Abstract 1842: Breast cancer brain metastasis (BCBM) model for determination of therapeutic brain penetration

Abstract Purpose Brain metastases are presenting an increasing problem in the clinic, and especially in treatment of patients with human epidermal growth factor receptor-2 (HER2)-amplified breast cancer. Although extracranial metastases respond well to HER2 inhibitors, human clinical data shows brain metastases hide behind an intact blood-brain barrier (BBB) and are largely untreatable. Many current preclinical models lack this barrier integrity, limiting their utility in understanding delivery of drugs to the brain. We present here the development of a new model suitable for evaluating therapeutic brain penetration in addition to efficacy. Experimental procedures Human HER2-amplified BT-474 breast cancer cells were inoculated intravenously (tail vein) in female Rag2-/-;Il2rg-/- mice (2 million cells/mouse) to induce multiorgan metastasis. Formation of metastatic brain lesions was monitored by magnetic resonance imaging (MRI). For comparison, BT-474 cells were inoculated intracranially for direct brain tumor implantation (50,000 cells/mouse). Response to a suite of HER2-targeted therapies known not to appreciably cross an intact BBB (trastuzumab, lapatinib, etc.) was monitored by MRI for both metastatic and implanted brain tumors. Mice were sacrificed following signs of prolonged distress or loss of >20% body weight. Organs were collected for standard histological and immunohistochemical analysis, as well as for CLARITY tissue clearing and large-scale 3D macromolecule mapping. Results Intravenous inoculation of BT-474 cells into Rag2-/-;Il2rg-/- mice consistently reproduced the full metastatic profile seen in humans, with metastases in the lung, bone, liver, ovary, lymph, and brain tissues. Brain metastases were detected in >90% of mice inoculated intravenously. Histological analysis of metastatic brain tumors showed different morphologies and invasive characteristics compared to those intracranially implanted. Additional differences in vasculature between metastatic and implanted brain tumors were identified by CLARITY. Importantly, HER2-targeted therapy markedly delayed progression of implanted brain tumors, but failed to control metastatic brain tumor growth, recapitulating the clinical situation. Conclusions These data, together with ongoing efforts to further characterize therapeutic transport to these brain tumors, suggest that intracranial inoculation disrupts the BBB and creates artificial routes for therapeutics to reach implanted brain lesions, resulting in anomalous tumor response. In contrast, this new metastatic model reproduces the discordant effects of HER2-targeted therapy in patients, and offers a platform for studying the efficiency of therapeutic delivery across an intact BBB as well as antitumor activity, both of which are critical to effective clinical translation. Citation Format: Emily A. Wyatt, Mark E. Davis. Breast cancer brain metastasis (BCBM) model for determination of therapeutic brain penetration [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 1842. doi:10.1158/1538-7445.AM2017-1842