Abstract P4-08-13: The Use of Reverse Phase Protein Arrays (RPPA), Principal Component Analysis (PCA), and CScape Pathway Mapping to Identify New Tumor Vulnerability and Actionable Targets in Human Malignant Triple-Negative Breast cancer cell lines
Authors: Howell Andrew P. , Wulfkuhle Julia , Gallagher Rosa I. , Petricoin Emanuel F. , Tang Amy H. 
Published: March 2023

Abstract
Breast cancer is the major leading cause of cancer-related fatalities nationally and globally. There will be 287,850 new breast cancer cases and 43,250 breast cancer related deaths in the United States in 2022. The relapsed, treatment-resistant, undruggable, and incurable breast cancers are often associated with EGFR/HER2/K-RAS/SIAH pathway activation. The EGFR/HER2/K-RAS/SIAH pathway is a major tumor-driver whose hyperactivation is associated malignant tumor growth, multidrug-resistant phenotypes, early tumor relapse, and systematic metastasis. Seven-In-Absentia (SINA) homologues (SIAH) are extraordinarily evolutionarily-conserved E3 ubiquitin ligases that play a critical gatekeeper role downstream of the EGFR/HER2/K-RAS pathway. SIAH is a major tumor vulnerability that is ideally positioned to become an attractive target for innovative targeted therapy development against metastatic breast cancer (MBC). Prior studies have shown that tumor growth was abolished in malignant tumor cell lines such as MDA-MB-231, MDA-MB-468, MiaPaCa, A459, and HeLa following SIAH inhibition in xenograft models; however, the underpinning molecular mechanisms that give rise to this striking anti-EGFR/K-RAS and anticancer phenotype remain unclear. Specific objectives: to delineate the molecular mechanism(s) of why anti-SIAH2PD targeted therapy is so effective in impeding and eradicating the stage IV and aggressive tumors, we conducted reverse phase protein array (RPPA)-based kinomic analysis to delineate how major cancer signaling pathways and EGFR/HER2/K-RAS/SIAH-dependent signaling networks are rewired and remodeled in response to anti-SIAH2 targeted therapy. Brief statement of methods: About 300 proteins/phosphoproteins were quantititatively measured by the RPPA platform to identify new tumor vulnerabilities and actionable targets, compensatory signaling network activation/inhibition in response to anti-SIAH targeted therapies in five highly malignant cancer cell lines. Doxycycline (DOX)-inducible Tet-ON MDA-MB-231, MDA-MB-468, MiaPaCa, HeLa and A459 cell lines were amplified from single cell and DOX-induced SIAH2PD expression was confirmed. Each of the cell lines was then subjected to one of four experimental conditions: Tet-ON control cells without DOX induction (group A), Tet-ON control cells with DOX induction (group B), Tet-ON-SIAH2PD cancer cells without DOX-induction (no SIAH2PD inhibitor) (group C), Tet-ON-SIAH2PD cancer cells with DOX-induction (SIAH2PD inhibitor) (group D). Reverse Phase Protein Array (RPPA) in conjunction with Principal Component Analysis (PCA) was conducted to quantify fold-changes of proteins/phosphoproteins in response to SIAH inhibition. The ratios of D/C/B/A, D/C, D/B, C/A, and B/A were calculated using GAPDH normalized data. Summary of results: Supported by statistical analyses, we identified 6 unique phospho-proteins that were either up- or down-regulated in response to SIAHLoss-of-function. Many have known roles in controlling and regulating cell growth, cell death, NFκB signaling, stress response, DNA damage, and cell attachment pathways, supporting a tumor eradication phenotype in the absence of SIAH function in these cancer cell lines. Conclusion: Cancer landscape (CScape) functional protein pathway mapping has categorized the synergistic feedforward, feedback, and compensatory signaling pathway activation/inactivation in response to SIAH blockade in these EGFR/HER2/K-RAS-driven malignant human cell lines. Further validation analysis will be conducted to gain better insight into the global cancer pathway alterations to reveal the molecular mechanism(s) of why SIAH inhibition works so effectively to shut down malignant tumor growth in the preclinical models.
Citation Format: Andrew P. Howell, Julia Wulfkuhle, Rosa I. Gallagher, Emanuel F. Petricoin, Amy H. Tang. The Use of Reverse Phase Protein Arrays (RPPA), Principal Component Analysis (PCA), and CScape Pathway Mapping to Identify New Tumor Vulnerability and Actionable Targets in Human Malignant Triple-Negative Breast cancer cell lines [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-13.