Activation of the IGF1R pathway potentially mediates acquired resistance to mutant-selective 3rd-generation EGF receptor tyrosine kinase inhibitors in advanced non-small cell lung cancer

Safety and efficacy of SNK01 (autologous natural killer cells) in combination with cytotoxic chemotherapy and/or cetuximab after failure of prior tyrosine kinase inhibitor in non-small cell lung cancer: non-clinical mouse model and phase I/IIa clinical study

BACKGROUND

Choosing treatments for epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC) patients with osimertinib resistance is challenging. We evaluated the safety and efficacy of SNK01 (autologous natural killer (NK) cells) in combination with cytotoxic chemotherapy and/or cetuximab (an anti-EGFR monoclonal antibody) in treating EGFR-mutated NSCLC in this non-clinical and phase I/IIa clinical trial.

METHODS

We developed a cell line-derived xenograft-humanized mouse model with an osimertinib-resistant lung cancer cell line. The mice were divided into four groups based on treatment (no treatment, cetuximab, SNK01, and combination groups) and treated weekly for 5 weeks. In the clinical study, 12 patients with EGFR-mutated NSCLC who failed prior tyrosine kinase inhibitor (TKI) received SNK01 weekly in combination with gemcitabine/carboplatin (n=6) or cetuximab/gemcitabine/carboplatin (n=6) and dose escalation of SNK01 following the "3+3" design.

RESULTS

In the non-clinical study, an increase in NK cells in the blood and enhanced NK cell tumor infiltration were observed in the SNK01 group. The volume of tumor extracted after treatment was the smallest in the combination group. In the clinical study, 12 patients (median age, 60.9 years; all adenocarcinoma cases) received SNK01 weekly for 7-8 weeks (4×109 cells/dose (n=6); 6×109 cells/dose (n=6)). The maximum feasible dose of SNK01 was 6×109 cells/dose without dose-limiting toxicity. Efficacy outcomes showed an objective response rate of 25%, disease control rate of 100%, and median progression-free survival of 143 days.

CONCLUSION

SNK01 in combination with cytotoxic chemotherapy, including cetuximab, for EGFR-mutated NSCLC with TKI resistance was safe and exerted a potential antitumor effect.

TRIAL REGISTRATION NUMBER

NCT04872634.

SOS2 modulates the threshold of EGFR signaling to regulate osimertinib efficacy and resistance in lung adenocarcinoma

Son of sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic receptor tyrosine kinase (RTK)-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR tyrosine kinase inhibitor (EGFR-TKI) osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion (SOS2KO ) sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation, oncogenic transformation, and survival. Bypassing RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2KO inhibited hepatocyte growth factor (HGF)-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long-term in situ resistance assay, most osimertinib-resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2KO cultures that became osimertinib resistant primarily underwent non-RTK-dependent epithelial-mesenchymal transition (EMT). Since bypassing RTK reactivation and/or tertiary EGFR mutations represent most osimertinib-resistant cancers, these data suggest that targeting proximal RTK signaling, here exemplified by SOS2 deletion, has the potential to delay the development osimertinib resistance and enhance overall clinical responses for patients with EGFR-mutated LUAD.

In situ modeling of acquired resistance to RTK/RAS-pathway-targeted therapies

Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Here, we describe an in situ resistance assay (ISRA) that reliably models acquired resistance to RTK/RAS-pathway-targeted therapies across cell lines. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show that acquired osimertinib resistance can be significantly delayed by inhibition of proximal RTK signaling using SHP2 inhibitors. Isolated osimertinib-resistant populations required SHP2 inhibition to resensitize cells to osimertinib and reduce MAPK signaling to block the effects of enhanced activation of multiple parallel RTKs. We additionally modeled resistance to targeted therapies including the KRASG12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance.

Modification of osimertinib to discover new potent EGFRC797S-TK inhibitors

The EGFRC797S mutation is a dominant mechanism of acquired resistance after the treatment of non-small cell lung cancer (NSCLC) with osimertinib in clinic. To date, there is no inhibitor approved to overcome the resistance caused by osimertinib. In this study, a series of compounds with phenylamino-pyrimidine scaffold deriving from osimertinib were designed, synthesized and evaluated as fourth-generation EGFRC797S-TK inhibitors. Consequently, compound Os30 exhibited potent inhibitory activities against both EGFRDel19/T790M/C797S TK and EGFRL858R/T790M/C797S TK with IC50 values of 18 nM and 113 nM, respectively. Moreover, Os30 can powerfully inhibit the proliferation of KC-0116 (BaF3-EGFRDel19/T790M/C797S) and KC-0122 (BaF3-EGFRL858R/T790M/C797S) cells. In addition, Os30 can suppress EGFR phosphorylation in a concentration-dependent manner in KC-0116 cells, arrest KC-0116 cells at G1 phase and induce the apoptosis of KC-0116 cells. More importantly, Os30 showed potent antitumor efficacy in the KC-0116 cells xenograft nude mice tumor model with the tumor growth inhibitory rate of 77.6% at a dosage of 40 mg/kg. These findings demonstrate that modification of osimertinib can discover new potent EGFRC797S-TK inhibitors, and compound Os30 is a potent fourth-generation EGFR inhibitor to treat NSCLC with EGFmRC797S mutation.

SOS1 and KSR1 modulate MEK inhibitor responsiveness to target resistant cell populations based on PI3K and KRAS mutation status

KRAS is the most commonly mutated oncogene. Targeted therapies have been developed against mediators of key downstream signaling pathways, predominantly components of the RAF/MEK/ERK kinase cascade. Unfortunately, single-agent efficacy of these agents is limited both by intrinsic and acquired resistance. Survival of drug-tolerant persister cells within the heterogeneous tumor population and/or acquired mutations that reactivate receptor tyrosine kinase (RTK)/RAS signaling can lead to outgrowth of tumor-initiating cells (TICs) and drive therapeutic resistance. Here, we show that targeting the key RTK/RAS pathway signaling intermediates SOS1 (Son of Sevenless 1) or KSR1 (Kinase Suppressor of RAS 1) both enhances the efficacy of, and prevents resistance to, the MEK inhibitor trametinib in KRAS-mutated lung (LUAD) and colorectal (COAD) adenocarcinoma cell lines depending on the specific mutational landscape. The SOS1 inhibitor BI-3406 enhanced the efficacy of trametinib and prevented trametinib resistance by targeting spheroid-initiating cells in KRASG12/G13-mutated LUAD and COAD cell lines that lacked PIK3CA comutations. Cell lines with KRASQ61 and/or PIK3CA mutations were insensitive to trametinib and BI-3406 combination therapy. In contrast, deletion of the RAF/MEK/ERK scaffold protein KSR1 prevented drug-induced SIC upregulation and restored trametinib sensitivity across all tested KRAS mutant cell lines in both PIK3CA-mutated and PIK3CA wild-type cancers. Our findings demonstrate that vertical inhibition of RTK/RAS signaling is an effective strategy to prevent therapeutic resistance in KRAS-mutated cancers, but therapeutic efficacy is dependent on both the specific KRAS mutant and underlying comutations. Thus, selection of optimal therapeutic combinations in KRAS-mutated cancers will require a detailed understanding of functional dependencies imposed by allele-specific KRAS mutations.

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.

SOS2 regulates the threshold of mutant EGFR-dependent oncogenesis

Son of Sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic RTK-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR-TKI osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit PI3K/AKT pathway activation, oncogenic transformation, and survival. Bypass RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2 KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2 KO inhibited HGF-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long term in situ resistance assay, a majority of osimertinib resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2 KO cultures that became osimertinib resistant primarily underwent non-RTK dependent EMT. Since bypass RTK reactivation and/or tertiary EGFR mutations represent the majority of osimertinib-resistant cancers, these data suggest that targeting SOS2 has the potential to eliminate the majority of osimertinib resistance.

In situ modeling of acquired resistance to RTK/RAS pathway targeted therapies

Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Preclinical studies that identify synergistic combinations enhance therapeutic efficacy to target intrinsic resistance, however, methods to study acquired resistance in cell culture are lacking. Here, we describe a novel in situ resistance assay (ISRA), performed in a 96-well culture format, that models acquired resistance to RTK/RAS pathway targeted therapies. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show acquired resistance can be reliably modeled across cell lines using objectively defined osimertinib doses. Similar to patient populations, isolated osimertinib-resistant populations showed resistance via enhanced activation of multiple parallel RTKs so that individual RTK inhibitors did not re-sensitize cells to osimertinib. In contrast, inhibition of proximal RTK signaling using the SHP2 inhibitor RMC-4550 both re-sensitized resistant populations to osimertinib and prevented the development of osimertinib resistance as a primary therapy. Similar, objectively defined drug doses were used to model resistance to additional RTK/RAS pathway targeted therapies including the KRASG12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance.

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.

Different roles of the insulin-like growth factor (IGF) axis in non-small cell lung cancer

Abstract:

Non-small cell lung cancer (NSCLC) remains one of the deadliest malignant diseases, with high incidence and mortality worldwide. The insulin-like growth factor (IGF) axis, consisting of IGF-1, IGF-2, related receptors (IGF-1R, -2R), and high-affinity binding proteins (IGFBP 1–6), is associated with promoting fetal development, tissue growth, and metabolism. Emerging studies have also identified the role of the IGF axis in NSCLC, including cancer growth, invasion, and metastasis. Upregulation of IGE-1 and IGF-2, overexpression of IGF-1R, and dysregulation of downstream signaling molecules involved in the PI-3K/Akt and MAPK pathways jointly increase the risk of cancer growth and migration in NSCLC. At the genetic level, some noncoding RNAs could influence the proliferation and differentiation of tumor cells through the IGF signaling pathway. The resistance to some promising drugs might be partially attributed to the IGF axis. Therapeutic strategies targeting the IGF axis have been evaluated, and some have shown promising efficacy. In this review, we summarize the biological roles of the IGF axis in NSCLC, including the expression and prognostic significance of the related components, noncoding RNA regulation, involvement in drug resistance, and therapeutic application. This review offers comprehensive understanding of NSCLC and provides insightful ideas for future research.

Preclinical Models for Acquired Resistance to Third-Generation EGFR Inhibitors in NSCLC: Functional Studies and Drug Combinations Used to Overcome Resistance

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) are currently recommended as first-line treatment for advanced non-small-cell lung cancer (NSCLC) with EGFR-activating mutations. Third-generation (3rd G) EGFR-TKIs, including osimertinib, offer an effective treatment option for patients with NSCLC resistant 1st and 2nd EGFR-TKIs. However, the efficacy of 3rd G EGFR-TKIs is limited by acquired resistance that has become a growing clinical challenge. Several clinical and preclinical studies are being carried out to better understand the mechanisms of resistance to 3rd G EGFR-TKIs and have revealed various genetic aberrations associated with molecular heterogeneity of cancer cells. Studies focusing on epigenetic events are limited despite several indications of their involvement in the development of resistance. Preclinical models, established in most cases in a similar manner, have shown different prevalence of resistance mechanisms from clinical samples. Clinically identified mechanisms include EGFR mutations that were not identified in preclinical models. Thus, NRAS genetic alterations were not observed in patients but have been described in cell lines resistant to 3rd G EGFR-TKI. Mainly, resistance to 3rd G EGFR-TKI in preclinical models is related to the activation of alternative signaling pathways through tyrosine kinase receptor (TKR) activation or to histological and phenotypic transformations. Yet, preclinical models have provided some insight into the complex network between dominant drivers and associated events that lead to the emergence of resistance and consequently have identified new therapeutic targets. This review provides an overview of preclinical studies developed to investigate the mechanisms of acquired resistance to 3rd G EGFR-TKIs, including osimertinib and rociletinib, across all lines of therapy. In fact, some of the models described were first generated to be resistant to first- and second-generation EGFR-TKIs and often carried the T790M mutation, while others had never been exposed to TKIs. The review further describes the therapeutic opportunities to overcome resistance, based on preclinical studies.

A review of research progress on mechanisms and overcoming strategies of acquired osimertinib resistance

Targeted therapy with epidermal growth factor receptor tyrosine kinase inhibitors(EGFR-TKIs) is the standard first-line treatment for advanced EGFR-mutated non-small cell lung cancer (NSCLC). Third-generation EGFR-TKIs, represented by osimertinib, have been approved to overcome the EGFR T790M mutation in patients who are resistant to first- or second-generation TKIs, which brings more survival benefits for patients with advanced NSCLC. However, resistance to the third generation of EGFR-TKIs is still inevitable. Acquired drug resistance is the main reason for limiting the long-term effectiveness of targeted therapy in EGFR-mutated NSCLC patients. The mechanism of EGFR-TKI resistance of the third generation has become a focus of research in the field of targeted therapy. In this review, we summarize the research progress in resistance mechanisms of advanced NSCLC to osimertinib and the potential overcoming strategies and hope to provide a clinical basis and ideas for precision treatment of NSCLC.

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.

Overcoming Resistance to Tumor-Targeted and Immune-Targeted Therapies

Resistance to anticancer therapies includes primary resistance, usually related to lack of target dependency or presence of additional targets, and secondary resistance, mostly driven by adaptation of the cancer cell to the selection pressure of treatment. Resistance to targeted therapy is frequently acquired, driven by on-target, bypass alterations, or cellular plasticity. Resistance to immunotherapy is often primary, orchestrated by sophisticated tumor-host-microenvironment interactions, but could also occur after initial efficacy, mostly when only partial responses are obtained. Here, we provide an overview of resistance to tumor and immune-targeted therapies and discuss challenges of overcoming resistance, and current and future directions of development. SIGNIFICANCE: A better and earlier identification of cancer-resistance mechanisms could avoid the use of ineffective drugs in patients not responding to therapy and provide the rationale for the administration of personalized drug associations. A clear description of the molecular interplayers is a prerequisite to the development of novel and dedicated anticancer drugs. Finally, the implementation of such cancer molecular and immunologic explorations in prospective clinical trials could de-risk the demonstration of more effective anticancer strategies in randomized registration trials, and bring us closer to the promise of cure.

Multi-Omics Data Analysis Uncovers Molecular Networks and Gene Regulators for Metabolic Biomarkers

The insulin-like growth factors (IGFs)/insulin resistance (IR) axis is the major metabolic hormonal pathway mediating the biologic mechanism of several complex human diseases, including type 2 diabetes (T2DM) and cancers. The genomewide association study (GWAS)-based approach has neither fully characterized the phenotype variation nor provided a comprehensive understanding of the regulatory biologic mechanisms. We applied systematic genomics to integrate our previous GWAS data for IGF-I and IR with multi-omics datasets, e.g., whole-blood expression quantitative loci, molecular pathways, and gene network, to capture the full range of genetic functionalities associated with IGF-I/IR and key drivers (KDs) in gene-regulatory networks. We identified both shared (e.g., T2DM, lipid metabolism, and estimated glomerular filtration signaling) and IR-specific (e.g., mechanistic target of rapamycin, phosphoinositide 3-kinases, and erb-b2 receptor tyrosine kinase 4 signaling) molecular biologic processes of IGF-I/IR axis regulation. Next, by using tissue-specific gene–gene interaction networks, we identified both well-established (e.g., IRS1 and IGF1R) and novel (e.g., AKT1, HRAS, and JAK1) KDs in the IGF-I/IR-associated subnetworks. Our results, if validated in additional genomic studies, may provide robust, comprehensive insights into the mechanisms of IGF-I/IR regulation and highlight potential novel genetic targets as preventive and therapeutic strategies for the associated diseases, e.g., T2DM and cancers.

Epidermal Growth Factor Receptor and its Trafficking Regulation by Acetylation: Implication in Resistance and Exploring the Newer Therapeutic Avenues in Cancer

BACKGROUND

The EGFR is overexpressed in numerous cancers. So, it becomes one of the most favorable drug targets. Single-acting EGFR inhibitors on prolong use induce resistance and side effects. Inhibition of EGFR and/or its interacting proteins by dual/combined/multitargeted therapies can deliver more efficacious drugs with less or no resistance.

OBJECTIVE

The review delves deeper to cover the aspects of EGFR mediated endocytosis, leading to its trafficking, internalization, and crosstalk(s) with HDACs.

METHODS AND RESULTS

This review is put forth to congregate relevant literature evidenced on EGFR, its impact on cancer prognosis, inhibitors, and its trafficking regulation by acetylation along with the current strategies involved in targeting these proteins (EGFR and HDACs) successfully by involving dual/hybrid/combination chemotherapy.

CONCLUSION

The current information on cross-talk of EGFR and HDACs would likely assist researchers in designing and developing dual or multitargeted inhibitors through combining the required pharmacophores.

Efficacy of the CDK7 Inhibitor on EMT-Associated Resistance to 3rd Generation EGFR-TKIs in Non-Small Cell Lung Cancer Cell Lines

Epithelial to mesenchymal transition (EMT) is associated with resistance during EGFR tyrosine kinase inhibitor (EGFR-TKI) therapy. Here, we investigated whether EMT is associated with acquired resistance to 3rd generation EGFR-TKIs, and we explored the effects of cyclin-dependent kinase 7 (CDK7) inhibitors on EMT-mediated EGFR-TKIs resistance in non-small cell lung cancer (NSCLC). We established 3rd generation EGFR-TKI resistant cell lines (H1975/WR and H1975/OR) via repeated exposure to WZ4002 and osimertinib. The two resistant cell lines showed phenotypic changes to a spindle-cell shape, had a reduction of epithelial marker proteins, an induction of vimentin expression, and enhanced cellular mobility. The EMT-related resistant cells had higher sensitivity to THZ1 than the parental cells, although THZ1 treatment did not inhibit EGFR activity. This phenomenon was also observed in TGF-β1 induced EMT cell lines. THZ1 treatment induced G2/M cell cycle arrest and apoptosis in all of the cell lines. In addition, THZ1 treatment led to drug-tolerant, EMT-related resistant cells, and these THZ1-tolerant cells partially recovered their sensitivity to 3rd generation EGFR-TKIs. Taken together, EMT was associated with acquired resistance to 3rd generation EGFR-TKIs, and CDK7 inhibitors could potentially be used as a therapeutic strategy to overcome EMT associated EGFR-TKI resistance in NSCLC.

[Research Progress of New Generation EGFR-TKIs after Third-generation]

肺癌是全球死亡率最高的癌种。第一、二代表皮生长因子受体酪氨酸激酶抑制剂（epidermal growth factor receptor-tyrosine kinase inhibitors, EGFR-TKIs）的出现，在一定程度上极大地提高了非小细胞肺癌（non-small cell lung cancer, NSCLC）患者的生存期及生活质量，但大多数患者在经过一段时间的无进展生存期后会产生耐药性，其中以T790M突变为主要耐药机制。针对此耐药突变出现的是以奥希替尼为代表的第三代EGFR-TKIs，其效果显著，然而仍不可避免的出现耐药性，如：C797S突变、间质表皮转化（mesenchymal-epithelial transition, MET）、RAS突变、BRAF突变、小细胞肺癌（small cell lung cancer, SCLC）转化、上皮间质细胞转化（epithelial mesenchymal transition, EMT）等。但是目前第三代EGFR-TKIs耐药后并没有标准有效的治疗方案。故本文主要阐述三代后的新一代EGFR-TKIs的研究进展，为后续的研究及治疗提供一定的参考。

Marked synergy by vertical inhibition of EGFR signaling in NSCLC spheroids shows SOS1 is a therapeutic target in EGFR-mutated cancer

Drug treatment of 3D cancer spheroids more accurately reflects in vivo therapeutic responses compared to adherent culture studies. In EGFR-mutated lung adenocarcinoma, EGFR-TKIs show enhanced efficacy in spheroid cultures. Simultaneous inhibition of multiple parallel RTKs further enhances EGFR-TKI effectiveness. We show that the common RTK signaling intermediate SOS1 was required for 3D spheroid growth of EGFR-mutated NSCLC cells. Using two distinct measures of pharmacologic synergy, we demonstrated that SOS1 inhibition strongly synergized with EGFR-TKI treatment only in 3D spheroid cultures. Combined EGFR- and SOS1-inhibition markedly inhibited Raf/MEK/ERK and PI3K/AKT signaling. Finally, broad assessment of the pharmacologic landscape of drug-drug interactions downstream of mutated EGFR revealed synergy when combining an EGFR-TKI with inhibitors of proximal signaling intermediates SOS1 and SHP2, but not inhibitors of downstream RAS effector pathways. These data indicate that vertical inhibition of proximal EGFR signaling should be pursued as a potential therapy to treat EGFR-mutated tumors.

Lung cancer is the leading cause of cancer-related deaths worldwide. In non-smokers, this disease is usually caused by a mutation in a protein found on the surface of a cell, called EGFR. In healthy lung cells, these proteins trigger a chain of chemical signals that tell the cells to multiply. However, faulty forms of EFGR make the cells grow uncontrollably, leading to the formation of tumors.

Current treatments use EGFR inhibitors that block the activity of these proteins. But cancer cells often become resistant to these treatments by activating other types of growth proteins. One way to overcome this resistance has been by targeting the signaling pathways within individual tumors. But since those pathways differ between tumors, it has been challenging to find a single therapy that can treat all drug-resistant cancer cells.

Now, Theard et al. assessed the therapeutic effects of blocking a specific protein inside lung cells, called SOS1, which is involved in growth signaling in all tumor cells. Six different types of human lung cancer cells were used, all of which had faulty forms of EGFR, with three of the cell types showing drug resistance to current therapies. The cancer cells were either exposed to EGFR inhibitors only or to a combination of EGFR and SOS1 inhibitors. The most effective treatment was found to be through combinational therapy, with enhanced killing of drug-resistant cells.

Theard et al. further assessed the effect of combinational therapy using cells kept in two different ways. Cancer cells were either grown in a two-dimensional format, with cells forming a single cell layer, or in a three-dimensional format, where cells were multi-layered and grew on top of each other as self-aggregating spheroids. Combinational therapy treatment was only successful when the cells where grown in a three-dimensional format.

These findings highlight that future drug development studies should give consideration to the way cells are grown, as it can impact the results. They also provide a steppingstone towards tackling drug resistance in lung cancers that arise from EGFR mutations.

Recent updates on the resistance mechanisms to epidermal growth factor receptor tyrosine kinase inhibitors and resistance reversion strategies in lung cancer

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have led to a substantial improvement in the prognosis of lung cancer patients by explicitly targeting the activating mutations within the EGFR. Initially, patients harboring tumors with EGFR mutations show progression-free survival and improvement in the response rates toward all-generation EGFR-TKIs; however, these agents fail to deliver the intended results in the long-term due to drug resistance. Therefore, it is necessary to recognize specific cardinal mechanisms that regulate the resistance phenomenon. Understanding the intricate mechanisms underlying EGFR-TKIs resistance in lung cancer could provide cognizance for more advanced targeted therapeutics. The present review features insights into current updates on the discrete mechanisms, including secondary or tertiary mutations, parallel and downstream signaling pathways, acquiring an epithelial-to-mesenchymal transition (EMT) signature, microRNAs (miRNAs), and epigenetic alterations, which lead to intrinsic and acquired resistance against EGFR-TKIs in lung cancer. In addition, this paper also reviews current possible strategies to overcome this issue using combination treatment of recently developed MET inhibitors, allosteric inhibitors or immunotherapies, transformation of EMT, targeting miRNAs, and epigenetic alterations in intrinsic and acquired EGFR-TKIs resistant lung cancer. In conclusion, multiple factors are responsible for intrinsic and acquired resistance to EGFR-TKIs and understanding of the detailed molecular mechanisms, and recent advancements in pharmacological studies are needed to develop new strategies to overcome intrinsic and acquired EGFR-TKIs resistance in lung cancer.

Long non-coding RNAs regulate drug resistance in cancer

Chemoresistance, whether intrinsic or acquired, is a major obstacle in the treatment of cancer. The resistance of cancer cells to chemotherapeutic drugs can result from various mechanisms. Over the last decade, it has been reported that 1ong noncoding RNAs (lncRNAs) can mediate carcinogenesis and drug resistance/sensitivity in cancer cells. This article reviews, in detail, recent studies regarding the roles of lncRNAs in mediating drug resistance.

Long non-coding RNAs regulate drug resistance in cancer

Chemoresistance, whether intrinsic or acquired, is a major obstacle in the treatment of cancer. The resistance of cancer cells to chemotherapeutic drugs can result from various mechanisms. Over the last decade, it has been reported that 1ong noncoding RNAs (lncRNAs) can mediate carcinogenesis and drug resistance/sensitivity in cancer cells. This article reviews, in detail, recent studies regarding the roles of lncRNAs in mediating drug resistance.

Frontiers of ctDNA, targeted therapies, and immunotherapy in non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC), a main subtype of lung cancer, is one of the most common causes of cancer death in men and women worldwide. Circulating tumor DNA (ctDNA), tyrosine kinase inhibitors (TKIs) and immunotherapy have revolutionized both our understanding of NSCLC, from its diagnosis to targeted NSCLC therapies, and its treatment. ctDNA quantification confers convenience and precision to clinical decision making. Furthermore, the implementation of TKI-based targeted therapy and immunotherapy has significantly improved NSCLC patient quality of life. This review provides an update on the methods of ctDNA detection and its impact on therapeutic strategies; therapies that target epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) using TKIs such as osimertinib and lorlatinib; the rise of various resistant mechanisms; and the control of programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1), and cytotoxic T-lymphocyte antigen-4 (CTLA-4) by immune checkpoint inhibitors (ICIs) in immunotherapy; blood tumor mutational burden (bTMB) calculated by ctDNA assay as a novel biomarker for immunotherapy. However, NSCLC patients still face many challenges. Further studies and trials are needed to develop more effective drugs or therapies to treat NSCLC.

IGF2 Autocrine-Mediated IGF1R Activation Is a Clinically Relevant Mechanism of Osimertinib Resistance in Lung Cancer

EGFR-mutated lung cancer accounts for a significant proportion of lung cancer cases worldwide. For these cases, osimertinib, a third-generation EGFR tyrosine kinase inhibitor, is extensively used as a first-line or second-line treatment. However, lung cancer cells acquire resistance to osimertinib in 1 to 2 years. Thus, a thorough clarification of resistance mechanisms to osimertinib is highly anticipated. Recent next-generation sequencing (NGS) of lung cancer samples identified several genetically defined resistance mechanisms to osimertinib, such as EGFR C797S or MET amplification. However, nongenetically defined mechanisms are not well evaluated. For a thorough clarification of osimertinib resistance, both genetic and nongenetic mechanisms are essential. By using our comprehensive protein phosphorylation array, we detected IGF1R bypass pathway activation after EGFR abolishment. Both of our established lung cancer cells and patient-derived lung cancer cells demonstrated IGF2 autocrine-mediated IGF1R pathway activation as a mechanism of osimertinib resistance. Notably, this resistance mechanism was not detected by a previously performed NGS, highlighting the essential roles of living cancer cells for a thorough clarification of resistance mechanisms. Interestingly, the immunohistochemical analysis confirmed the increased IGF2 expression in lung cancer patients who were treated with osimertinib and met the established clinical definition of acquired resistance. The findings highlight the crucial roles of cell-autonomous ligand expression in osimertinib resistance. Here, we report for the first time the IGF2 autocrine-mediated IGF1R activation as a nongenetic mechanism of osimertinib resistance in lung cancer at a clinically relevant level. IMPLICATIONS: Using comprehensive protein phosphorylation array and patient-derived lung cancer cells, we found that IGF2 autocrine-mediated IGF1R pathway activation is a clinically relevant and common mechanism of acquired resistance to osimertinib.

The emerging treatment landscape of targeted therapy in non-small-cell lung cancer

Lung cancer is one of the most common cancer in the world. In 2018, there were over 2 million new cases of lung cancer and over 1.7 million deaths were attributed to lung cancer. Targeted therapy has emerged as an important mean of the disease management for patients with non-small-cell lung cancer (NSCLC). Herein, we review and analyze recent literature, discuss the targeting pathways and ongoing clinical trials in lung cancer. Chemotherapy is no longer the best available treatment for all patients. Therapeutic decisions should be guided by an understanding of the molecular features of patient's tumor tissues. The future gains will likely emerge from finding optimal ways of combining targeted therapy, immunotherapy, and chemotherapy.

Activation of insulin-like growth factor-1 receptor confers acquired resistance to osimertinib in non-small cell lung cancer with EGFR T790M mutation

Background

Osimertinib (AZD9291) is a third‐generation EGFR‐tyrosine kinase inhibitor (TKI) that selectively inhibits the activating EGFR mutation and T790M mutation, and is currently used globally to treat EGFR‐mutant non‐small cell lung cancer (NSCLC). However, acquired resistance to osimertinib is inevitable.

Methods

We established osimertinib‐resistant cells (PC9/T790M/AZDR and H1975/AZDR) derived from EGFR‐mutant NSCLC cells harboring T790M mutation, and investigated the mechanism of acquired resistance to osimertinib by whole‐exome sequencing and multiple phospho‐receptor tyrosine kinase (RTK) array. A tumor specimen from an EGFR‐mutant NSCLC patient with acquired resistance to osimertinib was also subjected to immunohistochemical analysis.

Results

Whole‐exome sequencing analysis demonstrated that genetic alterations, such as acquisition of EGFR C797S, loss of T790M mutation, MET amplification, or mutated KRAS, MEK, BRAF, PIK3CA, were not detected. Analysis of phospho‐RTK array revealed that insulin‐like growth factor‐1 receptor (IGF1R) was activated in PC9/T790M/AZDR and H1975/AZDR cells. Knockdown of IGF1R by siRNA as well as inhibition of IGF1R activation by linstinib (IGF1R inhibitor) significantly restored the sensitivity to osimertinib. Immunohistochemical analysis revealed that the expression level of phosphorylated IGF1R was higher in the tumor specimen from the EGFR‐mutant NSCLC patient with acquired resistance to osimertinib than in the specimen collected prior to the treatment.

Conclusions

IGF1R activation could occur following treatment with osimertinib in EGFR‐mutant NSCLC with T790M mutation, and might be one of the mechanisms underlying osimertinib resistance. Combined treatment of osimertinib and IGF1R inhibitor might be effective in overcoming the acquired resistance to osimertinib induced by IGF1R activation.

Key points

Significant findings of the study: Using osimertinib‐resistant cells, we found that IGF1R activation induced by osimertinib treatment in EGFR‐mutant NSCLC with T790M mutation is involved in resistance. Increased phosphorylation of IGF1R was observed in the tumor specimen from an EGFR‐mutant NSCLC patient with acquired osimertinib resistance.

What this study adds: IGF1R activation might be one of the mechanisms of osimertinib resistance. A combination therapy with osimertinib and an IGF1R inhibitor might be an optimal approach for overcoming the acquired resistance to osimertinib induced by IGF1R activation.

Discovery of novel 9-heterocyclyl substituted 9H-purines as L858R/T790M/C797S mutant EGFR tyrosine kinase inhibitors

Targeting L858R/T790M/C797S mutant EGFR is a major challenge in the new-generation EGFR tyrosine kinase inhibitors development for conquering drug resistant NSCLC. In this study, a series of novel 9-heterocyclyl substituted 9H-purine derivatives were designed as EGFR^{L858 R/T790 M/C797S} tyrosine kinase inhibitors. Among these compounds, D4, D9, D11 and D12 showed significantly potent anti-proliferation and EGFR^{L858 R/T790 M/C797S} inhibition activity. In particular, the most potent compound D9 showed anti-proliferation against HCC827 and H1975 cell lines with the IC₅₀ values of 0.00088 and 0.20 μM, respectively. And D9 inhibited the EGFR^{L858R/T790M/C797S} with an IC₅₀ value of 18 nM. Furtherly, D9 could significantly suppress the EGFR phosphorylation, induce the apoptosis, arrest cell cycle at G0/G1, and inhibit colony formation in HCC827 cell line by a concentration-dependent manner. Molecular docking indicated that the introduction of a cyclopropylsulfonamide group in D9 led to the formation of additional two hydrogen bonds with mutant Ser797 which played key roles in generating efficient EGFR^{L858 R/T790 M/C797S} inhibitory activity. These findings strongly indicated that 9-heterocyclyl substituted 9H-purine derivatives were promising L858R/T790M/C797S mutant EGFR-TKIs. The introduction of extra hydrogen bond interaction with mutant Ser797 is efficient method for the design of the fourth-generation EGFR-TKIs.

Exosomal PD-L1 promotes tumor growth through immune escape in non-small cell lung cancer

Programmed cell death protein-1/programmed cell death ligand-1 (PD-1/PD-L1) pathway blockade is a promising new cancer therapy. Although PD-1/PD-L1 treatment has yielded clinical benefits in several types of cancer, further studies are required to clarify predictive biomarkers for drug efficacy and to understand the fundamental mechanism of PD-1/PD-L1 interaction between host and tumor cells. Here, we show that exosomes derived from lung cancer cells express PD-L1 and play a role in immune escape by reducing T-cell activity and promoting tumor growth. The abundance of PD-L1 on exosomes represented the quantity of PD-L1 expression on cell surfaces. Exosomes containing PD-L1 inhibited interferon-gamma (IFN-γ) secretion by Jurkat T cells. IFN-γ secretion was restored by PD-L1 knockout or masking on the exosomes. Both forced expression of PD-L1 on cells without PD-L1 and treatment with exosomes containing PD-L1 enhanced tumor growth in vivo. PD-L1 was present on exosomes isolated from the plasma of patients with non-small cell lung cancer, and its abundance in exosomes was correlated with PD-L1 positivity in tumor tissues. Exosomes can impair immune functions by reducing cytokine production and inducing apoptosis in CD8⁺ T cells. Our findings indicate that tumor-derived exosomes expressing PD-L1 may be an important mediator of tumor immune escape.

An immune suppressant protein expressed by non-small cell lung cancer cells (NSCLC) to facilitate tumor growth could be a valuable therapeutic target. NSCLC is often diagnosed at advanced stages, making treatment challenging. Therapies that inhibit an immune suppressant protein called programmed cell death ligand-1 (PD-L1) have shown promise for other cancers, but how PD-L1 interacts with host and tumor cells in NSCLC needs clarification. In experiments on human cell lines and mice, Jae Cheol Lee and Jin Kyung Rho at the University of Ulsan in Seoul, South Korea, and co-workers found that microvesicles (or ‘exosomes’) released by NSCLC cells carry PD-L1, which interacts with tumor-infiltrating immune cells, inhibiting their activity. The amount of PD-L1 in exosomes directly correlates with PD-L1 expression levels on tumor cell surfaces, providing a useful indication of disease activity.

Comparison of T790M Acquisition Between Patients Treated with Afatinib and Gefitinib as First-Line Therapy: Retrospective Propensity Score Matching Analysis

Afatinib, a second-generation, irreversible pan-HER inhibitor, shows better suppression of T790M-positive lung cancer cells than gefitinib in preclinical studies. However, whether the effect of afatinib on T790M acquisition differs from that of gefitinib when used clinically as first-line therapy remains unclear. To reaffirm the preclinical efficacy of afatinib on T790M-positive lung cancer cells, H1975 cells and established PC-9 cells resistant to gefitinib and erlotinib by T790M were used. In total, 398 patients with second biopsy at progression with stage IIIB/IV non–small cell lung cancer with EGFR mutation, treated with afatinib or gefitinib as first-line therapy, were retrospectively reviewed. Propensity score matching was used to balance covariates. Afatinib inhibited the growth of lung cancer cells with low T790M allele frequencies, which are resistant to gefitinib, but not those with high T790M allele frequencies. Afatinib and gefitinib showed similar efficacy in terms of progression-free survival (PFS) (11.5 vs 13.4 months, P = .08) and overall survival (OS) (29.3 vs 28.5 months, P = .76). T790M patients had better PFS and OS than those without T790M. There was no significant difference in the cumulative T790M acquisition ratio over time between afatinib and gefitinib (48.8% vs 59.3%, P = .317). The median time to acquire T790M was 12.9 months for afatinib and 15.7 months for gefitinib (P = .342). Although afatinib inhibited the growth of lung cancer cells with low T790M allele frequencies in preclinical studies, this could not be translated into clinical efficacy in terms of lowering the rate or delaying the time of T790M acquisition.

Mechanism of Resistance to Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitors and a Potential Treatment Strategy

Treatment with epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) improves the overall survival of patients with EGFR-mutated non-small-cell lung cancer (NSCLC). First-generation EGFR-TKIs (e.g., gefitinib and erlotinib) or second-generation EGFR-TKIs (e.g., afatinib and dacomitinib) are effective for the treatment of EGFR-mutated NSCLC, especially in patients with EGFR exon 19 deletions or an exon 21 L858R mutation. However, almost all cases experience disease recurrence after 1 to 2 years due to acquired resistance. The EGFR T790M mutation in exon 20 is the most frequent alteration associated with the development of acquired resistance. Osimertinib-a third-generation EGFR-TKI-targets the T790M mutation and has demonstrated high efficacy against EGFR-mutated lung cancer. However, the development of acquired resistance to third-generation EGFR-TKI, involving the cysteine residue at codon 797 mutation, has been observed. Other mechanisms of acquired resistance include the activation of alternative pathways or downstream targets and histological transformation (i.e., epithelial⁻mesenchymal transition or conversion to small-cell lung cancer). Furthermore, the development of primary resistance through overexpression of the hepatocyte growth factor and suppression of Bcl-2-like protein 11 expression may lead to problems. In this report, we review these mechanisms and discuss therapeutic strategies to overcome resistance to EGFR-TKIs.

Overexpression of lncRNA EGFR‑AS1 is associated with a poor prognosis and promotes chemotherapy resistance in non‑small cell lung cancer

Chemoresistance is one of the most important biological elements affecting the progression and prognosis of cancer. Long non‑coding RNAs (lncRNAs) are important regulators and are aberrantly expressed in various types of cancer in humans, including non‑small cell lung cancer (NSCLC). The present study aimed to investigate the effect of lncRNAs on NSCLC resistance to chemotherapy. The relative expression level of epidermal growth factor receptor antisense RNA 1 (EGFR‑AS1) was quantified by reverse transcription-quantitative polymerase chain reaction analysis in NSCLC tissues, paired adjacent normal tissues, patient plasma and NSCLC cell lines, and its association with prognosis was assessed by multivariate analysis. The biological functions of EGFR‑AS1 in NSCLC cells were determined in vitro. It was found that EGFR‑AS1 was abnormally upregulated in NSCLC tissues compared with adjacent normal lung tissues. Furthermore, patients with NSCLC with increased expression of EGFR‑AS1 had a poor prognosis. EGFR‑AS1 knockdown significantly inhibited NSCLC malignancy in vitro, including cell proliferation and chemoresistance. Furthermore, the expression levels of EGFR‑AS1 were increased in plasma samples from patients with cisplatin-based chemotherapy resistance. Bioinformatics analysis and a luciferase reporter assay confirmed that EGFR‑AS1 mediated cell proliferation and chemoresistance through directly binding to microRNA‑223. Therefore, EGFR‑AS1 overexpression-induced chemoresistance can contribute to poor prognosis in NSCLC.

[Mechanisms of Resistance to the Third-generation Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitors in Non-small Cell Lung Cancer]

表皮生长因子受体酪氨酸激酶抑制剂（epidermal growth factor receptor-tyrosine kinase inhibitors, EGFRTKIs）靶向治疗已成为EGFR基因突变晚期非小细胞肺癌（non-small cell lung cancer, NSCLC）患者的一线治疗方法。第三代EGFR-TKIs用于一、二代TKIs耐药EGFR T790M突变NSCLC的治疗，给晚期肺癌患者带来更多的生存获益。然而，第三代EGFR-TKIs应用一段时间后不可避免地会出现耐药。肿瘤的异质性决定了耐药机制的多样性，第三代EGFR-TKIs的耐药包括依赖EGFR通路（新发突变、T790M减少或消失和EGFR基因扩增等）和不依赖EGFR通路（旁路途径的激活和细胞表型的转变）两大类，现就此问题进行简单的综述。

Therapeutic approaches for T790M mutation positive non-small-cell lung cancer

INTRODUCTION

Epidermal growth factor receptor (EGFR) mutation positive non-small cell lung cancer (NSCLC) is a subset of lung cancer with demonstrated response to targeted therapies. However, resistance to the first targeted approach usually occurs within the first year, and it is associated in 50-60% of cases to the T790M resistance mutation. Areas covered: The review provides an overview on the significance of the presence of the T790M mutation, its detection, treatment options and subsequent mechanisms of resistance. Expert commentary: Osimertinib is the current treatment option for T790M mutation positive NSCLC after progression to first or second-generation EGFR TKIs, with activity also on brain metastasis. However, the scenario is in continuous evolution and results from clinical trials are awaited in first-line setting and in combination strategies.

Resistance to gefitinib and cross-resistance to irreversible EGFR-TKIs mediated by disruption of the Keap1-Nrf2 pathway in human lung cancer cells

The development of resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) occurs by various mechanisms and appears to be almost inevitable, even in patients with lung cancer who initially respond well to EGFR-TKIs. Consequently, considerable efforts have been made to develop more effective EGFR-TKIs. Therefore, an understanding of the mechanisms behind TKI resistance is essential for improving EGFR-TKI therapeutic efficacy in non-small cell lung cancer (NSCLC) patients. In this study, we discovered that overexpression of antioxidant-responsive element (ARE)-containing Nrf2 target genes by increased transactivation of Nrf2 occurred because of an acquired Keap1 mutation in the gefitinib-resistant (GR) NSCLC cell line we established. These GR cells also acquired cross-resistance to the irreversible EGFR-TKIs, afatinib and osimertinib, and showed increased viability, invasiveness, proliferation, and tumorigenicity both in vitro and in vivo. These results were confirmed by the fact that inhibition of Nrf2 activity, either by treatment with brusatol or by inducing expression of exogenously introduced wild-type Keap1, suppressed tumor cell proliferation and tumorigenicity in vitro and in vivo. Our data suggest that disruption of the Keap1-Nrf2 pathway is one of the mechanisms by which EGFR-TKI resistance occurs, a fact that must be considered when treating patients with EGFR-TKI.-Park, S.-H., Kim, J. H., Ko, E., Kim, J.-Y., Park, M.-J., Kim, M. J., Seo, H., Li, S., Lee, J.-Y. Resistance to gefitinib and cross-resistance to irreversible EGFR-TKIs mediated by disruption of the Keap1-Nrf2 pathway in human lung cancer cells.

IGF1R depletion facilitates MET-amplification as mechanism of acquired resistance to erlotinib in HCC827 NSCLC cells

EGFR-mutated non-small cell lung cancer patients experience relapse within 1-2 years of treatment with EGFR-inhibitors, such as erlotinib. Multiple resistance mechanisms have been identified including secondary EGFR-mutations, MET-amplification, and epithelial-mesenchymal transition (EMT). Previous studies have indicated a role of Insulin-like growth factor 1 receptor (IGF1R) in acquired resistance to EGFR-directed drugs as well as in EMT. In the present study, we have investigated the involvement of IGF1R in acquired high-dose erlotinib resistance in the EGFR-mutated lung adenocarcinoma cell line HCC827. We observed that IGF1R was upregulated in the immediate response to erlotinib and hyperactivated in erlotinib resistant HCC827 cells. Resistant cells additionally acquired features of EMT, whereas MET-amplification and secondary EGFR-mutations were absent. Using CRISPR/Cas9, we generated a HCC827(IGFR1-/-) cell line and subsequently investigated resistance development in response to high-dose erlotinib. Interestingly, HCC827(IGFR1-/-) cells were now observed to specifically amplify the MET gene. Additionally, we observed a reduced level of mesenchymal markers in HCC827(IGFR1-/-) indicating an intrinsic enhanced epithelial signature compared to HCC827 cells. In conclusion, our data show that IGF1R have an important role in defining selected resistance mechanisms in response to high doses of erlotinib.

Afatinib in advanced NSCLC: a profile of its use

Afatinib [Giotrif^® (EU); Gilotrif^® (USA)] is an orally administered, irreversible inhibitor of the ErbB family of tyrosine kinases that provides an important first-line treatment option for advanced non-small cell lung cancer (NSCLC) with activating epidermal growth factor receptor (EGFR) mutations (i.e. EGFR^actMUT+), and an additional treatment option for squamous NSCLC that has progressed following first-line platinum-based chemotherapy. Relative to gefitinib in the first-line treatment of EGFR^actMUT+ advanced lung adenocarcinoma, afatinib prolonged progression-free survival (PFS) and time to treatment failure (TTF), but not overall survival (OS). Afatinib also prolonged PFS, but not OS, versus cisplatin-based chemotherapy in this setting; however, afatinib improved OS versus chemotherapy in the subgroup of patients with deletions in exon 19. As a second-line treatment for advanced squamous NSCLC, afatinib prolonged PFS and OS compared with erlotinib, regardless of EGFR mutation status. Afatinib had a predictable and manageable tolerability profile.

Gallic acid inhibition of Src-Stat3 signaling overcomes acquired resistance to EGF receptor tyrosine kinase inhibitors in advanced non-small cell lung cancer

Tyrosine kinase inhibitors (TKIs) targeting epidermal growth factor receptor (EGFR) have clinically benefited to lung cancer patients harboring a subset of activating EGFR mutations. However, even with the remarkable therapeutic response at the initial TKI treatment, most lung cancer patients eventually have relapsed aggressive tumors due to acquired resistance to the TKIs. Here, we report that 3, 4, 5-trihydroxybenzoic acid or gallic acid (GA), a natural polyphenolic compound, shows anti-tumorigenic effects in TKI-resistant non-small cell lung cancer (NSCLC). Using both in vitro growth assay and in vivo xenograft animal model, we demonstrated tumor suppressive effect of GA was more selective for the TKI-resistant cancer compared to the TKI-sensitive one. Mechanistically, GA treatment inhibited Src-Stat3-mediated signaling and decreased the expression of Stat3-regulated tumor promoting genes, subsequently inducing apoptosis and cell cycle arrest in the TKI-resistant lung cancer but not in the TKI-sensitive one. Consistent with the in vitro results, in vivo xenograft experiments showed the TKI-resistant tumor-selective growth inhibition and suppression of Src-Stat3-dependent signaling in the GA-treated tumors isolated from the xenograft model. This finding identified an importance of Src-Stat3 signaling cascade in GA-mediated tumor-suppression activity and, more importantly, provides a novel therapeutic insight of GA for advanced TKI-resistant lung cancer.

Recent Progress of Small-Molecule Epidermal Growth Factor Receptor (EGFR) Inhibitors against C797S Resistance in Non-Small-Cell Lung Cancer

The epidermal growth factor receptor (EGFR) has been a particular interest for drug development for treatment of non-small-cell lung cancer (NSCLC). The current third-generation EGFR small-molecule inhibitors, especially osimertinib, are at the forefront clinically for treatment of patients with NSCLC. However, a high percentage of these treated patients developed a tertiary cystein-797 to serine-790 (C797S) mutation in the EGFR kinase domain. This C797S mutation is thought to induce resistance to all current irreversible EGFR TKIs. In this Miniperspective, we present key mechanisms of resistance in response to third-generation EGFR TKIs, and emerging reports on novel EGFR TKIs to combat the resistance. Specifically, we analyze the allosteric and ATP-competitive inhibitors in terms of drug discovery, binding mechanism, and their potency and selectivity against EGFR harboring C797S mutations. Lastly, we provide some perspectives on new challenges and future directions in this field.

Mechanisms of resistance to irreversible epidermal growth factor receptor tyrosine kinase inhibitors and therapeutic strategies in non-small cell lung cancer

Epidermal growth factor receptor (EGFR) T790M mutation is the most frequent mechanism which accounts for about 60% of acquired resistance to first-generation EGFR tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) patients harboring EGFR activating mutations. Irreversible EGFR-TKIs which include the second-generation and third-generation EGFR-TKIs are developed to overcome T790M mediated resistance. The second-generation EGFR-TKIs inhibit the wide type (WT) EGFR combined with dose-limiting toxicity which limits its application in clinics, while the development of third-generation EGFR-TKIs brings inspiring efficacy either in vitro or in vivo. The acquired resistance, however, will also occur and limit their response. Understanding the mechanisms of resistance to irreversible EGFR-TKIs plays an important role in the choice of subsequent treatment. In this review, we show the currently known mechanisms of resistance which can be summarized as EGFR dependent and independent mechanisms and potential therapeutic strategies to irreversible EGFR-TKIs.

Insulin-Like Growth Factor (IGF) Pathway Targeting in Cancer: Role of the IGF Axis and Opportunities for Future Combination Studies

Despite a strong preclinical rationale for targeting the insulin-like growth factor (IGF) axis in cancer, clinical studies of IGF-1 receptor (IGF-1R)-targeted monotherapies have been largely disappointing, and any potential success has been limited by the lack of validated predictive biomarkers for patient enrichment. A large body of preclinical evidence suggests that the key role of the IGF axis in cancer is in driving treatment resistance, via general proliferative/survival mechanisms, interactions with other mitogenic signaling networks, and class-specific mechanisms such as DNA damage repair. Consequently, combining IGF-targeted agents with standard cytotoxic agents, other targeted agents, endocrine therapies, or immunotherapies represents an attractive therapeutic approach. Anti-IGF-1R monoclonal antibodies (mAbs) do not inhibit IGF ligand 2 (IGF-2) activation of the insulin receptor isoform-A (INSR-A), which may limit their anti-proliferative activity. In addition, due to their lack of specificity, IGF-1R tyrosine kinase inhibitors are associated with hyperglycemia as a result of interference with signaling through the classical metabolic INSR-B isoform; this may preclude their use at clinically effective doses. Conversely, IGF-1/IGF-2 ligand-neutralizing mAbs inhibit proliferative/anti-apoptotic signaling via IGF-1R and INSR-A, without compromising the metabolic function of INSR-B. Therefore, combination regimens that include these agents may be more efficacious and tolerable versus IGF-1R-targeted combinations. Herein, we review the preclinical and clinical experience with IGF-targeted therapies to-date, and discuss the rationale for future combination approaches as a means to overcome treatment resistance.

Acquisition of EGFR TKI resistance and EMT phenotype is linked with activation of IGF1R/NF-κB pathway in EGFR-mutant NSCLC

Epithelial-mesenchymal transition (EMT) is clinically associated with acquired resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI) in non-small cell lung cancers (NSCLC). However, the mechanisms promoting EMT in EGFR TKI-resistant NSCLC have not been fully elucidated. Previous studies have suggested that IGF1R signaling is involved in both acquired EGFR TKI resistance in NSCLC and induction of EMT in some types of tumor. In this study, we further explored the role of the IGF1R signaling in the acquisition of EMT phenotype associated with EGFR TKI resistance in mutant-EGFR NSCLC. Compared to gefitinib-sensitive parental cells, gefitinib-resistant (GR) cells displayed an EMT phenotype associated with increased migration and invasion abilities with the concomitant activation of IGF1R and NF-κB p65 signaling. Inhibition of IGF1R or p65 using pharmacological inhibitor or specific siRNA partially restored sensitivity to gefitinib with the concomitant reversal of EMT in GR cells. Conversely, exogenous IGF1 induced both gefitinib resistance and accompanying EMT in parental cells. We also demonstrated that IGF1R could phosphorylate downstream Akt and Erk to activate NF-κB p65. Taken together, our findings indicate that activation of IGF1R/Akt/Erk/NF-κB signaling is linked to the acquisition of EGFR TKI resistance and EMT phenotype in EGFR-mutant NSCLC and could be a novel therapeutic target for advanced NSCLC.

Can we define the optimal sequence of epidermal growth factor receptor tyrosine kinase inhibitors for the treatment of epidermal growth factor receptor-mutant nonsmall cell lung cancer?

PURPOSE OF REVIEW

The most common mechanism of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) is acquisition of the T790M gatekeeper mutation. Third-generation EGFR TKIs irreversibly inhibit EGFR mutants (EGFRm), especially T790M, while sparing wild-type EGFR. There are several third-generation EGFR TKIs under development, including osimertinib, CO-1686 (rociletinib), HM61713 (olmutinib), ASP8273, and EGF816. These third-generation EGFR TKIs have shown promising efficacy with favorable toxicity profiles in the management of advanced nonsmall cell lung cancer (NSCLC) with an acquired T790M mutation (EGFR). In the present review, we will discuss the evolving treatment landscape of EGFRm NSCLC.

RECENT FINDINGS

The LUX-Lung 7 study demonstrated superior progression-free survival, time-to-treatment failure, and objective response rate with afatinib versus gefitinib, but no significant overall survival improvement in TKI-naïve EGFRm NSCLC patients. In EGFRm NSCLC patients harboring T790M after treatment with first-generation or second-generation EGFR TKIs, third-generation EGFR TKIs showed robust efficacy with tolerable toxicity. The updated results of phase I studies have demonstrated encouraging activity of first-line osimertinib in patients with EGFRm NSCLC.

SUMMARY

Following progression with first-generation or second-generation EGFR TKIs, osimertinib was recently approved for the treatment of EGFR NSCLC. Encouraging early results with osimertinib have sparked interest in first-line treatment of EGFRm NSCLC, and head-to-head comparison studies of third-generation versus first-generation EGFR TKIs are being developed.