Polycentric chromosomes induced by x-rays in giant cells of Chinese hamster in vitro

Computerized video time-lapse (CVTL) analysis of the fate of giant cells produced by X-irradiating EJ30 human bladder carcinoma cells

This study was designed to examine the viability and proliferation of uninucleated and multinucleated giant cells formed after 6 Gy X irradiation. The pedigrees of 102 individual EJ30 giant cells present 5 days after irradiation were analyzed from time-lapse movies captured over 6.3 days from 100 fields (100x). Pedigree analysis enabled us to study the proliferation of giant cells. The average starting size (area) of the giant cells (14500 +/- 9100 microm(2)) was approximately 25 times larger than the normal-sized cells observed after irradiation (560 +/- 200 microm(2)). From a total of 76 pedigrees of uninucleated giant cells, 42 had giant cells that either died or were arrested, while 34 divided at least once and produced progeny that divided again (five three times and three four times) before the progeny died or were arrested. Twenty-four pedigrees contained progeny that were lost from observation after dividing at least once. While most progeny continued to have giant cell morphology, two uninucleated giant cells ultimately produced progeny that contained two normal-sized cells. From a total of 26 multinucleated giant cells, only three divided. Two divided only once, but one produced progeny that divided two times. In all, 37 out of 102 giant cells divided at least once; eight of these divided four or five times with two of these pedigrees ultimately producing two normal-sized daughter cells. These results suggest that a small fraction of giant cells might be potentially clonogenic.

Prediction of the initial slope of the acute clonogenic survival curve by the post-irradiation behaviour of cytochalasin-induced polykaryons

We have investigated the behaviour of 11 lines of cultured cells in a survival assay whose endpoint is the ability of cells to become polyploid when incubated in the presence of cytochalasin B (CB). Single cells were induced by CB to form polykaryons after irradiation, and, by analogy with the colony-forming assay, the survival of polykaryon-forming units (PFUs) was defined as the fraction of cells able to achieve a given DNA content (at least 16C in most experiments). There was a radiation dose-dependent reduction in PFU survival, which, following the appearance of cells containing at least 16C DNA, was not markedly dependent upon the sampling time. In all cases, PFUs appeared to be more radioresistant than clonogens, especially at high dose. In 9/11 lines the PFU dose-response curves were exponential, while in two there was a pronounced curvature (quadratic parameter). There was a highly significant positive correlation between PFU response and the corresponding clonogenic initial slope. We suggest that in polykaryons the opportunity for the mechanical loss of DNA fragments may be reduced because the cells do not divide, and therefore that DNA damage resulting from chromosome aberrations may be less important in PFUs than in clonogens. Consequently, PFUs may express lesions not directly associated with mechanical gene loss. This assay may yield an alternative estimate for the clonogenic initial slope, and could be of use where colony-forming assays fail due to incomplete cell monodispersion.