Fyn is a redox sensor involved in solar ultraviolet light-induced signal transduction in skin carcinogenesis.

Solar ultraviolet (UV) light is a major etiological factor in skin carcinogenesis, with solar UV-stimulated signal transduction inducing pathological changes and skin damage. The primary sensor of solar UV-induced cellular signaling has not been identified. We use an experimental system of solar simulated light (SSL) to mimic solar UV and we demonstrate that Fyn is a primary redox sensor involved in SSL-induced signal transduction. Reactive oxygen species (ROS) generated by SSL exposure directly oxidize Cys488 of Fyn, resulting in increased Fyn kinase activity. Fyn oxidation was increased in mouse skin after SSL exposure and Fyn-knockout mice formed larger and more tumors compared with Fyn wild-type mice when exposed to SSL for an extended period of time. Murine embryonic fibroblasts (MEFs) lacking Fyn and cells in which Fyn expression was knocked down were resistant to SSL-induced apoptosis. Furthermore, cells expressing mutant Fyn (C448A) were resistant to SSL-induced apoptosis. These findings suggest that Fyn acts as a regulatory nexus between solar UV, ROS and signal transduction during skin carcinogenesis.

EFFECT OF SELENIUM SUPPLEMENTATION ON PROTEOMIC SERUM BIOMARKERS IN ELDERLY MEN.

OBJECTIVES: To determine the effect of selenium supplementation on the human proteomic profile. DESIGN: Serum samples were collected in this pilot study from a randomized placebo controlled Phase 2 clinical trial (Watchful Waiting (WW)). SETTING: Subjects were followed every three months for up to five years at the University of Arizona Prostate Cancer Prevention Program. PARTICIPANTS: One hundred and forty men (age < 85 years) had biopsy-proven prostate cancer, a Gleason sum score less than eight, no metastatic cancer, and no prior treatment for prostate cancer. INTERVENTION: As part of the WW trial, men were randomized to placebo, selenium 200 µg/day or selenium 800 µg/day. For the purpose of the current study, 40 subjects enrolled in the WW study (20 from the placebo group and 20 from Se 800 µg/day group) were selected. MEASUREMENTS: Baseline serum samples were collected at each follow-up visit and stored at -80 degrees Celsius. A multiplexed proteomic panel investigated changes in 120 proteins markers simultaneously. RESULTS: Thirteen proteins (Apolipoprotein J, IL-10, IL-1 alpha, MMP-3, IL-12p70, IL-2 receptor alpha, cathepsin B, eotaxin, EGFR, FGF-basic, myeloperoxidase, RANTES, TGF-beta) were determined to be either statistically (p-value < 0.05) or marginally significantly (0.05 < p-value <0.1) changed in the selenium supplemented group as compared to placebo. CONCLUSION: Although independent validation of these results is needed, this study is the first of its kind to utilize high throughput fluorescence based protein multiplex panel in analyzing changes in the proteomic profile due to selenium supplementation. Results from this study provide insight into the ability of selenium to modulate numerous protein markers and thus impact various biological processes in humans.

A phase IB trial of 24-hour intravenous PX-12, a thioredoxin-1 inhibitor, in patients with advanced gastrointestinal cancers.

We investigated the safety, pharmacokinetics, and pharmacodynamics of PX-12, a thioredoxin-1 (Trx-1) inhibitor, administered as a 24-hour infusion every 7 or 14 days in patients with gastrointestinal malignancies. PX-12 is the first Trx-1 inhibitor to undergo clinical development. The first Phase 1 study of PX-12 demonstrated promising clinical activity, but the 1 and 3 hour-infusion schedules investigated were associated with a strong and irritating odor due to exhalation of one of its metabolites, 2-butanethiol. In an effort to achieve tolerability and achieve a drug exposure level necessary for biological activity, the current study was undertaken. While the maximally tolerated dose was estimated to be 300 mg/m(2) /24 h once a week as the 2-butanethiol expirate was tolerable at that dose level, no evidence of clinical activity was observed. Pharmacokinetic studies of the parent compound PX-12 demonstrated rapid, irreversible binding to plasma components, resulting in low (ng/ml) peak plasma concentrations of non-bound PX-12 during infusion. DCE-MRI was performed pre-and post-infusion in three patients. There were no significant trends observed in changes in plasma Trx-1, vascular endothelial growth factor (VEGF), or beta fibroblast growth factor (FGF-2) pre- or post-treatment. However, there was a trend for a decrease in circulating Trx-1 during the first four PX-12 treatment cycles in patients that had a Trx-1 baseline level >18 ng/mL. Aggregate clinical trial results suggest that further clinical development of PX-12, as an intravenous infusion, is not feasible. However, the Trx-1 pathway remains a target of interest in patients with gastrointestinal malignancies.

Differences in characteristics of men with localised prostate cancer who demonstrate low, intermediate or high prostate-specific antigen velocity.

BACKGROUND: Current diagnostic tools are inadequate for reliable prediction of prostate cancer (PCa) aggressiveness in patients with localised disease. This results in many patients being exposed to potentially unnecessary invasive treatment and its associated morbidities. In order to develop appropriate treatment strategies, it is essential to understand the differences between patients who will develop aggressive disease and those who will not. METHODS: A longitudinal study was conducted in men with localised PCa on active surveillance for their disease in which 140 subjects were followed every 3 months for up to 5 years. Change in prostate-specific antigen (PSA) over time (PSA velocity) was used as a marker for PCa progression. Subjects were categorised as slow, intermediate and fast progressors based on tertiles of PSA velocity. Differences in baseline markers were investigated using logistic regressions. Two approaches were used, slow progressors were compared with fast progressors (model 1) and slow progressors were compared with combination of intermediate and fast progressors (model 2). RESULTS: Aspirin was negatively associated with high PSA velocity in model 1 (odds ratio (95% confidence interval): 0.24 (0.06, 0.94), P-value = 0.04) and model 2 (odds ratio = 0.22 (0.08, 0.59), P-value = 0.003), whereas smoking was positively associated with high PSA velocity in model 1 (1.03 (0.92, 1.13), P-value = 0.01). CONCLUSIONS: These findings highlight the role of aspirin and smoking in PCa progression. They have potential towards risk stratification as well as PCa prevention and hence need to be investigated further.

Attenuation of catalase activity in the malignant phenotype plays a functional role in an in vitro model for tumor progression.

We have developed an in vitro model to study the molecular mechanisms of tumor progression. Using repeated treatments with ionizing radiation or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), we caused malignant progression of a papilloma producing mouse keratinocyte cell line, 308 cells. In a previous study we have shown that the malignant variants of 308 cells have elevated reactive oxygen species (ROS) levels, and have established a functional role for the pro-oxidant state in the progressed phenotype (Carcinogenesis 20 (1999) 2063). In this study, we have evaluated the status of intracellular defense mechanisms for ROS scavenging in the progressed phenotype to identify sources that contribute to their pro-oxidant state. Our results demonstrate that a reduction in several anti-oxidant defense mechanisms, including catalase and glutathione S-transferase mu, correlates with the emergence of the malignant phenotype. We provide evidence that attenuation of catalase activity may play a functional role in the malignant progression of mouse keratinocytes.

Prevention of non-melanoma skin cancer.

Basal cell and squamous cell carcinomas comprise the majority of non-melanoma skin cancers. Whereas the incidence of skin cancer is equivalent to that of all other cancers combined, non-melanoma skin cancer receives a disproportionate share of attention because mortality is relatively low. However, the impact on public health is striking. This review is intended to update readers on the current findings in research on the prevention of these diseases. Topics covered include preventive strategies targeting high-risk populations, chemoprevention (including treatment of intraepithelial neoplasia), and an overview of recent and ongoing clinical and preclinical studies involving new chemopreventive agents.

Dermal toxicity of topical (-)epigallocatechin-3-gallate in BALB/c and SKH1 mice.

(-)Epigallocatechin-3-gallate (EGCG), the major polyphenolic component of green tea, inhibits experimental chemical and physical carcinogenesis, yet little toxicological data has been reported. Therefore, we performed studies on the dermal toxicity of EGCG applied in an ointment formulation in mice. Female BALB/c mice were dehaired with a topical depilatory and administered 75 microl EGCG in hydrophilic Ointment U.S.P. at three concentrations (10, 3, and 1%, all w/w) daily for 30 days. At the 10% concentration, gross toxicity was manifested by the formation of erythema and papular lesions by day 5. A 7% reduction in weight was observed by day 15. No toxicity was observed at the two lower concentrations or in the vehicle control group. Also, no toxicity was observed when mice were dehaired by shaving. This study was repeated in female SKH1 mice, an outbred hairless strain that does not require depilation. No toxicity was observed in the SKH1 mice, indicating that daily topical EGCG appears non-toxic in normal skin. However, use of topical depilatories may potentiate dermal toxicity of EGCG.

The state-of-the-art in chemoprevention of skin cancer.

The incidence of skin cancer (both melanoma and non-melanoma) continues to grow at an alarming rate. Our chemoprevention strategies include the development of novel agents evaluated by (1) preclinical mechanistic studies in models of ultraviolet (UV) radiation-induced skin carcinogenesis; (2) clinical studies of immunohistochemical surrogate endpoint biomarkers in high-risk patients; and (3) randomised, placebo-controlled phase I, II and III clinical chemoprevention trials. Recent clinical results validate this development model. Molecular targets of chemopreventive strategies for melanoma and non-melanoma skin cancers include the ras and activator protein-1 (AP-1) signal transduction pathways. A transgenic murine melanoma model has been developed for evaluating potential agents in vivo. Agents at various stages of study include the green tea catechin epigallocatechin gallate (EGCG), the limonene derivative perillyl alcohol, the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO), selenium, retinoids and salicylates. New chemopreventive agents that can be used to complement sunscreens may result in decreased incidence, morbidity and mortality of skin cancer.

Determination of singlet oxygen-specific versus radical-mediated lipid peroxidation in photosensitized oxidation of lipid bilayers: effect of beta-carotene and alpha-tocopherol.

Photosensitized oxidation reactions damage tissue by catalyzing the formation of oxyradicals and singlet oxygen. beta-Carotene is hypothesized to exert photoprotective effects by quenching singlet oxygen formed by Type II reactions and by scavenging free radicals formed by Type I reactions. beta-Carotene antioxidant mechanisms were studied in a phospholipid membrane model of photooxidation with a new isotope dilution gas chromatography-mass spectrometry (GC-MS) assay that quantitatively distinguishes singlet oxygen-mediated and radical-mediated lipid peroxidation. This assay measures 9- and 10-hydroxylinoleate methyl esters and was used to generate photooxidation profiles for the photosensitizers methylene blue, Rose Bengal, and tetraphenylporphine. These profiles indicate a shift from Type II to Type I photooxidation mechanisms in later stages of photooxidation. beta-Carotene (0.45 mol %) inhibited singlet oxygen-mediated lipid peroxidation at early stages of methylene blue-sensitized photooxidation. Production of radical-mediated products increased faster than singlet oxygen-mediated products at later stages. beta-Carotene-5,8-endoperoxide, a specific marker for singlet oxygen oxidation of beta-carotene in solution, was unstable under the incubation conditions and was not detected in this system. alpha-Tocopherol (0.45 mol %) was ineffective in inhibiting photosensitized lipid peroxidation, whereas 4.5 mol % alpha-tocopherol inhibited almost all radical-mediated lipid peroxidation as well as early-stage singlet oxygen-mediated lipid peroxidation. Cumene hydroperoxide stimulated radical-mediated lipid peroxidation, indicating that accumulation of hydroperoxides from Type II photooxidation may enhance Type I reactions. These data suggest that singlet oxygen quenching, rather than radical scavenging reactions, accounts for the photoprotective actions of beta-carotene.

Antioxidant actions of beta-carotene in liposomal and microsomal membranes: role of carotenoid-membrane incorporation and alpha-tocopherol.

beta-Carotene and other carotenoids are widely regarded as biological antioxidants. However, recent clinical trials indicate that beta-carotene supplements are not effective in disease prevention and raise questions about the biological significance of carotenoid antioxidant actions. To further explore this issue, we have reevaluated the antioxidant actions of beta-carotene in liposomal and biological membrane systems. In dilinoleoylphosphatidylcholine liposomes in which 0.35 mol % beta-carotene was incorporated into the bilayer during liposome preparation, the carotenoid inhibited lipid peroxidation initiated by 10 mm azobis[amidinopropane HCl] (AAPH). In carotenoid-free liposome suspensions to which the same amount of beta-carotene was added, no antioxidant effect was observed. Supplementation of rat liver microsomes with beta-carotene in vitro yielded microsomes containing 1.7 nmol beta-carotene mg-1 and 0.16 nmol alpha-tocopherol mg-1 microsomal protein. In beta-carotene supplemented microsomes incubated with 10 mm AAPH under an air atmosphere, lipid peroxidation did not occur until alpha-tocopherol was depleted by approximately 60%. beta-Carotene exerted no apparent antioxidant effect and was not significantly depleted in the incubations. Similar results were obtained when the incubation was done at 3.8 torr O2. In liver microsomes from Mongolian gerbils fed beta-carotene-supplemented diets, beta-carotene levels were 16-37% of alpha-tocopherol levels. The kinetics of AAPH-induced lipid peroxidation were no different in beta-carotene-supplemented microsomes than in microsomes from unsupplemented animals, although the kinetics of beta-carotene and alpha-tocopherol depletion were similar. The results indicate that beta-carotene is ineffective as an antioxidant when added to preformed lipid bilayer membranes and that alpha-tocopherol is a much more effective membrane antioxidant than beta-carotene, regardless of the method of carotenoid-membrane incorporation. These results support a reevaluation of the proposed antioxidant role for beta-carotene in biological membranes.

Isolation and identification of singlet oxygen oxidation products of beta-carotene.

Singlet oxygen is a highly reactive form of oxygen produced by many toxic photosensitizers. beta-Carotene quenches singlet oxygen catalytically through a very efficient physical reaction. However, concomitant chemical reactions during photosensitized oxidations consume beta-carotene. To investigate the hypothesis that chemical reactions with singlet oxygen consume beta-carotene, we characterized products of the photosensitized oxidation of beta-carotene. beta-Carotene and the photosensitizer rose bengal were dissolved in toluene/methanol (85:15 v/v), which was bubbled with O2 and illuminated with a quartz-halogen lamp for 30 min at 5 degrees C. Reaction products were analyzed by reverse-phase HPLC, UV-vis spectrophotometry, and mass spectrometry. beta-Carotene oxidation products were identified as beta-ionone, beta-apo-14'-carotenal, beta-apo-10'-carotenal, beta-apo-8'-carotenal, and beta-carotene 5,8-endoperoxide. Formation of these products was dependent on the presence of the photosensitizer. The products apparently were formed from the action of singlet oxygen rather than by photochemically-initiated beta-carotene autoxidation, since suppression of autoxidation by equimolar alpha-tocopherol did not diminish product formation. beta-Carotene autoxidation initiated by 2,2'-azobis(2,4-dimethylvaleronitrile), which generates peroxyl radicals, yielded a different product distribution than that from photosensitized oxidation. Specific products formed by singlet oxygen oxidation of beta-carotene may serve as markers for singlet oxygen quenching in biological systems.