Abstract 726: Constitutive NF-kB-activation loop enhances resistance to trastuzumab in HER2 positive luminal B breast cancer

Abstract

Abstract [Purpose] Luminal B breast cancer patients are significantly at the risk of relapse with in 5 years. Acquired resistance to the receptor tyrosine kinase HER2 targeting antibody trastuzumab is a major clinical problem in the treatment of recurrent HER2-positive breast cancer. The molecular mechanisms leading to trastuzumab resistance (TZR) remain unclear in luminal B breast cancer. Here, we investigated the mechanism of TZR in HER2-positive luminal B breast cancer cells with acquired resistance. [Methods and Results] We generated trastuzumab resistant breast cancer cell line (BT-474-R) by treating BT-474 cells with trastuzumab for over long-term. Initial validation showed that HER2 overexpression in the BT-474-R cells remained unaltered suggesting that probably HER2 independent signaling pathway is involved in the development of TZR. We demonstrated that NF-κB is constitutively activated in the BT-474-R cells by quantitative realtime RT-PCR, western blotting and immunofluorescent microscopy. Expression of pro-inflammatory cytokines were also demonstrated. Pharmacologic inhibition of NF-κB improved sensitivity to trastuzumab in BT-474-R cells. We identified both IKK-α and IKK-β as the major determinants of the activation of the NF-κB signaling in the resistant cells. [Conclusion] Our study suggests by activating NF-κB pathway, luminal B cells may facilitate acquiring basal-like, Her2+ phenotype a notion consistent with “progression through grade” hypothesis. Finally, our study suggests that blocking NF-κB will provide a new treatment option to limit relapse in HER2 positive breast cancer patients treated with trastuzumab. Citation Format: Hirotaka Kanzaki, Nishit Makhopadhya, Xiaojiang Cui, Krishnan V. Ramanujan, Tatsuaki Takeda, Yoshihisa Kitamura, Toshiaki Sendo, Ramachandran Murali. Constitutive NF-kB-activation loop enhances resistance to trastuzumab in HER2 positive luminal B 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 726. doi:10.1158/1538-7445.AM2015-726