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.