exhibiting three or more nuclei per cell were: normal mammary cells, 5%; preneoplastic mammary cells, 4%; primary mammary tumor cells, 36%; transplanted mammary tumors, 70%; tumorigenic established cell lines, 80%; and nontumorigenic established cell lines, 5%. The frequency of tumor cells exhibiting multinucleation increased with serial transplantation in vivo and with serial passage in vitro. The results demonstrate that neoplastic cells within a primary tumor exhibit uncontrolled nuclear division and that uncontrolled nuclear division is a distinguishing characteristic between preneoplastic and neoplastic mammary cells.