Relationship Between Chromosome Ploidy and Radiosensitivity in Selected Tumor Sublines of Common Origin2

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Abstract
A predominantly hypertetraploid subline, ELT/stock was derived from a predominantly hyperdiploid Ehrlich ascites tumor, ELD, after homotransplantation of sublethally X-irradiated cells. The ploidy shift was probably the result of immunoselection based on the differential resistance of the polyploid cells against the homograft reaction. Two additional sublines, a pure hypertetraploid, ELT/clone, and a predominantly hyperdiploid population, ELTD, were subsequently selected from ELT/stock. The former was obtained by isolating a hypertetraploid clone (s), and the latter by carrying ELT/stock in serial passage in the absence of immunoselection, in which case hyperdiploid cells regain dominance. The ELTD subline was cytologically indistinguishable from the main ELD line. After irradiation in vitro with different X-ray doses, all sublines were grown intraperitoneally within Millipore diffusion chambers with an average pore size of 0.45 µ, thus isolated from direct contact with host cells. The size of cell population was determined quantitatively at various intervals after inoculation. The growth behavior of all untreated sublines was closely similar. There was a difference in their radiosensitivity, however. After the same dose of X rays, the hypertetraploid sublines started to grow earlier and/or reached a larger population size than the hyperdiploid lines.