Introduction: Triple negative breast cancer (TNBC) accounts for 15% of all breast cancer cases in the United States, and despite its lower incidence, contributes to a disproportionately higher rate of morbidity and mortality compared to other breast cancer subtypes. Because these tumors lack expression of the estrogen, progesterone, or HER-2 receptors (“triple negative”), TNBC patients do not respond to targeted therapies that have been successfully used against tumors that over-express these proteins. Thus, there exists a critical need to improve the outcomes of TNBC patients through the implementation of novel targeted agents.

Methods: RNA-seq data from 94 TNBCs (from Indiana University and TCGA) and 20 microdissected normal breast tissues (Komen Tissue Bank) were merged and imported into Partek Genomics Suite. The merged transcript RPKMs were transformed, batch effect corrected, and analyzed for differential expression. Statistically significant genes were imported into Ingenuity Pathway Analysis (IPA) to identify therapeutic targets. For cell based studies, we tested a panel of seven TNBC cell lines using BKM120 and LGK974, a WNT pathway inhibitor, individually. To further enhance antitumor efficacy, we then tested these TNBC cell lines using variable dilutions of both drugs in combination with one another. Cell viability was assessed via Celltiter-Fluor. Synergy between the two drugs was calculated using the Chou-Talalay method.

Results: Using next-generation RNA sequencing data of TNBCs and microdissected normal breast tissue, Ingenuity Pathway Analysis identified over-expression and hyper-activation of the PI3K/AKT/mTOR and Wnt pathways. When anti-tumor efficacy against these pathways was assessed, a significant reduction in cell viability in combination was observed across the panel of cell lines. Using the Chou-Talalay method, we found for MDA-MB-231 and Hs578T, a ∼50% reduction in cell viability at 100nM concentration of each drug that was highly synergistic (Combination Index = 0.33, and 0.36 respectively). For HCC70, this cell line was more resistant to the combination and we observed ∼50% reduction at 1uM each that had an additive, non-synergistic effect.

Conclusion: PI3K/mTOR/AKT and Wnt pathways are a vital target for treatment of TNBC. Using small molecule inhibitors that are in phase trials (BKM120 and LGK974) we have found that there is a strong synergy when given at low nanomolar doses. In vitro studies of inhibitors of these two pathways in a panel of TNBC cell lines demonstrated significant efficacy in reducing cell viability with substantial synergy when used in combination. Furthermore, initial mouse studies display a similar synergy and actual amplification of drug concentration and half-life in the blood of both drugs when given in combination when compared to these two drugs alone.

Citation Format: Jeffrey P. Solzak, Rutuja Atale, Brad Hancock, Milan Radovich. Dual PI3K and Wnt pathway inhibition is a synergistic combination against triple-negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5340. doi:10.1158/1538-7445.AM2015-5340