MMP9 and breast cancer: Omeprazole also inhibited lung metastasis of MDA-MB-231 cells (tail vein injection) in a mouse model and the antimetastatic pathway was linked to decreased expression of MMP-9 and AHR-dependent suppression of the pro-metastatic gene CXCR4. Decreased invasion and CXCR4 expression was also observed in MCF-7 and SKBR3 breast cancer cell lines treated with omeprazole.