Activity of tarloxotinib-E in cells with EGFR exon-20 insertion mutations and mechanisms of acquired resistance

A patent review of small molecular inhibitors targeting EGFR exon 20 insertion (Ex20ins) (2019-present)

INTRODUCTION

Mutations in epidermal growth factor receptor (EGFR) kinase domain consistently activate downstream signaling pathways, such as the PI3K/AKT/mTOR and RAS/RAF/MEK, thereby promoting tumor growth. Although the majority of non-small cell lung cancer (NSCLC) patients harboring EGFR mutations are sensitive to existing EGFR tyrosine kinase inhibitors (EGFR-TKIs), there remains an unmet clinical need for effective therapies targeting EGFR Ex20ins mutations, making direct targeting EGFR Ex20ins mutations a promising therapeutic strategy.

AREAS COVERED

This review covers the progress of clinical studies targeting EGFR Ex20ins inhibitors and summarizes recent (1 January 2019 - 30 April 2024) patents disclosing EGFR Ex20ins inhibitors available in the Espacenet and CAS SciFinder databases.

EXPERT OPINION

An increasing number of EGFR Ex20ins inhibitors are being developed and reported. Existing inhibitors are focused on enhancing the efficacy of EGFR Ex20ins inhibitors and addressing the challenge of targeted resistance by optimizing the second - or third-generation EGFR inhibitors and developing innovative skeleton molecules. Moreover, the development of targeted protein degraders, allosteric inhibitors, and combination therapies provide additional approaches to address EGFR Ex20ins mutations. However, bypass resistance, selectivity, and drug sensitivity still pose challenges in this field.

Discovery of flavonoid-containing compound Lupalbigenin as anti-NSCLC cancer agents via suppression of EGFR and ERK1/2 pathway

Epidermal growth factor receptor exon 20 insertions (EGFR Ex20ins) driver mutations in non-small cell lung cancer (NSCLC) is insensitive to EGFR tyrosine kinase inhibitors (TKIs). Therefore, it is necessary to develop more novel strategy to address the limitations of existing therapies targeting EGFR-mutated NSCLC. Lupalbigenin (LB), a flavonoid compound extracted from Derris scandens, has shown preclinical activity in lung cancer. However, the activity of LB in Ex20ins-driven tumors has not yet been elucidated. In this study, a series of stable BaF/3 cell-line that contains a high proportion (>90 %) of EGFR-eGFP Ex20ins were generated using an IL3-deprivation method. Ba/F3 cell models harboring dissimilar Ex20ins were used to characterize the antineoplastic mechanism of LB. Molecular docking confirmed that the LB could effectively bind to key target EGFR. The in vitro anticancer activity of LB was investigated in engineered Ba/F3 cells bearing diverse uncommon EGFR mutations. LB was shown to be more potent in inhibiting the viability of various uncommon EGFR-mutated cell lines. Mechanistic studies disclosed that LB repressed EGFR phosphorylation and downstream survival pathways in Ba/F3 cells expressing EGFR Ex20ins, resulting in caspase activation by activating the intrinsic apoptotic pathway. Further analyses showed that LB significantly induced G0/G1 cell cycle arrest and apoptosis in cells. LB also reduced the protein expression levels of CDK4, CDK6, CDK8, cyclin D1, cyclin A2, and Bcl2 and promoted the expression of cytochrome C, p27, and p53. In summary, we explored the possible potential targets of LB through network pharmacology and verified the target using in vitro experiments. Furthermore, our results demonstrated that LB showed potential anti-Ex20ins cancer activity through suppression of the EGFR and ERK1/2 signaling pathway in Ba/F3 cells bearing two to three amino acid insertion mutations. These findings suggested that LB might be valuable for further investigation as a potential candidate in the treatment of associated diseases.

Potential Utility of a 4th-Generation EGFR-TKI and Exploration of Resistance Mechanisms-An In Vitro Study

The emergence of acquired resistance to EGFR-tyrosine kinase inhibitors (TKIs) is almost inevitable even after a remarkable clinical response. Secondary mutations such as T790M and C797S are responsible for the resistance to 1st/2nd-generation (1/2G) TKIs and 3G TKIs, respectively. To overcome both the T790M and C797S mutations, novel 4G EGFR-TKIs are now under early clinical development. In this study, we evaluated the efficacy of a 4G EGFR-TKI in the treatment of lung cancer with EGFR mutation as well as explored resistance mechanisms to a 4G TKI. First, we compared the efficacies of seven TKIs including a 4G TKI, BI4020, against Ba/F3 cell models that simulate resistant tumors after front-line osimertinib treatment failure because of a secondary mutation. We also established acquired resistant cells to BI4020 by chronic drug exposure. Ba/F3 cells with an osimertinib-resistant secondary mutation were refractory to all 3G TKIs tested (alflutinib, lazertinib, rezivertinib, almonertinib, and befotertinib). BI4020 inhibited the growth of C797S-positive cells; however, it was not effective against L718Q-positive cells. Erlotinib was active against all Ba/F3 cells tested. In the analysis of resistance mechanisms of BI4020-resistant (BIR) cells, none harbored secondary EGFR mutations. HCC827BIR cells had MET gene amplification and were sensitive to a combination of capmatinib (MET-TKI) and BI4020. HCC4006BIR and H1975BIR cells exhibited epithelial-to-mesenchymal transition. This study suggests that erlotinib may be more suitable than 4G TKIs to overcome secondary mutations after front-line osimertinib. We found that off-target mechanisms that cause resistance to earlier-generation TKIs will also cause resistance to 4G TKIs.

Advances in the Diagnosis and Treatment of Advanced Non-Small-Cell Lung Cancer With EGFR Exon 20 Insertion Mutation

The discovery of epidermal growth factor receptor (EGFR) mutations has greatly changed the clinical outlook for patients with advanced non-small-cell lung cancer (NSCLC). Unlike the most common EGFR mutations, such as exon 19 deletion (del19) and exon 21 L858R point mutation, EGFR exon 20 insertion mutation (EGFR ex20ins) is a rare mutation of EGFR. Due to its structural specificity, it exhibits primary resistance to traditional epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), leading to poor overall survival prognosis for patients. In recent years, there has been continuous progress in the development of new drugs targeting EGFR ex20ins, bringing new hope for the treatment of this patient population. In this regard, we conducted a systematic review of the molecular characteristics, diagnostic advances, and treatment status of EGFR ex20ins. We summarized the latest data on relevant drug development and clinical research, aiming to provide reference for clinical diagnosis, treatment, and drug development.

Targeting EGFR Exon 20 Insertion Mutations in Non-small-Cell Lung Cancer: Changes in Treatment Strategies are Coming

Epidermal growth factor receptor (EGFR) exon 20 insertion (ex20ins) mutations are the third most frequent EGFR mutation type, following only exon 19 deletions and exon 21 L858R point mutations. EGFR ex20ins mutations are found in approximately 4%-12% of all EGFR-positive non-small cell lung cancers (NSCLCs). Unlike classical EGFR mutations, EGFR ex20ins mutations display remarkable subtype diversity and heterogeneity. Patients harboring these mutations generally have an inferior prognosis because of insensitivity to conventional treatment approaches such as immunotherapy, chemotherapy, and targeted therapy. Consequently, there remains a significant unmet medical need for efficacious treatments. Recently, amivantamab and sunvozertinib have demonstrated notable efficacy as first-line treatments, and several other promising novel targeted drugs are also challenging the status quo of traditional first-line platinum-based chemotherapy regimens. These developments are anticipated to further improve survival outcomes for NSCLC patients with EGFR ex20ins mutations. Hence, this review summarizes the epidemiology, molecular attributes, detection methodologies, and therapeutic advancements for EGFR ex20ins mutations in NSCLC, and briefly discusses the mechanisms of drug resistance.

Secondary Mutations of the EGFR Gene That Confer Resistance to Mobocertinib in EGFR Exon 20 Insertion

INTRODUCTION

Approximately 10% of mutations in the EGFR gene in NSCLC are in-frame insertions in exon 20 (X20ins). These tumors usually do not respond to conventional EGFR tyrosine kinase inhibitors (TKIs). Several novel EGFR TKIs active for X20ins are in clinical development, including mobocertinib, which was recently approved by the U.S. Food and Drug Administration. However, acquired resistance during treatment with these TKIs still occurs as in the case of EGFR TKIs of earlier generations.

METHODS

We chronically exposed murine pro-B-cell line cells transduced with the five most common X20ins (A763_Y764insFQEA, V769_D770insASV, D770_N771insSVD, H773_V774insNPH and H773_V774insH) to mobocertinib in the presence of N-ethyl-N-nitrosourea and searched for secondary EGFR mutations. We evaluated the efficacies of several EGFR X20ins inhibitors, including zipalertinib and sunvozertinib, against cells with acquired resistant mutations.

RESULTS

All secondary mutations resulting in acquired resistance to mobocertinib were exclusively C797S in insFQEA and insSVD. However, in the case of other X20ins (insASV, insNPH, and insH), T790M or C797S secondary mutations contributed to acquired resistance to mobocertinib. The emergence of T790M was more frequent in cells treated with lower drug concentrations. Sunvozertinib exhibited good activity against resistant cells with T790M. Cells with C797S were refractory to all EGFR TKIs, except for erlotinib, which was active for insFQEA with C797S.

CONCLUSIONS

T790M or C797S, depending on the original X20ins mutations, conferred acquired resistance to mobocertinib. Sunvozertinib may be the treatment of choice for patients with tumors resistant to mobocertinib because of T790M.

EGFR exon20 insertion mutations in non-small cell lung cancer: Clinical implications and recent advances in targeted therapies

The advent of targeted therapies for oncogenic mutations has led to a major paradigm shift in the management of non-small cell lung cancer (NSCLC). Molecular targets, such as epidermal growth factor receptor (EGFR)-activating mutations in the region of exons 18 through 21 are the most common oncogenic driver in NSCLC. Classical activating mutations, such as in-frame deletions in exon 19 and point mutations in exon 21 (L858R), are strong predictors for good clinical response to the approved EGFR-tyrosine kinase inhibitors (EGFR-TKIs). However, low frequency mutations occurring within exon 20 (ex20ins) have poorer responses to first/second generation EGFR-TKIs. Moreover, patients with NSCLC harboring EGFR ex20ins are known to have poorer prognosis than those with other EGFR-TKI sensitive mutations, leading to unmet clinical need of novel specific therapeutic options. Rapid changes in molecular diagnostics identifying specific causes have hastened the translation of diagnostic recommendations into clinical practice. Emergence of treatment strategies targeting EGFR ex20ins, such as newer EGFR-TKIs with increased specificity and novel approaches using bispecific monoclonal antibodies, may hold promising therapeutic options in the near future. In this review, we describe the structural, molecular characteristics, and detection strategies of EGFR ex20ins mutations and summarize the latest clinical data on approved treatments and emerging therapies for patients with NSCLC harboring EGFR ex20ins mutations. Further, we will discuss the response heterogeneity of ex20ins mutations to new drugs and acquired drug resistance mechanisms.

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

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

Clinical Relevance of Patient-Derived Organoid of Surgically Resected Lung Cancer as an In Vitro Model for Biomarker and Drug Testing

Introduction

Lung tumor organoids (LTOs) have attracted attention as in vitro preclinical models; however, their clinical and experimental applications have not been fully established.

Methods

We attempted to establish LTOs from resected specimens of patients with lung cancer who underwent lung resection. Clinicopathologic characteristics related to the establishment of LTOs were evaluated. Histologic assessment and genetic analysis were conducted for both LTOs and their parental tumors. Organoid-derived xenografts were generated in immunocompetent mice. Drug sensitivity was assessed using cell proliferation assays.

Results

We established 53 LTOs from 79 lung cancer samples, including 10 long-term culture models. The establishment rate was significantly lower in squamous cell carcinomas than in other histologic types (48% versus 75%, p = 0.034). Histologic similarities were confirmed among LTOs, the parental tumors, and organoid-derived xenografts. Seven mutations, including two EGFR L858R and one EGFR exon 20 H773delinsYNPY mutations, were detected in both LTO and parental tumors; the other four mutations were detected in either LTO or parental tumors. The extensive culture ability of LTO (passaged >10 times) correlated with poor patient prognosis. LTO9 cells harboring EGFR H773delinsYNPY were sensitive to osimertinib. The parental patient, who had new metastatic lesions, was treated with osimertinib and exhibited a remarkable response.

Conclusions

The establishment and growth rates of LTOs were associated with the histologic subtype and tumor size. LTOs derived from resected specimens have become preclinical models that can be used to predict drug responses and accelerate the development of treatment strategies for patients with rare mutations.

BBT-176, a Novel Fourth-Generation Tyrosine Kinase Inhibitor for Osimertinib-Resistant EGFR Mutations in Non-Small Cell Lung Cancer

PURPOSE

Resistance to third-generation EGFR inhibitors including osimertinib arises in part from the C797S mutation in EGFR. Currently, no targeted treatment option is available for these patients. We have developed a new EGFR tyrosine kinase inhibitor (TKI), BBT-176, targeting the C797S mutation.

PATIENTS AND METHODS

Recombinant EGFR proteins and Ba/F3 cell lines, patient-derived cells, and patient-derived xenografts expressing mutant EGFRs were used to test the inhibitory potency and the anticancer efficacy of BBT-176 both in vitro and in vivo. Patient case data are also available from an ongoing phase I clinical trial (NCT04820023).

RESULTS

The half maximal inhibitory concentration (IC50) of BBT-176 against EGFR 19Del/C797S, EGFR 19Del/T790M/C797S, and EGFR L858R/C797S proteins were measured at 4.36, 1.79, and 5.35 nmol/L, respectively (vs. 304.39, 124.82, and 573.72 nmol/L, for osimertinib). IC50 values of BBT-176 against Ba/F3 cells expressing EGFR 19Del/C797S, EGFR 19Del/T790M/C797S, EGFR L858R/C797S, and EGFR L858R/T790M/C797S were 42, 49, 183, and 202 nmol/L, respectively (vs. 869, 1,134, 2,799, and 2,685 nmol/L for osimertinib). N-ethyl-N-nitrosourea mutagenesis suggested that BBT-176 treatment does not introduce any secondary mutations in the EGFR gene but increases EGFR expression levels. Combined with the EGFR antibody cetuximab, BBT-176 effectively suppressed the growth of BBT-176-resistant clones. BBT-176 strongly inhibited the tumor growth, and in some conditions induced tumor regression in mouse models. In the clinical trial, two patients harboring EGFR 19Del/T790M/C797S in blood showed tumor shrinkage and radiologic improvements.

CONCLUSIONS

BBT-176 is a fourth-generation EGFR inhibitor showing promising preclinical activity against NSCLC resistant to current EGFR TKI, with early clinical efficacy and safety.

[Progress in Detection of EGFR Exon 20 Insertion Mutation and Targeted Therapies in Non-small Cell Lung Cancer]

Epidermal growth factor receptor exon 20 insertion (EGFR ex20ins) is one of the earliest driver gene activation mutations in non-small cell lung cancer (NSCLC). However, due to the unique structure of protein variation caused by this mutation, most patients with EGFR ex20ins mutation (except A763_Y764insFQEA) have poor response to the launched first/second/third generation EGFR-tyrosine kinase inhibitors (EGFR-TKIs). With the successive approval of new specific targeted drugs for EGFR ex20ins in Food and Drug Administration (FDA) and other national regulatory agencies, the development and clinical research of targeted drugs for EGFR ex20ins in China have also developed rapidly and Mobocertinib has been approved recently in China. It is worth noting that EGFR ex20ins is a variant type with strong molecular heterogeneity. How to detect it comprehensively and accurately in clinical practice, so as to enable more patients to benefit from targeted therapy, is a very important and urgent problem to be solved. This review introduces the molecular typing of EGFR ex20ins, then discusses the importance of EGFR ex20ins detection and the differences of various detection methods, and summarizes the research and development of new drugs progress of EGFR ex20ins, in order to optimize the diagnosis and treatment path of EGFR ex20ins patients by selecting accurate, rapid and appropriate detection methods, so as to improve the clinical benefits of the patients.
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Advances in the management of non-small-cell lung cancer harbouring EGFR exon 20 insertion mutations

Epidermal growth factor receptor (EGFR) mutation is one of the key oncogenic mutations in non-small-cell lung cancer with adenocarcinoma histology. Exon 19 deletions and exon 21 L858R substitutions account for 90%, while EGFR exon 20 insertions constitute 4-10% of EGFR mutations and are the third most prevalent activating EGFR mutations. EGFR exon 20 insertions are associated with decreased sensitivity to EGFR tyrosine kinase inhibitors and, until recently, effective targeted therapy against these tumours remained an unmet clinical need and chemotherapy was the only treatment of choice available. The approval of amivantamab and mobocertinib for patients who have progressed after chemotherapy represents an important step forward in the management of these patients. Here in this review, we summarize the epidemiology, structure and the tumour microenvironment of EGFR exon 20 insertion and also review the systemic treatments, including targeted therapies and ongoing clinical trials in EGFR exon 20 insertion mutations, as well as detection methods for EGFR exon 20 insertion. Lastly, resistant mechanisms and future directions are addressed.

Targeting exon 20 insertion mutations in lung cancer

PURPOSE OF REVIEW

The application of tyrosine kinase inhibitor (TKI) has successfully changed the standard of care in epidermal growth factor receptor ( EGFR ) positive non-small cell lung cancer. However, clinical survivals for patients with EGFR exon 20 insertions have failed to improve over the long period and the mutation appeared resistant to EGFR -TKIs. This overview focused on the current treatment strategies, summarized the emerging regimens for patients with EGFR exon 20 insertions, and demonstrated historical challenges and future development.

RECENT FINDING

Current clinical trials suggested that several regimens selectively-targeted EGFR exon 20 insertions presented potent antitumor activity, like mobocertinib and the bispecific anti- EGFR-MET monoclonal antibody amivantamab and were approved by Food and Drug Administration (FDA) in patients progressed beyond first-line treatment. Novel treatments, including DZD9008, CLN-081, revealed modest clinical efficacy as well and clinical trials are underway, which may lead to improvement of survival outcomes.

SUMMARY

Recent clinical evidence indicates that targeted therapies could improve survival benefits to some extent. More efforts on drug development are underway to bring higher response rates both extracranial and intracranial, sustained clinical remission, and better survival benefits.

Hypoxia, a key factor in the immune microenvironment

The physical and chemical pressures in the tumor microenvironment (TME) play an important role in tumor development by regulating stromal elements, including immune cells. Hypoxia can induce a cascade of events in tumor initiation and development via immune regulation. As a dangerous factor, hypoxia activates multiple signaling pathways to reshape the immune microenvironment, leading to immunosuppression. Consequently, targeting hypoxia in the TME is a potential strategy to prevent immune escape and inhibit malignant tumor progression. In this review, we summarized the role of hypoxia-induced factors in the tumor immune escape process and provide a novel pathway to restrain tumor progression and development.

Novel targeted therapies for advanced non-small lung cancer

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer accounting for almost 80%-85% of all lung cancer cases. Unfortunately, more than half of the patients will be diagnosed with advanced disease at the time of presentation, which makes their disease incurable. Historically, the 5 year overall survival for advanced NSCLC was 5%. However, there has been a significant increase in our understanding of the genetic basis of NSCLC, which has led to development of both immunotherapy and targeted therapy agents. This has improved the 5 year overall survival to become within the range of 15%-50% depending on certain mutations and biomarkers. Over the last decade the United States Food and Drug Administration (FDA) has approved almost 20 new targeted therapies and clinical trials are still undergoing to evaluate more novel agents. In this review, we will present recent updates on novel targeted therapies.

[Advances in Treatment of Non-small Cell Lung Cancer Harboring EGFR Exon 20 Insertion Mutations]

Epidermal growth factor receptor (EGFR) exon 20 insertion mutations are the third most prevalent activating EGFR mutation in non-small cell lung cancer (NSCLC), accounting for 5%-12% of all EGFR mutations in NSCLC cases. Patients harboring EGFR exon 20 insertion mutations exhibit similar clinical characteristics except for worse prognosis as compared to those with 'classic' EGFR mutations. EGFR exon 20 insertion mutations are considered as a heterogeneous class of alterations that cause different conformational changes in EGFR. The majority of mutations (almost 90% of cases) is positioned in the loop that immediately follows the C-terminal of the C-helix, and the most widely reported subtype of insertion mutations is D770_N771>ASVDN(A767_V769dupASV) with frequency of 21%-28%. NSCLC patients with EGFR exon 20 insertion mutations show primary drug resistance to previously approved EGFR tyrosine kinase inhibitors and are generally insensitive to conventional chemotherapy and immunotherapy. The recently approved targeted drugs Amivantamab and Mobocertinib shift the treatment paradigm for NSCLC patients harboring EGFR exon 20 insertion mutations. There are also several new compounds targeting NSCLC EGFR exon 20 insertion mutations are in development. In this article, we provide a through overview on the treatment development in EGFR exon 20 insertion mutant NSCLC.
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Therapeutic exploration of uncommon EGFR exon 20 insertion mutations in advanced non-small cell lung cancer: breaking through brambles and thorns

BACKGROUND

EGFR exon 20 insertion (EGFR ex20ins) mutations account for about 10-12% of all EGFR-mutated tumors, which are usually associated with primary drug resistance to conventional EGFR-TKI therapy and worse survival outcomes, and are currently a major problem for clinicians in clinical management. In recent years, with the rapid improvement of sequencing technology and careful review of clinical data, investigators have gained a deeper understanding and clearer cognition of the clinicopathological features and molecular mechanisms of these EGFR ex20ins mutations.

PURPOSE

The aim of this study was to systemically review the molecular structure and clinical characteristics of EGFR ex20ins mutations, and focus on summarizing the latest data of emerging therapies (including novel small-molecule EGFR-TKI drugs, specific monoclonal antibodies, novel drugs targeting other mechanisms, and immunotherapy) for those patients.

CONCLUSION

Advances in overcoming these systemic challenges have greatly accelerated the development of new drugs targeting EGFR ex20ins, and are committed to designing more rational combination therapies to overcome or delay the emergence of drug resistance, ultimately improve the prognosis of such uncommon mutant populations.

Targeting EGFR Exon 20 Insertions in Non-Small Cell Lung Cancer: Recent Advances and Clinical Updates

Approximately 10% of EGFR-activating mutations occur as in-frame insertion mutations in exon 20 of the EGFR kinase domain (EGFR ins20). EGFR ins20 mutations have not demonstrated the same sensitivity to early generations of EGFR tyrosine kinase inhibitors (TKI) as canonical activating EGFR mutations such as del19 and L858R. Development of effective therapies for this subset of patients has been challenging, but recent years have seen more rapid progress in these efforts. In this review, we describe the molecular and clinicopathologic features of EGFR ins20 mutations and summarize recent data on emerging therapies for patients with this subtype of EGFR-mutant non-small cell lung cancer (NSCLC). SIGNIFICANCE: When activating mutations in EGFR were first discovered in lung cancer, the lack of sensitivity of tumors harboring EGFR ins20 mutations to early-generation EGFR TKIs resulted in this subset of EGFR-mutant tumors being initially classified as an untargetable or intrinsically resistant subpopulation. In addition, the diversity of mutations within EGFR exon 20 and resultant challenges identifying them on routine clinical genotyping tests led to underestimation of their frequency. However, recent scientific progress in targeting EGFR ins20 mutations as well as more effective identification of this clinical cohort has enhanced our ability to develop effective therapies for patients with this subtype of EGFR-mutant NSCLC.

Hypoxia-activated prodrug derivatives of anti-cancer drugs: a patent review 2006 - 2021

INTRODUCTION

The hypoxic tumor microenvironment represents a persistent obstacle in the treatment of most solid tumors. In the past years, significant efforts have been made to improve the efficacy of anti-cancer drugs. Therefore, hypoxia-activated prodrugs (HAPs) of chemotherapeutic compounds have attracted widespread interest as a therapeutic means to treat hypoxic tumors.

AREAS COVERED

This updated review paper covers key patents published between 2006 and 2021 on the developments of HAP derivatives of anti-cancer compounds.

EXPERT OPINION

Despite significant achievements in the development of HAP derivatives of anti-cancer compounds and although many clinical trials have been performed or are ongoing both as monotherapies and as part of combination therapies, there has currently no HAP anti-cancer agent been commercialized into the market. Unsuccessful clinical translation is partly due to the lack of patient stratification based on reliable biomarkers that are predictive of a positive response to hypoxia-targeted therapy.

Activity of tarloxotinib-E in cells with EGFR exon-20 insertion mutations and mechanisms of acquired resistance

BACKGROUND

Approximately 10% of non-small cell lung cancers (NSCLCs) that harbor epidermal growth factor receptor (EGFR) gene mutations have in-frame insertions in exon 20 of the EGFR gene. These tumors do not usually respond to currently available EGFR-tyrosine kinase inhibitors (TKIs). Tarloxotinib is a novel hypoxia-activated prodrug that releases a potent, irreversible pan-ERBB TKI (tarloxotinib-E) under solid tumor hypoxia.

METHODS

We examined the efficacy of tarloxotinib-E against several types of Ba/F3 cells with introduced EGFR exon 20 mutations (EGFR A763insFQEA, V769insASV, D770insSVD, H773insH and H773insNPH mutations). We assayed growth inhibition for tarloxotinib (prodrug), tarloxotinib-E (active form), poziotinib, afatinib, and osimertinib in Ba/F3 cells with each EGFR exon 20 mutation. We also explored acquired resistance mechanisms to tarloxotinib-E by establishing cells with resistance to tarloxotinib-E via chronic drug exposure after N-ethyl-N-nitrosourea mutagenesis treatment.

RESULTS

Among all tested Ba/F3 cell lines, IC₅₀ was ≥72.1 times higher for tarloxotinib than for tarloxotinib-E, which implies a wide therapeutic window with this prodrug strategy. Tarloxotinib-E was efficacious against all tested Ba/F3 cells except for H773insH, which was less sensitive to all tested EGFR-TKIs. As acquired resistance mechanisms to tarloxotinib-E, we identified either T790M or C797S secondary mutations, depending on the original EGFR exon 20 mutation.

CONCLUSIONS

These findings indicate that tarloxotinib-E could be effective for NSCLC with EGFR exon 20 mutations. Our results also show that T790M or C797S mutations can confer acquired resistance to tarloxotinib-E; and suggest that resistance mechanisms are influenced by the baseline EGFR exon 20 mutations.