Preclinical functional characterization of AGEN1181, a clinical stage Fc-engineered anti-CTLA-4 antibody for the treatment of patients with early and advanced malignancies.

e14126 Background: Cytotoxic T lymphocyte-associated protein 4 (CTLA-4) is an inhibitory receptor that modulates T cell priming and CD28-dependent T cell activation. Modulation of this pathway by CTLA-4 antibodies has demonstrated clinical responses in patients with advance disease, however the mechanism of action of these antibodies remains controversial. It is currently understood that anti-CTLA-4 antibodies mediate antitumor effects through receptor-ligand blockade, and, in preclinical models, through depletion of intratumoral regulatory T (Treg) cells via an Fc-dependent mechanism. Recently, we reported a novel Fc-mediated contribution to T cell priming underscored the importance of Fc selection for optimal CTLA-4 antibody activity. AGEN1181 is a clinical stage Fc-engineered IgG1 antibody that leverages this novel mechanism for enhanced functionality. Methods: Fab-mediated biology of AGEN1181 was confirmed by assessing binding affinity, specificity, and blockade of CTLA-4:CD80/86 interactions. Fc-mediated functions of AGEN1181 were evaluated by FcγR binding, reporter-based FcγR signaling, and antibody-mediated Treg cell cytotoxicity assays. In vitro and in vivo pharmacology of AGEN1181 (alone or in combination with anti-PD-1) were evaluated in superantigen (staphylococcal enterotoxin)-mediated T cell stimulation assays and in a non-human primate (NHP) model. Safety and tolerability of AGEN1181 were assessed in cynomolgus monkeys administered 5 once-weekly intravenous bolus infusions at doses of 5, 30, or 100 mg/kg. Results: AGEN1181 bound to CTLA-4 with high affinity and specificity and demonstrated a range of enhanced functional activities relative to first-generation CTLA-4 antibodies. This included superior CD16 (FcγRIIIA) binding, Treg depletion and T cell priming (as measured by ZAP70 phosphorylation and interleukin-2 secretion). In NHP studies, a single dose of AGEN1181, alone or in combination with anti-PD-1 antibody upregulated Ki67 and ICOS expression on peripheral T cells. Finally, AGEN1181 exhibited an acceptable toxicologic profile in multi-dose NHP studies. Conclusions: AGEN1181, an Fc-engineered anti-CTLA-4 antibody exhibits a range of enhanced functional attributes relative to first-generation anti-CTLA-4 antibodies in preclinical studies. Phase 1 clinical studies for AGEN1181 will be initiated imminently.