Abstract
The human epidermal growth factor receptor 2 (HER2) is a clinically validated target for cancer therapy, and targeted therapies are often used in regimens for patients with a high HER2 expression level. Despite the success of current drugs, a number of patients succumb to their disease, which motivates development of novel drugs with other modes of action. We have previously shown that an albumin binding domain-derived affinity protein with specific affinity for HER2, ADAPT6, can be used to deliver the highly cytotoxic protein domain PE25, a derivative of Pseudomonas exotoxin A, to HER2 overexpressing malignant cells, leading to potent and specific cell killing. In this study we expanded the investigation for an optimal targeting domain and constructed two fusion toxins where a HER2-binding affibody molecule, ZHER2:2891, or the dual-HER2-binding hybrid ZHER2:2891-ADAPT6 were used for cancer cell targeting. We found that both targeting domains conferred strong binding to HER2; both to the purified extracellular domain and to the HER2 overexpressing cell line SKOV3. This resulted in fusion toxins with high cytotoxic potency toward cell lines with high expression levels of HER2, with EC50 values between 10 and 100 pM. For extension of the plasma half-life, an albumin binding domain was also included. Intravenous injection of the fusion toxins into mice showed a profound influence of the targeting domain on biodistribution. Compared to previous results, with ADAPT6 as targeting domain, ZHER2:2891 gave rise to further extension of the plasma half-life and also shifted the clearance route of the fusion toxin from the liver to the kidneys. Collectively, the results show that the targeting domain has a major impact on uptake of PE25-based fusion toxins in different organs. The results also show that PE25-based fusion toxins with high affinity to HER2 do not necessarily increase the cytotoxicity beyond a certain point in affinity. In conclusion, ZHER2:2891 has the most favorable characteristics as targeting domain for PE25.
Highlights
Therapeutic approaches targeting particular pathways or molecular abnormalities on cancer cells have shown great progress during recent years and have led to impressive treatment responses in some cases
A possibility is to utilize the bivalent analyte binding model in the Biacore software package, as we have done in this study. It assumes that the two human epidermal growth factor receptor 2 (HER2)-binding parts of ZHER2:2891-ADAPT6-albumin binding domain (ABD)-PE25 are interacting identically with HER2, as would e.g., the two antigen binding arms of an antibody
Since the kinetic constants for the interaction between ADAPT6-ABD-PE25 and HER2 [31] is different from the kinetic constants derived for the interaction between ZHER2:2891-ABD-PE25 and HER2 in the present study, the kinetic constants derived from the bivalent analyte binding model for ZHER2:2891-ADAPT6-ABD-PE25 can only be regarded as an approximation
Summary
Therapeutic approaches targeting particular pathways or molecular abnormalities on cancer cells have shown great progress during recent years and have led to impressive treatment responses in some cases. HER2 is a single-pass plasma membrane anchored receptor that belongs to the epidermal growth factor receptor family. It can form homo- or hetero-dimers with other members of its family to trigger activation of e.g., the mitogen activated protein kinase (MAPK) and PI3K/Akt pathways [3]. This leads to a more aggressive phenotype which is characterized by increased proliferation, survival, and motility, and a poorer prognosis for the patient [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
