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¹ Veterans Affairs Medical Center; ² Department of Medicine, School of Medicine, University of Colorado Health Sciences Center; and ³ University of Colorado Comprehensive Cancer Center, Denver, Colorado

Requests for reprints: Pamela L. Rice, Department of Medicine, A009-151, School of Medicine, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262. Phone: 303-399-8020, ext. 3655; Fax: 303-393-5145. E-mail: pamela.rice{at}uchsc.edu

Colorectal cancer is the second leading cause of cancer mortality in the United States. Substantial human and animal data support the ability of nonsteroidal anti-inflammatory drugs to cause regression of existing colon tumors and prevent new tumor formation. The mechanism by which the nonsteroidal anti-inflammatory drug sulindac prevents tumor growth is poorly understood and seems complex as sulindac can modulate several growth-related signaling pathways. Sulindac metabolites simultaneously (a) increase cellular cyclic GMP and subsequently activate cyclic GMP–dependent protein kinase (PKG); (b) activate c-jun NH₂-terminal kinase (JNK); (c) inhibit extracellular signal–regulated kinase 1/2 (ERK1/2); and (d) decrease ß-catenin protein expression at times and doses consistent with apoptosis. The purpose of this study was to determine if PKG, ERK1/2, JNK, and ß-catenin are independent targets for sulindac in vitro. Pharmacologic activation of PKG with YC-1 increases JNK phosphorylation and induces apoptosis in colon cancer cells without modulating ERK1/2 phosphorylation or ß-catenin protein expression. Inhibition of ERK1/2 with U0126 induces apoptosis but fails to activate JNK phosphorylation or down-regulate ß-catenin protein expression. Cotreatment with U0126 and YC-1 synergistically increases apoptosis in colorectal cancer cells and recapitulates the effects of sulindac treatment on ERK1/2, JNK, and ß-catenin. These results indicate that sulindac metabolites modulate ERK1/2 and PKG pathways independently in colon cancer cells and suggest that the full apoptotic effect of sulindac is mediated by more than one pathway. Using similar combinatorial approaches in vivo may provide more effective, less toxic chemopreventive and chemotherapeutic strategies. Such therapies could dramatically reduce the incidence and death rate from colorectal cancer. [Mol Cancer Ther 2006;5(3):746–54]

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Received 6/24/05; revised 11/21/05; accepted 1/ 5/06.

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