Characterization of epidermal growth factor receptor ( EGFR ) P848L, an unusual EGFR variant present in lung cancer patients, in a murine Ba/F3 model

Lung cancer patients with mutations in epidermal growth factor receptor ( EGFR ) benefit from treatments targeting tyrosine kinase inhibitors ( TKI s). However, both intrinsic and acquired resistance of tumors to TKI s are common, and EGFR variants have been identified that are resistant to multiple TKI s. In the present study, we characterized selected EGFR variants previously observed in lung cancer patients and expressed in a murine bone marrow pro‐B Ba/F3 cell model. Among these EGFR variants, we report that an exon 20 deletion/insertion mutation S768ins VGH is resistant to erlotinib (a first‐generation TKI ), but sensitive to osimertinib (a third‐generation TKI ). We also characterized a rare exon 21 germline variant, EGFR P848L, which transformed Ba/F3 cells and conferred resistance to multiple EGFR ‐targeting TKI s. Our analysis revealed that P848L (a) does not bind erlotinib; (b) is turned over less rapidly than L858R (a common tumor‐derived EGFR mutation); (c) is not autophosphorylated at Tyr 1045 [the major docking site for Cbl proto‐oncogene (c‐Cbl) binding]; and (d) does not bind c‐Cbl. Using viability assays including 300 clinically relevant targeted compounds, we observed that Ba/F3 cells transduced with EGFR P848L, S768ins VGH , or L858R have very different drug‐sensitivity profiles. In particular, EGFR P848L, but not L858R or S768ins VGH , was sensitive to multiple Janus kinase 1/2 inhibitors. In contrast, cells driven by L858R, but not by P848L, were sensitive to multikinase MAPK /extracellular‐signal‐regulated kinase (ERK) kinase and ERK inhibitors including EGFR ‐specific TKI s. These observations suggest that continued investigation of rare TKI ‐resistant EGFR variants is warranted to identify optimal treatments for cancer.