[Biological Differences between EGFR ex19del and ex21L858R-Preclinical Models Using an Engineered Pair of Isogenic...

Epidermal growth factor receptor (EGFR) mutations are among the most common genetic alterations in non‒small cell lung cancer (NSCLC), with ex19del and ex21L858R being the most prevalent. Ex19del correlates with better outcomes of EGFR tyrosine kinase inhibitors (EGFR‒TKIs) than L858R. The RELAY phase Ⅲ study showed that ramucirumab plus erlotinib as first‒line therapy provided similar progression‒free survival for both mutations. Preclinical studies using NSCLC cell line PC9 (ex19del) and its CRISPR‒engineered subline PC9EX21 (ex21L858R mutations) were conducted to explore the molecular basis of these clinical observations and assess the impact of these mutations on cell biology and responses to EGFR‒TKI and ramucirumab. PC9 and PC9EX21 cells had similar morphology, but PC9EX21 cells were larger, grew slower, had greater migratory potential, and exhibited delayed tumor formation in vivo. Fluorescence‒activated cell sorting analysis showed lower EGFR and higher human epidermal growth factor receptor 2 (HER2)/HER3 expression in PC9EX21, with vascular endothelial growth factor receptor 2 mRNA levels 8‒times higher than ex19del. Transcriptomic profiling and multiplex proteomics identified significant gene expression differences (receptor tyrosine kinase) and altered signaling pathways in PC9EX21. Ramucirumab enhanced erlotinib's anti‒proliferative effect in PC9EX21 but had a limited effect in ex19del. These findings highlight key biological differences between ex19del and L858R mutations, emphasizing the need for personalized treatment strategies in NSCLC.