AO-176, a Differentiated Clinical-Stage Anti-CD47 Antibody, Demonstrates Potent Anti-Tumor Activity across Multiple Preclinical Models of B Cell Neoplasms

Upregulation of CD47, the "don't eat me" signal, on the surface of tumors to evade immune surveillance is a common escape mechanism utilized during hematological malignancy and solid tumor development, progression, and relapse. We recently reported that AO-176, a clinical stage humanized anti-CD47 IgG2 antibody, possesses differentiated characteristics such as preferential binding of tumor cells compared to normal cells, negligible binding to red blood cells, non-ADCC direct tumor killing and elicits immunogenic cell death and DAMP induction, all in addition to single-agent phagocytosis. In vivo, AO-176 has exhibited broad anti-tumor activity in preclinical xenograft models of multiple myeloma (MM), acute myeloid leukemia, T cell acute lymphoblastic leukemia, and Burkitt lymphoma. In this study, the anti-tumor activity of AO-176 in an expanded set of preclinical models of B cell neoplasms was evaluated. We assessed In vivo anti-tumor activity in a diffuse large B cell lymphoma (DLBCL) preclinical xenograft model by inoculating Toledo cells into NSG mice and treating once weekly with either 25 mg/kg AO-176 or human IgG2 isotype control. Treatment with AO-176 resulted in profound tumor shrinkage, achieved complete responses in 8/10 mice, and extended survival for all treated mice through the 46 day dosing period, compared to all isotype control treated tumors reaching endpoint by day 21.

Having previously observed significant tumor shrinkage and extension of survival in subcutaneous xenograft models of MM, we sought to evaluate anti-tumor activity of AO-176 in an orthotopic model of MM. Luciferase expressing RPMI-8226 cells were inoculated via intratibial injection into NOD-SCID mice and treated with either 25 mg/kg of AO-176 or human IgG2 isotype control once weekly. AO-176-treated mice showed significant reductions of bioluminescence on study days 7, 21, 35, and 41, and serum paraprotein at study end. Evaluation of bone lesions by x-ray showed significantly reduced average bone lysis score in the AO-176 treatment group at study day 41. We then compared the anti-tumor activity of AO-176 against the second generation proteosome inhibitor carfilzomib in a myeloma xenograft model. AO-176 dosed at 25 mg/kg once weekly achieved 72% TGI, compared to 47% and 27% TGI for tumors treated with 5 mg/kg and 2.5 mg/kg carfilzomib at day 29 post treatment.

To elucidate the pathways and processes that may be underpinning the anti-tumor activity of AO-176, we performed bulk RNA sequencing on AO-176 or isotype control-treated tumors harvested at multiple time points from a MM xenograft model we previously reported as exhibiting profound sensitivity to AO-176 in vivo. Murine transcripts from harvested tumor RNA were evaluated to assess differences in immune infiltrate resulting from AO-176 treatment. Days 3 and 7 post treatment with AO-176 showed the greatest number of differentially expressed genes compared to control treated tumors. The top enriched pathway on day 3 was microglia phagocytosis. Principal component analysis of gene expression indicated partitioning of day 3 post AO-176 treatment from the rest of the groups. Furthermore, deconvolution of abundances of infiltrating immune cells using CIBERSORT via TIMER analytical tool showed an enrichment of macrophages relative to other cell types on day 3 post treatment.

To extend our RNA sequencing findings, we then sought to evaluate intratumoral immune cell populations after AO-176 treatment in a subcutaneous MM xenograft model. MM cells were inoculated into NOD-SCID mice, then treated with 25 mg/kg AO-176 or human IgG2 isotype control. At 48 hours post treatment, tumors were harvested, and we observed an increase of macrophages in the AO-176 treated tumors, confirming our previous results.

In summary, the robust preclinical data in DLBCL and MM warrants further development of AO-176 for treatment of hematological malignancies. AO-176 is being evaluated in phase 1/2 clinical trials for the treatment of patients with solid tumors (NCT03834948) and with MM (NCT04445701).