Csf1r-mApple transgene expression and ligand binding in vivo reveal dynamics of CSF1R expression within the mononuclear phagocyte system

CSF1 is the primary growth factor controlling macrophage numbers, but whether expression of the CSF1 receptor differs between discrete populations of mononuclear phagocytes remains unclear. We have generated a Csf1r-mApple transgenic fluorescent reporter mouse that, in combination with lineage tracing, Alexa Fluor 647-labeled CSF1-Fc and CSF1, and a modified Delta Csf1-enhanced cyan fluorescent protein (ECFP) transgene that lacks a 150 bp segment of the distal promoter, we have used to dissect the differentiation and CSF1 responsiveness of mononuclear phagocyte populations in situ. Consistent with previous Csf1r-driven reporter lines, Csf1r-mApple was expressed in blood monocytes and at higher levels in tissue macrophages, and was readily detectable in whole mounts or with multiphoton microscopy. In the liver and peritoneal cavity, uptake of labeled CSF1 largely reflected transgene expression, with greater receptor activity in mature macrophages than monocytes and tissue-specific expression in conventional dendritic cells. However, CSF1 uptake also differed between subsets of monocytes and discrete populations of tissue macrophages, which in macrophages correlated with their level of dependence on CSF1 receptor signaling for survival rather than degree of transgene expression. A double Delta Csf1r-ECFP-Csf1r-mApple transgenic mouse distinguished subpopulations of microglia in the brain, and permitted imaging of interstitial macrophages distinct from alveolar macrophages, and pulmonary monocytes and conventional dendritic cells. The Csf1r-mApple mice and fluorescently labeled CSF1 will be valuable resources for the study of macrophage and CSF1 biology, which are compatible with existing EGFP-based reporter lines

Combatting acquired resistance to osimertinib in EGFR-mutant lung cancer

The discovery of activating mutations in epidermal growth factor receptor (EGFR) in non-small-cell lung cancer transformed the care and prognosis of patients and heralded the era of ‘personalized medicine’ in thoracic oncology. Osimertinib, a third-generation EGFR inhibitor, has been established as the preferred EGFR inhibitor for newly diagnosed patients which urged the need to develop treatment options for patients progressing on first-line osimertinib. However, acquired resistance invariably emerges and numerous efforts have been attempted to delay or overcome acquired resistance. In this article, we thoroughly reviewed the current understanding of osimertinib resistance mechanisms and explored the established and emerging treatment options. Newer treatment strategies targeting EGFR-dependent or -independent resistance mechanisms, novel approaches using bispecific antibodies and antibody–drug conjugates will be discussed. Moreover, what to do with brain only progression, and how to incorporate immunotherapy in EGFR-mutant lung cancer will be discussed. Lastly, future perspectives on the ongoing clinical trials and combination of front-line therapy will be introduced

Activity and Safety of Mobocertinib (TAK-788) in Previously Treated Non–Small Cell Lung Cancer with EGFR Exon 20 Insertion Mutations from a Phase I/II Trial

Mobocertinib, an oral epidermal growth factor receptor (EGFR) inhibitor targeting EGFR gene mutations, including exon 20 insertions (EGFRex20ins), in non-small cell lung cancer, was evaluated in a phase I/II dose-escalation/expansion trial (ClinicalTrials.gov NCT02716116). Dose escalation identified 160 mg/d as the recommended phase 2 dose and maximum tolerated dose. Among 136 patients treated with 160 mg/d, the most common any-grade treatment-related adverse events (TRAE; >25%) were diarrhea (83%), nausea (43%), rash (33%), and vomiting (26%), with diarrhea (21%) the only grade ≥3 TRAE >5%. Among 28 EGFRex20ins patients treated at 160 mg/d, the investigator-assessed confirmed response rate was 43% (12/28; 95% confidence interval, 24%-63%) with median duration of response of 14 months (5.0-not reached) and median progression-free survival of 7.3 months (4.4-15.6). Mobocertinib demonstrated antitumor activity in patients with diverse EGFRex20ins variants with a safety profile consistent with other EGFR inhibitors. SIGNIFICANCE: No oral EGFR-targeted therapies are currently approved for patients with EGFRex20ins NSCLC. Mobocertinib demonstrated antitumor activity with manageable toxicity in patients with advanced EGFRex20ins NSCLC in this study, supporting additional development of mobocertinib in this patient population.See related commentary by Pacheco, p. 1617.This article is highlighted in the In This Issue feature, p. 1601

Activity and Safety of Mobocertinib (TAK-788) in Previously Treated Non-Small Cell Lung Cancer With EGFR Exon 20 Insertion Mutations From a Phase 1/2 Trial

Mobocertinib, an oral epidermal growth factor receptor (EGFR) inhibitor targeting EGFR gene mutations including exon 20 insertions (EGFRex20ins) in non-small cell lung cancer, was evaluated in a phase 1/2 dose-escalation/expansion trial (ClinicalTrials.gov NCT02716116). Dose escalation identified 160 mg daily as the recommended phase 2 dose and maximum tolerated dose. Among 136 patients treated with 160 mg daily, the most common any grade treatment-related adverse events (TRAEs; \u3e25%) were diarrhea (83%), nausea (43%), rash (33%), and vomiting (26%), with diarrhea (21%) the only grade {greater than or equal to}3 TRAE \u3e5%. Among 28 EGFRex20ins patients treated at 160 mg daily, the investigator-assessed confirmed response rate was 43% (12/28; 95% confidence interval (CI): 24-63%) with median duration of response of 14 months (5.0-not reached), and median progression-free survival of 7.3 months (4.4-15.6). Mobocertinib demonstrated antitumor activity in patients with diverse EGFRex20ins variants with a safety profile consistent with other EGFR inhibitors

Circulating tumour DNA profiling reveals heterogeneity of EGFR inhibitor resistance mechanisms in lung cancer patients

Circulating tumour DNA (ctDNA) analysis facilitates studies of tumour heterogeneity. Here we employ CAPP-Seq ctDNA analysis to study resistance mechanisms in 43 non-small cell lung cancer (NSCLC) patients treated with the third-generation epidermal growth factor receptor (EGFR) inhibitor rociletinib. We observe multiple resistance mechanisms in 46% of patients after treatment with first-line inhibitors, indicating frequent intra-patient heterogeneity. Rociletinib resistance recurrently involves MET, EGFR, PIK3CA, ERRB2, KRAS and RB1. We describe a novel EGFR L798I mutation and find that EGFR C797S, which arises in ∼33% of patients after osimertinib treatment, occurs in <3% after rociletinib. Increased MET copy number is the most frequent rociletinib resistance mechanism in this cohort and patients with multiple pre-existing mechanisms (T790M and MET) experience inferior responses. Similarly, rociletinib-resistant xenografts develop MET amplification that can be overcome with the MET inhibitor crizotinib. These results underscore the importance of tumour heterogeneity in NSCLC and the utility of ctDNA-based resistance mechanism assessment