Tumorigenicity of human lymphoma and lymphoblastoid B-cell lines was assessed by their ability to form growing and transplantable masses on subcutaneous inoculation into neonatally thymectomized, Ara-C-protected, total-body-irradiated mice. By these criteria, 12 lines of known malignant origin were tumorigenic, 11 lymphoblastoid lines, tested after less than one year of in vitro growth, were non-tumorigenic and 8/18 long-established lymphoblastoid lines produced transplantable tumours. All of the long-established lines had acquired karyotypic changes on prolonged culture, the predominant characteristic being a gain of whole chromosomes or of major chromosome segments. None showed the classical 8:14 translocation associated with Burkitt's lymphoma. Comparisons with nontumorigenic precursors (recovered from liquid nitrogen storage) and with other non-tumorigenic but chromosomally abnormal, lymphoblastoid lines suggest that imbalance of the dosage of genes carried on chromosomes 7,8 and 9 may be important in determining the tumorigenic phenotype.
Summary Xenograft tumours from an oestrogen-dependent human breast cancer cell line MCF-7 have been established and characterised in thymectomised, irradiated female CBA strain mice. There was evidence for selection in xenografts of a subpopulation of MCF-7 cells with an altered pattern of gene expression as measured by mRNA levels compared with the original cells in vitro. Tumorigenicity increased significantly on repeated animal passage but oestrogen dependence was retained. Following injection of the mice with oestrogen, mitosis was induced in the tumour cells with associated increases in thymidine uptake and percentage of cells in S-phase. In accord with these changes, c-myc and p53 expression were increased and TGF-beta was suppressed. Thereafter the expression of the c-myc and p53 genes fell whilst that of the TGF-beta gene was induced-as the oestrogenic stimulus declined. The oestrogen-regulated mRNA pS2 showed a biphasic response to oestrogen and levels declined as the serum oestrogen fell to undetectable levels. This xenograft system demonstrates that changes in transcription of oncogenes, growth factor and oestrogenregulated genes can be detected in vivo in response to oestrogen. It thus provides an in vivo model for studies of the biochemical and molecular basis for therapeutic manipulation of hormone-sensitive human breast cancer.In studying the molecular biology of cancer cells, the significance of in vitro observations may be uncertain due to the absence of host factors that influence tumour behaviour in vivo. Recent work on experimental human breast tumours in vivo has made use, almost exclusively, of congenitally athymic ('nude') mice Brunner et al., 1989). We have previously reported the growth of a range of human tumours in thymectomised, irradiated mice (Busuttil et al., 1986) which have advantages in ease of husbandry and cost (Steel et al., 1978;Morten et al., 1984;Hay et al., 1985). We report here the characterization of an oestrogenresponsive tumour derived from the MCF-7 human breast carcinoma cell line grown in vivo in female thymectomised and irradiated CBA mice. In addition, we have examined the kinetics of the expression of a range of related genes (c-myc, p53, TGF-beta and pS2) following oestrogenic stimulation in this tumour model system. Materials and methods Twenty
Tumours were raised in both congenitally athymic ('nude') Swiss mice and in neonatally thymectomized, Ara-C-protected, whole-body irradiated CBA mice by subcutaneous inoculation of cells from a variety of cultured human lines. In both types of animal, tumours tended to grow massively at the site of inoculation, with some infiltration of adjacent tissues but only rarely with evidence of metastatic spread. Tumours derived from Burkitt's lymphoma (BL) lines or from EB virus-transformed lymphoblastoid cell lines (LCL) were all classified as high grade malignant lymphomas with a limited range of appearances on conventional histological examination. In the material studied there were no consistent features distinguishing BL-derived from LCL-derived tumours. Cell lines originating from other haematopoietic malignancies tended to produce tumours interpreted as immunoblastic lymphomas though there were distinctive characteristics in some cases, such as highly convoluted or pleomorphic nuclei in the cells of some tumours derived from T-cell leukaemia lines and plasmacytoid differentiation in tumours originating from myeloma lines. Malignant cell lines of epithelial origin gave rise to tumours with the histological appearances of anaplastic carcinomas readily distinguishable from the high grade lymphomas produced by haematopoietic cells.
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