Abstract 837: Novel sulindac derivatives that inhibit colon cancer growth by a COX independent mechanism involving PDE5 inhibition and the suppression of nuclear β-catenin levels

Abstract

Abstract Many colon cancers harbor APC mutations that prevent the proteosomal degradation of oncogenic β-catenin. Previous studies have found that certain nonsteroidal anti-inflammatory drugs (NSAIDs) have the ability to reduce nuclear levels of β-catenin and inhibit tumor cell growth through a cyclooxygenase (COX)-independent mechanism, which might be responsible for their cancer chemopreventive activity. A potential mechanism may involve cGMP phosphodiesterase (PDE) inhibition and the activation of protein kinase G (PKG). In this study we evaluated over 500 novel sulindac derivatives for colon tumor cell growth inhibitory activity. Select compounds were also evaluated for COX and cGMP PDE inhibitory activity to determine which activity is associated with colon tumor cell growth inhibition and ability to suppress nuclear β-catenin levels. A subset of derivatives was identified that displayed reduced COX-1 and COX-2 inhibitory activity, yet increased potency to inhibit the growth of several colon tumor cell lines (HT29, HCT116, SW480, and COLO741) with IC50 values of 2-10 µM compared with IC50 values of 80-110 µM for the parent compound, sulindac sulfide (SS). Certain derivatives also displayed increased potency to inhibit recombinant phosphodiesterase 5 (PDE5), which appears to be the isozyme responsible for the cGMP PDE inhibitory activity of SS. Treatment of colon tumor cells with such compounds also increased the phosphorylation of vasoactive stimulated protein (VASP), a known PKG substrate. Furthermore, nuclear levels of β-catenin decreased within the same time period as PKG activation, which is consistent with previous reports suggesting that PKG can phosphorylate β-catenin to induce proteosomal degradation. Together, these data indicate that sulindac can be chemically modified to eliminate COX inhibitory activity while enhancing its ability to inhibit colon tumor cell growth. We conclude that the suppression of nuclear β-catenin levels by SS is independent of COX inhibition and that novel derivatives can be developed with improved antineoplastic activity while reducing the toxicities associated with COX inhibition. Funding provided by NIH/NCI grants CA131378 and CA148817. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 837. doi:10.1158/1538-7445.AM2011-837