Experimental elimination and recovery of double minute chromosomes in malignant cell populations

摘要

The influence of the environment on the frequency of cells with double minute chromosomes (dms) was studied in the SEWA mouse ascites tumor. Under normal in vivo conditions, this tumor contained about 90%., cells with one or more dms. Explantation in vitro resulted in a decrease of the dms carrying cells, which after 100 days only amounted to 5% of the population. Following reimplantation in vivo. the original proportion of these cells was restored after an interval of 170 days. A mathematical model is presented describing these changes as selective phenomena.In the stock tumor almost all minute chromosomes were C-band negative. In the experimental populations. both in vivo and in vitro, another type of minute chromosomes appeared which were C-band positive. Also by other morphologic and functional criteria they were shown to be small chromosomes and not dms. In the present paper they have been referred to as microchromosomes.The fact that dms have been found only in malignant cells, and the correlation established in the present experiments between presence of dms and in vivo environment, led to speculations concerning their function. One possibility is that they involve amplification of genic material of significance to tumor development.