Preclinical Characterization of the Anti-Leukemia Activity of the CD33/CD16a/NKG2D Immune-Modulating TriNKET? CC-96191

Simple Summary: Current therapies are often insufficiently effective in patients with acute myeloid leukemia (AML), prompting ongoing interest in developing new drugs for this aggressive type of blood cancer. Many efforts focus on drugs that target CD33, a cell surface protein that is widely expressed on AML cells. Gemtuzumab ozogamicin (GO), which consists of a CD33 antibody linked to a small molecule toxin, benefits some AML patients but not many others, leaving room for other CD33-targeted therapeutics. Here, we examined CC-96191, a "TriNKET" protein drug that binds CD33 on AML cells at the same time it binds two different proteins, CD16a and NKG2D, on natural killer (NK) cells, thereby activating these immune cells and engaging them to kill AML cells. In preclinical studies, we found CC-96191 to be broadly active against human AML cells that express CD33. CC-96191 activated NK cells but not T cells; while maximum anti-AML efficacy was similar, soluble cytokine levels were 10- to >100-fold lower than with a protein drug that binds CD33 and CD3 on T cells. Moreover, CC-96191 eliminated AML cells but not normal CD33+ monocytes, suggesting selectivity toward leukemic cells. Together, these findings support the clinical exploration of CC-96191 as is currently ongoing. Increasing efforts are focusing on natural killer (NK) cell immunotherapies for AML. Here, we characterized CC-96191, a novel CD33/CD16a/NKG2D immune-modulating TriNKET (R). CC-96191 simultaneously binds CD33, NKG2D, and CD16a, with NKG2D and CD16a co-engagement increasing the avidity for, and activation of, NK cells. CC-96191 was broadly active against human leukemia cells in a strictly CD33-dependent manner, with maximal efficacy requiring the co-engagement of CD16a and NKG2D. A frequent CD33 single nucleotide polymorphism, R69G, reduced CC-96191 potency but not maximal activity, likely because of reduced CD33 binding. Similarly, the potency, but not the maximal activity, of CC-96191 was reduced by high concentrations of soluble CD33; in contrast, the soluble form of the NKG2D ligand MICA did not impact activity. In the presence of CD33+ AML cells, CC-96191 activated NK cells but not T cells; while maximum anti-AML efficacy was similar, soluble cytokine levels were 10- to >100-fold lower than with a CD33/CD3 bispecific antibody. While CC-96191-mediated cytolysis was not affected by ABC transporter proteins, it was reduced by anti-apoptotic BCL-2 family proteins. Finally, in patient marrow specimens, CC-96191 eliminated AML cells but not normal monocytes, suggesting selectivity of TriNKET-induced cytotoxicity toward neoplastic cells. Together, these findings support the clinical exploration of CC-96191 as in NCT04789655.