Toll Like Receptor 4 Inhibition Improves Antitumor Responses to MBQ‐167 in Triple Negative Breast Cancer Cells in vitro

Abstract

Triple negative breast cancer (TNBC) is an aggressive variant of breast cancer that lacks the expression of estrogen, progesterone, and human epithelial growth factor receptors. Due to the scarce availability of receptor‐targeted or hormonal treatments, TNBC patients are submitted to taxane‐based chemotherapies like paclitaxel. Patients initially respond to paclitaxel, but 4 out of 10 patients may develop tumor recurrence along with high metastasis and mortality rates. Several studies demonstrate that paclitaxel may induce chemoresistance and metastasis through the activation of Toll‐Like Receptor 4 (TLR4)/NFKB signaling pathway, a known cancer prognostic marker in breast cancer. Hence, new treatments are needed to improve TNBC prognosis in patients. Recently, our laboratory and collaborators developed MBQ‐167, a potent Rac and Cdc42 inhibitor that decreases tumor burden, cell proliferation, and metastasis in TNBC mouse models. In preliminary studies with TNBC mice, we observed that MBQ‐167/Paclitaxel combination treatment prevented metastasis progression compared to paclitaxel treatment alone. This led us to hypothesize that MBQ‐167 chemosensitizes aggressive breast cancer cells and reduces metastasis by blocking Rac/Cdc4, hence decreasing their downstream target NfkB activity. This research project aims to evaluate cellular and molecular events that explain how MBQ‐167 prevents paclitaxel‐induced metastasis. Here, we generated TLR4‐knockdowns (TLR4‐KD) in MDA‐MB‐231 TNBC cell lines using lentiviral particles with shRNAs against the TLR4 mRNA. After knockdown validation with western blot analysis (WB), Wildtype (MDA‐MB‐231), Scramble control knockdowns (Sc‐KD), and TLR4‐KD cells were treated with different concentrations of MBQ‐167, paclitaxel, doxorubicin, or combinations. After treatments, we evaluated the effect on cell viability from MTT assays at 96 and 120 hours, cell apoptosis through Caspase‐Glo 3/7 Assays at 48 hours, and cellular migration through scratch wound healing assays. Our results demonstrate that partial inhibition of TLR4 decreases the cell viability of cells, increases apoptosis, and decreases cell migration after treatment with MBQ‐167 (250 nM and 500 nM), Paclitaxel (5 nM and 10 nM), or Doxorubicin (250 nM and 500 nM). We also observed an additive response upon combinatorial treatments with MBQ‐167/Paclitaxel and MBQ‐167/Doxorubicin when TLR4‐KD cells were compared to wild‐type and Sc‐KD cells. Altogether, these results suggest that TLR4‐KD chemosensitizes cells to Paclitaxel and Doxorubicin chemotherapies. In addition, TLR4 inhibition improves cellular response to Rac/Cdc42 inhibitor, MBQ‐167. Therefore, TLR4‐KD may reduce Rac and NfkB signaling, improving treatment response to MBQ‐167, MBQ‐167/Paclitaxel, and MBQ‐167/Doxorubicin. Other cellular studies, including Rac and NfkB activation assays, are being evaluated in our laboratory.