The oncogenic potential of three different 7,12-dimethylbenz(a)anthracene transformed C3H/10T1/2 cell clones at various passages and the importance of the mode of immunosuppression

Anti-tumor surveillance of non-contact-inhibited transformed cell lines

In order to determine if the correlated expression of transformation and tumorigenicity is affected by the agents used to induce transformants or by the immune status of the host used to test the tumorigenicity of transformants, we derived a series of cloned cell lines from foci of transformed cells induced by treatment of the contact-inhibited mouse cell line B/C-N7.ICI with the DNA demethylating agent 5-azacytidine (5-AZC) or the DNA demethylating and mutating agent benzo(a)pyrene dihydrodiol epoxide (BPDE). The transformed cell lines were injected into syngeneic nude and normal mice to determine their tumorigenicity. The results of this analysis showed that 93% of the transformants induced by 5-AZC treatment grew as tumors when injected into nude mice. Of those lines capable of growing as tumors in nude mice, 86% were also tumorigenic when injected into normal mice. In contrast, only 64% of BPDE-induced transformants grew as tumors in nude mice, and of those, only 44% were also tumorigenic in normal mice. The existence of non-contact-inhibited transformants that are tumorigenic only in nude mice indicates that host anti-tumor immune surveillance mechanisms are operative in normal mice. Further, the difference in both the percentage of transformed cell lines that are tumorigenic and the percentage of tumorigenic transformants that are susceptible to immune surveillance when transformants are induced by BPDE as compared to 5-AZC indicates that the transforming agent can affect both the correlation between the expression of transformation and tumorigenicity, and the interaction between the immune system and tumorigenic transformants.

A new in vitro assay for cell motility and proliferation

We have described and characterized a new micropore membrane assay for migration and proliferation of cells of various tumourigenic potential. The assay was developed to facilitate analysis of some aspects of cancer invasion and metastasis. Tumorigenic and non-tumorigenic C3H/10 T 1/2 cells grow in and migrate out of a culture chamber during a 1-11 day period, the shorter periods are used for chambers with 6 micron thick polycarbonate membranes, the longer ones for 140 micron thick cellulose nitrate membranes. Cell growth within the chambers, in their micropore membranes and on the outside of the membranes, was assessed with microscopy, electronic cell counting, flow cytometry of propidium iodide (PI) stained cells, and 3H-thymidine [( 3H]TdR) incorporation. A complete retrieval of intact cells that have traversed the membraneous chamber wall is possible, and these cells can be recultured or used in other studies. The tumorigenic cells had a steeper growth curve in vitro than the non transformed cells, but the relative sizes of the emigrated subpopulations were not significantly different. The subpopulation of tumorigenic cells that emigrated spontaneously from the chambers was less able than the subpopulation retained to populate secondary chamber cultures, suggesting that the clonogenic (stem) tumour cells are 'slow movers'.

The genetic toxicology of Kathon biocide, a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one

Kathon biocide, an aqueous solution containing a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in an approximate ratio of 3:1, was tested for mutagenic activity in Salmonella typhimurium, L5178Y mouse lymphoma cells in culture and Drosophila melanogaster. Tests also were conducted for chromosome aberrations in vivo on mouse bone marrow cells, for DNA damage/repair in primary rat hepatocytes in culture, and for morphological transformation in C3H 10T1/2 cells in culture. Kathon biocide produced point mutations in the absence of a rat-liver metabolizing system in bacteria (strain TA 100) and mammalian cells in culture. In the presence of rat-liver metabolizing system a 10-fold higher concentration was required to induce point mutations in mammalian cells in culture. No mutagenic activity was observed with the metabolizing system and S. typhimurium. Negative results were obtained in the sex-linked recessive lethal assay in Drosophila, the in vivo cytogenetic assay in mice, the unscheduled DNA synthesis assay in cultured rat hepatocytes, and the in vitro cell transformation assay.

In vitro transformation assays for chemical carcinogens

A variety of in vitro mammalian cell assays, designed specifically for the identification of carcinogenic compounds, have been in operation for more than a decade. Although no individual transformation system has won universal acceptance during this time, recent advances have led to the improved reliability and sensitivity of a number of these short-term tests. The underlying problems associated with the most widely used assays are identified and new developments in this rapidly expanding field are noted and discussed.

Relationship between fibrin clot retraction and tumorigenesis in C3H/10T1/2 cells

Fibrin clot retraction (FCR) was studied in C3H/10T1/2 murine fibroblasts. These cells were able to induce FCR with high efficiency during resting phase as well as during active growth. C3H/10/T1/2 cells which became tumorigenic after X-irradiation lacked FCR activity. Non-tumorigenic revertant clones regained the capacity to induce FCR, while revertants which progressively back-reverted to the neoplastic state showed intermediate FCR activity. These unstable revertants, when again fully tumorigenic, completely lost FCR activity.

Uptake of hematoporphyrin derivative and sensitized photoinactivation of C3H cells with different oncogenic potential

Four types of mouse embryo fibroblast cells of different oncogenic potential were investigated with respect to uptake of the tumor localizing agent hematoporphyrin derivative (Hpd) and sensitized photoinactivation. Cell size and cellular content of Hpd were measured simultaneously for single cells by means of flow cytofluorimetry. The more malignant cell types had a slightly higher porphyrin uptake per unit cellular volume than the untransformed type, while the photosensitivity of cells incubated with Hpd was equal for all the cell types. Since Hpd seems to concentrate in membranes, this may be related to the fact that the membrane areas of malignant cells are relatively larger than that of untransformed cells, due to the presence of more microvilli. The present study indicates that the preferential localization of Hpd in tumors, as well as the high efficiency of phototherapy reported in the literature, are due to extracellular differences between the tumors and normal tissue.

Photodynamic effects of haematoporphyrin derivative on synchronized and asynchronous cells of different origin

Phototherapy in the presence of haematoporphyrin derivative has been shown to have a preferential effect on malignant tumours when compared to normal tissue. This communication presents a comparison of the sensitivity to photochemotherapy in vitro of different cell lines. Asynchronous populations of cells were exposed to light in the presence of haematoporphyrin derivative, and found to be inactivated with a comparable efficiency. The lines were of human, Chinese-hamster or mouse origin and had different abilities to form tumours after heterotransplantation into nude mice or transplantation into syngeneic, immunosuppressed mice. Synchronized cells from 4 of the lines showed a similar variation in sensitivity to light throughout the cell cycle. Cells near the middle of interphase showed the highest sensitivity, whilst cells in early G1 were found to be least sensitive towards treatment with haematoporphyrin derivative and light.