Abstract 1403: SOX2 as a marker of oral cancer stem-like cells: Cell division patterns and chromosomal instability

Abstract

Abstract Introduction: Oral squamous cell carcinoma (OSCC) is a serious public health problem, caused primarily by smoking and alcohol consumption. The prognosis remains poor due in part to therapeutic resistance. The cancer stem cell (CSC) theory posits that oral cancer stem-like cells (CSLCs) show unique characteristics, including self-renewal by symmetric cell division and tumor recapitulation by asymmetric cell division. Identifying markers of CSLCs is an important step in better understanding the biology of these cells. Chromosomal instability is a feature of cancer cells that leads to altered gene copy numbers; some of which is caused by chromosome segregation defects (CSDs). We observed previously that chromosomal instability occurs in colon CSLCs. Here, we compare instability between OSCC CSLCs and non-CSLCs from the same tumors. Methods: We assessed CSLCs in two OSCC cell lines (UPCI:SCC040 and UPCI:SCC131) using spheroid enrichment assays. We examined the marker, SOX2 in our cell lines using double antibody staining with division and other stemness markers. We then evaluated the cell division patterns of CSLCs marked by SOX2 to test the hypothesis that cell division patterns change from asymmetric to symmetric after ionizing radiation (IR) treatment. Finally, we analyzed the CSDs after IR in CSLCs marked by SOX2 compared to non-CSLCs. Results: Both cell lines formed spheroids. Strongly SOX2-positive cells were a rare population (∼3%) in our OSCC cell lines. SOX2 positivity was highly correlated with other CSLC markers, including CD44, CD133 and BMI1. A cluster plot of the mitotic pair analysis revealed that SOX2-positive cells divide both symmetrically and asymmetrically (p<0.05) at a ratio of ∼4:1 with a percentage difference cut-off of 20%. Phospho-histone H3 and alpha-tubulin co-staining with SOX2 confirmed the occurrence of both division patterns. Short-term and long-term IR treatment did not change this proportion. CSLCs showed fewer and different CSDs after IR treatment than non-CSLCs. Conclusions: Our results show that therapeutic intervention does not change the ratio of symmetric to asymmetric cell division in CSLCs. These results suggest that only therapies that target the self-renewal potential of CSLCs might effectively eradicate these cells. CSLCs showed less chromosomal instability as assessed by CSDs, possibly due either to the relative quiescence of these cells or enhanced checkpoints that result in cell death when CSDs are present. Cell division and chromosome segregation patterns in CSLCs may provide insight into the biology of therapeutic resistance in CSLCs and reveal strategies to eradicate these cells. Keywords: Oral squamous cell carcinoma (OSCC), Cancer stem-like cells (CSLCs), ionizing radiation (IR), chromosome segregation defects (CSDs). Citation Format: Hatem Kaseb, Dale Lewis, Sussane Gollin. SOX2 as a marker of oral cancer stem-like cells: Cell division patterns and chromosomal instability. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1403. doi:10.1158/1538-7445.AM2015-1403