Comparative analysis of HER2 specific oligopeptides: diagnostics and drug targeting

HER2 is overexpressed in 15-30% of breast cancers, its increased level reduces survival rate of patients and enhances the development of metastases. Monoclonal antibodies and inhibitors are used to target HER2, though resistance occurs in high percentage of patients. The use of tumor specific peptides is common in targeted tumor therapy due to their easy synthesis and beneficial pharmacokinetical properties that make them appropriate candidates for both diagnostical and therapeutical purposes. Among the HER2 binding oligopeptides studied in the MTA-ELTE Research Group of Peptide Chemistry, peptide P1 was the most specific that bound with the highest affinity to receptors of HER2-expressing breast cancer cells. The sequence of P1 shows high similarity with the HER2-specific antibody mimetics Affibody molecule, thus, we planned the development of Affibody variants that contain the sequence of peptide P1. Based on the results of molecular dinamical (MD) simulations, the synthesis of a new, more stable peptide carrier will be also carried out and the development of new ones is also aimed according to the results of MD simulations and high resolution NMR studies between the HER2 extracellular domain and binding peptides/Affibodies. The aim of our project is to prepare (beside diagnostical HER2 peptides) oligopeptide-drug conjugates and perform their functional characterization using HER2-overexpressing breast cancer cell lines. As HER2-specific peptides bind to the extracellular domain of HER2, the linker between the oligopeptide and drug has to be cleaved in the extracellular space, thus, we plan to use linkers that can be cleaved by matrix metalloproteinases (whose level is increased near tumor cells). Our goal is to perform cellular uptake, cytotoxicity and localization studies on HER2-expressing breast cancer cell lines to choose the most specific and effective conjugates. Our further goal is to express and purify the extracellular domain of HER2 in an eukaryotic expresison system to determine the binding affinity, the site of interaction and protein structure of the complexes. These studies can serve as a basis for the further optimization of the sequence and enhancement of binding affinity.

Beáta Biri-Kovács, Ildikó Szabó, Pál Stráner