Mechanisms of resistance to EGFR tyrosine kinase inhibitors gefitinib/erlotinib and to ALK inhibitor crizotinib

The discovery of several molecular alterations that underlie non-small cell lung cancer (NSCLC) pathogenesis has led to the development of targeted therapies. In particular, gefitinib and erlotinib have become the standard of care in patients harboring epidermal growth factor receptor mutations, while crizotinib showed an impressive efficacy in patients with ALK-positive NSCLC. Nevertheless, the occurrence of clinical resistance limits the long term results of these novel agents. The identification of the molecular mechanisms responsible for acquired resistance to targeted therapy is crucial in order to pursue the creation of rational strategies to overcome resistance. In the current review, we will focus on the acquired resistance mechanisms to EGFR-TKIs and crizotinib and the therapeutic strategies currently under study to overcome resistance.     

Combined targeted therapies in non-small cell lung cancer: a winner strategy?

PURPOSE OF REVIEW: Current treatment modalities provide limited improvement in the natural course of lung cancer, and prognosis remains poor. Lung cancer is a malignancy with great molecular heterogeneity. The complexity of the signalling process leading to cancer cell proliferation and to the neoplastic phenotype supports the necessity of interfering at different stages to avoid cancer cell resistance to therapy. RECENT FINDINGS: Use of several agents with multiple growth factor receptor or intracellular targets has shown encouraging results in phase I and II clinical trials in non-small cell lung cancer. ZD6474 is a dual epidermal growth factor receptor and vascular endothelial growth factor receptor 2 small-molecule tyrosine kinase inhibitor; sorafenib is an oral kinase inhibitor of Raf-1 and is also active against vascular endothelial growth factor receptors 2 and 3, platelet-derived growth factor receptor beta, and c-KIT. Sunitinib is a vascular endothelial growth factor receptor 1, 2, and 3, c-KIT, and platelet-derived growth factor receptor alpha and beta tyrosine kinase inhibitor. SUMMARY: Combined use of epidermal growth factor receptor-tyrosine kinase inhibitor erlotinib and the humanized vascular endothelial growth factor receptor monoclonal antibody bevacizumab in advanced, chemotherapy-refractory non-small cell lung cancer has shown promising results.     

Overcoming Osimertinib Resistance in Advanced Non-small Cell Lung Cancer

Osimertinib is used as a first-line treatment for metastatic non-small cell lung cancer with positive epidermal growth factor receptor mutations based on the results of the FLAURA trial. However, as with any other epidermal growth factor receptor tyrosine kinase inhibitor, resistance also develops for osimertinib. Various genetic aberrations associated with the molecular heterogeneity of cancer cells contribute to osimertinib resistance. It is also important to choose an appropriate subsequent treatment for osimertinib-resistant non-small cell lung cancer. In this overview, we discuss the underlying mechanisms of osimertinib resistance and the efficacy of possible subsequent treatment measures.     

The accelerated path of ceritinib: Translating pre-clinical development into clinical efficacy

The discovery of anaplastic lymphoma kinase (ALK)-rearranged non–small-cell lung cancer (NSCLC) in 2007 led to the development and subsequent approval of the ALK inhibitor crizotinib in 2011. However, despite its clinical efficacy, resistance to crizotinib invariably develops. There is now a next generation of ALK inhibitors, including two that have been approved—ceritinib and alectinib—and others that are in development—brigatinib, lorlatinib and X-396. Ceritinib and the other next-generation ALK inhibitors are more potent than crizotinib and can overcome tumor cell resistance mechanisms. Ceritinib gained US Food and Drug Administration approval in 2014 following accelerated review for the treatment of patients with ALK-positive (ALK+) metastatic NSCLC who have progressed on or are intolerant to crizotinib. In pre-clinical studies, it demonstrated more potent inhibition of ALK than crizotinib in enzymatic assays, more durable responses in xenograft models and the ability to potently overcome crizotinib resistance mutations in vitro (including the gatekeeper mutation). There is also evidence for ceritinib penetration across the blood-brain barrier. In clinical trials, ceritinib has demonstrated durable responses and progression-free survival in ALK-inhibitor–pre-treated and –naïve NSCLC patients, including high overall and intracranial response rates in those with central nervous system metastases. Selective gastrointestinal toxicity of ceritinib, such as diarrhea, nausea and vomiting is generally manageable with prophylactic medication and prompt dose reduction or interruption. Future progress in treating ALK+ NSCLC will focus on determining the optimal sequencing of therapies and strategies to overcome acquired resistance, an ongoing challenge in treating ALK-mutation–driven tumors.     

Erlotinib in the treatment of non-small cell lung cancer

Inhibition of the epidermal growth factor receptor is one of the most promising novel therapeutic strategies to be used in the treatment of patients with non-small cell lung cancer. A number of compounds that target the epidermal growth factor receptor are in an advanced stage of clinical development including both antibodies directed against the receptor and small molecule inhibitors of epidermal growth factor receptor tyrosine kinase activity. This drug profile focuses on the development of erlotinib, an orally available inhibitor of epidermal growth factor receptor tyrosine kinase. Results of clinical trials are reviewed, two trials of erlotinib in combination, one with paclitaxel and carboplatin, the other with gemcitabine and cisplatin, and the National Cancer Institute of Canada – Clinical Trials Group BR21, the first study to demonstrate a survival benefit for this class of compound in non-small cell lung cancer. The future role of erlotinib in the management of patients with non-small cell lung cancer is also discussed.     

Erlotinib in the treatment of non-small cell lung cancer

Inhibition of the epidermal growth factor receptor is one of the most promising novel therapeutic strategies to be used in the treatment of patients with non-small cell lung cancer. A number of compounds that target the epidermal growth factor receptor are in an advanced stage of clinical development including both antibodies directed against the receptor and small molecule inhibitors of epidermal growth factor receptor tyrosine kinase activity. This drug profile focuses on the development of erlotinib, an orally available inhibitor of epidermal growth factor receptor tyrosine kinase. Results of clinical trials are reviewed, two trials of erlotinib in combination, one with paclitaxel and carboplatin, the other with gemcitabine and cisplatin, and the National Cancer Institute of Canada--Clinical Trials Group BR21, the first study to demonstrate a survival benefit for this class of compound in non-small cell lung cancer. The future role of erlotinib in the management of patients with non-small cell lung cancer is also discussed.     

化疗序贯EGFR-TKIs治疗晚期非小细胞肺癌的机制及疗效

随着肿瘤分子生物学研究的发展,表皮生长因子受体酪氨酸激酶抑制剂(EGFR-TKIs)在晚期非小细胞肺癌治疗中占有重要地位,特别针对于EGFR突变型患者.但基于分子靶向药物并未明显改善患者的总生存时间及出现获得性耐药问题,如何将传统化疗药物与靶向药物有机结合延长晚期患者的总生存时间受到广泛关注.化疗序贯EGFR-TKIs模式被证实为其中一项颇有前景的治疗策略.本文将结合相关研究对化疗序贯EGFR-TKIs治疗晚期非小细胞肺癌(NSCLC)的机制及疗效进行综述.     

Defining clinically relevant molecular subsets of lung cancer

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib, induce dramatic responses in certain patients with non-small cell lung cancer (NSCLC). As such, the drugs provide an unexpected tool to dissect clinically relevant molecular subsets of NSCLC. For example, using mutational profiling of tumor DNA from patients with sensitivity, primary resistance, and secondary resistance to these agents, we and others have demonstrated that somatic mutations in the tyrosine kinase domain of EGFR are associated with sensitivity to gefitinib and erlotinib, while mutations in KRAS, which encodes a GTPase downstream of EGFR, are associated with primary resistance. Furthermore, second site mutations in the EGFR kinase domain are commonly found in patients with acquired resistance. We are now using a variety of molecular and biological approaches to help further define molecular subsets of lung cancer that have relevance in the clinic.     

Personalized therapy of lung cancer

The implementation of personalized approaches in the treatment of patients with non-small cell lung cancer (NSCLC) requires a precise understanding of tumor biology, a reorientation of clinical development with a strong focus on genetically stratified early phase 'proof of concept' trials, the availability of high-quality 'realtime' genetic diagnostics, and the establishment of networks for molecular screening of lung cancer patients. To achieve this goal, a close interaction between basic researchers, clinical scientists, molecular pathologists, and pharmaceutical companies is essential. We believe that this approach is worth the effort, since personalized therapy in lung cancer has the potential to substantially improve survival in an increasing number of patients. At the moment, established personalized treatment approaches include treatment of patients with NSCLC and activating epidermal growth factor receptor (EGFR) mutations with the EGFR-directed tyrosine kinase inhibitors gefitinib or erlotinib, and treatment of NSCLC patients with genetic aberrations in the anaplastic lymphoma kinase (ALK) oncogene with the mesenchymal-epithelial transition factor (MET)/ALK inhibitor crizotinib. A new approach, the treatment of fibroblast growth factor receptor 1 (FGFR1)-amplified squamous cell lung cancer patients with FGFR inhibitors, is currently being tested in phase I clinical trials.     

Antiangiogenic drugs in non-small cell lung cancer treatment

PURPOSE OF REVIEW: A promising therapeutic target is the vascular endothelial growth factor pathway - a key mediator of tumor angiogenesis - which is important in tumor growth, invasion, and metastasis. This review focuses on the available clinical data on drugs targeting the vascular endothelial growth factor - vascular endothelial growth factor receptor pathway in the treatment of non-small cell lung cancer. RECENT FINDINGS: The therapeutic value of inhibiting the vascular endothelial growth factor pathway has been demonstrated by using drugs that prevent vascular endothelial growth factor receptor binding and by using drugs that inhibit receptor activation. Two antiangiogenic drugs exemplify these mechanisms: bevacizumab (Avastin; Genentech, South San Francisco, California, USA), a humanized monoclonal antibody that acts by binding and neutralizing vascular endothelial growth factor; and ZD6474 (Zactima; AstraZeneca, Macclesfield, UK), a small-molecule inhibitor of vascular growth factor receptor and epidermal growth factor receptor tyrosine kinase activity. Recently, the first results of a large, phase III randomized clinical trial of bevacizumab in combination with platinum-based doublet chemotherapy have been reported in patients with nonsquamous non-small cell lung cancer. SUMMARY: The inhibition of tumor angiogenesis is a key therapeutic strategy that holds great promise for the advancement of metastatic lung cancer therapy. The combination of bevacizumab and conventional chemotherapy could offer a new therapeutic option in selected non-small cell lung cancer histotypes.     

The role of EGFR inhibitors in nonsmall cell lung cancer

PURPOSE OF REVIEW: The epidermal growth factor receptor is a cell membrane receptor that plays a key role in cancer development and progression. Ligand-activated epidermal growth factor receptor-dependent signaling is involved in cell proliferation, apoptosis, angiogenesis, invasion, and metastasis. Targeting the epidermal growth factor receptor represents a promising molecular approach in cancer treatment. Several antiepidermal growth factor receptor agents are in clinical development. This review focuses on the available clinical data on epidermal growth factor receptor-targeting drugs in the treatment of nonsmall cell lung cancer. RECENT FINDINGS: Three drugs are currently in phase 2 and phase 3 development as single agents or in combination with other anticancer therapies in nonsmall cell lung cancer patients: cetuximab (Erbitux), a chimeric human-mouse monoclonal IgG1 antibody that blocks ligand binding and functional epidermal growth factor receptor activation; and erlotinib (Tarceva) and gefitinib (Iressa), two orally bioavailable, small-molecule epidermal growth factor receptor inhibitors of tyrosine kinase enzymatic activity that prevent epidermal growth factor receptor autophosphorylation and activation. Single-agent gefitinib treatment has determined a 10 to 20% response rate and a 30 to 50% symptom improvement in previously treated, chemotherapy-refractory advanced nonsmall cell lung cancer patients. Gefitinib has been the first epidermal growth factor receptor-targeting agent to be registered as an anticancer drug in several countries, including Japan, Australia, and the United States, for the third-line treatment of chemoresistant nonsmall cell lung cancer patients. SUMMARY: Antiepidermal growth factor receptor has shown promising antitumor activity in nonsmall cell lung cancer patients with a mild toxicity profile. However, a series of important clinical issues such as selection of potentially responsive patients and optimal combination with conventional anticancer treatments needs to be addressed to use these drugs better in lung cancer.     

Predictive factors for epidermal growth factor receptor inhibitors--the bull's-eye hits the arrow

Studies have shown that epidermal growth factor receptor (EGFR) signaling is important to normal development and neoplastic transformation, and that EGFR inhibition reduces cancer cell proliferation. The promising response rates of the EGFR inhibitor gefitinib in patients with chemotherapy-refractory non-small cell lung cancer (NSCLC) led to its approval for clinical use. However, there was little understanding of why gefitinib was effective in only some NSCLC patients. Two recent studies have identified somatic mutations in EGFR that confer its sensitivity to gefitinib in vitro and correlate strongly with patients' clinical response to the inhibitor.     

Targeting ALK: a promising strategy for the treatment of non-small cell lung cancer, non-Hodgkin’s lymphoma, and neuroblastoma

Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor that affects a number of biological and biochemical functions through normal ligand-dependent signaling. It has oncogenic functions in a number of tumors including non-small cell lung cancer (NSCLC), anaplastic large cell lymphoma, and neuroblastoma when altered by translocation or amplification or mutation. On August 2011, a small molecule inhibitor against ALK, crizotinib, was approved for therapy against NSCLC with ALK translocations. As we determine the molecular heterogeneity of tumors, the potential of ALK as a relevant therapeutic target in a number of malignancies has become apparent. This review will discuss some of the tumor types with oncogenic ALK alterations. The activity and unique toxicities of crizotinib are described, along with potential mechanisms of resistance and new therapies beyond crizotinib.     

Ligand‐triggered resistance to molecular targeted drugs in lung cancer: Roles of hepatocyte growth factor and epidermal growth factor receptor ligands

Recent advances in molecular biology have led to the identification of new molecular targets, such as epidermal growth factor receptor ( EGFR ) mutations and echinoderm microtubule‐associated protein‐like 4 (EML4) – anaplastic lymphoma kinase (ALK) fusion gene, in lung cancer. Dramatic response has been achieved with EGFR inhibitors (gefitinib and erlotinib) and an ALK inhibitor (crizotinib) in lung cancer expressing corresponding targets. However, cancer cells acquire resistance to these drugs and cause recurrence. Known major mechanisms for resistance to molecular targeted drugs include gatekeeper mutations in the target gene and activation of bypass survival signal via receptors other than the target receptors. The latter mechanism can involve receptor gene amplification and ligand‐triggered receptor activation as well. For example, hepatocyte growth factor (HGF), the ligand of a tyrosine kinase receptor Met, activates Met and the downstream PI3K/Akt pathway and triggers resistance to EGFR inhibitors in EGFR mutant lung cancer cells. Moreover, EGFR ligands activate EGFR and downstream pathways and trigger resistance to crizotinib in EML4‐ALK lung cancer cells. These observations indicate that signals from oncogenic drivers (EGFR signaling in EGFR ‐mutant lung cancer and ALK signaling in EML4‐ALK lung cancer) and ligand‐triggered bypass signals (HGF‐Met and EGFR ligands‐EGFR, respectively) must be simultaneously blocked to avoid the resistance. This review focuses specifically on receptor activation by ligand stimulation and discusses novel therapeutic strategies that are under development for overcoming resistance to molecular targeted drugs in lung cancer. (Cancer Sci 2012; 103: 1189–1194)     

Novel Therapeutic Targets in Non-small Cell Lung Cancer

The development of personalized medicine with a focus on novel targeted therapies has supplanted the one-size-fits-all approach to the treatment of many cancers, including non-small cell lung cancer. Targeted therapies, if given to a patient subpopulation enriched by the presence of relevant molecular targets, can often abrogate cell signaling that perpetuates cancer progression. Critical targets activating procancer pathways include, but are not limited to, epidermal growth factor receptor (EGFR), hepatocyte growth factor receptor (MET), vascular endothelial growth factor (VEGF), VEGF receptor, GTPase KRAS (KRAS), receptor tyrosine protein kinase erbB-2 (HER2), echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha isoform (PIK3CA), serine/threonine-protein kinase B-raf (BRAF), and insulin-like growth factor 1 receptor (IGF-1R). Some target-directed therapies, such as epidermal growth factor receptor tyrosine kinase inhibitors and anti-VEGF monoclonal antibody, have already been approved for clinical use. Others, such as those targeted to MET, VEGFR, HER2, PIK3CA, and IGF-1R, are in clinical testing. This review describes molecular targets in non-small cell lung cancer that are in development or being clinically applied and their implications for developing novel anticancer therapies for this previously refractory malignancy.     

肺癌分子分型与靶向治疗研究进展

随着肺癌发生、发展和预后相关分子机制研究的不断深入,肺癌靶向治疗取得了较大的进展,每一种分子分型的发现都会带来相应靶向药物的研究。2004年表皮生长因子受体(epidermal growth factor receptor,EGFR)基因在非小细胞肺癌中的发现,为我们带来了EGFR突变高度敏感有效的酪氨酸激酶抑制剂(tyrosine kinase inhibitor,TKI)。2007年棘皮类微管相关样蛋白-4-间变型淋巴瘤激酶(EML4-ALK)融合基因的出现为肺癌的分子发展带来了新的有效靶点。目前多个肺癌分子靶点及其靶向药物正在研究中。本文旨在回顾并总结肺癌分子分型及其靶向治疗的研究进展。     

Continuous inhibition of epidermal growth factor receptor phosphorylation by erlotinib enhances antitumor activity of chemotherapy in erlotinib-resistant tumor xenografts

Erlotinib, an epidermal growth factor receptor tyrosine kinase inhibitor, has been shown to have benefits for non-small cell lung cancer and pancreatic cancer patients; however, almost all patients develop progressive disease during the therapy. On the other hand, it has been reported that a tumor continues to express epidermal growth factor receptor even after developing progressive disease. To demonstrate the clinical relevance of erlotinib treatment after progressive disease, we investigated whether continuous administration of erlotinib in combination with chemotherapy has a useful effect on progressive disease development during erlotinib treatment. For this purpose, we examined the antitumor effect of a combination therapy of a chemotherapeutic agent with erlotinib using two types of erlotinib-resistant tumor xenograft models: a non-small cell lung cancer model, in which EBC-1, H1975 and HCC827TR3 tumors were implanted, and an HPAC pancreatic cancer cell xenograft which generates erlotinib-resistant tumors in vivo. As a result, the combination therapy showed a significantly higher antitumor activity compared with chemomonotherapy in all xenograft models except the H1975 xenografts. Furthermore, erlotinib alone suppressed the phosphorylation of epidermal growth factor receptor in HPAC tumors and the two non-small cell lung cancer cell lines other than H1975. Therefore, combination therapy which uses erlotinib can be considered effective if epidermal growth factor receptor phosphorylation is inhibited by erlotinib, even in erlotinib-resistant tumor xenograft models. Our results suggest that the continuous inhibition of epidermal growth factor receptor phosphorylation by erlotinib after progressive disease enhances the antitumor activity of chemotherapy.     

Strategies for overcoming resistance to EGFR family tyrosine kinase inhibitors

The first-generation epidermal growth factor receptor tyrosine kinase inhibitors erlotinib and gefitinib have been incorporated into treatment paradigms for patients with advanced non-small cell lung cancer. These agents are particularly effective in a subset of patients whose tumors harbor activating epidermal growth factor receptor mutations. However, most patients do not respond to these tyrosine kinase inhibitors, and those who do will eventually acquire resistance that typically results from a secondary epidermal growth factor receptor mutation (e.g., T790M), mesenchymal-epithelial transition factor amplification, or activation of other signaling pathways. For patients whose tumors have wild-type epidermal growth factor receptor, there are several known mechanisms of initial resistance (e.g., Kirsten rat sarcoma viral oncogene homolog mutations) but these do not account for all cases, suggesting that unknown mechanisms also contribute. To potentially overcome the issue of resistance, next-generation tyrosine kinase inhibitors are being developed, which irreversibly block multiple epidermal growth factor receptor family members (e.g., afatinib [BIBW 2992] and PF-00299804) and/or vascular endothelial growth factor receptor pathways (e.g., BMS-690514 and XL647). In addition, drugs that block parallel signaling pathways or signaling molecules downstream of the epidermal growth factor receptor, such as the insulin-like growth factor-1 receptor and the mammalian target of rapamycin, are undergoing clinical evaluation. As drug resistance appears to be pleomorphic, combinations of drugs or drugs with multiple targets may be more effective in circumventing resistance.     

Second-generation epidermal growth factor receptor tyrosine kinase inhibitors in non-small cell lung cancer

Inhibiting epidermal growth factor receptor (EGFR) signaling has proven to be an effective strategy for treating non-small cell lung cancer (NSCLC) patients and the first generation of agents developed for this purpose, gefitinib and erlotinib, stimulated a unique escalation in both biologic and clinical research within the field. Second-generation EGFR-targeted agents that aim to further improve patient outcomes are now in preclinical and clinical trials. This review discusses four promising agents that are currently being studied in NSCLC: EKB-569, HKI-272, CI-1033, and ZD6474.     

ZD1839 (IRESSA™): a selective EGFR-TK inhibitor

The recent development of highly selective, target-based cancer therapeutics, such as ZD1839 has resulted from a greater understanding of tumor biology. Amongst the most promising of new target-based agents are inhibitors of the epidermal growth factor receptor. ZD1839 is a potent, selective epidermal growth factor receptor tyrosine kinase inhibitor that has demonstrated promising results in early clinical trials.