Oral niacin prevents photocarcinogenesis and photoimmunosuppression in mice.

Topical nicotinamide (niacinamide) has demonstrable preventive activity against photocarcinogenesis in mice. To better understand how this vitamin prevents ultraviolet (UV) carcinogenesis, we tested systemic administration of another form of the vitamin, niacin, and its capacity to elevate cutaneous nicotinamide-adenine dinucleotide (NAD) content as well as to decrease photoimmunosuppression and photocarcinogenesis. BALB/cAnNTacfBR mice were fed the AIN-76A diet supplemented with 0%, 0.1%, 0.5%, or 1.0% niacin throughout the experiment. UV irradiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps for 22 weeks in the carcinogenesis experiments, yielding a total cumulative dose of approximately 1.41 x 10(6) Jm-2 of UV-B radiation. Dietary supplementation with 0.1%, 0.5%, or 1.0% niacin reduced the control incidence of skin cancer from 68% to 60%, 48%, and 28%, respectively, at 26.5 weeks after the first UV treatment. Two potential mechanisms by which niacin prevents tumor formation were identified. Photoimmunosuppression, critical for photocarcinogenesis, is measured by a passive transfer assay. Syngeneic, antigenic tumor challenges grew to an average of 91.6 +/- 19.7, 79.8 +/- 11.5, 41.9 +/- 11.7, or 13.2 +/- 4.1 mm2 in naive recipients of splenocytes from UV-irradiated mice treated with 0%, 0.1%, 0.5%, or 1.0% niacin supplementation, respectively, demonstrating niacin prevention of immunosuppression. Niacin supplementation elevated skin NAD content, which is known to modulate the function of DNA strand scission surveillance proteins p53 and poly(ADP-ribose) polymerase, two proteins critical in cellular responses to UV-induced DNA damage. These results clearly demonstrate a dose-dependent preventive effect of oral niacin on photocarcinogenesis and photoimmunosuppression and establish the capacity of oral niacin to elevate skin NAD levels.

Inhibitory effects of perillyl alcohol on UVB-induced murine skin cancer and AP-1 transactivation.

The monoterpene perillyl alcohol (POH) has proven efficacious against the formation and progression of a variety of cancers. In this study, we tested the ability of POH to inhibit photocarcinogenesis in a nonmelanoma model of mouse skin carcinogenesis and its ability to inhibit UVB-induced activator protein 1 (AP-1) transactivation in mouse skin and human keratinocytes. POH (10 mM) was applied topically to the ears and shaved dorsal surface of groups of 35 BALB/c mice throughout the experiment, during and after UVB treatment. Topical POH significantly inhibited tumor incidence and multiplicity, average tumor size, and the average tumor burden/mouse without any apparent toxicity. POH inhibited UVB-induced AP-1 transactivation in both cultured human keratinocytes and transgenic mice that stably express a luciferase reporter driven by AP-1 elements. The results suggest that POH might be used for chemoprevention of human skin cancer, and that inhibition of AP-1 activity is functionally related to inhibition of skin carcinogenesis.

Inhibition of cyclobutane pyrimidine dimer formation in epidermal p53 gene of UV-irradiated mice by alpha-tocopherol.

Mutations or alterations in the p53 gene have been observed in 50-100% of ultraviolet light (UV)-induced squamous cell carcinoma in humans and animals. Most of the mutations occurred at dipyrimidine sequences, suggesting that pyrimidine dimers in the p53 gene play a role in the pathogenesis of cutaneous squamous cell carcinoma. We previously showed that topical alpha-tocopherol prevents UV-induced skin carcinogenesis in the mouse. In the present study we asked whether topical alpha-tocopherol reduces the level of UV-induced cyclobutane pyrimidine dimers in the murine epidermal p53 gene. Mice received six dorsal applications of 25 mg each of alpha-tocopherol, on alternate days, before exposure to 500 J/m2 of UV-B irradiation. Mice were killed at selected times after irradiation. The level of dimers in the epidermal p53 gene was measured using the T4 endonuclease V assay with quantitative Southern hybridization. Topical alpha-tocopherol caused a 55% reduction in the formation of cyclobutane pyrimidine dimers in the epidermal p53 gene. The rate of reduction of pyrimidine dimers between 1 and 10 hours after irradiation was similar in UV-irradiated mice, regardless of alpha-tocopherol treatment. Therefore, the lower level of cyclobutane pyrimidine dimers in UV-irradiated mice treated with alpha-tocopherol than in control UV-irradiated mice resulted from the prevention of formation of the dimers, and not from enhanced repair of these lesions. Our results indicate that alpha-tocopherol acts as an effective sunscreen in vivo, preventing the formation of premutagenic DNA lesions in a gene known to be important in skin carcinogenesis.

Prevention of photoimmunosuppression and photocarcinogenesis by topical nicotinamide.

Ultraviolet (UV) B irradiation leads to a potent immunosuppression of the capacity to reject syngeneic, antigenic tumors. If this immunosuppression is critical for the development of most skin tumors, then its prevention should result in prevention of photocarcinogenesis. We previously showed a correlation between the inhibition of photoimmunosuppression and prevention of photocarcinogenesis by dl-alpha-tocopherol, tannic acid, or alpha-difluoromethylornithine. The current study was designed to determine whether topical nicotinamide, the active form of vitamin B-3, or niacin, prevents immunosuppression and skin cancer in UV-irradiated mice. In a passive transfer assay for immunosuppression, splenocytes from UV-irradiated mice enhanced the growth of antigenic tumor challenges in recipient mice. Treatment of the UV-irradiated mice with 40 mumol of nicotinamide twice weekly starting two weeks before UV irradiation and throughout the experiment prevented this immunosuppression. UVB irradiation consisted of five weekly 30-minute exposures to banks of six FS40 Westinghouse fluorescent sunlamps. Mice received approximately 6.2 x 10(5) J/m2 in the passive transfer assays and 1.09 x 10(6) J/m2 in the photocarcinogenesis studies. Application of nicotinamide to UV-irradiated mice reduced skin tumor incidence from 75% to 42.5% (p = 0.016, Cox proportional hazards analysis). Thus topical nicotinamide prevented the immunosuppression and skin tumor induction by UVB irradiation.

Importance of the form of topical vitamin E for prevention of photocarcinogenesis.

With increasing solar ultraviolet (UV)-B radiation reaching the Earth's surface and the incidence of skin cancer rising steadily, there is an ever-increasing need to determine agents that modulate photocarcinogenesis and to understand the mechanisms underlying this modulation. Our laboratory has demonstrated that topical application of the dl-alpha-tocopherol form of vitamin E to mice prevents skin cancer and the immunosuppression induced by UVB irradiation. However, dl-alpha-tocopherol has limited stability at room temperature. The current study was designed to ask whether the thermostable esters of vitamin E, alpha-tocopheryl acetate, or alpha-tocopheryl succinate prevent skin cancer and immunosuppression induced in mice by UV radiation. In the alpha-tocopheryl acetate study, skin cancers developed in 70% of UVB-irradiated control mice and in 90%, 73%, and 90% of mice receiving topical applications of 12.5, 25, and 50 mg of dl-alpha-tocopheryl acetate, respectively. In the alpha-tocopheryl succinate study, skin cancer developed in 59.3% of control UVB-irradiated mice and in 82%, 100%, and 81.5% of mice treated with 2.5, 12.5, and 25 mg d-alpha-tocopheryl succinate, respectively. Thus neither alpha-tocopheryl acetate nor alpha-tocopheryl succinate prevented photocarcinogenesis. At 12.5 and 25 mg/treatment, alpha-tocopheryl acetate and alpha-tocopheryl succinate, respectively, enhanced photocarcinogenesis (p = 0.0114 and 0.0262, respectively, log rank test). On the basis of high-performance liquid chromatography analysis at 16-17 weeks after the first vitamin E treatment, the esterified forms of vitamin E applied epicutaneously accumulated in the skin, but the levels of free alpha-tocopherol remained low. Neither alpha-tocopheryl acetate nor alpha-tocopheryl succinate prevented the induction by UV radiation of immunosusceptibility to implanted syngeneic antigenic UV-induced tumor cells. Thus alpha-tocopheryl acetate or alpha-tocopheryl succinate not only failed to prevent photocarcinogenesis, but may have enhanced to process. Considering that alpha-tocopherol esters are included in many skin lotions, cosmetics, and sunscreens, further studies are needed to determine the conditions under which topical alpha-tocopheryl acetate and alpha-tocopheryl succinate enhance photocarcinogenesis.

Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea.

Topical application of purified (-)-epigallocatechin-3-gallate (EGCG), a polyphenolic antioxidant isolated from green tea, inhibited photocarcinogenesis in BALB/cAnNHsd mice with no visible toxicity. Mice were treated with 0, 10, or 50 mg of EGCG in 200 microliters of acetone three times weekly for three weeks before ultraviolet (UV) treatments began and throughout the experiment. UV radiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps for 25 weeks. In the photocarcinogenesis study, mice received a total dose of approximately 2.1 x 10(6) J/m2. Skin cancer incidence in UV-irradiated mice was 96% at 28 weeks after the first UV treatment; EGCG at 10 or 50 mg reduced this incidence to 62% and 29%, respectively. UV-induced immunosuppression, assessed by the inability of UVB-irradiated mice to reject a syngeneic antigenic tumor, was not influenced by topical EGCG. Oral administration of 0, 100, or 500 mg of pure EGCG per liter of drinking water (approximately 0, 0.56, or 2.8 mg/day, respectively) did not decrease UV-induced skin tumor incidence, rate of primary tumor growth, or inability to reject antigenic tumors. Thus induction of skin tumors by UV radiation was significantly reduced by topical, but not by oral, administration of purified EGCG through a mechanism distinct from inhibition of photoimmunosuppression.

Reduction of interferon-gamma as a critical mechanism by which ultraviolet radiation prevents tumor rejection.

Mice irradiated with UVB, unlike nonirradiated mice, are highly susceptible to syngeneic, immunogenic tumors induced by UVB irradiation or by chemicals. We postulated that UV induced susceptibility to immunogenic tumors results from a reduction in host capacity to generate an interferon (IFN)-gamma immune response to tumor antigens. Shaved BALB/c mice were exposed to 6 x 10(5) J m-2 of UVB radiation delivered intermittently over 12 weeks. The UVB-irradiated and nonirradiated mice received intradermal injections of UVM12 or BP2 tumor cells. After 0, 1.5, 3, 7 or 21 days, draining lymph nodes were excised. Lymph node cells were incubated with UVM12 or BP2 cells that had received 2.5 Gy of gamma-radiation. After 48 h in culture, supernatants were analyzed for IFN-gamma content by enzyme-linked immunosorbent assay and cellular RNA was extracted for mRNA detection by reverse transcriptase-polymerase chain reaction analysis. At 7 days after tumor injection, draining lymph node cells from nonirradiated control mice secreted significant levels of IFN-gamma and contained at least 0.0729 amol of IFN-gamma mRNA/microgram cDNA upon in vitro exposure to gamma-irradiated tumor cells. Draining lymph node cells removed from UV-irradiated mice contained only 18% as much IFN-gamma mRNA and secreted little or no IFN-gamma when exposed to gamma-irradiated tumor cells. A single injection of antibody directed against murine IFN-gamma rendered normal mice as susceptible as UV-irradiated mice to BP2 tumor cells. Thus, chronic UV irradiation leads to an inability of host tumor draining lymph node cells to mount an IFN-gamma response to tumor antigens.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of photocarcinogenesis and UV-induced immunosuppression in mice by topical tannic acid.

Topical application of tannic acid, a phenolic antioxidant derived from plants, was found to inhibit the cutaneous carcinogenesis and the immunosuppression induced by ultraviolet B (UVB) irradiation with no visible toxicity. BALB/cAnNTacfBR mice were treated with 200 micrograms of tannic acid three times weekly for two weeks before UV treatments began and throughout the experiment. UVB irradiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps. In the photocarcinogenesis study, mice received a total dose of approximately 1.09 x 10(6) J/m2. Skin cancer incidence in UV-irradiated mice was 75% at 26 weeks after the first UV exposure; tannic acid reduced this to 42%. Immunosuppression induced by UVB irradiation normally prevents the host from rejecting antigenic syngeneic UV-induced tumors. Immunosuppression in these experiments was measured by a passive transfer assay. Tumor challenges grew to an average of 88 +/- 20, 36 +/- 11, and 20 +/- 8 mm2 in naive recipients of splenocytes from UVB-irradiated mice, nonirradiated control mice, and UVB-irradiated mice treated with tannic acid, respectively. Thus topical tannic acid treatment prevented the transfer of enhanced tumor susceptibility with splenocytes from UVB-irradiated mice.

Prevention of photocarcinogenesis by dietary vitamin E.

Ultraviolet B (UV-B) irradiation of C3H/HeN mice induces skin cancer. In this study, the ability of dietary d-alpha-tocopheryl acetate to reduce photocarcinogenesis was tested in this murine model. Skin cancers developed in 67.5% of UV-B-irradiated mice by 31 weeks after the first UV exposure. Supplementation with 100 or 200 IU of d-alpha-tocopheryl acetate per kilogram of diet led to a reduction of the incidence to 46% and 19%, respectively. The latter value was significantly different from that found in mice fed the basal diet (p = 0.039, one-sided P value by log-rank test). Skin levels of alpha-tocopherol varied with the dietary dose of d-alpha-tocopheryl acetate. No toxicity was evident in unirradiated mice fed the vitamin E-supplemented diet, but 40% of the UV-B-irradiated mice fed 200 IU of vitamin E per kilogram of diet died by 31 weeks after the first UV-B treatment. Decreased relative spleen weight was observed in the UV-B-irradiated mice fed the vitamin E-supplemented diet. In summary, oral d-alpha-tocopheryl acetate prevented photocarcinogenesis, but at doses that were toxic to inbred C3H/HeN mice after exposure to 8.6 x 10(5) J/m2 of UV-B irradiation.

Inhibition of DFMO-induced audiogenic seizures by chlordiazepoxide.

Mice given 1% alpha-difluoromethylornithine (DFMO) in the drinking water for 5 weeks developed a hyperactive behavior characterized by uncontrolled running upon stimulation with noise. The running was followed by seizures and sometimes death. These behaviors are characteristic of audiogenic seizures. Strain differences in susceptibility to DFMO-induced audiogenic seizures were observed. The order of sensitivity to this DFMO effect was: C3HeB/FEJ = C3H/HeN > CBA/J = BALB/c. Chronic DFMO treatment was found to deplete whole brain putrescine and spermidine, but not spermine nor gamma-aminobutyric acid (GABA), in the 2 strains of mice analyzed, C3H/HeN and BALB/c. The audiogenic seizures were eliminated by pretreatment with the benzodiazepine, chlordiazepoxide (Librium) (40 mg/kg, ip) 105 minutes prior to testing for seizures.

Reduction in plasma or skin alpha-tocopherol concentration with long-term oral administration of beta-carotene in humans and mice.

BACKGROUND: Beta-carotene is one of the most commonly used compounds in clinical trials of chemopreventive agents in various neoplastic diseases. Animal studies, including our own, have documented that dietary beta-carotene can reduce plasma alpha-tocopherol (vitamin E) levels, but few published studies have examined the clinical or pharmacokinetic ramifications of long-term, high-dose beta-carotene regimens on other fat-soluble vitamins such as alpha-tocopherol. PURPOSE: This study was designed to determine the effects of long-term beta-carotene supplementation on plasma concentrations of alpha-tocopherol in normal human subjects and in an experimental C3H/HeN mouse model. METHODS: In a double-blind study, 45 normal subjects were randomly assigned to receive 0 (placebo), 15, 30, 45, or 60 mg of oral beta-carotene daily for approximately 9 months. Monthly plasma samples were collected. Thirty-five C3H/HeN mice were fed a basal diet with or without beta-carotene and treated topically with or without alpha-tocopherol, except for the control mice, which received UV radiation for 27 weeks from week 3 to week 30. Plasma and dorsal skin samples were taken after 40 weeks and were analyzed for alpha-tocopherol and/or beta-carotene by high-performance liquid chromatography. RESULTS: Long-term dietary beta-carotene administration resulted in statistically significant reductions in levels of alpha-tocopherol in the skin and plasma of UV-irradiated mice. In the human study, the decrease in plasma alpha-tocopherol levels was progressive and significant between 6 and 9 months of beta-carotene dosing in all dosage groups. The greatest decrease was observed during the 9th (last) month of dosing, with a decrease of 40% from baseline. All oral beta-carotene doses (15-60 mg/d), however, resulted in similar decreases in steady-state plasma levels of alpha-tocopherol and in only small differences in beta-carotene plasma levels. CONCLUSION: Long-term oral administration of beta-carotene decreased steady-state plasma concentrations of alpha-tocopherol. The lack of a significant dose-response effect between doses of beta-carotene and alpha-tocopherol plasma levels is not unexpected, given the small differences in steady-state beta-carotene plasma levels in the four beta-carotene dose groups. IMPLICATIONS: Studies are needed to determine how long-term beta-carotene dosing influences tissue distribution of dietary alpha-tocopherol. Careful surveillance for this and other potentially harmful nutrient interactions should become part of all long-term intervention studies.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion in murine skin by systemic effects of ultraviolet irradiation.

Systemic effects of UVB irradiation (280-320 nm) have been shown to prevent subsequent chemical tumorigenesis induced by an initiation-promotion protocol. The present investigation was designed to determine whether initiation or promotion is prevented by UV irradiation. Groups of 25 B6D2F1/J mice received 12 weeks of intermittent dorsal UVB radiation treatments administered before, or 3 weeks after, initiation with a single application of 7,12-dimethylbenz[a]anthracene on the ventral skin. All mice were promoted ventrally with 5 micrograms 12-O-tetradecanoylphorbol-13-acetate (TPA) applied three times weekly throughout the experiment. UV irradiation consisted of five 30-min exposures per week to a bank of 6 Westinghouse FS40 sunlamps. UV irradiation applied before or after initiation resulted in a decrease of 18-16 tumors per group of 25 mice, for a reduction of 61 and 50%, respectively, at 24 weeks after the first TPA treatment. Thus, prevention of tumor development was similar whether the UV influence was present or not during initiation. This finding suggests that the UV prevention of promotion could account for UV inhibition of skin tumors induced by an initiation-promotion regimen. Consistent with this concept, pretreatment of mice with dorsal UVB radiation was found to reduce DNA synthesis after exposure to TPA by 46%, although it did not decrease tritiated benzo[a]pyrene binding to DNA, in ventral epidermis. Thus, UVB irradiation systemically reduced TPA-induced tumor promotion in murine skin.

Prevalence of tumor prevention rather than tumor enhancement when repetitive UV radiation treatments precede initiation and promotion.

UV irradiation can act as a tumor initiator in mouse skin, yet repetitive UV irradiation can systemically prevent chemically induced two-stage skin tumorigenesis. The present study addressed the question of whether repetitive dorsal UV irradiation would enhance or inhibit subsequent initiation and promotion applied dorsally. Approximately 4.25 x 10(5) J/m2 was applied intermittently to 30 shaved CDF1 mice over an 8 week period. Mice were then initiated dorsally with 100 micrograms of 7,12-dimethylbenz[a]anthracene and subsequently promoted with 7.5 micrograms 12-O-tetradecanoylphorbol-13-acetate (TPA) applied twice weekly for 19 weeks. Initiated and promoted mice that had been treated repetitively with 1.06 x 10(4) J/m2 showed a decrease in tumor incidence from 92 to 28%, and a reduction in tumor yield per mouse from 5.35 to 0.58, at 19 weeks after the first TPA treatment. Histological analysis revealed that the UVB radiation treatments used in these experiments did not produce permanent loss of epidermal cells or sebaceous gland atrophy. When the same dose of UVB irradiation was applied after initiation and promotion, no increased conversion of papillomas to carcinomas was found, within a 48 weeks experimental duration. Thus, repetitive UV irradiation prevented rather than enhanced subsequent two-stage tumorigenesis. Repetitive UVB irradiation at late stages of promotion failed to enhance conversion of papillomas to carcinomas within the time frame in which chemical initiators mediate conversion to malignancy.

Systemic modulation by ultraviolet irradiation of cutaneous N-methyl-N'-nitro-N-nitrosoguanidine-induced carcinogenesis.

Ultraviolet irradiation can systemically enhance subsequent skin cancer induction by benzo[a]pyrene, methylcholanthrene, or UV radiation. The present study was designed to determine whether UVB irradiation influences host susceptibility to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Female C3H/HeJ mice were exposed dorsally to UVB radiation from banks of 6 Westinghouse FS40 sun lamps. The mice received a total UV dose of approximately 8.1 x 10(5) J m-2 over a 15-week period. After termination of UVB treatments, ventral tumors were induced by 4 applications of 30 mumol of MNNG at 8-day intervals. At 20 weeks after the first MNNG treatment, UVB-irradiated mice had 7-fold more MNNG-induced, ventral tumors than did the unirradiated control mice (P = 0.026, Wilcoxon rank sum test). Ventral application of MNNG after cessation of dorsal UVB exposure, but before UV tumor appearance, did not influence photocarcinogenesis. These results demonstrate that UV irradiation can systemically decrease host resistance to tumor induction by the methylating agent, MNNG.

Reduction of murine cutaneous UVB-induced tumor-infiltrating T lymphocytes by dietary canthaxanthin.

The effect of dietary canthaxanthin, retinyl palmitate, or their combination on the tumor-infiltrating T-lymphocyte response (T-TIL) in de novo murine ultraviolet type B irradiation-induced tumors was investigated to elucidate potential mechanisms of action of these compounds. We found that dietary canthaxanthin greatly reduced the number of tumor-infiltrating helper/inducer, suppressor/cytotoxic, and interleukin-2 receptor-positive T lymphocytes and also observed a concomitant statistically significant increase in tumour incidence in canthaxanthin-fed animals. The addition of retinyl palmitate to the canthaxanthin diet ameliorated this negative effect on TIL and the development of skin tumors. We conclude that dietary retinyl palmitate and canthaxanthin can modulate the host T-cell immune response within a growing tumor and may affect tumorigenicity.

Enhanced growth and experimental metastasis of chemically induced tumor in ultraviolet irradiated syngeneic mice.

Recent studies have shown that ultraviolet (UV) irradiation induces a systemic effect which enhances subsequent tumor induction by benzo[a]pyrene in a manner which is dependent on the dose of benzo[a]pyrene. The present study was designed to test whether UV-B irradiation renders mice susceptible to subcutaneous or intravenous injection of a regressor tumor induced by benzo[a]pyrene. The sources of UV-B irradiation were banks of 6 Westinghouse FS-40 sunlamps, situated 20 cm above the mouse cages. Female BALB/cAnNHsd received five 30-min dorsal UV-B radiation treatments per week for 12 weeks, resulting in a total dose of approx. 6.4 x 10(5) J m-2. Two to seven days after termination of UV treatments, syngeneic regressor tumor cells (BP2) induced by benzo[a]pyrene were injected subcutaneously or intravenously into irradiated mice and unirradiated controls. By 38 days post subcutaneous implantation, 24/30 and 3/30 BP2 implants were detectable in the irradiated and unirradiated mice, respectively. Ultraviolet irradiated mice were also unable to reject lung colonies resulting from intravenous administration of BP2 cells, although they were rejected by unirradiated mice. The mean number of lung colonies per mouse was 16- to 35-fold greater in UV irradiated mice than in unirradiated controls, at 14 to 17 days post injection. Thus, UV irradiation rendered mice, with no known exposure to benzo[a]pyrene, susceptible to a subcutaneous or intravenous injection of a regressor tumor induced by benzo[a]pyrene.

Prevention by alpha-difluoromethylornithine of skin carcinogenesis and immunosuppression induced by ultraviolet irradiation.

Administration of alpha-difluoromethylornithine (DFMO) to mice was found to inhibit both the cutaneous carcinogenesis and the immunosuppression induced by ultraviolet B (UVB) irradiation. BALB/cAnNTacfBR mice were given 1% F2MeOrn in their drinking water throughout the experiment. After 3 weeks, mice received UVB irradiation consisting of five 30-min exposures per week to banks of six FS40 Westinghouse sunlamps. In the photocarcinogenesis study, mice received a total dose of approximately 1273 kJ m-2. Skin cancer incidence in UV-irradiated mice was 38% 28 weeks after the first UV exposure; DFMO reduced this incidence to 9% (P = 0.025, log-rank test). Although DFMO has been demonstrated to be chemopreventive of chemical carcinogenesis, this is the first report that it is effective against cancers induced by a physical carcinogen. The immunosuppression induced by UVB irradiation prevents the host from rejecting antigenic, syngeneic UV-induced tumors, which normal mice can reject. The level of immunosuppression in UV-irradiated mice treated with DFMO was measured by a passive-transfer assay. Splenocytes from UV-irradiated mice to naive mice prevented the recipients from rejecting 20/24 UV-induced tumor challenges, whereas splenocytes from UV-irradiated mice treated with DFMO did not prevent recipients from rejecting such challenges (2/24 grew). The difference between these values was significant (P less than 0.001, two-sample test for binomial proportions). Phenotypic analysis of splenocytes used in the passive transfer, using a biotin-avidin-immunoperoxidase technique, revealed that DFMO treatment prevented the reduction of Ia expression normally seen in UV-irradiated mice. Thus, administration of DFMO reduced skin carcinogenesis and immunosuppression induced by UVB irradiation.

Topical vitamin E inhibition of immunosuppression and tumorigenesis induced by ultraviolet irradiation.

Ultraviolet (UV) irradiation of C3H/HeN mice induces skin cancer and an immunosuppression that prevents the host from rejecting antigenic UV-induced tumors. The capacity of topical vitamin E (dl-alpha-tocopherol) to prevent photocarcinogenesis or the immunosuppression induced by UV irradiation were assessed. Skin cancer incidence in UV-irradiated mice was 81% at 33 weeks after the first UV exposure; application to mice of 25 mg vitamin E three times per week for three weeks before UV irradiation, and throughout the experiment, reduced this incidence to 42% (p = 0.0065, log rank test). Immunoenhancement by vitamin E was assessed by comparing levels of immunosuppression by splenocytes from normal or UV-irradiated mice, with and without topical vitamin E treatment. Transfer of splenocytes from UV-irradiated mice to naive mice prevented the recipients from rejecting a UV-induced tumor challenge, whereas splenocytes from UV-irradiated mice treated with vitamin E did not prevent recipients from rejecting a similar tumor challenge. Phenotypic analysis of splenocytes used in the passive transfer assay, conducted with a biotin-avidin-immunoperoxidase technique, revealed that vitamin E treatment of mice undergoing UV irradiation prevented the UV-induced down regulation of Ia expression in splenocytes and increased the proportion of Lyt-2+ and L3T4+ splenocytes. Therefore, chronically applied vitamin E can effectively reduce cancer formation and immunosuppression induced by UV irradiation. Prevention of UV-induced down regulation of Ia expression may have contributed to this immunomodulation.

Cumulative reduction of primary skin tumor growth in UV-irradiated mice by the combination of retinyl palmitate and canthaxanthin.

The effects of dietary supplementation with retinyl palmitate, canthaxanthin, or the combination of both, on photocarcinogenesis was determined in pigmented C3H/HeN mice. The basal diet was the American Institute of Nutrition Diet 76A, to which was added 120 IU of retinyl palmitate per g diet, 1% canthaxanthin, or the combination of both. Administration of the diets began 18 weeks before the first UVB radiation (280-320 nm) treatment and continued throughout the study. The UV source was a bank of 6 Westinghouse FS40 lamps which delivered to the mice a total dose of 9.9 x 10(5) J/m2, delivered over 24 weeks. These diets significantly reduced the tumor burden per mouse induced by UV irradiation, however they did not influence tumor incidence. The combination of retinyl palmitate plus canthaxanthin was more effective than either agent alone at reducing autochthonous tumor growth, a result which has not been previously reported.

Enhanced resistance to an antigenic tumor in immunosuppressed mice by dietary retinyl palmitate plus canthaxanthin.

Retinoids and certain carotenoids, e.g., beta-carotene and canthaxanthin, have been found to prevent photocarcinogenesis in mice and also to act as immunoenhancers. The hypothesis that retinoids and carotenoids inhibit photocarcinogenesis by preventing UV induction of immunosuppression predicts that mice treated with these agents before and during periods of UV radiation treatments should be as resistant as unirradiated mice to an antigenic UV-induced tumor. To test this prediction, mice were fed 120 IU of retinyl palmitate per gram of diet, and/or 1% canthaxanthin, before UV irradiation treatments began, and during the entire experiment. After 4.95 x 10(5) Jm-2, delivered over 12 weeks, resistance of mice to antigenic UV-induced tumor implants (UV20) was studied. Dietary supplementation with retinyl palmitate plus canthaxanthin, but not with either agent alone at these doses, prevented the enhanced growth of UV20 in UV irradiated mice.