Abstract 5834: Discovery of a novel Trop2-targeting immune-stimulating antibody conjugate with efficacy in pancreatic cancer models

Abstract Background: Toll-like receptor (TLR) and Stimulator of interferon genes (STING) agonists are emerging as potent agents in cancer immunotherapy. However, systemic administration of these small molecules carries the risk of severe off-target toxicities, such as cytokine storm. A more targeted delivery approach could enhance specificity and reduce these toxic effects. Immune-stimulating antibody-drug conjugates (ISACs), which utilize TLR or STING agonists conjugated to antibodies via specific linkers, have gained attention for their improved targeting. Our team previously designed a potent TLR7 agonist, E104, and developed a successful E104-based HER2 targeting ISAC. This new study summarizes the identification of a novel Trop2-targeting ISAC with efficacy in pancreatic cancer models. Methods: We synthesized a library of novel linkers and their corresponding E104 ISACs. These ISACs include both glycosylated and deglycosylated versions of sacituzumab, an anti-Trop2 monoclonal antibody, alongside a control Trop2_mcValCitPABC_E104 ISAC. The ISACs were then tested for NFκB/IRF-7 activation and IL-6 induction in co-culture models and for in vivo efficacy using mouse xenograft models. Results: Both glycosylated and deglycosylated ISACs exhibited drug-to-antibody ratios (DAR) of 6-8. The next-generation ISACs showed significantly reduced aggregation (<1-2%) compared to the control Trop2_mcValCitPABC_E104 ISAC (30%) and were significantly less hydrophobic, thus imparting an improved PK profile. In co-culture studies using BXPC3/ CFPAC-1 and RAW-Dual mouse macrophage reporter cell lines, deglycosylated ISACs triggered more specific NFκB activation than their glycosylated counterparts. Similar results were observed for the coculture of BXPC3/ CFPAC-1 and Ramos Blue, a human B lymphocyte cell line. Further, co-culture of BxPC-3/CFPAC-1 with mouse splenocytes/bone marrow-derived dendritic cells (BMDCs) resulted in strong antigen-dependent IL-6 induction. In vivo testing of these ISACs in immunodeficient mice with CFPAC xenograft models revealed that one specific ISAC, has efficacy against this pancreatic tumor model. Furthermore, a DAR 4 version of this ISAC, showed complete tumor regression in C57BL/6J mice using a hTrop2-MC38 model. Conclusion: Pancreatic cancer is aggressive and has a poor prognosis. It has limited treatment options and urgently needs more effective therapies. Toward this end, we have designed and evaluated a library of novel Trop2-targeting ISACs. These engineered ISACs exhibited reduced aggregation and improved pharmacokinetics. One of these achieved complete tumor regression in vivo in two different tumor models leading to the identification of an efficient ISAC for pancreatic cancer. These findings highlight the critical role of linker engineering in the development of more effective ISACs. Citation Format: Mohan Reddy Mullapudi, Anqi Zhang, Steven J. McKay, Tracy A. Brooks, Nathan L. Tumey. Discovery of a novel Trop2-targeting immune-stimulating antibody conjugate with efficacy in pancreatic cancer models [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 5834.