Statins Reduce Intratumor Cholesterol Affecting Adrenocortical Cancer Growth

Abstract

Mitotane causes hypercholesterolemia in ACC patients. We suppose that cholesterol increases within the tumor and can be used to activate proliferative pathways. In this study, we used statins to decrease intratumor cholesterol and investigated the effects on ACC growth related to ERα action at the nuclear and mitochondrial levels. We first used microarray to investigate mitotane effect on genes involved in cholesterol homeostasis and evaluated their relationship with patients' survival in ACC TCGA.We then blocked cholesterol synthesis with simvastatin and determined the effects on H295R cell proliferation, estradiol production and ERα activity in vitro and in xenograft tumors. We found that mitotane increases intratumor cholesterol content and expression of genes involved in cholesterol homeostasis, among them INSIG, whose expression affects patients' survival. Treatment of H295R cells with simvastatin to block cholesterol synthesis decreased cellular cholesterol content and this affected cell viability. Simvastatin reduced estradiol production and decreased nuclear and mitochondrial ERα function. A mitochondrial target of ERα, the respiratory complex IV (COX IV) was reduced after simvastatin treatment, which profoundly affected mitochondrial respiration activating apoptosis. In vivo experiments confirmed the ability of simvastatin to reduce tumor volume and weight of grafted H295R cells, intratumor cholesterol content, Ki-67 and ERα, COX IV expression and activity and increase TUNEL positive cells. Collectively these data demonstrate that a reduction in intratumor cholesterol content prevents estradiol production, inhibits mitochondrial respiratory chain inducing apoptosis in ACC cells. Inhibition of mitochondrial respiration by simvastatin represents a novel strategy to counteract ACC growth.

The Role of Biomarkers in Adrenocortical Carcinoma: A Review of Current Evidence and Future Perspectives

“…To come to a generally accepted conclusion, further investigations on a large cohort of ACC patients are urgent. Furthermore, mitotane use can cause hypercholesterolemia in patients with adrenocortical carcinoma and it is possible that cholesterol increases intratumor activity [220]. Simvastatin addition can reduce tumor volume and weight, prevent estradiol production and inhibit mitochondrial respiratory chain-inducing apoptosis in ACC cells [220].…”

Molecular Mechanisms of Mitotane Action in Adrenocortical Cancer Based on In Vitro Studies

“…Weigand et al retrospectively analyzed data of 231 patients with ACC treated with mitotane in 12 reference centers and did not find any significant differences between tumors with high or low SOAT1 expression in terms of recurrence-free survival (in 158 patients treated with adjuvant mitotane), progression-free survival (in 73 patients with advanced ACC), or disease-specific survival (in both settings) [60]. In vitro, mitotane induces ER stress through inhibition of SOAT1, which leads to the blockade of cholesterol synthesis and steroidogenesis, and this accumulation of free cholesterol rapidly becomes toxic to the cells (Figure 2) [58,61]. Furthermore, mitotane in H295R subclones reduces the expression of ABCA1, which is involved in the cellular efflux of cholesterol [62], and of SCARB1, which encodes for scavenger receptor B1 (SR-BI), In vitro, mitotane induces ER stress through inhibition of SOAT1, which leads to the blockade of cholesterol synthesis and steroidogenesis, and this accumulation of free cholesterol rapidly becomes toxic to the cells (Figure 2) [58,61].…”

“…In vitro, mitotane induces ER stress through inhibition of SOAT1, which leads to the blockade of cholesterol synthesis and steroidogenesis, and this accumulation of free cholesterol rapidly becomes toxic to the cells (Figure 2) [58,61]. Furthermore, mitotane in H295R subclones reduces the expression of ABCA1, which is involved in the cellular efflux of cholesterol [62], and of SCARB1, which encodes for scavenger receptor B1 (SR-BI), In vitro, mitotane induces ER stress through inhibition of SOAT1, which leads to the blockade of cholesterol synthesis and steroidogenesis, and this accumulation of free cholesterol rapidly becomes toxic to the cells (Figure 2) [58,61]. Furthermore, mitotane in H295R subclones reduces the expression of ABCA1, which is involved in the cellular efflux of cholesterol [62], and of SCARB1, which encodes for scavenger receptor B1 (SR-BI), the most important transporter for adrenal cholesterol uptake [46,63].…”

“…In vitro, mitotane induces ER stress through inhibition of SOAT1, which leads to the blockade of cholesterol synthesis and steroidogenesis, and this accumulation of free cholesterol rapidly becomes toxic to the cells ( Figure 2 ) [ 58 , 61 ]. Furthermore, mitotane in H295R subclones reduces the expression of ABCA1, which is involved in the cellular efflux of cholesterol [ 62 ], and of SCARB1 , which encodes for scavenger receptor B1 (SR-BI), the most important transporter for adrenal cholesterol uptake [ 46 , 63 ].…”

“…This effect is of particular importance as it could potentially self-promote drug resistance [ 1 , 26 ]. On this basis, several in vitro and clinical studies were recently conducted to evaluate how to counteract resistance to mitotane by lowering lipoprotein levels through, for example, statins or PCSK9 inhibitors [ 61 , 62 , 68 ]. In a recent clinical case, the strategy of targeting the PCSK9 gene [ 68 ], which encodes an enzyme expressed mainly in the liver and intestine with an important role in lipid metabolism, was reported.…”