Cloudman S91 mouse melanoma cells vary in constitutive and inducible melanin levels. Survival, mutation induction and DNA damage were quantitated after exposure to UVB, UVA and FS20 lamps. Assuming that the observed differences are related to melanin, induced pigment is photo-protective for survival and mutation after UVB and FS20 exposure, and is photosensitizing for survival after UVA exposure. No changes in pyrimidine dimers could be measured. DNA damage in pigmented mouse melanocytes (melan-a and melan-b) was greater than that in albino melanocytes (melan-c) after UVB and FS20, and the pigmented cells were more sensitive to killing. Pigment appears to be protective for killing by UVA in these melanocytes. Human melanocytes from different skin types vary in both melanin amount and composition (eu- and pheomelanin). Effects of pigmentation on UVB responses are unclear. In UVA, heavily pigmented cells have more DNA damage than lightly pigmented cells, but are resistant to killing. Increased pheomelanin photosensitizes DNA damage in lightly pigmented cells. Since eumelanin predominates in the mouse melanoma cells and melanocytes, they are less likely than human cells to provide a satisfactory model for human solar melanomagenesis. In order to understand the mechanism of photocarcinogenesis of melanoma, melanins in human melanocytes from different pigment types should be carefully quantitated and characterized. Mutations induced in them by solar wavelength-emitting lamps with well-characterized spectra should be measured, and mutant DNA should be sequenced to determine the nature of the solar-induced lesions. Research should focus on UVA and pheomelanin.
The results of three Phase III studies of DTIC in 580 patients with metastatic melanoma were reviewed to evaluate the subsequent course of 26 patients who achieved a complete response (CR) to chemotherapy. The majority (17 of 26) of these patients had soft tissue metastases. Six of the 26 patients remained in CR at last report (30–259 weeks), two died of other causes while remaining free of melanoma, and 18 relapsed and died. Ninety‐five percent of the 26 patients were alive at 1 year, and survival was 31.1% at 72 months. Seven of the eight patients with sustained remission received chemotherapy for at least 6 months after CR developed, whereas 10 of 18 relapsing patients were treated for less than 6 months after CR was achieved. Long‐term sustained CR to chemotherapy occurs in 1% to 2% of patients treated with DTIC, and late relapse is rare in patients who remain in CR for 2 years. Cancer 53:1299‐1305, 1984.
A prospectively randomized study of postoperative chemotherapy with dimethyl triazeno imidazole carboxamide (DTIC) was conducted by the Central Oncology Group from 1972 until 1976. Of 174 patients operated upon for melanoma and entered into the study, 87 were randomly selected to receive DTIC, four courses in 12 months, at 4.5 mg/kg/d x 10. One-hundred-sixty-five (95%) of the cases were evaluable, including 40 high risk Stage I, 96 Stage XI, and 29 Stage 111 cases. At a median follow-up period of 2.5 years, the control group had a better median disease-free interval (40 weeks vs. 73 weeks), median survival time (103 weeks vs. 133 weeks), and percentage of patients living free of disease (28% vs. 44%) than the DTIC-treated group. While disease-free interval appeared to be improved in the 25% of patients on DTIC therapy who developed thrombocytopenia, the overall effect of postoperative DTIC therapy was apparently not beneficial (P < 0.05). Cancer 47:2556-2562, 1981. ELANOMA is a relatively uncommon tumor, ac-M counting for approximately 1.4% of the annual mortality from cancer in the United States. An estimated 9600 new cases and 4000 deaths occurred from melanoma in the United States in 1978.' In spite of the low frequency of this tumor, melanoma has evoked interest amongst oncologists because of its many unusual or unique aspects. These features include geographic and racial variations in incidence, family clusters, immunologic aspects, questions of viral presence , radiation resistance, unusually long free intervals followed by rapid progression in some patients, hormonal aspects, and reports of spontaneous remissions.2
Synthetic eumelanin prepared by autooxidation of D,L-DOPA causes DNA strand breaks, as determined by alkaline elution after cell lysis with detergent and proteolysis, in B16CL4 mouse melanoma cells. The melanin is toxic to the cells in the range of doses that causes strand breaks. When the melanin was incubated with the cells at 37 degrees C in tissue culture medium, it was maximally effective after 15 to 20 min at causing strand breaks in the DNA. The extent of damage is concentration dependent, but the effect plateaus at 1 mg/ml. The nature of the interaction of the cellular DNA with melanin is consistent with strand breaks, not DNA-DNA crosslinks. The strand break damage is repaired, even in the continued presence of melanin, but repair is more rapid if the cells are washed and the melanin is removed. The form of the melanin is important for obtaining the effect. Sonication for 3 min abrogates the effect to a considerable extent, and repeated cycles of sonication can completely destroy the activity. Lost activity returns slowly with storage at 4 degrees C. Melanin is more effective at damaging DNA in a protein-free medium. It is also DNA-damaging at 4 degrees C, but less so than at 37 degrees C. Preliminary studies indicate that the strand breaks caused by melanin are additive with those caused by ionizing radiation. The extent of DNA strand breaks and alkali-labile sites caused by several other melanins was also determined. Some melanins did not cause frank strand breaks, but were active in causing alkali-labile sites.(ABSTRACT TRUNCATED AT 250 WORDS)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.