Abstract 4714: Mechanisms by which the Rac & Cdc42 inhibitor MBQ-167 overcomes the adverse effects of paclitaxel in TNBC

Abstract Triple-negative breast cancer (TNBC) is the most aggressive, recurrent, and metastatic type of BC. Since there are limited targeted therapies available, the standard treatment is taxane-based chemotherapy, which still results in recurrence and metastasis. Therefore, we developed MBQ-167, a clinical-stage Rac/Cdc42 inhibitor that reduces tumor progression and metastasis in TNBC mouse models. In vitro studies show that PXL increased Rac activation, which MBQ-167 reduced in combination with PXL. In mouse models of TNBC, we found that PXL increases metastasis and that MBQ-167 prevents it. Therefore, this study aimed to identify potential mechanisms to explain the antimetastatic effects of MBQ-167 in combination with PXL. Previous studies suggest that PXL may act as an agonist to the Toll-Like 4 Recceptor (TLR4) and activate NfkB signaling to promote metastasis. We hypothesize that MBQ-167 chemosensitizes TNBC cells to PXL and reduces metastasis by blocking Rac/Cdc42 and TLR4/NF-kB signaling. Treatment of SCID mice with orthotopic MDA-MB-468 TNBC tumors with MBQ-167, PXL, or the combination increased lung metastases in mice treated with PXL, which MBQ-167 suppressed. Flow cytometry of spleens harvested from the mice with or without tumors demonstrated increased M2 immunosuppressive macrophages (F480+, CD206+) compared to M1 macrophages (F480+, CD206-), where macrophage differentiation has been implicated with TLR4 signaling. To determine the role of TLR4 signaling, we treated MDA-MB-231 cells stably expressing scrambled or TLR4 shRNA with MBQ-167, PXL, or the combination. Treated cells were evaluated for cell viability, apoptosis, migration, mammosphere assay, and NF-kB p65 activation. Results show that MBQ-167 reduced cell viability stem-cell-like features and increased apoptosis comparable to vehicle or PXL. TLR4 knockdown (kd) did not change cell viability, apoptosis, or migration in vehicle-treated cells. However, TLR4 kd further reduced the decreased cell viability and increased apoptosis in response to MBQ-167, PXL, or the combination, indicating that PXL effects on cell growth are at least partially dependent on TLR4. PXL treatment did not affect cell migration in the control cells but reduced migration in TLR4 kd cells. TLR4 kd exacerbated the inhibitory effects of MBQ-167 or the combination. MBQ-167, but not PXL, reduced LPS-induced (i. e. , TLR4-regulated) NfkB translocation to the nucleus, with a similar effect as the combination. Therefore, MBQ-167 may prevent PXL-induced metastasis by partially inhibiting the NF-kB pathway in TNBC tumors and reducing inflammation and immunosuppression from M1 and M2 macrophages in vivo. Citation Format: Nilmary Grafals-Ruiz, Patricia Sánchez-Orive, Anamaris Torres-Sánchez, Ailed Cruz-Collazo, Derealise García-Almedina, Stephanie Dorta-Estremera, Suranganie Dharmawardhane. Mechanisms by which the Rac Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4714.