Therapeutic Potential of AO-176, a Next Generation Humanized CD47 Antibody, for Hematologic Malignancies

Inhibitors of adaptive immune checkpoints have shown promise as cancer treatments. CD47 is an innate immune checkpoint receptor broadly expressed on normal tissues and over-expressed on several tumors. Binding of tumor CD47 to signal regulatory protein alpha (SIRPalpha) on macrophages and dendritic cells triggers a "don't eat me" signal that inhibits phagocytosis enabling escape of innate immune surveillance. Blocking CD47/SIRPα interaction promotes phagocytosis reducing tumor burden in numerous xenograft and syngeneic animal models.

We have developed a next generation humanized anti-CD47 antibody, AO-176, that not only blocks the CD47/SIRPalpha interaction and induces phagocytosis of hematologic and solid tumor cells, but also exhibits several unique functional properties. The first property is the ability of AO-176 to induce direct tumor cytotoxic cell death in hematologic (ex. Jurkat, Raji and Molt-4) as well as solid human tumor cell lines by a cell autonomous mechanism (not ADCC). Secondly, AO-176 exhibits preferential binding to tumor versus normal cells, including red blood cells (RBCs), T cells, endothelial cells, skeletal muscle cells and epithelial cells. A0-176 also does not affect the function of any of these primary cells when assayed ex vivo. The negligible binding of AO-176 to RBCs versus hematologic (ex. Jurkat, Raji or Molt-4) or solid tumor cells is particularly profound and different from other reported anti-CD47 antibodies. AO-176 also does not induce hemagglutination of RBCs. These properties are expected not only to decrease the antigen sink, but also to minimize on-target clinical adverse effects observed following treatment with other reported RBC-binding anti-CD47 antibodies. Consistent with this attribute, AO-176 was well tolerated in cynomolgus monkeys with no adverse effects in general nor with respect to RBCs which was consistent with ex vivo results. A third novel property of AO-176 is its enhanced binding to tumor cells at acidic pH. Because the microenvironment of leukemic bone marrow and solid tumors has an acidic pH, this enhanced binding of AO-176 at low pH has the potential added advantage of tumor-specific targeting. Lastly, we show that AO-176 demonstrates dose-dependent anti-tumor activity in hematologic and solid tumor xenograft models.

Taken together, the unique properties and anti-tumor activity of our next generation anti-CD47 antibody, AO-176, distinguishes it from other CD47/SIRPalpha axis targeting agents as it progresses to clinical development.