Abstract B011: GDF-15 is a biomarker of aggressiveness in epithelioid hemangioendothelioma and is down-regulated by sirolimus through ATF4 suppression

Abstract Background: Epithelioid hemangioendothelioma (EHE) is an ultra-rare vascular sarcoma marked by two fusions - TAZ-CAMTA1 (~90%) and YAP-TFE3 (~10%) - that lead to Hippo-pathway activation. EHE clinical behavior ranges from indolent disease to highly aggressive presentation, but no biomarkers are known to predict the clinical outcome at disease onset. Conventional chemotherapy has limited effectiveness in advanced EHE patients and new treatment options are needed, as well as novel biomarkers of aggressiveness. We exploited i) two independent patient series to identify circulating biomarkers of EHE aggressiveness; ii) an EHE patient-derived xenograft (PDX) model and the derived cell line to investigate the effectiveness of sirolimus, one of the antitumor agents considered more effective in EHE. Methods: Two independent patient series were exploited to test the association between Growth/differentiation factor 15 (GDF-15) serum levels and EHE aggressiveness. A PDX model was generated from a patient with advanced EHE and showed consistency with the original tumor in terms of histomorphology, presence of the TAZ-CAMTA1 fusion and transcriptomic profile. This model - the only human EHE model available worldwide - has been used to generate a corresponding cell line. GDF-15 release from EHE cells and PDX was quantified by ELISA. Drugs cytotoxicity on EHE cells was assessed through cell counting and TUNEL assay. Western blotting was used to investigate sirolimus effects on EHE cells. Results: Analyses of blood samples from two independent patient series showed a statistically significant correlation between GDF-15 levels and EHE aggressiveness. ELISA on the blood of EHE-carrying mice and EHE cell culture medium revealed that GDF-15 is released by tumor cells. Sirolimus induced a significantly higher tumor growth inhibition (80%) compared to doxorubicin, whose activity was almost negligible in the EHE PDX. Also in EHE cells, sirolimus showed a lower IC50 (0.01µM versus 0.1µM) and a greater apoptotic response (TUNEL-positive cells: 20% vs 10%) than doxorubicin. Interestingly, sirolimus reduced GDF-15 expression/release in both in vivo and in vitro EHE models by reducing the expression of the GDF-15 transcription factor ATF4, as a consequence of the drug-induced inhibition of phosphorylation/activation of 4E-BP1, which is involved in the regulation of ATF4 translation. Conclusions: Results from this study indicate that: i) GDF-15 is a novel biomarker of EHE aggressiveness; ii) sirolimus is more effective than doxorubicin in our experimental model, supporting the suitability of the model for comparative studies on the activity of anticancer drugs for EHE treatment. Moreover, the notion that sirolimus inhibits the release of GDF-15 from EHE would suggest the relevance of this cytokine as a biomarker for monitoring sirolimus activity in patients. Further investigations are ongoing to clarify the role of GDF-15 in EHE progression. Citation Format: Alessia Beretta, Valentina Zuco, Silvia Martini, Anna Maria Frezza, Sandro Pasquali, Silvia Stacchiotti, Nadia Zaffaroni. GDF-15 is a biomarker of aggressiveness in epithelioid hemangioendothelioma and is down-regulated by sirolimus through ATF4 suppression [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B011.