Abstract C112: L1CAM targeting antibody-based therapy as a novel approach for L1CAM positive lymphomas

Abstract Background. L1CAM (L1 Cell Adhesion Molecule) is a glycoprotein identified as a key mediator of the metastatic process in many different tumor types. It facilitates the detachment of tumor cells from the primary tumor and their entry into the circulation. By promoting cell-cell interactions, it also directly stimulates the colonization of distant organs by circulating tumor cells. The expression and role of L1CAM in B and T cell lymphomas is poorly explored. The aim of this project was to evaluate L1CAM expression in different subtypes of lymphoma and its role as novel therapeutic target. Methods. RNA was extracted with Monarch Total RNA Miniprep Kit and qPCR performed with QuantiFast SYBR Green RT-PCR. For flow cytometry (FACS), cells were stained either with anti-L1CAM antibody or isotype control at a dilution of 1:1000. For immunohistochemistry (IHC) samples were stained for 20 minutes at a dilution of 1:100. For direct killing assay, cells were exposed six days to compounds, followed by MTT assay. Antibody dependent cellular cytotoxicity (ADCC) was performed with ADCC Reporter Bioassay (Promega). Results. L1CAM mRNA expression was assessed in 59 lymphoma cell lines. Whereas expression in most cell lines appeared low, a subgroup of cells displayed high to very high expression of L1CAM. Surface L1CAM expression was confirmed by FACS. L1CAM mRNA and protein expression levels correlated well across the cell lines and revealed that Sezary syndrome (SS) cell lines displayed the highest expression, followed by mantle cell lymphoma (MCL) and activated B cell diffuse large B cell lymphoma (ABC DLBCL) cell lines. By IHC L1CAM expression was assessed on different tissue microarrays covering multiple lymphoma subtypes; L1CAM expression was observed especially in a subset of cutaneous T-cell lymphoma and MCL. The data confirmed the findings in lymphoma cell lines. Anti-L1CAM monoclonal antibody (mAb) and four L1CAM targeting antibody drug conjugates (ADCs) (ADC1, ADC4, ADC5, ADC6), differing for the linker and payload, were tested in L1CAM positive and negative cell lines. mAB did not show any sign of direct antitumoral activity. Among ADCs, highest activity was observed with ADC6 (SG3199 payload), followed by ADC4 (MMAE payload). ADC1 and ADC5 (also containing MMAE as payload) showed limited activity. ADC6 showed the best correlation between killing activity and L1CAM expression levels, indicating a high level of target specific activity. The in vitro activity of ADC4 and ADC6 was validated in an in vivo xenograft using the MCL cell line Z138. Finally, mAb and a bispecific anti-CD3/L1CAM antibody were tested for their ability to induce ADCC. Both induced strong intracellular signaling in the reporter cell line upon co-incubation with L1CAM expressing lymphoma cells, indicative of the induction of killing activity in effector cells. Conclusions. In summary, we have demonstrated the in vitro and in vivo activity of anti-L1CAM antibody-based therapeutic approach as novel treatment for L1CAM positive lymphomas. Citation Format: Filippo Spriano, Giulio Sartori, Luca Aresu, Luciano Cascione, Elisa Civanelli, Afua A. Mensah, Chiara Tarantelli, Stefano Pileri, Flavio Mehli, Gunther Spohn, Francesco Bertoni. L1CAM targeting antibody-based therapy as a novel approach for L1CAM positive lymphomas [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C112.