Acquisition of anoikis resistance is a critical step in the progression of oral tongue cancer

Abstract 

We hypothesized that acquisition of resistance to anoikis is a critical step in oral cancer progression. To test this hypothesis, we compared a panel of cell lines derived from human oral tissues across the spectrum of tumor progression from oral keratinocytes (HOK-16B), invasive oral squamous cell carcinoma (Tu167), and finally metastatic carcinoma (TxCS-1, MDA1986) for their sensitivity to detachment from the extracellular matrix. The relationship between stage of tumor progression and anoikis resistance was demonstrated by the apoptotic fractions after 48 h in suspension culture which were 93.33, 61.6, 34.5, and 3.71%, respectively. To further demonstrate that anoikis resistance is important for tumor progression, we selected a highly anoikis resistant cell line, JMAR, by serial passage of the Tu167 cell line in suspension culture. Initially, the JMAR line, and clones derived from it, were characterized for anoikis resistance in vitro, and after 72 h in suspension culture the rates of anoikis in the Tu167 and JMAR lines were found to be 73 and 26%, respectively. The degree of anoikis resistance was found to correlate with survival of nude mice orthotopically injected with 5×10⁵ Tu167 or JMAR cells. The JMAR mice had a median survival of 17 days versus over 30 days in mice implanted with the Tu167 line. Finally, we found that in vivo selection in the orthotopic model for a regionally metastatic cell line by implantation of Tu167 into the tongues of nude mice and harvesting and culturing cervical lymph nodes led to production of a cell line, Tu167LN1, which was found to be anoikis-resistant. This cell line had an apoptotic cell fraction of 16.2% (±3.14%) after 48 h in suspension culture.

Keywords:  Anoikis, Oral cancer, Squamous cell carcinoma, Apoptosis