In Vivo Evaluation of a Novel Format of a Bivalent HER3-Targeting and Albumin-Binding Therapeutic Affibody Construct

摘要

Overexpression and excessive signaling of human epidermal growth factor receptor 3 (HER3) is involved in resistance to several therapies for malignant tumors. Currently, a number of anti-HER3 monoclonal antibodies are under clinical development. We introduce an alternative approach to HER3-targeted therapy based on engineered scaffold proteins, affibody molecules. A small (22.5 kDa) bivalent construct, denoted 3A3, consists of two high-affinity anti-HER3 affibody molecules ZHER3:08699 flanking an albumin-binding domain ABD, introduced for prolonged circulation time in vivo. In vitro, 3A3 efficiently inhibited growth of HER3-expressing BxPC-3 cells. Biodistribution in mice was measured using a 3A3 variant labeled with 111In via DOTA chelators incorporated site-specifically at the C-terminus. The residence time of 111In-DOTA-3A3 in blood was extended compared with the residence time of the monomeric affibody molecule. However, 111In-DOTA-3A3 cleared more rapidly from blood than a Taq polymerase binding control construct 111In-DOTA-TAT, most likely due to sequestering of 3A3 by mErbB3, the murine counterpart of HER3. Repeated dosing and increase of injected protein dose decreased uptake of 111In-DOTA-3A3 in mErbB3-expressing tissues. It was further demonstrated that 111In-DOTA-3A3 accumulated specifically in HER3-expressing BxPC-3 xenografts in mice. In addition, delay of tumor growth was obtained in an experimental (pilot-scale) therapy study for BxPC-3 xenografts in mice treated with 3A3. We conclude that 3A3 affibody format seems promising for treatment of HER3-overexpressing tumors.