Komen for the Get rid of (to I. is unable to inhibit NFB activity. Also, the cell-permeable thiol advanced stage, therapy-resistant, recurrent, or metastatic) are limited. As a result, the prognosis remains poor, and aggressive disease accounts for more than 90% of breast cancer-related deaths. Although the underlying mechanisms are not fully understood, inflammation has emerged as a key instigator and driver of aggressive breast cancers (1, 2). More specifically, the nuclear factor B (NFB)2 pathway promotes multiple aggressive tumor phenotypes, including cell survival, migration, invasion, angiogenesis, and resistance to therapy (3, 4). The link between the inflammatory NFB pathway Rabbit polyclonal to UCHL1 and breast cancer is also supported by the fact that a deregulated, or constitutively active, NFB pathway is associated with aggressive breast cancer phenotypes and therapy resistance (5,C9). More recently, activation of the NFB pathway has been shown to regulate the survival and propagation of breast cancer stem cells (CSCs) (10,C12), which are a small subset of tumor cells that evade all standard therapies and are involved in metastasis and tumor recurrence (13,C18). Given that the NFB pathway is essential for breast cancer progression and aggressiveness, its inhibition can be exploited to eradicate CSCs and other detrimental NFB-dependent tumor phenotypes. However, to date, there are no such NFB pathway inhibitors available in the clinic. Therapeutic targeting of NFB activity has been directed at inhibiting various players in the pathway (19). The canonical NFB pathway consists of p65 (RelA) and p50 transcription factors, which are held in the cytoplasm by an inhibitor protein, IB. Upon stimulation by inflammatory cytokines, such as TNF, IL-1, or other factors, the IB kinase (IKK) complex, consisting of IKK, IKK, and the scaffolding protein NFB essential modulator (NEMO), is activated. This leads to phosphorylation and proteasomal degradation of IB. As a result, p65/p50 factors are liberated and can translocate to the nucleus, where they bind to DNA and induce gene transcription (20). Therefore, inhibitors targeting the proteasome and upstream kinases have been investigated as a new class of anti-inflammatory drugs, but most have failed because of inhibition of other non-NFB targets and toxic side effects (21). In addition, given that NFB is also critical to the innate immune system, most NFB inhibitors cause long-lasting immune suppression. As a result, the development of safe NFB inhibitors is even more challenging (22), especially for anti-cancer therapy where continued inhibitor use is required. This raises the issue of how to safely and effectively inhibit the NFB pathway. One option is to use the anti-inflammatory drug Tecfidera (dimethyl fumarate, DMF). DMF was approved in the United States in March 2013 for multiple sclerosis and is now the number one prescribed oral therapy for relapsing forms of the disease. DMF is neuroprotective and is proposed to act via inhibition of NFB and activation of Nrf2 pathways (23,C26). Most importantly, DMF has a proven safety in humans; it has immune-modulatory properties without significant immune suppression (27). This makes DMF an attractive candidate for NFB inhibition. Moreover, its therapeutic potential in breast cancer therapy has yet to be explored. Our studies indicate that DMF inhibits NFB activity in multiple breast cancer cell ABT-639 hydrochloride lines. Consistent with its anti-NFB activity, DMF also inhibits mammosphere (MS) formation, cell proliferation, and xenograft tumor growth. Mechanistically, we found that DMF covalently modifies the NFB transcription ABT-639 hydrochloride factor p65 to block its nuclear translocation and DNA binding activity. These results provide proof-of-principle evidence that DMF can be used to inhibit NFB activity in breast cancer cells. Understanding the mechanism of action of DMF could provide the needed rationale ABT-639 hydrochloride to advance DMF into the clinic for aggressive breast cancer therapy. Experimental Procedures.