Abstract 2684: Synergistic efficacy of HSP90 and PI3K inhibitors in adrenocortical carcinoma

Abstract Adrenocortical cancer (ACC) is a rare and aggressive cancer (0.5-2 cases/million/year) with poor 5-year survival. Most patients inevitably succumb to widespread metastasis due to a lack of effective systemic treatment; therefore, it is critically important to identify new therapies for clinical trials. In this direction, we identified a potent synergistic combination of Heat Shock Protein 90 (HSP90) and PI3K inhibitors via quantitative high-throughput drug screening (qHTS) for ACC, using a pharmaceutical library of ~5000 drugs (FDA approved or investigational), and evaluating the drug synergy by computerized drug combination matrix analysis. Preclinical in vitro studies were performed to validate the efficacy of HSP90 inhibitors (STA9090, AUY922, HSP990), with PI3K inhibitors; PIK75 (investigational) or clinically available BGT226, and their pairwise combinations, in NCI-H295R and SW13 ACC cells. The drug combination of STA9090 and PIK75 significantly inhibited cell proliferation (monolayer and 3-dimensional culture and induced apoptosis more effectively than the individual drugs, with simultaneous upregulation of apoptotic protein markers (cleaved-Caspase3, cleaved-PARP), inhibition of the phosphorylated members of PI3K signaling pathway (AKT1, mTOR, S6K, 4EB1 and GSK3α/β), and the G2/M phase cell cycle arrest in ACC cells. Additionally, the synergetic effect of the drug combination was effective in reducing the metastatic potential as revealed by invasion/migration assay, which was confirmed by the downregulation of the epithelial-to-mesenchymal transition proteins (Vimentin, N-cadherin, SNAIL and Zeb1). An inhibition of cortisol production and altered oncogenic proteomic profiling was also observed. We validated the synergy of BGT226 with STA9090 and observed similar phenotypic changes by the drug combination in ACC cells. Interestingly, RNA sequencing and pathway analysis further revealed distinct gene expression profiles of STA9090 combined with PIK75 or BGT226, indicating different mechanism of cell death in both the PI3K drug combination treatment groups. Consistent with our in vitro findings, observations from the gene expression data from TCGA revealed significant mRNA overexpression of genes in HSP90 and PI3K signaling pathways (HSP90AA1, HSP90AB1 HSP90B1, TRAP1, PI3KCA, PI3KCB, AKT2, CDK1, CDK4, NR3C1) in 64% (n=59/92) ACC samples, with a positive correlation of mesenchymal markers TWIST1, ZEB1, VIM with HSP90AB1 and PI3KCA, suggesting our drug combination can be applicable in patients with ACC. A similar pattern of gene expressions was confirmed in independent GEO datasets. Conclusively, combination of HSP90 and PI3K inhibitors demonstrated a promising in vitro synergistic efficacy by inhibiting the key oncogenic targets of ACC. Further validation of in vivo efficacy is warranted. Citation Format: Prachi Mishra, Dipranjan Laha, Brieann Sobieski, Min Shen, Ya-Qin Zhang, Matthew Hall, Naris Nilubol. Synergistic efficacy of HSP90 and PI3K inhibitors 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 2684.