Abstract B007: Vandetanib abrogates antiestrogen resistance in MAPK-driven ER+ breast cancer by halting key intracellular signaling pathways and multiple druggable kinases
Authors: Kakati Rasha T , Whitman Austin , Kim Hyunsoo , Spanheimer Philip M 
Published: February 2024

Abstract
Introduction: Vandetanib has been shown to abrogate ER+ breast cancer growth via inhibition of MAPK; we sought to elucidate the effects of Vandetanib on MAPK-driven endocrine-resistant breast cancer. Methods: Chronically treated MCF7-TAM (Tamoxifen), MCF7-EXE (Exemestane), and wild-type MCF7 ER+ breast cancer cell lines were treated with Vandetanib and/or Tamoxifen. Cell viability assays were conducted with CellTiter-Glo. Cells were treated with Vandetanib (10 uM) and vehicle for 24 hours, and mRNA sequencing was performed. To elicit TKI-specific proteomic changes, cells were treated with control or IC90 Vandetanib for 48 hours, and the signatures of kinase activity were determined using a multiplex inhibitor bead library coupled with mass spectrometry. Differential gene (DGE) and protein (DPE) expression analyses were performed to determine enriched and depleted transcripts and kinase activity with Vandetanib treatment. Gene set enrichment analysis was performed to determine the shared and unique pathways regulated by Vandetanib for each model. A Vandetanib response signature was compiled using the top 20 downregulated genes and analyzed with METABRIC and SCAN-B datasets to assess effects on survival in ER+ breast cancer patients. Results: MCF7-TAM and MCF7-EXE demonstrated lower Tamoxifen IC50 when treated with Vandetanib compared to Tamoxifen alone, which showed synergistic effects. Data analysis of mRNA libraries showed reduced tumor progression and signaling of MAPK, PI3K/AKT, RAS, CCND1, MYC, and EGFR across all three lines, as well as increased ERBB2 signaling, which may denote a potential adaptive bypass mechanism to Vandetanib treatment. Gene sets showed increased estrogen response, ESR1 activity, and sensitivity to tamoxifen across all three lines. Notable key players in PI3K/AKT and MAPK signaling such as TYRO3 were significantly downregulated at both the gene and protein levels. Additionally, JAK2 demonstrated dual upregulation and has been implicated with favorable prognosis due to associations with immune infiltration. The downregulated Vandetanib gene set conferred significantly improved OS (HR=0.75, p&lt;0.0001, METABRIC; HR=0.87, p=0.034, SCAN-B) and RFS (HR=0.60, p&lt;0.0001, METABRIC) in ER+ breast cancer patients from both datasets. Multiple druggable kinases such as RET, EGFR, FGFR2/3, CDK6, and SRC were depleted by Vandetanib treatment. Upregulated druggable kinases identified with Vandetanib treatment include MTOR, FGFR4, ERBB2, and JAK1. Conclusions: Vandetanib overcomes antiestrogen resistance in MAPK-driven models of ER+ breast cancer by halting key signaling pathways such as MAPK, PI3K/AKT, MYC, and ERBB2, among others. Upregulated druggable kinases may serve as targets to overcome resistance to Vandetanib. Downregulated targets with Vandetanib could serve as biomarkers to select patients most likely to benefit from Vandetanib treatment.
Citation Format: Rasha T Kakati, Austin Whitman, Hyunsoo Kim, Philip M Spanheimer. Vandetanib abrogates antiestrogen resistance in MAPK-driven ER+ breast cancer by halting key intracellular signaling pathways and multiple druggable kinases [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B007.