Evaluation of a novel ¹⁷⁷Lu-labelled therapeutic Affibody molecule with a deimmunized ABD domain and improved biodistribution profile

Fusion of Affibody molecules with an albumin-binding domain (ABD) provides targeting agents, which are suitable for radionuclide therapy. To facilitate clinical translation, the low immunogenic potential of such constructs with targeting properties conserved is required.

The HER2-targeting Affibody molecule ZHER2:2891 was fused with a deimmunized ABD variant and DOTA was conjugated to a unique C-terminal cysteine. The novel construct, PEP49989, was labelled with ¹⁷⁷Lu. Affinity, specificity, and in vivo targeting properties of [¹⁷⁷Lu]Lu-PEP49989 were characterised. Experimental therapy in mice with human HER2-expressing xenografts was evaluated.

The maximum molar activity of 52 GBq/µmol [¹⁷⁷Lu]Lu-PEP49989 was obtained. [¹⁷⁷Lu]Lu-PEP49989 bound specifically to HER2-expressing cells in vitro and in vivo. The HER2 binding affinity of [¹⁷⁷Lu]Lu-PEP49989 was similar to the affinity of [¹⁷⁷Lu]Lu-ABY-027 containing the parental ABD035 variant. The renal uptake of [¹⁷⁷Lu]Lu-PEP49989 was 1.4-fold higher, but hepatic and splenic uptake was 1.7-2-fold lower than the uptake of [¹⁷⁷Lu]Lu-ABY-027. The median survival of xenograft-bearing mice treated with 21 MBq [¹⁷⁷Lu]Lu-PEP49989 (> 90 days) was significantly longer than the survival of mice treated with vehicle (38 days) or trastuzumab (45 days). Treatment using a combination of [¹⁷⁷Lu]Lu-PEP49989 and trastuzumab increased the number of complete tumour remissions. The renal and hepatic toxicity was minimal to mild.

In preclinical studies, [¹⁷⁷Lu]Lu-PEP49989 demonstrated favourable biodistribution and a strong antitumour effect, which was further enhanced by co-treatment with trastuzumab.