Abstract PD10-08: Remodeling the inflammatory breast cancer tumor microenvironment to enhance immunotherapy: Novel therapeutic development

Background: Inflammatory breast cancer (IBC) is the most lethal and aggressive form of breast cancer, yet no targeted therapy has been approved specifically for this disease. There is a critical need for innovative treatment approaches for patients with IBC. There is a paucity of data on immune checkpoint inhibitors (ICIs) in IBC, yet a strong biological rationale exists to lay the groundwork for testing the efficacy of ICIs in IBC. We have previously shown that an anti–epidermal growth factor receptor (EGFR) antibody, panitumumab (sponsored by Amgen), combined with Abraxane (sponsored by Bristol Myers Squibb), and carboplatin followed by 5-fluorouracil, epirubicin, and cyclophosphamide achieves a very high pathologic complete response (42%) in patients with triple-negative receptor status (TN-IBC) (NCT01036087). We hypothesize that inducing a broad shift in the IBC tumor microenvironment (TME), a critical driver of the IBC clinical phenotype and metastasis, from an immunosuppressive to an immunoreactive phenotype can enhance the efficacy of ICIs. Here we report the impact of targeting EGFR on ICI effectiveness by modulating the immunosuppressive TME in TN-IBC. Methods: We examined the effects of panitumumab on components of the immune TME in IBC patient tissues collected before and after panitumumab treatment. Furthermore, we analyzed panitumumab effects in an IBC SUM149 humanized mouse model (SUM149-hu-NSG-SGM3) by using multiplex immunofluorescence staining (mIF) of single-cell RNA-sequencing (scRNA-seq) and multicolor flow cytometry. We examined the changes in chemokines in humanized mouse tissue after panitumumab treatment using a cytokine antibody array and enzyme-linked immunosorbent assay (ELISA). We also studied the mechanism of EGFR regulation of immunosuppressive chemokine expression via transcription factor EGR1 by using reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and chromatin immunoprecipitation (ChIP) assays. In addition, we tested the efficacy of panitumumab combined with anti-PD-L1 antibody (Bio X Cell, clone 29E.2A3) in reducing IBC tumor growth in a humanized IBC SUM149 mouse model. Results: IBC patients who achieved pathologic complete response after receiving panitumumab/neoadjuvant chemotherapy had increased levels of CD8+ T-cells and decreased levels of M2 macrophages and T-reg cells. In the humanized mouse model, panitumumab treatment reduced IBC tumor growth and increased immune response that favors an antitumor effect, as shown by scRNA-seq, flow cytometry, and mIF analyses. In addition, we observed that panitumumab treatment increased the expression of chemokines that function as a chemoattractant for CD8+ T-cells, including CXCL10, CCL4, and CXCL9. We also observed that panitumumab treatment reduced EGR1 expression, leading to the downregulation of chemokines involved in the recruitment of immunosuppressive M2 macrophages and T-reg cells, including CCL2, CCL20 CXCL5, and IL-8. Finally, panitumumab enhanced the reduction in tumor growth by anti-PD-L1 antibody treatment; furthermore, the combination of panitumumab and anti-PD-L1 antibody increased the presence of CD8+ T-cells and reduced the presence of T-reg cells and M2 macrophages more effectively than either treatment alone. Conclusion: Panitumumab treatment converts the immunosuppressive IBC TME to an immunoreactive status by modulating the global expression of chemokines by downregulating the EGR1 transcription factor. This modulation of the TME by panitumumab improves the inhibition of IBC tumor growth by an ICI. Our study is the first to demonstrate that targeting the EGFR/EGR1 axis remodels the IBC TME by regulating chemokine expression, thus boosting the antitumor immune response in IBC and response to ICI. Citation Format: Xiaoping Wang, Takashi Semba, Ganiraju C. Manyam, Jing Wang, Shan Shao, Francois Bertucci, Pascal Finetti, Savitri Krishnamurthy, Lan ThiHanh Phi, Troy Pearson, Jared K. Burks, Evan N. Cohen, James M. Reuben, Fei Yang, Hu Min, Nicholas Navin, Toshiaki Iwase, Yichao Shen, Xiang Zhang, Debu Tripathy, Naoto T. Ueno. Remodeling the inflammatory breast cancer tumor microenvironment to enhance immunotherapy: Novel therapeutic development [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 PD10-08.