Abstract 5282: Mitotane induces GDF-15 expression in vitro and in vivo: A potential therapy-induced mechanism of immune escape in adrenocortical carcinoma

Abstract Context: Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with poor prognosis and limited treatment options. The only approved therapy is mitotane, an adrenal toxicant, alone or in combination with cytotoxic chemotherapy. Response rate is only ~20%. Results of later line immune checkpoint inhibition (ICI) in ACC are disappointing, most likely due to an immunologically cold, immunosuppressive microenvironment. Among the factors induced in mitotane-treated ACC cell lines, we previously found growth/differentiation factor 15 (GDF-15), an anti-inflammatory cytokine physiologically expressed during pregnancy. Aim: As GDF-15 is an emerging mediator of tumor immune escape, we investigated changes in GDF-15 secretion upon mitotane treatment in ACC in vitro and in vivo, and explored a potential correlation with response to therapy and survival. Methods: Four different human ACC cell lines (NCI-H295R, CU-ACC1, CU-ACC2 and JIL-2266) were treated with mitotane. GDF-15 secretion and expression were determined by ELISA and immunoblot. GDF-15 levels in sera of 142 ACC patients (94 prior and 48 during mitotane) were analyzed by ELISA and correlated with survival from the time point of blood collection. GDF-15 serum levels were quantified in three responders and seven non-responders to ICI treatment. Results: In vitro, 24h treatment with 25 µM mitotane-induced GDF-15 secretion and expression in all cell lines by up to one order of magnitude. In 32 patient samples, GDF-15 serum concentrations increased from 0.6±1 ng/l prior mitotane to 2.1 ± 2.7 ng/l after mitotane initiation, p<0.0001.Importantly, patients with low serum GDF-15 levels before and during mitotane treatment had a significantly longer overall survival compared to patients with higher GDF-15 serum levels. This association retained statistical significance after adjustment for the known prognostic factors Ki67 and ENSAT tumour stage in the mitotane treated group (95% CI 1.15-.1.73, HR1.41, p=0.001). In an exploratory cohort of three responders and seven non-responders to ICI we found a trend for higher GDF-15 serum concentrations in the non-responders. Conclusion: Mitotane induces GDF-15 both in vivo and in vitro and potentially contributes to the poor response rates to ICI in ACC. Citation Format: Isabel Weigand, Tanja Anderlik, Jochen Schreiner, Hanna Remde, Otilia Kimpel, Laura-Sophie Landwehr, Eva Hoster, Florian Wedekink, Alexandra S. Triebig, Tanja Maier, Jörg Wischhusen, Martin Reincke, Martin Fassnacht, Matthias Kroiss. Mitotane induces GDF-15 expression in vitro and in vivo: A potential therapy-induced mechanism of immune escape in adrenocortical carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5282.