Abstract 2965: LBL-033, a novel bispecific antibody targeting MUC16 and CD3, for the treatment of tumors over-expressing MUC16

Background: MUC16 is a large glycoprotein overexpressed on cell membrane of solid tumors, especially in almost 80% of ovarian cancer. The extracellular part of MUC16 could be cleaved as CA125, which is well known as a diagnosis biomarker for ovarian cancer. Despite recent advances in therapies such as PARP inhibitors, advanced ovarian cancer remains a disease of high unmet need. Herein a novel bispecific antibody targeting MUC16 and CD3, LBL-033, is developed to specifically kill MUC16 positive tumor cells by engaging T cells. Methods: LBL-033 was constructed using our unique T cell engager platform, which is a 2:1 format bispecific antibody with two arms targeting MUC16 membrane-proximal domain with high affinity and one arm targeting CD3 with fine-tuned affinity. The binding affinity of LBL-033 to MUC16 and CD3 was determined with Fortebio, while the activity was measured using several cell based assays including reporter gene and TDCC assays. The anti-tumor activity of LBL-033 was investigated in C57BL/6-huCD3e mice implanted with MC38-huMUC16 cells. GLP-compliant repeat-dose toxicologic study was evaluated in cynomolgus monkeys. Results: The binding affinity of LBL-033 to MUC16 and CD3 protein was 2.67 nM and 29.6 nM, respectively. The epitope that anti-MUC16 binds was identified at the C-terminal of MUC16 extracellular domain; and the activity was not affected in the presence of soluble CA-125. In CD3 reporter gene assay, LBL-033 could activate the NFAT reporter element through MUC16 antigen-dependent CD3 cross-linking with an EC50 value of 1.068 nM. LBL-033 was shown a potent TDCC activity in OVCAR3 cells with T cell activation. In C57BL/6-huCD3e transgenic mice implanted with MC38-huMUC16 tumor cells, LBL-033 was shown a dose dependent anti-tumor activity. In addition, LBL-033 had a significant synergistic effect, when combined with anti-PD-1. LBL-033 was shown favorable pharmacokinetic properties with a good safety profile in cynomolgus monkeys. Conclusion: LBL-033, a novel bispecific antibody targeting CD3 and MUC16 with a unique epitope, which is located at the MUC16 membrane-proximal domain, with affinity differentiation between anti-MUC16 and anti-CD3. It is shown a great anti-tumor efficacy in animal models, with a good safety profile in monkeys. These data support LBL-033 as a novel therapeutic bispecific antibody for ovarian cancer and other MUC16 positive tumors. A dose escalation study in humans will begin in Q1 2023. Citation Format: Jian