Abstract 2823: Immunodeficient mice differentially sensitize to estrogen and exhibit severe estrogen-related adverse effects in orthotopic breast cancer model
Authors: Kähkönen Tiina E. , Suominen Mari I. , Mäki-Jouppila Jenni , Halleen Jussi , Tanaka Azusa , Seiler Michael P. , Bernoulli Jenni 
Published: July 2017

Abstract
Estrogen-induced growth induction and stimulation of hormone receptor positive breast cancer is commonly acknowledged and thus external estrogen stimulus is used in animal models to support and accelerate growth of the tumors. However, estrogen is known to have adverse effects in the animals and the experiments may have to be preliminary terminated due to animal welfare issues. The aim of the study was to characterize and to compare estrogen caused adverse effects in athymic nude and NOG mice in orthotopic breast cancer model.
Athymic nude (Hsd:Athymic Nude-Foxn 1nu) and CIEA NOG (NOD.Cg-Prkdcscid Il2rgtm1Sug/JicTac, provided by Taconic Biosciences) were implanted with estrogen (17β-estradiol, E2) releasing hormone rods (5 µg/day) prior to cancer cell inoculation. 5x106 BT-474 (ER, PR and HER+) human breast cancer cells were inoculated to left inguinal mammary fat pad of the mice and the tumor growth was monitored by measuring the tumor volumes twice a week by caliber. The clinical condition and weight development of the mice was carefully monitored with special attention to E2-caused adverse effects. If the mice met the termination criteria (i.e. significant weight loss or general worsening of the overall health) they were sacrificed individually before the intended end of the study.
Nude mice exhibited severe estrogen-caused adverse effects as no adverse effect were observed in NOG mice. Most common adverse effect was redness and skin lesions in the urogenital area observed in 63% of the animals. More severe effects were observed in the lower urinary track including urinary stones and bladder obstruction in 67% of the mice. Also internal effects were observed including appearance change in kidneys and spleen in size and color. Due to severity of these effects 50% of the mice had to preliminary sacrificed. Tumor take (100% vs 85%) and final tumor volumes in average (110 mm2 vs 120 mm2) were comparable between nude and NOG mice.
A clear mouse strain specific impact was observed in the study. Nude mice sensitize to estrogen and exhibit severe estrogen-related adverse effects as no effects were observed in NOG mice. In breast cancer studies where E2 supplementation is needed for sufficient tumor growth, the choice of mouse strain should be carefully considered. Special attention should be paid to possible adverse effects keeping in mind the animal welfare issues.
Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jenni Mäki-Jouppila, Jussi Halleen, Azusa Tanaka, Michael P. Seiler, Jenni Bernoulli. Immunodeficient mice differentially sensitize to estrogen and exhibit severe estrogen-related adverse effects in orthotopic breast cancer model [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 2823. doi:10.1158/1538-7445.AM2017-2823