Molecular and hydrodynamic properties of human epidermal growth factor receptor HER2 extracellular domain and its homodimer: Experiments and multi-scale simulations

Exploring the Combined Action of Adding Pertuzumab to Branded Trastuzumab versus Trastuzumab Biosimilars for Treating HER2+ Breast Cancer

The binding activity of various trastuzumab biosimilars versus the branded trastuzumab towards the glycosylated extracellular domain of the human epidermal growth factor receptor 2 (HER2) target in the presence of pertuzumab was investigated. We employed size exclusion chromatography with tetra-detection methodology to simultaneously determine absolute molecular weight, concentration, molecular size, and intrinsic viscosity. All trastuzumab molecules in solution exhibit analogous behavior in their binary action towards HER2 regardless of the order of addition of trastuzumab/pertuzumab. This analogous behavior of all trastuzumab molecules, including biosimilars, highlights the robustness and consistency of their binding activity towards HER2. Furthermore, the addition of HER2 to a mixture of trastuzumab and pertuzumab leads to increased formation of high-order HER2 complexes, up to concentrations of one order of magnitude higher than in the case of sequential addition. The observed increase suggests a potential synergistic effect between these antibodies, which could enhance their therapeutic efficacy in HER2-positive cancers. These findings underscore the importance of understanding the complex interplay between therapeutic antibodies and their target antigens, providing valuable insights for the development of more effective treatment strategies.

Binding Affinity of Trastuzumab and Pertuzumab Monoclonal Antibodies to Extracellular HER2 Domain

The binding affinity of trastuzumab and pertuzumab to HER2 has been studied using both experimental and in silico methods. The experiments were conducted using the antibodies in their complete IgG form, as used in clinical therapy, and the extracellular domain of the HER2 protein in solution. This approach provides a precise, reproducible, and reliable view of the interaction between them in physicochemical conditions similar to those found in the tumoral environment. Dynamic light scattering and size exclusion chromatography coupled with tetra detection were utilized to characterize the protein complexes, measure their concentrations, and calculate the equilibrium-free binding energy, ΔGbind. In addition, PRODIGY, a QSAR-like model with excellent predictive ability, was employed to obtain in silico ΔGbind estimations. The results obtained indicate that pertuzumab exhibits a slightly higher binding affinity to HER2 than trastuzumab. The difference in binding affinity was explained based on the contribution of the different interfacial contact (IC) descriptors to the ΔGbind value estimated by the PRODIGY model. Furthermore, experiments revealed that the pertuzumab IgG antibody binds preferentially to two HER2 proteins, one per Fab fragment, while trastuzumab mainly forms a monovalent complex. This finding was interpreted based on a geometrical model that identified steric crowding in the trastuzumab-HER2 complex as compared with the pertuzumab-HER2 complex.

Integrated approach to functional analysis of an ERBB2 variant of unknown significance detected by a cancer gene panel test

Purpose

Dealing with variants of unknown significance (VUS) is an important issue in the clinical application of NGS-based cancer gene panel tests. We detected a novel ERBB2 extracellular domain VUS, c.1157A > G p.(E401G), in a cancer gene panel test. Since the mechanisms of activation by ERBB2 extracellular domain (ECD) variants are not fully understood, we aimed to clarify those mechanisms and the biological functions of ERBB2 E401G.

Methods

ERBB2 E401G was selected as VUS for analysis because multiple software tools predicted its pathogenicity. We prepared ERBB2 expression vectors with the E401G variant as well as vectors with S310F and E321G, which are known to be activating mutations. On the basis of wild-type ERBB2 or mutant ERBB2 expression in cell lines without ERBB2 amplification or variants, we evaluated the phosphorylation of human epidermal growth factor receptor 2 and related proteins, and investigated with molecular dynamics (MD) simulation the mechanisms conferred by the variants. The biological effects of ERBB2 E401G were also investigated, both in vitro and in vivo.

Results

We found that ERBB2 E401G enhances C-terminal phosphorylation in a way similar to S310F. MD simulation analysis revealed that these variants maintain the stability of the EGFR-HER2 heterodimer in a ligand-independent manner. Moreover, ERBB2 E401G-transduced cells showed an increased invasive capacity in vitro and an increased tumor growth capacity in vivo.

Conclusion

Our results provide important information on the activating mechanisms of ERBB2 extracellular domain (ECD) variants and illustrate a model workflow integrating wet and dry bench processes for the analysis of VUS detected with cancer gene panel tests.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13402-021-00656-3.

Hydrodynamic and Electrophoretic Properties of Trastuzumab/HER2 Extracellular Domain Complexes as Revealed by Experimental Techniques and Computational Simulations

The combination of hydrodynamic and electrophoretic experiments and computer simulations is a powerful approach to study the interaction between proteins. In this work, we present hydrodynamic and electrophoretic experiments in an aqueous solution along with molecular dynamics and hydrodynamic modeling to monitor and compute biophysical properties of the interactions between the extracellular domain of the HER2 protein (eHER2) and the monoclonal antibody trastuzumab (TZM). The importance of this system relies on the fact that the overexpression of HER2 protein is related with the poor prognosis breast cancers (HER2++ positives), while the TZM is a monoclonal antibody for the treatment of this cancer. We have found and characterized two different complexes between the TZM and eHER2 proteins (1:1 and 1:2 TZM:eHER2 complexes). The conformational features of these complexes regulate their hydrodynamic and electrostatic properties. Thus, the results indicate a high degree of molecular flexibility in the systems that ultimately leads to higher values of the intrinsic viscosity, as well as lower values of diffusion coefficient than those expected for simple globular proteins. A highly asymmetric charge distribution is detected for the monovalent complex (1:1 complex), which has strong implications in correlations between the experimental electrophoretic mobility and the modeled net charge. In order to understand the dynamics of these systems and the role of the specific domains involved, it is essential to find biophysical correlations between dynamics, macroscopic transport and electrostatic properties. The results should be of general interest for researchers working in this area.

Anticancer efficiency of cycloartane triterpenoid derivatives isolated from Cimicifuga yunnanensis Hsiao on triple-negative breast cancer cells

Background

The roots and rhizomes of Cimicifuga yunnanensis Hsiao are commonly used as anti-inflammatory, antipyretic, and analgesic remedies and detoxification agents in traditional Chinese medicine (TCM). Although C. yunnanensis has been considered as supplementary medicine for several disorders, the antitumor effect of this herb and its key components has not been explored.

Materials and methods

The rhizomes of C. yunnanensis were isolated by chromatographic techniques. Structures of isolated compounds were identified based on spectroscopic methods and comparison with published data. The in vitro anticancer activities of purified components were also performed by MTT experiments. The in vivo anticancer activities were examined by subcutaneous tumor model or a breast cancer liver metastasis model.

Results

In this study, we aimed to identify and characterize the effective antitumor components from the rhizomes of C. yunnanensis. By bioassay-guided fractionation techniques and chemical characterization, 12 cycloartane triterpenes and four chromones were isolated, among them, 11 compounds were identified in this genus at first. The identified two compounds showed dramatic inhibitory activities against breast cancer cells: compound 4 (23-epi-26-deoxyactein) and compound 13 (cimigenol). Then, we examined the antitumor effect of these two selective candidate chemicals on triple-negative breast cancer (TNBC) cells in vivo and found that they could reduce tumor growth in subcutaneous tumor model or breast cancer liver metastasis model.

Conclusion

These results suggested that the selective compounds isolated from C. yunnanensis Hsiao could be the promising new agents for TNBC treatment.

Silencing the expression of copine-III enhances the sensitivity of hepatocellular carcinoma cells to the molecular targeted agent sorafenib

Background

The application of the oral targeted therapeutic agent sorafenib provides new hope for patients suffering from advanced stages of hepatocellular carcinoma (HCC), but the prognosis of such patients remains poor due to the rapid development of the multidrug resistance process in cancer pathogenesis. The present work evaluated whether copine-III, a novel cancer regulator encoded by the CPNE3 gene, would be a potential indicator of sorafenib resistance in HCC treatment.

Materials and methods

The endogenous expression of copine-III in clinical specimens was examined by quantitative polymerase chain reaction. Copine-III siRNA was transfected into HCC cells to downregulate copine-III expression. The effect of copine-III on sorafenib’s antitumor activation was identified by in vitro and in vivo experiments (MTT, Transwell, and flow cytometry as well as a nude mice model).

Results

High levels of copine-III in clinical specimens are related to poor prognosis of advanced HCC patients on sorafenib treatment. Infection of Ad-siCPNE3 significantly decreased the endogenous expression of copine-III and enhanced the susceptibility of MHCC97-H cells to sorafenib: the IC₅₀ value decreased from 1.15±0.11 to 0.25±0.05 μmol/L. Moreover, silencing copine-III enhanced the effect of sorafenib on apoptosis, in vitro invasion/migration, and subcutaneous or intrahepatic growth of MHCC97-H cells in nude mice.

Conclusion

Copine-III is a novel potential indicator of prognosis for patients who received sorafenib for advanced HCC treatment.