Transfection of metastatic capability with total genomic DNA from human and mouse metastatic tumour cell lines.

From a large series of experiments involving transfer of high molecular weight total genomic DNA from highly metastatic human and mouse tumour cell lines to other mouse tumour cell lines we have derived a few cell lines with greatly augmented metastatic properties. In one of these experiments the transfected cell line (designated AH8 Test) not only colonised the lungs but also formed secondary tumour colonies in several extrapulmonary sites including the skin, skeletal muscles, bone, liver diaphragm, spleen and heart. There were no qualitative and quantitative effects of this magnitude when we used DNA from several non-metastatic or non-tumourigenic sources. Secondary transfection of metastatic capability with DNA obtained from a metastasis formed by one of the primary transfectant lines (AH8 Test) has also been accomplished. Concomitant transfer of human DNA through both transfection cycles in this experiment was confirmed by a variety of methods including Southern blot analysis, in situ hybridisation and polymerase chain reaction (PCR) amplification of DNA using primers recognising human-specific Alu repeat sequences. The findings offer opportunities for the isolation of sequences programming metastatic behaviour and we have cloned and sequenced a fragment of human DNA, which has not been previously characterised, from the transfected cells.

Effects of altering surface glycoprotein composition on metastatic colonisation potential of murine mammary tumour cells.

This study has examined cells from naturally-occurring murine mammary tumours to ascertain whether cell surface glycoproteins play a significant role in colonisation of the lungs after intravenous inoculation. It was found that gel electrophoretic analysis of membrane extracts and lectin adsorption studies did not reveal any consistent differences in glycoprotein composition of cells from tumours which can heavily colonise the lungs relative to ones from tumours which cannot do so or to cells from pulmonary metastases. Also, alteration of structural and functional properties of surface glycoproteins by treatment with succinylated lectins or with drugs such as tunicamycin and swainsonine, which inhibit glycosylation of membrane proteins, had no specific effects on metastatic colonisation of the lungs. Tunicamycin apparently decreased capability to form experimental metastases but also diminished tumourigenicity on subcutaneous inoculation, although it did not affect tumour cell viability in vitro. This information supports earlier studies from this laboratory involving enzymic digestion of the surface of living tumour cells before inoculation and demonstrates that the pulmonary colonisation capability of these mammary tumour cells can withstand global disorganisation of membrane glycoprotein structure and composition. This implies that either the surface glycoproteins are not important in the colonisation process, or that these tumour cells have great capability for rapid repair of their surfaces. It is concluded that a clear answer to whether surface glycoprotein composition has a decisive role in pulmonary colonisation by these mammary tumour cells requires introduction of stable heritable traits into tumour cell populations by genetic manipulation.

Analysis of organ-specific effects on metastatic tumor formation by studies in vitro.

After entry into the blood, cells from disseminating malignant tumors are rapidly distributed to many organs, but they only grow to form metastases in certain sites. Clinical and pathologic observations on tumor metastasis in humans and in animals have confirmed that the distribution of these secondary neoplasms is related to the site and type of the primary neoplasm. Numerous studies now indicate that success or failure in producing metastatic deposits is influenced by interaction between the tumor cells and the microenvironment of the organ in which they lodge. In the present investigation, the mechanisms by which the microenvironmental conditions of specific organs may influence tumor cell survival and behavior and hence metastasis distribution were investigated in vitro with the use of spontaneous mouse mammary carcinomas from C3H/Avy mice. Some organs (lung, ovary) promoted the survival and the attachment of the tumor cells to the substratum, while others (liver, thyroid gland) consistently diminished survival of the tumor cells in the flask. These effects were shown to be due to soluble substances diffusing out of the organs, the dose dependency of which was demonstrated. It is known that in vivo murine mammary tumors develop metastases mainly in the lungs and occasionally in the kidneys or ovaries (if inoculated via the aorta). The effects of these same organs on tumor cells in vitro were thus in good agreement with the in vivo observations. The findings are compatible with the hypothesis that normal organs can usually suppress the formation of tumor metastases and that tumors that succeed in establishing metastases have evolved means of escaping the inhibitory effects of organs in which the deposits are found.