Abstract 2913: Co-expression of extracellular matrix enzymes heparanase or PH-20 augments the anti-tumor efficacy of folate receptor 1-targeting CAR T cells in an ovarian cancer model
Authors: Steimle Brittany L. , Hu Peirong , Tran Ngoc , Lee Jia-Jye , Baysac Kathleen , Luo Kun , Wang Xu , Liang Genqing , Nurmukhambetova Saule , Tran Tri , Dash Pradyot , Schneider Dina 
Published: March 2024

Abstract
Introduction: The tumor extracellular matrix (ECM) is a physical barrier which obstructs trafficking of CAR T cells to tumors. We hypothesize that co-expressing ECM remodeling/degrading enzymes heparanase (HPSE) or PH-20 with a CAR directed against folate receptor 1 (FolR1) will overcome the physical tumor microenvironment barrier and improve anti-tumor efficacy of anti-FolR1 CAR in a human ovarian cancer model.
Methods: ECM CARs were constructed by combining anti-FolR1 ScFv with a CD8 hinge and transmembrane domain, 4-1BB, and CD3ζ endodomains, followed by a P2A element and full-length HPSE or GPI-anchored PH-20 sequence. CAR T cells were prepared from CD4+ and CD8+ T cells of healthy donors by lentiviral transduction. CAR expression was evaluated by flow cytometry; HPSE and PH-20 expression were measured via ELISA and Western blotting, respectively. CAR-mediated killing and cytokine release were observed in overnight co-culture assays with FolR1-expressing tumor cells. ECM CARs’ migration through CultrexTM and sodium hyaluronate matrices were assessed for HPSE and PH-20 function, respectively. ECM CARs’ efficacy was evaluated in vivo using a FolR1-expressing subcutaneous OV90 ovarian cancer xenograft model in NOD SCID Gamma (NSG) mice, and representative OV90 tumors were harvested at day 7 post-CAR T treatment for immunohistochemical staining.
Results: FolR1 expression was confirmed in ovarian cancer cell lines and substrates targeted by HPSE (perlecan, glypican 3, CD138) and PH-20 (hyaluronan) were detected by immunofluorescence in human ovarian tumors’ sections. Lentiviral transduced primary T cells yielded robust expression of FolR1 CAR and ECM enzymes. Anti-FolR1 CAR and ECM CARs secreted pro-inflammatory cytokines IL-2, TNFα, IFNƳ and lysed OVCAR3 tumor cells with similar efficacy. ECM CARs with HPSE or PH-20 exhibited enhanced migration through ECM-rich matrices as compared to anti-FolR1 CAR alone. In vivo, all anti-FolR1 CAR T cells rejected OV90 tumors and extended survival compared to tumor alone or untransduced T cells (UTD). However, ECM CARs co-expressing HPSE or PH-20 accelerated tumor regression as compared to anti-FolR1 CAR alone. Tumor histology revealed CAR T cell infiltration (CD3+, CD8+) in mice treated with anti-FolR1 CARs but not UTD, indicating that anti-FolR1 CARs can effectively infiltrate OV90 tumors. Imaging studies are underway to evaluate the function of ECM CARs in the tumor microenvironment.
Conclusions: The anti-FolR1 CARs boosted with ECM enzymes HPSE or PH-20 demonstrated specific lysis of FolR1-expressing cell lines, improved penetration through ECM-rich matrices in vitro, and accelerated tumor regression in an ovarian cancer model in vivo. Therefore, ECM CARs may help improve clinical outcomes in patients with ovarian tumors.
Citation Format: Brittany L. Steimle, Peirong Hu, Ngoc Tran, Jia-Jye Lee, Kathleen Baysac, Kun Luo, Xu Wang, Genqing Liang, Saule Nurmukhambetova, Tri Tran, Pradyot Dash, Dina Schneider. Co-expression of extracellular matrix enzymes heparanase or PH-20 augments the anti-tumor efficacy of folate receptor 1-targeting CAR T cells in an ovarian cancer model [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 2913.