Effect of cyclooxygenase inhibition on CXCR3 ligand secretion in breast cancer.

45 Background: In murine cancer models, the two IFN-γ inducible chemokines CXCL9 and CXCL10, those bind to the common receptor CXCR3, recruit NK cells and tumor-suppressive lymphocytes into the tumor site and impair tumor growth and metastatic spread. In human breast cancer (BC), we and others have shown that high levels of CXCL9 mRNA correlate with favorable prognosis and the number of infiltrating lymphocytes. Raising the intratumoral level of CXCR3 ligands might therefore be a feasible way to enhance the infiltration by tumor-suppressive immune cells and to improve immune intervention in breast cancer. Inhibition of cyclooxygenases (COX) has been shown to inhibit tumor growth and metastases formation in a lymphocytic and IFN-γ dependent manner. We therefore tested whether COX inhibition induces CXCR3 ligand secretion from breast cancer cells. Methods: Human MCF-7 and MDA-MB 231 BC cells were stimulated with IFN-γ with or without prostaglandin E2 (PGE2) or COX inhibitors (indomethacin, aspirin, celecoxib). CXCL9 and CXCL10 release was measured by ELISA. COX-1 and COX-2 expression was measured in 45 BC samples and correlated with intratumoral CXCR3 ligand concentration. Results: Prostaglandin E2 inhibits CXCL10 and CXCL9 release from breast cancer cells. Aspirin and indomethacin enhance the INF-γ mediated secretion of these CXCR3 ligands by inhibition of endogenous cyclooxygenases. Celecoxib has this effect only at low concentrations, at higher concentrations is shows PGE2 agonistic effects. In human breast cancer samples, COX-2 overexpression inversely correlates with CXCR3 ligand concentration, which shows that the mechanism of PGE2 induced CXCL9/CXCL10 suppression might also be relevant in vivo. Conclusions: Suppressing endogenous PGE2 by cyclooxygenase inhibition increases CXCL9 and CXCL10 release from breast cancer cells and is therefore a feasible way to enhance the infiltration of breast tumors by tumor-suppressive lymphocytes. However, our results show that unselective COX inhibitors might be more suitable than the COX-2 specific celecoxib. Clinical trials are now warranted to clarify the mechanisms and therapeutic efficacy of COX inhibition in breast cancer.