Rational design of EGFR dimerization-disrupting peptides: A new strategy to combat drug resistance in targeted lung cancer therapy

Current therapeutic approaches and promising perspectives of using bioengineered peptides in fighting chemoresistance in triple-negative breast cancer

Breast cancer is a collation of malignancies that manifest in the mammary glands at the early stages. Among breast cancer subtypes, triple-negative breast cancer (TNBC) shows the most aggressive behavior, with apparent stemness features. Owing to the lack of response to hormone therapy and specific targeted therapies, chemotherapy remains the first line of the TNBC treatment. However, the acquisition of resistance to chemotherapeutic agents increase therapy failure, and promotes cancer recurrence and distant metastasis. Invasive primary tumors are the birthplace of cancer burden, though metastasis is a key attribute of TNBC-associated morbidity and mortality. Targeting the chemoresistant metastases-initiating cells via specific therapeutic agents with affinity to the upregulated molecular targets is a promising step in the TNBC clinical management. Exploring the capacity of peptides as biocompatible entities with the specificity of action, low immunogenicity, and robust efficacy provides a principle for designing peptide-based drugs capable of increasing the efficacy of current chemotherapy agents for selective targeting of the drug-tolerant TNBC cells. Here, we first focus on the resistance mechanisms that TNBC cells acquire to evade the effect of chemotherapeutic agents. Next, the novel therapeutic approaches employing tumor-targeting peptides to exploit the mechanisms of drug resistance in chemorefractory TNBC are described.

A growth-based platform for detecting domain-peptide interactions in the cytoplasm of mammalian cells

Development of a method for detecting protein-protein interactions (PPIs) in living cells is important for therapeutic drug screening against various diseases including infectious diseases. We have recently developed a method named SOS localization-based interaction screening (SOLIS), in which we designed membrane-anchored and SOS-fused chimeric proteins, whose PPI-dependent association triggers membrane localization of the SOS-fused chimeric protein, activates the Ras/MAPK pathway, and induces cell growth. While SOLIS was able to detect relatively strong PPIs, further sensitivity was required for detecting intracellular endogenous PPIs typically having a micromolar order of dissociation constant (K_d). Here we develop high-sensitive SOLIS (H-SOLIS) that could universally detect PPIs with lower affinities. In order to improve the sensitivity, H-SOLIS introduces a heterodimeric helper interaction, in which addition of a small-molecule helper ligand could accommodate association of the two chimeric proteins and regulate the sensitivity. Four types of domain-peptide interactions having known K_d values are employed to examine the versatility and detection limit of H-SOLIS. Consequently, the heterodimer-inducible helper ligand dramatically enhances detection sensitivity, lowering the detection limit to a ten-micromolar order of K_d. Thus, H-SOLIS could be a platform to detect disease-related domain-peptide interactions for drug discovery screening.

Evolving Experimental Techniques for Structure-Based Drug Design

Structure-based drug design (SBDD) is a prominent method in rational drug development and has traditionally benefitted from the atomic models of protein targets obtained using X-ray crystallography at cryogenic temperatures. In this perspective, we highlight recent advances in the development of structural techniques that are capable of probing dynamic information about protein targets. First, we discuss advances in the field of X-ray crystallography including serial room-temperature crystallography as a method for obtaining high-resolution conformational dynamics of protein-inhibitor complexes. Next, we look at cryogenic electron microscopy (cryoEM), another high-resolution technique that has recently been used to study proteins and protein complexes that are too difficult to crystallize. Finally, we present small-angle X-ray scattering (SAXS) as a potential high-throughput screening tool to identify inhibitors that target protein complexes and protein oligomerization.

Recent Progress Using De Novo Design to Study Protein Structure, Design and Binding Interactions

De novo protein design is a powerful methodology used to study natural functions in an artificial-protein context. Since its inception, it has been used to reproduce a plethora of reactions and uncover biophysical principles that are often difficult to extract from direct studies of natural proteins. Natural proteins are capable of assuming a variety of different structures and subsequently binding ligands at impressively high levels of both specificity and affinity. Here, we will review recent examples of de novo design studies on binding reactions for small molecules, nucleic acids, and the formation of protein-protein interactions. We will then discuss some new structural advances in the field. Finally, we will discuss some advancements in computational modeling and design approaches and provide an overview of some modern algorithmic tools being used to design these proteins.

Allosteric Inhibition of the Epidermal Growth Factor Receptor

We previously reported a family of hydrocarbon-stapled peptides designed to interact with the epidermal growth factor receptor (EGFR) juxtamembrane (JM) segment, blocking its ability to form a coiled coil dimer that is essential for receptor activation. These hydrocarbon-stapled peptides, most notably E1^S, decreased the proliferation of cell lines that express wild-type EGFR (H2030 and A431) as well as those expressing the oncogenic mutants EGFR L858R (H3255) and L858R/T790M (H1975). Although our previous investigations provided evidence that E1^S interacted with EGFR directly, the location and details of these interactions were not established. Here we apply biochemical and cross-linking mass spectrometry tools to better define the interactions between E1^S and EGFR. Taken with previously reported structure-activity relationships, our results support a model in which E1^S interacts simultaneously with both the JM and the C-lobe of the activator kinase, effectively displacing the JM of the receiver kinase. Our results also reveal potential interactions between E1^S and the N-terminal region of the C-terminal tail. We propose a model in which E1^S inhibits EGFR by both mimicking and inhibiting JM coiled coil formation. This model could be used to design novel, allosteric (and perhaps nonpeptidic) EGFR inhibitors.