Inhibition of DDX3 modulates immune signaling in aggressive breast cancers

Triple-negative breast cancers (TNBCs) and inflammatory breast cancer (IBC) are by far the most deadly among all breast cancer subtypes mainly due to being resistant to current treatments. Existing therapies for TNBC and IBC are inadequate due to a limited number of targetable biomarkers and the heterogeneous nature of this disease. In our ongoing search to identify targetable biomarkers for TNBC and IBC, we have found that a member of the RNA helicase protein family, DDX3, is overexpressed in IBC and can be targeted by a small molecule inhibitor which we rationally synthesized, referred to as RK-33. Preliminary data indicate that RK-33 can efficiently and specifically kill TNBC and IBC cell lines without affecting normal breast cells. In the present study, we demonstrate the effectiveness of targeting DDX3 with RK-33 to induce cell death, decrease mammosphere formation, and alter the self-renewal capacity of IBC cells. Additionally, RK-33 was able to disrupt inflammatory cytokine expression in IBC cells. Furthermore, we show that RK-33 sequesters β-catenin in the cytoplasm and decreases Survivin levels in TNBC cells. Moreover, targeting DDX3 with RK-33 promotes multipolar division, leading to cellular death. Importantly, the use of RK-33 also converts high glycolytic tumors to a low glycolytic state, resulting in decreased lactate levels, inhibiting tumor growth, and activating the immune system in an immunocompetent preclinical model of TNBC. Collectively, our data supports the use of RK-33 as a novel therapeutic option for treating TNBC and IBCs.