Mechanisms behind COX-1 and COX-2 inhibition of tumor growth in vivo.

Non-steroidal anti-inflammatory drugs (NSAIDs) attenuate tumor net growth in clinical and experimental cancer. Evaluations in cell culture experiments have implied involvement of growth factor and G-protein related signaling pathways to explain decreased proliferation, angiogenesis, increased cell adhesion and apoptosis. Sparse information is however available from studies on growing tumors in vivo. The aim of the present study was to map alterations in selected signal proteins in relation to heterogeneous tissue expression of COX-2 in tumors during COX inhibition. MCG 101 cells were exposed to indomethacin treatment both in vivo and in vitro to reduce PGE2 production. Tumor tissue specimens were taken for immunohistochemical analyses and qPCR determinations. Protein markers were selected to reflect cell proliferation and cell cycling, angiogenesis and metastasis in relationship to COX-2 staining in tumor tissue. Indomethacin did not change overall COX-2 staining in tumor tissue, but altered its distribution towards increased staining in cell nuclei/nucleoli and decreased COX-2 staining heterogeneity in tumor tissue. P53 staining was decreased, while PCNA and TGFβ3 staining were increased by indomethacin in tumor areas with high presence of COX-2, which correlated to staining of BAX, TUNEL, Bcl-2, c-jun, p21, p27, p53 and NM23. Net tumor growth was predicted by EGF-R, p21 and p27 proteins in tumor tissue during indomethacin treatment (multivariate analysis). RNA transcript analyses showed decreased EGF-R and KRas expression in vivo, following indomethacin treatment, which also included KRas, PI3K, JAK1, STAT3 and c-jun, mRNAs in cultured tumor cells. In conclusion, our results extend earlier studies on cell culture experiments and demonstrate that EGF-R and downstream KRas pathways communicate effects of increased prostaglandin activity in tumor tissue in vivo.