Discovery and Optimization of Dibenzodiazepinones as Allosteric Mutant-Selective EGFR Inhibitors

Discovery of new cyclopropane sulfonamide derivatives as EGFR inhibitors to overcome C797S-mediated resistance and EGFR double mutation

The C797S mutation of EGFR leads to Osimertinib resistance by blocking the covalent binding of Cys797. To develop new agents that can overcome EGFR mutation resistance, thirty seven new cyclopropane sulfonamide derivatives were synthesized and evaluated as EGFRL858R/T790M/C797S or EGFRDel19/T790M/C797S inhibitors by structure-based screening. Most of the synthesized compounds exhibit good to excellent anti proliferation activity against to BaF3-EGFR L858R/T790M/C797S and BaF3-C797S/Del19/T790M cancer cell lines. Representative compounds 8l showed inhibitory activity against the two cancer cell lines with the IC50 values of 0.0012 and 0.0013 μM, respectively. Another compound 8h, exhibited slightly lower activity (0.0042 and 0.0034 μM of the IC50 values) to both of the two tri-mutation cell lines, but excellent activities against H1975 and PC9 cells with IC50 values of 13 and 19 nM, respectively. Considering the acquired drug resistance of tumors is a gradual process, we chose 8h for further in vivo and mechanism study. 8h was demonstrated significantly inhibited tumor growth with 72.1 % of the TGI in the BaF3/EGFR-TM xenograft tumor model and 83.5 % in the H1975-DM xenograft tumor model. Compound 8h was confirmed to be safe with no significant side effects as showed by the results of in vitro assay of human normal cells and the sections of animals major organs. Mechanism studies showed that in addition to inhibiting EGFR mutations, 8h can also target the tumor microenvironment and induce tumor cell apoptosis. All these results indicate that 8h deserves further investigation as an EGFR inhibitor to overcome C797S-mediated resistance.

Design, synthesis, and anticancer assessment of structural analogues of (E)-1-((3,4,5-trimethoxybenzylidene)amino)-4-(3,4,5-trimethoxyphenyl)imidazo[1,2-a]quinoxaline-2-carbonitrile (6b), an imidazo[1,2-a]quinoxaline-based non-covalent EGFR inhibitor

In our quest to find improved anticancer therapeutics, we expedite the lead optimization of (E)-1-((3,4,5-trimethoxybenzylidene)amino)-4-(3,4,5-trimethoxyphenyl)imidazo[1,2-a]quinoxaline-2-carbonitrile (6b), an EGFR inhibitor previously discovered in our laboratory through an in-house screening program. The lead optimization was rationally initiated considering the catalytic site of EGFR. We synthesized twenty-nine new analogues of 6b and assessed their anticancer activities. SAR studies highlighted the role of important groups in controlling anticancer activities. Among all, 5a and 5l were found to exhibit improved EGFR inhibition with anticancer asset potential. In silico studies corroborated with in vitro EGFR inhibitory results. The deeper analysis of 5a and 5l revealed that these synthetics could alter the MMP (ΔΨ m) and significantly reduce the ROS levels in lung cancer cells. This is a vital prerequisite for better plausible EGFR inhibitors devoid of cardiotoxicity. qPCR analysis further revealed that the investigational compounds 5a and 5l were able to downregulate the expression of key oncogenes, viz., KRAS, MAP2K, and EGFR. The downregulation of these genes suggests that the investigational compounds could interact and inhibit key players in the signalling cascade along with the EGFR, which may lead to the inhibition of the growth and prognosis of cancer cells via a holistic approach.

Structural Analysis of the Macrocyclic Inhibitor BI-4020 Binding to EGFR Kinase

A novel macrocyclic inhibitor of mutant EGFR (BI-4020) has shown promise in pre-clinical studies of T790M and C797S drug-resistant non-small cell lung cancer. To better understand the molecular basis for BI-4020 selectivity and potency, we have carried out biochemical activity assays and structural analysis with X-ray crystallography. Biochemical potencies agree with previous studies indicating that BI-4020 is uniquely potent against drug-resistant L858R/T790M and L858R/T790M/C797S variants. X-ray structures with wild-type (2.4 Å) and T790M/V948R (3.1 Å) EGFR kinase domains show that BI-4020 is likely rendered selective due to interactions with the kinase domain hinge region as well as T790M, akin to Osimertinib. Additionally, BI-4020 is also rendered more potent due to its constrained macrocycle geometry as well as additional H-bonds to conserved K745 and T845 residues in both active and inactive conformations. These findings taken together show how this novel macrocyclic inhibitor is both highly potent and selective for mutant EGFR in a reversible mechanism and motivate structure-inspired approaches to developing targeted therapies in medicinal oncology.

Gaining Insights into Key Structural Hotspots within the Allosteric Binding Pockets of Protein Kinases

Protein kinases are essential regulators of cell function and represent one of the largest and most diverse protein families. They are particularly influential in signal transduction and coordinating complex processes like the cell cycle. Out of the 518 human protein kinases identified, 478 are part of a single superfamily sharing catalytic domains that are related in sequence. The dysregulation of protein kinases due to certain mutations has been associated with various diseases, including cancer. Although most of the protein kinase inhibitors identified as type I or type II primarily target the ATP-binding pockets of kinases, the structural and sequential resemblances among these pockets pose a significant challenge for selective inhibition. Therefore, targeting allosteric pockets that are beside highly conserved ATP pockets has emerged as a promising strategy to prevail current limitations, such as poor selectivity and drug resistance. In this article, we compared the binding pockets of various protein kinases for which allosteric (type III) inhibitors have already been developed. Additionally, understanding the structure and shape of existing ligands could aid in identifying key interaction sites within the allosteric pockets of kinases. This comprehensive review aims to facilitate the design of more effective and selective allosteric inhibitors.

Chemical Scaffolds for the Clinical Development of Mutant-Selective and Reversible Fourth-Generation EGFR-TKIs in NSCLC

In nonsmall cell lung cancer (NSCLC), as well as in other tumors, the targeted therapy is mainly represented by tyrosine kinase inhibitors (TKIs), small molecules able to target oncogenic driver alterations affecting the gene encoding the epidermal growth factor receptor (EGFR). Up to now, several different TKIs have been developed. However, cancer cells showed an incredible adaptive tumor response to the inhibition of the sequentially mutated EGFR (EGFRM+), triggering the need to explore novel pharmacochemical strategies. This Review summarizes the recent efforts in the development of new reversible next-generation EGFR TKIs to fight the resistance against T790M and C797S mutations. Specifically, after giving an overview of the role of the EGFR's signaling pathways in cancer progression, we are going to discuss the most relevant approved drugs and drug candidates in terms of chemical structure, binding modalities, and their potency and selectivity against the mutated EGFR over the wild-type form. This could provide important guidelines and rationale for the discovery and iterative development of new drugs.

Linking ATP and allosteric sites to achieve superadditive binding with bivalent EGFR kinase inhibitors

Bivalent molecules consisting of groups connected through bridging linkers often exhibit strong target binding and unique biological effects. However, developing bivalent inhibitors with the desired activity is challenging due to the dual motif architecture of these molecules and the variability that can be introduced through differing linker structures and geometries. We report a set of alternatively linked bivalent EGFR inhibitors that simultaneously occupy the ATP substrate and allosteric pockets. Crystal structures show that initial and redesigned linkers bridging a trisubstituted imidazole ATP-site inhibitor and dibenzodiazepinone allosteric-site inhibitor proved successful in spanning these sites. The re-engineered linker yielded a compound that exhibited significantly higher potency (~60 pM) against the drug-resistant EGFR L858R/T790M and L858R/T790M/C797S, which was superadditive as compared with the parent molecules. The enhanced potency is attributed to factors stemming from the linker connection to the allosteric-site group and informs strategies to engineer linkers in bivalent agent design.

Identification of novel aminopyrimidine derivatives for the treatment of mutant NSCLC

Starting from the binding mode of allosteric EGFR inhibitor JBJ-04-125-02 and the key pharmacophore of the third-generation EGFR inhibitors, we designed and synthesized a novel series of EGFR inhibitors, represented by (R)-N-(4-((2-aminopyrimidin-4-yl)amino)phenyl)-2-(5-(4-(4-methylpiperazin-1-yl)phenyl)-1-oxoisoindolin-2-yl)-2-phenylacetamide (6q). Docking study demonstrated that top compound 6q spanned orthosteric and allosteric sites of EGFR, and formed three key H-bonds with the residues Asp855, Lys745, and Met793 located in two sites. Biological evaluation indicated that compound 6q showed potential inhibitory activity against Ba/F3-EGFRL858R/T790M/C797S and Ba/F3-EGFRDel19/T790M/C797S cells, with IC50 values of 0.42 μM and 0.41 μM, respectively. Furthermore, compound 6q showed excellent activity against mutant NSCLC cell line NCI-H1975-EGFRL858R/T790M/C797S cells, with IC50 value of 0.82 μM which was superior to that of osimertinib (IC50 = 2.94 μM), JBJ-04-125-02 (IC50 = 3.66 μM), and coadministration of JBJ-04-125-02 and osimertinib (IC50 = 1.25 μM). Cell cycle arrest and cell apoptosis assay indicated that compound 6q could promote apoptosis of NCI-H1975-EGFRL858R/T790M/C797S cells at the concentration of 0.8 μM and no obvious cell cycle arrest was found.

Metal-catalyzed coupling/carbonylative cyclizations for accessing dibenzodiazepinones: an expedient route to clozapine and other drugs

A sequential strategy to access 10,11-dihydro-5H-dibenzo[b,e][1,4]diazepinones (DBDAPs) is disclosed in this article through a palladium and copper-catalyzed amination (Buchwald-Hartwig (B-H) or Chan-Lam (C-L)) followed by a palladium-catalyzed intramolecular aminocarbonylation with Mo(CO)6 as CO surrogate (to avoid toxic CO handling) of readily available o-phenylenediamines and either 1,2-dibromobenzene or 2-bromophenylboronic acid. The 10,11-dihydro-5H-dibenzo[b,e][1,4]diazepinone could be synthezised in good yield using a sequential catalytic procedure, using both C-L and B-H approaches. Gratifingly, the use of the C-L reaction was more impressive, and afforded the dibenzodiazepinones in good yields (up to 45%; 2 steps) and much milder conditions using copper as the catalyst. The synthetic utility of this novel strategy was showcased by demonstrating a formal synthesis for the antipsychotic drug clozapine and to an anticancer triazole-DBDAP hybrid.

Machine Learning-Based Virtual Screening and Identification of the Fourth-Generation EGFR Inhibitors

Epidermal growth factor receptor (EGFR) plays a pivotal regulatory role in treating patients with advanced nonsmall cell lung cancer (NSCLC). Following the emergence of the EGFR tertiary CIS C797S mutation, all types of inhibitors lose their inhibitory activity, necessitating the urgent development of new inhibitors. Computer systems employ machine learning methods to process substantial volumes of data and construct models that enable more accurate predictions of the outcomes of new inputs. The purpose of this article is to uncover innovative fourth-generation epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) with the aid of machine learning techniques. The paper's data set was high-dimensional and sparse, encompassing both structured and unstructured descriptors. To address this considerable challenge, we introduced a fusion framework to select critical molecule descriptors by integrating the full quadratic effect model and the Lasso model. Based on structural descriptors obtained from the full quadratic effect model, we conceived and synthesized a variety of small-molecule inhibitors. These inhibitors demonstrated potent inhibitory effects on the two mutated kinases L858R/T790M/C797S and Del19/T790M/C797S. Moreover, we applied our model to virtual screening, successfully identifying four hit compounds. We have evaluated these hit ADME characteristics and look forward to conducting activity evaluations on them in the future to discover a new generation of EGFR-TKI.

Pitfalls and Considerations in Determining the Potency and Mutant Selectivity of Covalent Epidermal Growth Factor Receptor Inhibitors

Enzyme inhibitors that form covalent bonds with their targets are being increasingly pursued in drug development. Assessing their biochemical activity relies on time-dependent assays, which are distinct and more complex compared with methods commonly employed for reversible-binding inhibitors. To provide general guidance to the covalent inhibitor development community, we explored methods and reported kinetic values and experimental factors in determining the biochemical activity of various covalent epidermal growth factor receptor (EGFR) inhibitors. We showcase how liquid handling and assay reagents impact kinetic parameters and potency interpretations, which are critical for structure-kinetic relationships and covalent drug design. Additionally, we include benchmark kinetic values with reference inhibitors, which are imperative, as covalent EGFR inhibitor kinetic values are infrequently consistent in the literature. This overview seeks to inform best practices for developing new covalent inhibitors and highlight appropriate steps to address gaps in knowledge presently limiting assay reliability and reproducibility.

A Constitutive EGFR Kinase Dimer to Study Inhibitor Pharmacology

Lung cancer is commonly caused by activating mutations in the epidermal growth factor receptor (EGFR). Allosteric kinase inhibitors are unaffected by common ATP-site resistance mutations and represent a promising therapeutic strategy for targeting drug-resistant EGFR variants. However, allosteric inhibitors are antagonized by kinase dimerization, and understanding this phenomenon has been limited to cellular experiments. To facilitate the study of allosteric inhibitor pharmacology, we designed and purified a constitutive EGFR kinase dimer harboring the clinically relevant L858R/T790M mutations. Kinetic characterization revealed that the EGFR kinase dimer is more active than monomeric EGFR(L858R/T790M) kinase and has the same Km,ATP Biochemical profiling of a large panel of ATP-competitive and allosteric EGFR inhibitors showed that allosteric inhibitor potency decreased by >500-fold in the kinase dimer compared with monomer, yielding IC50 values that correlate well with Ba/F3 cellular potencies. Thus, this readily purifiable constitutive asymmetric EGFR kinase dimer represents an attractive tool for biochemical evaluation of EGFR inhibitor pharmacology, in particular for allosteric inhibitors. SIGNIFICANCE STATEMENT: Drugs targeting epidermal growth factor receptor (EGFR) kinase are commonly used to treat lung cancers but are affected by receptor dimerization. Here, we describe a locked kinase dimer that can be used to study EGFR inhibitor pharmacology.

4D-QSAR and MIA-QSAR Studies of Aminobenzimidazole Derivatives as Fourth-generation EGFR Inhibitors

BACKGROUND

The epidermal growth factor receptor (EGFR) protein has been intensively studied as a therapeutic target for non-small cell lung cancer (NSCLC). The aminobenzimidazole derivatives as the fourth-generation EGFR inhibitors have achieved promising results and overcame EGFR mutations at C797S, del19 and T790M in NSCLC.

OBJECTIVE

In order to understand the quantitative structure-activity relationship (QSAR) of aminobenzimidazole derivatives as EGFRdel19 T790M C797S inhibitors, the four-dimensional QSAR (4D-QSAR) and multivariate image analysis (MIA-QSAR) have been performed on the data of 45 known aminobenzimidazole derivatives.

METHODS

The 4D-QSAR descriptors were acquired by calculating the association energies between probes and aligned conformational ensemble profiles (CEP), and the regression models were established by partial least squares (PLS). In order to further understand and verify the 4D-QSAR model, MIA-QSAR was constructed by using chemical structure pictures to generate descriptors and PLS regression. Furthermore, the molecular docking and averaged noncovalent interactions (aNCI) analysis were also performed to further understand the interactions between ligands and the EGFR targets, which was in good agreement with the 4D-QSAR model.

RESULTS

The established 4D-QSAR and MIA-QSAR models have strong stability and good external prediction ability.

CONCLUSION

These results will provide theoretical guidance for the research and development of aminobenzimidazole derivatives as new EGFRdel19 T790M C797S inhibitors.

Uncovering the Structural and Binding Insights of Dual Inhibitors Simultaneously Targeting Two Distinct Sites on EGFR Kinase

Epidermal growth factor receptor (EGFR) is the first growth factor receptor identified in normal cells that is related to the receptor tyrosine kinase, which causes regular cell division. A point mutation in EGFR intracellular kinase domain forces the abnormal cell divisions throughout time, leading to non-small cell lung cancer (NSCLC) transformation. Thus, competitive inhibitors that bind to the ATP binding pocket have been developed as a targeted therapy for NSCLC. The third-generation kinase inhibitor Osimertinib is currently playing a very vital role in the treatment of NSCLC. However, it is not effective toward the C797S kinase domain mutation. For this reason, fourth-generation kinase noncompetitive inhibitors are introduced which work through binding to an allosteric pocket near the ATP binding region and act as a better binding agent for this mutated kinase domain. However, the problem is that these single fourth-generation kinase inhibitors may not be as effective as a single agent. The aim of this work was to apply combinations of these two inhibitors together in different binding regions of EGFR without overlapping the resistance mechanism to obtain the key direct and indirect interactions occurring between them. Moreover, the free energy of dissociation of an inhibitor from its binding sites in the presence of a second inhibitor immobilized in another binding site was also the focus of the study. To realize this aim, we performed conventional molecular dynamics simulations and principal component analysis and dynamic cross-correlation matrices along with umbrella sampling. Our results demonstrated that binding of dual inhibitors triggered conformational changes of the protein more toward the inactive state. Furthermore, allosteric inhibitors bound more strongly to protein kinase EGFR than the orthosteric inhibitors in the presence of dual inhibitors. Finally, the binding mechanism and important hydrogen-bonding residues during unbinding of the inhibitors were fully elucidated. This study provides insight into the binding of the receptor-orthosteric inhibitor-allosteric inhibitor, which can be helpful for further design of novel inhibitors that have a better inhibitory action.

20 years since the approval of first EGFR-TKI, gefitinib: Insight and foresight

Epidermal growth factor receptor (EGFR) actively involves in modulation of various cancer progression related mechanisms including angiogenesis, differentiation and migration. Therefore, targeting EGFR has surfaced as a prominent approach for the treatment of several types of cancers, including non-small cell lung cancer (NSCLC), pancreatic cancer, glioblastoma. Various first, second and third generation of EGFR tyrosine kinase inhibitors (EGFR-TKIs) have demonstrated effectiveness as an anti-cancer therapeutics. However, rapid development of drug resistance and mutations still remains a major challenge for the EGFR-TKIs therapy. Overcoming from intrinsic and acquired resistance caused by EGFR mutations warrants the further exploration of alternative strategies and discovery of novel inhibitors. In this review, we delve into the breakthrough discoveries have been made in previous 20 years, and discuss the currently ongoing efforts aimed to circumvent the chemo-resistance. We also highlight the new challenges, limitations and future directions for the development of improved therapeutic approaches such as fourth-generation EGFR-TKIs, peptides, nanobodies, PROTACs etc.

Targeting Epidermal Growth Factor Receptor for Cancer Treatment: Abolishing Both Kinase-Dependent and Kinase-Independent Functions of the Receptor

Epidermal growth factor receptor (EGFR), a receptor tyrosine kinase, is activated by ligand binding, overexpression, or mutation. It is well known for its tyrosine kinase-dependent oncogenic activities in a variety of human cancers. A large number of EGFR inhibitors have been developed for cancer treatment, including monoclonal antibodies, tyrosine kinase inhibitors, and a vaccine. The EGFR inhibitors are aimed at inhibiting the activation or the activity of EGFR tyrosine kinase. However, these agents have shown efficacy in only a few types of cancers. Drug resistance, both intrinsic and acquired, is common even in cancers where the inhibitors have shown efficacy. The drug resistance mechanism is complex and not fully known. The key vulnerability of cancer cells that are resistant to EGFR inhibitors has not been identified. Nevertheless, it has been increasingly recognized in recent years that EGFR also possesses kinase-independent oncogenic functions and that these noncanonical functions may play a crucial role in cancer resistance to EGFR inhibitors. In this review, both kinase-dependent and -independent activities of EGFR are discussed. Also discussed are the mechanisms of actions and therapeutic activities of clinically used EGFR inhibitors and sustained EGFR overexpression and EGFR interaction with other receptor tyrosine kinases to counter the EGFR inhibitors. Moreover, this review discusses emerging experimental therapeutics that have shown potential for overcoming the limitation of the current EGFR inhibitors in preclinical studies. The findings underscore the importance and feasibility of targeting both kinase-dependent and -independent functions of EGFR to enhance therapeutic efficacy and minimize drug resistance. SIGNIFICANCE STATEMENT: EGFR is a major oncogenic driver and therapeutic target, but cancer resistance to current EGFR inhibitors remains a significant unmet clinical problem. This article reviews the cancer biology of EGFR as well as the mechanisms of actions and the therapeutic efficacies of current and emerging EGFR inhibitors. The findings could potentially lead to development of more effective treatments for EGFR-positive cancers.

Tackling Osimertinib Resistance in EGFR-Mutant Non-Small Cell Lung Cancer

The current landscape of targeted therapies directed against oncogenic driver alterations in non-small cell lung cancer (NSCLC) is expanding. Patients with EGFR-mutant NSCLC can derive significant benefit from EGFR tyrosine kinase inhibitor (TKI) therapy, including the third-generation EGFR TKI osimertinib. However, invariably, all patients will experience disease progression with this therapy mainly due to the adaptation of cancer cells through primary or secondary molecular mechanisms of resistance. The comprehension and access to tissue and cell-free DNA next-generation sequencing have fueled the development of innovative therapeutic strategies to prevent and overcome resistance to osimertinib in the clinical setting. Herein, we review the biological and clinical implications of molecular mechanisms of osimertinib resistance and the ongoing development of therapeutic strategies to overcome or prevent resistance.

Linking ATP and allosteric sites to achieve superadditive binding with bivalent EGFR kinase inhibitors

Bivalent molecules consisting of groups connected through bridging linkers often exhibit strong target binding and unique biological effects. However, developing bivalent inhibitors with the desired activity is challenging due to the dual motif architecture of these molecules and the variability that can be introduced through differing linker structures and geometries. We report a set of alternatively linked bivalent EGFR inhibitors that simultaneously occupy the ATP substrate and allosteric pockets. Crystal structures show that initial and redesigned linkers bridging a trisubstituted imidazole ATP-site inhibitor and dibenzodiazepinone allosteric-site inhibitor proved successful in spanning these sites. The reengineered linker yielded a compound that exhibited significantly higher potency (~60 pM) against the drug-resistant EGFR L858R/T790M and L858R/T790M/C797S, which was superadditive as compared with the parent molecules. The enhanced potency is attributed to factors stemming from the linker connection to the allosteric-site group and informs strategies to engineer linkers in bivalent agent design.

Structural elements that enable specificity for mutant EGFR kinase domains with next-generation small-molecule inhibitors

Specificity for a desired enzyme target is an essential property of small-molecule inhibitors. Molecules targeting oncogenic driver mutations in the epidermal growth factor receptor (EGFR) kinase domain have had a considerable clinical impact due to their selective binding to cancer-causing mutants compared to wild type. Despite the availability of clinically approved drugs for cancers driven by EGFR mutants, persistent challenges in drug resistance in the past decades have led to newer generations of drugs with divergent chemical structures. The current clinical challenges are mainly due to acquired resistance to third-generation inhibitors, including by the acquisition of the C797S mutation. Several diverse fourth-generation candidates and tool compounds that inhibit the C797S mutant have emerged, and their structural characterization has revealed molecular factors that allow for EGFR mutant selective binding. Here, we have reviewed all known structurally-characterized EGFR TKIs targeting clinically-relevant mutations to identify specific features that enable C797S inhibition. Newer generation EGFR inhibitors exhibit consistent and previously underutilized hydrogen bonding interactions with the conserved K745 and D855 residue side chains. We also consider binding modes and hydrogen bonding interactions of inhibitors targeting the classical ATP and the more unique allosteric sites.

Recent Advances in Boosting EGFR Tyrosine Kinase Inhibitors-Based Cancer Therapy

Epidermal growth factor receptor (EGFR) plays a key role in signal transduction pathways associated with cell proliferation, growth, and survival. Its overexpression and aberrant activation in malignancy correlate with poor prognosis and short survival. Targeting inhibition of EGFR by small-molecular tyrosine kinase inhibitors (TKIs) is emerging as an important treatment model besides of chemotherapy, greatly reshaping the landscape of cancer therapy. However, they are still challenged by the off-targeted toxicity, relatively limited cancer types, and drug resistance after long-term therapy. In this review, we summarize the recent progress of oral, pulmonary, and injectable drug delivery systems for enhanced and targeting TKI delivery to tumors and reduced side effects. Importantly, EGFR-TKI-based combination therapies not only greatly broaden the applicable cancer types of EGFR-TKI but also significantly improve the anticancer effect. The mechanisms of TKI resistance are summarized, and current strategies to overcome TKI resistance as well as the application of TKI in reversing chemotherapy resistance are discussed. Finally, we provide a perspective on the future research of EGFR-TKI-based cancer therapy.

Structural features of the protein kinase domain and targeted binding by small-molecule inhibitors

Protein kinases are key components in cellular signaling pathways as they carry out the phosphorylation of proteins, primarily on Ser, Thr, and Tyr residues. The catalytic activity of protein kinases is regulated, and they can be thought of as molecular switches that are controlled through protein-protein interactions and post-translational modifications. Protein kinases exhibit diverse structural mechanisms of regulation and have been fascinating subjects for structural biologists from the first crystal structure of a protein kinase over 30 years ago, to recent insights into kinase assemblies enabled by the breakthroughs in cryo-EM. Protein kinases are high-priority targets for drug discovery in oncology and other disease settings, and kinase inhibitors have transformed the outcomes of specific groups of patients. Most kinase inhibitors are ATP competitive, deriving potency by occupying the deep hydrophobic pocket at the heart of the kinase domain. Selectivity of inhibitors depends on exploiting differences between the amino acids that line the ATP site and exploring the surrounding pockets that are present in inactive states of the kinase. More recently, allosteric pockets outside the ATP site are being targeted to achieve high selectivity and to overcome resistance to current therapeutics. Here, we review the key regulatory features of the protein kinase family, describe the different types of kinase inhibitors, and highlight examples where the understanding of kinase regulatory mechanisms has gone hand in hand with the development of inhibitors.

Emerging strategies to overcome resistance to third-generation EGFR inhibitors

Epidermal growth factor receptor (EGFR), the receptor for members of the epidermal growth factor family, regulates cell proliferation and signal transduction; moreover, EGFR is related to the inhibition of tumor cell proliferation, angiogenesis, invasion, metastasis, and apoptosis. Therefore, EGFR has become an important target for the treatment of cancer, including non-small cell lung cancer, head and neck cancer, breast cancer, glioma, cervical cancer, and bladder cancer. First- to third-generation EGFR inhibitors have shown considerable efficacy and have significantly improved disease prognosis. However, most patients develop drug resistance after treatment. The challenge of overcoming intrinsic and acquired resistance in primary and recurrent cancer mediated by EGFR mutations is thus driving the search for alternative strategies in the design of new therapeutic agents. In view of resistance to third-generation inhibitors, understanding the intricate mechanisms of resistance will offer insight for the development of more advanced targeted therapies. In this review, we discuss the molecular mechanisms of resistance to third-generation EGFR inhibitors and review recent strategies for overcoming resistance, new challenges, and future development directions.

Targeting EGFR in melanoma - The sea of possibilities to overcome drug resistance

Melanoma is considered one of the most aggressive skin cancers. It spreads and metastasizes quickly and is intrinsically resistant to most conventional chemotherapeutics, thereby presenting a challenge to researchers and clinicians searching for effective therapeutic strategies to treat patients with melanoma. The use of inhibitors of mutated serine/threonine-protein kinase B-RAF (BRAF), e.g., vemurafenib and dabrafenib, has revolutionized melanoma chemotherapy. Unfortunately, the response to these drugs lasts a limited time due to the development of acquired resistance. One of the proteins responsible for this process is epidermal growth factor receptor (EGFR). In this review, we summarize the role of EGFR signaling in the multidrug resistance of melanomas and discuss possible applications of EGFR inhibitors to overcome the development of drug resistance in melanoma cells during therapy.

Molecular basis for cooperative binding and synergy of ATP-site and allosteric EGFR inhibitors

Lung cancer is frequently caused by activating mutations in the epidermal growth factor receptor (EGFR). Allosteric EGFR inhibitors offer promise as the next generation of therapeutics, as they are unaffected by common ATP-site resistance mutations and synergize with the drug osimertinib. Here, we examine combinations of ATP-competitive and allosteric inhibitors to better understand the molecular basis for synergy. We identify a subset of irreversible EGFR inhibitors that display positive binding cooperativity and synergy with the allosteric inhibitor JBJ-04-125-02 in several EGFR variants. Structural analysis of these complexes reveals conformational changes occur mainly in the phosphate-binding loop (P-loop). Mutation of F723 in the P-loop reduces cooperative binding and synergy, supporting a mechanism in which F723-mediated contacts between the P-loop and the allosteric inhibitor are critical for synergy. These structural and mechanistic insights will aid in the identification and development of additional inhibitor combinations with potential clinical value.

Acquired drug resistance is common during chemotherapy. Here, the authors describe the structural basis and molecular mechanism by which allosteric and clinically approved, ATP-competitive inhibitors of EGFR synergize to overcome resistance in lung cancer.

Conformational Constrained 4-(1-Sulfonyl-3-indol)yl-2-phenylaminopyrimidine Derivatives as New Fourth-Generation Epidermal Growth Factor Receptor Inhibitors Targeting T790M/C797S Mutations

Tertiary C797S mutation of epidermal growth factor receptor (EGFR)-mediated resistance in non-small-cell-lung-cancer (NSCLC) patients is still an unmet clinical need. Several classes of adenosine 5'-triphosphate-competitive or allosteric EGFR^T790M/C797S inhibitors and degraders have been developed, but none of them have received approval from the regulatory agencies. Herein, we report the structure-based design of conformational constrained 4-(1-ethylsufonyl-3-indolyl)-2-phenylaminopyrimidines as new EGFR^T790M/C797S inhibitors by using a macrocyclization strategy. Representative compound 18j potently inhibited EGFR^{19del/T790M/C797S} and EGFR^{L858R/T790M/C797S} mutants with IC₅₀ values of 15.8 and 23.6 nM and suppressed Ba/F3-EGFR^{L858R/T790M/C797S} and Ba/F3-EGFR^{19del/T790M/C797S} cells with IC₅₀ values of 0.036 and 0.052 μM, respectively, which is 10-20-fold more potent than brigatinib. 18j also potently inhibited the EGFR^{19del/T790M/C797S}-mutated PC-9-OR NSCLC cell proliferation with an IC₅₀ value of 0.644 μM but was less potent for parental Ba/F3 and A431 cells. This study provides a new lead compound for drug discovery to combat EGFR^C797S-mediated resistance in NSCLC patients.

Silver-promoted dearomative [3+4] cycloaddition of anthranils with α-isocyanoacetates: access to benzodiazepines

The first example of silver-promoted [3+4] cycloaddition of α-isocyanoacetates with anthranils as aromatic Michael accepters, offering access to benzo[d][1,3]diazepinones, has been developed. Mechanistic studies revealed that an "oxygen migration" rearrangement process was involved in this dearomative cycloaddition reaction. Additionally, benzo[d][1,3]diazepinones were obtained efficiently as well under catalytic conditions. Broad functional groups were well tolerated under mild reaction conditions.

An allosteric inhibitor against the therapy-resistant mutant forms of EGFR in non-small cell lung cancer

Epidermal growth factor receptor (EGFR) therapy using small-molecule tyrosine kinase inhibitors (TKIs) is initially efficacious in patients with EGFR-mutant lung cancer, although drug resistance eventually develops. Allosteric EGFR inhibitors, which bind to a different EGFR site than existing ATP-competitive EGFR TKIs, have been developed as a strategy to overcome therapy-resistant EGFR mutations. Here we identify and characterize JBJ-09-063, a mutant-selective allosteric EGFR inhibitor that is effective across EGFR TKI-sensitive and resistant models, including those with EGFR T790M and C797S mutations. We further uncover that EGFR homo- or heterodimerization with other ERBB family members, as well as the EGFR L747S mutation, confers resistance to JBJ-09-063, but not to ATP-competitive EGFR TKIs. Overall, our studies highlight the potential clinical utility of JBJ-09-063 as a single agent or in combination with EGFR TKIs to define more effective strategies to treat EGFR-mutant lung cancer.

Design of a "Two-in-One" Mutant-Selective Epidermal Growth Factor Receptor Inhibitor That Spans the Orthosteric and Allosteric Sites

Inhibitors targeting the epidermal growth factor receptor (EGFR) are an effective therapy for patients with non-small cell lung cancer harboring drug-sensitive activating mutations in the EGFR kinase domain. Drug resistance due to treatment-acquired mutations has motivated the development of successive generations of inhibitors that bind in the ATP site. The third-generation agent osimertinib is now a first-line treatment for this disease. Recently, allosteric inhibitors have been developed to overcome drug-resistant mutations that confer a resistance to osimertinib. Here, we present the structure-guided design and synthesis of a mutant-selective lead compound, which consists of a pyridinyl imidazole-fused benzylisoindolinedione scaffold that simultaneously occupies the orthosteric and allosteric sites. The compound potently inhibits enzymatic activity in L858R/T790M/C797S mutant EGFR (4.9 nM), with a significantly lower activity for wild-type EGFR (47 nM). Additionally, this compound achieves modest cetuximab-independent and mutant-selective cellular efficacies on the L858R (1.2 μM) and L858R/T790M (4.4 μM) variants.

Chronicles of EGFR Tyrosine Kinase Inhibitors: Targeting EGFR C797S Containing Triple Mutations

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase widely expressed in many cancers such as non-small cell lung cancer (NSCLC), pancreatic cancer, breast cancer, and head and neck cancer. Mutations such as L858R in exon 21, exon 19 truncation (Del19), exon 20 insertions, and others are responsible for aberrant activation of EGFR in NSCLC. First-generation EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib have clinical benefits for EGFR-sensitive (L858R and Del19) NSCLC patients. However, after 10-12 months of treatment with these inhibitors, a secondary T790M mutation at the gatekeeper position in the kinase domain of EGFR was identified, which limited the clinical benefits. Second-generation EGFR irreversible inhibitors (afatinib and dacomitinib) were developed to overcome this T790M mutation. However, their lack of selectivity toward wild-type EGFR compromised their clinical benefits due to serious adverse events. Recently developed third-generation irreversible EGFR TKIs (osimertinib and lazertinib) are selective toward driving mutations and the T790M mutation, while sparing wildtype EGFR activity. The latest studies have concluded that their efficacy was also compromised by additional acquired mutations, including C797S, the key residue cysteine that forms covalent bonds with irreversible inhibitors. Because second- and thirdgeneration EGFR TKIs are irreversible inhibitors, they are not effective against C797S containing EGFR triple mutations (Del19/T790M/C797S and L858R/T790M/C797S). Therefore, there is an urgent unmet medical need to develop next-generation EGFR TKIs that selectively inhibit EGFR triple mutations via a non-irreversible mechanism.

Approach in Improving Potency and Selectivity of Kinase Inhibitors: Allosteric Kinase Inhibitors

Allostery is an efficient and particular regulatory mechanism to regulate protein functions. Different from conserved orthosteric sites, allosteric sites have a distinctive functional mechanism to form the complex regulatory network. In drug discovery, kinase inhibitors targeting the allosteric pockets have received extensive attention for the advantages of high selectivity and low toxicity. The approval of trametinib as the first allosteric inhibitor validated that allosteric inhibitors could be used as effective therapeutic drugs for the treatment of diseases. To date, a wide range of allosteric inhibitors have been identified. In this perspective, we outline different binding modes and potential advantages of allosteric inhibitors. In the meantime, the research processes of typical and novel allosteric inhibitors are described briefly in terms of structure-activity relationships, ligand-protein interactions, and in vitro and in vivo activity. Additionally, challenges, as well as opportunities, are also presented.

A structural perspective on targeting the RTK/Ras/MAP kinase pathway in cancer

Precision oncology is premised on identifying and drugging proteins and pathways that drive tumorigenesis or are required for survival of tumor cells. Across diverse cancer types, the signaling pathway emanating from receptor tyrosine kinases on the cell surface to RAS and the MAP kinase pathway is the most frequent target of oncogenic mutations, and key proteins in this signaling axis including EGFR, SHP2, RAS, BRAF, and MEK have long been a focus in cancer drug discovery. In this review, we provide an overview of historical and recent efforts to develop inhibitors targeting these nodes with an emphasis on the role that an understanding of protein structure and regulation has played in inhibitor discovery and characterization. Beyond its well-established role in structure-based drug design, structural biology has revealed mechanisms of allosteric regulation, distinct effects of activating oncogenic mutations, and other vulnerabilities that have opened new avenues in precision cancer drug discovery.

Emerging Approaches to Overcome Acquired Drug Resistance Obstacles to Osimertinib in Non-Small-Cell Lung Cancer

The pyrimidine core-containing compound Osimertinib is the only epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) from the third generation that has been approved by the U.S. Food and Drug Administration to target threonine 790 methionine (T790M) resistance while sparing the wild-type epidermal growth factor receptor (WT EGFR). It is nearly 200-fold more selective toward the mutant EGFR as compared to the WT EGFR. A tertiary cystein 797 to serine 797 (C797S) mutation in the EGFR kinase domain has hampered Osimertinib treatment in patients with advanced EGFR-mutated non-small-cell lung cancer (NSCLC). This C797S mutation is presumed to induce a tertiary-acquired resistance to all current reversible and irreversible EGFR TKIs. This review summarizes the molecular mechanisms of resistance to Osimertinib as well as different strategies for overcoming the EGFR-dependent and EGFR-independent mechanisms of resistance, new challenges, and a future direction.

Fighting tertiary mutations in EGFR-driven lung-cancers: Current advances and future perspectives in medicinal chemistry

Third-generation inhibitors of the epidermal growth factor receptor (EGFR), best exemplified by osimertinib, have been developed to selectively target variants of EGFR bearing activating mutations and the mutation of gatekeeper T790 in patients with EGFR-mutated forms of Non-Small Cell Lung Cancer (NSCLC). While the application of third-generation inhibitors has represented an effective first- and second-line treatment, the efficacy of this class of inhibitors has been hampered by the novel, tertiary mutation C797S, which may occur after the treatment with osimertinib. More recently, other point mutations, including L718Q, G796D, G724S, L792 and G719, have emerged as mutations mediating resistance to third-generation inhibitors. The challenge of overcoming newly developed and recurrent resistances mediated by EGFR-mutations is thus driving the search of alternative strategies in the design of new therapeutic agents able to block EGFR-driven tumor growth. In this manuscript we review the recently emerged EGFR-dependent mechanisms of resistance to third-generation inhibitors, and the achievements lately obtained in the development of next-generation EGFR inhibitors.

Untangling Dual-Targeting Therapeutic Mechanism of Epidermal Growth Factor Receptor (EGFR) Based on Reversed Allosteric Communication

Dual-targeting therapeutics by coadministration of allosteric and orthosteric drugs is drawing increased attention as a revolutionary strategy for overcoming the drug-resistance problems. It was further observed that the occupation of orthosteric sites by therapeutics agents has the potential to enhance allosteric ligand binding, which leads to improved potency of allosteric drugs. Epidermal growth factor receptor (EGFR), as one of the most critical anti-cancer targets belonging to the receptor tyrosine kinase family, represents a quintessential example. It was revealed that osimertinib, an ATP-competitive covalent EGFR inhibitor, remarkably enhanced the affinity of a recently developed allosteric inhibitor JBJ-04-125-02 for EGFRL858R/T790M. Here, we utilized extensive large-scale molecular dynamics simulations and the reversed allosteric communication to untangle the detailed molecular underpinning, in which occupation of osimertinib at the orthosteric site altered the overall conformational ensemble of EGFR mutant and reshaped the allosteric site via long-distance signaling. A unique intermediate state resembling the active conformation was identified, which was further stabilized by osimertinib loading. Based on the allosteric communication pathway, we predicted a novel allosteric site positioned around K867, E868, H893, and K960 within the intermediate state. Its correlation with the orthosteric site was validated by both structural and energetic analysis, and its low sequence conservation indicated the potential for selective targeting across the human kinome. Together, these findings not only provided a mechanistic basis for future clinical application of the dual-targeting therapeutics, but also explored an innovative perception of allosteric inhibition of tyrosine kinase signaling.

Computational Approaches for the Design of (Mutant-)Selective Tyrosine Kinase Inhibitors: State-of-the-Art and Future Prospects

Kinases remain one of the major attractive therapeutic targets for a large number of indications such as cancer, rheumatoid arthritis, cardiac failure and many others. Design and development of kinase inhibitors (ATP-competitive, allosteric or covalent) is a clinically validated and successful strategy in the pharmaceutical industry. The perks come with limitations, particularly the development of resistance to highly potent and selective inhibitors. When this happens, the cycle needs to be repeated, i.e., the design and development of kinase inhibitors active against the mutated forms. The complexity of tumor milieu makes it awfully difficult for these molecularly-targeted therapies to work. Every year newer and better versions of these agents are introduced in the clinic. Several computational approaches such as structure-, ligand-based or hybrid ones continue to live up to their potential in discovering novel kinase inhibitors. New schools of thought in this area continue to emerge, e.g., development of dual-target kinase inhibitors. But there are fundamental issues with this approach. It is indeed difficult to selectively optimize binding at two entirely different or related kinases. In addition to the conventional strategies, modern technologies (machine learning, deep learning, artificial intelligence, etc.) started yielding the results and building success stories. Computational tools invariably played a critical role in catalysing the phenomenal progress in kinase drug discovery field. The present review summarized the progress in utilizing computational methods and tools for discovering (mutant-)selective tyrosine kinase inhibitor drugs in the last three years (2017-2019). Representative investigations have been discussed, while others are merely listed. The author believes that the enthusiastic reader will be inspired to dig out the cited literature extensively to appreciate the progress made so far and the future prospects of the field.

Identification of novel allosteric binding sites and multi-targeted allosteric inhibitors of receptor and non-receptor tyrosine kinases using a computational approach

EGFR1, VEGFR2, Bcr-Abl and Src kinases are key drug targets in non-small cell lung cancer (NSCLC), bladder cancer, pancreatic cancer, CML, ALL, colorectal cancer, etc. The available drugs targeting these kinases have limited therapeutic efficacy due to novel mutations resulting in drug resistance and toxicity, as they target ATP binding site. Allosteric drugs have shown promising results in overcoming drug resistance, but the discovery of allosteric drugs is challenging. The allosteric binding pockets are difficult to predict, as they are generally associated with high energy conformations and regulate protein function in yet unknown mechanisms. In addition, the discovery of drugs using conventional methods takes long time and goes through several challenges, putting the lives of many cancer patients at risk. Therefore, the aim of the present work was to apply the most successful, drug repurposing approach in combination with computational methods to identify kinase inhibitors targeting novel allosteric sites on protein structure and assess their potential multi-kinase binding affinity. Multiple crystal structures belonging to EGFR1, VEGFR2, Bcr-Abl and Src tyrosine kinases were selected, including mutated, inhibitor bound and allosteric conformations to identify potential leads, close to physiological conditions. Interestingly the potential inhibitors identified were peptides. The drugs identified in this study could be used in therapy as a single multi-kinase inhibitor or in a combination of single kinase inhibitors after experimental validation. In addition, we have also identified new hot spots that are likely to be druggable allosteric sites for drug discovery of kinase-specific drugs in the future.Communicated by Ramaswamy H. Sarma.

Allosteric mutant-selective fourth-generation EGFR inhibitors as an efficient combination therapeutic in the treatment of non-small cell lung carcinoma

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) show most preferable treatment for non-small cell lung carcinoma (NSCLC) with EGFR activating mutations. Despite initial impressive response of first-, to third-generation EGFR-TKIs, these agents become ineffective because of rapid emergence of EGFR mutations (T790M or C797S) mediated resistance. Allosteric mutant-selective fourth-generation EGFR inhibitors appeared to be possible therapeutic option to overcome resistance. These EGFR inhibitors are less effective as a single agent but provide synergistic effect as a combinatorial drug with conventional chemo- or immunotherapeutic. Here, we aim to highlight the comprehensive overview on combined therapeutic efficacy of allosteric EGFR inhibitors for the treatment of EGFR mutant NSCLC.

Molecular mechanism study of EGFR allosteric inhibitors using molecular dynamics simulations and free energy calculations

ABTRACTThe epidermal growth factor receptor (EGFR) kinase inhibitors Gefitinib, Erlotinib, Afatinib and Osimertinib have been approved for the treatments of non-small cell lung cancer patients harboring sensitive EGFR mutations, but resistance arises rapidly. To date all approved EGFR inhibitors are ATP-competitive inhibitors, highlighting the need for therapeutic agents with alternative mechanisms of action. Allosteric kinase inhibitors offer a promising new therapeutic strategy to ATP-competitive inhibitors. The mutant-selective allosteric EGFR inhibitors EAI045 exhibited higher potency for EGFR^L858R&T790M compared to WT, which was also effective in EGFR-mutant models including those harboring the C797S mutation. However, it was not effective as a single-agent inhibitor, and require the co-administration of the anti-EGFR antibody Cetuximab. Further efforts produced a more potent analog JBJ-04-125-02, which can inhibit cell proliferation as a single-agent inhibitor. In the present study, molecular dynamics simulations and free energy calculations were performed and revealed the detailed inhibitory mechanism of JBJ-04-125-02 as more potent EGFR inhibitor. Moreover, the energy difference between HOMO and LUMO calculated by DFT implied the higher interaction of JBJ-04-125-02 than EAI045 in the active site of the EGFR. The identified key features obtained from the molecular modeling enabled us to design novel EGFR allosteric inhibitors.Communicated by Ramaswamy H. Sarma.

Synthesis of 1,3-Benzodiazepines through [5 + 2] Annulation of N-Aryl Amidines with Propargylic Esters

In this paper, an efficient synthesis of functionalized 1,3-benzodiazepines through an unprecedented [5 + 2] annulation of N-aryl amidines with propargylic esters is presented. The reactions proceed through Rh(III)-catalyzed C(sp²)-H alkenylation followed by annulation and deacetoxylation along with cascade C-H/N-H/C-O bond cleavage and C-C/C-N bond formation. Furthermore, the cytotoxicity of selected products against several human cancer cell lines was tested, which demonstrated their good potential for pharmaceutical applications.

Complex Crystal Structures of EGFR with Third-Generation Kinase Inhibitors and Simultaneously Bound Allosteric Ligands

Osimertinib is a third-generation tyrosine kinase inhibitor (TKI) and currently the gold-standard for the treatment of patients suffering from non-small cell lung cancer (NSCLC) harboring T790M-mutated epidermal growth factor receptor (EGFR). The outcome of the treatment, however, is limited by the emergence of the C797S resistance mutation. Allosteric inhibitors have a different mode of action and were developed to overcome this limitation. However, most of these innovative molecules are not effective as a single agent. Recently, mutated EGFR was successfully addressed with osimertinib combined with the allosteric inhibitor JBJ-04-125-02, but surprisingly, structural insights into their binding mode were lacking. Here, we present the first complex crystal structures of mutant EGFR in complex with third-generation inhibitors such as osimertinib and mavelertinib in the presence of simultaneously bound allosteric inhibitors. These structures highlight the possibility of further combinations targeting EGFR and lay the foundation for hybrid inhibitors as next-generation TKIs.

The new opportunities in medicinal chemistry of fourth-generation EGFR inhibitors to overcome C797S mutation

Epidermal growth factor receptor (EGFR) is a receptor for epithelial growth factor (EGF) cell proliferation and signaling, which is related to the inhibition of tumor cell proliferation, angiogenesis, tumor invasion, metastasis, and apoptosis. Thus, it has become an important target for the treatment of non-small cell lung cancer (NSCLC). The first to the third-generation EGFR inhibitors have demonstrated powerful efficacy and brought a prospect to patients. Unfortunately, after 9-15 months of treatment, they all developed resistance without exception. As for the resistance of third-generation inhibitors, no major breakthrough has been made in this field. In this review, we discussed the recent advances in medicinal chemistry of fourth-generation EGFR-TKIs, as well as further discussed the clinical challenges and future prospects of treating patients with EGFR mutations resistant to third-generation EGFR-TKIs.

Mutant-Selective Allosteric EGFR Degraders are Effective Against a Broad Range of Drug-Resistant Mutations

Targeting epidermal growth factor receptor (EGFR) through an allosteric mechanism provides a potential therapeutic strategy to overcome drug-resistant EGFR mutations that emerge within the ATP binding site. Here, we develop an allosteric EGFR degrader, DDC-01-163, which can selectively inhibit the proliferation of L858R/T790M (L/T) mutant Ba/F3 cells while leaving wildtype EGFR Ba/F3 cells unaffected. DDC-01-163 is also effective against osimertinib-resistant cells with L/T/C797S and L/T/L718Q EGFR mutations. When combined with an ATP-site EGFR inhibitor, osimertinib, the anti-proliferative activity of DDC-01-163 against L858R/T790M EGFR-Ba/F3 cells is enhanced. Collectively, DDC-01-163 is a promising allosteric EGFR degrader with selective activity against various clinically relevant EGFR mutants as a single agent and when combined with an ATP-site inhibitor. Our data suggests that targeted protein degradation is a promising drug development approach for mutant EGFR.

Advances in targeting EGFR allosteric site as anti-NSCLC therapy to overcome the drug resistance

BACKGROUND

The epidermal growth factor receptor (EGFR) inhibitors represent the first-line therapy regimen for non-small cell lung cancer (NSCLC). Most of these inhibitors target the ATP-site to stop the aggressive development of NSCLC. Stabilization of the ATP-binding on EGFR is difficult due to autophosphorylation of the EGFR domain. This leads to activation of nonintrinsic influence of the tumor microenvironment and expression of anti-apoptotic pathways and drug resistance.

METHODS

The NSCLC related literature search was carried out using online databases such as Scopus, Web of Sciences, PubMed, Protein Data Bank and UniPort for the last ten years and selected articles are referred for discussion in this review.

RESULTS

To overcome the problem of mutations in NSCLC, the allosteric site of EGFR was targeted, which shows significant therapeutic outcome without causing resistance. Compounds like EAI001, EAI045 JBJ-04-125-02, DDC4002 and a series of small molecules with an affinity towards the EGFR allosteric site are reported and are under the investigational stage. These compounds are categorized under fourth-generation anti-NSCLC agents.

CONCLUSION

Composition of this review highlights the advantage of inhibiting allosteric site in the EGFRTK receptor domains and presents a comparative analysis of the new fourth-generation anti-NSCLC agents to overcome the drug resistance.

Medicinal Chemistry Strategies for the Development of Kinase Inhibitors Targeting Point Mutations

Clinically acquired resistance to small molecule kinase inhibitors (SMKIs) has become a major "unmet clinical need" in cancer therapy. To date, there are six SMKIs to be approved for the treatment of cancer patients through targeting of clinically acquired resistance caused by on-target mutations. These are mainly focused on the mutant kinases Bcr-Abl T315I, EGFR T790M, and ALK L1196M. Herein, we summarize the major medicinal chemistry strategies employed in the discovery of these representative SMKIs, such as avoiding steric hindrance, making additional interactions with mutated residues, and forming a covalent bond with an active site cysteine to override resistance observed for reversible inhibitors. Additionally, we also briefly describe allosteric kinase inhibitors and proteolysis targeting chimera (PROTAC) as two other potential strategies while addressing future opportunities in this area.

Structural Basis for EGFR Mutant Inhibition by Trisubstituted Imidazole Inhibitors

Acquired drug resistance in epidermal growth factor receptor (EGFR) mutant non-small-cell lung cancer is a persistent challenge in cancer therapy. Previous studies of trisubstituted imidazole inhibitors led to the serendipitous discovery of inhibitors that target the drug resistant EGFR(L858R/T790M/C797S) mutant with nanomolar potencies in a reversible binding mechanism. To dissect the molecular basis for their activity, we determined the binding modes of several trisubstituted imidazole inhibitors in complex with the EGFR kinase domain with X-ray crystallography. These structures reveal that the imidazole core acts as an H-bond acceptor for the catalytic lysine (K745) in the "αC-helix out" inactive state. Selective N-methylation of the H-bond accepting nitrogen ablates inhibitor potency, confirming the role of the K745 H-bond in potent, noncovalent inhibition of the C797S variant. Insights from these studies offer new strategies for developing next generation inhibitors targeting EGFR in non-small-cell lung cancer.