Abstract 3130: In vitro characterization of a novel TROP2-targeting antibody-drug conjugate OBI-992

Abstract BACKGROUND TROP2, a transmembrane glycoprotein widely expressed on epithelial cancers, has emerged as an attractive target for antibody-drug conjugate (ADC) development. Sacituzumab govitecan, a TROP2 ADC conjugated to topoisomerase inhibitor (TOP1) SN-38, has been approved for patients with triple-negative breast cancer. This study aims to investigate the characteristics of a novel TROP2 antibody (R4702) and its ADC OBI-992, which is derived from the conjugation of R4702 with a TOP1 inhibitor exatecan. METHODS Clinical study: Prognostic roles of TROP2 and TOP1 in patients were accessed through the “Kaplan-Meier plotter” database from more than 1055 colon cancer patients. In vitro study: An ELISA study was conducted to investigate the binding epitope of R4702. Cell binding assay and Surface Plasmon Resonance were carried out to measure non-specific binding activity and binding affinity, respectively. DNA damage activity, cytotoxicity, and immunogenic cell death (ICD) effects of three TOP1 inhibitors exatecan, deruxtecan (Dxd), and SN-38, were evaluated. Cytotoxicity of OBI-992 along with other ADC was measured in both 2D and 3D spheroids cancer cells (gastric cancer NCI-N87, pancreatic cancer Capan1, and prostate cancer DU145). TROP2 and BCRP expression as well as potential mutations in TOP1 were investigated in TROP2 ADCs-induced resistant colon cancer cells. The synergistic effects of the combination of OBI-992 with PARP inhibitors were evaluated. RESULTS Clinical study: Positive correlations between high mRNA expressions of both TROP2 (p=0. 0075) and TOP1 (p=0. 043) with poor overall survival for colon cancer patients were found. In vitro: The R4702 antibody displayed different binding epitopes from sacituzumab and datopotamab. In addition, R4702 showed lower non-specific binding and better binding affinity to TROP2 antigen than datopotamab. The payload exatecan demonstrated excellent ICD effects. Relatively higher cytotoxicity was observed by exatecan when compared to that of Dxd and SN-38. OBI-992 exhibited excellent activities on cell growth inhibition in 2D cell cultures and 3D cell spheroids. TROP2 down-regulation and BCRP upregulation were not found in OBI-992-induced resistant cells. A mutation R364H was identified in TOP1 in the resistance study with OBI-992, which is critical for the binding to TOP1 inhibitors camptothecin analogs. Finally, a synergistic effect of OBI-992 and PARP inhibitors (talazoparib, rucaparib, niraparib, and olaparib) on the enhancement of cancer cell killing and DNA damage was observed. CONCLUSION High expression of both TROP2 and TOP1 is associated with poor survival in patients with colon cancer. R4702 is a novel TROP2 antibody with a unique binding epitope and low non-specific binding. Exatecan and exatecan-conjugated ADC OBI-992 showed high cytotoxic activities. Combination of OBI-992 with PARP inhibitors have potential in TROP2-expressing malignancies. Citation Format: Tzer-Min Kuo, Ting-Yu Chang, Jye-Yu Huang, Wei-Chien Tang, Chun-Jung Lin, Yi-Chen Wu, Chi-Huan Lu, Hao-Cheng Weng, Yu-Jung Chen, Yu-Hsuan Tsao, Cheng-Yen Wei, Lifen Shen, Wan-Fen Li, Ming-Tain Lai. In vitro characterization of a novel TROP2-targeting antibody-drug conjugate OBI-992 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 (6Suppl): Abstract nr 3130.