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Caffeine Inhibits Adenosine-Induced Accumulation of Hypoxia-Inducible Factor-1, Vascular Endothelial Growth Factor, and Interleukin-8 Expression in Hypoxic Human Colon Cancer Cells

Department of Clinical and Experimental Medicine, Pharmacology Unit, University of Ferrara, Ferrara, Italy (S.M., A.B., S.G., K.V., C.S., P.A.B.); Department of Human Anatomy, Pharmacology, and Forensic Medicine, Human Anatomy Section, University of Parma, Parma, Italy (P.M.); King Pharmaceuticals R&D, Cary, North Carolina (S.M.L., E.L.); Department of Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy (P.G.B.); and Interdisciplinary Center for the Study of Inflammation, Ferrara, Italy (P.A.B.)

Frequent coffee consumption has been associated with a reduced risk of colorectal cancer in a number of case-control studies. Coffee is a leading source of methylxanthines, such as caffeine. The induction of vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8) is an essential feature of tumor angiogenesis, and the hypoxia-inducible factor-1 (HIF-1) transcription factor is known to be a key regulator of this process. In this study, we investigated the effects of caffeine on HIF-1 protein accumulation and on VEGF and IL-8 expression in the human colon cancer cell line HT29 under hypoxic conditions. Our results show that caffeine significantly inhibits adenosine-induced HIF-1 protein accumulation in cancer cells. We show that HIF-1 and VEGF are increased through A₃ adenosine receptor stimulation, whereas the effects on IL-8 are mediated via the A_2B subtype. Pretreatment of cells with caffeine significantly reduces adenosine-induced VEGF promoter activity and VEGF and IL-8 expression. The mechanism of caffeine seems to involve the inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and Akt, leading to a marked decrease in adenosine-induced HIF-1 accumulation, VEGF transcriptional activation, and VEGF and IL-8 protein accumulation. From a functional perspective, we observe that caffeine also significantly inhibits the A₃ receptor-stimulated cell migration of colon cancer cells. Conditioned media prepared from colon cells treated with an adenosine analog increased human umbilical vein endothelial cell migration. These data provide evidence that adenosine could modulate the migration of colon cancer cells by an HIF-1/VEGF/IL-8-dependent mechanism and that caffeine has the potential to inhibit colon cancer cell growth.

Address correspondence to: Dr. Pier Andrea Borea, Department of Clinical and Experimental Medicine, Pharmacology Section, Via Fossato di Mortara 17-19, 44100 Ferrara, Italy. E-mail: bpa{at}unife.it