Cancer of the upper aerodigestive tract (UADT), including esophageal and oral cancer, is a major cause of cancer deaths worldwide. In humans, dietary zinc deficiency is associated with an increased risk of esophageal and oral cancer. In rodents, zinc deprivation creates a precancerous condition in the UADT by causing increased cell proliferation and extensive gene expression changes, including upregulation of cyclooxygenase-2 (COX-2), an enzyme overexpressed in a variety of human premalignant and malignant lesions. Thus, zinc deficiency promotes UADT carcinogenesis by 4-nitroquinoline 1-oxide (NQO) and esophageal carcinogenesis by N-nitrosomethylbenzylamine (NMBA) in rodents. Zinc replenishment reverses cell proliferation, stimulates apoptosis, corrects COX-2 overexpression in esophageal epithelium, and inhibits carcinogenesis. We have obtained new data showing that (i) transcription factor NF-kappaB and COX-2 are co-overexpressed in zinc deficient (ZD) rat esophagi;(ii) zinc-deficient COX-2 null mice do not show the expected reduction in NMBA-induced tumor yield;and (iii) celecoxib, a COX-2 selective inhibitor, given singly to ZD rats formerly treated with NQO, is not as effective in tumor prevention as treatments that includes zinc. We propose that dietary zinc plays critical roles in UADT cancer initiation and chemoprevention and will examine the mechanisms whereby zinc affects these processes in vivo by the following interrelated AIMS: 1) to define the link between NF-kappaB and COX-2 induction in rat esophagus under in vivo zinc deficit by determining whether inhibitors targeting the kappaB kinase (IKK)/NF-kappaB activation pathway, including bortezomib, PS-1145, and NF-kappaB p65 small interfering (si)RNA are effective in knocking- down COX-2 expression. Effects on COX-2 expression, proliferation, and apoptosis will be compared with effects of zinc replenishment;2) to determine the mechanism whereby zinc deficiency increases NMBA- induced forestomach carcinogenesis in COX-2 null mice, by investigating signals in arachidonic acid metabolism, independent of COX-2;3) to investigate cancer prevention in the ZD rat UADT cancer model by evaluating efficacy and assessing biomarker modulating effects of zinc supplementation;zinc in combination with low doses of curcumin (inhibitor of NF-kappaB), zileuton (inhibitor of 5-LOX), and with low doses of dual treatment of inhibitors. A combination of zinc and low doses of inhibitors might be effective in prevention without the risk of the side effects associated with high doses of these agents. We will evaluate in lesions the localization of specific proliferation, apoptosis, and other relevant markers by immunohistochemistry. We will then use an appropriate subset of these markers as surrogate endpoints to assess the efficacy of each chemotherapeutic regimen. We will also compare gene expression changes caused by treatments with zinc or zinc plus inhibitors. The results of these studies will provide a new understanding of the role of dietary zinc in UADT carcinogenesis, as well as a basis for novel dietary approaches for the chemoprevention of these deadly cancers.
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