Abstract 2966: The anti-tumor activity of a novel anti-Her2 and anti-c-Met bispecific antibody-drug conjugate

Abstract Background: Her2 and c-Met, two tumor-associated antigens (TAAs), are well-established cancer targets, as evidenced by the approval of several anti-Her2 antibody-drug conjugates (ADCs), a bispecific anti-c-Met/EGFR antibody, and promising Phase 2 efficacy of an anti-c-Met ADC. Her2 and c-Met are expressed separately or co-expressed in various cancer types, including lung, pancreatic and kidney cancers, reflecting the heterogeneity of tumor TAA expression. Dual TAA-targeting may reduce the probability of cancer escape, commonly seen in the treatment of single TAA-targeting ADCs, due to the heterogeneity of TAA expression. Methods: We developed a novel bispecific anti-Her2/anti-c-Met ADC, BB-205. BB-205 was engineered using humanized anti-Her2 and anti-c-Met VHH fragments, fused with a human IgG1 Fc, and conjugated with vc-MMAE. Whole cell binding assays were conducted to determine the binding affinity of BB-205 to TAAs. In vitro cytotoxicity assays were performed to evaluate the cytotoxic effects of BB-205 on various cancer cell lines. The in vivo efficacy of BB-205 was tested in HPAC and NCI-H1975 xenograft mouse models. Results: BB-205 maintained the high binding affinities of its parental VHH-Fc antibodies to Her2 and c-Met. It exhibited remarkable cytotoxic effects on cancer cells that express either Her2 or c-Met, or both. Its cytotoxic potency was comparable to Trastuzumab-MMAE (T-MMAE) in Her2-high expressing cancer cells and to Telisotuzumab vedotin (Teliso-V) in c-Met-high expressing cancer cells. BB-205 demonstrated superior cytotoxicity than either reference ADC or combination of both reference ADCs in dual TAA-expressing cancer cells with low to medium level of expression. Additionally, BB-205 showed higher internalization compared to either reference ADC in cancer cells. In the in vivo HPAC xenograft model, where HPAC cells express medium levels of c-Met and low levels of Her2, both BB-205 and Teliso-V significantly inhibited tumor growth, achieving 100% and 91% tumor growth inhibition (TGI), respectively. In contrast, treatments with T-MMAE had a low efficacy in suppression of tumor growth. At the end of study, 50% of mice in the BB-205 group were tumor-free, whereas no mice in other groups were tumor-free. BB-205 was also tested in an NCI-H1975 xenograft model, where NCI-H1975 cells express medium levels of Her2 and c-Met. Treatment with either BB-205 or T-MMAE significantly reduced tumor size. Four weeks after a single dose, 50% mice in BB-205 group and 25% mice in T-MMAE group were tumor-free. While Teliso-V initially shrank tumors, the tumors gradually regrew in the fifth week post-treatment. No obvious side effects were observed in both in vivo studies. Conclusions: The novel anti-Her2/anti-c-Met bispecific ADC BB-205 demonstrates superior anti-tumor activity in preclinical studies. BB-205 shows promising therapeutic potential as a first-in-class ADC drug candidate. Citation Format: Hongyan Zhong, Daniel Li, Daniel Guo, Phuong Nguyen, Ming Yang. The anti-tumor activity of a novel anti-Her2 and anti-c-Met bispecific antibody-drug conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2966.