IgA Fc-folate conjugate activates and recruits neutrophils to directly target triple-negative breast cancer cells.

PURPOSE: According to the American Cancer Society, 1 in 8 women in the U.S. will develop breast cancer, with triple-negative breast cancer (TNBC) comprising 15-20% of all breast cancer cases. TNBC is an aggressive subtype due to its high metastatic potential and lack of targeted therapy. Recently, folate receptor alpha (FRA) is found to be expressed on 80% of TNBC with high expression correlating with poor prognosis. In this study, we examined whether binding IgA Fc-folate molecules to FRA receptors on TNBC cells can elicit and induce neutrophils (PMNs), by binding their FcαR1 receptors, to destroy TNBC cells. METHODS: FRA was analyzed on TNBC cells and binding assays were performed using 3H-folate. Fc-folate was synthesized by linking Fc fragments of IgA via amine groups to folate. Binding specificity and antibody-dependent cellular cytotoxicity (ADCC) potential of Fc-folate to FcαR1 were confirmed by measuring PMN adhesion and myeloperoxidase (MPO) release in a cell-based ELISA. Fc-folate binding to FRA-expressing TNBC cells inducing PMNs to destroy these cells was determined using 51Cr-release and calcein-labeling assays. RESULTS: Our results demonstrate expression of FRA on TNBC cells at levels consistent with folate binding. Fc-folate binds with high affinity to FRA compared to whole IgA-folate and induces MPO release from PMN when bound to FcαR1. Fc-folate inhibited binding of 3H-folate to TNBC cells and induced significant cell lysis of TNBC cells when incubated in the presence of PMNs. CONCLUSION: These findings support the hypothesis that an IgA Fc-folate conjugate can destroy TNBC cells by eliciting PMN-mediated ADCC.

Riluzole mediates anti-tumor properties in breast cancer cells independent of metabotropic glutamate receptor-1.

Riluzole, the only drug approved by the FDA for treating amyotrophic lateral sclerosis, inhibits melanoma proliferation through its inhibitory effect on glutamatergic signaling. We demonstrated that riluzole also inhibits the growth of triple-negative breast cancer (TNBC) and described a role for metabotropic glutamate receptor-1 (GRM1) in regulating TNBC cell growth and progression. However, the role of GRM1 in mediating riluzole's effects in breast cancer has not been fully elucidated. In this study, we seek to determine how much of riluzole's action in breast cancer is mediated through GRM1. We investigated anti-tumor properties of riluzole in TNBC and ER+ cells using cell growth, invasion, and soft-agar assays and compared riluzole activity with GRM1 levels. Using Lentiviral vectors expressing GRM1 or shGRM1, these studies were repeated in cells expressing high or low GRM1 levels where the gene was either silenced or overexpressed. Riluzole inhibited proliferation, invasion, and colony formation in both TNBC and ER+ cells. There was a trend between GRM1 expression in TNBC cells and their response to riluzole in both cell proliferation and invasion assays. However, silencing and overexpression studies had no effect on cell sensitivity to riluzole. Our results clearly suggest a GRM1-independent mechanism through which riluzole mediates its effects on breast cancer cells. Understanding the mechanism by which riluzole mediates breast cancer progression will be useful in identifying new therapeutic targets for treating TNBC and in facilitating stratification of patients in clinical trials using riluzole in conjunction with conventional therapy.