Abstract B59: A combination of resveratrol and ursolic acid produces synergistic inhibitory effects on markers of skin tumor promotion

Abstract

Abstract Resveratrol (RES), found in grapes and Ursolic Acid (UA), found in rosemary and apples, delay the onset and reduce the number of experimentally-induced skin tumors in mice and inhibit the oncogenic Akt/mammalian target of rapamycin (Akt/mTOR) and Nuclear Factor kappa B (NF\#954;B) pathways. Based on their similar downstream effects via different proximal targets, we hypothesized that a combination treatment of RES and UA would synergize to produce a stronger inhibitory effect on skin tumor promotion. Methods: The dorsal skin of FVB mice (n=8) were shaved and treated topically twice per week for 2 weeks with sub-optimal doses of 2 μmol UA, 2 μmol RES, or a combination of both in 200 μL acetone. Each treatment was followed 30 minutes later with topical application of 3.4 nmol of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in 200 μL acetone. Animals were sacrificed either 6 h (Western blotting) or 48 h (histology) after the final TPA treatment. The skins of five mice per group were removed and the epidermis was collected by scraping for Western blotting. For immunohistochemical (IHC) analysis of epidermal proliferation three mice per group were i.p. injected with 100 mg/kg Bromodeoxyuridine (BrdU) in PBS 30 min. prior to sacrifice. Mouse skin from treated areas was fixed in formalin, paraffin embedded, and analyzed via IHC. Results: RES and UA in combination had a stronger effect on hallmarks of skin tumor promotion than was expected based on the sum of their individual inhibitory effects, indicating synergism between RES and UA. RES and UA in combination synergistically inhibited TPA-induced epidermal thickening (80.2% inhibition vs 66.1 % expected) and epidermal proliferation (100.0% inhibition vs 90.0% expected). Western blotting revealed that components of the NF\#954;B and Akt/mTOR pathways were synergistically downregulated by the RES + UA combination in mouse epidermis. TPA-induced Akt (thr308) phosphorylation (86.0% inhibition vs 26.6% expected) and NFkB subunit p65 (ser536) phosphorylation (100.0% inhibition vs 73.3% expected) were suppressed to a much stronger degree with the combination treatment than that predicted. Similar results were seen for other pathway components, such as p70S6K and ribosomal S6. The synergistic activities of RES and UA were also manifest in the HaCaT human keratinocyte cell line. Cells were treated with sub-optimal doses of RES, UA, or RES + UA and stimulated with 10 ng/ml human tumor necrosis factor alpha (TNFα) for 30 min. and cell lysates were analyzed via Western blotting. TNFα-mediated phosphorylation of p65 was not inhibited by 25 μM RES or 0.1 μM −1 μM UA, but combinations of RES + UA resulted in strong synergistic inhibition of p65 phosphorylation (>66% inhibition vs 0% expected). Also, when HaCaT cells were treated with NFkB- and Akt/mTOR-inhibitory doses of RES (150 μM-200 μM) and UA (5 μM-10 μM), a strong increase (5 fold) in phosphorylation/activation of the energy sensing AMP-activated protein kinase (AMPK) was observed by Western blotting. AMPK also inhibits NF\#954;B and Akt/mTOR activities in other systems, suggesting that AMPK activation may function as a mediator of the synergistic anti-tumor promoting effects of RES and UA. Conclusions: These results indicate that UA and RES synergize to inhibit markers of tumor promotion in both in vivo and in vitro skin models. Future studies will further elucidate the synergistic mechanism of RES and UA and also determine if RES and UA have a synergistic preventive effect on skin tumor promotion during two-stage skin carcinogenesis in vivo. Supported by NIH grants CA079065, supplemental CA079065-10S1 (ARRA), CA129409 and CA037111. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B59.