Jennifer M. Thomas-Ahner

Gender Differences in UVB-Induced Skin Carcinogenesis, Inflammation, and DNA Damage

The American Cancer Society reports the incidence of squamous cell carcinoma in males to be thrice the incidence in females. This increased squamous cell carcinoma incidence has been attributed to men accumulating more sun exposure and using less sun protection than women. To date, there have been no controlled studies examining the effect of gender on skin tumor development following equal doses of UVB. Gender differences in UVB-induced skin carcinogenesis were examined using the Skh-1 mouse model. After chronic exposure to equal doses of UVB, male mice developed tumors earlier and had more tumors than female mice; tumors in male mice tended to be larger, and the total tumor burden was greater than in females. In addition, tumors in males were of more advanced histologic grade compared with those of female mice. To evaluate the contribution of differences in inflammation and DNA damage to differences in skin carcinogenesis, male and female Skh-1 mice were exposed once to 2,240 J/m(2) UVB and examined 48 h after exposure. Surprisingly, male mice developed less of an inflammatory response, as determined by skin fold thickness and myeloperoxidase activity, compared with females. Interestingly, male mice showed more cutaneous oxidative DNA damage than the females and lower antioxidant levels. These results show a gender bias in skin carcinogenesis and suggest that the gender difference in tumor development is more influenced by the extent of oxidative DNA damage and antioxidant capacities than by inflammatory response.

Definition of a FoxA1 Cistrome that is crucial for G1 to S-phase cell-cycle transit in castration-resistant prostate cancer.

The enhancer pioneer transcription factor FoxA1 is a global mediator of steroid receptor (SR) action in hormone-dependent cancers. In castration-resistant prostate cancer (CRPC), FoxA1 acts as an androgen receptor cofactor to drive G₂ to M-phase cell-cycle transit. Here, we describe a mechanistically distinct SR-independent role for FoxA1 in driving G₁ to S-phase cell-cycle transit in CRPC. By comparing FoxA1 binding sites in prostate cancer cell genomes, we defined a codependent set of FoxA1-MYBL2 and FoxA1-CREB1 binding sites within the regulatory regions of the Cyclin E2 and E2F1 genes that are critical for CRPC growth. Binding at these sites upregulate the Cyclin E2 and Cyclin A2 genes in CRPC but not in earlier stage androgen-dependent prostate cancer, establishing a stage-specific role for this pathway in CRPC growth. Mechanistic investigations indicated that FoxA1, MYBL2, or CREB1 induction of histone H3 acetylation facilitated nucleosome disruption as the basis for codependent transcriptional activation and G₁ to S-phase cell-cycle transit. Our findings establish FoxA1 as a pivotal driver of the cell-cycle in CRPC which promotes G₁ to S-phase transit as well as G₂ to M-phase transit through two distinct mechanisms.

Sirolimus reduces the incidence and progression of UVB-induced skin cancer in SKH mice even with co-administration of cyclosporine A.

Transplant immunosuppressants have been implicated in the increased incidence of non-melanoma skin cancer in transplant recipients, most of whom harbor considerable UVB-induced DNA damage in their skin prior to transplantation. This study was designed to evaluate the effects of two commonly used immunosuppressive drugs, cyclosporine A (CsA) and sirolimus (SRL), on the development and progression of UVB-induced non-melanoma skin cancer. SKH-1 hairless mice were exposed to UVB alone for 15 weeks, and then were treated with CsA, SRL, or CsA+SRL for 9 weeks following cessation of UVB treatment. Compared with vehicle, CsA treatment resulted in enhanced tumor size and progression. In contrast, mice treated with SRL or CsA+SRL had decreased tumor multiplicity, size, and progression compared with vehicle-treated mice. CsA, but not SRL or combined treatment, increased dermal mast cell numbers and TGF-beta1 levels in the skin. These findings demonstrate that specific immunosuppressive agents differentially alter the cutaneous tumor microenvironment, which in turn may contribute to enhanced development of UVB-induced skin cancer in transplant recipients. Furthermore, these results suggest that CsA alone causes enhanced growth and progression of skin cancer, whereas co-administration of SRL with CsA causes the opposite effect. JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article please go to http://network.nature.com/group/jidclub

Clinically relevant immunosuppressants influence UVB-induced tumor size through effects on inflammation and angiogenesis.

Immunosuppressive therapies allow long‐term patient and transplant survival, but are associated with increased development of UV‐induced skin cancers, particularly squamous cell carcinomas. The mechanisms by which CsA, MMF, tacrolimus (TAC) or sirolimus (SRL), alone or in dual combinations, influence tumor development and progression are not completely understood. In the current study, chronically UV‐exposed mice treated with SRL alone or in combination with CsA or TAC developed more tumors than mice treated with vehicle or other immunosuppressants, but the tumors were significantly smaller and less advanced. Mice treated with CsA or TAC developed significantly larger tumors than vehicle‐treated mice, and a larger percentage in the CsA group were malignant. The addition of MMF to CsA, but not to TAC, significantly reduced tumor size. Immunosuppressant effects on UVB‐induced inflammation and tumor angiogenesis may explain these findings. CsA enhanced both UVB‐induced inflammation and tumor blood vessel density, while MMF reduced inflammation. Addition of MMF to CsA reduced tumor size and vascularity. SRL did not affect inflammation, but significantly reduced tumor vascularity. Thus the choice of immunosuppressants has important implications for tumor number, size and progression, likely due to the influence of immunosuppressants on UVB‐induced inflammation and angiogenesis.

Tomato-based food products for prostate cancer prevention: what have we learned?

Evidence derived from a vast array of laboratory studies and epidemiological investigations have implicated diets rich in fruits and vegetables with a reduced risk of certain cancers. However, these approaches cannot demonstrate causal relationships and there is a paucity of randomized, controlled trials due to the difficulties involved with executing studies of food and behavioral change. Rather than pursuing the definitive intervention trials that are necessary, the thrust of research in recent decades has been driven by a reductionist approach focusing upon the identification of bioactive components in fruits and vegetables with the subsequent development of single agents using a pharmacologic approach. At this point in time, there are no chemopreventive strategies that are standard of care in medical practice that have resulted from this approach. This review describes an alternative approach focusing upon development of tomato-based food products for human clinical trials targeting cancer prevention and as an adjunct to therapy. Tomatoes are a source of bioactive phytochemicals and are widely consumed. The phytochemical pattern of tomato products can be manipulated to optimize anticancer activity through genetics, horticultural techniques, and food processing. The opportunity to develop a highly consistent tomato-based food product rich in anticancer phytochemicals for clinical trials targeting specific cancers, particularly the prostate, necessitates the interactive transdisciplinary research efforts of horticulturalists, food technologists, cancer biologists, and clinical translational investigators.

Anti-tumorigenicity of dietary α-mangostin in an HT-29 colon cell xenograft model and the tissue distribution of xanthones and their phase II metabolites

SCOPE This study investigated the in vivo and in vitro activity of α-mangostin (α-MG), the most abundant xanthone in mangosteen pericarp, on HT-29 cell tumorigenicity, proliferation, and several markers of tumor cell activity, as well as the profile and amounts of xanthones in serum, tumor, liver, and feces. METHODS AND RESULTS Balb/c nu/nu mice were fed either control diet or diet containing 900 mg α-MG/kg. After 1 week of acclimation to diet, mice were injected subcutaneously with HT-29 cells and fed the same diets ad libitum for an additional 2 or 4 weeks. After 2 and 4 weeks, tumor mass and the concentrations of BcL-2 and β-catenin in tumors of mice fed diet with α-MG were significantly less than in mice fed control diet. Xanthones and their metabolites were identified in serum, tumor, liver, and feces. In vitro treatment of HT-29 cells with α-MG also inhibited cell proliferation and decreased expression of BcL-2 and β-catenin. CONCLUSION Our data demonstrate that the anti-neoplastic effect of dietary α-MG is associated with the presence of xanthones in the tumor tissue. Further investigation of the impact of beverages and food products containing xanthones on the prevention of colon cancer or as complementary therapy is merited.

Inhibition of Bladder Cancer by Broccoli Isothiocyanates Sulforaphane and Erucin: Characterization, Metabolism and Interconversion

SCOPE Epidemiologic evidence suggests diets rich in cruciferous vegetables, particularly broccoli, are associated with lower bladder cancer risk. Our objectives are to investigate these observations and determine the role of isothiocyanates in primary or secondary bladder cancer prevention. METHODS AND RESULTS We initially investigate the mechanisms whereby broccoli and broccoli sprout extracts and pure isothiocyanates inhibit normal, noninvasive (RT4), and invasive (J82, UMUC3) human urothelial cell viability. Sulforaphane (IC(50) = 5.66 ± 1.2 μM) and erucin (IC(50) = 8.79 ± 1.3 μM) are found to be the most potent inhibitors and normal cells are least sensitive. This observation is associated with downregulation of survivin, epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2/neu), G(2) /M cell cycle accumulation, and apoptosis. In a murine UMUC3 xenograft model, we fed semipurified diets containing 4% broccoli sprouts, or 2% broccoli sprout isothiocyanate extract; or gavaged pure sulforaphane or erucin (each at 295 μmol/kg, similar to dietary exposure); and report tumor weight reduction of 42% (p = 0.02), 42% (p = 0.04), 33% (p = 0.04), and 58% (p < 0.0001), respectively. Sulforaphane and erucin metabolites are present in mouse plasma (micromolar range) and tumor tissue, with N-acetylcysteine conjugates as the most abundant. Interconversion of sulforaphane and erucin metabolites was observed. CONCLUSION This work supports development of fully characterized, novel food products containing broccoli components for phase I/II human studies targeting bladder cancer prevention.

Agonist and antagonist switch DNA motifs recognized by human androgen receptor in prostate cancer

Human transcription factors recognize specific DNA sequence motifs to regulate transcription. It is unknown whether a single transcription factor is able to bind to distinctly different motifs on chromatin, and if so, what determines the usage of specific motifs. By using a motif‐resolution chromatin immunoprecipitation‐exonuclease (ChIP‐exo) approach, we find that agonist‐liganded human androgen receptor (AR) and antagonist‐liganded AR bind to two distinctly different motifs, leading to distinct transcriptional outcomes in prostate cancer cells. Further analysis on clinical prostate tissues reveals that the binding of AR to these two distinct motifs is involved in prostate carcinogenesis. Together, these results suggest that unique ligands may switch DNA motifs recognized by ligand‐dependent transcription factors in vivo. Our findings also provide a broad mechanistic foundation for understanding ligand‐specific induction of gene expression profiles.

CCI-779 Inhibits Cell-Cycle G2/M Progression and Invasion of Castration Resistant Prostate Cancer via Attenuation of UBE2C Transcription and mRNA Stability

The cell-cycle G(2)-M phase gene UBE2C is overexpressed in various solid tumors including castration-resistant prostate cancer (CRPC). Our recent studies found UBE2C to be a CRPC-specific androgen receptor (AR) target gene that is necessary for CRPC growth, providing a potential novel target for therapeutic intervention. In this study, we showed that the G(1)-S cell-cycle inhibitor-779 (CCI-779), an mTOR inhibitor, inhibited UBE2C mRNA and protein expression in AR-positive CRPC cell models abl and C4-2B. Treatment with CCI-779 significantly decreased abl cell proliferation in vitro and in vivo through inhibition of cell-cycle progression of both G(2)-M and G(1)-S phases. In addition, exposure of abl and C4-2B cells to CCI-779 also decreased UBE2C-dependent cell invasion. The molecular mechanisms for CCI-779 inhibition of UBE2C gene expression involved a decreased binding of AR coactivators SRC1, SRC3, p300, and MED1 to the UBE2C enhancers, leading to a reduction in RNA polymerase II loading to the UBE2C promoter, and attenuation of UBE2C mRNA stability. Our data suggest that, in addition to its ability to block cell-cycle G(1) to S-phase transition, CCI-779 causes a cell-cycle G(2)-M accumulation and an inhibition of cell invasion through a novel UBE2C-dependent mechanism, which contributes to antitumor activities of CCI-779 in UBE2C overexpressed AR-positive CRPC.

Topical treatment with OGG1 enzyme affects UVB-induced skin carcinogenesis.

Nonmelanoma skin cancer resulting from UVB exposure is a large and growing problem in the United States. Production of reactive oxygen species (ROS) during the UVB‐induced inflammatory response results in the formation of oxidative DNA adducts such as 8‐hydroxy‐2‐deoxyguanine (8‐oxo‐dG), which have been shown to contribute to the development of this cancer. The 8‐oxoguanine DNA glycosylase (OGG1) enzyme repairs 8‐oxo‐dG adducts, suggesting that enhancing its activity in the skin might increase 8‐oxo‐dG repair thus preventing skin cancer development. We therefore used the SKH‐1 murine model to examine the effect of topically applied OGG1 on UVB‐induced skin cancer development. Mice were exposed three times weekly to UVB followed immediately by topical treatment with a formulation of liposome‐encapsulated OGG1 enzyme for 25 weeks. While this treatment did not affect UVB‐induced tumor multiplicity, it did reduce tumor size and dramatically reduced tumor progression, as indicated by tumor grade. These results suggest that oxidative DNA damage contributes to the progression of UVB‐induced skin tumors and that a topical formulation containing OGG1, perhaps in conjunction with other DNA repair enzymes such as T4 endonuclease V, could be used in populations at high risk for skin cancer development.