Figure 3

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 CD44^low and CD44^high 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 CD44^high cells than in the CD44^low 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 CD44^low cells than for CD44^high cells and consistently larger fractions of CD44^high 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 CD44^high cells which also showed a marked increase in the proportion of cells in G2. Graph showing the consistent difference in G2 block between CD44^high and CD44^low 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 CD44^high cells at various levels of NCZ exposure (D).