Structure Defines Function: Clinically Relevant Mutations in ErbB Kinases

Combination of betulinic acid and EGFR-TKIs exerts synergistic anti-tumor effects against wild-type EGFR NSCLC by inducing autophagy-related cell death via EGFR signaling pathway

BACKGROUND

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of lung cancer patients with mutated EGFR. However, the efficacy of EGFR-TKIs in wild-type EGFR tumors has been shown to be marginal. Methods that can sensitize EGFR-TKIs to EGFR wild-type NSCLC remain rare. Hence, we determined whether combination treatment can maximize the therapeutic efficacy of EGFR-TKIs.

METHODS

We established a focused drug screening system to investigate candidates for overcoming the intrinsic resistance of wild-type EGFR NSCLC to EGFR-TKIs. Molecular docking assays and western blotting were used to identify the binding mode and blocking effect of the candidate compounds. Proliferation assays, analyses of drug interactions, colony formation assays, flow cytometry and nude mice xenograft models were used to determine the effects and investigate the molecular mechanism of the combination treatment.

RESULTS

Betulinic acid (BA) is effective at targeting EGFR and synergizes with EGFR-TKIs (gefitinib and osimertinib) preferentially against wild-type EGFR. BA showed inhibitory activity due to its interaction with the ATP-binding pocket of EGFR and dramatically enhanced the suppressive effects of EGFR-TKIs by blocking EGFR and modulating the EGFR-ATK-mTOR axis. Mechanistic studies revealed that the combination strategy activated EGFR-induced autophagic cell death and that the EGFR-AKT-mTOR signaling pathway was essential for completing autophagy and cell cycle arrest. Activation of the mTOR pathway or blockade of autophagy by specific chemical agents markedly attenuated the effect of cell cycle arrest. In vivo administration of the combination treatment caused marked tumor regression in the A549 xenografts.

CONCLUSIONS

BA is a potential wild-type EGFR inhibitor that plays a critical role in sensitizing EGFR-TKI activity. BA combined with an EGFR-TKI effectively suppressed the proliferation and survival of intrinsically resistant lung cancer cells via the inhibition of EGFR as well as the induction of autophagy-related cell death, indicating that BA combined with an EGFR-TKI may be a potential therapeutic strategy for overcoming the primary resistance of wild-type EGFR-positive lung cancers.

ERBB2 Targeting Reveals a Significant Suppression of Tumorigenesis in Murine Endometrial Cancer with Pten Mutation

Endometrial cancer is the most common gynecologic malignancy. PTEN is a negative regulator of PI3K signaling and is deficient in > 50% of primary human endometrial cancer. Amplification of ERBB2 promotes tumorigenesis and pathogenesis of several human cancers. However, the effect of ERBB2 targeting has not been studied in endometrial cancer with PTEN mutations. The murine model Pgrcre/+Erbb2f/fPtenf/f (Erbb2d/d Ptend/d) was developed to evaluate the effect of ERBB2 targeted therapy in endometrial cancer with PTEN deficiency. Histopathological and molecular analysis was performed for Ptend/d and Erbb2d/dPtend/d mice. Histopathological analysis revealed that Erbb2d/dPtend/d mice significantly reduced development and progression of endometrial cancer compared to Ptend/d mice. Furthermore, percentage of proliferative cells in Erbb2d/dPtend/d mice revealed anti-tumorigenic effect of Erbb2 ablation compared to Ptend/d mice. Our results demonstrate that Erbb2 ablation reveals a significant suppression of tumorigenesis on endometrial cancer of Ptend/d mice. Our results suggest that Erbb2 functions as an oncogene in endometrial cancer of Ptend/d mice implying that Erbb2 targeting can be used as an effective therapeutic approach for treatment of endometrial cancer with PTEN deficiency to hinder cancer development.

Structural Mechanism and Inhibitors Targeting EGFR Exon 20 Insertion (Ex20ins) Mutations

Epidermal growth factor receptor (EGFR) targeted therapy is one of the most important and effective strategies to combat EGFR mutant nonsmall-cell lung cancer (NSCLC). However, a substantial number of patients bearing EGFR exon 20 insertion (Ex20ins) mutations respond poorly to common EGFR targeted therapies. This clinical need remained unmet until recently, when the EGFR Ex20ins mutation inhibitor mobocertinib was approved by the FDA. Despite this progress, the structural mechanisms of EGFR Ex20ins mutation resistance and characterization of inhibitor binding modes have not been systematically summarized. Herein, we analyze the structural mechanisms for ligand binding and resistance and summarize recent developments for the reported inhibitors of EGFR Ex20ins mutations. Furthermore, this Perspective aims to provide insights for the design of the next generation of EGFR Ex20ins inhibitors.

Discovery of YK-029A, a novel mutant EGFR inhibitor targeting both T790 M and exon 20 insertion mutations, as a treatment for NSCLC

Although traditional EGFR-TKIs have advanced the treatment landscape of NSCLC with sensitive driver mutations (del19 or L858R), some NSCLC patients with EGFR exon 20 insertion mutations have been left with few effective therapies. The development of novel TKIs is still in progress. Herein, we describe the structure-guided design of a novel selective and orally bioavailable inhibitor, YK-029A, which could overcome both the T790 M mutations and exon 20 insertion of EGFR. YK-029A inhibited EGFR signaling, suppressed sensitive mutations and ex20ins of EGFR-driven cell proliferation, and was largely effective with oral administration in vivo. Furthermore, YK-029A exhibited significant antitumor activity in EGFRex20ins-driven patients-derived xenograft (PDX) models, preventing tumor progression or causing tumor regression at well-tolerated dosages. Based on the outcomes of preclinical efficacy and safety studies, YK-029A will enter phase Ⅲ clinical trials for the treatment of EGFRex20ins NSCLC.

A sulfonyl fluoride derivative inhibits EGFRL858R/T790M/C797S by covalent modification of the catalytic lysine

The emergence of the C797S mutation in EGFR is a frequent mechanism of resistance to osimertinib in the treatment of non-small cell lung cancer (NSCLC). In the present work, we report the design, synthesis and biochemical characterization of UPR1444 (compound 11), a new sulfonyl fluoride derivative which potently and irreversibly inhibits EGFR^{L858R/T790M/C797S} through the formation of a sulfonamide bond with the catalytic residue Lys745. Enzymatic assays show that compound 11 displayed an inhibitory activity on EGFR^WT comparable to that of osimertinib, and it resulted more selective than the sulfonyl fluoride probe XO44, recently reported to inhibit a significant part of the kinome. Neither compound 11 nor XO44 inhibited EGFR^{del19/T790M/C797S} triple mutant. When tested in Ba/F3 cells expressing EGFR^{L858R/T790M/C797S}, compound 11 resulted significantly more potent than osimertinib at inhibiting both EGFR autophosphorylation and proliferation, even if the inhibition of EGFR autophosphorylation by compound 11 in Ba/F3 cells was not long lasting.

Expanding the Disorder-Function Paradigm in the C-Terminal Tails of Erbbs

ErbBs are receptor tyrosine kinases involved not only in development, but also in a wide variety of diseases, particularly cancer. Their extracellular, transmembrane, juxtamembrane, and kinase folded domains were described extensively over the past 20 years, structurally and functionally. However, their whole C-terminal tails (CTs) following the kinase domain were only described at atomic resolution in the last 4 years. They were shown to be intrinsically disordered. The CTs are known to be tyrosine-phosphorylated when the activated homo- or hetero-dimers of ErbBs are formed. Their phosphorylation triggers interaction with phosphotyrosine binding (PTB) or Src Homology 2 (SH2) domains and activates several signaling pathways controling cellular motility, proliferation, adhesion, and apoptosis. Beyond this passive role of phosphorylated domain and site display for partners, recent structural and function studies unveiled active roles in regulation of phosphorylation and interaction: the CT regulates activity of the kinase domain; different phosphorylation states have different compaction levels, potentially modulating the succession of phosphorylation events; and prolines have an important role in structure, dynamics, and possibly regulatory interactions. Here, we review both the canonical role of the disordered CT domains of ErbBs as phosphotyrosine display domains and the recent findings that expand the known range of their regulation functions linked to specific structural and dynamic features.

Targeting Her2-insYVMA with Covalent Inhibitors-A Focused Compound Screening and Structure-Based Design Approach

Mutated or amplified Her2 serves as a driver of non-small cell lung cancer or mediates resistance toward the inhibition of its family member epidermal growth factor receptor with small-molecule inhibitors. To date, small-molecule inhibitors targeting Her2 which can be used in clinical routine are lacking, and therefore, the development of novel inhibitors was undertaken. In this study, the well-established pyrrolopyrimidine scaffold was modified with structural motifs identified from a screening campaign with more than 1600 compounds, which were applied against wild-type Her2 and its mutant variant Her2-A775_G776insYVMA. The resulting inhibitors were designed to covalently target a reactive cysteine in the binding site of Her2 and were further optimized by means of structure-based drug design utilizing a set of obtained complex crystal structures. In addition, the analysis of binding kinetics and absorption, distribution, metabolism, and excretion parameters as well as mass spectrometry experiments and western blot analysis substantiated our approach.