Transformation of hamster embryo cells by 7-methyl benz(a)anthracene in vitro: tumorigenicity, chromosome pattern and spheroid formation

Perturbations in Osteogenic Cell Fate Following Exposure to Constituents Present in Tobacco: A Combinatorial Study

Tobacco smoke contains between 7000 and 10,000 constituents, and only an evanescently low number of which have been identified, let alone been evaluated for their toxicity. Recently, the Food and Drug Administration has published a list of 93 chemical tobacco constituents that are harmful or potentially harmful to a number of cellular processes. However, their effect on developing skeletal cells is unknown. In this study, we used ToxPI, a computational tool, to prioritize constituents on this list for screening in osteogenically differentiating human embryonic stem cells and fibroblasts. In selected endpoint assays, we evaluated the potential of these chemicals to inhibit osteogenic differentiation success as well as their cytotoxicity. Six of these chemicals, which were ascribed an embryotoxic potential in our screen, as well as nicotine, which was not found to be osteotoxic in vitro, were then evaluated in combinatorial exposures, either in pairs of two or three. No one single chemical could be pinpointed as the culprit of reduced calcification in response to tobacco exposure. Combining chemicals at their half-maximal inhibitory concentration of differentiation often elicited expected decreases in calcification over the individual exposures; however, cytotoxicity was improved in many of the dual combinations. A reverse response was also noted, in which calcification output improved in combinatorial exposures. Results from ternary combinations reflected those from double combinations. Thus, the results from this study suggest that it may be difficult to isolate single chemicals as the primary drivers of skeletal embryotoxicity and that the full combination of chemicals in tobacco smoke may produce the hypomineralization phenotype that we have so far observed in vitro in human embryonic stem cells as well as in vivo in zebrafish.

Growth in serum-free medium of NIH3T3 cells transformed by the EJ-H-ras oncogene: evidence for multiple autocrine growth factors

Rodent fibroblastic cells transformed by ras oncogenes can grow in serum-free (S-) medium. We have studied clonal lines of mouse NIH3T3 fibroblasts transfected with the EJ-H-ras oncogene, and observed that practically all become independent of exogenous growth and attachment factors shortly after transfection. Moreover, all the clones tested soon form anchorage-independent (AI) colonies in S- medium, and most give rise to spheroids able to grow in suspension. The cell-conditioned S- medium of the transformed (TR) cells stimulates autocrinally the AI and anchored growth of these cells, in the absence of serum, and it contains growth factors related to TGF-alpha (or EGF), PDGF and bFGF, and other uncharacterized factors. Some of these factors are not found, or are found only in very small amounts, in the S- medium of non-transformed NIH3T3 cells, which also stimulates the growth of the TR cells, in the absence of serum. In addition, the TR cells contain 4-6 times more cell-associated bFGF than the non-transformed cells and release more latent TGF-beta activatable by acid treatments. However, no active TGF-beta is secreted by either cell type. Activated TGF-beta and pure TGF-beta 1 stimulate the growth of the anchored TR and NIH3T3 cells, but inhibit the AI growth of the TR cells. Another inhibitor of this growth is also found in the concentrated medium of the NIH3T3 cells.

Chemically and virally transformed cells able to grow without anchorage in serum-free medium: evidence for an autocrine growth factor

BA10-IR transformed cells, obtained by treating Syrian hamster embryo fibroblasts (HEF) with 7-methylbenz(a)anthracene and cultivated for a long period, are highly tumorigenic and grow in suspension as aggregates (spheroids) (Levy et al., 1976). They also grow in attached form or as spheroids in serum-free (S-) synthetic medium, without insulin and transferrin, and form anchorage-independent (AI) colonies in this same, but semi-solid, medium. This exceptional phenotype was acquired stepwise, after other transformation parameters, and appears to be related to the capacity of the transformed cells to respond to a mitogenic growth factor which they secrete. The response to this autocrine factor is amplified by insulin and transferrin. Untransformed HEF, at late and early passages, and also mouse and rat embryo fibroblasts, secrete factors equally active on BA10-IR cells; but HEF do not respond, in S- medium, to their factor, or that of BA10-IR cells. Rat FR3T3 fibroblasts transformed by Kirsten murine sarcoma virus (FR3T3-Ki cells) also form AI colonies in semi-solid S- medium, secrete an autocrine factor potentiated by insulin and transferrin, and respond to the factors active on BA10-IR cells. However, they form far fewer colonies without additives, and respond as well to the mitogenic factors only in the presence of insulin and transferrin. BA10-IR cells and FR3T3-Ki cells also release beta-TGF, or a related factor, in an active and a latent form, activable by acidification, and HEF latent, activable beta-TGF. However, the factors shed by BA10-IR cells or HEF which stimulate AI growth of BA10-IR and FR3T3-Ki cells are proteins which seem unrelated to known transforming growth factors. Two major cellular alterations characteristic of the transformed phenotype in vitro are the ability to grow in the absence of anchorage, in semi-solid medium, and reduced dependence on serum growth factors (Hanafusa, 1977; Tooze, 1980). These alterations are often expressed together, and anchorage independence also appears to be the in vitro transformation parameter which correlates best with the tumorigenicity of the transformed cells (Pollack et al., 1975; Shin et al., 1975; Cifone and Fidler, 1980). However, this correlation is not constant (cf., Tooze, 1980). The cellular changes which confer anchorage independence remain unknown, but the culture conditions which allow anchorage-independent (AI) growth are better known. This growth occurs in the same media which permit the growth of attached cells, but generally requires serum.(ABSTRACT TRUNCATED AT 400 WORDS)

Genotoxicity of flavoring agents

The genotoxicity of 9 flavoring agents widely used in everyday foods was studied by a bacterial mutation test in the Salmonella/microsome system and by a chromosome test in Chinese hamster (CH) cells. In the mutation test none of the flavorings exhibited significant induction of his+ revertants in Salmonella typhimurium TA98 or TA100, either with or without rat-liver microsome as the metabolic activation system. On the other hand, in the chromosome test most of the agents induced severe chromosome aberration in the treated CH cells, suggesting a potential genotoxicity.