title: The shape of the dose-response curve for radiation-induced neoplastic transformation in vitro: evidence for an adaptive response against neoplastic transformation at low doses of low-LET radiation.
abstract: A dose-response curve for gamma-radiation-induced neoplastic transformation of HeLa x skin fibroblast human hybrid cells over the dose range 0.1 cGy to 1 Gy is presented. In the experimental protocol used, the spontaneous (background) frequency of neoplastic transformation of sham-irradiated cultures was compared to that of cultures which had been irradiated with (137)Cs gamma radiation and either plated immediately or held for 24 h at 37 degrees C prior to plating, for assay for neoplastic transformation. The pooled data from a minimum of three repeat large-scale experiments at each dose demonstrated a reduced transformation frequency for the irradiated compared to the sham-irradiated cells for doses of 0.1, 0.5, 1, 5 and 10 cGy for the delayed-plating arm. The probability of this happening by chance is given by 1/2(n), where n is the number of observations (5); i.e., 1/32 congruent with 0.031. This is indicative of an adaptive response against spontaneous neoplastic transformation at least up to a dose of 10 cGy of gamma radiation. The high-dose data obtained at 30 and 50 cGy and 1 Gy showed a good fit to a linear extrapolation through the sham-irradiated, zero-dose control. The delayed-plating data at 10 cGy and below showed a statistically significant divergence from this linear extrapolation.
authors.affiliation: Department of Radiation Oncology and Division of Epidemiology, University of California Irvine, Irvine, CA 92697, USA. jlredpat@uci.edu.
authors.forename: J L
authors.initials: JL
authors.lastname: Redpath
authors.forename: D
authors.initials: D
authors.lastname: Liang
authors.forename: T H
authors.initials: TH
authors.lastname: Taylor
authors.forename: C
authors.initials: C
authors.lastname: Christie
authors.forename: E
authors.initials: E
authors.lastname: Elmore
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects*; D002471:Cell Transformation, Neoplastic / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006367:HeLa Cells; D006801:Humans; D006822:Hybrid Cells; D018499:Linear Energy Transfer