In the past two decades, several molecular targeted inhibitors have been developed and evaluated clinically to improve the survival of patients with cancer. Molecular targeted inhibitors inhibit the activities of pathogenic tyrosine kinases. Particularly, aberrant receptor tyrosine kinase (RTK) activation is a potential therapeutic target. An increased understanding of genetics, cellular biology and structural biology has led to the development of numerous important therapeutics. Pathogenic RTK mutations, deletions, translocations and amplification/over-expressions have been identified and are currently being examined for their roles in cancers. Therapies targeting RTKs are categorized as small-molecule inhibitors and monoclonal antibodies. Studies are underway to explore abnormalities in 20 types of RTK subfamilies in patients with cancer or other diseases. In this review, we describe representative RTKs important for developing cancer therapeutics and predicting or evaluated resistance mechanisms.

Cancer therapies targeting epidermal growth factor receptor (EGFR), such as small-molecule kinase inhibitors and monoclonal antibodies, have been developed as standard therapies for several cancers, such as non-small cell lung cancer, colorectal cancer, pancreatic cancer, breast cancer, and squamous cell carcinoma of the head and neck. Although these therapies can significantly prolong progression-free survival, curative effects are not often achieved because of intrinsic and/or acquired resistance. The resistance mechanisms to EGFR-targeted therapies can be categorized as resistant gene mutations, activation of alternative pathways, phenotypic transformation, and resistance to apoptotic cell death. Analysis of the processes that modulate EGFR signal transduction by EGFR-targeted inhibitors, such as tyrosine kinase inhibitors and monoclonal antibodies, has revealed new therapeutic opportunities and has elucidated novel mechanisms contributing to the discovery of more effective anticancer treatments. In this review, we discuss the roles of EGFR in cancer development, therapeutic strategies for targeting EGFR, and resistance mechanisms to EGFR-targeted therapies, with a focus on cancer therapies for individual patients.

The tyrosine kinase activity of epidermal growth factor receptors (EGFRs) plays critical roles in cell proliferation, regeneration, tumorigenesis, and anticancer resistance. Non-small-cell lung cancer patients who responded to EGFR-tyrosine kinase inhibitors (EGFR-TKIs) and obtained survival benefits had somatic EGFR mutations. EGFR-TKI-related adverse events (AEs) are usually tolerable and manageable, although serious AEs, including lung injury (specifically, interstitial lung disease (ILD), causing 58% of EGFR-TKI treatment-related deaths), occur infrequently. The etiopathogenesis of EGFR-TKI-induced ILD remains unknown. Risk factors, such as tobacco exposure, pre-existing lung fibrosis, chronic obstructive pulmonary disease, and poor performance status, indicate that lung inflammatory circumstances may worsen with EGFR-TKI treatment because of impaired epithelial healing of lung injuries. There is limited evidence from preclinical and clinical studies of the mechanisms underlying EGFR-TKI-induced ILD in the available literature. Herein, we evaluated the relationship between EGFR-TKIs and AEs, especially ILD. Recent reports on mechanisms inducing lung injury or resistance in cytokine-rich circumstances were reviewed. We discussed the relevance of cytotoxic agents or immunotherapeutic agents in combination with EGFR-TKIs as a potential mechanism of EGFR-TKI-related lung injury and reviewed recent developments in diagnostics and therapeutics that facilitate recovery from lung injury or overcoming resistance to anti-EGFR treatment.

Pneumonitis is the leading cause of death associated with the use of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKIs) against non-small cell lung cancer (NSCLC). However, the risk factors and the mechanism underlying this toxicity have not been elucidated. Tumor necrosis factor (TNF) has been reported to transactivate EGFR in pulmonary epithelial cells. Hence, we aimed to test the hypothesis that EGFR tyrosine kinase activity regulates TNF-mediated bronchial epithelial cell survival, and that inhibition of EGFR activity increases TNF-induced lung epithelial cell apoptosis. We used surfactant protein C (SPC)-TNF transgenic (tg) mice which overexpress TNF in the lungs. In this model, gefitinib, an EGFR-TKI, enhanced lung epithelial cell apoptosis and lymphocytic inflammation, indicating that EGFR tyrosine kinase prevents TNF-induced lung injury. Furthermore, IL-17A was significantly upregulated by gefitinib in SPC-TNF tg mice and p38MAPK activation was observed, indicative of a pathway involved in lung epithelial cell apoptosis. Moreover, in lung epithelial cells, BEAS-2B, TNF stimulated EGFR transactivation via the TNF-α-converting enzyme in a manner that requires heparin binding (HB)-EGF and transforming growth factor (TGF)-α. These novel findings have significant implications in understanding the role of EGFR in maintaining human bronchial epithelial cell homeostasis and in NSCLC treatment.

To date, there have been no head-to-head randomized controlled trials (RCTs) comparing the safety and efficacy of lorlatinib and alectinib in anaplastic lymphoma kinase (ALK) rearrangement-positive (ALK-p) ALK-inhibitor‒naïve advanced non-small cell lung cancer (NSCLC). We performed a network meta-analysis comparing six treatment arms (lorlatinib, brigatinib, alectinib, ceritinib, crizotinib, and platinum-based chemotherapy) in overall participants and in Asian and non-Asian subgroups. Primary endpoints were progression-free survival (PFS), overall survival (OS), and grade 3 or higher adverse events (G3-AEs). There were no significant differences between lorlatinib and alectinib in overall participants for both PFS (hazard ratio [HR], 0.742; 95% credible interval [CrI], 0.466–1.180) and OS (HR, 1.180; 95% CrI, 0.590–2.354). In the Asian subgroup, there were no significant differences in PFS between lorlatinib and alectinib (HR, 1.423; 95% CrI, 0.748–2.708); however, in the non-Asian subgroup, PFS was significantly better with lorlatinib than with alectinib (HR, 0.388; 95% CrI, 0.195–0.769). The incidence of G3-AEs in overall participants was significantly higher with lorlatinib than with alectinib (risk ratio, 1.918; 95% CrI, 1.486–2.475). These results provide valuable information regarding the safety and efficacy of lorlatinib in ALK-p ALK-inhibitor‒naïve advanced NSCLC. Larger head-to-head RCTs are needed to validate the study results.

To date, no head-to-head trials have compared the efficacy of brigatinib and alectinib against anaplastic lymphoma kinase (ALK) rearrangement-positive (ALK-p), ALK-inhibitor-naïve, advanced non-small cell lung cancer (NSCLC) with central nervous system (CNS) metastasis. We conducted an indirect treatment comparison (ITC) between brigatinib and alectinib, with crizotinib as a common comparator, using a Bayesian model with non-informative prior distribution and assessed the between-study heterogeneity of the studies. The primary efficacy endpoint was progression-free survival (PFS), and efficacy was ranked using the surface under the cumulative ranking (SUCRA) curve values. ITC analysis showed that there were no significant differences in PFS between the brigatinib and alectinib arms. However, the SUCRA values revealed that alectinib ranked the highest by efficacy in the overall patient population, whereas brigatinib ranked the highest by efficacy in the CNS metastasis sub-group. Although there were no significant differences in the incidence of G3–5 adverse events between the brigatinib and alectinib arms in the overall patient population, the data were deemed insufficient for the CNS metastasis sub-group analysis. This study provides critical information to clinicians regarding the efficacy of brigatinib for ALK-p, ALK-inhibitor-naïve, advanced NSCLC patients, with and without CNS metastasis. Larger randomized, controlled trials are warranted to confirm our results.