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(PP365) Hypersensitivity of cultured fibroblasts from retinoblastoma family members and apparently normal controls: colony formation during continuous low-dose rate irradiation and G2 chromosomal radiosensitivity.
Wilson, Paul*,1, Nagasawa, Hatsumi1, Warner, Christy1, Little, John2, Bedford, Joel1, 1 Environmental and Radiological Health Sciences, Fort Collins, CO, United States2 Center for Radiation Sciences and Environmental Health, Boston, MA, United States
ABSTRACT- The capacity of cells to form colonies during continuous low dose-rate (LDR) irradiation was examined for 14 fibroblast strains derived from radiosensitive bilateral retinoblastoma (Rb) family members and 15 apparently normal NIGMS cell bank controls. Cs-137 gamma rays were delivered continuously during the growth period at nine different dose-rates ranging from 0.5 to 8.4 cGy/h. The majority of fibroblasts obtained from the NIGMS cell bank from apparently normal individuals will grow with only a modest reduction (to 10%) in the proportion of cells capable of forming colonies during continuous irradiation at dose rates up to 3 cGy/h. This proportion decreases more markedly from 3 cGy/h to 6 cGy/h, where survival is further reduced to 0.1% (here termed the proliferation-limiting LDR). Fibroblasts derived from both affected Rb1+/- probands and the unaffected Rb1+/+ parents of probands in the Rb families, however, demonstrate a 90% reduction in colony formation ability by 1-2 cGy/h and more severely compromised colony formation ability (to 0.1%) by 3-3.5 cGy/h. A subset (33%) of apparently normal NIGMS cell bank fibroblast strains show a similarly high degree of hyper-radiosensitivity in this assay. The genetic basis of hyper-radiosensitivity of this group or the Rb family members (whose sensitivities do not seem attributable to Rb1 status) is not known. This assay is currently being applied as a genetic screen using a viral cDNA correction/complementation strategy, to potentially identify and further characterize genetic factors underlying LDR radiation sensitivity in these fibroblast strains. These hyper-radiosensitive groups also display 2-3-fold higher levels of G2 chromatid breaks following 50 and 100 cGy of acute Cs-137 gamma irradiation compared to normal fibroblast strains. Some unaffected parents of the Rb families also display high levels of tetraploidy and endoreduplication, indicating potential G2/M and S-phase checkpoint defects. Deficiencies in genes or pathways underlying these phenomena may help to explain the hyper-radiosensitivity demonstrated in these cells, but may also provide insight into why the large majority (75-90%) of bilateral Rb cases do not involve previous family history of the disease. This work was supported by grant DE-FG03-01ER63235 from the U.S. Department of Energy.
Key words: LDR, continuous irradiation, retinoblastoma, G2 assay
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