Chemoprevention of upper aerodigestive tract cancer by dietary zinc

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Though cancer mortality rates have declined worldwide since the mid 1980s, upper aerodigestive (UADT) cancer, including esophageal squamous cell cancer (ESCC, predominant subtype of esophageal cancer) and tongue SCC (major site of oral cancer), remains deadly. Thus, clarification of pathogenetic mechanisms and new prevention strategies are urgently needed. Global dietary zinc (Zn) deficiency (ZD) is estimated to affect 30% of the population (4-73% across subregions), with higher rates in developing countries. Importantly, ZD increases the risk of UADT cancer. In the past six years we have made significant progress toward understanding the molecular role of Zn in UADT cancer development and prevention. Using unbiased whole genome expression profiling, bioinformatics, molecular pathology, and our well-characterized animal models, we have found that: (i) short-term dietary ZD in rats induces overexpression of proinflammation mediators, S100a8 and S100a9, associated with esophageal hyperplasia. Zn modulates the link between S100A8-RAGE interaction and downstream NF-kB/COX-2 signaling, evidence that Zn regulates an inflammatory pathway in early esophageal carcinogenesis; (ii) prolonged ZD induces a cancer-associated inflammatory gene signature that fuels ESCC and oral Zn replenishment reverses this signature and prevents ESCC. (iii) Zn- supplementation suppresses UADT tumor development in rats and tumor suppressor-deficient mouse strains on a Zn-sufficient diet through attenuation of inflammation, evidence that Zn has chemopreventive effects even in Zn-sufficient subjects; (iv) Using the nanoStringTM technology, we discovered that dietary ZD alters microRNA expression in a tissue-specific manner. The inflammatory ZD esophagus has a distinct microRNA gene signature with overexpression of oncogenic miR-31 and miR-21, resembling that in human ESCC/tongue SCC. In ZD rats esophageal miR-31 and miR-21 levels are directly associated with the appearance of ESCC. In situ hybridization study of miR-31 and miR-21 expression in rat/human tongue SCC reveals that their upregulation is cell type-specific and is Zn-therapy responsive. In Aim 1, we test the hypothesis that dietary ZD bypasses the requirement for RAGE-signaling in sustaining inflammation and promotes forestomach carcinogenesis in Rage-/- mice by activating alternative inflammatory pathway(s). In Aim 2, we dissect dietary Zn modulation of gene expression (microRNA, mRNA) in tongue cancer development and regression in carcinogen-treated rats. In Aim 3, we test the hypothesis that in vivo inhibition of miR-21 in ZD rats that is induced by dietary ZD in stroma might offset the inflammation-promoting effect of ZD and inhibit ESCC. In Aim 4, we determine the requirement for Zn in the prevention of UADT cancer by investigating the dose response relationship between dietary ZD and alterations of inflammation-related mRNA and microRNA expression in the rat esophagus. The data from the proposed studies should advance our knowledge of how Zn affects genes (mRNA and microRNAs) related to inflammation in the development and prevention of UADT cancer.
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