SAT-464 Preclinical Investigation Of Phosphatidylinositol-3-kinase And Heat Shock Protein 90 Inhibitors Combination Therapy In Adrenocortical Carcinoma

Abstract Disclosure: P. Mishra: None. B. Sobieski: None. D. Laha: None. S.A. Forsythe: None. M. Shen: None. Y. Zhang: None. B. Ramamurthy: None. S.M. Sadowski: None. J.D. Rivero: None. J.M. Hernandez: None. N. Nilubol: None. Adrenocortical cancer (ACC) is a rare, aggressive cancer with poor survival due to a lack of effective treatments; therefore, it is critically important to identify therapies to be readily studied in clinical trials. Quantitative high-throughput drug combination screening identified potential synergy between phosphatidylinositol-3-kinase (PI3K) inhibitors and heat shock protein 90 (HSP90) inhibitors. We determined the effective doses and cytotoxicity of the HSP90 inhibitors (STA9090, HSP990, NVP-AUY922) and PI3K inhibitors (PIK-75, BGT-226) and their combinations in preclinical models of ACC. The synergistic effects of drug combinations were determined on cancer phenotypes and the mechanism of action using RNA-sequencing with appropriate confirmatory protein studies. Preclinical in-vitro and in-vivo studies were performed to validate the synergistic efficacy of the inhibitor combinations in ACC cell lines, patient-derived organoids (PDOs), and human ACC xenografts. The combination of PIK75 or BGT226 and either STA9090, HSP990, or NVP-AUY922 synergistically inhibited cell proliferation (monolayer and 3-dimensional), reduced cell migration-invasion, epithelial-to-mesenchymal transition, with decreased phosphorylated proteins in PI3K/mTOR signaling pathway. To assess the clinical relevance of the associated genes, we analyzed transcriptomic data of genes in the HSP90 and PI3K/AKT signaling pathway and the overall survival (OS) and disease-free survival (DFS) of patients with ACC in The Cancer Genome Atlas cohort (N=79). ACC patients with high expression of HSP90 family members HSP90B1 (OS: P =0.007, DFS: P <0.001), HSP90B3P (OS: P =0.092, DFS: P =0.084), HSP90AB2P (DFS: P=0.019) and HSP90B2P (DFS: P=0.044) and PI3K family members PIK3R1 (OS: P <0.010, DFS: P =0.092), AKT2 (OS: P=0.002, DFS: P <0.001), had either shorter OS or shorter DFS or both. The mRNA expression of HSP90B1, HSP90B2P, and AKT2 was significantly higher in primary human ACC samples with stage III/IV (N=31) and in samples with distant metastasis (N=15). Mechanistically, PIK75-STA9090 combination induced G2/M cell cycle arrest and caspase-dependent apoptosis, while the BGT226-STA9090 combination induced autophagy-related cell death in ACC cells. These combinations were more effective than the respective monotherapies in the PDOs (n=5) with different pathogenic mutations at clinically achievable concentrations. Further validation of synergistic efficacy of BGT226 and STA9090 in NOD SCID-gamma mice showed a reduction in the mean volume of ACC xenografts in STA9090-BGT226 treatment group to 28.4% of the vehicle control group and 38.4% and 37.7 % of those in STA9090-only and BGT226-only groups, respectively. In conclusion, the synergistic combinations of the PI3K and HSP90 inhibitors were effective in preclinical studies of ACC, warranting a clinical trial in patients with advanced ACC. Presentation: Saturday, July 12, 2025