A drug resistance screen using a selective MET inhibitor reveals a spectrum of mutations that partially overlap with activating mutations found in cancer patients

Case report: Acquired resistance to crizotinib from a MET Y1230H mutation in a patient with non-small cell lung cancer and KIF5B-MET fusion

Background

The c-met proto-oncogene (MET) serves as a significant primary oncogenic driver in non-small cell lung cancer (NSCLC) and has the potential to fuse with other genes, such as KIF5B, although it occurs infrequently. Only a limited number of reported cases have examined the clinical efficacy of crizotinib in patients with KIF5B-MET gene fusion, with no known data regarding acquired resistance to crizotinib and its potential mechanisms. In this report, we present the clinical progression of a female patient diagnosed with NSCLC and harboring a KIF5B-MET gene fusion.

Case description

The patient initially exhibited partial response to first-line crizotinib treatment, albeit for a short duration and with limited efficacy. Subsequent disease progression revealed the emergence of a secondary MET mutation, specifically MET Y1230H, leading to acquired resistance to crizotinib.

Conclusion

The reporting of this case is imperative for informing clinical practice, given the uncommon occurrence of NSCLC with MET fusion, displaying responsiveness to MET tyrosine kinase inhibitor therapy, as well as the emergence of the secondary Y1230H alteration as a potential resistance mechanism.

Molecular features and clinical outcomes of EGFR-mutated, MET-amplified non-small-cell lung cancer after resistance to dual-targeted therapy

Background

Some studies of dual-targeted therapy (DTT) targeting epidermal growth factor receptor (EGFR) and mesenchymal-epithelial transition (MET) have shown promising efficacy in non-small-cell lung cancer (NSCLC). Consequently, patient management following DTT resistance has gained significance. However, the underlying resistance mechanisms and clinical outcomes in these patients remain unclear.

Objectives

This study aimed to delineate the molecular characteristics and survival outcomes of patients with NSCLC harboring EGFR mutations and acquired MET amplification after developing resistance to DTT.

Design

We conducted a retrospective analysis of patients with NSCLC with EGFR mutations and acquired MET amplification who exhibited resistance to EGFR/MET DTT.

Methods

Next-generation sequencing (NGS) was performed on patients with available tissue samples before and/or after the development of resistance to DTT. Stratified analyses were carried out based on data sources and subsequent salvage treatments. Univariate/multivariate Cox regression models and survival analyses were employed to explore potential independent prognostic factors.

Results

The study included 77 NSCLC patients, with NGS conducted on 19 patients. We observed many resistance mechanisms, including EGFR-dependent pathways (4/19, 21.1%), MET-dependent pathways (2/19, 10.5%), EGFR/MET co-dependent pathways (2/19, 10.5%), and EGFR/MET-independent resistance mechanisms (11/19, 57.9%). Post-progression progression-free survival (pPFS) and post-progression overall survival (pOS) significantly varied among patients who received the best supportive care (BSC), targeted therapy, or chemotherapy (CT), with median pPFS of 1.5, 3.9, and 4.9 months, respectively (p = 0.003). Median pOS were 2.3, 7.7, and 9.2 months, respectively (p < 0.001). The number of treatment lines following DTT resistance and the Eastern Cooperative Oncology Group performance status emerged as the independent prognostic factors.

Conclusion

This study revealed a heterogeneous landscape of resistance mechanisms to EGFR/MET DTT, with a similar prevalence of on- and off-target mechanisms. Targeted therapy or CT, as compared to BSC, exhibited the potential to improve survival outcomes for patients with advanced NSCLC following resistance to DTT.

Biophysical and structural characterization of the impacts of MET phosphorylation on tepotinib binding

The receptor tyrosine kinase MET is activated by hepatocyte growth factor binding, followed by phosphorylation of the intracellular kinase domain (KD) mainly within the activation loop (A-loop) on Y1234 and Y1235. Dysregulation of MET can lead to both tumor growth and metastatic progression of cancer cells. Tepotinib is a highly selective, potent type Ib MET inhibitor and approved for treatment of non-small cell lung cancer harboring METex14 skipping alterations. Tepotinib binds to the ATP site of unphosphorylated MET with critical π-stacking contacts to Y1230 of the A-loop, resulting in a high residence time. In our study, we combined protein crystallography, biophysical methods (surface plasmon resonance, differential scanning fluorimetry), and mass spectrometry to clarify the impacts of A-loop conformation on tepotinib binding using different recombinant MET KD protein variants. We solved the first crystal structures of MET mutants Y1235D, Y1234E/1235E, and F1200I in complex with tepotinib. Our biophysical and structural data indicated a linkage between reduced residence times for tepotinib and modulation of A-loop conformation either by mutation (Y1235D), by affecting the overall Y1234/Y1235 phosphorylation status (L1195V and F1200I) or by disturbing critical π-stacking interactions with tepotinib (Y1230C). We corroborated these data with target engagement studies by fluorescence cross-correlation spectroscopy using KD constructs in cell lysates or full-length receptors from solubilized cellular membranes as WT or activated mutants (Y1235D and Y1234E/1235E). Collectively, our results provide further insight into the MET A-loop structural determinants that affect the binding of the selective inhibitor tepotinib.

MET in Non-Small-Cell Lung Cancer (NSCLC): Cross 'a Long and Winding Road' Looking for a Target

Non-Small-Cell Lung Cancer (NSCLC) can harbour different MET alterations, such as MET overexpression (MET OE), MET gene amplification (MET AMP), or MET gene mutations. Retrospective studies of surgical series of patients with MET-dysregulated NSCLC have shown worse clinical outcomes irrespective of the type of specific MET gene alteration. On the other hand, earlier attempts failed to identify the 'druggable' molecular gene driver until the discovery of MET exon 14 skipping mutations (METex14). METex14 are rare and amount to around 3% of all NSCLCs. Patients with METex14 NSCLC attain modest results when they are treated with immune checkpoint inhibitors (ICIs). New selective MET inhibitors (MET-Is) showed a long-lasting clinical benefit in patients with METex14 NSCLC and modest activity in patients with MET AMP NSCLC. Ongoing clinical trials are investigating new small molecule tyrosine kinase inhibitors, bispecific antibodies, or antibodies drug conjugate (ADCs). This review focuses on the prognostic role of MET, the summary of pivotal clinical trials of selective MET-Is with a focus on resistance mechanisms. The last section is addressed to future developments and challenges.

Resistance to MET inhibition in MET-dependent NSCLC and therapeutic activity after switching from type I to type II MET inhibitors

OBJECTIVES

Resistance to MET inhibition occurs inevitably in MET-dependent non-small cell lung cancer and the underlying mechanisms are insufficiently understood. We describe resistance mechanisms in patients with MET exon 14 skipping mutation (METΔ^ex14), MET amplification, and MET fusion and report treatment outcomes after switching therapy from type I to type II MET inhibitors.

MATERIALS AND METHODS

Pre- and post-treatment biopsies were analysed by NGS (next generation sequencing), digital droplet PCR (polymerase chain reaction), and FISH (fluorescense in situ hybridization). A patient-derived xenograft model was generated in one case.

RESULTS

Of 26 patients with MET tyrosine kinase inhibitor treatment, eight had paired pre- and post-treatment biopsies (Three with MET amplification, three with METΔ^ex14, two with MET fusions (KIF5B-MET and PRKAR2B-MET).) In six patients, mechanisms of resistance were detected, whereas in two cases, the cause of resistance remained unclear. We found off-target resistance mechanisms in four cases with KRAS mutations and HER2 amplifications appearing. Two patients exhibited second-site MET mutations (p.D1246N and p. Y1248H). Three patients received type I and type II MET tyrosine kinase inhibitors sequentially. In two cases, further progressive disease was seen hereafter. The patient with KIF5B-MET fusion received three different MET inhibitors and showed long-lasting stable disease and a repeated response after switching therapy, respectively.

CONCLUSION

Resistance to MET inhibition is heterogeneous with on- and off-target mechanisms occurring regardless of the initial MET aberration. Switching therapy between different types of kinase inhibitors can lead to repeated responses in cases with second-site mutations. Controlled clinical trials in this setting with larger patient numbers are needed, as evidence to date is limited to preclinical data and case series.

Mutations in the MET tyrosine kinase domain and resistance to tyrosine kinase inhibitors in non-small-cell lung cancer

BACKGROUND

The Mesenchymal epithelial transition factor (MET) gene encodes a receptor tyrosine kinase with pleiotropic functions in cancer. MET exon 14 skipping alterations and high-level MET amplification are oncogenic and targetable genetic changes in patients with non-small-cell lung cancer (NSCLC). Resistance to tyrosine kinase inhibitors (TKIs) has been a major challenge for targeted therapies that impairs their clinical efficacies.

METHODS

Eighty-six NSCLC patients were categorized into three cohorts based on the time of detecting MET tyrosine kinase domain (TKD) mutations (cohort 1: at baseline; cohort 2: after MET-TKI treatment; cohort 3: after EGFR-TKI treatment). Baseline and paired TKI treatment samples were analyzed by targeted next-generation sequencing.

RESULTS

MET TKD mutations were highly prevalent in METex14-positive NSCLC patients after MET-TKI treatment, including L1195V, D1228N/H/Y/E, Y1230C/H/N/S, and a double-mutant within codons D1228 and M1229. Missense mutations in MET TKD were also identified at baseline and in post-EGFR-TKI treatment samples, which showed different distribution patterns than those in post-MET-TKI treatment samples. Remarkably, H1094Y and L1195F, absent from MET-TKI-treated patients, were the predominant type of MET TKD mutations in patients after EGFR-TKI treatment. D1228H, which was not found in treatment-naïve patients, also accounted for 14.3% of all MET TKD mutations in EGFR-TKI-treated samples. Two patients with baseline EGFR-sensitizing mutations who acquired MET-V1092I or MET-H1094Y after first-line EGFR-TKI treatment experienced an overall improvement in their clinical symptoms, followed by targeted therapy with MET-TKIs.

CONCLUSIONS

MET TKD mutations were identified in both baseline and patients treated with TKIs. MET-H1094Y might play an oncogenic role in NSCLC and may confer acquired resistance to EGFR-TKIs. Preliminary data indicates that EGFR-mutated NSCLC patients who acquired MET-V1092I or MET-H1094Y may benefit from combinatorial therapy with EGFR-TKI and MET-TKI, providing insights into personalized medical treatment.

The multi-molecular mechanisms of tumor-targeted drug resistance in precision medicine

Clinically, cancer drug therapy is still dominated by chemotherapy drugs. Although the emergence of targeted drugs has greatly improved the survival rate of patients with advanced cancer, drug resistance has always been a difficult problem in clinical cancer treatment. At the current level of medicine, most drugs cannot escape the fate of drug resistance. With the emergence and development of gene detection, liquid biopsy ctDNA technology, and single-cell sequencing technology, the molecular mechanism of tumor drug resistance has gradually emerged. Drugs can also be updated in response to drug resistance mechanisms and bring higher survival benefits. The use of new drugs often leads to new mechanisms of resistance. In this review, the multi-molecular mechanisms of drug resistance are introduced, and the overcoming of drug resistance is discussed from the perspective of the tumor microenvironment.

Met inhibitors in the treatment of lung cancer: the evidence to date

INTRODUCTION

: The hepatocyte growth factor (HGF) receptor MET is an oncogenic driver in a subpopulation of Non-small Lung Cancer Cells (NSCLC) at the primary tumor stage or in acquired resistance to treatment with tumor-targeting tyrosine kinase inhibitors (TKIs).

AREAS COVERED

This article summarizes the mechanisms leading to overexpression and activation of MET by amplification and mutations including exon 14 aberrations. Furthermore, the methods to detect and categorize MET as a tumor driver and the selective TKIs for patient treatment are discussed.

EXPERT OPINION

: Activating mutations and rearrangements of kinases in NSCLC are the target of successful therapeutic intervention. However, MET activation involves a number of complex alterations including gene amplification, prevention of degradation by METex14 exon skipping and a host of gene mutations. A high-level of MET expression is the precondition for tumor responses to TKIs and the confirmation of MET-dependent tumor progression is difficult in primary lesions and in tumors exhibiting resistance to mutated EGFR-directed therapy in absence of standardized and concordant assays of MET amplification.

KRAS and MET in non-small-cell lung cancer: two of the new kids on the 'drivers' block

Non-small-cell lung cancer (NSCLC) is a heterogeneous disease, and therapeutic management has advanced to identify various critical oncogenic mutations that promote lung cancer tumorigenesis. Subsequent studies have developed targeted therapies against these oncogenes in the hope of personalized treatment based on the tumor's molecular genomics. This review presents a comprehensive review of the biology, new therapeutic interventions, and resistance patterns of two well-defined subgroups, tumors with KRAS and MET alterations. We also discuss the status of molecular testing practices for these two key oncogenic drivers, considering the progressive introduction of next-generation sequencing (NGS) and RNA sequencing in regular clinical practice.

Case Report: Sequential Combination Targeted Therapy With Type I and II MET Inhibitors in a Metastatic EGFR-Mutated, MET-Amplified NSCLC Patient With Acquired MET Y1230H Mutation

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are the standard of care for advanced non-small-cell lung cancer (NSCLC) patients. However, most patients will eventually develop resistance. For EGFR-TKI resistance mediated by MET amplification, the combination of EGFR and MET TKIs has shown promising results in early clinical trials. However, acquired resistance to MET inhibitors forms a formidable challenge to this dual blockade approach. Here, we presented an NSCLC patient with EGFR exon 19 deletion (ex19del) who was resistant to first-line erlotinib treatment but responded to chemotherapy. Given the finding of MET overexpression/amplification after disease progression, the patient received gefitinib plus crizotinib with a partial response. Her disease progressed again, and molecular testing revealed a novel MET Y1230H mutation and a PD-L1 TPS score of 75%. She received a salvage regime consisting of gefitinib, cabozantinib, and pembrolizumab with a partial response. Since we now know that EGFR ex19del NSCLC patients generally do not respond to PD-1 blockade therapy, this response is more likely the contribution from gefitinib plus cabozantinib. Therefore, sequential use of type I and II MET inhibitors in EGFR/MET dual blockade may be an effective therapeutic option for EGFR-mutant, MET-amplified NSCLC.

Targeted Treatment of Non-Small Cell Lung Cancer: Focus on Capmatinib with Companion Diagnostics

MET dysregulation promoting tumorigenesis in non-small cell lung cancer (NSCLC) is associated with worse outcomes following chemotherapy as compared to non-driver mutated NSCLC and occurs either through mutations causing MET exon 14 skipping (METex14) or gene amplification and overexpression that result in enhanced receptor signaling. Capmatinib is the first FDA-approved targeted therapy for NSCLC with METex14 skipping mutations, approved in 2020. FoundationOne^® CDx, a comprehensive genomic profiling test for solid tumors, was concurrently approved as a companion diagnostic for capmatinib use. The GEOMETRY mono-1 phase II trial of capmatinib monotherapy demonstrated an overall response rate (ORR) of 68% in treatment naïve (n=28) and 41% in pre-treated (n=69) METex14 skipping advanced NSCLC; in MET amplified advanced NSCLC (gene copy number ≥ 10) ORRs of 40% in treatment naïve and 29% in pre-treated disease was seen. This review outlines the clinical data supporting capmatinib approval in the treatment of NSCLC and FoundationOne^® CDx approval as a companion diagnostic. We detail the practical clinical administration of capmatinib, including dosing and toxicity management, compare capmatinib to other approved and investigational MET-targeted therapies, discuss limitations of capmatinib, and highlight ongoing trials of capmatinib in combinatorial approaches.

Combination of type I and type II MET tyrosine kinase inhibitors as therapeutic approach to prevent resistance

MET targeted therapies are clinically effective in MET amplified and MET exon 14 deletion mutant (METex14) non-small cell lung cancers (NSCLC) but their efficacy is limited by the development of drug resistance. Structurally distinct MET tyrosine kinase inhibitors (TKIs) (type I/II) have been developed or are under clinical evaluation, which may overcome MET mediated drug resistance mechanisms. In this study, we assess secondary MET mutations likely to emerge in response to treatment with single-agent or combinations of type I/type II MET TKIs using TPR-MET transformed Ba/F3 cell mutagenesis assays. We found that these inhibitors gave rise to distinct secondary MET mutant profiles. However, a combination of type I/II TKI inhibitors (capmatinib and merestinib) yielded no resistant clones in vitro. The combination of capmatinib/merestinib was evaluated in vivo and led to a significant reduction in tumor outgrowth compared to either MET inhibitor alone. Our findings demonstrate in vitro and in vivo that a simultaneous treatment with a type I and type II MET TKI may be a clinically viable approach to delay and/or diminish the emergence of on target MET mediated drug resistance mutations.

Therapeutic strategies in METex14 skipping mutated non-small cell lung cancer

METex14 skipping mutations occur in about 3–4% of lung adenocarcinoma patients and 1–2% of patients with other lung cancer histology. The MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) are established oncogenic drivers of NSCLC. A mutation that results in loss of exon 14 in the MET gene leads to dysregulation and inappropriate signaling that is associated with increased responsiveness to MET TKIs. Results from GEOMETRY mono-1 and VISION Phase I/II clinical trials demonstrated significant clinical activity in patients treated with the MET Exon 14 skipping mutation inhibitors capmatinib and tepotinib with tolerable toxicity profile. In the GEOMETRY mono-1 trial, capmatinib was especially active in treatment-naïve patients supporting the upfront testing of this oncogenic driver. Tepotinib demonstrated superior activity in the pretreated patients in the VISION trial. Savolitinib is another MET TKI that has shown efficacy in the first- and second-line settings, including patients with aggressive pulmonary sarcomatoid carcinoma. These studies have demonstrated that these TKIs can cross the blood brain barrier and demonstrated some activity toward CNS metastases. MET Exon 14 skipping mutation is detected by NGS-based testing of liquid or tissue biopsies, with preference for RNA-based NGS. The activity of capmatinib and tepotinib is limited by the development of acquired resistance. Current research is focused on strategies to overcome resistance and improve the effectiveness of these agents. Our aim is to review the current status of MET Exon 14 skipping mutation as it pertains NSCLC.

MET D1228N and D1246N are the Same Resistance Mutation in MET Exon 14 Skipping

Comprehensive genetic profiling using next-generation sequencing technologies has become an integral part of precision oncology. Variant annotation requires translating the DNA findings into protein level predictions. In this article we highlight inconsistencies in variant annotation for the MET D1228N exon 19 resistance mutations. MET D1228N and D1246N represent the same resistance mutation in MET exon 14 skipping alterations annotated on different transcripts. Additional examples of relevant variants annotated on different transcripts emphasize the importance of avoiding erroneous interpretation when realizing precision oncology.

Novel Therapies for Metastatic Non-Small Cell Lung Cancer with MET Exon 14 Alterations: A Spotlight on Capmatinib

MET exon 14 (METex14) alterations are now an established therapeutically tractable target in non-small cell lung cancer (NSCLC). Recently reported trials of several MET tyrosine kinase inhibitors (TKI) in this patient population have demonstrated promising efficacy data in both the treatment naïve and pre-treated settings and have led to regulatory approvals. This review will focus on practical diagnostic considerations for METex14 alterations, the trial evidence for capmatinib in this molecular subset including dosing and toxicity management, and the future therapeutic landscape of METex14 altered NSCLC.

Non-small cell lung cancer with MET exon 14 skipping alteration responding to immunotherapy: a case report

Immunotherapy has been proved to be a promising candidate for advanced non-small cell lung cancer (NSCLC). Despite MET mutations are regarded as an independent factor of programmed death ligand 1 (PD-L1) high expression, the efficacy of immune checkpoint inhibitors (ICIs) across NSCLC harboring Mesenchymal-epithelial transition factor exon 14 skipping alteration (METex14) is still uncleared. Moreover, when the resistance of PD-1 antibody occurs, the questions of how to interpret the resistance and how to overcome the resistance are worth exploring. We report a case of NSCLC with METex14 developed a right femoral metastasis after responding well to neoadjuvant immunotherapy, a successful lobectomy, and adjuvant immunotherapy. The subsequent attempts of MET targeted inhibitor, concurrent chemoradiotherapy, and notably programmed cell death protein 1 (PD-1) antibody plus vascular endothelial growth factor receptor tyrosine kinase inhibitor (VEGFR-TKI) failed to prevent disease progression. However, a regimen of anti-PD-1 plus anti-cytotoxic t-lymphocyte associated protein 4 (CTLA-4) reversed the progression to a complete response. This case shows that METex14 had a significant response to immunotherapy, which would be especially beneficial for those who developed targeted therapy resistance. Importantly, this is the first case reporting that salvage CTLA-4 antibody and PD-1 antibody could reverse the progression in NSCLC harboring METex14 when the anti-PD-1 resistance occurred.

Synthesis and Anti-Proliferative Evaluations of New Heterocyclic Derivatives Using 5,6,8,9-Tetrahydropyrazolo[5,1-b]quinazolin-7(3H)-one Derivatives Derived from Cyclohexa-1,4-dione

BACKGROUND

Recentlty, pyrazoloquinazoline derivatives acquired a special attention due to their wide range of pharmacological activities, especially therapeutic. Through the market, it was found that many pharmacological drugs containing the quinazoline nucleus were known.

OBJECTIVE

The aim of this work is to synthesize target molecules possessing not only anti-tumor activities but also kinase inhibitors. The target molecules were obtained through the synthesis of a series of 5,6,8,9- tetrahydropyrazolo[5,1-b]quinazolin-7(3H)-one derivatives 4a-i using the multi-component reactions of cyclohexane- 1,4-dione (1), the 5-amino-4-(2-arylhydrazono)-4H-pyrazol-3-ol derivatives 2a-c, the aromatic aldehydes 3a-c, respectively. The synthesized compounds were evaluated against c-Met kinase, PC-3 cell line, and different kinds of cancer cell lines together with normal cell line, tyrosine kinases, and Pim-1 kinase.

METHODS

Multi-component reactions were adopted using compound 1 to get different 5,6,8,9- tetrahydropyrazolo[5,1-b]quinazolin-7(3H)-one derivatives which underwent further heterocyclization reactions. The c-Met kinase activity of all compounds was evaluated using Homogeneous Time-Resolved Fluorescence (HTRF) assay, taking foretinib as the positive control. The anti-proliferative activity of all target compounds against the human prostatic cancer PC-3 cell line was measured using MTT assay using SGI-1776 as the reference drug. All the synthesized compounds were assessed for inhibitory activities against A549 (non-small cell lung cancer), H460 (human lung cancer), HT-29 (human colon cancer), and MKN-45 (human gastric cancer) cancer cell lines together with foretinib as the positive control by an MTT assay.

RESULTS

Antiproliferative evaluations and c-Met kinase, Pim-1 kinase inhibitions were performed for the synthesized compounds, where the varieties of substituents through the aryl ring and the thiophene moiety afforded compounds with high activities.

CONCLUSION

The compounds with high antiproliferative activity were tested towards c-Met and the results showed that compounds 4e, 4f, 4g, 4i, 6i, 6k, 6l, 8f, 8i, 10d, 10e, 10f, 10h, 12e, 12f, 12g, 12h, 12i, 14f, 14g, 14h, and 14i were the most potent compounds. A further selection of compounds for the Pim-1 kinase inhibition activity showed that compounds 4f, 6i, 6l, 8h, 8i, 8g, 10d, 12i, and 14f were the most active compounds to inhibit Pim-1.

The METeoric rise of MET in lung cancer

Over the years, there has been a continuous increase in clinically relevant driver mutations in patients with non-small cell lung cancer (NSCLC). Among these, dysregulated activation of the MET tyrosine kinase receptor has gained importance due to the recent development of quite effective treatments. MET dysregulation encompasses a heterogeneous array of alterations leading to the prolonged activation of the cellular MET (c-MET or MET) receptor and downstream proliferation pathways. It can arise through several mechanisms, including gene amplification, overexpression of the receptor and/or its ligand hepatocyte growth factor, and the acquisition of activating mutations. MET mutations are found in approximately 3% to 5% of patients with NSCLC, mainly adenocarcinoma, and are overrepresented in the sarcomatoid subtype. De novo MET amplifications are found in 1% to 5% of NSCLC cases, also predominantly in adenocarcinoma. In the current review, the authors discussed the biology of MET, how to diagnose clinically relevant alterations, and the rising clinical importance of these alterations in light of the emergence of multiple targeted therapies, both within the context of MET as a driver of resistance and in its own right.

Targeting MET Dysregulation in Cancer

Aberrant MET signaling can drive tumorigenesis in several cancer types through a variety of molecular mechanisms including MET gene amplification, mutation, rearrangement, and overexpression. Improvements in biomarker discovery and testing have more recently enabled the selection of patients with MET-dependent cancers for treatment with potent, specific, and novel MET-targeting therapies. We review the known oncologic processes that activate MET, discuss therapeutic strategies for MET-dependent malignancies, and highlight emerging challenges in acquired drug resistance in these cancers. SIGNIFICANCE: Increasing evidence supports the use of MET-targeting therapies in biomarker-selected cancers that harbor molecular alterations in MET. Diverse mechanisms of resistance to MET inhibitors will require the development of novel strategies to delay and overcome drug resistance.

MET receptor in oncology: From biomarker to therapeutic target

First discovered in the 1984, the MET receptor tyrosine kinase (RTK) and its ligand hepatocyte growth factor or HGF (also known as scatter factor or SF) are implicated as key players in tumor cell migration, proliferation, and invasion in a variety of cancers. This pathway also plays a key role during embryogenesis in the development of muscular and nervous structures. High expression of the MET receptor has been shown to correlate with poor prognosis and resistance to therapy. MET exon 14 splicing variants, initially identified by us in lung cancer, is actionable through various tyrosine kinase inhibitors (TKIs). For this reason, this pathway is of interest as a therapeutic target. In this chapter we will be discussing the history of MET, the genetics of this RTK, and give some background on the receptor biology. Furthermore, we will discuss directed therapeutics, mechanisms of resistance, and the future of MET as a therapeutic target.

MET-dependent solid tumours - molecular diagnosis and targeted therapy

Attempts to develop MET-targeted therapies have historically focused on MET-expressing cancers, with limited success. Thus, MET expression in the absence of a genomic marker of MET dependence is a poor predictor of benefit from MET-targeted therapy. However, owing to the development of more sensitive methods of detecting genomic alterations, high-level MET amplification and activating MET mutations or fusions are all now known to be drivers of oncogenesis. MET mutations include those affecting the kinase or extracellular domains and those that result in exon 14 skipping. The activity of MET tyrosine kinase inhibitors varies by MET alteration category. The likelihood of benefit from MET-targeted therapies increases with increasing levels of MET amplification, although no consensus exists on the optimal diagnostic cut-off point for MET copy number gains identified using fluorescence in situ hybridization and, in particular, next-generation sequencing. Several agents targeting exon 14 skipping alterations are currently in clinical development, with promising data available from early-phase trials. By contrast, the therapeutic implications of MET fusions remain underexplored. Here we summarize and evaluate the utility of various diagnostic techniques and the roles of different classes of MET-targeted therapies in cancers with MET amplification, mutation and fusion, and MET overexpression.

A cell-based high-throughput screen identifies inhibitors that overcome P-glycoprotein (Pgp)-mediated multidrug resistance

Multidrug resistance (MDR) to chemotherapeutic drugs remains one of the major impediments to the treatment of cancer. Discovery and development of drugs that can prevent and reverse the acquisition of multidrug resistance constitute a foremost challenge in cancer therapeutics. In this work, we screened a library of 1,127 compounds with known targets for their ability to overcome Pgp-mediated multidrug resistance in cancer cell lines. We identified four compounds (CHIR-124, Elesclomol, Tyrphostin-9 and Brefeldin A) that inhibited the growth of two pairs of parental and Pgp-overexpressing multidrug-resistant cell lines with similar potency irrespective of their Pgp status. Mechanistically, CHIR-124 (a potent inhibitor of Chk1 kinase) inhibited Pgp activity in both multidrug-resistant cell lines (KB-V1 and A2780-Pac-Res) as determined through cell-based Pgp-efflux assays. Other three inhibitors on the contrary, were effective in Pgp-overexpressing resistant cells without increasing the cellular accumulation of a Pgp substrate, indicating that they overcome resistance by avoiding efflux through Pgp. None of these compounds modulated the expression of Pgp in resistant cell lines. PIK-75, a PI3 Kinase inhibitor, was also determined to inhibit Pgp activity, despite being equally potent in only one of the two pairs of resistant and parental cell lines. Strong binding of both CHIR-124 and PIK-75 to Pgp was predicted through docking studies and both compounds inhibited Pgp in a biochemical assay. The inhibition of Pgp causes accumulation of these compounds in the cells where they can modulate the function of their target proteins and thereby inhibit cell proliferation. In conclusion, we have identified compounds with various cellular targets that overcome multidrug resistance in Pgp-overexpressing cell lines through mechanisms that include Pgp inhibition and efflux evasion. These compounds, therefore, can avoid challenges associated with the co-administration of Pgp inhibitors with chemotherapeutic or targeted drugs such as additive toxicities and differing pharmacokinetic properties.

Mechanisms of Acquired Resistance to Savolitinib, a Selective MET Inhibitor in MET-Amplified Gastric Cancer

PURPOSE

Some gastric cancers harbor MET gene amplifications that can be targeted by selective MET inhibitors to achieve tumor responses, but resistance eventually develops. Savolitinib, a selective MET inhibitor, is beneficial for treating patients with MET-driven gastric cancer. Understanding the resistance mechanisms is important for optimizing postfailure treatment options.

PATIENTS AND METHODS

Here, we identified the mechanisms of acquired resistance to savolitinib in 3 patients with gastric cancer and MET-amplified tumors who showed a clinical response and then cancer progression. Longitudinal circulating tumor DNA (ctDNA) is useful for monitoring resistance during treatment and progression when rebiopsy cannot be performed.

RESULTS

Using a next-generation sequencing 100-gene panel, we identified the target mechanisms of resistance MET D1228V/N/H and Y1230C mutations or high copy number MET gene amplifications that emerge when resistance to savolitinib develops in patients with MET-amplified gastric cancer.

CONCLUSION

We demonstrated the utility of ctDNA in gastric cancer and confirmed this approach using baseline tumor tissue or rebiopsy.

Molecular Mechanisms of Acquired Resistance to MET Tyrosine Kinase Inhibitors in Patients with MET Exon 14-Mutant NSCLC

PURPOSE

Molecular mechanisms of acquired resistance to MET tyrosine kinase inhibitors (TKI) are poorly understood. We aimed to characterize the genomic mechanisms of resistance to type I and type II MET TKIs and their impact on sequential MET TKI therapy outcomes in patients with metastatic MET exon 14-mutant NSCLC.

EXPERIMENTAL DESIGN

Genomic alterations occurring at the time of progression on MET TKIs were studied using plasma and tissue next-generation sequencing (NGS).

RESULTS

A total of 20 patients had tissue or plasma available for analysis at the time of acquired resistance to a MET TKI. Genomic alterations known or suspected to be mechanisms of resistance were detected in 15 patients (75%). On-target acquired mechanisms of resistance, including single and polyclonal MET kinase domain mutations in codons H1094, G1163, L1195, D1228, Y1230, and high levels of amplification of the MET exon 14-mutant allele, were observed in 7 patients (35%). A number of off-target mechanisms of resistance were detected in 9 patients (45%), including KRAS mutations and amplifications in KRAS, EGFR, HER3, and BRAF; one case displayed both on- and off-target mechanisms of resistance. In 2 patients with on-target resistant mutations, switching between type I and type II MET TKIs resulted in second partial responses.

CONCLUSIONS

On-target secondary mutations and activation of bypass signaling drive resistance to MET TKIs. A deeper understanding of these molecular mechanisms can support the development of sequential or combinatorial therapeutic strategies to overcome resistance.

Defining the landscape of ATP-competitive inhibitor resistance residues in protein kinases

Kinases are involved in disease development and modulation of their activity can be therapeutically beneficial. Drug-resistant mutant kinases are valuable tools in drug discovery efforts, but the prediction of mutants across the kinome is challenging. Here, we generate deep mutational scanning data to identify mutant mammalian kinases that drive resistance to clinically relevant inhibitors. We aggregate these data with subsaturation mutagenesis data and use it to develop, test and validate a framework to prospectively identify residues that mediate kinase activity and drug resistance across the kinome. We validate predicted resistance mutations in CDK4, CDK6, ERK2, EGFR and HER2. Capitalizing on a highly predictable residue, we generate resistance mutations in TBK1, CSNK2A1 and BRAF. Unexpectedly, we uncover a potentially generalizable activation site that mediates drug resistance and confirm its impact in BRAF, EGFR, HER2 and MEK1. We anticipate that the identification of these residues will enable the broad interrogation of the kinome and its inhibitors.

MET inhibitors in cancer: pitfalls and challenges

Introduction: The HGF/MET axis is a key therapeutic pathway in cancer; it is aberrantly activated because of mutations, fusions, amplification or aberrant ligand production. Extensive efforts have been made to discover predictive factors of anti-MET therapeutic efficacy, but they have mostly unsuccessful. An understanding of the intrinsic and acquired mechanism of MET resistance will be fundamental for the development of new therapeutic interventions.Areas covered: This article provides a systematic review of phase II randomized and phase III clinical trials investigating the use of MET inhibitors in the treatment of cancer. We discuss preliminary findings on efficacy and methodologic design flaws in these trials.Expert opinion: MET inhibitors showed poor activity in unselected patients or patients selected by MET expression, p-MET or high HGF basal levels. The efficacy in advanced solid tumors is very modest and in phase III clinical trials, survival differences did not fulfill the stringent requirements of ESMO-Magnitude Clinical Benefit Score (MCBS). Prospective novel liquid biomarker-driven studies and novel trial designs such as Umbrella and Basket trials are necessary to progress MET inhibitor development.

Co-occurring Alterations in the RAS-MAPK Pathway Limit Response to MET Inhibitor Treatment in MET Exon 14 Skipping Mutation-Positive Lung Cancer

PURPOSE

Although patients with advanced-stage non-small cell lung cancers (NSCLC) harboring MET exon 14 skipping mutations (METex14) often benefit from MET tyrosine kinase inhibitor (TKI) treatment, clinical benefit is limited by primary and acquired drug resistance. The molecular basis for this resistance remains incompletely understood.

EXPERIMENTAL DESIGN

Targeted sequencing analysis was performed on cell-free circulating tumor DNA obtained from 289 patients with advanced-stage METex14-mutated NSCLC.

RESULTS

Prominent co-occurring RAS-MAPK pathway gene alterations (e.g., in KRAS, NF1) were detected in NSCLCs with METex14 skipping alterations as compared with EGFR-mutated NSCLCs. There was an association between decreased MET TKI treatment response and RAS-MAPK pathway co-occurring alterations. In a preclinical model expressing a canonical METex14 mutation, KRAS overexpression or NF1 downregulation hyperactivated MAPK signaling to promote MET TKI resistance. This resistance was overcome by cotreatment with crizotinib and the MEK inhibitor trametinib.

CONCLUSIONS

Our study provides a genomic landscape of co-occurring alterations in advanced-stage METex14-mutated NSCLC and suggests a potential combination therapy strategy targeting MAPK pathway signaling to enhance clinical outcomes.

Structural and Molecular Insight into Resistance Mechanisms of First Generation cMET Inhibitors

Many small molecule inhibitors of the cMET receptor tyrosine kinase have been evaluated in clinical trials for the treatment of cancer and resistance-conferring mutations of cMET are beginning to be reported for a number of such compounds. There is now a need to understand specific cMET mutations at the molecular level, particularly concerning small molecule recognition. Toward this end, we report here the first crystal structures of the recent clinically observed resistance-conferring D1228V cMET mutant in complex with small molecule inhibitors, along with a crystal structure of wild-type cMET bound by the clinical compound savolitinib and supporting cellular, biochemical, and biophysical data. Our findings indicate that the D1228V alteration induces conformational changes in the kinase, which could have implications for small molecule inhibitor design. The data we report here increases our molecular understanding of the D1228V cMET mutation and provides insight for future inhibitor design.

Sensitivity and Resistance of MET Exon 14 Mutations in Lung Cancer to Eight MET Tyrosine Kinase Inhibitors In Vitro

BACKGROUND

MNNG HOS transforming gene (MET) exon 14 mutations in lung cancer, including exon 14 skipping and point mutations, have been attracting the attention of thoracic oncologists as new therapeutic targets. Tumors with these mutations almost always acquire resistance, which also occurs in other oncogene-addicted lung cancers. However, the resistance mechanisms and treatment strategies are not fully understood.

METHODS

We generated Ba/F3 cells expressing MET exon 14 mutations by retroviral gene transfer. The sensitivities of these cells to eight MET-tyrosine kinase inhibitors (TKIs) were determined using a colorimetric assay. In addition, using N-ethyl-N-nitrosourea mutagenesis, we generated resistant clones, searched for secondary MET mutations, and then examined the sensitivities of these resistant cells to different TKIs.

RESULTS

Ba/F3 cells transfected with MET mutations grew in the absence of interleukin-3, indicating their oncogenic activity. These cells were sensitive to all MET-TKIs except tivantinib. We identified a variety of secondary mutations. D1228 and Y1230 were common sites for resistance mutations for type I TKIs, which bind the active form of MET, whereas L1195 and F1200 were common sites for type II TKIs, which bind the inactive form. In general, resistance mutations against type I were sensitive to type II, and vice versa.

CONCLUSIONS

MET-TKIs inhibited the growth of cells with MET exon 14 mutations. We also identified mutation sites specific for TKI types as resistance mechanisms and complementary activities between type I and type II inhibitors against those mutations. These finding should provide relevant clinical implication for treating patients with lung cancer harboring MET exon 14 mutations.

Synthesis, and anti-proliferative, Pim-1 kinase inhibitors and molecular docking of thiophenes derived from estrone

Heterocyclization of steroids were reported to give biologically active products where ring D modification occured. Estrone (1) was used as a template to develop new heterocyclic compounds. Ring D modification of 1 through its reaction with cyanoacetylhydrazine and elemental sulfur gave the thiophene derivative 3. The latter compound reacted with acetophenone derivatives 4a-c to give the hydrazide-hydrazone derivatives 5a-c, respectively. In addition, compound 3 formed thiazole derivatives through its first reaction with phenylisothiocyanate to give the thiourea derivative 9 followed by the reaction of the later with α-halocarbonyl compounds. In the present work a series of novel estrone derivatives were designed, synthesized and evaluated for their in vitro biological activities against c-Met kinase, and six typical cancer cell lines (A549, H460, HT-29, MKN-45, U87MG and SMMC-7721). The most promising compounds 5b, 5c, 11a, 13c, 15b, 15c, 15d, 17a and 17b were further investigated against the five tyrosine kinases c-Kit, Flt-3, VEGFR-2, EGFR, and PDGFR. Compounds 5b, 15d, 17a and 17b were selected to examine their Pim-1 kinase inhibition activity where compounds 15d and 17b showed high activities. Molecular docking of some of the most potent compounds was demonstrated.

[MET Exon 14 Skipping Mutations in Non-small Cell Lung Cancer]

近年来，靶向治疗在非小细胞肺癌（non-small cell lung cancer, NSCLC）患者的治疗中取得了巨大成功。间质-上皮细胞转化因子（mesenchymal-epithelial transition factor, MET）被认为是继表皮生长因子受体（epidermal growth factor receptor, EGFR）、间变性淋巴瘤激酶（anaplastic lymphoma kinase, ALK）之后又一重要的NSCLC分子治疗靶点。MET 14外显子跳跃突变患者在一些临床试验及个案报道中显示出对MET抑制剂良好的疗效，提示MET 14外显子跳跃突变或可成为靶向治疗的良好指标，但这仍需大样本量的临床研究来证实。本文就MET 14外显子跳跃突变的分子机制、人群特征、治疗策略及耐药机制作一综述。

Comparison of the Kinase Profile of Midostaurin (Rydapt) with That of Its Predominant Metabolites and the Potential Relevance of Some Newly Identified Targets to Leukemia Therapy

The multitargeted protein kinase inhibitor midostaurin is approved for the treatment of both newly diagnosed FLT3-mutated acute myeloid leukemia (AML) and KIT-driven advanced systemic mastocytosis. AML is a heterogeneous malignancy, and investigational drugs targeting FLT3 have shown disparate effects in patients with FLT3-mutated AML, probably as a result of their inhibiting different targets and pathways at the administered doses. However, the efficacy and side effects of drugs do not just reflect the biochemical and pharmacodynamic properties of the parent compound but are often comprised of complex cooperative effects between the properties of the parent and active metabolites. Following chronic dosing, two midostaurin metabolites attain steady-state plasma trough levels greater than that of the parent drug. In this study, we characterized these metabolites and determined their profiles as kinase inhibitors using radiometric transphosphorylation assays. Like midostaurin, the metabolites potently inhibit mutant forms of FLT3 and KIT and several additional kinases that either are directly involved in the deregulated signaling pathways or have been implicated as playing a role in AML via stromal support, such as IGF1R, LYN, PDPK1, RET, SYK, TRKA, and VEGFR2. Consequently, a complex interplay between the kinase activities of midostaurin and its metabolites is likely to contribute to the efficacy of midostaurin in AML and helps to engender the distinctive effects of the drug compared to those of other FLT3 inhibitors in this malignancy.

[MET exon 14 splicing sites mutations: A new therapeutic opportunity in lung cancer]

The mutations leading to MET exon 14 skipping represent a new class of molecular alterations described in various cancers. These alterations are observed in 2 to 3 % of cases of non-small cell lung cancer (NSCLC). Several cases of NSCLC carrying such alterations and achieving objective response to MET tyrosine kinase inhibitorshave recently been published. This review summarizes the molecular mechanisms responsible for MET exon 14 skipping as well as the consequences of the loss of this exon on receptor activity. We also describe the clinical characteristics of patients with METΔ14 mutations. Finally, we address the issues related to the detection of these mutations in lung cancer, and the need to anticipate resistance to MET inhibitors.

The multiple paths towards MET receptor addiction in cancer

Targeted therapies against receptor tyrosine kinases (RTKs) are currently used with success on a small proportion of patients displaying clear oncogene activation. Lung cancers with a mutated EGFR provide a good illustration. The efficacy of targeted treatments relies on oncogene addiction, a situation in which the growth or survival of the cancer cells depends on a single deregulated oncogene. MET, a member of the RTK family, is a promising target because it displays many deregulations in a broad panel of cancers. Although clinical trials having evaluated MET inhibitors in large populations have yielded disappointing results, many recent case reports suggest that MET inhibition may be effective in a subset of patients with unambiguous MET activation and thus, most probably, oncogene addiction. Interestingly, preclinical studies have revealed a particularity of MET addiction: it can arise through several mechanisms, and the mechanism involved can differ according to the cancer type. The present review describes the different mechanisms of MET addiction and their consequences for diagnosis and therapeutic strategies. Although in each cancer type MET addiction affects a restricted number of patients, pooling of these patients across all cancer types yields a targetable population liable to benefit from addiction-targeting therapies.

Circulating tumor DNA profiling by next generation sequencing reveals heterogeneity of crizotinib resistance mechanisms in a gastric cancer patient with MET amplification

Crizotinib has been used to counter MET gene amplification in a number of different human malignancies. Transient response to crizotinib in MET-amplified gastric cancer has been reported, but the mechanisms of resistance are not well studied. Here, we reported a stage IV gastric cancer patient with high levels of MET amplification. The implementation of crizotinib treatment led to significant symptomatic improvement in the first 2 months, but was followed by rapid disease progression. Periodic mutation profiling of patient's circulating tumor DNA (ctDNA) by next generation sequencing (NGS) revealed a number of genetic alterations including re-occurrence of MET amplification, multiple secondary MET mutations, a dramatic increase of FGFR2 gene relative copy number as well as mutations in other downstream and bypassing elements, which may collectively related to the patient's cancer progression. Our results illustrate the complex and heterogeneous molecular mechanisms for crizotinib resistance in this patient, and demonstrate the great potential of ctDNA profiling for treatment decision-making and prognosis in clinical practice.

Identification of Bisindolylmaleimide IX as a potential agent to treat drug-resistant BCR-ABL positive leukemia

Chronic myeloid leukemia (CML) treatment with BCR-ABL inhibitors is often hampered by development of drug resistance. In a screen for novel chemotherapeutic drug candidates with genotoxic activity, we identified a bisindolylmaleimide derivative, IX, as a small molecule compound with therapeutic potential against CML including drug-resistant CML. We show that Bisindolylmaleimide IX inhibits DNA topoisomerase, generates DNA breaks, activates the Atm-p53 and Atm-Chk2 pathways, and induces cell cycle arrest and cell death. Interestingly, Bisindolylmaleimide IX is highly effective in targeting cells positive for BCR-ABL. BCR-ABL positive cells display enhanced DNA damage and increased cell cycle arrest in response to Bisindolylmaleimide IX due to decreased expression of topoisomerases. Cells positive for BCR-ABL or drug-resistant T315I BCR-ABL also display increased cytotoxicity since Bisindolylmaleimide IX inhibits B-Raf and the downstream oncogene addiction pathway. Mouse cancer model experiments showed that Bisindolylmaleimide IX, at doses that show little side effect, was effective in treating leukemia-like disorders induced by BCR-ABL or T315I BCR-ABL, and prolonged the lifespan of these model mice. Thus, Bisindolylmaleimide IX presents a novel drug candidate to treat drug-resistant CML via activating BCR-ABL-dependent genotoxic stress response and inhibiting the oncogene addiction pathway activated by BCR-ABL.

Discovery of novel 2-substituted-4-phenoxypyridine derivatives as potential antitumor agents

A series of 2-substituted-4-phenoxypyridine derivatives were designed, synthesized, and evaluated for their antiproliferative activity against 4 cancer cell lines (A549, HT-29, H460, and U87MG) in vitro. Most compounds showed moderate to excellent potency. Nine tyrosine kinases (c-Met, Flt-3, ALK, VEGFR-2, VEGFR-3, PDGFR-α, PDGFR-β, c-Kit, and EGFR) were used to evaluate the inhibitory activities with the most promising analogue 39, which showed the Flt-3/c-Met IC₅₀ values of 2.18/2.61 nM. Structure-activity relationship studies indicated that n-Pr served as R¹ group showed a higher preference, and stronger mono-EWGs on the phenyl ring (such as R² = 4-F) was benefited to the potency.

Oncogenic MET as an Effective Therapeutic Target in Non-Small Cell Lung Cancer Resistant to EGFR Inhibitors: The Rise of the Phoenix

Anecdotal reports have shown that concomitant inhibition of EGFR and MET can be clinically effective in patients with non-small cell lung cancer carrying EGFR mutations and MET amplification, but large phase III trials in genetically unselected individuals have failed to confirm the benefit of this combination therapy. A new study corroborates the evidence that lung cancer susceptibility to EGFR and MET blockade is sustained by genetically based activation of both targets and identifies a mutation in MET that confers acquired resistance to standard MET inhibitors hitting the active kinase, yet is vulnerable to other MET-directed compounds with a different binding mode. Cancer Discov; 6(12); 1306-8. ©2016 AACR.See related article by Bahcall and colleagues, p. 1334.

Uses of Cyclohexan-1,4-dione for the Synthesis of 2-Amino-4,5-dihydrobenzo[b]thiophen-6(7H)-one Derivatives with Anti-proliferative and Pim-1 Kinase Activities

The reaction of cyclohexan-1,4-dione with elemental sulfur and any of the 2-cyano-N-arylacetamide derivatives 2a-c gave the 2-amino-4,5-dihydrobenzo[b]thiophen-6(7H)-one derivatives 3a-c to be used in some heterocyclization reactions. The multicomponent reactions of any of compounds 3a-c with aromatic aldehydes 6a-c and either of malononitrile or ethylcyanoacetate gave the 5,9-dihydro-4H-thieno[2,3-f]chromene derivatives 9a-r, respectively. The anti-proliferative evaluation of the newly synthesized compounds against the six cancer cell lines A549, HT-29, MKN-45, U87MG, SMMC-7721 and H460 showed that the nine compounds 3c, 5c, 9e, 9h, 9i, 9j, 9l, 9q, 11e and 13e with highest cytotoxcity. Toxicity of these compounds against shrimp larvae revealed that compounds 3c, 9j, 9q, and 13e showed no toxicity against the tested organisms. The c-Met kinase inhibition of the most potent compounds showed that compounds 9j, 9q, 10e, 12e and 13e have the highest activities. Compounds 9j, 9l, 9q and 11e showed high activity towards tyrosine kinases. Moreover, compounds 9j, 9q and 13e showed the highest inhibitor activity towards Pim-1 kinase.

Synthesis and antiproliferative activity of pyrrolo[2,3-b]pyridine derivatives bearing the 1,8-naphthyridin-2-one moiety

A series of pyrrolo[2,3-b]pyridine derivatives bearing the 1,8-naphthyridin-2-one moiety were synthesized, and evaluated for their antiproliferative activity against four cancer cell lines (HT-29, A549, H460, and U87MG) and six tyrosine kinases (c-Met, Flt-3, PDGFR-β, VEGFR-2, EGFR, and c-Kit) inhibitory activities in vitro. Most compounds showed moderate to excellent potency, with the most promising analogue 32 showing Flt-3/c-Met IC₅₀ value of 1.16/1.92 nM. Structure-activity relationship studies indicated that the hydrogen atom served as R₁ group was benefited to the potency, and mono-electron-withdrawing groups (mono-EWGs) on the phenyl ring (such as R₃ = 4-F) showed a higher preference for antiproliferative activity.