Abstract 1573: Association between TGF-β signaling and HMGA2, a potential biomarker for bintrafusp alfa in triple negative breast cancer
Authors: Yeung Tsz-Lun , Locke George , Lazorchak Adam , Qin Guozhong , Yu Huakui , Qi Jin , Marelli Bo , Jenkins Molly , Rolfe Alex , Ojalvo Laureen S. , Dussault Isabelle , Lan Yan 
Published: September 2020

Abstract
Background: Bintrafusp alfa (M7824) is a first-in-class bifunctional fusion protein composed of the extracellular domain of the TGF-βRII receptor, to function as a TGF-β “trap”, fused to a human IgG1 antibody blocking PD-L1, which has shown early evidence of clinical activity in phase 1 studies in patients with advanced solid tumors. We recently reported high expression of HMGA2 in patients with triple negative breast cancer (TNBC) who experienced disease control (response or stable disease) with bintrafusp alfa treatment compared with those who had progressive disease, suggesting that HMGA2 may predict response to bintrafusp alfa in this indication. HMGA2 is a transcriptional regulator whose expression is upregulated by TGF-β signaling and is known to be an important factor in mediating TGF-β–induced epithelial–mesenchymal transition (EMT). The purpose of this study was to evaluate the association between HMGA2 expression and TGF-β signaling in TNBC and the effect of bintrafusp alfa on HMGA2/TGF-β signaling.
Methods: The syngeneic murine 4T1 tumor model was utilized for this study because it closely mimics human stage IV TNBC, has high baseline levels of HMGA2 expression, and bintrafusp alfa directly modulates canonical TGF-β signaling and induces antitumor activity in this model.
Results: Tumors from mice treated with isotype control, anti–PD-L1, anti–PD-L1(mut)/TGF-β trap (trap control), or bintrafusp alfa were analyzed by RNAseq and both bintrafusp alfa or trap control treatment decreased HMGA2 expression relative to anti–PD-L1 or isotype control treatment. In isotype control-treated 4T1 tumors Spearman's rho correlation coefficient showed that 29% (26/89) of the TGF-β signaling-related genes significantly correlated with HMGA2 expression, indicating that there is a strong association between HMGA2 and TGF-β signaling. In bintrafusp alfa-treated tumors, the association of HMGA2 and TGF-β signaling was even stronger, with 55% (49/89) of TGF-β signaling-related genes significantly associated with HMGA2, suggesting that there is a relationship between HMGA2, TGF-β signaling, and bintrafusp alfa pharmacodynamic effects in this TNBC model. Analysis of individual TGF-β signaling-related genes from this signature showed significant correlation between HMGA2 expression and the expression of TGF-β receptors, ligands, collagen, and EMT-related genes. Furthermore, both bintrafusp alfa and trap control treatment significantly reduced expression of these HMGA2-correlated TGF-β signaling-related genes relative to anti–PD-L1 or isotype control treatment in the 4T1 model, suggesting that HMGA2 is associated with TGF-β-related signaling more strongly in the presence of TGF-β sequestration.
Conclusions: Taken together, these observations warrant further analysis of the potential link between HMGA2 and bintrafusp alfa antitumor efficacy.
Citation Format: Tsz-Lun Yeung, George Locke, Adam Lazorchak, Guozhong Qin, Huakui Yu, Jin Qi, Bo Marelli, Molly Jenkins, Alex Rolfe, Laureen S. Ojalvo, Isabelle Dussault, Yan Lan. Association between TGF-β signaling and HMGA2, a potential biomarker for bintrafusp alfa in triple negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1573.