Abstract 3232: Combined inhibition of mTOR and HSP90 potentiates cisplatin antitumor effect and reverts cisplatin resistance in vitro and in vivo models of epithelial ovarian cancer by modulating HSF1-dependent transactivation

Abstract INTRODUCTION: Epithelial ovarian cancer (EOC) represents the most lethal gynecological disease, with a 5-year relative survival rate of 46% after the diagnosis. The standard treatment of advanced EOC is based on surgery, followed by platinum (Pt)-based chemotherapy. However, the development of platinum resistant disease could occur and strongly impact on the survival of EOC patients for whom we still do not have valid therapeutic options. By using a proteomic approach followed by a bioinformatic analysis, we previously validated the role of HSP90 in the mechanism of platinum-resistance. Here, we propose a novel therapeutic strategy based on the combined pharmacologic inhibition of HSP90 and mTOR to further potentiate Pt-based chemotherapy and to revert Pt-resistance in EOC and non-small-cell lung cancer (NSCLC) models. METHODS: TOV-112D parental and Pt-resistant cells were characterized by phosphoproteomics followed by functional analysis and proteins validation by western blot. Synergistic anti-tumor effect was evaluated in Pt-sensitive and Pt-resistant EOC and NSCLC cell lines by calculating combination indexes (CI), colony formation assay, apoptosis and DNA damage, as well as on 3D in vitro microtissues obtained by co-culturing cancer cells with normal fibroblasts and in vivo EOC and NSCLC xenograft models. RESULTS: 542 differentially phosphorylated expressed proteins were identified in Pt-resistant TOV-112D compared with parental cells, and mTOR and the transcription factor HSF1 emerged as the most enriched pathways. The up-regulation of the phosphorylated form of PDK1, AKT, mTOR and rpS6 was observed in Pt-resistant compared to parental cells. Moreover, we also demonstrated the up-regulation of the activity of HSF1 along with the elevation of its targets such as heat shock proteins HSP90, HSP70 and HSP40, crucial components of chaperone complex machinery. Interestingly, among the differentially expressed proteins, we identified the kinase DYRK2 able to phosphorylate HSF1, supporting its transactivation. Accordingly, the combination of HSP90 inhibitor ganetespib and the mTOR inhibitor temsirolimus plus cisplatin, synergistically reduced colony formation, cancer cells and microtissues cell growth in vitro by increasing DNA-damage and apoptosis and in vivo by enhancing mouse survival. Mechanistically, the triple combination treatment, impaired the proteins involved in mTOR signalling and HSF1 transactivation. Notably, all these data were confirmed in Pt-resistant NSCLC models, supporting the possibility that the same mechanism is present in different tumor types. CONCLUSIONS: Our findings identify a promising new antitumor strategy based on the combination of HSP90 and mTOR inhibitors to revert Pt-resistance that that warrant further clinical evaluation. Citation Format: Rita Lombardi, Laura Addi, Biagio Pucci, Maura Sonego, Maria Serena Roca, Francesca Capone, Federica Iannelli, Francesca Bruzzese, Gustavo Baldassarre, Alfredo Budillon. Combined inhibition of mTOR and HSP90 potentiates cisplatin antitumor effect and reverts cisplatin resistance in vitro and in vivo models of epithelial ovarian cancer by modulating HSF1-dependent transactivation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3232.