Abstract 55: Generation of half-life extended anti-CD33 BiTE® antibody constructs compatible with once-weekly dosing

T cell engaging bispecific antibody constructs (BiTE®), such as blinatumomab which targets CD19-positive cells, have shown great promise for treating certain CD19-positive hematological malignancies. Blinatumomab comprises a single chain Fv (scFv) that binds CD19 and a scFv that targets the T cell CD3 protein. The molecular weight of this “canonical” BiTE® is ~ 55 kDa, making it susceptible to kidney-mediated clearance and resulting in a short serum half-life (~ 4 hours). To maintain effective serum concentrations, canonical BiTE® antibody constructs must be administered by continuous IV (cIV) infusion. While there are many advantages associated with cIV administration (e.g., safety and uniform PK profile), patient convenience could be enhanced if the BiTE® antibody construct were compatible with once-weekly administration. To achieve this, the serum half-life of the BiTE® antibody construct would need to be extended. A canonical BiTE® targeting CD33 (AMG 330) is currently being evaluated in a phase I clinical trial. Like blinatumomab, AMG 330 is dosed cIV. To extend the serum half-life of AMG 330 and enable once-weekly dosing, several approaches were evaluated including fusion of AMG 330 to human albumin and Fc-containing moieties. Each of these half-life extended (HLE) constructs was evaluated in vitro, in mouse xenograft models and in non-human primates. In vitro assays evaluated 1) binding to both human and cynomolgus CD33 and CD3 proteins, and 2) cytotoxicity using human and cynomolgus target and effector cells. In each of these assays the canonical and HLE BiTE® antibody constructs demonstrated similar activity: single-digit nM binding and single digit pM cytotoxicity. Canonical and HLE BiTE® antibody constructs were subsequently evaluated in an orthotopic mouse model in which MOLM13 cells were administered IV and activated human T cells were administered IP two days later. The Fc-based HLE BiTE® antibody constructs provided a similar survival advantage when administered Q4D or Q5D as the canonical BiTE® when administered QD. However, the albumin fusion–based HLE BiTE® was less efficacious when administered Q4D than the QD- administered canonical BiTE®. Lastly, the PK/PD relationship was evaluated for each of the constructs in non-human primates. The serum half-lives varied from 6 hours for the canonical BiTE® to 44-167 hours for the HLE BiTE® antibody constructs. Each of the HLE BiTE® antibody constructs showed on-target depletion of CD33-positive monocytes and neutrophils in the blood and depletion of CD33-positive cells in the bone marrow. These data demonstrate that half-life extended BiTE® antibody constructs can be generated that retain comparable in vitro and in vivo activity as a canonical BiTE® and achieve a serum half-life compatible with once weekly dosing. Citation Format: Tara L. Arvedson, Mercedesz Balazs, Pamela Bogner, Kurt Black, Kevin Graham, Anja Henn, Matthias Friedrich, Patrick Hoffmann, Roman Kischel, Peter Kufer, Ralf Lutterbuese, Markus Muenz, Tobias Raum, Benno Rattel, Karen Rex, Dan Rock, Oliver Thomas, Joachim Wahl, Andreas Wolf, Angela Coxon. Generation of half-life extended anti-CD33 BiTE® antibody constructs compatible with once-weekly dosing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 55. doi:10.1158/1538-7445.AM2017-55