Abstract 6603: A TBX2-driven Signaling Switch from Androgen Receptor to Glucocorticoid Receptor Confers Enzalutamide Resistance in Prostate Cancer

Abstract Background: Recent studies suggest that glucocorticoid receptor (GR) activation can cause enzalutamide resistance in advanced prostate cancer (PCa) via functional bypass of androgen receptor (AR) signaling. However, the specific molecular mechanism(s) driving this process remain unknown. In an effort to identify drivers of prostate cancer progression, in a previous study, we determined that TBX2, a developmental T-box transcription factor (TF) master regulator, is over-expressed in CRPC and drives bone metastatic progression. A recent report confirmed that TBX2 and GR are two of the four TFs that drive enzalutamide resistance in advanced PCa. Our current study demonstrates that TBX2 with known repressor and activator functions, is the molecular switch that represses AR levels while activating GR expression thereby resulting in the replacement of AR signaling to control tumor growth. Methods: We genetically modulated TBX2 using multiple approaches: a) dominant negative, DN, to block TBX2 (TBX2DN), and b) overexpression, OE, to increase TBX2 expression (TBX2OE), c) shRNA mediated knockdown (shTBX2). RNA-seq was performed, and qRT-PCR, Western blot and immunohistochemical (IHC) analyses were used for validation. Further, we used chromatin immunoprecipitation (ChIP) and site directed mutagenesis (SDM) to confirm TBX2 binding on the AR promoter. We also used co-immunoprecipitation (Co-IP) to determine protein partners of TBX2. Results: Mechanistically, our studies revealed that TBX2 bound to the promoters of both AR and GATA2, an AR coregulator, thereby resulting in a bimodal repression of AR expression. Conversely, TBX2 upregulated GR via direct GR promoter binding and TBX2-GR protein-protein interaction. Together, concurrent repression of the AR and activation of GR resulted in enzalutamide resistance. Importantly, we found that SP2509, an allosteric inhibitor of the demethylase-independent function of LSD1, a TBX2-interacting protein in the COREST complex, can disrupt both TBX2-LSD1 and TBX2-GR protein-protein interactions thereby uncovering a unique mode of SP2509 action in CRPC. Together, our study supports a molecular model of CRPC wherein: 1) TBX2, LSD1 and GR proteins interface with each other, and 2) pharmacological inhibition of LSD1 blocks the TBX2-driven AR-to-GR switch through disruption of TBX2-GR interaction. Conclusions: In summary, our study identifies TBX2 as the molecular switch that drives the AR to GR signaling bypass thereby conferring enzalutamide resistance. Further, our study provides key insights into a potential therapeutic modality for targeting the AR to GR signaling switch via disruption of the TBX2-LSD1 and TBX2-GR protein-protein interactions Citation Format: Sayanika Dutta, Girijesh Kumar Patel, Hamed Khedmatgozar, Daniel Latour, Jonathan Welsh, Manisha Tripathi, Srinivas Nandana. A TBX2-driven signaling switch from androgen receptor to glucocorticoid receptor confers enzalutamide resistance in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6603.