Correlation between the metastasizing activity ofin vitro spontaneously transformed hamster cells and their natural resistance-depressing activity

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Abstract
In our previous experiments in Syrian hamsters the in vivo semiquantitative method of determination of the natural resistance‐depressing (NRD) activity of tumor cells was described. It was demonstrated that inactivated cells of different tissue culture cell lines derived from in vivo tumors in contrast to normal, or in vitro spontaneously transformed hamster embryo (STHE) cells, bear the NRD factor. It was suggested that NRD activity of tumor cells might be essential for the development of primary tumors and metastases (Deichman et al., 1979). Therefore, in this study we compared the NRD activity and metastatic activity (MA) of the parelal STHE cells never passaged in vivo and STHE in vivo sublines, obtained from subcutaneous tumor nodules and from individual spontaneous lung metastases (LM) after s.c. transplantation of STHE cells. Five LM sublines of STHE strain (out of eight investigated) were NRD active as well as the cells of one of two s.c. tumor nodules. Study of MA, i.e. the relation between the number of cells inoculated retroorbitally in the bloodstream of hamsters and the number of experimental metastases developed in the lungs of inoculated animals, demonstrated that the highest MA was observed with the cells of LM sublines possessing the highest NRD activity. Parental STHE cells did not depress natural anti‐tumor resistance and their MA was the lowest. The data presented demonstrate the heterogeneity of the population of constantly cultured in vitro STHE cells in relation to their NRD activity and the selection of NRD active cells during the development of lung metastases.