Abstract. Shikonin, a natural naphthoquinone isolated from a traditional Chinese medicinal herb, has been reported to promote tumor cell death. However, there are few reports concerning its effect on metastasis-related cell invasion and migration behavior. In the present study, we investigated the effect of shikonin on human breast cancer invasion and migration. We found that shikonin inhibited phorbol 12-myristate 13-acetate (PMA)-induced cell migration and invasion in MCF-7 breast cancer cells, which was correlated with modulation of matrix metalloproteinase-9 (MMP-9) through suppression of both expression and proteolytic and promoter activity. We also found that shikonin inhibited both MMP-9 expression and promoter activity in MDA-MB-231 cells with high metastatic potential. These results indicated that shikonin induces the suppression of migration and invasion through modulation of MMP-9 in human breast cancer cells. Therefore, shikonin may be a potential anticancer drug for human breast cancer therapy.
IntroductionBreast cancer ranks among the most common malignant tumors afflicting women worldwide (1). Cancer metastasis is the leading cause of mortality in patients with breast cancer; breast cancer survival rates fall from 90% for localized to 20% for metastatic disease. Therefore, controlling metastasis and invasion represents an important therapeutic strategy (2). Metastasis requires that invasive cells detach from localized tumors by degrading the extracellular matrix using proteases, including matrix metalloproteinases (MMPs); survive in the circulation as circulating tumor cells (CTCs); and colonize distant locations. Thus, understanding the molecular mechanisms underlying each of these steps is essential for targeting metastatic cells at an early stage and improving patient survival (3).MMPs are a family of extracellular matrix (ECM)-degrading enzymes comprising 24 members. Based on their substrates, MMPs are divided into four subclasses: collagenase, gelatinase, stromelysin and membrane-associated (4). As a main ECM-degrading enzyme family, MMPs have essential roles in physiologic processes such as tissue development, remodeling and wound healing (5). However, they are also involved in certain tissue destructive diseases, such as atherosclerosis, inflammation, rheumatoid arthritis, and tumor invasion, metastasis and neoangiogenesis (6). Recent studies have shown that MMPs are important elements of the tumor microenvironment, regulating tumor progression, metastatic niche formation and inflammation in cancer (7). Among human MMPs, MMP-2 (gelatinase-A) and MMP-9 (gelatinase-B) are key enzymes in the degradation of type IV collagen, which is an important component of the ECM. MMP-2 and MMP-9 are the MMP members primarily associated with tumor migration, invasion and metastasis of various types of cancers (8). It has been shown that enhanced expression of MMP-9 is associated with the progression and invasion of tumors, whereas MMP-2 is usually expressed constitutively (9,10). Thus, researchers have focu...