RF07 | PSUN356 Synergistic Combination of HSP90 and PI3K inhibitors in Adrenocortical Cancer

Abstract Adrenocortical cancer (ACC) is a rare and aggressive cancer (0.5-2 cases/ million/ year) with a poor 5-year survival (<40%). Most patients inevitably succumb to the wide-spread metastasis because of the lack of effective systemic treatment options or to complications from uncontrolled hypercortisolism. Therefore, it is critically important to identify new effective treatments that can be readily used in a clinical trial. 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 comprised of ∼5000 drugs (FDA approved or investigational), and evaluation of drug synergy by a computerized drug combination matrix analysis. The synergistic efficacy of HSP90 inhibitor STA9090 and PI3K inhibitor, PIK75 was validated in vitro, in ACC cell lines H295R and SW13, by proliferation assay, which also determined the most efficacious doses of individual and combinatorial drugs. The drug combination significantly induced apoptosis and disintegrated the 3D-ACC spheroids as compared to the individual drugs, with a simultaneous upregulation of apoptotic protein markers (cleaved-Caspase3, cleaved-PARP), inhibition of the phosphorylation of PI3K pathway members (AKT1, mTOR, S6K, 4EB1 and GSK3α/β), and alteration in the G2/M phase of the cell cycle, in ACC cells. The synergetic effect of the drug combination was also effective in reducing the metastatic potential as revealed by invasion/migration assay, which was confirmed by the downregulation of the mesenchymal protein (Vimentin, N-cadherin, SNAIL and Zeb1) markers. Consistent with our data, observations from the gene expression data from The Cancer Genome Analysis (TCGA) & Gene Expression Omnibus (GEO) databases, revealed significant mRNA overexpression of HSP90AA1, HSP90AB1 HSP90B1 and its clients AKT2, CDK1, CDK4, NR3C1 indicating both HSP90 and PI3K/AKT pathways are highly activated in ACC cohorts. Overexpression and a positive correlation of mesenchymal markers TWIST1, ZEB1, VIM with HSP90AB1 and PI3KCA, in GEO and TCGA respectively, was consistent with the invasive potential of the ACC cells. In conclusion, our studies on the combination of HSP90 and PI3K inhibitors demonstrated a promising preliminary synergistic efficacy by inhibiting proliferation and epithelial-to-mesenchymal transition of ACC. Our findings can lead to development of an efficient mechanism-specific novel combination therapy that can be expedited to clinical trial in advanced ACC patients. Presentation: Saturday, June 11, 2022 1:12 p.m. - 1:17 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.