Abstract 1449: Targeting squalene epoxidase for breast cancer brain metastasis: The evaluation of a new therapeutic target for brain extravasation and colonization using animal models
Authors: Lee Pony Yu-Ling , Lin Kun-Yuan , Chang Chao-Di , Cheng Shan-Yun , Hung Ya-Wen , Yang Chih-Chieh , Chang Yu-Hsien , Shen Chien-Chang , Yeh Jia-Yun , Yu Yung-Lung , Wang Shu-Ping 
Published: March 2024

Abstract
Breast cancer brain metastasis is one of the most common forms of breast cancer metastasis and a major cause of morbidity and mortality. Patients who develop brain metastases tend to be associated with progressive neurologic deficits and short overall survival, which represents an unmet medical need. Extensive research has been conducted to elucidate the mechanism of cancer metastasis with limited information gained as to how cancer cells extravasate and colonize to the brain. Recently, we identified a novel mechanism by which squalene epoxidase (SQLE), the second rate-limiting enzyme in cholesterol biosynthesis, plays a critical role in the process of breast cancer metastasis to the brain. Thus, toward a better understanding of the underlying molecular mechanisms and applications of molecular target(s) for brain metastasis therapy, murine models were employed for investigation of brain extravasation and colonization with intracardiac or direct intracranial injections of GFP/FLuc-labeled human MDA-MB-231 metastatic breast carcinoma cells. The MDA-MB-231 cells were found to metastasize to the brain and other organs following intracardiac implantation into nude mice and were further isolated from each tissue. Interestingly, the isolated brain-metastasized tumor cells (MDA-MB-231-BrM) exhibited a significant upregulation of SQLE expression when compared with those that metastasized to other distal sites. The essential role of SQLE in the specific steps of the breast cancer-to-brain metastatic process was evaluated by ex vivo immunofluorescence analysis and immunohistochemistry staining of brain slices from the study subjects. Our data demonstrate that high SQLE expression is essential for MDA-MB-231-BrM to extravasate into the parenchyma, as well as the formation of micro- and macro-metastases in the brain. Interestingly, we found that blood vessel co-option and the surrounding neuronal cells play key roles in supporting MDA-MB-231-BrM to develop brain macro-metastases. In vitro blood-brain barrier (BBB) models further demonstrated the critical role of SQLE in promoting tumor cell invasion and penetration through the BBB. To verify SQLE as an oncogenic factor that can be selected as a potential therapeutic target in suppressing breast cancer brain metastasis, we evaluated the inhibitory effects of terbinafine (a SQLE inhibitor) in both the MDA-MB-231-BrM orthotopic and intracardiac mouse models. Pharmacologic inhibition of SQLE by terbinafine suppressed MDA-MB-231-BrM tumor growth at the mammary fat pad and distal metastases to the brain, suggesting that targeting SQLE represents a therapeutic opportunity for breast cancer brain metastasis.
Citation Format: Pony Yu-Ling Lee, Kun-Yuan Lin, Chao-Di Chang, Shan-Yun Cheng, Ya-Wen Hung, Chih-Chieh Yang, Yu-Hsien Chang, Chien-Chang Shen, Jia-Yun Yeh, Yung-Lung Yu, Shu-Ping Wang. Targeting squalene epoxidase for breast cancer brain metastasis: The evaluation of a new therapeutic target for brain extravasation and colonization using animal models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1449.