Malignant transformation of mouse bone marrow cells induced in vitro by 60Co gamma-ray irradiation

Mouse bone marrow cells were irradiated in vitro with 300, 200 and 100 rad of 60Co gamma-ray. Morphological transformation ensued from day 42 after exposure, but only in cells receiving 300 rad. Malignant transformation appeared in the 2nd generation in the subcultures. Some biological characteristics of malignant transformation were observed as follows: The attaching rate was 40.0%. Malignant transformation rate was 0.10-0.45%; Some colonies and clusters were formed in the semi-solid agar medium; There was no cell proliferation or colony formation in anti-ouabain inhibition test which implies that no mutation took place in the malignant transformation cells; Cytochalasin B rendered the cells to form a large number of multinuclear cells; Obvious chromosome aberration in number and structure was observed; Subsequent induction of fibrosarcomas in sites of subcutaneous inoculation of the malignant transformed cells in immunosuppressed mice. The results show that mouse bone marrow mesenchymal cells can undergo malignant transformation by large dose of gamma-ray irradiation in vitro. Criteria of malignant transformation: some clusters of cells formed in the semi-solid agar medium, multinuclear cell formation by action of cytochalasin B, and tumor mass induced in the location of inoculation.