Small-molecule Modulators Of Protein-protein Interactions Research Articles

Small molecules targeting protein-protein interactions for cancer therapy.

Protein-protein interactions (PPIs) are fundamental to many biological processes that play an important role in the occurrence and development of a variety of diseases. Targeting the interaction between tumour-related proteins with emerging small molecule drugs has become an attractive approach for treatment of human diseases, especially tumours. Encouragingly, selective PPI-based therapeutic agents have been rapidly advancing over the past decade, providing promising perspectives for novel therapies for patients with cancer. In this review we comprehensively clarify the discovery and development of small molecule modulators of PPIs from multiple aspects, focusing on PPIs in disease, drug design and discovery strategies, structure-activity relationships, inherent dilemmas, and future directions.

Research progress in small-molecule modulators of protein-protein interactions

Research progress in small-molecule modulators of protein-protein interactions

Abstract P098: A chemoproteomic platform for identifying small-molecule modulators of protein-protein interactions, discovering new cancer targets, and revealing previously unknown targets for well-known drugs

Abstract BridGene Biosciences has developed a novel chemoproteomic platform IMTACTM (Isobaric Mass-Tagged Affinity Characterization) for discovering small-molecule inhibitors of protein-protein interactions, disclosing new cancer targets, and identifying previously unknown targets for known drugs. The key components of the IMTACTM platform include a unique library of drug-like covalent small molecules containing an alkyne tag, live-cell screening, and quantitative mass spec analysis. The IMTACTM analysis begins with treating live cells with probes from the covalent library, proceeds with enrichment of the probe-modified proteins, and then employs Mass Spec to identify the probe-modified proteins and determine the relative binding affinity. This powerful chemoproteomic platform enables systematic mapping of the direct interactions of small-molecules across the proteome. A prominent application of BridGene’s IMTACTM platform is to identify hits for “hard to drug” targets from live-cell screening. IMTAC TM screening is well suited for identifying drug-like ligands for such hard-to-drug targets, including those with shallow binding pockets or temporary pockets formed under certain cellular settings. Lead optimization can be immediately initiated after confirmation of the ligand’s binding to relevant targets. Using the IMTACTM platform, BridGene has discovered small-molecule ligands for a number of “hard-to-drug” targets as well as oncogenic mutants, including GTPases (e.g. RhoA), transcription factors (e.g. TEAD), splicing factors (e.g. SRSF1), epigenetic modulators (e.g. WDR5), E3 ligases, etc. The potency of the hits ranges from low nanomolar to micromolar. Because of the IMTACTM platform’s proteome-wide profiling capability, BridGene has also, for the first time, revealed new targets for some well-known drugs. Combining IMTAC TM screening with phenotypic screening, BridGene is also discovering new/unknown targets that drive certain disease phenotypic changes. IMTACTM is a novel platform to discover small molecule drugs for hard-to-drug targets. It allows the mapping of targets for small molecules on a proteome-wide scale, which can provide comprehensive selectivity information to facilitate lead optimization and lower off-target toxicity. IMTACTM has the potential to redefine precision medicine, discover new drugs and new targets, and identify new indications of known drugs. Citation Format: Cindy Huang, Vivian Zhang, Ning Deng, Irene Yuan, Linda Pullan, C. Glenn Begley, Ping Cao. A chemoproteomic platform for identifying small-molecule modulators of protein-protein interactions, discovering new cancer targets, and revealing previously unknown targets for well-known drugs [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P098.

Development of Allosteric Modulators of Voltage-Gated Na+ Channels: A Novel Approach for an Old Target.

Given their primacy in governing the action potential (AP) of excitable cells, voltage-gated Na+ (Nav) channels are important pharmacological targets of therapeutics for a diverse array of clinical indications. Despite historically being a traditional drug target, therapeutics targeting Nav channels lack isoform selectivity, giving rise to off-target side effects. To develop isoform-selective modulators of Nav channels with improved target-specificity, the identification and pharmacological targeting of allosteric sites that display structural divergence among Nav channel isoforms represents an attractive approach. Despite the high homology among Nav channel α subunit isoforms (Nav1.1-Nav1.9), there is considerable amino acid sequence divergence among their constituent C-terminal domains (CTD), which enables structurally and functionally specific protein: protein interactions (PPI) with auxiliary proteins. Although pharmacological targeting of such PPI interfaces between the CTDs of Nav channels and auxiliary proteins represents an innovate approach for developing isoform-selective modulators of Nav channels, appreciable modulation of PPIs using small molecules has conventionally been difficult to achieve. After briefly discussing the challenges of modulating PPIs using small molecules, this current frontier review that follows subsequently expounds on approaches for circumventing such difficulties in the context of developing small molecule modulators of PPIs between transmembrane ion channels and their auxiliary proteins. In addition to broadly discussing such approaches, the implementation of such approaches is specifically discussed in the context of developing small molecule modulators between the CTD of Nav channels and auxiliary proteins. Developing allosteric modulators of ion channels by targeting their PPI interfaces with auxiliary proteins represents an innovative and promising strategy in ion channel drug discovery that could expand the "druggable genome" and usher in first-in-class PPI-targeting therapeutics for a multitude of channelopathies.

SMMPPI: a machine learning-based approach for prediction of modulators of protein-protein interactions and its application for identification of novel inhibitors for RBD:hACE2 interactions in SARS-CoV-2.

Small molecule modulators of protein–protein interactions (PPIs) are being pursued as novel anticancer, antiviral and antimicrobial drug candidates. We have utilized a large data set of experimentally validated PPI modulators and developed machine learning classifiers for prediction of new small molecule modulators of PPI. Our analysis reveals that using random forest (RF) classifier, general PPI Modulators independent of PPI family can be predicted with ROC-AUC higher than 0.9, when training and test sets are generated by random split. The performance of the classifier on data sets very different from those used in training has also been estimated by using different state of the art protocols for removing various types of bias in division of data into training and test sets. The family-specific PPIM predictors developed in this work for 11 clinically important PPI families also have prediction accuracies of above 90% in majority of the cases. All these ML-based predictors have been implemented in a freely available software named SMMPPI for prediction of small molecule modulators for clinically relevant PPIs like RBD:hACE2, Bromodomain_Histone, BCL2-Like_BAX/BAK, LEDGF_IN, LFA_ICAM, MDM2-Like_P53, RAS_SOS1, XIAP_Smac, WDR5_MLL1, KEAP1_NRF2 and CD4_gp120. We have identified novel chemical scaffolds as inhibitors for RBD_hACE PPI involved in host cell entry of SARS-CoV-2. Docking studies for some of the compounds reveal that they can inhibit RBD_hACE2 interaction by high affinity binding to interaction hotspots on RBD. Some of these new scaffolds have also been found in SARS-CoV-2 viral growth inhibitors reported recently; however, it is not known if these molecules inhibit the entry phase.

Development of Practical Artificial Intelligence System for Drug Discovery and Its Application to Activity Prediction of Small Molecule Protein-Protein Interaction Modulators

Development of Practical Artificial Intelligence System for Drug Discovery and Its Application to Activity Prediction of Small Molecule Protein-Protein Interaction Modulators

Structure-Based Design of Small-Molecule Protein–Protein Interaction Modulators: The Story so Far

As the pivotal role of protein-protein interactions in cell growth, transcriptional activity, intracellular trafficking, signal transduction and pathological conditions has been assessed, experimental and in silico strategies have been developed to design protein-protein interaction modulators. State-of-the-art structure-based design methods, mainly pharmacophore modeling and docking, which have succeeded in the identification of enzyme inhibitors, receptor agonists and antagonists, and new tools specifically conceived to target protein-protein interfaces (e.g., hot-spot and druggable pocket prediction methods) have been applied in the search for small-molecule protein-protein interaction modulators. Many successful applications of structure-based design approaches that, despite the challenge of targeting protein-protein interfaces with small molecules, have led to the identification of micromolar and submicromolar hits are reviewed here.

Pharmaceutical Implications of Helix Length Control in Helix-Mediated Protein–Protein Interactions

The most abundant protein secondary structure in nature - the α-helix - is frequently found at protein interfaces, making it an important lead structure for the design of small-molecule modulators of protein-protein interactions (PPIs). Nature's ability to precisely control the length of α-helices, especially in the context of helix-mediated PPIs, is key to ensuring the optimal interaction of protein partners. By extension, precise control over the length of α-helix mimetics is necessary to ensure optimal disruption of α-helix-mediated PPIs. This article will highlight the emerging importance of helix length control in the context of helix-mediated PPIs through a discussion of the contemporary chemical approaches to identifying novel helix mimetic inhibitors, including all-hydrocarbon stapling, hydrogen bond surrogates and optimized peptides emerging from in vitro screening methods. A current update on the therapeutic status of the different approaches is provided, as well as indications as to their long-term potential.

Comprehensive Peptidomimetic Libraries Targeting Protein–Protein Interactions

Transient protein-protein interactions (PPIs) are essential components in cellular signaling pathways as well as in important processes such as viral infection, replication, and immune suppression. The unknown or uncharacterized PPIs involved in such interaction networks often represent compelling therapeutic targets for drug discovery. To date, however, the main strategies for discovery of small molecule modulators of PPIs are typically limited to structurally characterized targets. Recent developments in molecular scaffolds that mimic the side chain display of peptide secondary structures have yielded effective designs, but few screening libraries of such mimetics are available to interrogate PPI targets. We initiated a program to prepare a comprehensive small molecule library designed to mimic the three major recognition motifs that mediate PPIs (α-helix, β-turn, and β-strand). Three libraries would be built around templates designed to mimic each such secondary structure and substituted with all triplet combinations of groups representing the 20 natural amino acid side chains. When combined, the three libraries would contain a member capable of mimicking the key interaction and recognition residues of most targetable PPIs. In this Account, we summarize the results of the design, synthesis, and validation of an 8000 member α-helix mimetic library and a 4200 member β-turn mimetic library. We expect that the screening of these libraries will not only provide lead structures against α-helix- or β-turn-mediated protein-protein or peptide-receptor interactions, even if the nature of the interaction is unknown, but also yield key insights into the recognition motif (α-helix or β-turn) and identify the key residues mediating the interaction. Consistent with this expectation, the screening of the libraries against p53/MDM2 and HIV-1 gp41 (α-helix mimetic library) or the opioid receptors (β-turn mimetic library) led to the discovery of library members expected to mimic the known endogenous ligands. These efforts led to the discovery of high-affinity α-helix mimetics (K(i) = 0.7 μM) against HIV-1 gp41 as well as high-affinity and selective β-turn mimetics (K(i) = 80 nM) against the κ-opioid receptor. The results suggest that the use of such comprehensive libraries of peptide secondary structure mimetics, built around effective molecular scaffolds, constitutes a powerful method of interrogating PPIs. These structures provide small molecule modulators of PPI networks for therapeutic target validation, lead compound discovery, and the identification of modulators of biological processes for further study.

Discovery of Modulators of Protein-Protein Interactions: Current Approaches and Limitations

Protein-protein interactions are involved in most of the essential processes that occur in living organisms from cell motility to DNA replication, which makes them interesting targets for drug discovery. However, due to the lack of deep pockets, and the large contact surfaces involved in these interactions, they are considered challenging targets and have been often times dismissed as "undruggable". Nonetheless, significant efforts in pharmaceutical and academic laboratories have been devoted to finding ways to exploit protein-protein interactions as drug targets. This article provides an overview of the principles underlying the main general strategies for discovering small-molecule modulators of protein-protein interactions, namely: high-throughput screening, fragment-based drug discovery, peptide-based drug discovery, protein secondary structure mimetics, and computer-aided drug discovery. In addition, examples of successful discovery of modulators of protein-protein interactions are discussed for each of those strategies.

Identifying small-molecule modulators of protein-protein interactions.

This unit outlines methods for identifying cyclic peptides that inhibit protein-protein interactions. Proteins of interest are cloned into a two-hybrid system engineered to operate in reverse, allowing the disruption of a protein complex to be coupled to cell growth. Cyclic peptide libraries are generated using an intein-based plasmid construct, and the cyclized sequence is randomized using a PCR procedure. By transforming plasmid libraries into host cells containing the two-hybrid fusions, cyclic peptide inhibitors can be identified by growing the cells under the appropriate selective conditions. A detailed procedure for performing the genetic selection and identifying false positives is provided. Methods for building the two-hybrid protein fusions and optimizing media conditions, as well as an additional protocol for constructing cyclic peptide libraries are also provided.

Targeting Protein-Protein Interactions with Small Molecules: Challenges and Perspectives for omputational Binding Epitope Detection and Ligand Finding

A promising way to interfere with biological processes is through the control of protein-protein interactions by means of small molecules that modulate the formation of protein-protein complexes. Although the feasibility of this approach has been demonstrated in principle by recent results, many of the small-molecule modulators known to date have not been found by rational design approaches. In large part this is due to the challenges that one faces in dealing with protein binding epitopes compared to, e.g., enzyme binding pockets. Recent advances in the understanding of the energetics and dynamics of protein binding interfaces and methodological developments in the field of structure-based drug design methods may open up a way to apply rational design approaches also for finding protein-protein interaction modulators. These advances and developments include (I) computational approaches to dissect binding interfaces in terms of energetic contributions of single residues (to identify "hot spot" residues), (II) prediction of potential binding sites from unbound protein structures, (III) recognition of allosteric binding sites as alternatives to directly targeting interfaces, (IV) docking approaches that consider protein flexibility and improved descriptions of the solvent influence on electrostatic interactions, and (V) data-driven docking approaches. Here, we will summarize these developments with a particular emphasis on their applicability to screen for or design small-molecule modulators of protein-protein interactions.

Strategies for Targeting Protein—Protein Interactions with Synthetic Agents

AbstractFor Abstract see ChemInform Abstract in Full Text.

Strategies for Targeting Protein–Protein Interactions With Synthetic Agents

The development of small-molecule modulators of protein-protein interactions is a formidable goal, albeit one that possesses significant potential for the discovery of novel therapeutics. Despite the daunting challenges, a variety of examples exists for the inhibition of two large protein partners with low-molecular-weight ligands. This review discusses the strategies for targeting protein-protein interactions and the state of the art in the rational design of molecules that mimic the structures and functions of their natural targets.