Background: Accumulating evidence indicates that breast cancer progression, resistance to therapies and development of metastasis are driven by cancer cells with stem cell-like characteristics. The increased numbers of cancer stem-like cells (CSCs) have been reported in triple negative breast cancers (TNBCs). Therefore, novel methods for targeting CSC population are needed. Aurora-A kinase (AURKA) has been shown to play a key role in acquisition of stem cell-like properties by breast cancer cells. Furthermore, the CSCs have been demonstrated to have increased sensitivity to AURKA specific inhibitor, MLN8237 (Alisertib). Our group has previously reported that oncolytic vaccinia virus (OVV) preferentially infects CSCs. Therefore we hypothesize that the combined treatment of OVV and AURKA inhibitor will result in overall enhanced anti-tumor activity due to improved elimination of CSCs.

Results: We confirmed that AURKA overexpression in MCF-7 breast cancer cell line (MCF-7 AURKA) resulted in increased number of CSCs as shown by upregulation of CD44 antigen and decreases in expression of CD24 antigen. The MCF-7 and MCF-7 AURKA cells were subsequently infected with 0.1 pfu/cell of OVV expressing EGFP (OVV-EGFP). After 72h of incubation, viral replication was analyzed by fluorescent microscopy and standard plaque-forming assay. The analysis revealed over 2-fold increases in viral replication in MCF-7 AURKA cells as compared to the parental counterparts. The enhanced viral replication resulted in decreased viability of MCF-7 AURKA cells when compared to OVV-treated MCF-7 (64% vs 81%, p<0.031). The efficacy of combined treatment of OVV-EGFP and alisertib was next analyzed in MCF-7AURKA cells. The MTT assay analysis revealed 73% decreases in viability of cells treated with combination of oncolytic viortherapy and alisertib, whereas the effect of single treatment resulted in 34% and 52% reduction of viability for OVV-EGFP and alisertib, respectively (p <0.01 and p< 0.024). We next tested the efficiency of OVV-EGFP and Alisertib combination treatment against TNBC cell line, BT549. The cells treated with combination of OVV-EGFP and alisertib showed 63% decreases in cell viability compared to 25% and 46% reductions mediated by OVV-EGFP and alisertib, respectively (p<0.003 and p< 0.03).

Conclusions: Combination therapy of alisertib and OVV has a significantly higher anti-cancer cell activity in vitro than either agent used alone, and it is particularly applicable for treatment of cells with CSC phenotype. In vivo studies are currently in progress. The combined treatment of alisertib and OVV represents novel therapeutic approach in treating breast cancer with increased numbers of CSCs, resistance to standard therapies and worse clinical outcomes. The results present a novel treatment approach with high translational potential.

Citation Format: Malgorzata Gil, Marcin Komorowski, Danuta Kozbor, Mateusz Opyrchal. Concurrent use of alisertib and vaccinia virus demonstrate increased in vitro efficacy against breast cancer models with elevated numbers of cancer stem-like cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B35.