Abstract P6-02-04: Atorvastatin insensitivity is associated with increased lipid droplets accumulation and fatty acid metabolism in breast cancer cells
Authors: Lettiero B , Kimbung S , Borgquist S 
Published: March 2017

Abstract
Lipophilic statins, including atorvastatin, may exert significant antiproliferative and proapoptotic effects in breast cancer as demonstrated in both clinical trials and cell models. However, heterogeneity in treatment response still remains a noteworthy challenge to be addressed. In this regard, we previously proposed a multigene signature including genes involved in cholesterol biosynthesis, which were dysregulated upon atorvastatin treatment and was shown to predict statin responsiveness in breast cancer (BC) cell lines and primary tumors. To further delineate the molecular mechanisms underlying this variability, we sought to characterize the differential statin-induced effects on intracellular lipid regulation observed in BC cell lines based on their sensitivity to atorvastatin treatment. BC cells were classified as insensitive (MCF-7 and T47D) or sensitive (MDA-MB-231) to atorvastatin by virtue of growth inhibition rate consequent to treatment with doses ranging up to 10 μM. Under complete culture conditions, atorvastatin-induced decrease in cell proliferation was inversely correlated to a progressive accumulation of neutral lipids in lipid droplets (LDs) in the insensitive cells following 72 hours treatment. Interestingly, in the sensitive MDA-MB-231 cells no significant change in LDs formation was observed despite the very potent antiproliferative effects (60% impairment of growth). However, in correspondence of severe inhibition of growth rate of at least 80% by atorvastatin treatment, MDA-MB-231 cells displayed a consistent reduction in LDs accumulation, suggesting beneficial effects of LDs biosynthesis on proliferation of BC cells. Transcriptional profiling of genes involved in lipid metabolism using microarrays and validated by qRT-PCR ruled out the likelihood that atorvastatin treatment altered lipid uptake and export mechanisms in sensitive cells in the presence of exogenous lipid supply. Nevertheless, gene ontology analysis indicated that an induction of cell stress responses was likely associated to atorvastatin sensitivity. Significant deregulation of genes involved in the fatty acid metabolic process, including biosynthesis of monounsaturated fatty acids (MUFAs), and cholesterol biosynthesis were instead linked to atorvastatin insensitivity. Accordingly, we found that the magnitude of the induction of the mRNAs of stearoyl-CoA desaturase (SCD), the key effector in MUFAs metabolism, and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the established target of statins, were consistently lower in sensitive cells compared to the insensitive counterpart in response to atorvastatin treatment. Therefore, we suggest that the ability to significantly increase the number of stored neutral lipids in response to statin treatment may likely confer a proliferative advantage to BC cells. Our results also identified MUFAs metabolism as an attractive pathway to be further investigated in view of finding promising biomarkers for unraveling the molecular basis of statin sensitivity in breast cancer.
Citation Format: Lettiero B, Kimbung S, Borgquist S. Atorvastatin insensitivity is associated with increased lipid droplets accumulation and fatty acid metabolism in breast cancer cells [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-02-04.