Podoplanin-positive cancer-associated fibroblasts in the tumor microenvironment induce primary resistance to EGFR-TKIs in lung adenocarcinoma with EGFR mutation.

PURPOSE The biologic characteristics of microenvironmental constituents, especially cancer-associated fibroblasts (CAF), can be key regulators of the cellular sensitivity to molecular-targeted therapy. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI) have marked therapeutic effects against non-small cell lung cancer (NSCLC) with EGFR mutations, but some patients have exhibited primary resistance to EGFR-TKIs. We recently reported that podoplanin-positive fibroblasts are associated with a tumor-promoting phenotype of CAFs in lung adenocarcinoma. The aim of this study was to evaluate whether the susceptibility of NSCLC to EGFR-TKIs could be affected by podoplanin-expressing CAFs. EXPERIMENTAL DESIGN We evaluated the EGFR-TKI sensitivity of EGFR-mutant lung adenocarcinoma cell lines cocultured with podoplanin-expressing CAFs. We also examined the association between the expression of podoplanin in CAFs in surgical specimens and EGFR-TKI response of postoperative recurrent patients with EGFR mutations (N = 106). RESULTS Lung adenocarcinoma cell lines became more resistant to EGFR-TKI when cocultured with podoplanin-expressing CAFs, compared with control CAFs in vitro. The knockdown of podoplanin expression on CAFs cancelled the resistance to EGFR-TKIs in cancer cells. Compared with control CAFs, the cancer cells that were cocultured with podoplanin-positive CAFs continued to exhibit significantly higher p-ERK levels after treatment with gefitinib. Furthermore, postoperative recurrent patients with podoplanin-positive CAFs had a significantly lower overall response rate to EGFR-TKIs compared with those with podoplanin-negative CAFs (53% vs. 83%; P < 0.01). CONCLUSIONS Podoplanin-positive CAFs play an important role in primary resistance to EGFR-TKIs and may be an ideal therapeutic target for use in combination therapy with EGFR-TKIs.