In Vitro Sensitivity of Normal and Hereditary Retinoblastoma Fibroblasts to DNA-damaging Agents

Abstract

We investigated the ability of nine fibroblast cell strains from patients with the hereditary from of retinoblastoma (RB) to handle various types of DNA-damaging agents and compared the results with those obtained in nine normal strains. Cell strains were exposed to γ-radiation, which causes DNA scission; actinomycin D, a DNA-intercalating agent; and mitomycin C, a bifunctional alkylating agent leading to DNA-DNA crosslinking. Cell strains were studied for their ability to survive in a cytotoxicity assay. Nine normal strains exhibited a mean D₀ (inverse of the slope of the straight line portion of the survival curve) of 134–178 cGy after radiation exposure, compared to a range of 119–186 cGy in the nine RB strains (P = 0.33). Similarly, exposure to actinomycin D led to D₀ values of 0.024–0.069 µg/ml in the nine normal strains and D₀ values of 0.016–0.067 µg/ml in the RB strains (P = 0.64). The nine RB strains did exhibit a small overall increase in sensitivity after exposure to mitomycin C, with D₀ values ranging from 0.14–0.32 µg/ml versus 0.19–0.66 µg/ml in the nine normal strains (P = 0.002); however, when the two most resistant normal strains were excluded from analysis, results were similar. Three RB cell strains derived from individuals who had either developed second cancers or who had a family history of additional sarcomas consistently exhibited increases in sensitivity to all three DNA-damaging agents studied compared with other hereditary RB cell strains as well as normal strains. The results suggest that normal human fibroblast cell strains exhibit a wide response to DNA-damaging agents, especially chemical agents. Most hereditary RB strains exhibit sensitivity well within the normal range; however, strains from RB patients predisposed to second cancers exhibit increases in sensitivity to DNA-damaging agents. The heterogeneous ability to repair DNA damage may play a role in the development of second malignant neoplasms in hereditarily predisposed individuals.