John H. Epstein

Ultraviolet and ionizing radiation enhance the growth of BCCs and trichoblastomas in patched heterozygous knockout mice

Basal cell carcinomas, the commonest human skin cancers, consistently have abnormalities of the hedgehog signaling pathway and often have PTCH gene mutations. We report here that Ptch+/– mice develop primordial follicular neoplasms resembling human trichoblastomas, and that exposure to ultraviolet radiation or ionizing radiation results in an increase in the number and size of these tumors and a shift in their histologic features so that they more closely resemble human basal cell carcinoma. The mouse basal cell carcinomas and trichoblastoma-like tumors resemble human basal cell carcinomas in their loss of normal hemidesmosomal components, presence of p53 mutations, frequent loss of the normal remaining Ptch allele, and activation of hedgehog target gene transcription. The Ptch mutant mice provide the first mouse model, to our knowledge, of ultraviolet and ionizing radiation-induced basal cell carcinoma-like tumors, and also demonstrate that Ptch inactivation and hedgehog target gene activation are essential for basal cell carcinoma tumorigenesis.

Photocarcinogenesis, skin cancer, and aging

Nonmelanoma skin cancers, like most malignancies, increase in incidence with increasing age. However, in general they are not due to the aging process but are primarily due to solar radiation. Clinically, squamous cell carcinomas and basal cell epitheliomas are the most common cancers that occur in the Caucasian population in the United States. The role of radiation from the sun was suggested by a number of astute clinical observations reported around 1900 and subsequently has been established by epidemiologic and experimental studies. Action spectrum evaluations indicate that the ultraviolet B (UVB) rays are the most carcinogenic. However, recent studies indicate that the UVA rays can augment the cancer-producing effects of UVB rays. Other physical stimuli, including heat and wind, can also accelerate UVB carcinogenesis. Chemicals such as the polycyclic hydrocarbons, the nitrosoureas, and nitrogen mustard have an additive carcinogenic effect with UVB radiation. Also, some chemicals such as croton oil, the phorbol ester--TPA, and all-trans-retinoic (RA) acid can promote UVB-initiated carcinogenesis. RA can also inhibit UVB-induced cancer formation. The role of the immune status has received a great deal of attention. Both in experimental and clinical situations, nonspecific immune suppression results in increased cancer formation. Also, recent studies indicate that a specific T cell suppressor population can be induced in experimental animals with UVB which will inhibit rejection of tumors produced by UVB radiation. Finally, damage to DNA by UVB radiation is well established. Studies with the genetic disease xeroderma pigmentosum support the concept that such damage, if not repaired, will lead to cancer formation. It also has been suggested that unrepaired damage to deoxyribonucleic (DNA) and other macromolecules is at least in part responsible for the aging process in general.

Effects of ultraviolet radiation on the mitotic cycle and DNA, RNA and protein synthesis in mammalian epidermis in vivo.

Abstract— Acute effects of ultraviolet radiation on the mitotic cycle and macromolecular synthesis were investigated on hairless mouse epidermis in vivo. Colcemid was used to arrest mitoses in metaphase and thus allow more accurate mitotic counts. The radioactive tracers, TdR‐3H, cytidine‐3H, and the amino acids, histidine‐3H and methionine‐3H were used to examine DNA, RNA and protein synthesis, respectively. Using these techniques, we found that wavelengths shorter than 320 nm markedly inhibited mitosis, increased the basal cell turnover time and depressed DNA, RNA and protein synthesis within the first few hours post‐irradiation. By 24hr, recovery and acceleration of these functions were in progress, reaching a peak by 48–72 hr and persisting though to a lesser degree for 7 days. This stage of acceleration was associated with epidermal hyperplasia and most likely represented post‐injury cell renewal.

Defect in DNA synthesis in skin of patients with xeroderma pigmentosum demonstrated in vivo.

Exposure of normal human skin in vivo to ultraviolet irradiation at wavelengths shorter than 320 nanometers stimtulated an unscheduled DNA synthesis in all of the cell layers of the epidermis and in the upper dermnial fibrocytes. The skin of patients with xeroderma pigmentosum did not show this response. correlation of these findings with previous tissue culture studies suggests that the defect in repair of the damaged DNA in xeroderma cells occurs in vivo as well as in vitro.

EFFECTS OF β‐CAROTENE ON ULTRAVIOLET INDUCED CANCER FORMATION IN THE HAIRLESS MOUSE SKIN

Cutaneous cancers are by far the most common of all human malignancies and the vast majority of these tumors are induced by chronic sun exposure (Urbach et al., 1974). Experimental studies indicate that the primary carcinogenic action spectrum falls in the UVB range (290-320 nm) (Blum, 1959; Epstein, 1970). To date, cancer prevention has depended on external protective measures such as clothing and sunscreening agents. Recently, Mathews-Roth and her co-workers reported that !-carotene (Mathews-Roth et al., 1972) and phytoene, its triene precursor (Mathews-Roth and Pathak, 1975) produce a limited but significant reduction in the UVB induced sunburn erythema response. In addition, Wennersten and Swanbeck (1974) noted an increase in minimal erythema dose requirements in a number of light sensitive and normal individuals following prolonged b-carotene ingestion. The purpose of this study was to examine the potential influence of 8-carotene on UV induced skin cancer formation under controlled conditions.

EARLY EFFECTS OF ULTRAVIOLET LIGHT ON DNA SYNTHESIS IN HUMAN SKIN IN VIVO.

The early effects of ultraviolet light (UV) irradiation on deoxyribonucleic acid (DNA) synthesis in human skin were studied in vivo. Volunteers exposed to 3 minimal erythema doses (MED) (8.2-40.8 × 106ergs/sq cm) were injected intradermally with tritiated thymidine (TdR-H3), immediately, 15 minutes, 3, 5, and 24 hours afterward, and biopsies processed for light microscopy autoradiography. Comparison of the results with findings in unirradiated human skin indicated: (1) a depression in the number of germinative basal cells synthesizing DNA prior to division at three and five hours after UV, as seen in other systems; (2) a population of sparsely labeled cells not only in the basal layer but also in the malpighian and granular layers and not seen in unirradiated skin or after several other types of acute injury. This aberrant type of TdR-3H incorporation has been seen in other systems and is thought to represent dark reactivation repair of irradiated DNA as occurs in microorganisms.

Effects of 8-methoxypsoralen-induced phototoxic effects on mammalian epidermal macromolecule synthesis in vivo.

Abstract— The influence of 8‐methoxypsoralen (8‐MOP) and ultraviolet (UVA; 315–400 nm) radiation‐induced phototoxic responses on DNA, RNA and protein synthesis and the DNA repair phenomenon were investigated utilizing the hairless mouse epidermis in vivo. The radioactive tracers TdR‐3H, cytidine‐3H and histidine‐3H were used to examine changes in these macromolecules. Using these techniques, we found that the 8‐MOP‐UVA phototoxic injury inhibited premitotic semiconservative DNA synthesis in the germanitive layer of the epidermis within the first few hours post‐irradiation. Recovery occurred by 24 h, followed by a progressive acceleration of this function over the next 7 days. No depression in RNA or protein formation was noted through 36 h. By 48 h the cells in the upper 1/2 to 1/3 of the epidermis lost their normal appearance and discontinued synthesizing these macromolecules. At 72 h RNA and protein synthesis was again active throughout the epidermis and the apparently dead cells had desquamated. At this time the epidermis was notably acanthotic and the epidermal cells were markedly enlarged. Examination for the dark repair response revealed no evidence of unscheduled DNA synthesis following irradiation indicating that the excision repair process was not demonstrable within the first 15min after the phototoxic injury. These responses differ in a number of parameters from the phototoxic reactions induced by UV rays shorter than 320 nm.

Porphyria cutanea tarda. A study of the effect of phlebotomy.

Abstract The effect of phlebotomy on porphyrin metabolism was studied in 20 patients with characteristic clinical and chemical evidence of porphyria cutanea tarda. The removal of 2500 to 8500 ml of...

PSORALENS, UVA (PUVA) AND PHOTOCARCINOGENESIS

For hundreds of years, naturally-occurring photoactive furocoumarins, i.e. psoralens, have been used therapeutically to stimulate pigment formation in vitiligo [43]. However, within the past 7 years, the therapeutic use of these molecules has received much deserved controlled examination because of the efforts of a group of clinical investigators under the direction of the Harvard Dermatology Department in the evaluation of psoralen compounds in the treatment of psoriasis [34,39]. One of the experimentally defined adverse effects of psoralen photosensitization has been its carcinogenic potential [23]. This issue achieved clinical significance with the report of Stern et ul. [46] which described a definitive cutaneous cancer inducing effect of 8-methoxypsoralen and long (near) ultraviolet energy (UVA-PUVA) which occurred during this therapeutic trial. It should be noted that this carcinogenic effect does not negate the usefulness of the treatment program but it does emphasize the necessity for definition of risk benefit ratios [16]. The present report is concerned primarily with the photocarcinogenic influences of psoralens and UV radiation. Since extensive reviews examining the photobiologic and photochemotherapeutic effects of these molecules have been published in 1979 [17, 451, this discussion will be confined to information published between January and December of 1980 (i.e. a Yearly Review). Though it would seem obvious that we are woefully ignorant concerning mechanisms of cancer induction, we have arbitrarily decided to confine our report to the following limited areas since at the present time they appear to have some relationship to cancer formation. These are (1) effects on DNA, (2) mutagenic responses, (3) immunological alterations, and (4) PUVA induced photocarcinogenesis.

Effect of Ultraviolet Light on RNA and Protein Synthesis in Differentiated Epidermal Cells

STUDIES of the effects of microbeam ultraviolet light on growing tissue culture cells have shown that nucleolar RNA synthesis decreases rapidly but protein synthesis is either not affected1 or is decreased as a result of inhibition of nuclear RNA synthesis2. The influence of ultraviolet light energy on formation of macromolecules in more differentiated cells, however, has not been adequately studied. In the present study we examined the effects of heterochromatic ultraviolet light on RNA and protein synthesis in granular cells of human epidermis in vivo. These cells are differentiated epidermal cells which do not replicate, but do actively synthesize RNA and protein.