Apoptosis and cell cycle parameters for CD44
low and CD44
high cell populations in carcinoma-derived cell lines and fresh biopsies from HNSCC. Representative FACS plots analysing apoptosis (left panel) and cell cycle (right panel) in CD44low and CD44high sub-populations of H357 cell line exposed to NCZ (A), showing that, in both control cells and cells exposed to 20 ng/ml NCZ, markedly lower levels of apoptosis and greater proportion of cells in the G2 phase of the cell cycle are found among CD44high cells than in the CD44low cells (for both p < 0.01). Data from cells isolated from fresh tumours (B) either untreated, treated with 20 ng/ml NCZ for 24 hours, or 250 μM Cisplatin for 48 hours showed a consistently higher level of apoptosis for CD44low cells than for CD44high cells and consistently larger fractions of CD44high cells in the G2 phase of the cell cycle and smaller fractions in G1 phase of the cell cycle (for both p < 0.05). After treatment with NCZ or Cisplatin the proportion of apoptotic cells in both cell fractions increased but remained 2-4 fold lower for CD44high cells which also showed a marked increase in the proportion of cells in G2. Graph showing the consistent difference in G2 block between CD44high and CD44low sub-populations of Ca1 cell line treated with increasing concentrations of NCZ (C) and the inverse correlation between the proportion of cells in G2 block and the proportion of Annexin V positive cells in CD44high cells at various levels of NCZ exposure (D).