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.
Davies
H E
HE
Radiation Science Unit, Velindre Hospital NHS Trust, Cardiff, UK.
Court
J B
JB
Burn
C
C
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects*; D006224:Cricetinae; D003571:Cytochalasin B / Q000494:pharmacology*; D004247:DNA / Q000032:analysis; D006367:HeLa Cells; D006801:Humans; D011123:Polyploidy
D003571:Cytochalasin B; D004247:DNA