12P Individualized breast cancer therapy using Mcl-1 inhibition based combination

Abstract

Background Breast cancer (BC)isleadingcauseofcancer-relatedmortalityinwomen. Anti-apoptotic Bcl-2 family members including Bcl-2, Bcl-xL and myeloid cell leukemia-1(Mcl-1) controltheintrinsicpathwayofapoptosis.ElevatedMcl-1levels have been correlated with poor prognosis. The aim of this study is to evaluate a rationally-derived combination of Mcl-1-inhibitor with Bcl-2 or Bcl-xL inhibitors as well as with conventional BC treatment and to provide the derived rationale to therapeutically target Mcl-1. Methods The anti-BC cell-activity of the novel small molecule Mcl-1 inhibitor EU5346 was evaluated alone or in combination with other antiapoptotic agents, hormone therapy, targeted therapy, or chemotherapy using proliferation and spheroid forming assays as well as immunoblotting in different BC cell lines. Synergistic activity of combination therapies was determined by the Chou-Talalay method. Results Using protein profiling Mcl-1 is consistently overexpressed in all BC subtypes while Bcl-2 and Bcl-xL are variably expressed. We then performed selective treatments with Mcl-1/Bcl-2/Bcl-xL inhibitors. As expected, cell proliferation was significantly reduced in correspondence to the protein levels of antiapoptotic Bcl-2 family member, thereby indicating the rational combination of Mcl-1 inhibitor with Bcl-2/Bcl-xL inhibitors. Importantly, Bak, Bim and Noxa protein levels predict the IC50 of EU-5346 in all BC subtypes. We then demonstrated that a protein level-based drug combination Mcl-1 inhibitor with Bcl-2/Bcl-xL inhibitors, induces synergistic anti- BC cell activity. Moreover, not only the combination of EU-5346 with tamoxifen, trastuzumab as well as paclitaxel triggers synergistic anti- BC cell activity, but also inhibiting Mcl-1 overcomes resistance to paclitaxel in paclitaxel-resistant TNBC cells. Conclusions Our data demonstrate an important role of Mcl-1 in BC cell survival, and provide the preclinical framework for the individualized, clinical use of Mcl-1-inhibitor- based drug combinations with antiapoptotic, antihormonal or chemotherapies to improve patient outcome in BC. Legal entity responsible for the study Klaus Podar Funding Eutropics Pharmaceuticals, Inc, Disclosure M.H.Bashari: received research support from EUTROPICS. M. H. Cardone: employee of Eutropics, Inc. All other authors have declared no conflicts of interest.