Targeting HER2 Expressing Tumors with a Potent Drug Conjugate Based on an Albumin Binding Domain-Derived Affinity Protein

Abstract

Albumin binding domain derived affinity proteins (ADAPTs) are a class of small and folded engineered scaffold proteins that holds great promise for targeting cancer tumors. Here, we have extended the in vivo half-life of an ADAPT, targeting the human epidermal growth factor receptor 2 (HER2) by fusion with an albumin binding domain (ABD), and armed it with the highly cytotoxic payload mertansine (DM1) for an investigation of its properties in vitro and in vivo. The resulting drug conjugate, ADAPT6-ABD-mcDM1, retained binding to its intended targets, namely HER2 and serum albumins. Further, it was able to specifically bind to cells with high HER2 expression, get internalized, and showed potent toxicity, with IC50 values ranging from 5 to 80 nM. Conversely, no toxic effect was found for cells with low HER2 expression. In vivo, ADAPT6-ABD-mcDM1, radiolabeled with 99mTc, was characterized by low uptake in most normal organs, and the main excretion route was shown to be through the kidneys. The tumor uptake was 5.5% ID/g after 24 h, which was higher than the uptake in all normal organs at this time point except for the kidneys. The uptake in the tumors was blockable by pre-injection of an excess of the monoclonal antibody trastuzumab (having an overlapping epitope on the HER2 receptor). In conclusion, half-life extended drug conjugates based on the ADAPT platform of affinity proteins holds promise for further development towards targeted cancer therapy.

Epithelial cell adhesion molecule‑targeting designed ankyrin repeat protein‑toxin fusion Ec1‑LoPE exhibits potent cytotoxic action in prostate cancer cells

“…In our recent study, Ec1-LoPE efficiently inhibited tumor growth of SKOV3 xenografts in mice, while having an IC 50 value of 0.53 µM in SKOV3 cells in the cytotoxicity assay (38). It must be noted that SKOV3 cells were shown to be more resistant to the cytotoxic action of drug (49) and toxin conjugates (50) based on affibody molecules and ADAPTs (43,51) in comparison to other cell lines. Therefore, picomolar IC 50 values of Ec1-LoPE in both PC-3 and DU145 cells suggest its potential for a therapeutic effect in PC models in vivo.…”

Effect of Inter-Domain Linker Composition on Biodistribution of ABD-Fused Affibody-Drug Conjugates Targeting HER2

“…However, the cytotoxicity to the SKOV3 cell line was different, where Z HER2:2891 -(G 3 S) 3 -ABD-mcDM1 demonstrated a stronger effect compared with Z HER2:2891 -G 4 S-ABD-mcDM1. It has to be noted that the SKOV3 cell line demonstrated strong resistance to anti-HER2 targeting drugs and toxins based on affibody molecules and other scaffold proteins, such as ADAPTs [ 12 , 36 , 37 ] and can be considered as the most challenging case for such treatment among the cell lines investigated in this study. The finding, in this study, of a molecular design, which increases the cytotoxic effect against this cell line, is an important achievement.…”