Abstract 144: Dasatinib enhances the effects of paclitaxel on chemotherapy-resistant breast cancer through targeting breast cancer stem cells

Many patients with triple negative breast cancer (TNBC) exhibit poor prognosis and are at high risk of tumor relapse and metastasis due to the resistance to conventional chemotherapy. These tumor recurrences have been attributed to the presence of breast cancer stem cells (BCSCs), a subpopulation of breast cancer cells that possesses stem-like properties and displays resistance to chemotherapy. Therefore, targeting BCSCs is a priority to overcoming chemotherapy failure in TNBCs. We generated chemotherapy-resistant TNBC cells through cyclic treatments with paclitaxel (pac). The pac-resistant cells displayed increased self-renewal potential compared to the parental TNBC cells, higher percentage BCSCs and increased phosphorylation of Src kinase at Tyr416. After performing a kinase library screening on BCSCs in chemotherapy-resistant cells, we identified dasatinib, a Src kinase family inhibitor, potently reduced BCSC self-renewal and two BCSC populations (ALDH+ and CD24lowCD44high) as well as phosphor-Src. We also demonstrated dasatinib to block pac-induced BCSC enrichment and Src activation in the parental TNBC cells. Interestingly, we found that dasatinib induced an epithelial differentiation of pac-resistant cells, resulting in their enhanced sensitivity to paclitaxel. The combination treatment of dasatinib and paclitaxel not only decreased the proportion of BCSCs and their self-renewal capacity but also synergistically reduced cell viability of pac-resistant cells. In vivo studies further demonstrated the effectiveness of dasatinib/paclitaxel combination treatment in inhibiting breast tumor growth. All these data suggest that dasatinib is a promising anti-BCSC agent and can be used in combination with paclitaxel to overcome chemotherapy resistance in TNBCs.

Citation Format: Jun Tian, Chieh Lo, Fatmah Al Raffa, Meiou Dai, Jean-Jacques Lebrun. Dasatinib enhances the effects of paclitaxel on chemotherapy-resistant breast cancer through targeting breast cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 144.

Cyclooxygenase-2 regulates TGFβ-induced cancer stemness in triple-negative breast cancer

Triple negative breast cancer (TNBC), an aggressive subtype of breast cancer, display poor prognosis and exhibit resistance to conventional therapies, partly due to an enrichment in breast cancer stem cells (BCSCs). Here, we investigated the role of the cyclooxygenase-2 (COX-2), a downstream target of TGFβ, in regulating BCSCs in TNBC. Bioinformatics analysis revealed that COX-2 is highly expressed in TNBC and that its expression correlated with poor survival outcome in basal subtype of breast cancer. We also found TGFβ-mediated COX-2 expression to be Smad3-dependent and to be required for BCSC self-renewal and expansion in TNBCs. Knocking down COX-2 expression strikingly blocked TGFβ-induced tumorsphere formation and TGFβ-induced enrichment of the two stem-like cell populations, CD24^lowCD44^high and ALDH+ BCSCs. Blocking COX-2 activity, using a pharmacological inhibitor also prevented TGFβ-induced BCSC self-renewal. Moreover, we found COX-2 to be required for TGFβ-induced expression of mesenchymal and basal breast cancer markers. In particular, we found that TGFβ-induced expression of fibronectin plays a central role in TGFβ-mediated breast cancer stemness. Together, our results describe a novel role for COX-2 in mediating the TGFβ effects on BCSC properties and imply that targeting the COX-2 pathway may prove useful for the treatment of TNBC by eliminating BCSCs.