No abstract

Recent observations indicate the existence of pathogenetically distinct groups of well-differentiated (WD) dedifferentiated (DD) liposarcomas. In the retroperitoneal WD-DD liposarcomas, the predominant phenotype is represented by the aberrant (overexpressed) mdm2+/p53+ wild-type profile. At the nonretroperitoneal site, the WD liposarcomas present a wider association of MDM2/P53 gene expression; i.e., mdm2+/p53+, mdm2+/p53-, mdm2-/p53+ and mdm2-/p53-, and TP53 mutations seem to correlate with the dedifferentiation process. A biochemical study of mdm2-p53 association in 11 tumor samples characterized by the presence of different mdm2 and p53 immunophenotypes was performed. Immunoprecipitation assays using a p53-specific antibody were performed on tumor tissue and surrounding normal tissue; the immunoprecipitated material was then investigated for the presence of p53 (control) and of coimmunoprecipitated mdm2. This biochemical analysis showed that, in mdm2+/p53+/wild-type retroperitoneal liposarcomas, a band corresponded to mdm2 protein in the cellular lysates immunoprecipitated with a p53-directed antibody. In contrast, the mdm2+/p53- liposarcoma did not evidence the presence of mdm2 protein nor was p53 protein available to direct immunoprecipitation, as in the p53 mutant tumor samples with mdm2-/p53+ and mdm2-/p53- phenotypes. From the normal counterpart of retroperitoneal liposarcoma lysates, no p53 protein was immunoprecipitated. The findings in this study agree with the molecular data and they show the physical association of mdm2 and p53 in fresh liposarcoma surgical specimens.

A leukemogenic treatment with urethan in infant (SWR x C57BL)F1 mice (1 mg/g body weight, 5 times, once every second day) induced a marked reduction of the thymus and spleen weight, of the number of RBC, WBC, and bone marrow cells, with an inverted lymphoid/myeloid cell ratio in the bone marrow. An analysis of the bone marrow population showed that the carcinogen acted selectively on the lymphoid cells and, to a lesser extent, on the erythroblastic ones, while the myeloid cells did not appear to be involved. The damage was still present 10 days after the end of treatment. A single intracardiac inoculum of 15–20 × 106 syngeneic normal bone marrow cells, 3 days after the last urethan injection, determined a recovery of the spleen weight and of the cell ratio in the bone marrow, whereas the thymus weight and the blood and bone marrow cell counts were uneffected. Moreover the bone marrow inoculum failed to inhibit the induction of thymic lymphosarcomas.

A systematic search for viral particles was carried out in thymuses of C3Hf inbred mice treated with leukemogenic doses of urethan. Thymuses collected during the tumor latent period and thymic lymphosarcomas were examined. A group of 38 mice was treated, starting at 10 days of age, with 5 i.p. doses of urethan (lmg/g body weight) once every two days. This treatment induces approximately 30 per cent thymic lymphosarcomas in C3Hf mice, after an average period of 20 weeks, whereas no spontaneous thymic lymphosarcomas develop in untreated controls. Six animals with thymic lymphosarcoma were killed between 16–32 weeks of age; the others were sacrificed at 3,5,10 and 14 weeks of age when they did not have any recognizable thymic tumor either grossly or microscopically. As control, thymuses of a group of 28 untreated mice were examined. Mature and immature type C particles morphologically indistinguishable from the murine leukemogenic viruses and intracisternal A particles were observed. The immature C particles and intracisternal A particles were found in all the groups of treated and untreated mice. Intracisternal A particles were more numerous in the untreated than in the treated animals. The number of A particles in the neoplastic thymuses was far inferior than that observed in the treated animals killed before development of lymphoma. The amount of immature C particles was always much less than that of A particles. No significant difference in the number of immature C particles was observed in all experimental groups. Mature C particles were only seen in the thymus of a few treated or untreated mice, never in thymic lymphosarcomas. Within the limits of this investigation, the results presented are not consistent with the view that urethan may act by stimulating viral multiplication.

An electron microscopic study of viral particles was conducted on pancreas, thymus, and bone marrow of normal and leukemic (C57BL x C3Hf) F1 (BC3) and SWR mice. The leukemic mice had developed thymic lymphosarcoma after neonatal injection of N-nitrosomethylurea or urethan. An intense proliferation of type C particles morphologically identical to the murine leukemia virus was found in the acinar cells of the exocrine pancreas of BC3 mice. The particles were predominantly located in intracytoplasmic vacuoles but they were also numerous in dilated cisternae of the rough endoplasmic reticulum and in extracellular spaces. A substantial quantitative difference of type C particles between the pancreases of leukemic and healthy mice was not observed. No viral particles were found in the pancreas of SWR mice. In the thymus and bone marrow of BC3 and SWR mice a small number of type C particles and intracisternal type A particles was found in all the experimental and control groups. The observation of a high number of type C particles in the exocrine pancreas of BC3 mice is discussed in relation to a viral etiology of chemically-induced lymphomas.