Inhaled uranium ore dust and lung cancer risk in rats

Using a nose-only inhalation system, male Sprague-Dawley rats were exposed 4.2 h d(-1), 5 days per week for 65 weeks to one of two concentrations of natural uranium ore dust aerosol (44% U, 50 mg m(-3) and 19 mg m(-3)) without significant radon content. After inhalation exposure ceased, the rats were allowed to live for their natural lifetime. Lung uranium burdens, measured at the time of death of each animal, declined exponentially after dust inhalation ceased, and the rate of decline was independent of the initial lung burden. Lymph node specific burdens ranged from 1 to 60 fold greater than the specific lung burden in the same animal. No lymph node tumors were observed. The frequency of primary malignant lung tumors was 0.016, 0.175 and 0.328 and primary non-malignant lung tumors 0.016, 0.135 and 0.131 in the control, low and high aerosol exposed groups, respectively. There was no difference in tumor latency between the groups. Absorbed dose to the lung was calculated for each animal in the study. The average doses for all the animals exposed to the low and high dust aerosol concentrations were 0.87 Gy and 1.64 Gy respectively, resulting in an average risk of malignant lung tumors of about 0.20 tumors per animal per Gy in both groups. The frequency of primary lung tumors was also calculated as a function of dose increment for both exposed groups individually and combined. The data indicate that, in spite of the above result, lung tumor frequency was not directly proportional to dose. However, when malignant lung tumor frequency was calculated as a function of dose rate (as measured by the lung burden at the end of dust inhalation) a direct linear relationship was seen (p < 0.01) suggesting dose rate may be a more important determinant of lung cancer risk than dose. Conversely, non-malignant lung tumors were significantly correlated with low lung burdens (p = 0.01). We conclude that chronic inhalation of natural uranium ore dust alone in rats creates a risk of primary malignant and non-malignant lung tumor formation and that malignant tumor risk was not directly proportional to dose, but was directly proportional to dose rate.

Effect of 3 growth control substances on foreign body sarcomagenesis: IFN, IUdR, MGBG

The purpose was to observe the effect on sarcomagenesis of 3 substances reported to inhibit neoplastic growth--interferon alpha-2/alpha-1 hybrid (IFN), 5-iodo-2-deoxyuridine (IUdR) and methylglyoxal bis(guanylhydrazone) (MGBG). Inhibitory effect might help diminish the sarcoma risk of human implants. The substances were applied respectively to groups of 25mm cellulose filters which were implanted subcutaneously 1 per animal in randomly assigned respective groups of 50 female BALB/c mice. The implant sites were palpated weekly. On detection of a tumour the animal was sacrificed. The number of tumours arising and the accumulated weeks of exposure to the implants were recorded per group and compared to those of controls with untreated filters. Tumour incidence in the 2 IFN groups was 33/45 and 35/48 mice--160 per cent that of the controls, 22/48 (chi-square p < 0.05). In the IUdR group tumour incidence was 24/44 mice--194 per cent that of controls (p < 0.05), and in the MGBG group 15/43--122 per cent that of controls (p < 0.75). Although the substances inhibit tumour growth in man, they did not inhibit but increased film sarcomagenesis, not significant for MGBG. Observation of the effects of such substances with dual neoplastic activity may furnish clues to the control processes of neoplasia.

Postirradiation sarcomas in Sprague-Dawley rats

A series of radiation-induced neoplasms occurred in Sprague-Dawley rats 4-8 months after irradiation of a single hind leg with 60Co gamma rays. The rats were exposed to fractionated cumulative doses that ranged from 0 to 106 Gy. Osteosarcomas, malignant fibrous histiocytomas and fibrosarcomas developed in the radiation fields of a number of the rats in the higher-dose groups. Tumors did not develop throughout an 8-month observation period in rats that received doses of only 0 or 46 Gy. The most common postirradiation sarcomas in humans are osteosarcoma, malignant fibrous histiocytoma and fibrosarcoma. The Sprague-Dawley rat may serve as a good animal model in studying the development of sarcoma in humans after regional radiotherapy.

Effect of film size on production of foreign body sarcoma by perforated film implants

Sarcoma may arise on unabsorbable foreign bodies in rodents and more rarely in man. Perforations of the implant reduce its carcinogenicity so that nitrocellulose filters of pore size 0.45 micron have failed to induce tumour. We examined whether increase of surface area would restore carcinogenesis to film with such pore size. Nitrocellulose filters of 25 mm diameter and pore size 0.45 micron were implanted singly, in pairs and in trios subcutaneously in 3 respective groups of BALB/c mice (total 97) and observed for sarcomagenesis for 100 weeks. No tumour arose on the singles (surface area 0.98 mm2), while 7 arose on the paired (1.96 mm2) at a mean of 54 weeks and 16 on the trios (2.95 mm2) at a mean of 46 weeks (differences significant at p > 0.01). A sufficiency of surface area restores carcinogenicity to perforated foreign surfaces in mice. Surface area is dominant over film perforation size in film sarcomagenesis.

Consideration of tissue response in the application of the two-mutation model to radiation carcinogenesis

The Moolgavkar-Venzon-Knudson (MVK) two-mutation model of carcinogenesis is an analytical model that predicts the variation of cancer yield-rate with time, and with dose of a carcinogen. The model is biologically based, and assumes that a specific mutation in a stem-cell will increase its rate of proliferation compared with that of unmutated cells, so that a clone of pre-malignant cells develops; a second specific mutation in any one of these will make it malignant, and a cancer will start to grow. The model has been used in recent years to analyse a number of sets of epidemiological data on carcinogenesis. The purpose of this paper is to point to a problem in the use of this model for radiation-induced carcinogenesis, namely that ionizing radiation causes reproductive death of stem cells, which leads to regenerative division and hence a change in the number of stem-cells at risk. The possible effects of such changes on the predictions of the model are discussed. At low dose-rates of continuous or chronic irradiation and at low doses of acute irradiation, it is expected that pre-malignant cells will be killed along with the unmutated cells, and that the regenerative division of the surviving pre-malignant cells will restore the numbers of both stem cells and pre-malignant cells to what they would have been in the absence of cell killing; hence, no net effect of the tissue regeneration is expected. At high dose-rates, the initial delay in regenerative division and subsequent faster proliferation are expected to lead to an initial reduction in tumour yield-rate with time (compared with that predicted by the MVK model) followed by a faster increase. For acute irradiation, in the particular case of beta-particle irradiation of the skin, at high doses where there are practically no surviving cells in the irradiated area, repopulation by unirradiated cells from the margin is predicted to lead to a decrease in tumour yield-rate with dose. The predictions have been compared with published data on the induction of osteosarcoma in mouse by repeated injection of 89Sr, the induction of skin tumours in rat by acute and chronic irradiation with electrons, and the induction of skin tumours in mouse by acute irradiation with beta-particles. At low doses and dose-rates the basic MVK model fitted the data well. At higher doses and dose-rates the expected effects of tissue regeneration were observed qualitatively, although there were some discrepancies in detail; these are discussed.

Biological effects of 137CsCl injected in beagle dogs of different ages

The toxicity of 137Cs in the beagle dog was investigated at the Inhalation Toxicology Research Institute (ITRI) and Argonne National Laboratory (ANL) as part of programs to evaluate the biological effects of both radionuclides in atomic bomb fallout and internally deposited fission-product radionuclides. In the ITRI study, young adult dogs were exposed once by intravenous injection to a range of 137Cs concentrations; the results have recently been published (Nikula et al., Radiat. Res. 142, 347-361, 1995). The purpose of the present report is to summarize the ANL study and to compare the results of the two studies. At ANL, 63 dogs in three age groups (15 juveniles, 142-151 days old; 38 young adults, 388-427 days old; and 10 middle-aged dogs, 1387-2060 days old) were given 137Cs intravenously at levels (61-162 MBq/kg) near those expected to be lethal within 30 days after injection. There were 17 control dogs from the same colony. Twenty-three of the dogs injected with 137Cs, including all middle-aged dogs, died within 52 days after injection due to hematopoietic cell damage resulting in severe pancytopenia that led to fatal hemorrhage and/or septicemia. The other significant early effect was damage to the germinal epithelium of the seminiferous tubules of all male dogs. These early effects are the same as those reported for the dogs injected with 137Cs at ITRI. In addition, the design of the ANL study revealed an age- and gender-related differential radiosensitivity for early effects: The middle-aged dogs died significantly earlier due to complications of hematological dyscrasia compared to the juvenile and young adult dogs, and the middle-aged females died significantly earlier than the middle-aged males. The most significant non-neoplastic late effects in the 137Cs-injected dogs from ANL and ITRI were atrophy of the germinal epithelium of seminiferous tubules with azoospermia, and a significant dose-dependent decrease in survival. However, the survival of the ANL dogs was decreased more than that of the ITRI dogs at similar radiation doses from 137Cs. Numerous neoplasms occurred at many different sites in the dogs injected with 137Cs at ANL and ITRI. Two differences in the findings of the two studies were that (1) there was an increased risk for malignant thyroid neoplasms in the ANL male dogs injected with 137Cs, but not the ITRI dogs of either gender, and (2) there was an increased relative risk for benign neoplasms excluding mammary neoplasms in the ITRI dogs injected with 137Cs, but not the ANL dogs. In both groups, there were dose-related increased incidences of malignant neoplasms, malignant neoplasms excluding mammary neoplasms, all sarcomas considered as a group, all non-mammary carcinomas considered as a group and malignant liver neoplasms. In summary, the similarity of the findings between the two studies and the dose-response relationships for survival and for large groupings of neoplasms suggests that these results are consistent findings in 137Cs-injected dogs and might be dose-related late effects in humans exposed to sufficient amounts of internally deposited 137Cs.

Pulmonary carcinogenesis in the F344 and Wistar rat after inhalation of plutonium dioxide

Pulmonary carcinogenesis was compared in female F344 and Wistar rats after inhalation of high-fired 239PuO2. Plutonium particle aggregation, as determined by quantitative light and scanning electron microscopic autoradiography, was greater for the F344 strain than for the Wistar strain. The median survival times were similar in control and low-dose (0.8-1.0 Gy) groups of both strains, but were significantly decreased in the high-dose (34-37 Gy) groups of both strains. Squamous metaplasia was not found in control or low-dose groups of either strain, but was found in 62-65% of high-dose groups of both strains. Adenomatous metaplasia was considerably higher in control and low-dose groups of F344 rats than in Wistar rats. A total of 87 lung tumors were found in 140 exposed F344 rats and 46 lung tumors in 176 exposed Wistar rats. The incidence of lung tumors in F344 rats was 1.7% in controls, 20% in the low-dose group and 82% in the high-dose group. The incidence of lung tumors in Wistar rats was 0.1% in controls, nil in the low-dose group and 68% in the high-dose group. About half of all lung tumors in both strains were considered to be the primary cause of death. The median survival times of rats of both strains in the high-dose groups that died with lung tumors were greater compared with rats in these groups that died without lung tumors. In contrast, these differences did not occur among rats in the low-dose groups. The absolute risk was 1900 lung tumors per 10(4) Rat-Gy for F344 rats receiving low doses and nil for Wistar rats receiving low doses, but about 210 lung tumors per 10(4) Rat-Gy for high-dose groups of both strains. The adenomatous tumor phenotype predominated in the F344 strain, while the squamous tumor phenotype predominated in the Wistar strain. Risk of squamous tumors was similar for both strains. Overall, the F344 strain appears to be more "sensitive" than the Wistar strain to formation of lung tumors at low to moderate doses from inhaled 239PuO2 due mostly to an increased incidence of adenomatous phenotype tumors.

Tumorigenicity of EBNA2-transfected cells

The Epstein-Barr virus nuclear antigen 2 (EBNA2) gene is thought to be important for transformation by Epstein-Barr virus (EBV), but the mechanism of this transformation is little understood. Here, to examine the transforming ability of EBNA2, we transfected a rat fibroblast cell line F2408 with a recombinant EBNA2 expression plasmid and examined cell morphology, colony formation in soft agar, and tumorigenicity in nude mice. The morphology of transfected clones was similar to those of untransfected cells, but two of seven clones grew in soft agar, and four clones of seven clones reproducibly formed tumors in nude mice. These four clones showed EBNA2 expression, but non-tumorigenic clones did not. These results indicate that the expression of EBNA2 is correlated with tumorigenicity.

A minor tyrosine phosphorylation site located within the CAIN domain plays a critical role in regulating tissue-specific transformation by erbB kinase

Avian c-erbB encodes a protein that is homologous to the human epidermal growth factor receptor. Truncation of the amino-terminal, ligand-binding domain of this receptor results in an oncogene product which is a potent inducing agent for erythroleukemias but not fibrosarcomas in chickens. Here we show that mutation of a single tyrosine residue, p5, in the carboxyl terminus of the erbB oncogene product allows it to become sarcomagenic in vivo and to transform fibroblasts in vitro. Mutations of other autophosphorylation sites do not generate comparable effects. The increased transforming activity of the p5 mutant is accompanied by an elevated level of mitogen-activated protein kinase phosphorylation. By analogy to the human epidermal growth factor receptor, p5 is a minor autophosphorylation site and is located in a domain known to be involved in regulating calcium influx and receptor internalization (CAIN domain). This area of the erbB product has been found to be repeatedly deleted in various sarcomagenic avian erythroblastosis virus isolates. We precisely deleted the CAIN domain and also made point mutations of the acidic residues within the CAIN domain. In both cases, fibroblast-transforming potential is activated. We interpret these data to mean that p5 and its surrounding region negatively regulate fibroblast-transforming and sarcomagenic potential. To our knowledge, this represents the first point mutation of an autophosphorylation site that activates erbB oncogenicity.

Two distinct target cells for v-jun mediated wound tumorigenesis

Transgenic mice expressing v-jun under the control of the H-2K promoter develop dermal fibrosarcomas and rhabdomyosarcomas via a multistep process following wounding. To assess the relative roles that wounding and the H-2K promoter play in this process, we compared the phenotype of H-2K-v-jun mice with that of animals expressing v-jun under the control of the metallothionein I (MTI) promoter. MT-v-jun animals also develop wound-induced neoplasms by a multistage process. Both early and late features of tumorigenesis in MT-v-jun mice are different, however, from what is observed in H-2K-v-jun animals. First, the acute hyperplastic response that is characteristic of H-2K-v-jun granulation tissue is not observed in MT-v-jun wounds. Second, the myogenic components that are readily detected in the majority of late stage H-2K neoplasms are never observed in their MT counterparts. Moreover, analysis of wound tumours arising in animals expressing both MT-v-jun and H-2K-v-jun reveals that the two transgenes are not expressed in identical malignant cell populations. These results imply that mesenchymal granulation tissue is heterogeneous in composition and that the different cellular phenotypes of MT-v-jun and H-2K-v-jun malignancies result from oncogenic activation of wound-derived cells which differ in their differentiation potential. Thus, whereas the wounding component of multistage tumorigenesis is attributable to the action of v-jun, the transcriptional regulatory elements which drive its expression determine the nature of the target cells which give rise to wound-induced neoplasms.

SV40 T antigen directed by a powerful erythroid enhancer-promoter produced sarcomas and pancreatic tumors but not erythroid-specific tumors in transgenic mice

We have expressed the simian virus 40 (SV40) large T antigen oncogene in erythroid tissues of mice to test its ability to immortilize erythroid cells. A transgene construct was built in which the SV40 large T antigen structural gene was linked to erythroid-specific enhancer and promoter sequences. The enhancer employed was the human beta-globin family microlocus control region, and the promoter sequences were derived from the human beta-globin promoter. Transgenic mice were generated and they expressed T antigen in the bone marrow and spleen cells. Yet, no hematopoietic neoplasia arose in these mice. Instead, after a lag period of 2-6 months, the mice developed soft tissue sarcomas and pancreatic islet-cell tumors that expressed high levels of T antigen.

Subcutaneous sarcomas of probable neuronal origin in a transgenic mouse strain containing an albumin promoter-fused simian virus 40 large T antigen gene

Frequent development of subcutaneous neurogenic sarcomas was observed in a hepatocellular carcinoma-producing transgenic mouse strain harboring an albumin-promoted simian virus 40 (SV40) large T antigen gene. Found unexpectedly in 19 out of 306 mice (6.2%) by 6 months of age, all the sarcomas were similar and were characterized as neurogenic on the basis of histological features including Homer-Wright type rosette formation, the presence of dense core granules of 100-200 nm diameter under the electron microscope, expression of neuron specific enolase, S-100 protein, and catecholamines, and nerve cell-like differentiation in culture in response to But2cAMP. Immunohistochemical study revealed tiny clusters of SV40 T antigen-expressing cells with neurogenic character in normal-appearing adult mouse subcutis as candidate progenitors of the sarcomas. The tumor cells strongly expressed large T antigen but did not express albumin or albumin mRNA at the detection sensitivity used. Transient transfection assay (CAT assay), however, revealed the presence of transcriptional factor(s) acting on the albumin promoter in tumor cells. Thus, the present investigation suggested the presence of specifically differentiated neurogenic cells in the mouse subcutis with aberrant expression of the transgene.

Development of transforming function during transduction of proto-ras into Harvey sarcoma virus

Oncogenic retroviruses are generated by transduction of the coding region of a protooncogene and acquire genetic changes during subsequent replication. Critical genetic events which occurred during and after transduction of rat proto-ras-1Ha into Harvey sarcoma virus were identified by evaluating the transforming activity of plausible synthetic progenitor proviruses encompassing the complete proto-ras genomic region with or without various 5' deletions. All progenitor proviruses induced phenotypic transformation of mouse NIH 3T3 cells, although with a 5- to 10-fold lower frequency than Harvey sarcoma provirus. Although no tumor formation was observed in vivo after inoculation in the absence of helper murine retrovirus, both wild-type and progenitor viruses inoculated in the presence of helper virus induced tumors in newborn BALB/c mice. No critical alterations of the p21ras coding region and no deletion of 5' genomic elements were detected in a progenitor virus encompassing the complete proto-ras genomic region that had been isolated from tumors. However, one progenitor virus that included all proto-ras exons induced tumors with a decreased latency. This virus contained a mutation in codon 12 (glycine to valine), which had apparently been selected during tumorigenesis in vivo. During the genesis of Harvey sarcoma virus, critical steps conferring transforming function are therefore transduction of coding proto-ras exons and enhancement of their transforming function by specific amino acid changes in p21ras.

Susceptibility to ultraviolet-induced corneal sarcomas is highly heritable in a laboratory opossum model

The laboratory opossum, Monodelphis domestica, develops hyperplasia and neoplasia of the corneal stroma after repeated exposure to low doses of ultraviolet radiation (UVR) (non-erythemic in skin). We exposed adult animals from genetically diverse families within our colony to determine whether there are any heritable components to the risk of this form of eye cancer. From about 5 months of age, animals were exposed 3 times a week to a dose of about 125 J/m2 of UVB (spectral peak = 302 nm). Thirty-three sibships (151 individuals) completed at least 30 weeks of the protocol and 137 individuals completed 45 weeks. For genetic analysis, each animal was classified at 30 and 45 weeks as affected with corneal sarcoma or not. Heritabilities were estimated for the dichotomous eye-tumor trait which was highly heritable at both time points. This eye-cancer model system is valuable as a source of material for in vitro studies of angiogenesis and neoplastic transformation, for in vivo studies of tumor therapy and prevention, and for further research on the genetic determinants of cancer.

Induction of nasal and nasopharyngeal tumours in Sprague-Dawley rats fed with Chinese salted fish

Epidemiological studies have implied that Chinese salted fish is a human nasopharyngeal carcinogen. In the present study, 162 Sprague-Dawley rats were randomly assigned to one of four experimental groups. Rats in groups 1 (n = 41) and 3 (n = 40) were exposed to salted fish from birth through the breast feeding period by giving the maternal rats a diet containing 10% and 5% salted fish, respectively, later feeding the rats with pellets containing 10% and 5% of salted fish respectively. In group 2, the rats (n = 41) were given pellets containing 10% of salted fish from 6 weeks of age. Rats in group 4 (n = 40), serving as controls, were only given ordinary pellets. Three rats had nasopharyngeal tumours, 2 from group 1 had a poorly differentiated carcinoma and a squamous cell carcinoma. One rat from group 2 had a squamous cell carcinoma. Four rats had nasal tumours, one fibrosarcoma and one adenocarcinoma were found in rats from group 1. One rhabdomyosarcoma was found in group 2, and one soft tissue sarcoma was found in a rat in group 3. No nasal or nasopharyngeal tumours appeared in the control group. The difference in the occurrence of malignant nasal and nasopharyngeal tumours among the four experimental groups was statistically significant (one tailed p for trend = 0.041). The frequency of tumours appearing in other organs such as the breast, kidney, lung, liver and brain was not significantly different between the salted fish treated groups and the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone sarcoma characteristics and distribution in beagles fed strontium-90

A total of 66 primary bone sarcomas were diagnosed in 47 beagles; 43 of these dogs were part of the 403 beagles fed 90Sr and 4 were part of the 162 controls. Multiple primary bone sarcomas were found in 15 of the 47 beagles (32%). The incidence of multiple primary bone sarcoma was restricted to the two highest dose groups, except for a single control dog which developed two bone sarcomas. A threshold-like radiation dose response was observed; no sarcomas were observed in the lowest three dose groups, but the number of primary bone sarcomas increased rapidly in the higher dose groups. Of the 66 primary sarcomas, 49 were osteosarcomas (74%). As the dose increased, the proportion of osteosarcomas increased sharply, 4/10 (40%), 26/29 (90%), and 16/18 (89%), in the three highest dose groups. Thirteen of the bone sarcomas of other types occurred in males, and 4 in females, whereas 21 osteosarcomas occurred in males, and 28 in females. The ratio of bone sarcomas of the appendicular skeleton to those in the axial skeleton was 40:26, with osteosarcomas occurring more often in the appendicular than the axial skeleton (32:17), whereas nonosteogenic tumors showed no predilection (8:9). A statistical study of the distribution of bone sarcomas among 16 separate bone groups showed a correlation only with the distribution of cancellous bone volume-to-surface ratio and not with either skeletal mass distribution or dose distribution. The highest occurrence of sarcomas was in the humeri, femora, and mandible, and no occurrence in the coccygeal vertebrae, paws, or sternum. It is postulated that the distribution of bone sarcomas reflects a critical combination of the osteosarcoma precursor cell population, their cell division rate, and the radiation dose absorbed by these cells.

Tumour induction by transplacental infection with polyoma virus of the F1 generation of Wistar rats

Intravenous polyoma virus inoculation into pregnant Wistar rats resulted in transplacental infection of the foetus, causing tumours and hydronephroses. Cyclosporin A reduced these effects significantly.

Tumor necrosis factor alpha and interleukin 1 alpha induce anchorage independence in v-jun transgenic murine cells

The oncogene jun encodes a transcription factor of the AP-1 family. In mice carrying viral jun (v-jun) as a transgene, wounding is a prerequisite for tumorigenesis, suggesting collaboration between the transgene and a wound-related event. To define possible candidates for this collaborative process, we examined the effect of several wound-related polypeptide growth factors on cells from transgenic mice. Tumor necrosis factor alpha and interleukin 1 alpha induce anchorage independence in embryo fibroblasts and tumor cell revertants from these mice. This effect was specific for the two cytokines and was restricted to cells from v-jun transgenic mice. Anchorage independence required the continued presence of the cytokines. Transfection of transgenic cells with a v-jun expression plasmid also induced anchorage independence and a tumorigenic phenotype in transgenic tumor cell revertants. However, there was no correlation between anchorage independence, expression of Jun, and AP-1 activity. These results suggest that while increased transgene expression can enhance the growth properties of v-jun transgenic cells, there exist other cytokine-dependent mechanisms that have a similar effect. Retinoic acid, dexamethasone, or forskolin inhibits induction of anchorage independence by tumor necrosis factor alpha, interleukin 1 alpha, and transfected v-jun. Although these agents affect both AP-1 transactivation potential and DNA binding in the transgenic cells, the changes are not correlated with the inhibition of growth.

Spontaneous histiocytic sarcoma with possible origin from the bone marrow and lymph node in Donryu and F-344 rats

Ninety-five male and 96 female Donryu rats reared up to 120 wk of age and 244 male and 243 female F-344 rats used as untreated controls in 5 carcinogenicity studies were examined histopathologically to clarify the primary site of histiocytic sarcoma. Histiocytic sarcoma in Donryu rats was observed in 5 of 95 (5.3%) males and 4 of 96 (4.2%) females. In F-344 rats, 4 of 244 (1.6%) males and 3 of 243 (1.2%) females had the neoplasms. Histologically, sarcomas consisting of large pleomorphic histiocytic cells were seen in the bone marrow, liver, lymph node, spleen, and lung. Among 16 sarcomas observed, 15 had neoplastic lesions in the bone marrow, and 1 F-344 rat had the lesions only in the lymph nodes. Eleven (6 F-344 rats and 5 Donryu rats) of the 15 cases had the lesions in the liver, and 4 Donryu rats had no lesions in the liver but lesions in the lymph node and/or spleen, except for 1 case where the sarcoma occurred only in the bone marrow. Among the 11 cases with the lesions both in the liver and bone marrow, neoplastic lesions were found also in the lymph node, spleen, and/or lung, but the severity of neoplastic proliferation of these organs was not so marked as that in the bone marrow except for 2 cases. Although histiocytic sarcomas in rats are considered to originate from the liver, peritoneum, or subcutis, the present results strongly suggest that some histiocytic sarcomas in Donryu and F-344 rats may also originate from the bone marrow and lymph nodes.

[Incidence of the development of 90Sr-induced osteosarcomas depending on the age of the animals]

In experiments with albino male rats, a study was made of the influence of age on the incidence of osteosarcomas induced by 90Sr. It was shown that the incidence of tumors decreases exponentially with age.

Multipotent marrow stromal cell line is able to induce hematopoiesis in vivo

Several murine marrow stromal cells were established from murine bone marrow cultures. Stromal cell lines transfected with a tumor-inducing polyoma virus middle T antigen (MTAg) were inoculated into nude mice subcutaneously. KUSA-MTAg cells, one of these cell lines, led to the rapid local development of bone marrow consisting of trilineage hematopoietic cells and bone; other cell lines produced spindle cell sarcoma or hemangiosarcoma. These results suggested that a single stromal cell line, KUSA-MTAg cells, may induce hematopoietic stem cells or early progenitors of three lineages of hematopoietic cells in vivo. Interestingly, untransfected KUSA cells expressed three new mesenchymal phenotypes, osteocytes, adipocytes, and myotubes, after treatment with 5-azacytidine.

Chronic variable stress facilitates tumoral growth: reversal by imipramine administration

The present study was conducted to examine whether a chronic variable stress procedure (CVS)--an animal model of depression--facilitates tumor growth, and whether this effect can be modified by concurrent administration of the antidepressant imipramine (IMI). Unstressed rats, with or without previous administration of the immunosuppressive agent cyclosporine (CS), were inoculated with 5 x 10(6) cells of a sarcoma. Another group of rats was inoculated with tumoral cells and later exposed to the CVS procedure with or without concurrent administration of IMI (10 mg/kg, i.p.). An additional group of animals was treated with CS and later given daily injections of IMI (10 mg/kg, i.p.) without stress manipulation. A lack of tumoral development was observed in unstressed animals without previous injections of CS, whereas, prior injections of this immunosuppressive agent increased tumoral growth in unstressed animals. Exposure to the CVS procedure facilitated tumoral growth even in animals without CS injections. This effect was clearly attenuated when chronically stressed rats were concurrently given IMI. These findings support the notion that the development of a tumoral process is facilitated when a state of experimental depression is induced and that the reversal of such a state by antidepressant treatment results in the inhibition of tumor development.

In vitro differentiation of rhabdomyosarcomas induced by nickel or by Moloney murine sarcoma virus

In vitro cultures and clonal derivatives have been established from rat rhabdomyosarcomas induced by Moloney-Murine Sarcoma Virus (MSV) or by nickel sulfide; differentiation ability has been studied as expression of desmin, embryonic and adult myosin isoforms, alpha-actin isoforms and cellular fusion. The two rhabdomyosarcoma models showed different levels of myogenic differentiation. Multinucleated myotube-like structures were frequently observed in cultures derived from nickel-induced tumours. Desmin was present in 50-80% of cells and embryonic myosin in up to 10%. In MSV-tumour-derived cultures and in their metastases or clonal derivatives two cell types are present in different ratios: spindle-shaped cells, adherent to plastic surfaces, and rounded cells, loosely attached or floating free in the medium. These cultures showed features of myogenic differentiation (10-80% desmin-positive cells), but embryonic myosin expression and production of multinucleated myotube-like structures were very rare events. Cultures from autochthonous lymph node and lung metastatic cells showed similar patterns of differentiation. Retinoic acid increased differentiated features (myotube formation and embryonic myosin expression) only in nickel-induced rhabdomyosarcoma cells. The two models described here mimic the heterogeneity in differentiation pattern found among human rhabdomyosarcomas. Myogenic differentiation ability was retained at a good level by nickel-induced tumours, whereas it was strongly impaired in MSV-induced tumours.