Afatinib plus PEM and CBDCA overcome osimertinib resistance in EGFR‐mutated NSCLC with high thrombospondin‐1 expression

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Abstract
Osimertinib induces a marked response in non–small‐cell lung cancer (NSCLC) patients harboring epidermal growth factor receptor (EGFR) gene mutations. However, acquired resistance to osimertinib remains an inevitable problem. In this study, we aimed to investigate osimertinib‐resistant mechanisms and evaluate the combination therapy of afatinib and chemotherapy. We established osimertinib‐resistant cell lines (PC‐9‐OR and H1975‐OR) from EGFR‐mutant lung adenocarcinoma cell lines PC‐9 and H1975 by high exposure and stepwise method. Combination therapy of afatinib plus carboplatin (CBDCA) and pemetrexed (PEM) was effective in both parental and osimertinib‐resistant cells. We found that expression of thrombospondin‐1 (TSP‐1) was upregulated in resistant cells using cDNA microarray analysis. We demonstrated that TSP‐1 increases the expression of matrix metalloproteinases through integrin signaling and promotes tumor invasion in both PC‐9‐OR and H1975‐OR, and that epithelial‐to‐mesenchymal transition (EMT) was involved in H1975‐OR. Afatinib plus CBDCA and PEM reversed TSP‐1‐induced invasion ability and EMT changes in resistant cells. In PC‐9‐OR xenograft mouse models (five female Balb/c‐Nude mice in each group), combination therapy strongly inhibited tumor growth compared with afatinib monotherapy (5 mg/kg, orally, five times per week) or CBDCA (75 mg/kg, intraperitoneally, one time per week) + PEM (100 mg/kg, intraperitoneally, one time per week) over a 28‐day period. These results suggest that the combination of afatinib plus CBDCA and PEM, which effectively suppresses TSP‐1 expression, may be a promising option in EGFR‐mutated NSCLC patients after the acquisition of osimertinib resistance.
Funding Information
  • Boehringer Ingelheim Japan

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