Abstract B099: Importance of hormone receptor and HER2/HER3 status verification in preclinical breast cancer models using immunodeficient and humanized mice
Authors: Kähkönen Tiina , Suominen Mari I. , Mäki-Jouppila Jenni , Halleen Jussi M. , Tanaka Azusa , Seiler Michael , Haapaniemi Teppo , Bernoulli Jenni 
Published: August 2018

Abstract
Introduction: Breast cancer expressing estrogen receptor (ER) and progesterone receptor (PR) is classified as hormone receptor positive, and triple-positive breast cancer expresses also human epidermal growth factor receptor (HER2). Despite the hormonal and HER2 targeted treatments, breast cancer metastasizes to bone in high frequency and may develop resistance against the used treatment. Prevention and treatment of bone metastases is challenging; moreover, hormones are strong regulators of both bone and immune system. The aim of the present study was to verify ER, PR, HER2, and also HER3 status in preclinical primary and bone metastasis breast cancer models utilizing immunodeficient and human immune system engrafted mice in order to verify predictive models for drug development. Materials and Methods: BT-474 human breast cancer cells were inoculated orthotopically into mammary fat pad of placebo or 17β-estradiol (E2) supplemented female immunodeficient NOG mice. In a bone tumor study, BT-474 cells were inoculated into the tibia of female NOG or humanized NOG mice (HSCFTL-NOG-F mice, Taconic Biosciences). Tumor growth was followed for 8 weeks, and histopathologic tumor evaluation and immunohistochemical stainings for ER, PR, HER2, and HER3 were performed. Results: Orthotopic tumor growth of BT-474 was hormone dependent and only minor growth was observed in the absence of estrogen. In the presence of E2 supplement, the orthotopic tumor expressed ER, PR, and HER2/HER3. However, in the absence of E2 supplement there was reduced PR expression but no major changes in the ER and HER2/HER3 expression. In contrast, when breast cancer cells were inoculated into the tibia, tumor growth was observed also without E2 supplement. In this case, tumor in the bone was positive for ER and HER2/HER3 but negative for PR. No significant changes were observed between immunodeficient and humanized mice regarding intratibial tumor growth and ER, PR, and HER2/HER3 expression. Conclusions: Estrogen supplementation is needed to support breast cancer BT-474 tumor growth when cancer cells are inoculated orthotopically into mammary fat pad. In contrast, BT-474 tumor growth was observed in bone even in the absence of supplied estrogen. ER and HER2/HER3 expression was observed in primary and bone tumors, but PR expression was significantly reduced if no estrogen supplement was used. Differences in tumor growth depending on the site and estrogen level highlight the importance of tumor microenvironment in breast cancer, and also refer why tumor may shift resistant to used hormonal or HER2 targeted therapy. Taking together, when developing new therapies against breast cancer, treatment targets in preclinical models should be carefully verified. Focus should be placed not only on primary tumor but also on bone metastasis where cancer cells are under influence of different tumor microenvironment and may express differently hormone receptors and HER2/HER3. While hormones influence breast cancer progression, they also regulate bone turnover and immune system, and therefore humanized mouse models provide an essential platform for novel therapy development.
Citation Format: Tiina Kähkönen, Mari I. Suominen, Jenni Mäki-Jouppila, Jussi M. Halleen, Azusa Tanaka, Michael Seiler, Teppo Haapaniemi, Jenni Bernoulli. Importance of hormone receptor and HER2/HER3 status verification in preclinical breast cancer models using immunodeficient and humanized mice [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B099.