Mitochondrial respiratory chain defects: a novel molecular mechanism of Mitotane for treatment of Adrenocortical Carcinoma

S. Hescot; A. Slama; A. Paci; H. Remy; R. Chadarevian; S. Trabado; A. Lombes; J. Young; E. Baudin; M. Lombes

Mitotane (o,p’DDD) represents the most effective treatment of adrenocortical carcinoma (ACC). However, molecular mechanisms of mitotane action remain poorly understood. Mitochondrial (mt) impact of mitotane has previously been suggested but not yet fully validated. We investigated functional consequences of mitotane exposure on mitochondrial steroidogenesis, respiratory chain activity and biogenesis, using human adrenocortical secreting H295R and non-secreting SW13 cells. We first confirmed that mitotane exposure inhibits cell proliferation in a dose- and time-dependent manner. We were however unable to detect mitotane metabolites, o,p’DDA and o’p’DDE, in cultured cells supernatant. We demonstrated that mitotane drastically reduces cortisol and 17-hydroxyprogesterone secretions by 70%, at a 50 μM (14 mg/L) concentration, considered as the therapeutic plasma level threshold. This was accompanied by significantly decreased expression of genes encoding mitochondrial proteins involved in steroidogenesis (STAR, CYP11B1, CYP11B2). In both H295R and SW13 cells, 50 μM mitotane induced a significant and reproducible 50% decrease of the maximum velocity of the respiratory chain complex IV (cytochrome c oxidase, COX) activity. This was associated with significantly decreased expression of both the mtDNA-encoded COX2 and the nuclear DNA encoded COX4 COX subunits, and with an important reduction of the whole COX steady state expression, as revealed by Blue Native PAGE. Enhanced mitochondrial biogenesis was shown by an increased mt DNA content and enhanced expression of the transcriptional regulator PGC1α, consistent with an adaptive and compensatory mechanism against mitochondrial defect. Mitotane exposure also triggered a morphologic shift from filamentous to punctuate aspects of mitochondrial network, providing additional support for alteration in the mitochondrial compartment dynamics.

Collectively, our results provided first evidence that mitotane induces mitochondrial respiratory chain defect. Better understanding of mitotane pharmacology should enable us to identify predictive factors of efficacy and toxicity.

(Supported by grants from Inserm, Univ Paris-Sud, HRA-Pharma)

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.

Endocrine Abstracts

P785