Combined EGFR/MEK Inhibition Prevents the Emergence of Resistance in EGFR-Mutant Lung Cancer

Novel computational method for predicting polytherapy switching strategies to overcome tumor heterogeneity and evolution

The success of targeted cancer therapy is limited by drug resistance that can result from tumor genetic heterogeneity. The current approach to address resistance typically involves initiating a new treatment after clinical/radiographic disease progression, ultimately resulting in futility in most patients. Towards a potential alternative solution, we developed a novel computational framework that uses human cancer profiling data to systematically identify dynamic, pre-emptive, and sometimes non-intuitive treatment strategies that can better control tumors in real-time. By studying lung adenocarcinoma clinical specimens and preclinical models, our computational analyses revealed that the best anti-cancer strategies addressed existing resistant subpopulations as they emerged dynamically during treatment. In some cases, the best computed treatment strategy used unconventional therapy switching while the bulk tumor was responding, a prediction we confirmed in vitro. The new framework presented here could guide the principled implementation of dynamic molecular monitoring and treatment strategies to improve cancer control.

Enhancer Remodeling during Adaptive Bypass to MEK Inhibition Is Attenuated by Pharmacologic Targeting of the P-TEFb Complex

Targeting the dysregulated BRAF-MEK-ERK pathway in cancer has increasingly emerged in clinical trial design. Despite clinical responses in specific cancers using inhibitors targeting BRAF and MEK, resistance develops often involving nongenomic adaptive bypass mechanisms. Inhibition of MEK1/2 by trametinib in patients with triple-negative breast cancer (TNBC) induced dramatic transcriptional responses, including upregulation of receptor tyrosine kinases (RTK) comparing tumor samples before and after one week of treatment. In preclinical models, MEK inhibition induced genome-wide enhancer formation involving the seeding of BRD4, MED1, H3K27 acetylation, and p300 that drives transcriptional adaptation. Inhibition of the P-TEFb-associated proteins BRD4 and CBP/p300 arrested enhancer seeding and RTK upregulation. BRD4 bromodomain inhibitors overcame trametinib resistance, producing sustained growth inhibition in cells, xenografts, and syngeneic mouse TNBC models. Pharmacologic targeting of P-TEFb members in conjunction with MEK inhibition by trametinib is an effective strategy to durably inhibit epigenomic remodeling required for adaptive resistance.Significance: Widespread transcriptional adaptation to pharmacologic MEK inhibition was observed in TNBC patient tumors. In preclinical models, MEK inhibition induces dramatic genome-wide modulation of chromatin, in the form of de novo enhancer formation and enhancer remodeling. Pharmacologic targeting of P-TEFb complex members at enhancers is an effective strategy to durably inhibit such adaptation. Cancer Discov; 7(3); 302-21. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 235.

Next-Generation EGFR Tyrosine Kinase Inhibitors for Treating EGFR-Mutant Lung Cancer beyond First Line

Tyrosine kinase inhibitors (TKIs) against the human epidermal growth factor receptor (EGFR) are now standard treatment in the clinic for patients with advanced EGFR mutant non-small-cell lung cancer (NSCLC). First-generation EGFR TKIs, binding competitively and reversibly to the ATP-binding site of the EGFR tyrosine kinase domain, have resulted in a significant improvement in outcome for NSCLC patients with activating EGFR mutations (L858R and Del19). However, after a median duration of response of ~12 months, all patients develop tumor resistance, and in over half of these patients this is due to the emergence of the EGFR T790M resistance mutation. The second-generation EGFR/HER TKIs were developed to treat resistant disease, targeting not only T790M but EGFR-activating mutations and wild-type EGFR. Although they exhibited promising anti-T790M activity in the laboratory, their clinical activity among T790M+ NSCLC was poor mainly because of dose-limiting toxicity due to simultaneous inhibition of wild-type EGFR. The third-generation EGFR TKIs selectively and irreversibly target EGFR T790M and activating EGFR mutations, showing promising efficacy in NSCLC resistant to the first- and second-generation EGFR TKIs. They also appear to have lower incidences of toxicity due to the limited inhibitory effect on wild-type EGFR. Currently, the first-generation gefitinib and erlotinib and second-generation afatinib have been approved for first-line treatment of metastatic NSCLC with activating EGFR mutations. Among the third-generation EGFR TKIs, osimertinib is today the only drug approved by the Food and Drug Administration and the European Medicines Agency to treat metastatic EGFR T790M NSCLC patients who have progressed on or after EGFR TKI therapy. In this review, we summarize the available post-progression therapies including third-generation EGFR inhibitors and combination treatment strategies for treating patients with NSCLC harboring EGFR mutations and address the known mechanisms of resistance.

Superior Efficacy and Selectivity of Novel Small-Molecule Kinase Inhibitors of T790M-Mutant EGFR in Preclinical Models of Lung Cancer

The clinical utility of approved EGFR small-molecule kinase inhibitors is plagued both by toxicity against wild-type EGFR and by metastatic progression in the central nervous system, a disease sanctuary site. Here, we report the discovery and preclinical efficacy of GNS-1486 and GNS-1481, two novel small-molecule EGFR kinase inhibitors that are selective for T790M-mutant isoforms of EGFR. Both agents were effective in multiple mouse xenograft models of human lung adenocarcinoma (T790M-positive or -negative), exhibiting less activity against wild-type EGFR than existing approved EGFR kinase inhibitors (including osimertinib). In addition, GNS-1486 showed superior potency against intracranial metastasis of EGFR-mutant lung adenocarcinoma. Our results offer a preclinical proof of concept for new EGFR kinase inhibitors with the potential to improve therapeutic index and efficacy against brain metastases in patients. Cancer Res; 77(5); 1200-11. ©2017 AACR.

Treatment in EGFR-mutated Non-small Cell Lung Cancer: How to Block the Receptor and overcome Resistance Mechanisms

In non-small cell lung cancer (NSCLC), the identification of epidermal growth factor receptor (EGFR) mutations and the parallel development of EGFR tyrosine kinase inhibitors (TKIs) have radically changed the therapeutic management strategies. Currently, erlotinib, gefitinib, and afatinib are all approved as standard first-line treatment in EGFR-mutated NSCLC. However, despite the proven efficacy, some EGFR-mutated NSCLCs do not respond to EGFR TKIs, while some patients, after a favorable and prolonged response to EGFR TKIs, inevitably progress within about 10-14 months. Epidermal growth factor receptor-dependent mechanisms, activation of alternative pathways, or phenotypic transformation can cause the resistance to EGFR TKIs. The exon 20 p.Thr790Met point mutation (T790M) is responsible for about 60% of cases of resistance when progression occurs. A third-generation TKI, osimertinib, improved outcome in patients harboring T790M after first- and second-generation TKI treatment. However, resistance develops even after treatment with third-generation drugs. To date, the Cys797Ser (C797S) mutation in exon 20 of EGFR is the most well-known resistance mutation after osimertinib. Fourth-generation TKIs are already under development. Nevertheless, additional information is needed to better understand and effectively overcome resistance. The aim of this review is to report recent advances and future perspectives in the treatment of EGFR-mutated NSCLC, highlighting the resistance mechanisms that underlie disease progression.

CDK4/6 or MAPK blockade enhances efficacy of EGFR inhibition in oesophageal squamous cell carcinoma

Oesophageal squamous cell carcinoma is a deadly disease where systemic therapy has relied upon empiric chemotherapy despite the presence of genomic alterations pointing to candidate therapeutic targets, including recurrent amplification of the gene encoding receptor tyrosine kinase epidermal growth factor receptor (EGFR). Here, we demonstrate that EGFR-targeting small-molecule inhibitors have efficacy in EGFR-amplified oesophageal squamous cell carcinoma (ESCC), but may become quickly ineffective. Resistance can occur following the emergence of epithelial–mesenchymal transition and by reactivation of the mitogen-activated protein kinase (MAPK) pathway following EGFR blockade. We demonstrate that blockade of this rebound activation with MEK (mitogen-activated protein kinase kinase) inhibition enhances EGFR inhibitor-induced apoptosis and cell cycle arrest, and delays resistance to EGFR monotherapy. Furthermore, genomic profiling shows that cell cycle regulators are altered in the majority of EGFR-amplified tumours and a combination of cyclin-dependent kinase 4/6 (CDK4/6) and EGFR inhibitors prevents the emergence of resistance in vitro and in vivo. These data suggest that upfront combination strategies targeting EGFR amplification, guided by adaptive pathway reactivation or by co-occurring genomic alterations, should be tested clinically.

Oesophageal squamous cell carcinoma often develop resistance to EGFR tyrosine kinase inhibitors. Here, the authors demonstrate that inhibition of cell cycle regulators CDK4/6 or MAPK blockade enhances the efficacy of EGFR inhibitors for these tumours in mice.

Mechanisms of Resistance to Target Therapies in Non-small Cell Lung Cancer

Targeted therapies are revolutionizing the treatment of advanced non-small cell lung cancer (NSCLC). The discovery of key oncogenic events mainly in lung adenocarcinoma, like EGFR mutations or ALK rearrangements, has changed the treatment landscape while improving the prognosis of lung cancer patients. Inevitably, virtually all patients initially treated with targeted therapies develop resistance because of the emergence of an insensitive cellular population, selected by pharmacologic pressure. Diverse mechanisms of resistance, in particular to EGFR, ALK and ROS1 tyrosine-kinase inhibitors (TKIs), have now been discovered and may be classified in three different groups: (1) alterations in the target (such as EGFR T790M and ALK or ROS1 mutations); (2) activation of alternative pathways (i.e. MET amplification, KRAS mutations); (3) phenotype transformation (to small cell lung cancer, epithelial-mesenchymal transition). These basic mechanisms are informing the development of novel therapeutic strategies to overcome resistance in the clinic. Novel-generation molecules include osimertinib, for EGFR-T790M-positive patients, and new ALK-TKIs. Nevertheless, the possible concomitant presence of multiple resistance mechanisms, as well as their heterogeneity among cells and disease localizations, makes research in this field particularly arduous. In this chapter, available evidence and perspectives concerning precise mechanisms of escape to pharmacological inhibition in oncogene-addicted NSCLC are reported for single targets, including but not limited to EGFR and ALK.

Combine and conquer: challenges for targeted therapy combinations in early phase trials

Our increasing understanding of cancer biology has led to the development of molecularly targeted anticancer drugs. The full potential of these agents has not, however, been realised, owing to the presence of de novo (intrinsic) resistance, often resulting from compensatory signalling pathways, or the development of acquired resistance in cancer cells via clonal evolution under the selective pressures of treatment. Combinations of targeted treatments can circumvent some mechanisms of resistance to yield a clinical benefit. We explore the challenges in identifying the best drug combinations and the best combination strategies, as well as the complexities of delivering these treatments to patients. Recognizing treatment-induced toxicity and the inability to use continuous pharmacodynamically effective doses of many targeted treatments necessitates creative intermittent scheduling. Serial tumour profiling and the use of parallel co-clinical trials can contribute to understanding mechanisms of resistance, and will guide the development of adaptive clinical trial designs that can accommodate hypothesis testing, in order to realize the full potential of combination therapies.

Cancer resistance to therapies against the EGFR-RAS-RAF pathway: The role of MEK

The mitogen-activated protein kinases (MAPKs) mediate intracellular signals activated by a wide variety of extracellular stimuli. The activation of the RAS-RAF-MEK-MAPK cascade culminates in the regulation of gene transcription promoting cancer cell proliferation, survival, migration and angiogenesis. MEK (mitogen-activated protein kinase kinase-MAPKK) 1/2 is a transducer of the growth factor receptor-RAS-RAF-MAPK signalling cascade and plays a relevant role in development and progression of human cancers, such as colorectal cancer (CRC), non small cell lung cancer (NSCLC). Direct inhibition of MEK is a promising strategy and several inhibitors are currently under evaluation in clinical trials showing initial clinical activity in different tumours. MEK activation, by different genetic mechanisms, has been described for both intrinsic and acquired resistance to drugs targeting the EGFR (Epidermal Growth Factor Receptor)-RAS-RAF pathway in CRC, NSCLC. Combination therapies with chemotherapy and/or with molecular targeted agents are warranted and biomarkers studies are needed to identify those tumours dependent on MEK signalling.

Co-clinical quantitative tumor volume imaging in ALK-rearranged NSCLC treated with crizotinib

PURPOSE

To evaluate and compare the volumetric tumor burden changes during crizotinib therapy in mice and human cohorts with ALK-rearranged non-small-cell lung cancer (NSCLC).

METHODS

Volumetric tumor burden was quantified on serial imaging studies in 8 bitransgenic mice with ALK-rearranged adenocarcinoma treated with crizotinib, and in 33 human subjects with ALK-rearranged NSCLC treated with crizotinib. The volumetric tumor burden changes and the time to maximal response were compared between mice and humans.

RESULTS

The median tumor volume decrease (%) at the maximal response was -40.4% (range: -79.5%-+11.7%) in mice, and -72.9% (range: -100%-+72%) in humans (Wilcoxon p=0.03). The median time from the initiation of therapy to maximal response was 6 weeks in mice, and 15.7 weeks in humans. Overall volumetric response rate was 50% in mice and 97% in humans. Spider plots of tumor volume changes during therapy demonstrated durable responses in the human cohort, with a median time on therapy of 13.1 months.

CONCLUSION

The present study described an initial attempt to evaluate quantitative tumor burden changes in co-clinical imaging studies of genomically-matched mice and human cohorts with ALK-rearranged NSCLC treated with crizotinib. Differences are noted in the degree of maximal volume response between the two cohorts in this well-established paradigm of targeted therapy, indicating a need for further studies to optimize co-clinical trial design and interpretation.

Third-generation epidermal growth factor receptor-tyrosine kinase inhibitors in T790M-positive non-small cell lung cancer: review on emerged mechanisms of resistance

Osimertinib, third-generation epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI), has been approved in the US and EU for the treatment of EGFR mutant T790M-positive non-small cell lung cancer (NSCLC) patients resistant to first- or second-generation EGFR-TKIs, such as gefitinib, erlotinib and afatinib. Although exciting survival data and response rates have been registered in patients treated with this and other third-generation EGFR-TKIs, unfortunately acquired resistance still occurs after approximately 10 months. Mechanisms determining progression of disease are heterogeneous and not fully understood. EGFR-dependent resistance mechanisms (such as new EGFR mutations), bypass pathway activation [as erb-b2 receptor tyrosine kinase 2 (HER2) or MET amplification] and histological transformation [in small cell lung cancer (SCLC)] have been reported, similarly to previous generation TKIs. Here, we review principle mechanisms of innate and acquired resistance described in literature both in clinical and preclinical settings during NSCLC treatment with third-generation EGFR-TKIs.

Stratified Treatment in Lung Cancer

Even though great efforts have been made to improve chemotherapy-based treatment approaches for lung cancer, the prognosis of patients with advanced and metastasized disease remains particularly poor. In recent years, a growing number of genetic aberrations driving lung cancer have been identified. Targeted inhibition of some of these aberrations, most prominently mutated EGFR and ALK, by tyrosine kinase inhibitors has dramatically increased efficacy and tolerability of systemic lung cancer treatment in subsets of patients. However, the duration of response is limited due to the acquisition of molecular mechanisms of resistance to targeted treatment. Modern next-generation inhibitors aim to break resistance. A deep understanding of the mechanisms of treatment failure is imperative to the development of new approaches. In this review, we focus on the current status of stratified therapy in lung cancer and highlight new, potentially promising treatment approaches.

Targeting the Gatekeeper: Osimertinib in EGFR T790M Mutation-Positive Non-Small Cell Lung Cancer

In 2015, the FDA approved an unprecedented number of new therapies for non-small cell lung cancer (NSCLC), among them therapies addressing specific genomic tumor subsets in the setting of development of resistance to first-line targeted therapy. Osimertinib (Tagrisso, formerly AZD9291; AstraZeneca) is indicated for patients with metastatic EGFR T790M mutation-positive NSCLC, as detected by an FDA-approved test, who have progressed on or after EGFR tyrosine kinase inhibitor therapy. It received breakthrough therapy designation, priority review status, and accelerated approval from the FDA. Clin Cancer Res; 23(3); 618-22. ©2016 AACR.

Osimertinib in the treatment of patients with epidermal growth factor receptor T790M mutation-positive metastatic non-small cell lung cancer: clinical trial evidence and experience

Patients with advanced epidermal growth factor receptor (EGFR) mutant non-small cell lung cancer (NSCLC) are particularly sensitive to treatment with first- or second-generation EGFR tyrosine kinase inhibitors such as gefitinib, erlotinib and afatinib, which block the cell-signaling pathways that drive the growth of tumor cells. Unfortunately, the majority of patients develop resistance to them after a median duration of response of around 10 months, and in over half of these patients the emergence of the EGFR T790M resistance mutation is detected. Osimertinib is an oral, highly selective, irreversible inhibitor of both EGFR-activating mutations and the T790M-resistance mutation, while sparing the activity of wild-type EGFR. This article reviews clinical trial development of osimertinib in patients with NSCLC, presenting efficacy and safety evidence for its value in the EGFR T790M mutation-positive population and in different settings, including patients with metastatic disease. The preclinical background of clinically acquired resistance to osimertinib is presented and the combination tactics being investigated in an attempt to circumvent this are addressed.

Primary Double-Strike Therapy for Cancers to Overcome EGFR Kinase Inhibitor Resistance: Proposal from the Bench

Diverse molecular mechanisms that confer acquired resistance to EGFR tyrosine kinase inhibitors (TKIs) in lung cancers with sensitive EGFR mutations have been reported. However, it is not realistic to analyze for all these mechanisms at the time of resistance in clinical practice and establish adequate treatment targeting these numerous resistance mechanisms. Therefore, we believe that we should move our research focus from the exploration of "established" diverse resistance mechanisms to the elucidation of molecular mechanisms that enable cancer cells to remain alive at the early phase of the treatment. Here in this review, we summarize up-to-date molecular mechanisms that maintain residual tumor cells against EGFR TKI monotherapy in lung cancers with EGFR mutations. We classified these mechanisms into three categories. The first is a preexisting minor subpopulation with a resistance mechanism such as a pretreatment T790M mutation that can be detected by highly sensitivity methods. The second is the reversible drug-tolerant state that is often observed in cell line models and accounts for the lack of complete response and continued survival of cells exposed to EGFR TKIs in patients. And the last is the role of the microenvironment, including survival signaling from fibroblasts or dying cancer cells and the role of poor vascularization. Primary double-strike cancer therapy, or even initial multiple-strike therapy, to cancer cells that cotarget EGFR and survival mechanism(s) simultaneously would be a promising strategy to improve the outcomes of patients with EGFR mutations.

Polo-like kinase 1 inhibition diminishes acquired resistance to epidermal growth factor receptor inhibition in non-small cell lung cancer with T790M mutations

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are effective against non-small cell lung cancer (NSCLC) with activating EGFR mutations, but resistance is inevitable. Mechanisms of acquired resistance include T790M mutations and epithelial-mesenchymal transition (EMT). One potential strategy for overcoming this resistance is the inhibition of polo-like kinase 1 (PLK1) based on our previous studies showing that mesenchymal NSCLC cell lines are more sensitive to PLK1 inhibition than epithelial cell lines. To determine the extent to which PLK1 inhibition overcomes EGFR TKI resistance we measured the effects of the PLK1 inhibitor volasertib alone and in combination with the EGFR inhibitor erlotinib in vitro and in vivo in EGFR mutant NSCLC cell lines with acquired resistance to erlotinib. Two erlotinib-resistant cell lines that underwent EMT had higher sensitivity to volasertib, which caused G2/M arrest and apoptosis, than their parental cells. In all NSCLC cell lines with T790M mutations, volasertib markedly reduced erlotinib resistance. All erlotinib-resistant NSCLC cell lines with T790M mutations had higher sensitivity to erlotinib plus volasertib than to erlotinib alone, and the combination treatment caused G2/M arrest and apoptosis. Compared with either agent alone, the combination treatment also caused significantly more DNA damage and greater reductions in tumor size. Our results suggest that PLK1 inhibition is clinically effective against NSCLC that becomes resistant to EGFR inhibition through EMT or the acquisition of a T790M mutation. These results uncover new functions of PLK1 inhibition in the treatment of NSCLC with acquired resistance to EGFR TKIs.

CRISPR-Barcoding for Intratumor Genetic Heterogeneity Modeling and Functional Analysis of Oncogenic Driver Mutations

Intratumor genetic heterogeneity underlies the ability of tumors to evolve and adapt to different environmental conditions. Using CRISPR/Cas9 technology and specific DNA barcodes, we devised a strategy to recapitulate and trace the emergence of subpopulations of cancer cells containing a mutation of interest. We used this approach to model different mechanisms of lung cancer cell resistance to EGFR inhibitors and to assess effects of combined drug therapies. By overcoming intrinsic limitations of current approaches, CRISPR-barcoding also enables investigation of most types of genetic modifications, including repair of oncogenic driver mutations. Finally, we used highly complex barcodes inserted at a specific genome location as a means of simultaneously tracing the fates of many thousands of genetically labeled cancer cells. CRISPR-barcoding is a straightforward and highly flexible method that should greatly facilitate the functional investigation of specific mutations, in a context that closely mimics the complexity of cancer.

Adaptive and Acquired Resistance to EGFR Inhibitors Converge on the MAPK Pathway

Both adaptive and acquired resistance significantly limits the efficacy of the epidermal growth factor receptor (EGFR) kinase inhibitors. However, the distinct or common mechanisms of adaptive and acquired resistance have not been fully characterized. Here, through systematic modeling of erlotinib resistance in lung cancer, we found that feedback reactivation of MAPK signaling following erlotinib treatment, which was dependent on the MET receptor, contributed to the adaptive resistance of EGFR inhibitors. Interestingly, acquired resistance to erlotinib was also associated with the MAPK pathway activation as a result of CRAF or NRAS amplification. Consequently, combined inhibition of EGFR and MAPK impeded the development of both adaptive and acquired resistance. These observations demonstrate that adaptive and acquired resistance to EGFR inhibitors can converge on the same pathway and credential cotargeting EGFR and MAPK as a promising therapeutic approach in EGFR mutant tumors.

Epithelial-to-Mesenchymal Transition Defines Feedback Activation of Receptor Tyrosine Kinase Signaling Induced by MEK Inhibition in KRAS-Mutant Lung Cancer

KRAS is frequently mutated in lung cancer. Whereas MAPK is a well-known effector pathway of KRAS, blocking this pathway with clinically available MAPK inhibitors is relatively ineffective. Here, we report that epithelial-to-mesenchymal transition rewires the expression of receptor tyrosine kinases, leading to differential feedback activation of the MAPK pathway following MEK inhibition. In epithelial-like KRAS-mutant lung cancers, this feedback was attributed to ERBB3-mediated activation of MEK and AKT. In contrast, in mesenchymal-like KRAS-mutant lung cancers, FGFR1 was dominantly expressed but suppressed by the negative regulator Sprouty proteins; MEK inhibition led to repression of SPRY4 and subsequent FGFR1-mediated reactivation of MEK and AKT. Therapeutically, the combination of a MEK inhibitor (MEKi) and an FGFR inhibitor (FGFRi) induced cell death in vitro and tumor regressions in vivo These data establish the rationale and a therapeutic approach to treat mesenchymal-like KRAS-mutant lung cancers effectively with clinically available FGFR1 and MAPK inhibitors.

SIGNIFICANCE

Adaptive resistance to MEKi is driven by receptor tyrosine kinases specific to the differentiation state of the KRAS-mutant non-small cell lung cancer (NSCLC). In mesenchymal-like KRAS-mutant NSCLC, FGFR1 is highly expressed, and MEK inhibition relieves feedback suppression of FGFR1, resulting in reactivation of ERK; suppression of ERK by MEKi/FGFRi combination results in tumor shrinkage. Cancer Discov; 6(7); 754-69. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 681.

Emerging role of mTOR in the response to cancer therapeutics

The movement toward precision medicine with targeted therapeutics for cancer treatment has been hindered by both innate and acquired resistance. Understanding the molecular wiring and plasticity of oncogenic signaling networks is essential to the development of therapeutic strategies to avoid or overcome resistance. The mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) represents a highly integrated signaling node that is dysregulated in the majority of human cancers. Several studies have revealed that sustained mTORC1 inhibition is essential to avoid resistance to targeted therapeutics against the driving oncogenic pathway in a given cancer. Here we discuss the role of mTORC1 in dictating the response of tumors to targeted therapeutics and review recent examples from lung cancer, breast cancer, and melanoma.

Drug Resistance to EGFR Inhibitors in Lung Cancer

BACKGROUND

The discovery of mutations in epidermal growth factor receptor (EGFR) has dramatically changed the treatment of patients with non-small-cell lung cancer (NSCLC), the leading cause of cancer deaths worldwide. EGFR-targeted therapies show considerable promise, but drug resistance has become a substantial issue.

METHODS

We reviewed the literature to provide an overview of the drug resistance to EGFR tyrosine kinase inhibitors (TKIs) in NSCLC.

RESULTS

The mechanisms causing primary, acquired and persistent drug resistance to TKIs vary. Researchers and clinicians, who have used study findings to develop more effective therapeutic approaches, have found that the sequential use of single agents presents a formidable challenge, suggesting that multidrug combinations must be considered.

CONCLUSIONS

In the era of precision medicine, oncologists should promptly obtain an accurate diagnosis of drug resistance in each patient to be able to design the most relevant combination therapy to overcome patient-specific drug resistance.

Epidermal growth factor receptor targeting and challenges in glioblastoma

With the evolution of technology, there is now a deeper understanding of glioblastoma as an inter- and intraheterogeneous disease comprising a multitude of genetically and epigenetically different cancer cells. Greater characterization of glioblastoma at the molecular level has improved its initial pathophysiological staging and classification. With this knowledge comes the hope that more efficacious therapies to combat this highly lethal disease are on the horizon. One possibility for intervention is represented by the targeting of epidermal growth factor receptor (EGFR), which is amplified and mutated in a large subset of patients. In this review, we provide a brief overview of EGFR and its mutated form, EGFR variant III, describing the downstream cellular pathways activated by each receptor, available animal models, therapeutic strategies to inhibit the receptor, and possible intervention routes to efficiently target this receptor and prevent the emergence of resistant mechanisms which to date have hampered a successful therapeutic outcome.

AZD9291 in EGFR-mutant advanced non-small-cell lung cancer patients

Non-small-cell lung cancer (NSCLC) patients whose tumors have an EGFR-activating mutation develop acquired resistance after a median of 9–11 months from the beginning of treatment with erlotinib, gefitinib and afatinib. T790M mutation is the cause of this resistance in approximately 60% of cases. AZD9291 is an oral, irreversible, mutant-selective EGF receptor (EGFR) tyrosine kinase inhibitor (TKI) developed to have potency against EGFR mutations, including T790M mutation, while sparing wild-type EGFR. A Phase I trial of AZD9291 in EGFR-mutant NSCLC patients, demonstrated high activity, essentially among T790M-mutant tumors, with a manageable tolerability profile. Ongoing Phase III trials are evaluating AZD9291 in EGFR-mutant patients as first-line treatment compared with erlotinib and gefitinib; and as second-line treatment compared with chemotherapy after progression on EGFR TKI in T790M-mutant tumors. Better identification of T790M-mutant tumors post EGFR TKI relapse and mechanisms of resistance to AZD9291 are the future challenges. This article reviews the emerging data regarding AZD9291 in the treatment of patients with advanced NSCLC.

AKT inactivation causes persistent drug tolerance to EGFR inhibitors

Drug resistance is a major obstacle to the success of EGFR-targeted therapy. We recently studied the mechanism by which a small subset of EGFR mutant lung cancer cells remains viable after EGFR inhibition. We found that this drug-tolerant subpopulation develops because EGFR inhibition prevents AKT activity and thus inactivates Ets-1 function. In this article, we discuss how changes in intrinsic cell signaling after EGFR inhibition open a new avenue to drug resistance in NSCLCs, and comment on combined TKI and MEK inhibitor treatment to reduce the probability of emergent resistance to EGFR TKIs.

Genetic Evidence for XPC-KRAS Interactions During Lung Cancer Development

Lung cancer causes more deaths than breast, colorectal and prostate cancers combined. Despite major advances in targeted therapy in a subset of lung adenocarcinomas, the overall 5-year survival rate for lung cancer worldwide has not significantly changed for the last few decades. DNA repair deficiency is known to contribute to lung cancer development. In fact, human polymorphisms in DNA repair genes such as xeroderma pigmentosum group C (XPC) are highly associated with lung cancer incidence. However, the direct genetic evidence for the role of XPC for lung cancer development is still lacking. Mutations of the Kirsten rat sarcoma viral oncogene homolog (Kras) or its downstream effector genes occur in almost all lung cancer cells, and there are a number of mouse models for lung cancer with these mutations. Using activated Kras, Kras(LA1), as a driver for lung cancer development in mice, we showed for the first time that mice with Kras(LA1) and Xpc knockout had worst outcomes in lung cancer development, and this phenotype was associated with accumulated DNA damage. Using cultured cells, we demonstrated that induced expression of oncogenic KRAS(G12V) led to increased levels of reactive oxygen species (ROS) as well as DNA damage, and both can be suppressed by anti-oxidants. Our results suggest that XPC may help repair DNA damage caused by KRAS-mediated production of ROS.

The Impact of Genomic Profiling for Novel Cancer Therapy--Recent Progress in Non-Small Cell Lung Cancer

There is high expectation for significant improvements in cancer patient care after completion of the human genome project in 2003. Through pains-taking analyses of genomic profiles in cancer patients, a number of targetable gene alterations have been discovered, with some leading to novel therapies, such as activating mutations of EGFR, BRAF and ALK gene fusions. As a result, clinical management of cancer through targeted therapy has finally become a reality for a subset of cancers, such as lung adenocarcinomas and melanomas. In this review, we summarize how gene mutation discovery leads to new treatment strategies using non-small cell lung cancer (NSCLC) as an example. We also discuss possible future implications of cancer genome analyses.

ETS1 inactivation causes innate drug resistance to EGFR inhibitors

Mutations in epidermal growth factor receptor (EGFR) are found in approximately 10% of lung cancers. Treatment with EGFR inhibitors, although promising, has surprisingly resulted in greater than 90% tumor reduction in only 5% of cases, prompting us to investigate the mechanism of innate drug resistance.

EGFR-independent mechanisms of acquired resistance to AZD9291 in EGFR T790M-positive NSCLC patients

BACKGROUND

AZD9291 is an oral, irreversible, mutant-selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKI), which specifically targets both sensitizing and resistant T790M mutations. This compound has shown outstanding activity, in a phase I/II (AURA) trial. However, despite impressive tumor responses in T790M-positive patients, acquired resistance to this drug limits the benefit of this compound. Mutations at the EGFR C797 codon, located within the kinase-binding site, were very recently reported to be a potential mechanism of resistance to AZD9291 in T790M-positive patients.

PATIENTS AND METHODS

To identify potential mechanisms of resistance to AZD9291, we report here on two patients with resistant biopsy specimens that had been treated with AZD9291.

RESULTS

We identified in two distinct cases, HER2 and MET amplification by FISH and CGH as a potential mechanism of acquired resistance to third-generation EGFR-TKI. Interestingly, this event occurred with complete loss of the T790M mutation. In one case, we observed a different molecular status at two biopsy sites (the T790M mutation at the primary site and wild-type T790M at the metastatic site with different pathways of acquired resistance to AZD9291).

CONCLUSION

Our observations suggest that T790M-positive and wild-type T790M clones may coexist at baseline. AZD9291 efficiently suppresses the growth of T790M-positive cells, but a population of wild-type T790M cells at baseline will mediate the development of resistance, here via a by-pass pathway activating either HER2 or MET.