Abstract 2640: An innovative site-specific dual-payload antibody drug conjugate (dpADC) combining a novel Topo1 inhibitor and an immune agonist delivers a strong immunogenic cell death (ICD) and antitumor response in vitro and in vivo

Abstract Background: Antibody-drug conjugate, also known as a targeted chemotherapy, leverages the targeting feature of mAb and the efficient cell-killing ability of cytotoxin to deliver cytotoxic drugs to tumor specifically. Among the FDA approved 15 ADCs and over 100 in clinical trial, the majority contains a single type cytotoxin payload. Combination of chemotherapies or multiple agents are widely therapeutic approach to enhance treatment efficiency, although frequently combo therapies could lead to higher toxicity, long term chemotherapies could result in drug resistance and tumor relapse. To solve above challenge, here we report an innovative dual-payload antibody-drug conjugate (dpADC) with 2 type of different drug payloads with different MoA, the conjugate is constructed based on unique enzymatic site-specific conjugation technology iLDC/iGDC. The dpADC leads to an enhanced immunogenic cell death (ICD) and antitumor response in vitro and in vivo via a synergistic MoA. Results: A novel Topo1 inhibitor TopoIx and an immune agonist were stably conjugated to an anti-Trop2 mAb in a site-specific manner, conjugate homogeneity and precise DAR were characterized. The dpADC showed a strong cytotoxicity on the proliferation of Trop2-expressing cells, meanwhile bystander killing activity of TopoIx also effectively inhibits growth ofTrop2-negative cells. This dpADC also triggers IP10/IL6 secretion when co-cultured with PBMC/monocyte and Trop2-positive cancer cells, with induction level correlated with Trop 2 expression level. No free payload was released after 96hr incubation at 37 oC in human plasma, demonstrating high linker stability. The dpADC demonstrated a robust antitumor response against diverse Trop2+ tumors in vivo. Its’ combination with anti-mPD-1 resulted in synergistic anti-tumor response. In a tumor rechallenge model, the mice that had cleared of Trop2+ tumors after dpADC treatment were protected against the re-implantation of tumor cells with same or different neoantigen, suggesting the presence of a robust immunological memory. Conclusion: In summary, this novel dpADC demonstrates potent antitumor activities in vitro and in vivo and leads to an enhanced tumor cell killing ability and a prolonged immunological memory via a synergistic MoA. Based on this site-specific, dual-enzyme orthogonal catalytic conjugation platform, we can easily integrate MoA-varied drugs in one targeting modality to realize a synergistic, durable anti-tumor therapy. Citation Format: Meijun Xiong, Beibei Fan, Xinju Gao, Yajun Sun, Cao Lv, Yu Si, Xiao Liu, Lili Shi, Paul H. Song, Gang Qin. An innovative site-specific dual-payload antibody drug conjugate (dpADC) combining a novel Topo1 inhibitor and an immune agonist delivers a strong immunogenic cell death (ICD) and antitumor response in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2640.