Effects of the tropical ginger compound,1’-acetoxychavicol acetate, against tumor promotion in K5.Stat3C transgenic mice

Effects of the tropical ginger compound, 1’-acetoxychavicol acetate, against tumor promotion in K5.Stat3C transgenic mice Batra et al. Batra et al. Journal of Experimental & Clinical Cancer Research 2012, 31:57 http://www.jeccr.com/content/31/1/57 Batra et al. Journal of Experimental & Clinical Cancer Research 2012, 31:57 http://www.jeccr.com/content/31/1/57 RESEARCH Open Access Effects of the tropical ginger compound, 1’-acetoxychavicol acetate, against tumor promotion in K5.Stat3C transgenic mice Vinita Batra1,5, Zanobia Syed2,5, Jennifer N Gill2,5, Malari A Coburn1,5, Patrick Adegboyega3,5, John DiGiovanni6, J Michael Mathis4,5, Runhua Shi7,5, John L Clifford2,5 and Heather E Kleiner-Hancock1,5* Abstract The purpose of the current study was to determine whether a tropical ginger derived compound 1’-acetoxychavicol acetate (ACA), suppresses skin tumor promotion in K5.Stat3C mice. In a two-week study in which wild-type (WT) and K5.Stat3C mice were co-treated with either vehicle, ACA, galanga extract, or fluocinolone acetonide (FA) and tetradecanoyl phorbol acetate (TPA), only the galanga extract and FA suppressed TPA-induced skin hyperproliferation and wet weight. None of these agents were effective at suppressing p-Tyr705Stat3 expression. However, ACA and FA showed promising inhibitory effects against skin tumorigenesis in K5.Stat3C mice. ACA also suppressed phospho-p65 NF-κB activation, suggesting a potential mechanism for its action. Keywords: NF-κB, Stat3, Squamous cell carcinoma, Carcinogenesis, TPA, Tropical ginger Introduction An alarming rate of increase in the incidence of nonmelanoma skin cancer (NMSC) is observed worldwide [1]. Within the United States itself, it has been estimated that about 1.7 million new cases of all forms of skin cancer are expected to be diagnosed each year [2]. To investigate the underlying pathophysiology of skin carcinogenesis, the multistage model delineates the cellular, biochemical and molecular processes involved in the various stages of skin cancer development [3-5]. Application of tumor promoters to initiated cells can induce epigenetic changes in the skin which culminate into visible clonal outgrowths known as papillomas [5-7]. Although the exact mechanism of action of tumor promotion remains unclear, sustained hyperplasia and cellular proliferation in the epidermis correlates with the tumor promoting activity. Moreover, treatment with tetradecanoyl phorbol acetate (TPA) can alter signaling of nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription 3 (Stat3) signaling in the * Correspondence: 1 Department of Pharmacology, Toxicology & Neuroscience, Louisiana State University Health Sciences Center, Shreveport, LA, USA 5 Feist-Weiller Cancer Center, Shreveport, LA, USA Full list of author information is available at the end of the article process of skin carcinogenesis [8]. Stat3 is a transcription factor that plays a critical role in the control of cell proliferation, survival and angiogenesis, all hallmarks of malignancy [9]. Stat3 activity is constitutive in several malignant cell types and is required for initiation, promotion and progression to a more malignant phenotype in squamous cell carcinomas of the skin (SCC) [8,10-15]. The critical role of Stat3 in skin tumor development was further supported by data obtained from the K5.Stat3C transgenic mouse model in which the DiGiovanni and Clifford research groups expressed the Stat3C protein in skin under the control of the keratin-5 promoter [11]. Stat3C is a constitutively active mutant of Stat3 that dimerizes through formation of covalent disulfide linkages between cysteines instead of phosphotyrosines [16]. These mice have a skin phenotype closely resembling psoriasis in humans and, when subjected to the two-stage skin chemical carcinogenesis protocol, rapidly developed carcinomas, bypassing the papilloma stage that is normally observed in this model [17]. The transcription factor NF-κB is also activated during inflammation and carcinogenesis [18]. The activated form of NF-κB triggers transcription of specific genes involved in proliferation (cyclin D1, c-myc), angiogenesis (VEGF), antiapoptosis (survivin, BclXL, FLIP) and © 2012 Batra et al. licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Batra et al. Journal of Experimental & Clinical Cancer Research 2012, 31:57 http://www.jeccr.com/content/31/1/57 invasion (MMP9, ICAM-1) proteins [19]. NF-κB activation has been strongly implicated in many types of cancer [18] including skin SCCs [20]. Ablation of β-catenin in murine skin grafts resulted in up-regulation of NF-κB target genes [21]. The skin grafts, which resembled human grade III skin SCCs, were hyperproliferative, the layers of epidermis were disorganized, and contained invasive keratinocytes [21]. Kobielak and Fuchs analyzed human skin SCCs and found 33/40 with low/no β-catenin, and nuclear, activated NF-κB, also characterized by inflammation and interestingly, nuclear phosphorylated Stat3 [21]. Finally, many NF-κB regulated genes are also induced by Stat3 and the interaction between these proteins and their signaling pathways may be involved in the different phases of skin carcinogenesis. Non-specific drug-related side effects of pharmaceuticals hamper their clinical efficacy and underscore the need for investigating better treatment options. Cruciferous vegetables, tomatoes, garlic, citrus fruits and beverages like black tea and green tea contain phytochemicals such as resveratrol, flavonoids, and lycopene, that have been shown to afford protection against skin cancer development in vivo [22-24]. Easy accessibility and cost-effectiveness provide a reasonable rationale to explore phytochemicals for mechanism-based interventions in cancer management. ACA is a natural component of traditional Thai condiments found in the seeds, rhizomes or in the root of the tropical ginger [25]. ACA suppressed carcinogenesis in a number of rodent models, including the two-stage mouse skin model [26,27], the 4-nitroquinoline oxide oral carcinogenesis model [28,29], and the azoxymethane colon carcinogenesis model [30,31]. In the skin model, pre-treatment of mice with ACA during TPA treatment in 7, 12-dimethylbenz [a] anthracene (DMBA)-initiated mice was remarkably effective, inhibiting skin tumor promotion by 44% and 90% at 1.6 nmol and 160 nmol doses, respectively [27]. Some of the proposed anticarcinogenic mechanisms of ACA included the ability to inhibit ornithine decarboxylase (ODC) activity, inhibition of xanthine oxidase and suppression of the formation of superoxide anion, induction of detoxifying enzymes, and causing apoptosis in cancer cells [29,30,32-35]. We found that ACA induced apo (...truncated)