Abstract 2923: JAB-X1800: A potent immunostimulatory antibody-drug conjugate (iADC) targeting CD73

Abstract Background: STING emerges as a key immune sensor and activated STING pathway plays a key role in innate and adaptive immune response. STING agonist has shown promising potency to stimulate anti-tumor immunity. Considering immune-related toxicity due to systemic administration, as well as difficulty in intra-tumor administration, targeted delivery of STING agonist by iADC is warranted. We developed CD73-STING iADC JAB-X1800, which uses anti-CD73 mAb for targeted delivery of payload JAB-27670, a highly potent non-cyclic dinucleotide STING agonist. Method: Binding assay and HEK293-STING-luciferase reporter assay were performed to test affinity of JAB-27670. Tumor cells with CD73 expression and THP-1 cells were co-cultured in the presences of iADC JAB-X1800 to assess the IFN-β production. The cell killing activity of iADC JAB-X1800 was evaluated when cancer cells co-cultured with human PBMCs. Furthermore, human and mouse plasma stability of iADC JAB-X1800 was assessed. Finally, the anti-tumor effects of iADC JAB-X1800 alone or in combination with anti-PD-1 were evaluated in animal models. Results: JAB-27670 is a highly potent STING agonist with sub-nanomolar EC50 in binding and luciferase reporter assays. In CD73-expressing cancer cells and THP-1 co-culture experiments, iADC JAB-X1800 induced IFN-β production with significant improvement compared with the free payload. JAB-X1800 also induced potent killing in vitro. JAB-X1800 is stable in human and mouse plasma. A single dose of JAB-X1800 induced tumor regression in MDA-MB-231 xenograft model and hCD73-MC38 syngeneic model. JAB-X1800 conferred immunologic memory when tumor free mice were re-challenged. JAB-X1800 showed synergistic anti-tumor activity with anti-PD-1 in hCD73-MC38 syngeneic model. Conclusions: The CD73-targeted STING agonist iADC JAB-X1800 demonstrated high stability in plasma, robust activity, and good tolerability in animal models, supporting clinical development of JAB-X1800 alone and in combination with anti-PD-1 for patients with CD73-expressing tumors. Citation Format: Yang Ye, Guiqun Yang, Hongling Wang, Xin Sun, Yanping Wang, Fashun Yan, Lei Wang, Wei Long. JAB-X1800: A potent immunostimulatory antibody-drug conjugate (iADC) targeting CD73 [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 2923.