Abstract 379: Allosteric AKT1/2-inhibitor BAY 1125976 as potent inhibitor in luminal breast cancer resistant to antihormone therapy
Authors: Politz Oliver , Baerfacker Lars , Ince Stuart , Haegebarth Andrea , Liu Ningshu , Neuhaus Roland , Boemer Ulf , Michels Martin , Ziegelbauer Karl , Mumberg Dominik 
Published: July 2016

Abstract
The PI3K-AKT-mTOR signaling cascade is one of the major drivers in the development of cancer. It is constitutively activated in many types of cancers and is one of the prominent pathways that promote tumor cell survival and confers resistance to antihormonal therapies for patients with breast cancer.
Breast cancer has been classified into at least four distinct subtypes, based on molecular profiling. Luminal-B breast cancer, although still expressing the hormone receptor, has been identified as relatively insensitive to endocrine therapy and is an entity with highest need for novel treatments and combination approaches. Despite the notable improvements in endocrine therapy, the invariable appearance of endocrine resistance, either primary or secondary, remains an important issue in this type of tumor. Main cancer signaling pathways, including PI3K/Akt/mTOR and CCND1/CDK4-6, are thought to play an important role in development of this resistance.
Therefore AKT is considered an attractive drug target for the treatment of breast cancer. BAY 1125976, an orally active, potent, highly selective, allosteric AKT1/2 inhibitor is currently in phase I clinical development (NCT01915576). BAY 1125976 is particularly effective in preclinical models with PI3K-AKT pathway aberrations and luminal B status as shown by profiling in a panel of tumor cell lines as well as respective in vivo studies. The efficacy of BAY 1125976 in inhibition of cell proliferation is correlated with luminal status of the tumor as shown in several cell line panels. In vitro combination with anti-hormonal therapeutics showed synergistic anti-proliferative effects and rendered resistant cell lines sensitive towards tamoxifen or fulvestrant treatment. In the MCF-7 cell line tamoxifen combined with BAY 1125976 resulted in a 14 fold reduction of the IC50 for inhibition of cell proliferation compared to monotherapy. This translated into additive to synergistic activity in combination with tamoxifen in a ER+ MCF7 (PIK3CAE545K) BC model and enabled the use of alternative dosing schedules with improved efficacy versus monotherapy.
BAY 1125976 also showed potent inhibition of tumor cell growth in a tamoxifen- and fulvestrant-resistant derivate of MCF-7 enabling a reduction of the therapeutic dose of BAY 1125976 and thereby improving tolerability while keeping efficacy.
Combination of the allosteric AKT inhibitor BAY 1125976 therefore provides an interesting opportunity in improving efficacy of antihormonal therapy in luminal B type breast cancer.
Citation Format: Oliver Politz, Lars Baerfacker, Stuart Ince, Andrea Haegebarth, Ningshu Liu, Roland Neuhaus, Ulf Boemer, Martin Michels, Karl Ziegelbauer, Dominik Mumberg. Allosteric AKT1/2-inhibitor BAY 1125976 as potent inhibitor in luminal breast cancer resistant to antihormone therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 379.