DNA repair synthesis in fibroblast strains from patients with actinic keratosis, squamous cell carcinoma, basal cell carcinoma, or malignant melanoma after treatment with ultraviolet light, N-acetoxy-2-acetyl-aminofluorene, methyl methanesulfonate, and N-methyl-N-nitrosourea

Repair of UV dimers in skin DNA of patients with basal cell carcinoma

Epidemiologic studies suggest that exposure to sunlight is the primary etiologic agent for basal cell carcinoma. Formation of UV-induced DNA damage is believed to be a crucial event in the process leading to skin cancer. In this study, repair of photoproducts in DNA was followed in the skin of patients with basal cell carcinoma and control subjects. The subjects were exposed to 800 J/m(2) Commission Internationale de 1'Eclairag of solar-simulating radiation on buttock skin. Biopsies were taken at 0 hour, 24 hours, and 3 weeks after the exposure. Two cyclobutane pyrimidine dimers, TT=C and TT=T, were measured using a sensitive (32)P-postlabeling assay. Initial levels of both TT=C and TT=T differed between individuals in both groups. The levels of TT=T in patients with basal cell carcinoma and controls were similar (9.9 +/- 4.0 and 9.2 +/- 2.9 products per 10(6) normal nucleotides), whereas the level of TT=C was significantly lower in controls than in patients with basal cell carcinoma (6.2 +/- 3.1 versus 10.9 +/- 4.5 products per 10(6) normal nucleotides). The fractions of TT=T remaining after 24 hours and 3 weeks were significantly higher in patients with basal cell carcinoma (72% and 11%) compared with controls (48% and 5%). A slower removal in patients with basal cell carcinoma than in controls was indicated also for TT=C (52% versus 42% remaining at 24 hours); however, the difference between groups was not significant. When including data from our previously reported small-scale study, the fraction of dimers remaining at 24 hours was significantly higher in patients with basal cell carcinoma for both TT=C and TT=T. The data suggest that patients with basal cell carcinoma have a reduced capacity to repair UV-induced DNA lesions.

Topical treatment with liposomes containing T4 endonuclease V protects human skin in vivo from ultraviolet-induced upregulation of interleukin-10 and tumor necrosis factor-alpha

Exposing human skin to ultraviolet radiation causes DNA damage, sunburn, immune alterations, and eventually, skin cancer. We wished to determine whether liposomes containing a DNA repair enzyme could prevent any of the acute effects of irradiation when applied after ultraviolet exposure. Fifteen human patients with a prior history of skin cancer were exposed to two minimal erythema doses of ultraviolet radiation on their buttock skin. Liposomes containing T4 endonuclease V or heat-inactivated enzyme were applied immediately and at 2, 4, and 5 h after ultraviolet irradiation. Transmission electron microscopy after anti-T4 endonuclease V-staining and immunogold labeling on biopsies taken at 6 h after ultraviolet exposure revealed that the enzyme was present within cells in the skin. Immunohistochemical DNA damage studies suggested a trend toward improved DNA repair at the active T4 endonuclease V liposome-treated test sites. Although the active T4 endonuclease V liposomes did not significantly affect the ultraviolet-induced erythema response and microscopic sunburn cell formation, they nearly completely prevented ultraviolet-induced upregulation of interleukin-10 and tumor necrosis factor-alpha RNA message and of interleukin-10 protein. These studies demonstrate that liposomes can be used for topical intracellular delivery of small proteins to human skin and suggest that liposomes containing DNA repair enzymes may provide a new avenue for photoprotection against some forms of ultraviolet-induced skin damage.

Increased spontaneous formation of micronuclei in cultured fibroblasts of first-degree relatives of familial melanoma patients

The phenomenon of spontaneous increased micronuclei and enhanced UV-sensitivity, which is known for familial cutaneous malignant melanoma (CMM) patients, could be demonstrated again in fibroblasts of 17 familial CMM patients. In order to determine if close relatives of familial CMM patients show both a comparable spontaneous chromosomal instability and enhanced UV-sensitivity, cultured fibroblasts of 24 healthy, first-degree relatives of patients with familial malignant melanoma were investigated. The cytokinesis-block micronucleous technique was used to detect enhanced chromosomal instability. Fibroblasts of the investigated relatives showed a significantly increased spontaneous formation of micronuclei, in comparison to 19 healthy controls, but no enhanced UV-sensitivity was evident. We conclude that chromosomal instability might be a hereditary trait and a causative factor in developing familial malignant melanoma. This supports the concept of a genetic predisposition to familial CMM and may help to identify high-risk family members at a cytogenetic level in addition to the common clinicopathological traits.

Fibroblast subpopulations as accelerators of tumor progression: the role of migration stimulating factor

Tumor progression is a relatively indolent process, with many years commonly intervening between the inception of an initiating genetic lesion and the development of overt malignant disease. We suggest that the perturbation of normal epithelial-mesenchymal interactions caused by the inappropriate presence of fibroblast subpopulations displaying various 'fetal-like' phenotypic characteristics may significantly alter the kinetics of tumor progression and hence enhance susceptibility to cancer development. In this communication, we review our own data indicating the presence of fetal-like fibroblasts in cancer patients and put these observations in the context of similar published reports. We then discuss our interpretation of these findings, emphasising the possible direct involvement of fetal-like fibroblasts in cancer pathogenesis and putting forward an epigenetic 'clonal modulation' model to account for their presence in cancer patients.

The function of DNA polymerases in DNA repair synthesis of ultraviolet-irradiated human fibroblasts

Ultraviolet-induced DNA repair synthesis was measured in saponin-permeabilized normal human fibroblasts by the incorporation of [alpha-32P]dTMP into DNA. The involvement of DNA polymerases alpha, beta, delta, and epsilon in excision repair of pyrimidine dimers was examined using specific inhibitors. Dose-response curves resulting from experiments with up to 12 different inhibitor concentrations were analyzed by linear regression. Inhibitor concentrations at which repair activity was reduced to 50% were calculated. The following K50 values were found: aphidicolin, 0.2 microM; ddTTP, 12.5 microM; butylphenyl-dGTP, 7.6 microM; butylanilino-dATP, 6.0 microM. Comparison of K50 values with in vitro Ki values of DNA polymerases revealed that in permeabilized human fibroblasts reparative DNA synthesis is catalyzed by DNA polymerase delta and by DNA polymerase epsilon.

Biology of cutaneous squamous cell carcinoma

Nonmelanoma skin cancer is the leading cause of cancer in the United States. Cutaneous squamous cell carcinoma is second only to basal cell carcinoma in prevalence and its incidence is increasing. The biology of squamous cell carcinoma is reviewed under the broad areas of etiology, immunobiology, biochemistry, metastatic potential, and therapy, with emphasis on prevention, diagnosis, and management.

Biology of basal cell carcinoma (Part I)

Basal cell carcinoma is the most common malignancy in humans. Although rarely metastatic, it is capable of significant local destruction and disfigurement. This two-part article reviews the current understanding of basal cell carcinoma biology. Part I examines significant clinical, histologic, and ultrastructural features that relate to invasive potential. Genetic characteristics, including tumor growth rate, chromosomal abnormalities, and oncogene presence, are discussed, and expression of important cell and matrix proteins, including keratin, fibronectin, and HLA antigens, are reviewed. Further topics to be explored in Part II include host immunologic responses, theories of pathogenesis, and valuable second-line therapeutic regimens for treatment of multiple cancers.

Excision repair of pyrimidine dimers induced by simulated solar radiation in the skin of patients with basal cell carcinoma

One prominent lesion induced in DNA by ultraviolet (UV) radiation is the cyclobutyl pyrimidine dimer formed between adjacent pyrimidines on the same DNA strand. We investigated whether people who have developed basal cell carcinoma on sun-exposed skin have an altered ability to repair UV-induced pyrimidine dimers in DNA. Twenty-two patients with at least one basal cell carcinoma, aged 31-84 years, and 19 healthy volunteers, aged 25-61 years, took part in the study. Both groups were given one minimal erythema dose (MED) of simulated solar radiation on the lower back. DNA was extracted from the irradiated skin 0 to 6 h later, and the number of UV-induced pyrimidine dimers was determined using a dimer-specific endonuclease. At time 0, the average number of dimers per unit of DNA was similar in the two groups. After 6 h, an average of 22 +/- 4% of the dimers were removed in the group with basal cell carcinoma compared to 33 +/- 4% in the cancer-free group. In the basal cell carcinoma group, only 23% of the patients repaired more than 30% of the dimers after 6 h, compared with 53% of the cancer-free subjects (p less than 0.05). We conclude that patients who develop basal cell carcinoma on sun-exposed skin may have a decreased ability to repair pyrimidine dimers induced in skin exposed to simulated solar radiation.

Actinic DNA damage and the pathogenesis of cutaneous malignant melanoma

The near epidemic of melanoma and non-melanoma skin cancer in the United States and certain other industrialized nations is attributable to cutaneous exposure to sunlight more than to any other factor. Chronic exposure to UV irradiation and a high total cumulative dose may be less deleterious than are periodic bursts of large amounts of sun exposure leading to severe sunburn. Such an exposure pattern is characteristic of individuals such as office workers whose outdoor activities are irregular rather than daily, as with farmers or fisherman. Although UV irradiation is injurious to many cellular elements, the mechanisms underlying UV-mediated skin cancer are thought to be most likely related to DNA damage to cutaneous cells. Various types of UV-induced DNA damage have been identified, and they differ in biologic significance. Damage which is apt to be most cytotoxic is probably less effective as an inducer of skin cancer than is more subtle damage, which is tolerated but can initiate malignant transformation. Repair of DNA damage involves specific cellular activities which vary in their effectiveness in restoring cutaneous cell function to normal. Other biologic effects of UV irradiation may contribute to the development of skin cancer through effects on such defenses as pigmentation and the immune response. Sun-induced damage to DNA, however, is apparently necessary. Biologic consequences of dangerous environmental exposure to UV irradiation can be modulated by changes in life-style, the depth of the ozone layer, use of sunscreens, and possibly by hormones or their synthetic analogs.

Comparison of DNA-incising capacities in fibroblast strains from the Mannheim XP collection after treatment with N-acetoxy-2-acetylaminofluorene and UV light

The DNA-incising capacity was determined in 8 normal and 23 XP fibroblast strains of the Mannheim XP collection using the alkaline elution technique after treatment with both UV light and the "UV-like" carcinogen (Ac)2ONFln. Experimental conditions were chosen to allow for selective monitoring of repair-specific enzyme-catalyzed breaks. In order to compare DNA-incising capacities of the various cell strains after UV irradiation with those after treatment with (Ac)2ONFln, dose-response experiments including up to 8 dose levels were performed. The elution curves were analyzed by linear regression analysis. Elution velocities (in terms of DNA single-strand breaks per 10(6) nucleotides) were plotted against the square root of the doses. The slope of the resulting regression line yielded a characteristic term, designated EO, for the DNA-incising capacity of each cell strain. In contrast to normal fibroblasts, EO was found to be reduced in all XP cell strains belonging to the complementation groups A, C, D, E, F (or G) and I investigated, after treatment with both UV light or (Ac)2ONFln. Surprisingly, XP variant strains also exhibited lower EO values. A comparison of post-UV with post-(Ac)2ONFln DNA-incising capacities revealed that reduction in the EO values was very similar in all XP cell strains tested. These data suggest that the sensitivity of XP cells towards UV light or (Ac)2ONFln is due to the same enzymatic defect, namely impaired incision of DNA containing pyrimidine dimers or (Ac)2ONFln-DNA adducts.