Drug tolerance is the basis for acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) including osimertinib, through mechanisms that still remain unclear. Here, we show that while AXL-low expressing EGFR mutated lung cancer (EGFRmut-LC) cells are more sensitive to osimertinib than AXL-high expressing EGFRmut-LC cells, a small population emerge osimertinib tolerance. The tolerance is mediated by the increased expression and phosphorylation of insulin-like growth factor-1 receptor (IGF-1R), caused by the induction of its transcription factor FOXA1. IGF-1R maintains association with EGFR and adaptor proteins, including Gab1 and IRS1, in the presence of osimertinib and restores the survival signal. In AXL-low-expressing EGFRmut-LC cell-derived xenograft and patient-derived xenograft models, transient IGF-1R inhibition combined with continuous osimertinib treatment could eradicate tumors and prevent regrowth even after the cessation of osimertinib. These results indicate that optimal inhibition of tolerant signals combined with osimertinib may dramatically improve the outcome of EGFRmut-LC.

Background: Non‐small cell lung cancer patients with EGFR mutation have a high rate of brain metastases, and EGFR tyrosine kinase inhibitors (TKIs) are the principal therapeutic approach. However, acquired targeted therapy resistance is the main reason for EGFR‐TKIs' treatment failure. At present, the mechanism of intracranial acquired targeted therapy resistance is limited, mainly due to the lack of a cell line that can be used for its study.Methods: A brain parenchymal metastatic sample that progressed after third‐generation EGFR‐TKI treatment was used to establish a cell line named AlmoR1. The genetic characteristics of the cell line were evaluated by short tandem repeat (STR) profiling and whole‐exome sequencing analysis. The phenotypic characteristics were characterized by CCK8, western blot, HE staining, immunohistochemistry (IHC), and orthotopic brain tumor model.Results: The cell line we successfully established, AlmoR1, can be passed in vitro stably. STR analysis revealed it was a novel NSCLC BM cell line. It harbors the EGFR E746_A750del (ex19del) mutation, and the IC50 to almonertinib and osimertinib of AlmoR1 was significantly higher than that of sensitive cells. In our orthotopic brain tumor model construction with AlmoR1 cells, 75% (3/4) tumor formation can be observed in the living system.Conclusions: These data suggest that the established cell line, AlmoR1, preserved the resistance to broad third‐generation EGFR‐TKIs and good tumorigenicity in an intracranial orthotopic model, so that it can serve as a new tool to elucidate the pathogenesis, explore new treatment methods, and conduct the development of new drugs for targeted therapy resistance of brain metastases.

Genomic profiling has revolutionized treatment options for patients with oncogene-driven cancers, such as epidermal growth factor receptor (EGFR) mutant carcinoma. Rearranged during transfection (RET) rearrangement, as one of the main activated oncogenes, has been well studied and found to be involved in the malignant behavior of carcinogenesis, resulting in acquired resistance to EGFR tyrosine kinase inhibitors and inducing an intrinsic resistance to immunotherapy. Thus, targeted therapies have been investigated against RET arrangement cancers, including several multi-kinase inhibitors and selective RET inhibitors. However, modest efficacy, a relatively high rate of toxicity, and poor effectiveness against brain metastasis are common limitations of multi-targeted novel molecular inhibitors. A promising prospect was shown recently in selective RET inhibitors in several ongoing clinical trials. In this review, we reviewed the concurrent dilemmas of targeted therapies against RET arrangement cancer from preclinical and clinical studies and proposed several clinical considerations for clinical practice prospectively.