Serial xenotransplantation of a human embryonal carcinoma in experimental urology

Variability of differentiation patterns in xenotransplanted spindle cell sarcomas: a histomorphological, immunohistochemical, and ultrastructural study

Three leiomyosarcomas, 3 nerve sheath sarcomas, 1 rhabdomyosarcoma, and 1 sarcoma not otherwise classifiable with 17 of their xenografts, grown on nude mice, were analyzed to assess the degree of concordance between histomorphology, immunohistochemistry, and ultrastructure in spindle cell sarcoma xenograft differentiation. Histomorphology was inconclusive or misleading in 4/8 sarcoma strains and immunohistochemistry in 4/8 originals and in 10/17 xenografts, although specific patterns had been identified ultrastructurally. Electron microscopy was superior to immunohistochemistry and histomorphology in spindle cell sarcoma differential diagnosis. A further purpose of this study was to clarify whether spindle cell sarcoma xenografts retain the morphological characteristics of their primaries. Histomorphological features of the primaries were preserved over all passages, whereas the immunohistochemical marker profiles as well as the ultrastructural phenotypes changed in 14/17 xenografts and in 8/17 xenografts, respectively. Moreover, unusual bidirectional or tridirectional patterns of differentiation were identified ultrastructurally with leiomyomatous as well as Schwann cells occurring side by side and with MFH-like areas in 5/17 xenotransplants. These findings suggest genetic instability of tumor cells and may be important in the consideration of mesenchymal differentiation pathways.

Morphological heterogeneity and phenotypical instability versus metastatic stability in the murine tumor model ER 15-P

At clinical presentation, the majority of malignant tumors are composed of multiple clonal subpopulations of tumor cells with different phenotypic characteristics. Using the experimental tumor model ER 15-P, a methylcholanthrene-induced pleomorphic sarcoma of the C57 Bl6J mouse, we studied a system of long-term in vivo passages of this primary tumor for cell morphological changes, and alterations in the potential for spontaneous lung metastases. Transplants from the primary after the 4th, 20th, 40th and 80th i.m. passage (referred to as T4, T20, T40, and T80 respectively) together with their lung metastases were investigated by light microscopy, immunohistochemistry, and electron microscopy. In addition, the potential for metastasis to the lungs in each group was determined and compared with that of the parent T4 tumors. T4 tumors were mainly composed of spindle-shaped tumor cells with the ultrastructural features of fibroblasts and myofibroblasts, often arranged in a storiform or fasciculated growth pattern, and intermingled with tumor giant cells. Some small areas contained polygonal or rounded tumor cells, ultrastructurally undifferentiated, and sometimes arranged in a hemangiopericytoma-like growth pattern. Although electron-microscopical findings clearly demonstrated the mesenchymal origin of these tumor cells, immunostaining with a polyclonal antibody to vimentin was unspecific in all tumor cells and normal mouse tissue. Monoclonal antibodies to vimentin from different sources were completely negative in tumor cells and murine stromal components. In contrast, myofibroblast-like tumor cells showed immunohistochemically, a moderate to strong co-expression with monoclonal antibodies to desmin, muscle actin and alpha-smooth muscle actin. On the basis of these morphological findings, the primary ER 15-P was classified as a pleomorphic myofibrosarcoma. The lung metastases of T4 tumors were mainly composed of undifferentiated round to polygonal tumor cells, while the number of desmin-positive, muscle- and alpha-smooth muscle-actin-positive cells was reduced. The morphological features of T20 tumors and their lung metastases were the same as in T4, indicating a relative stability of the phenotype up to that stage. In contrast, T40 and T80 tumors and their lung metastases were found to contain almost exclusively undifferentiated tumor cells and many tumor giant cells. While fibroblast-like tumor cells were seen only occasionally, myofibroblast-like tumor cells had almost completely disappeared. The potential for lung metastases was nearly constant in all groups, suggesting metastatic stability. Obviously, the undifferentiated tumor cells of this model are associated with a higher metastatic potential.

The heterogeneity of solid human xenotransplant tumours

Fifteen xenograft tumour lines (4 osteosarcomas and 11 squamous carcinomas) were established on nude mice in numerous passages. Over a period of 4 years, samples were taken and studied systematically in more than 4000 histological slides. Of the tumour lines, 12 (4 osteosarcomas and 8 squamous carcinomas) showed remarkable dedifferentiation, but also redifferentiation towards a higher grade. There was a correlation between the rate of tumour takes in mice and poor prognosis in patients, but none between tumour doubling time and the phases of the cell cycle. Altogether, the results showed a great heterogeneity of human xenotransplants in terms of biological behaviour and morphological changes.

The vascular architecture of human xenotransplanted tumors: histological, morphometrical, and ultrastructural studies

This study was designed to examine the vascular system of human xenotransplanted tumors on nude mice with different complementary morphometrical and morphological methods. The vascular system shows a chaotic arrangement. There is an extreme heterogeneity in the vascular distribution and density. Large avascular regions could be identified in several non-necrotic tumors. There was no clear difference in the vascular density between the center and the periphery of the tumors, nor was there any zonal correlation for the distribution of the necrosis. With three-dimensional corrosion casts it could be demonstrated that clusters of vessels were directly beneath areas almost free of vessels. In the center, vessels often form a sinusoidal system with numerous blind ends without clearly discernible endothelial cells. Numerous irregular tumor-cell-lined sinusoids are visible next to endothelial-lined vessels with transmission electron microscopy. With scanning electron microscopy it could be demonstrated that large-calibre endotheliazed vessels were found in the direct vicinity or in the center of non-viable zones. Even large-calibre vessels have a capillary wall structure. Sometimes, a basement membrane cannot be observed at all or only incompletely. There are numerous indications of vascular discontinuities and leaks with a widespread intercellular occurrence of blood cells.

Instability of xenotransplanted soft tissue sarcomas. Morphologic and flow cytometric results

Human tumors transplanted into nude mice are widely considered to be identical to the tumor of origin. In addition, high histologic constancy of xenografts over many passages is generally accepted. We have checked these prerequisites for a therapy-orientated application of the nude mouse model using soft tissue sarcomas. Twenty-two primary soft tissue sarcomas and their xenografts were compared histologically and flow cytometrically over numerous passages. More than 30% of transplants showed a variation in cell differentiation, cell content, frequency of mitosis, tendency to necrotize, and connective tissue content compared to the original tumor. Furthermore, transplants from various regions in one tumor showed divergent results. Analyses of serial transplants showed histologic and flow cytometrical discrepancies in about 50% of cases, and new cell lines occurred in 26%. Our results show that the genetic instability found in human neoplasias also applies to xenotransplants and that the therapy-related usefulness of the nude mouse model is limited.

Dosimetry of a new holding device for fast d (14) + Be-neutron irradiation of human xenografts in nude mice

Fast neutron irradiation of human xenografts in the flanks of nude mice is mainly a technical problem. The feasibility is dependent on the distribution of the tumor absorbed dose DT and on an effective shielding of the bodies of the animals. Therefore a special holding device for simultaneous irradiation of two tumour-bearing animals was developed. Meticulous dosimetric investigations using TLD-300 detectors in a mouse phantom showed that a relatively homogeneous dose distribution could be achieved in the xenografts and that effective shielding of the mice from direct irradiation would be achieved; the dose for the bodies of the animals being less than 10% of the dose to the tumour. Thus survival and a sufficient follow-up period of the irradiated animals could be guaranteed for all preclinical dose ranges used.