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3010 Overcoming CAR T Resistance with Non-Covalent BTK Inhibitor Loxo-305 in Mantle Cell Lymphoma

Program: Oral and Poster Abstracts
Session: 625. Lymphoma: Pre-Clinical—Chemotherapy and Biologic Agents: Poster III
Hematology Disease Topics & Pathways:
apoptosis, Biological, apheresis, cell division, Diseases, Therapies, Mantle Cell Lymphoma, Non-Hodgkin Lymphoma, Biological Processes, enzyme inhibitors, B-Cell Lymphoma, white blood cells, Technology and Procedures, Cell Lineage, Xenograft models, Study Population, Lymphoid Malignancies, flow cytometry, TKI, molecular testing, pathways
Monday, December 7, 2020, 7:00 AM-3:30 PM

Yang Liu, PhD1*, Vivian Changying Jiang, PhD1, Joseph McIntosh, BS1*, Alexa A Jordan, BS1*, Yijing Li, MS1* and Michael Wang, MD1,2

1Department of Lymphoma and Myeloma, The University of Texas MD Anderson Cancer Center, Houston, TX
2Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas MD Anderson Cancer Center, Houston, TX

Background: Mantle cell lymphoma (MCL) is a distinctive B-cell non-Hodgkin’s lymphoma characterized by poor prognosis. Despite clinical success of the covalent Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib, a subset of patients need to discontinue ibrutinib therapy due to treatment related adverse events, which are primarily caused by off-target effects. Furthermore, primary or acquired resistance to ibrutinib continues to emerge and often leads to dismal clinical outcomes. Therefore, exploration of more target-specific BTK inhibitors is crucial to minimize the adverse events and provide clinical benefit. CAR T therapy has achieved unprecedented response in patients with relapsed or refractory MCL. However, the development of resistant phenotypes is a new emerging medical challenge in MCL patients with unknown mechanisms. Here, we characterize the therapeutic efficacy of LOXO-305, a next generation non-covalent small molecule inhibitor with high selectivity for BTK. Preclinical efficacy of LOXO-305 alone or in combination with venetoclax (ABT199), a selective Bcl-2 inhibitor, was evaluated in MCL using in vitro and in vivo CAR T-resistant PDX models.

Methods: In vitro cell viability was measured after 72 hour treatment with LOXO-305 alone and in combination with ABT-199 in MCL cell lines using Cell Titer Glo luminescent cell viability assay (Promega). To determine whether LOXO-305 induces cell death through cell apoptosis, we used annexin V/PI staining followed by flow cytometry analysis. To evaulate in vivo drug efficacy we used patient-derived xenograft (PDX) models established from primary patient samples.

Results: LOXO-305 treatment, as a single agent, resulted in effective MCL cell growth inhibition in a panel of MCL cell lines including ibrutinib and/or ABT-199-resistant cell lines (IC50=6.6-24.4μM), except for JeKo BTK KD cells with BTK knockdown (KD) via CRISPR/Cas9 technology (IC50>30 μM). To improve the efficacy, we decided to investigate the potential of LOXO-305 in combination with ABT199, since the combo of ibrutinib and ABT199 is clinically beneficial in MCL patients. Indeed, LOXO-305 significantly improved the inhibitory effect of ABT-199 in the ABT-199 resistant Mino-R and JeKo BTK KD cells, suggesting that this combination could be further explored in overcoming ABT-199 resistance in MCL. The compelling synergistic effect was further confirmed by annexin V/PI apoptosis assay. Next, we assessed the in vivo efficacy of LOXO-305 in an ibrutinib-CAR T dual-resistant PDX model. LOXO-305 effectively reduced tumor size after 40 days of treatment as a single agent. Moreover, LOXO-305 treatment showed significant anti-tumor effects in an ibrutinib-ABT199-CAR T triple-resistant PDX model that recapitulates the most aggressive human MCL variants in vivo. In this model, LOXO-305 treatment effectively decreased the tumor load in mice spleen and liver (p<0.05) as well as in bone marrow and peripheral blood, compared to vehicle-treated mice (p<0.001).

Conclusions: By using various in vitro and in vivo multiple resistant MCL models we determined that LOXO-305 holds great promise for an effective single agent or combined treatment of the most eggressive forms of MCL, and that a continued investigation of the rationale for a combined therapy with ABT-199 is imperative to understand its role in overcoming ibrutinib-ABT199-CAR T triple resistance.

Disclosures: Wang: OMI: Honoraria, Other: Travel, accommodation, expenses; MoreHealth: Consultancy; Celgene: Consultancy, Other: Travel, accommodation, expenses, Research Funding; AstraZeneca: Consultancy, Honoraria, Other: Travel, accommodation, expenses, Research Funding; Pharmacyclics: Consultancy, Honoraria, Other: Travel, accommodation, expenses, Research Funding; Janssen: Consultancy, Honoraria, Other: Travel, accommodation, expenses, Research Funding; Beijing Medical Award Foundation: Honoraria; Lu Daopei Medical Group: Honoraria; Loxo Oncology: Consultancy, Research Funding; Pulse Biosciences: Consultancy; Kite Pharma: Consultancy, Other: Travel, accommodation, expenses, Research Funding; Juno: Consultancy, Research Funding; BioInvent: Research Funding; VelosBio: Research Funding; Acerta Pharma: Research Funding; InnoCare: Consultancy; Oncternal: Consultancy, Research Funding; Nobel Insights: Consultancy; Guidepoint Global: Consultancy; Dava Oncology: Honoraria; Verastem: Research Funding; Molecular Templates: Research Funding; OncLive: Honoraria; Targeted Oncology: Honoraria.

*signifies non-member of ASH