Abstract 6641: ATG-031, a first-in-class humanized anti-CD24 antibody, demonstrates potent in vivo efficacy and repolarizes tumor-associated macrophages in the TME

Background: Tumor microenvironment (TME) is shaped by not only cancer cells but also a variety of resident and infiltrating cells, including stromal fibroblasts, endothelial cells and immune cells like tumor-associated macrophages (TAM) and lymphocytes (Roghayyeh et al., 2020). Most TAMs are considered as the M2 subtype with pro-tumor/anti-inflammation effects. CD24 is a small, highly glycosylated cell adhesion protein and was reported to be the dominant innate immune checkpoint in ovarian cancer and breast cancer, and acts as a novel “don’t eat me” target. CD24 is over-expressed on tumor cells and can help them avoid being engulfed by macrophages through its interaction with Siglec-10 expressed by TAM. ATG-031 is a humanized anti-CD24 monoclonal antibody that binds to CD24 with high affinity and specificity and blocks the interaction of CD24 with Siglec-10 on macrophages, enhancing macrophage-mediated phagocytosis of tumor cells. In this study, we evaluated the in vivo efficacy of ATG-031 and explored its pharmacodynamic effects. Methods: C57BL/6J mice were inoculated with wild-type (WT) MC38 cells on the left flank and MC38 cells that express human CD24 (MC38-hCD24) on the right flank. When the average tumor volume reached 120 to 140 mm3 for MC38-hCD24, mice were treated with vehicle control (PBS) or ATG-031 at 3 mg/kg intravenously twice a week for four doses. A group of mice inoculated with only MC38 tumor cells was set as the control and treated with ATG-031 by the same way. Tumor volume was measured twice a week to evaluate the efficacy of ATG-031. Tumor samples were isolated at the endpoint of this efficacy study, and a multiplex IHC staining was performed to evaluate the change of tumor-infiltrating immune cells in response to ATG-031. Results: ATG-031 treatment significantly inhibited the tumor growth of MC38-hCD24 on the right flank of mice with a tumor growth inhibition (TGI) of 60.52%. Interestingly, although the WT MC38 tumor on the left flank did not express the antigen, human CD24, ATG-031 still demonstrated efficacy in controlling the tumor growth with a TGI of 21.17%. Without the co-inoculation of MC38-hCD24, ATG-031 did not affect the WT MC38 tumor growth in the control group. Multiplex IHC staining revealed that the proportion of M1 macrophage increased in response to ATG-031 treatment, not only in MC38-hCD24 tumors but also in WT MC38 tumors on the left flank. Conclusions: ATG-031, a first-in-class anti-CD24 antibody, demonstrated potent anti-tumor activity in vivo, re-polarizing M2-like TAM to anti-tumor M1 subtype in the TME and induced systemic anti-tumor immunity. A clinical study to investigate the safety and efficacy of ATG-031 in cancer patients is being developed. Citation Format: Peng Chen, Min Deng, Yun Liu, Jiamei Luo, Linjie Tian, Jay Mei, Bo Shan, Bing Hou. ATG-031, a first-in-class humanized anti-CD24 antibody, demonstrates potent in vivo efficacy and repolarizes tumor-associated macrophages in the TME. [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 6641.