Abstract 1223: Evaluation of the dual p38/NLK kinase inhibitor as potential new therapeutic agent for tamoxifen-resistant breast cancer

Background: Endocrine therapy has been considered an effective initial treatment for ER positive breast cancer and tamoxifen is the most commonly used endocrine agent. However, about half of the patients develop resistance or relapse eventually. No effective targeted therapy exists to overcome it. In our previous study, we have identified the role of nemo-like kinase (NLK) in breast cancer endocrine resistance – a serine-threonine kinase that functions in stress response and neurite outgrowth. In addition to NLK, activation of the other stress kinases such as p38 MAPK has been reported to modulate ER signaling and promote endocrine resistance. In this study, we have identified a highly selective dual p38 and NLK kinase inhibitor (PNKI). This study aimed to evaluate the therapeutic effect of the PNKI inhibitor in tamoxifen-resistant breast cancers using in vitro and preclinical mouse models. Experimental design and methods: To determine the effect of PNKI on tamoxifen-resistant breast cancer cells, we treated a primary tamoxifen-resistant breast cancer cell line MDAMB415 and an acquired-resistant line MCF7 TamR, with 0.5 uM PNKI in the presence of different doses of Tamoxifen. To evaluate the therapeutic effect of PNKI in a T47D-derived xenograft tumor model with acquired tamoxifen resistance, we administered PNKI alone or in combination with Fulvestrant, or with the mTOR inhibitor Everolimus. Mice bearing T47D-TamR xenografts were randomized into six treatment groups (Vehicle, PNKI, Fulvestrant, Fulvestrant + PNKI, Everolimus, Everolimus + PNKI). Tumor growth was tracked closely. The tumors harvested 2 weeks following treatments were profiled with Reverse Phase Protein Array (RPPA) to assess the early signaling changes after treatments. Furthermore, the therapeutic effect of PNKI were also evaluated in a patient-derived xenograft (PDX) model of de novo endocrine resistant breast cancer. Mice bearing the PDX tumors were randomized to one of four treatment groups (Vehicle, PNKI, Everolimus, Everolimus + PNKI) and tumor growth curve was measured. Summary of the Results: Breast cancer cell lines with either de novo or acquired Tamoxifen resistance became more sensitive to tamoxifen when treated with 0.5 uM PNKI. The concomitant treatment of PNKI and Everolimus results in significant decrease of tumor growth in the T47D-TamR xenograft tumor compared to Fulvestrant, Fulvestrant + PNKI, PNKI, or Everolimus treatments. RPPA data revealed that a majority of key survival signaling in breast cancer are repressed only when PNKI are combined with Everolimus. The de novo endocrine-resistant PDX tumors showed diverse response to PNKI mono-treatment, whereas the combination of PNKI and Everolimus resulted in significantly decreased tumor growth. Conclusion: The PNKI exhibited potential therapeutic value as adjuvant agent to the mTOR inhibitor everolimus for acquired or de novo tamoxifen-resistant breast cancer. Citation Format: XIAN WANG, Xixi Cao, Jamunarani Veeraraghavan, Lanfang Qin, Jin-Ah Kim, Ying Tan, Susan G. Hilsenbeck, Rachel Schiff, Xiaosong Wang. Evaluation of the dual p38/NLK kinase inhibitor as potential new therapeutic agent for tamoxifen-resistant breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1223. doi:10.1158/1538-7445.AM2017-1223