Doxycycline and indomethacin synergistically downregulate beta-catenin signaling and inhibit colon cancer cell growth

Abstract

Introduction: Aberrant beta-catenin signaling, due to loss of the APC tumor suppressor gene, or mutation of beta-catenin, is found in the majority of colon cancers. We have recently demonstrated that doxycycline (DOX) decreases beta-catenin expression and transcriptional activity in colon cancer cells. NSAIDS also downregulate beta-catenin by an undefined mechanism. We demonstrate synergistic inhibition of beta-catenin signaling and colon cancer cell growth by DOX and indomethacin (INDO). Methods: APC-mutant SW480 human colon cancer cells were studied. DOX and INDO were used at clinically achievable concentrations. Beta-catenin levels were determined by western blotting. Beta-catenin-dependent transcription was measured by TOPFlash reporter assay. Cell viability was determined by tiazolyl blue (MTT) reduction and growth was determined by direct cell counting. In vivo, tumor growth was determined by measurement of subcutaneous xenografts in BALB/c nude mice. DOX was administered in drinking water, and INDO by IP injection. Results: In vitro, both DOX and INDO exposure result in a dose dependent down-regulation of beta-catenin protein and beta-catenin-dependent gene transcription, resulting in inhibition of cell viability and proliferation. A synergistic relationship of combining these two agents is evident. In vivo studies show an enhanced anti-tumor effect of combined DOX and INDO treatment on SW480 xenograft growth (Figure 1). Conclusions: DOX and INDO suppress beta-catenin expression and transcription activity in colon cancer cells, inhibiting cancer cell growth in vitro and in vivo. DOX and INDO may be of clinical use in therapeutic or chemopreventative strategies for colon cancer.