Abstract 2908: PT217, an anti-DLL3/anti-CD47 bispecific antibody, exhibits anti-tumor activity through novel mechanisms of action

Abstract

Abstract Small cell lung cancer (SCLC) is the most lethal subtype of lung cancers with few patients surviving more than 5 years from diagnosis. While SCLC initially responds well to standard chemotherapy treatment, chemotherapy-resistant recurrence is characteristic and available treatment options for recurrent and refractory diseases are limited. Immunotherapy as an alternative or additional treatment has been very successful in treating many cancers, yet it has shown disappointingly limited benefits in SCLC and notable treatment related toxicities have been observed. Delta like 3 (DLL3) is an attractive target for SCLC immunotherapy, as its expression is highly restricted to SCLC and can therefore be used for targeting purposes. On the other hand, CD47 is also strongly expressed on the surface of SCLC cells, where it inhibits macrophage-mediated tumor cell killing. We have developed PT217, a DLL3/CD47 bispecific antibody with effector effect competent Fc to specifically target SCLC cells via two mechanisms. First, PT217 blocks the CD47-SIRPα interaction and stimulates phagocytosis of tumor cells by macrophage. Second, PT217 exhibits robust effector effect (ADCC by NK cells and ADPC by macrophage) mediated by the functional Fc of PT217. Interestingly, it appears that the tumor cells targeted by NK cells are subsequently engulfed by macrophage. Elevated phagocytosis of the tumor cells by macrophages and dendritic cells is expected to increase the presentation of tumor neoantigens that may eventually lead to T cell-mediated killing of tumor cells that do not expression DLL3. In vivo, PT217 demonstrated tumor suppression activity in xenograft mouse models. In addition to the strong tumor killing activity, PT217 also demonstrated good safety profile in NHP studies. Furthermore, PT217 exhibits regular mAb-like manufacturability in process development and CMC. We expect to initiate a phase 1 trial to target SCLC in the first half of 2022. Citation Format: Haiqun(John) Jia, Dorthy Fang, Molly Lobsinger, Yan Long, Kelan Chen, Albert Lam, Yangyang Guo, Kaisa Selesniemi, Ming Wang, Hui Zou. PT217, an anti-DLL3/anti-CD47 bispecific antibody, exhibits anti-tumor activity through novel mechanisms of action [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2908.