Optimizing the sequence of anti-EGFR-targeted therapy in EGFR-mutant lung cancer

Metastatic EGFR-mutant lung cancers are sensitive to the first- and second-generation EGFR tyrosine kinase inhibitors (TKIs) gefitinib, erlotinib, and afatinib, but resistance develops. Acquired resistance to gefitinib or erlotinib occurs most commonly (>50%) via the emergence of a second-site EGFR mutation, T790M. Two strategies to overcome T790M-mediated resistance are dual inhibition of EGFR with afatinib plus the anti-EGFR antibody cetuximab (A+C), or mutant-specific EGFR inhibition with AZD9291. A+C and AZD9291 are now also being tested as first-line therapies, but whether these therapies will extend progression-free survival or induce more aggressive forms of resistance in this setting remains unknown. We modeled resistance to multiple generations of anti-EGFR therapies preclinically to understand the effects of sequential treatment with anti-EGFR agents on drug resistance and determine the optimal order of treatment. Using a panel of erlotinib/afatinib-resistant cells, including a novel patient-derived cell line (VP-2), we found that AZD9291 was more potent than A+C at inhibiting cell growth and EGFR signaling in this setting. Four of four xenograft-derived A+C-resistant cell lines displayed in vitro and in vivo sensitivity to AZD9291, but four of four AZD9291-resistant cell lines demonstrated cross-resistance to A+C. Addition of cetuximab to AZD9291 did not confer additive benefit in any preclinical disease setting. This work, emphasizing a mechanistic understanding of the effects of therapies on tumor evolution, provides a framework for future clinical trials testing different treatment sequences. This paradigm is applicable to other tumor types in which multiple generations of inhibitors are now available.

Therapeutic strategies utilized in the setting of acquired resistance to EGFR tyrosine kinase inhibitors

Patients with EGFR-mutant lung cancer derive significant therapeutic benefit from treatment with EGFR tyrosine kinase inhibitors (TKI). Unfortunately, acquired resistance is an inevitable consequence of this treatment strategy, with a broad variety of resistance mechanisms including acquired EGFR mutations (e.g., T790M) and activation of bypass signaling pathways, such as MET and HER2. Several therapeutic strategies hypothesized to delay or overcome resistance have been tested in clinical trials, including "next-generation" EGFR TKIs and rational combinations of targeted agents. However, to date, there are no FDA-approved therapies for patients with acquired resistance to first-line EGFR TKI therapy. There remains a critical need for more effective and better tailored treatments in this setting to match treatments to the individual patient and specific resistance mechanism at hand. In this review, we discuss known mechanisms of resistance to first-line EGFR TKI therapy and describe previous and ongoing strategies to overcome resistance.

Overcoming resistance to EGF receptor tyrosine kinase inhibitors in EGFR-mutated NSCLC

SUMMARY 

The development of EGF receptor (EGFR)-tyrosine kinase inhibitors has recently provided a new therapeutic option for patients with advanced EGFR-mutant NSCLC; however, the long-term efficacy of such therapies is generally limited by the development of resistance. Recognizing the mechanisms underlying resistance and developing therapies to overcome key resistance pathways is an area of intense, ongoing investigation. In this review, we will provide an overview of EGFR-mutated lung cancer, primary and acquired resistance to EGFR-tyrosine kinase inhibitors and emerging therapeutic strategies designed to circumvent resistance.

Discovery of selective and noncovalent diaminopyrimidine-based inhibitors of epidermal growth factor receptor containing the T790M resistance mutation

Activating mutations within the epidermal growth factor receptor (EGFR) kinase domain, commonly L858R or deletions within exon 19, increase EGFR-driven cell proliferation and survival and are correlated with impressive responses to the EGFR inhibitors erlotinib and gefitinib in nonsmall cell lung cancer patients. Approximately 60% of acquired resistance to these agents is driven by a single secondary mutation within the EGFR kinase domain, specifically substitution of the gatekeeper residue threonine-790 with methionine (T790M). Due to dose-limiting toxicities associated with inhibition of wild-type EGFR (wtEGFR), we sought inhibitors of T790M-containing EGFR mutants with selectivity over wtEGFR. We describe the evolution of HTS hits derived from Jak2/Tyk2 inhibitors into selective EGFR inhibitors. X-ray crystal structures revealed two distinct binding modes and enabled the design of a selective series of novel diaminopyrimidine-based inhibitors with good potency against T790M-containing mutants of EGFR, high selectivity over wtEGFR, broad kinase selectivity, and desirable physicochemical properties.

Moving from histological subtyping to molecular characterization: new treatment opportunities in advanced non-small-cell lung cancer

Over the last 10 years, the systemic treatment of advanced non-small-cell lung cancer has progressively moved away from the 'one-size-fits-all' approach to histological subtyping. Currently, there is a progressive implementation of targeted therapies based on specific molecular characteristics such as the EGF receptor sensitizing mutations and the anaplastic lymphoma kinase rearrangements. Despite the availability of effective agents against these abnormalities, acquired resistance is still a major issue. A new generation of tyrosine kinase inhibitors for EGF receptor and anaplastic lymphoma kinase targeting acquired resistance mechanisms have been recently investigated. Several promising tyrosine kinase inhibitors that hit other targets are also in clinical development, including: rat sarcoma gene/MEK, BRAF1, PIK3A, c-mesenchymal-epithelial transition, c-ros oncogene 1, rearranged during transfection, human EGFR 2, FGFR, VEGFR, PDGFR and discoidin death receptor 2. Furthermore, new advances in immunology have been achieved through the discovery of vaccines and immune checkpoint pathways such as the cytotoxic T-lymphocyte-associated antigen-4, programmed cell death protein 1 and its ligands.

Activity of the EGFR-HER2 dual inhibitor afatinib in EGFR-mutant lung cancer patients with acquired resistance to reversible EGFR tyrosine kinase inhibitors

BACKGROUND

The purpose of this study was to evaluate the efficacy of afatinib in EGFR-mutant metastatic NSCLC patients with acquired resistance to erlotinib or gefitinib.

MATERIALS AND METHODS

We retrospectively analyzed the outcome of patients with EGFR-mutant advanced NSCLC treated with afatinib after failure of chemotherapy and EGFR TKIs.

RESULTS

A total of 96 individuals were included in the study. According to EGFR status, most patients (n = 63; 65.6%) harbored a deletion in exon 19, and de novo T790M mutation was detected in 2 cases (T790M and exon 19). Twenty-four (25%) patients underwent repeated biopsy immediately before starting afatinib and secondary T790M was detected in 8 (33%) samples. Among the 86 patients evaluable for efficacy, response rate was 11.6%, with a median progression free-survival (PFS) and overall survival (OS) of 3.9 and 7.3 months, respectively. No significant difference in PFS and OS was observed according to type of last therapy received before afatinib, type of EGFR mutation or adherence to Jackman criteria, and patients benefiting from afatinib therapy had longer PFS and OS (P < .001). Outcome results for repeated biopsy patients were similar to the whole population, with no evidence of response in T790M-positive patients. All patients were evaluable for toxicity, and 81% experienced an AE of any grade, with grade 3 to 4 AEs, mainly diarrhea and skin toxicity, occurring in 19 (20%) patients.

CONCLUSION

Our results showed that afatinib has only modest efficacy in a real life population of EGFR mutant NSCLC patients with acquired resistance to erlotinib or gefitinib.