Figure 4. Cell Cycle Analysis of NB cell lines after treatment with TSPO Ligands. Cells were treated with 60 µM PK11195 for 18 h and then were fixed and stained with propridium iodide and analyzed by flow cytometry. Treatment with PK11195 caused G₁ cell cycle arrest in all cell lines tested. Representative flow cytometry histograms showing increase in G₁ percentage from 63.1% before treatment (A), to 81.4% after PK11195 treatment (B) in the SMS-KAN cell line. S and G₂ phase percentages fell from 32.5% to 16.7% for S phase and from 4.5% to 1.9% for cells in G₂ phase. (C) Percentages of cell population in G₁, S and G₂ phases before and after treatment with PK11195. All four cell lines treated showed statistically significant increases in the percentage of cells in G₁ phase compared with pre-treatment baseline; The cell cycle arrest was more pronounced in the SMS-KAN/KANR cell lines than in the SMS-KCN/KCNR cells.