Abstract 5262: Avasimibe abolishes the breast cancer preventative efficacy of statin in a spontaneous mouse model of breast cancer
Authors: Bhardwaj Anjana , Ju Zhenlin , Koh Alexander , Bhala Rhea , Wang Jing , Bedrosian Isabelle 
Published: April 2023

Abstract
Background: The cholesterol biosynthesis pathway plays a central role in the normal cellular development and carcinogenesis. Relevant to breast cancer prevention, the breast epithelium in women with atypical hyperplasia has been shown to have increased in cholesterol levels and oxidative products of cholesterol. Additionally, cholesterol pathway genes such as HMGCR and HMGCS1 are known to be upregulated during progression of breast cancer in patients. We have previously shown in SV40C3TAg mice that the cholesterol lowering drug-fluvastatin reduces breast tumor incidence and burden by 50% and have noted that the efficacy of statin is reduced due to the tight regulation of the cholesterol biosynthesis pathway through multiple restorative feedback loops, thus bypassing the effect of statin blockade.
Hypothesis: We hypothesize that fluvastatin efficacy can be improved by co-targeting the restorative feedback pathways that are involved in resistance to statins.
Methodology: RNA seq data from statin resistant MCF10.AT1-R cell clones was compared to the statin sensitive parental MCF10.AT1 cells in order to identify pathways and targets involved in statin resistance. Genes that were also found to be upregulated in the statin non-responders mice mammary tumors relative to responders mice were tested for dual targeting. Efficacy of avasimibe, an ACAT inhibitor, to sensitize MCF10.DCIS cells to statin therapy was studied by the colony formation assay. In vivo validation of the statin + avasimibe dual therapy was performed in SV40C3TAg mice that spontaneously develop triple negative breast cancer.
Results: We found ACAT1 and ACAT2 to be overexpressed in statin resistance cell clones and non-responder mouse breast tumors. ACATs are involved in cholesterol esterification that is required for storing cholesterol in lipid droplets. Cholesterol esterification in conjunction with cholesterol synthesis and export constitute key mechanisms involved in maintaining cholesterol homeostasis. Thus, we tested if avasimibe treatment potentiates the fluvastatin efficacy to inhibit colonizing ability. Avasimibe and fluvastatin combination completely abolished the ability of MCF10.DCIS cells to form colonies. Next, we tested the efficacy of combination treatment to prevent breast tumors in SV40C3TAg mice. The treatments started at the age of 6 weeks, prior to the onset of cancer and continued until 22 weeks of age. We found fluvastatin and avasimibe combination to be completely ineffective and 90% mice developed tumors. In addition, tumor burden was not reduced with dual treatment.
Conclusions: We postulate that avasimibe enhanced metabolism of fluvastatin in mouse system and thus completely abolishing the chemopreventive effects of statin. Genomically derived rationale drug combinations may result in unanticipated interactions and/or ancillary effects that limit efficacy in vivo/in patients.
Citation Format: Anjana Bhardwaj, Zhenlin Ju, Alexander Koh, Rhea Bhala, Jing Wang, Isabelle Bedrosian. Avasimibe abolishes the breast cancer preventative efficacy of statin in a spontaneous mouse model of breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5262.