Endocrine Abstracts

Introduction: Adrenocortical carcinoma (ACC) is a rare, but highly malignant endocrine tumor. Surgery is the primary choice of treatment. In case of inoperable disease or tumor recurrence, therapy with the adrenolytic drug mitotane is usually applied. Plasma mitotane concentrations of >14 mg/l (50 μM) seem required for an effect on tumor mass. Despite its clinical use, the effects of mitotane on cell proliferation and hormone production have been poorly investigated in vitro.

Aim of the study: To study the effect of mitotane on cell number and hormone production in primary cultures of human ACC.

Methods: Freshly isolated primary cultures of ACC (n=21) cells were cultured in DMEM-F12+5% FCS. Cells were treated for up to 144 h with increasing concentrations of mitotane (range: 10⁻⁷−10⁻⁴ M). After 144 h, media were collected for hormone measurement and cells were harvested for determination of cell number.

Results: Three groups of cultures were arbitrarily defined on the basis of response to 50 μM mitotane. Non-responders (NR): <33% inhibition of cell number (n=12, IC₅₀: >10⁻⁴ M); partial responders (PR): 33–66% inhibition (n=5, IC₅₀: 40±1 μM); responders (R): >66% response (n=4, IC₅₀: 20±1 μM). 10/21 (49%) ACC produced cortisol (n=9) or estradiol (n=1) in vitro. There was no difference in the effect of mitotane on cortisol in PR+R (IC₅₀: 2.4±1.2 μM, n=6), compared with NR (IC₅₀: 3.6±1.2 μM, n=3). Functional ACC were significantly more sensitive to mitotane treatment than non-functional ACC (7/9 PR+R and only 3/12 NR were functional; P<0.03, Fisher’s exact test).

Conclusions: Mitotane inhibits cortisol production in primary functional ACC cultures. Only 4/21 (19%) of the primary AAC showed a response of more than 66% inhibition of cell number by 50 μM mitotane, in agreement with the estimated in vivo efficacy of the drug. Cell number of functional ACC is significantly more potent inhibited by mitotane, compared with non-functional ACC.