Abstract 2777: Characterizing the molecular underpinnings of sorafenib sensitivity in desmoid tumors
Authors: Devine Max , Tang Joy , Stets Colin , Hays John , Chen James L. 
Published: June 2022

Abstract
Background: Desmoid tumors (DT) are rare fibroblastic sarcomas that have high recurrence rates. Though we know mutations in the beta-catenin (CTNNB1) gene are commonly observed with dysregulation of the Wnt signaling pathway in patients with DT, the molecular mechanisms driving DT growth remain poorly understood. There is currently no standard systemic treatment for DT. The multi-kinase inhibitor, sorafenib, has been identified as a potential front-line agent for DT after a recent clinical trial demonstrated an objective response in one third of patients. The mechanism for how sorafenib inhibits DT progression is still unclear, so it is unknown which characteristics predict response to the drug. Our work has identified the early growth response-1 (EGR1) gene as a downstream target of sorafenib.
Methods: Nine DT cell lines have previously been brought into culture with stable passage. These cell lines were treated with sorafenib at 10 μM. RNA was collected from parental and treated cells and subsequent RNA sequencing was performed. Differential gene expression was performed using R. Appropriate comparisons for multiplicity were performed. Western blots were performed to confirm changes in expression of key genes at the protein level. EGR1 overexpression vector was introduced to the 2 DT cell lines and further treated with sorafenib. Additional banked patient desmoid tumor samples were sequenced to assess EGR1 levels and correlation with the CTNNB1.
Results: We first evaluated the effect of sorafenib on CTNNB1 in the DT models. Western blot demonstrated no changes in protein levels of CTNNB1 in the 4 cell lines tested at 72 hours post-treatment. This was further confirmed on RNA-sequencing. To identify additional gene targets of sorafenib, additional differential gene expression analysis was performed resulting in 13 altered genes at an adjusted p &lt; 0.01. The most significantly altered gene, both by p-value and by fold change, was the EGR1 mRNA transcript. EGR1 transcript levels were significantly attenuated by sorafenib treatment (logFC = 2.720, adjusted p-value &lt;&lt; 0.0001). Western blot analysis confirmed this decrease. EGR1-high DT cell line models exhibited faster growth rates and also higher sensitivity to sorafenib. Fifteen additional patient desmoid tumor samples confirmed the steady state of CTNNB1 and high variability of the EGR1 transcript. There was no correlation between the EGR1 and CTNNB1 transcript.
Conclusion: This study found that sorafenib does not directly modulate CTNNB1, but does decrease EGR1 expression at both the mRNA and protein level. This suggests that EGR1 expression may be associated with aggressive DT and may also predict responsiveness to treatment with sorafenib. Confirmatory EGR1 modulation experiments are underway and will be provided at time of presentation.
Citation Format: Max Devine, Joy Tang, Colin Stets, John Hays, James L. Chen. Characterizing the molecular underpinnings of sorafenib sensitivity in desmoid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2777.