Wavelengths effective in induction of malignant melanoma.

Abstract

It is generally agreed that sunlight exposure is one of the etiologic agents in malignant melanoma of fairskinned 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.The incidence of malignant melanoma has been increasing for several years at a rate of -5% per year among fair-skinned individuals in North America and Europe, probably due to changes in lifestyle. The disease has a complex etiology. Although sunlight exposure is implicated, melanoma is not associated with chronic exposure nor is it located primarily on highly exposed areas of the body (1, 2). Because individuals with the DNA repair-deficient disease xeroderma pigmentosum are several thousandfold more susceptible than unaffected individuals (3), sunlight damages to DNA are thought to be initiating carcinogenic events. However, the wavelengths effective in melanoma induction are not known. The wavelengths in sunlight between 280 and 320 nm (UV-B) are more strongly absorbed by DNA than are the longer UV-A wavelengths. On the other hand, the melanin in melanocytes absorbs UV at all wavelengths and energy absorbed by this pigment might affect DNA by energy or free-radical transfer to DNA (4). Useful animal models for determining melanoma induction as a function of wavelength-the action spectrumare the hybrid offspring from intra-and interspecific crosses between pigmented and nonpigmented fishes of the genus Xiphophorus (5

An estimation of biological hazards due to solar radiation

“…If further data become available on an action spectrum for melanoma in humans, the method employed in this paper for evaluating personal biologically effective exposures can be utilised to determine the nature of the hazard for the induction of skin cancers. Figure 1 - (1) The fish melanoma action spectrum [4] and (2) the human erythema action spectrum [1]. Figure 2 -(a) The evaluated spectra for the (1) shoulder and (2) chest of subject 2 and (b) the spectral UVBE for the (1) shoulder and (2) chest for the fish melanoma action spectrum and for the (3) shoulder and (4) chest for human erythema.…”

“…This time period was long enough to produce a measurable change in the optical absorbance of the dosimeter materials. From the measured changes in absorbance, the UV spectrum incident on each of the sites for each of the subjects was evaluated and the biologically effective irradiance was calculated employing the erythema action spectrum and the action spectrum for melanoma in Xiphophorus fish [4]. In the literature, the erythema action spectrum is normalized to unity at 297 nm and the fish melanoma is normalized to unity at 302 nm.…”

“…In this Figure, the fish melanoma has been linearly interpolated between the measurement wavelength points of 302, 313, 365 and 405 nm employed by Setlow et al [4]. The fish melanoma action spectrum is approximately up to 5 times greater in the UVB waveband compared to the UVA waveband.…”

“…The incidence of melanoma may be linked to the exposure of solar UV [2]. There have been studies [3,4] on the relation of UV exposure and the induction of melanoma and the results suggest that the melanin in the melanocytes absorbs UV at all wavelengths. No action spectrum for induction of melanoma in humans is available.…”

“…No action spectrum for induction of melanoma in humans is available. Recently Setlow et al [4] derived an action spectrum for melanoma using a hybrid fish. The fish melanoma action spectrum has a relative effectiveness up to 800 times higher than that for erythema in the UVA waveband.…”