Multi-targeted kinase inhibition alleviates mTOR inhibitor resistance in triple-negative breast cancer

Abstract

Purpose Owing to its genetic heterogeneity and acquired resistance, triple-negative breast cancer (TNBC) is not responsive to single-targeted therapy, causing disproportional cancer-related death worldwide. Combined targeted therapy strategies to block interactive oncogenic signaling networks are being explored for effective treatment of the refractory TNBC subtype. Methods A broad kinase inhibitor screen was applied to profile the proliferative responses of TNBC cells, revealing resistance of TNBC cells to inhibition of the mammalian target of rapamycin (mTOR). A systematic drug combination screen was subsequently performed to identify that AEE788, an inhibitor targeting multiple receptor tyrosine kinases (RTKs) EGFR/ HER2 and VEGFR, synergizes with selective mTOR inhibitor rapamycin as well as its analogs (rapalogs) temsirolimus and everolimus to inhibit TNBC cell proliferation. Results The combination treatment with AEE788 and rapalog effectively inhibits phosphorylation of mTOR and 4EBP1, relieves mTOR inhibition-mediated upregulation of cyclin D1, and maintains suppression of AKT and ERK signaling, thereby sensitizing TNBC cells to the rapalogs. siRNA validation of cheminformatics-based predicted AEE788 targets has further revealed the mTOR interactive RPS6K members (RPS6KA3, RPS6KA6, RPS6KB1, and RPS6KL1) as synthetic lethal targets for rapalog combination treatment. Conclusions mTOR signaling is highly activated in TNBC tumors. As single rapalog treatment is insufficient to block mTOR signaling in rapalog-resistant TNBC cells, our results thus provide a potential multi-kinase inhibitor combinatorial strategy to overcome mTOR-targeted therapy resistance in TNBC cells. Keywords Multi-kinase inhibitor • mTOR-targeted therapy • Drug resistance • Triple-negative breast cancer (TNBC) • Polypharmacology Abbreviations BL Basal-like CDK4 Cyclin-dependent kinase 4 CI Combination index EGF Human epidermal growth factor FC Fold change IC50 Half-maximal inhibitory concentration IM Immunomodulatory KI Kinase inhibitor LAR Luminal androgen receptor-like MSL Mesenchymal stem-like mTOR The mammalian target of rapamycin RTK Receptor tyrosine kinase SRB Sulforhodamine B TNBC Triple-negative breast cancer Electronic supplementary material The online version of this article (

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