Advances in Small-Molecule Dual Inhibitors Targeting EGFR and HER2 Receptors as Anti-Cancer Agents.

As members of the protein tyrosine kinase family, the Epidermal Growth Factor Receptor (EGFR) and Human Epidermal Growth Factor Receptor 2 (HER2) play essential roles in cellular signal transduction pathways. Overexpression or abnormal activation of EGFR and HER2 can lead to the development of various solid tumors. Therefore, they have been confirmed as biological targets for the development of anticancer drugs. Due to the fact that many cancers are highly susceptible to developing resistance to single-target EGFR inhibitors in clinical practice, dual inhibitors that target both EGFR and HER2 have been developed to increase efficacy, reduce drug resistance and interactions, and improve patient compliance. Currently, a variety of EGFR/HER2 dual inhibitors have been developed, with several drugs already approved for marketing or in clinical trials. In this review, we summarize recent advancements in small-molecule EGFR/HER2 dual inhibitors by focusing on structure-activity relationships and share novel insights into developing anticancer agents.

De Novo Synthesis and Structural Elucidation of CDR-H3 Loop Mimics.

The binding affinity of antibodies to specific antigens stems from a remarkably broad repertoire of hypervariable loops known as complementarity-determining regions (CDRs). While recognizing the pivotal role of the heavy-chain 3 CDRs (CDR-H3s) in maximizing antibody-antigen affinity and specificity, the key structural determinants responsible for their adaptability to diverse loop sequences, lengths, and noncanonical structures are hitherto unknown. To address this question, we achieved a de novo synthesis of bulged CDR-H3 mimics excised from their full antibody context. CD and NMR data revealed that these stable standalone ß-hairpin scaffolds are well-folded and retain many of the native bulge CDR-H3 features in water. In particular, the tryptophan residue, highly conserved across CDR-H3 sequences, was found to extend the kinked base of these ß-bulges through a combination of stabilizing intramolecular hydrogen bond and CH/π interaction. The structural ensemble consistent with our NMR observations exposed the dynamic nature of residues at the base of the loop, suggesting that ß-bulges act as molecular hinges connecting the rigid stem to the more flexible loops of CDR-H3s. We anticipate that this deeper structural understanding of CDR-H3s will lay the foundation to inform the design of antibody drugs broadly and engineer novel CDR-H3 peptide scaffolds as therapeutics.

Passive Membrane Permeability of Sizable Acyclic ß-Hairpin Peptides.

The recent shift toward increasingly larger drug modalities has created a significant demand for novel classes of compounds with high membrane permeability that can inhibit intracellular protein-protein interactions (PPIs). While major advances have been made in the design of cell-permeable helices, stapled ß-sheets, and cyclic peptides, the development of large acyclic ß-hairpins lags far behind. Therefore, we investigated a series of 26 ß-hairpins (MW > 1.6 kDa) belonging to a chemical space far beyond the Lipinski "rule of five" (fbRo5) and showed that, in addition to their innate plasticity, the lipophilicity of these peptides (log D 7.4 ≈ 0 ± 0.7) can be tuned to drastically improve the balance between aqueous solubility and passive membrane permeability.

Recent advances on dual inhibitors targeting HIV reverse transcriptase associated polymerase and ribonuclease H.

Reverse transcriptase (RT) plays an indispensable role in the replication of human immunodeficiency virus (HIV) through its associated polymerase and ribonuclease H (RNase H) activities during the viral RNA genome transformation into proviral DNA. Due to the fact that HIV is a highly mutagenic virus and easily resistant to single-target RT inhibitors, dual inhibitors targeting HIV RT associated polymerase and RNase H have been developed. These dual inhibitors have the advantages of increasing efficacy, reducing drug resistance, drug-drug interactions, and cytotoxicity, as well as improving patient compliance. In this review, we summarize recent advances in polymerase/RNase H dual inhibitors focusing on drug design strategies, and structure-activity relationships and share new insights into developing anti-HIV drugs.

Exploiting the Innate Plasticity of the Programmed Cell Death-1 (PD1) Receptor to Design Pembrolizumab H3 Loop Mimics.

Checkpoint blockade of the immunoreceptor programmed cell death-1 (PD1) with its ligand-1 (PDL1) by monoclonal antibodies such as pembrolizumab provided compelling clinical results in various cancer types, yet the molecular mechanism by which this drug blocks the PD1/PDL1 interface remains unclear. To address this question, we examined the conformational motion of PD1 associated with the binding of pembrolizumab. Our results revealed that the innate plasticity of both C'D and FG loops is crucial to form a deep binding groove (371 Å3 ) across several distant epitopes of PD1. This analysis ultimately provided a rational-design to create pembrolizumab H3 loop mimics [RDYRFDMGFD] into ß-hairpin scaffolds. As a result, a 20-residue long ß-hairpin peptide 1 e was identified as a first-in-class potent PD1-inhibitor (EC50 of 0.29 µM; Ki of 41 nM).

Folding in Place: Design of ß-Strap Motifs to Stabilize the Folding of Hairpins with Long Loops.

Despite their pivotal role in defining antibody affinity and protein function, ß-hairpins harboring long noncanonical loops remain synthetically challenging because of the large entropic penalty associated with their conformational folding. Little is known about the contribution and impact of stabilizing motifs on the folding of ß-hairpins with loops of variable length and plasticity. Here, we report a design of minimalist ß-straps (strap = strand + cap) that offset the entropic cost of long-loop folding. The judicious positioning of noncovalent interactions (hydrophobic cluster and salt-bridge) within the novel 8-mer ß-strap design RW(V/H)W···WVWE stabilizes hairpins with up to 10-residue loops of varying degrees of plasticity (Tm up to 52 °C; 88 ± 1% folded at 18 °C). This "hyper" thermostable ß-strap outperforms the previous gold-standard technology of ß-strand-ß-cap (16-mer) and provides a foundation for producing new classes of long hairpins as a viable and practical alternative to macrocyclic peptides.

A Broad Substrate Scope of Aza-Friedel-Crafts Alkylation for the Synthesis of Quaternary α-Amino Esters.

A versatile synthetic protocol of aza-Friedel-Crafts alkylation has been developed for the synthesis of quaternary α-amino esters. This operationally simple alkylation proceeds under ambient conditions with high efficiency, regioselectivity, and an exceptionally broad scope of arene nucleophiles. A key feature of this alkylation is the role associated with the silver(I) salt counteranions liberated during the reaction. Taking advantage of a phase-transfer counteranion/Brønsted acid pair mechanism, we also report a catalytic enantioselective example of the reaction.

Synthesis of 2,3-Substituted ß-N-Glycosyl Indoles through C-H Activation/Annulation Process under Rh(III)-Catalysis.

An efficient and selective C-H activation method of readily available ß-N-aryl glycosides with various alkynes has been established. Using [Cp*RhCl2]2 as a catalyst and AgSbF6 in DCE, this protocol proved to be general to prepare a variety of 2,3-substituted N-glycosyl indoles in good yields.

Unexpected Oxidative Ring Opening of Electron-Rich 3-Aminobenzofurans into α-Ketoimines Derivatives.

An unexpected ring opening of 3-aminobenzofurans promoted by NaO tBu in hot toluene, leading to a variety of α-ketoimines, is described. In the presence of 3-iodobenzofurans, NaO tBu mediates the 3-aminobenzofurans ring opening via a possible radical pathway without the help of any external radical sources.

One-Pot Synthesis of 2-Styrylindoles from Ortho-Substituted Chloroenynes.

A facile one-pot synthesis of 2-styrylindoles, through Suzuki arylation of ortho-substituted chloroenynes followed by N-cyclization and N-demethylation, has been developed. A variety of 2-styrylindoles were obtained in good to excellent yields and were evaluated for their anticancer properties.