Radiation sensitivity of primary fibroblasts from hereditary retinoblastoma family members and some apparently normal controls: Colony formation ability during continuous low-dose-rate gamma irradiation

We previously described an enhanced sensitivity for cell killing and G1-phase cell cycle arrest after acute γ irradiation in primary fibroblast strains derived from 14 hereditary-type retinoblastoma family members (both affected RB1^+/- probands and unaffected RB1^+/+ parents) as well as distinctive gene expression profiles in unirradiated cultures by microarray analyses. In the present study, we measured the colony formation ability of these cells after exposure to continuous low-dose-rate (0.5-8.4 cGy/h) ¹³⁷Cs γ radiation for a 2-week growth period. Fibroblasts from all RB family members (irrespective of RB1 genotype) and from 5 of 18 apparently normal Coriell cell bank controls were significantly more radiosensitive than the remaining apparently normal controls. The average dose rates required to reduce relative survival to 10% and 1% were ∼3.1 and 4.7 cGy/h for the Coriell control strains with normal radiosensitivity and ∼1.4 and 2.5 cGy/h for the radiosensitive RB family member and remaining apparently normal Coriell control strains. The finding that a significant proportion of fibroblast strains derived from apparently normal individuals are sensitive to chronic low-doserate irradiation indicates such individuals may harbor hypomorphic genetic variants in genomic maintenance and/or DNA repair genes that may likewise predispose them or their children to cancer.