Cellular radiosensitivity of primary and metastatic human uveal melanoma cell lines

PURPOSE. To investigate the radiosensitivity of uveal melanoma cell lines by a clonogenic survival assay, to improve the efficiency of the radiation regimen. METHODS. Four primary and four metastatic human uveal melanoma cell lines were cultured in the presence of conditioned medium. After single-dose irradiation (0 - 12 Gy), colonies were allowed to form for 6 to 14 days. Two cutaneous melanomas cell lines were also tested for comparison. The survival curves were analyzed by the linear quadratic (LQ) model, and the surviving fraction at a dose of 2 Gy (SF2), the SF at 10 Gy (SF10), the ratio of initial irreparably damaged DNA (alpha-coefficient) to the capacity to repair sublet ally damaged DNA (beta-coefficient), and the plating efficiency were calculated. RESULTS. The melanomas displayed a wide range of initial irreparable DNA damage (alpha-component), as well as a capacity for repair of sublethal DNA damage (beta-component), which ultimately resulted in a wide range of alpha/beta ratios. These findings were similar in both primary and metastatic melanomas and were comparable with data obtained from two cutaneous melanomas. CONCLUSIONS. Cell lines obtained from primary and metastatic human uveal melanomas displayed a wide range of radiosensitivity, similar to that published for cutaneous melanomas. Translating these data to the clinical setting indicates that a fractionated dose of 8 to 10 Gy administered in three to four fractions, as currently delivered in many centers, should be sufficient to eradicate tumors of approximately 1 cm(3).