Recent studies indicate that type I collagen, an ECM protein shown to be highly up-regulated in pancreatic cancer, promotes the malignant phenotype in vitro and in vivo. We have recently demonstrated that the a2?1 integrin specifically mediates pancreatic cancer cell interactions with type I collagen, and that this integrin-ECM interaction is Mg2+-dependent and inhibited by Ca2+. These observations are similar to wound healing, which strongly parallels the pancreatic cancer paradigm. During wound healing, shifts in the concentrations of extracellular Mg2+ and Ca2+ occur early in the process, activating the a2?1 integrin-mediated migration of various cell types on type I collagen, including keratinocytes. This divalent cation shift is characterized by increased Mg2+ and decreased Ca2+. Similar shifts are also likely in pancreatic cancer, as pancreas juice contains 1200-fold more Mg2+ than Ca2+. With ductal basement membranes either discontinuous or absent in pancreatic cancer, pancreas juice would be expected to leak into the tumor microenvironment. Additionally and similar to wound healing, solid tumors are characterized by increased Mg2+ load. Collectively, these data suggest the hypothesis where pathophysiological changes in the concentrations of Mg2+ and Ca2+ activate the a2?1 integrin-mediated malignant phenotype in pancreatic cancer. Our published and preliminary data indicate that pancreatic cancer cells attach to type I collagen maximally when Mg2+ is greater than about 1mM, and that addition of increasing Ca2+ reduces this a2?1 integrin-mediated adhesion. These divalent cation-mediated effects are reversible in that previous cell attachment to type I collagen in Mg2+ can be reversed by the addition of Ca2+, and vice versa. We also demonstrate that cells migrate and proliferate on type I collagen in Mg2+ alone, but maximally when the Mg2+ to Ca2+ ratio is greater than one. In this proposal, we will pursue the following Specific Aim: We will utilize our red fluorescent protein orthotopic mouse model, in which cancer cells are labeled with RFP, to examine the use of divalent cations as surgical adjuvant therapy during pancreatic cancer resection and as therapy in the treatment of pancreatic cancer. We will conduct in vivo experiments in our established RFP orthotopic mouse model of pancreatic cancer, which recapitulates human disease. These experiments are designed to examine the inhibitory effects of divalent cations used as adjuvant therapy during surgical resection of established human pancreatic cancer tumors, and also as possible therapy. We will also conduct in vivo inhibition studies using function-blocking monoclonal antibodies directed against specific integrin subunits to determine which integrins are specifically impacted by divalent cation therapy. These studies have the potential to improve survival rates for pancreatic cancer following surgical resection, and also provide a novel therapeutic approach to this recalcitrant disease.

Public Health Relevance

Approximately 30,000 new cases of adenocarcinoma of the pancreas, the fourth leading cause of cancer related mortality in the United States, will be diagnosed each year with only 1 to 4% of patients surviving 5 years after their initial diagnosis. Surgical resection, radiation therapy and gemcitabine chemotherapy generally result in only a few months of extended life. The need for improved therapy for pancreatic cancer patients is urgently needed.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Exploratory/Developmental Grants (R21)
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Tumor Microenvironment Study Section (TME)
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Forry, Suzanne L
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University of California San Diego
Schools of Medicine
La Jolla
United States
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Grzesiak, John J; Tran Cao, Hop S; Burton, Douglas W et al. (2011) Knockdown of the ?(1) integrin subunit reduces primary tumor growth and inhibits pancreatic cancer metastasis. Int J Cancer 129:2905-15
Grzesiak, John J; Vargas, Fabian; Bouvet, Michael (2010) Divalent cations modulate alpha2beta1 integrin-mediated malignancy in a novel 3-dimensional in vitro model of pancreatic cancer. Pancreas 39:904-12
McElroy, Michele K; Kaushal, Sharmeela; Tran Cao, Hop S et al. (2009) Upregulation of thrombospondin-1 and angiogenesis in an aggressive human pancreatic cancer cell line selected for high metastasis. Mol Cancer Ther 8:1779-86