Cis-oriented solvent-front EGFR G796S mutation in tissue and ctDNA in a patient progressing on osimertinib: a case report and review of the literature

Preclinical Models for Acquired Resistance to Third-Generation EGFR Inhibitors in NSCLC: Functional Studies and Drug Combinations Used to Overcome Resistance

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) are currently recommended as first-line treatment for advanced non-small-cell lung cancer (NSCLC) with EGFR-activating mutations. Third-generation (3rd G) EGFR-TKIs, including osimertinib, offer an effective treatment option for patients with NSCLC resistant 1st and 2nd EGFR-TKIs. However, the efficacy of 3rd G EGFR-TKIs is limited by acquired resistance that has become a growing clinical challenge. Several clinical and preclinical studies are being carried out to better understand the mechanisms of resistance to 3rd G EGFR-TKIs and have revealed various genetic aberrations associated with molecular heterogeneity of cancer cells. Studies focusing on epigenetic events are limited despite several indications of their involvement in the development of resistance. Preclinical models, established in most cases in a similar manner, have shown different prevalence of resistance mechanisms from clinical samples. Clinically identified mechanisms include EGFR mutations that were not identified in preclinical models. Thus, NRAS genetic alterations were not observed in patients but have been described in cell lines resistant to 3rd G EGFR-TKI. Mainly, resistance to 3rd G EGFR-TKI in preclinical models is related to the activation of alternative signaling pathways through tyrosine kinase receptor (TKR) activation or to histological and phenotypic transformations. Yet, preclinical models have provided some insight into the complex network between dominant drivers and associated events that lead to the emergence of resistance and consequently have identified new therapeutic targets. This review provides an overview of preclinical studies developed to investigate the mechanisms of acquired resistance to 3rd G EGFR-TKIs, including osimertinib and rociletinib, across all lines of therapy. In fact, some of the models described were first generated to be resistant to first- and second-generation EGFR-TKIs and often carried the T790M mutation, while others had never been exposed to TKIs. The review further describes the therapeutic opportunities to overcome resistance, based on preclinical studies.

Case Report: Durable Response to the Combination of Brigatinib and Cetuximab Plus Icotinib in a NSCLC Patient Harboring EGFR L858R-T790M-cis-G796S and L718Q Resistance Mutations Following Progression With Osimertinib

The efficacy of osimertinib is severely limited by the emergence of EGFR C797S, which is detected in either the cis or trans position with T790M when osimertinib is used as a second-line treatment, and which is largely identified in combination with an EGFR 19 deletion. The EGFR T790M-cis-G796S mutation, which also occurs in exon 20 as C797S, participates in osimertinib resistance. To date, limited data for overcoming this resistance mutation have been reported. Here, we report data for an advanced NSCLC patient who developed EGFR L858R-T790M-cis-G796S and EGFR L718Q resistance co-mutations following progression with osimertinib. Such a case has rarely been reported, and under chemotherapy guidelines for this situation, no other effective treatment is recommended. The patient in our case experienced remarkable clinical improvement and good tolerance to the combination target therapy of brigatinib and cetuximab plus icotinib. At the time of our patient’s last follow-up and prior to publication, our patient had reached more than 9 months of progression-free survival (PFS) and felt very well. Our finding provides clinical evidence that the combined target therapy of brigatinib and cetuximab may potentially be an effective treatment strategy for patients with an acquired EGFR T790M-cis-G796S resistance mutation following osimertinib treatment.

The next tier of EGFR resistance mutations in lung cancer

EGFR mutations account for the majority of druggable targets in lung adenocarcinoma. Over the past decades the optimization of EGFR inhibitors revolutionized the treatment options for patients suffering from this disease. The pace of this development was largely dictated by the inevitable emergence of resistance mutations during drug treatment. As a result, a rapid understanding of the structural and molecular biology of the individual mutations is the key for the development of next-generation inhibitors. Currently, the field faces an unprecedented number of combinations of activating mutations with distinct resistance mutations in parallel to the approval of osimertinib as a first-line drug for EGFR-mutant lung cancer. In this review, we present a survey of the diverse landscape of EGFR resistance mechanisms with a focus on new insights into on-target EGFR kinase mutations. We discuss array of mutations, their structural effects on the EGFR kinase domain as well as the most promising strategies to overcome the individual resistance profiles found in lung cancer patients.

Making NSCLC Crystal Clear: How Kinase Structures Revolutionized Lung Cancer Treatment

The parallel advances of different scientific fields provide a contemporary scenario where collaboration is not a differential, but actually a requirement. In this context, crystallography has had a major contribution on the medical sciences, providing a “face” for targets of diseases that previously were known solely by name or sequence. Worldwide, cancer still leads the number of annual deaths, with 9.6 million associated deaths, with a major contribution from lung cancer and its 1.7 million deaths. Since the relationship between cancer and kinases was unraveled, these proteins have been extensively explored and became associated with drugs that later attained blockbuster status. Crystallographic structures of kinases related to lung cancer and their developed and marketed drugs provided insight on their conformation in the absence or presence of small molecules. Notwithstanding, these structures were also of service once the initially highly successful drugs started to lose their effectiveness in the emergence of mutations. This review focuses on a subclassification of lung cancer, non-small cell lung cancer (NSCLC), and major oncogenic driver mutations in kinases, and how crystallographic structures can be used, not only to provide awareness of the function and inhibition of these mutations, but also how these structures can be used in further computational studies aiming at addressing these novel mutations in the field of personalized medicine.

Analysis of resistance mechanisms to abivertinib, a third-generation EGFR tyrosine kinase inhibitor, in patients with EGFR T790M-positive non-small cell lung cancer from a phase I trial

BACKGROUND

Resistance to third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) presents a major clinical challenge in advanced non-small cell lung cancer (NSCLC). Here, we report resistance mechanisms to abivertinib, a novel third-generation EGFR TKI, from a phase I dose-escalation/expansion study (NCT02330367).

METHODS

Patients with EGFR T790M-positive advanced NSCLC and progression on prior EGFR TKIs received abivertinib in dose escalation (50-350 mg twice daily [BID]) or expansion (300 mg BID) cohorts. Patients enrolled at Guangdong Lung Cancer Institute who underwent next-generation sequencing (NGS)-based genomic profiling upon abivertinib progression (prior to October 30, 2018) were enrolled in this exploratory analysis.

FINDINGS

Thirty of 73 patients enrolled were eligible for resistance analysis. Upon abivertinib progression, 27 patients provided plasma samples (six patients also provided paired samples from the progression sites) and three patients only provided tissue samples from the progression sites for NGS. A heterogeneous landscape of resistance to abivertinib was observed: 15% (4/27) experienced EGFR T790M loss and 13% (4/30) developing EGFR tertiary mutations including C797S. EGFR amplification was observed in 11 patients (37%), and considered a putative resistance mechanism in seven (23%) patients. Other EGFR-independent resistance mechanisms involved CDKN2A, MET, PIK3CA, HER2, TP53, Rb1 and small-cell lung cancer transformation.

INTERPRETATION

Our findings reveal a heterogenous pattern of resistance mechanisms to abivertinib which is distinct from that previously reported with osimertinib. EGFR amplification was the most common resistance mechanism in this cohort. FUND: The National Key R&D Program of China (Grant No. 2016YFC1303800), Key Lab System Project of Guangdong Science and Technology Department - Guangdong Provincial Key Lab of Translational Medicine in Lung Cancer (Grant No. 2012A061400006/2017B030314120).

A "triple whammy" in adenocarcinoma lung

Osimertinib (AZD9291), a third-generation epidermal growth factor receptor (EGFR)-tyrosine-kinase inhibitor (TKI), is useful in the treatment of non-small cell lung cancer who show resistance to first-generation EGFR-TKIs and harbor T790M mutation. Acquisition of resistance to osimertinib due to several mechanisms has been reported. We report the first case of an Indian patient with osimertinib resistance, due to C797S mutation. A 52-year-old nonsmoker man was detected to have metastatic lung adenocarcinoma (Stage IV) with EGFR exon 19 deletion and treated with erlotinib. After 12 months of response with erlotinib, he developed resistance because of the development of T790M mutation. He was started on osimertinib, with which he responded for 20 months. A follow-up positron emission tomography scan showed progressive disease. Subsequent liquid biopsy did not detect any mutation. However, rebiopsy of the lung lesion showed additional C797S mutation (in cis association with T790M). Hence, the patient was diagnosed to have “triple whammy,” i.e., triple mutation of exon 19 deletion, T790M, and C797S mutations.

Liquid Biopsy to Identify Actionable Genomic Alterations

Liquid biopsy has been used extensively in solid malignancies to detect actionable driver mutations, to monitor treatment response, to detect recurrence, to identify resistance mechanisms, and to prognosticate outcome. Although many liquid biopsy sequencing platforms are being used, only five test kits have received government approval. We review representative literature on these government-approved liquid biopsy kits, which are primarily used to detect EGFR mutation in lung cancer and RAS ( KRAS, NRAS, BRAF) mutations in colorectal carcinoma. Another emerging use of single-gene liquid biopsy is to detect PIK3CA mutations and to understand resistance to hormonal blockade in breast and prostate cancers. The two most commonly used next-generation sequencing (NGS) liquid biopsy tests (Guardant 360, Guardant Health; FoundationACT, Foundation Medicine Inc.) are discussed. The ability and the applicability of NGS platform to detect tumor mutation burden are also addressed. Finally, the use of circulating tumor DNA (ctDNA) to detect minimal residual disease may be the most important use of ctDNA in the setting of tumor heterogeneity. The ability to identify "shedders" and "nonshedders" of ctDNA may provide important insight into the clinicopathologic characteristics of the tumor and portend important prognostic significance regarding survival.