Human epidermal growth factor (HER2) is a transmembrane tyrosine kinase receptor that is frequently overexpressed in breast cancer. Its increased level prognoses a poor patient outcome and a high mortality rate. Despite the widening spectrum of therapies that are becoming available to treat HER2+ breast cancer, its side effects and resistance still make this protein a valuable object of research in targeted tumor therapy. The role of tumor-targeting peptides has become more and more prominent in the last few decades due to their simple synthesis and pharmakokinetic properties. Here, we examine two fluorescently-labeled HER2-specific peptides and their combined analogues that are developed to target the extracellular region of HER2. The peptides are investigated on breast cancer cell lines with different HER2 expression profiles. Moreover, their extracellular localization and specificity are confirmed by flow cytometry and confocal microscopy. Therefore, a new, combined HER2 binding conjugate is obtained that interacts with HER2-overexpressing cells with high affinity and specificity. Furthermore, secondary structure prediction reveals that the α-helical content of the peptides is associated with their receptor recognition. This highly specific conjugate can be used as a starting point for diagnostical or drug-targeting purposes in upcoming studies.

Plants and fungi can be used for medical applications because of their accumulation of special bioactive metabolites. These substances might be beneficial to human health, exerting also anti-inflammatory and anticancer (antiproliferative) effects. We propose that they are mediated by influencing cellular adhesion and migration via various signaling pathways and by directly inactivating key cell adhesion surface receptor sites. The evidence for this proposition is reviewed (by summarizing the natural metabolites and their effects influencing cellular adhesion and migration), along with the classical measuring techniques used to gain such evidence. We systematize existing knowledge concerning the mechanisms of how natural metabolites affect adhesion and movement, and their role in gene expression as well. We conclude by highlighting the possibilities to screen natural compounds faster and more easily by applying new label-free methods, which also enable a far greater degree of quantification than the conventional methods used hitherto. We have systematically classified recent studies regarding the effects of natural compounds on cellular adhesion and movement, characterizing the active substances according to their organismal origin (plants, animals or fungi). Finally, we also summarize the results of recent studies and experiments on SARS-CoV-2 treatments by natural extracts affecting mainly the adhesion and entry of the virus.

The cell-penetrating peptide (CPP) penetratin has gained much attention over many years due to its potential role as a transporter for a broad range of cargo into cells. The modification of penetratin has been extensively investigated too. Aza-peptides are peptide analogs in which one or more of the amino residues are replaced by a semicarbazide. This substitution results in conformational restrictions and modifications in hydrogen bonding properties, which affect the structure and may lead to enhanced activity and selectivity of the modified peptide. In this work, the Trp residues of penetratin were substituted by aza-glycine or glycine residues to examine the effect of these modifications on the cellular uptake and the internalization mechanism. The substitution of Trp⁴⁸ or Trp^48,56 dramatically reduced the internalization, showing the importance of Trp⁴⁸ in cellular uptake. Interestingly, while aza-glycine in the position of Trp⁵⁶ increased the cellular uptake, Gly reduced it. The two Trp-modified derivatives showed altered internalization pathways, too. Based on our knowledge, this is the first study about the effect of aza-amino acid substitution on the cell entry of CPPs. Our results suggest that aza-amino acid insertion is a useful modification to change the internalization of a CPP.

The use of peptide-drug conjugates has generated wide interest as targeted antitumor therapeutics. The anthracycline antibiotic, daunomycin, is a widely used anticancer agent and it is often conjugated to different tumor homing peptides. However, comprehensive analytical characterization of these conjugates via tandem mass spectrometry (MS/MS) is challenging due to the lability of the O-glycosidic bond and the appearance of MS/MS fragment ions with little structural information. Therefore, we aimed to investigate the optimal fragmentation conditions that suppress the prevalent dissociation of the anthracycline drug and provide good sequence coverage. In this study, we comprehensively compared the performance of common fragmentation techniques, such as higher energy collisional dissociation (HCD), electron transfer dissociation (ETD), electron-transfer higher energy collisional dissociation (EThcD) and matrix-assisted laser desorption/ionization–tandem time-of-flight (MALDI-TOF/TOF) activation methods for the structural identification of synthetic daunomycin-peptide conjugates by high-resolution tandem mass spectrometry. Our results showed that peptide backbone fragmentation was inhibited by applying electron-based dissociation methods to conjugates, most possibly due to the “electron predator” effect of the daunomycin. We found that efficient HCD fragmentation was largely influenced by several factors, such as amino acid sequences, charge states and HCD energy. High energy HCD and MALDI-TOF/TOF combined with collision induced dissociation (CID) mode are the methods of choice to unambiguously assign the sequence, localize different conjugation sites and differentiate conjugate isomers.

The unicellular Tetrahymena distinguishes structure-related vertebrate hormones by its chemosensory reactions. In the present work, the selectivity of hormone receptors was evaluated by analyzing the effects of various gonadotropin-releasing hormone (GnRH) analogs (GnRH-I, GnRH-III) as well as truncated (Ac-SHDWKPG-NH₂) and dimer derivatives ([GnRH-III(C)]₂ and [GnRH-III(CGFLG)]₂) of GnRH-III on (i) locomotory behaviors, (ii) cell proliferation, and (iii) intracellular hormone contents of Tetrahymena pyriformis. The migration, intracellular hormone content, and proliferation of Tetrahymena were investigated by microscope-assisted tracking analysis, flow cytometry, and a CASY TT cell counter, respectively. Depending on the length of linker sequence between the two GnRH-III monomers, the GnRH-III dimers had the opposite effect on Tetrahymena migration. [GnRH-III(CGFLG)]₂ dimer had a slow, serpentine-like movement, while [GnRH-III(C)]₂ dimer had a rather linear swimming pattern. All GnRH-III derivatives significantly induced cell growth after 6 h incubation. Endogenous histamine content was uniformly enhanced by Ac-SHDWKPG-NH₂ and GnRH-III dimers, while some differences between the hormonal activities of GnRHs were manifested in their effects on intracellular levels of serotonin and endorphin. The GnRH peptides could directly affect Tetrahymena migration and proliferation in a structure-dependent manner, and they could indirectly regulate these reactions by paracrine/autocrine mechanisms. Present results support the theory that recognition ability and selectivity of mammalian hormone receptors can be deduced from a phylogenetically ancient level like the unicellular Tetrahymena.