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Wavelengths effective in induction of malignant melanoma
R B Setlow1, E Grist, K Thompson
1Biology Department, Brookhaven National Laboratory, Upton, NY 11973.
Abstract:
It is generally agreed that sunlight exposure is one of the etiologic agents in malignant melanoma of fair-skinned individuals. However, the wavelengths responsible for tumorigenesis are not known, although DNA is assumed to be the target because individuals defective in the repair of UV damage to DNA are several thousandfold more prone to the disease than the average population. Heavily pigmented backcross hybrids of the genus Xiphophorus (platyfish and swordtails) are very sensitive to melanoma induction by single exposures to UV. We irradiated groups of five 6-day-old fish with narrow wavelength bands at 302, 313, 365, 405, and 436 nm and scored the irradiated animals for melanomas 4 months later. We used several exposures at each wavelength to obtain estimates of the sensitivity for melanoma induction as a function of exposure and wavelength. The action spectrum (sensitivity per incident photon as a function of wavelength) for melanoma induction shows appreciable sensitivity at 365, 405, and probably 436 nm, suggesting that wavelengths not absorbed directly in DNA are effective in induction. We interpret the results as indicating that light energy absorbed in melanin is effective in inducing melanomas in this animal model and that, in natural sunlight, 90-95% of melanoma induction may be attributed to wavelengths > 320 nm--the UV-A and visible spectral regions.
Insights
Sunlight exposure causes malignant melanoma. This study in Xiphophorus fish found that UV-A and visible light wavelengths, not directly absorbed by DNA, are effective in melanoma induction, likely through absorption by melanin.
Area of Science:
- Oncology
- Genetics
- Photobiology
Background:
- Sunlight exposure is a known cause of malignant melanoma in fair-skinned individuals.
- The specific wavelengths responsible for melanoma induction remain unclear, though DNA damage is suspected.
- Individuals with DNA repair deficiencies are at significantly higher risk for melanoma.
Purpose of the Study:
- To determine the action spectrum for melanoma induction by UV radiation.
- To investigate the role of different wavelengths in melanoma development.
- To identify the primary chromophores involved in UV-induced melanoma.
Main Methods:
- Irradiation of Xiphophorus fish (platyfish and swordtails) with narrow wavelength bands (302, 313, 365, 405, and 436 nm).
- Dose-response assessment at each wavelength to estimate sensitivity.
- Scoring of irradiated fish for melanoma development over a 4-month period.
Main Results:
- Melanoma induction showed sensitivity at 365, 405, and 436 nm, indicating wavelengths not directly absorbed by DNA are effective.
- The action spectrum suggests that light energy absorbed by melanin plays a significant role.
- UV-A and visible light (wavelengths > 320 nm) may account for 90-95% of melanoma induction in natural sunlight.
Conclusions:
- Melanin absorption of light energy is implicated in UV-induced melanoma.
- Wavelengths beyond the direct DNA absorption range are critical for melanoma development.
- UV-A and visible light are major contributors to melanoma induction by sunlight.