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Purpose There is currently no curative treatment for patients diagnosed with triple-negative breast cancer brain metastases (TNBC-BM). CAR T cells hold potential for curative treatment given they retain the cytolytic activity of a T cell combined with the specificity of an antibody. In this proposal we evaluated the potential of EGFR re-directed CAR T cells as a therapeutic treatment against TNBC cells in vitro and in vivo . Methods We leveraged a TNBC-BM tissue microarray and a large panel of TNBC cell lines and identified elevated epidermal growth factor receptor (EGFR) expression. Next, we designed a second-generation antiEGFR CAR T construct incorporating a clinically relevant mAb806 tumor specific single-chain variable fragment (scFv) and intracellular 4-1BB costimulatory domain and CD3ζ using a lentivirus system and evaluated in vitro and in vivo anti-tumor activity. Results We demonstrate EGFR is enriched in TNBC-BM patient tissue after neurosurgical resection, with six of 13 brain metastases demonstrating both membranous and cytoplasmic EGFR. Eleven of 13 TNBC cell lines have EGFR surface expression ≥85% by flow cytometry. EGFR806 CAR T treated mice effectively eradicated TNBC-BM and enhanced mouse survival (log rank pConclusion Our results demonstrates anti-tumor activity of EGFR CAR T cells against TNBC cells in vitro and in vivo . Given EGFR CAR T cells are currently undergoing clinical trials in primary brain tumor patients without obvious toxicity, our results are immediately actionable against the TNBC-BM patient population.

There is currently no curative treatment for patients diagnosed with triple-negative breast cancer brain metastases (TNBC-BM). CAR T cells hold potential for curative treatment given they retain the cytolytic activity of a T cell combined with the specificity of an antibody. In this proposal we evaluated the potential of EGFR re-directed CAR T cells as a therapeutic treatment against TNBC cells in vitro and in vivo.We leveraged a TNBC-BM tissue microarray and a large panel of TNBC cell lines and identified elevated epidermal growth factor receptor (EGFR) expression. Next, we designed a second-generation anti-EGFR CAR T construct incorporating a clinically relevant mAb806 tumor specific single-chain variable fragment (scFv) and intracellular 4-1BB costimulatory domain and CD3ζ using a lentivirus system and evaluated in vitro and in vivo anti-tumor activity.We demonstrate EGFR is enriched in TNBC-BM patient tissue after neurosurgical resection, with six of 13 brain metastases demonstrating both membranous and cytoplasmic EGFR. Eleven of 13 TNBC cell lines have EGFR surface expression ≥ 85% by flow cytometry. EGFR806 CAR T treated mice effectively eradicated TNBC-BM and enhanced mouse survival (log rank p 0.004).Our results demonstrates anti-tumor activity of EGFR806 CAR T cells against TNBC cells in vitro and in vivo. Given EGFR806 CAR T cells are currently undergoing clinical trials in primary brain tumor patients without obvious toxicity, our results are immediately actionable against the TNBC-BM patient population.

Glioblastoma multiforme (GBM) is the most aggressive primary malignant brain cancer with a median survival of 16-20 months. Maximal safe resection and adjuvant chemotherapy improve survival but there is no cure and hence improved therapies are urgently needed. CAR T cell therapy has been FDA approved for hematologic malignancies but there are some barriers to their application for solid tumors in the clinic such as heterogenous tumor antigen expression. Chimeric Antigen Receptor (CAR) T Cells combine the cytolytic potency of T cells with the tumor specificity of an antibody. The interleukin 13 receptor alpha 2 (IL13Rα2) is an important target of CAR T cell therapy in ongoing GBM clinical trials. However, regulation of IL13Ra2 expression in GBM is unclear. Identifying upstream regulators of IL13Rα2 will not only help delineate IL13Rα2 carcinogenesis but also may help improve CAR T cell therapy. Utilizing knockout and overexpression constructs, we have identified protein kinase C family as an upstream regulator of IL13Rα2 transcription and translation in GBM cell lines. We have also identified a small molecule regulator of IL13Rα2, Ingenol-3-Angelate (I3A), that inhibits U87 tumor cell proliferation. Furthermore, I3A enhances IL13Rα2 re-directed CAR T cell mediated tumor cytolysis in vitro. Importantly, I3A treatment increases interferon gamma secretion by T cells. Taken together, our data implicates PKC isoforms as an upstream regulator of IL13Rα2. I3A treatment may serve as a therapeutic strategy to enhance CAR T mediated killing. Citation Format: Siddharth Subham, John D. Jeppson, Bryan Schatmeyer, Stephen J. Forman, Christine E. Brown, David Akhavan. Protein kinase C is an upstream regulator of IL13Ra2 and small molecular activator enhances CAR T mediated killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3235.