Lung adenocarcinoma cells floating in lymphatic vessels resist anoikis by expressing phosphorylated Src

The ability to resist anoikis is critical for carcinoma cells to metastasize. Although several lung adenocarcinoma cell lines were shown to repress anoikis through the activation of Src, it remains unknown whether Src actually plays a crucial role in anoikis resistance in lung adenocarcinoma tissues. We examined 20 human lung adenocarcinoma tissues with lymphatic permeation and nine cell lines to investigate whether intralymphatic floating carcinoma cells in the tissues, used as an in vivo model of anoikis resistance, actually suppressed anoikis and whether cell lines in suspension culture, an in vitro model of anoikis resistance, survived through Src activation. We observed that the intralymphatic carcinoma cells aggregated tightly to form nests expressing E-cadherin and phosphorylated Src (p-Src). The apoptotic indices of these cells were comparable to those of extracellular matrix adhesive cells in all tissues, indicating that the intralymphatic cells actually evaded anoikis. Next, we found that the nine cell lines in suspension aggregated loosely (five cell lines) or tightly (four cell lines), and all cells resisted anoikis. Upon detachment, four cell lines (LC-KJ, HCC827, H1650, and H1975) formed compact spheroids that expressed E-cadherin and p-Src. The spheroids were similar to intralymphatic tumour nests and were thus considered to be a suitable model of the nests. The spheroids of the four cell lines underwent apoptosis after treatment with the Src/Abl/Kit inhibitor PP1 or Src/Abl inhibitor bosutinib. On the other hand, the Abl/Kit inhibitor imatinib did not affect cell growth or apoptosis in the four types of spheroids. These results indicate that Src, but not Abl or Kit, plays an essential role in the development of anoikis resistance in lung adenocarcinomas.