Abstract P6-12-02: isomiR-140-3p-regulated mevalonic acid pathway as a potiental target for prevention of triple negative breast cancer
Authors: Bhardwaj A , Singh H , Trinidad CM , Albarracin C , Hunt KK , Bedrosian I 
Published: May 2019

Abstract
Background: Prevention of triple negative breast cancer (TNBC) is hampered by lack of knowledge about the drivers of tumorigenesis. Methods: In order to identify molecular markers and their downstream networks that can potentially be targeted for TNBC prevention, we analyzed small RNA and RNA sequencing of a cell line model that represents early stages of TNBC development. We identified direct gene targets of an isomiRNA and using cell based and in vivo model systems we demonstrate the utility of targeting downstream pathways for prevention of TNBC. Results: These analyses showed that 5'isomiRNA of miR-140-3p (miR-140-3p-1) were deregulated in the normal-to- preneoplastic transition. We also identified novel direct gene targets of miR140-3p-1, HMG-CoA reductase (HMGCR) and HMG-CoA synthase 1(HMGCS1), key enzymes in the cholesterol biosynthesis pathway, and found that these too are deregulated in the normal to preneoplastic transition, resulting in activation of the cholesterol synthesis pathway. Upregulation in the cholesterol pathway creates a metabolic vulnerability that can be targeted with the statin class of inhibitors. Consistent with this hypothesis, we found direct targeting of miR-140-3p-1 and its downstream pathway by fluvastatin inhibits growth of these preneoplastic MCF10.AT1 cells. However, although, fluvastatin inhibited the growth of MCF10.AT1-derived xenografts, histological progression remained unchanged. The cholesterol pathway is highly regulated, and HMGCR enzymatic activity inhibition is known to trigger a feedback response leading to restoration of the pathway. Indeed, we found fluvastatin treatment induced HMGCR transcript levels in the explanted xenografts, with higher transcript induction directly correlated with the degree of histological progression of lesions, indicating an adaptive resistance mechanism that circumvents statin targeting of HMGCR. Therefore, we hypothesized that dual targeting of HMGCR and the feedback loops are necessary to overcome this adaptive resistance. To test this hypothesis, we generated MCF10AT1 cells resistant to fluvastatin. We then treated these resistance AT1 cells with an activator of AMP-activated protein kinase (AMPK), a brake in the cholesterol feedback pathway. AMPK activation by aspirin effectively abrogated the statin-induced upregulation of HMGCR and sensitized these resistant cells to fluvastatin. Conclusions: Our preclinical data suggests that the statin treatment induced homeostatic upregulation of the cholesterol pathway is a barrier to effective chemoprevention with statins. However, our results also suggest that this adaptive resistance mechanism can be abrogated by combined treatment with statin and AMPK activators such as aspirin. Clinical studies of this combined regimen should be considered in high risk patients.
Citation Format: Bhardwaj A, Singh H, Trinidad CM, Albarracin C, Hunt KK, Bedrosian I. isomiR-140-3p-regulated mevalonic acid pathway as a potiental target for prevention of triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-12-02.