Mitotane Targets Lipid Droplets to Induce Lipolysis in Adrenocortical Carcinoma

Area of Science:

• Oncology
• Biochemistry
• Cell Biology

Background:

• Adrenocortical carcinoma (ACC) is an aggressive cancer with poor prognosis.
• Mitotane is an adjuvant therapy for ACC, but its effectiveness is limited by resistance and low response rates.
• Current understanding suggests mitotane's efficacy stems from free cholesterol accumulation, yet targeting this pathway has failed.

Purpose of the Study:

• To investigate the hypothesis that mitotane-induced free-cholesterol accumulation is also mediated by enhanced breakdown of lipid droplets.
• To explore the role of lipolysis in mitotane's mechanism of action and its potential as a therapeutic target in ACC.

Main Methods:

• Comparative analysis of lipid content and machinery in mitotane-sensitive (H295R) and mitotane-resistant (MUC-1) ACC cell lines.
• Utilized BODIPY dyes for lipid content assessment, immunoblotting and flow cytometry for protein expression, and propidium iodide staining for cell viability.
• Investigated the impact of mitotane and pharmacological lipolysis inhibitors on ACC cell viability.

Main Results:

• ACC cell lines exhibited distinct lipid storage profiles: H295R cells stored cholesteryl esters, while MUC-1 cells stored triacylglycerol.
• Mitotane treatment, particularly at toxic concentrations, induced lipolysis and decreased lipid droplets in both cell lines.
• Pharmacological inhibition of lipolysis significantly reduced mitotane-induced toxicity in both sensitive and resistant ACC models.

Conclusions:

• Lipid droplet breakdown and lipolysis activation represent a potential mechanism contributing to mitotane's cytotoxicity in ACC.
• These findings suggest that targeting lipid metabolism, specifically lipolysis, could offer novel therapeutic strategies for ACC, especially in cases of mitotane resistance.