Metformin exhibited anticancer activity by lowering cellular cholesterol content in breast cancer cells.

Ankit Sharma,Rekha Maheshwari,Gopal Chakrabarti,Vipin Kumar,Shreetama Bandyopadhayaya,Kaushik Chowdhury,Chandi C Mandal,Tanu Sharma,Amlan Das,Gokul M Das

doi:10.1371/journal.pone.0209435

Abstract

Metformin, a widely prescribed anti-diabetic drug, shows anticancer activity in various cancer types. Few studies documented that there was a decreased level of LDL and total cholesterol in blood serum of metformin users. Based on these views, this study aimed to determine if metformin exhibits anticancer activity by alleviating cholesterol level in cancer cells. The present study found that treatment of breast cancer MDA-MB-231 cells with metformin significantly decreased cholesterol content with concomitant inhibition of various cholesterol regulatory genes (e.g., HMGCoR, LDLR and SREBP1). Metformin decreased cell viability, migration and stemness in metastatic MDA-MB-231 cells. Similarly, metformin treatment suppressed expressions of anti-apoptotic genes BCL2 and Bcl-xL, and mesenchymal genes vimentin, N-cadherin, Zeb1 and Zeb2 with simultaneous enhancement of apoptotic caspase 3 and Bax, and epithelial genes E-cadherin and keratin 19 expressions, confirming an inhibitory effect of metformin in tumorigenesis. Similar to metformin, depletion of cholesterol by methyl beta cyclodextrin (MBCD) diminished cell viability, migration, EMT and stemness in breast cancer cells. Moreover, metformin-inhibited cell viability, migration, colony and sphere formations were reversed back by cholesterol treatment. Similarly, cholesterol treatment inverted metformin-reduced several gene expressions (e.g., Bcl-xL, BCL2, Zeb1, vimentin, and BMI-1). Additionally, zymography data demonstrated that cholesterol upregulated metformin-suppressed MMP activity. These findings suggested that metformin revealed anticancer activity by lowering of cholesterol content in breast cancer cells. Thus, this study, for the first time, unravelled this additional mechanism of metformin-mediated anticancer activity.

Highlights

Cancers are the most complex and complicated diseases where both mutations and epigenetic changes within cancer genome widely differ from one tumor to other
To scrutinise the molecular mechanism of cholesterol enrichment in malignant tissues, expressions of various cholesterol regulatory genes were measured by RT-PCR analysis. These analyses showed higher expressions of cholesterol regulatory gene (i.e., HMG-CoA reductase (HMGCoR), low density lipoprotein receptor (LDLR) and sterol regulatory element-binding protein 1 (SREBP1)) transcripts in malignant tissues as compared to benign breast tissues (Fig 1B and 1C)
This study focused on widely recommended antidiabetic metformin drug, since many studies documented its anticancer activity in various cancer types [4]

Summary

Introduction

Cancers are the most complex and complicated diseases where both mutations and epigenetic changes within cancer genome widely differ from one tumor to other. It causes a large number of mortality, and accounts a huge economic burden nationwide. Literature suggested a positive association of cancer risk and/or mortality with diabetes and high cholesterol [1,2,3]. Present treatment modalities are quite capable to increase overall survival in cancer patients; systemic and off-target toxicity are still the greatest hurdles for the success of cancer therapy. There is a high demand on the use of relatively non-toxic drugs for cancer treatment

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