TOXICITY, DNA DAMAGE AND INHIBITION OF DNA REPAIR SYNTHESIS IN HUMAN MELANOMA CELLS BY CONCENTRATED SUNLIGHT

A 1 m diameter water lens was used to focus solar radiation, giving an 8-fold concentration of the total spectrum and a cytocidal flux similar to that of laboratory UV sources. Survival curves for human melanoma cells were similar for sunlight and 254 nm UV, in that D _q, was usually larger than D _o. An xeroderma pigmentosum lymphoblastoid line was equally sensitive to both agents and human cell lines sensitive to ionizing radiation (lymphoblastoid lines), crosslinking agents or monofunctional alkylating agents (melanoma lines) had the same 254 nm UV and solar survival responses as appropriate control lines. Two melanoma sublines derived separately by 16 cycles of treatment with sunlight or 254 nm UV were crossresistant to both agents. In one melanoma cell line used for further studies, DNA strand breaks and DNA-protein crosslinking were induced in melanoma cells by sunlight but pyrimidine dimers (paper chromatography) and DNA interstrand crosslinking (alkaline elution) could not be detected. The solar fiuence response of DNA repair synthesis was much less than that from equitoxic 254 nm UV, reaching a maximum near the D _o value and then declining; semiconservative DNA synthesis on the other hand remained high. These effects were not due to changes in thymidine pool sizes. Solar exposure did not have a major effect on 254 nm UV-induced repair synthesis.