Abstract P3-05-01: Role of TRIM24 in metaplastic breast cancer and nomination of potential therapeutic targets
Authors: Shah Vrutant , Miao Shucheng , Yam Clinton , Chang Jeffrey T , Barton Michelle , Piwnica-Worms Helen , Moulder Stacy , Lozano Guillermina 
Published: March 2022

Abstract
Background: Within the Triple-Negative Breast Cancer (TNBC) subclass, metaplastic TNBC (MpBC) tumors are comprised of heterogeneous, malignant epithelial (carcinoma) and mesenchymal (sarcoma) elements and are rare, highly aggressive, poorly differentiated and chemorefractory. There is an unmet need to develop therapies that address and improve survival of MpBC TNBC patients. We and others found that protein and mRNA levels of tripartite motif-containing protein 24 (TRIM24) are elevated in breast cancers, and aberrant expression of TRIM24 is linked to poor patient survival. Our previous in vitro studies showed that TRIM24 is a multidomain protein with histone reader function via a PHD/bromodomain and E3 ligase function via a RING domain that targets p53 for degradation.Methods: To determine if TRIM24 is oncogenic in vivo, we created a mouse model with conditional over expression (COE) of TRIM24 in mammary epithelia (Trim24COE). Trim24COE mice develop tumors, which were subjected to pathology, immunohistochemistry, global transcriptional and single-cell protein expression profiling. Additionally, we determined expression of TRIM24 in MpBC patient-derived tumor arrays and xenografts (PDX). Trim24COE tumor-derived primary cell lines and 3D spheroids were assessed for function and response to targeted inhibition.Results: TRIM24 over expression is sufficient to drive development of murine metaplastic carcinosarcomas (70% of all tumors), which are highly penetrant and lacking ER, PR and HER2 expression. Using global RNA-sequencing and selected proteomic profiling (RPPA) followed by CyTOF, we found that EMT, glycolysis, angiogenesis, G2/M checkpoint regulators and cMET/PI3K/mTOR are top up-regulated pathways. We defined a TRIM24 gene expression signature for Trim24COE tumors to probe TNBC patient expression data and found that the TRIM24 signature positively correlates with MpBC TNBC. Using a PROTAC targeting TRIM24, we showed that degradation of TRIM24 reduces cell viability compared to control, both in TRIM24-driven primary tumor cell lines and MpBC PDX cell suspensions. Carbon 13 (C13) tracing and other metabolomics were used to determine the impact of TRIM24 in metabolic pathways, using 3D spheroids derived from Trim24COE carcinosarcomas. We found that up-regulation of TRIM24 lowers ROS to promote cell survival by increased production of NADPH via multiple metabolic pathways that can be reversed by knocking-down TRIM24 or with specific metabolic inhibitors.Conclusions: TRIM24 is a PHD/bromodomain histone reader and p53-targeting E3-ubiquitin ligase that, when aberrantly over expressed, promotes tumorigenesis in vivo. A majority of Trim24-driven tumors are carcinosarcomas, highly similar to MpBC TNBC. Genomewide RNA expression and protein profiling show TRIM24 over expression activates EMT and disrupts metabolic homeostasis. Findings from our mouse model are relevant to tumors derived from MpBC patients, as PDXs show high expression of TRIM24 and respond to PROTAC treatment of TRIM24. Further establishment of TRIM24’s role in metabolic pathways to reduce ROS and increase cell survival may reveal potential combinatorial therapeutic approaches for MpBC. These findings suggest exciting opportunities to exploit the Trim24COE mouse model as a means of understanding mechanisms of MpBC tumor development and for preclinical studies of new, epigenetic-based therapeutic approaches.
Citation Format: Vrutant Shah, Shucheng Miao, Clinton Yam, Jeffrey T Chang, Michelle Barton, Helen Piwnica-Worms, Stacy Moulder, Guillermina Lozano. Role of TRIM24 in metaplastic breast cancer and nomination of potential therapeutic targets [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-05-01.