Exquisite sensitivity of adrenocortical carcinomas to induction of ferroptosis

Adrenocortical carcinomas (ACCs) are rare and highly malignant cancers associated with poor survival of patients. Currently, mitotane, a nonspecific derivative of the pesticide DDT (1,1-(dichlorobiphenyl)-2,2-dichloroethane), is used as the standard treatment, but its mechanism of action in ACCs remains elusive. Here we demonstrate that the human ACC NCI-H295R cell line is remarkably sensitive to induction of ferroptosis, while mitotane does not induce this iron-dependent mode of regulated necrosis. Supplementation with insulin, transferrin, and selenium (ITS) is commonly used to keep NCI-H295R cells in cell culture. We show that this supplementation prevents spontaneous ferroptosis, especially when it contains polyunsaturated fatty acids (PUFAs), such as linoleic acid. Inhibitors of apoptosis (zVAD, emricasan) do not prevent the mitotane-induced cell death but morphologically prevent membrane blebbing. The expression of glutathione peroxidase 4 (GPX4) in H295R cells, however, is significantly higher when compared to HT1080 fibrosarcoma cells, suggesting a role for ferroptosis. Direct inhibition of GPX4 in H295R cells led to high necrotic populations compared to control, while cotreatment with ferrostatin-1 (Fer-1) completely reverted ferroptosis. Interestingly, the analysis of public databases revealed that several key players of the ferroptosis pathway are hypermethylated and/or mutated in human ACCs. Finally, we also detected that growth hormone-releasing hormone (GHRH) antagonists, such as MIA602, kill H295R cells in a nonapoptotic manner. In summary, we found elevated expression of GPX4 and higher sensitivity to ferroptosis in ACCs. We hypothesize that instead of treatment with mitotane, human adrenocortical carcinomas may be much more sensitive to induction of ferroptosis.