(a) Structure of Bz-423 and inactive congeners. (b) Effect of Bz-423, 4′-chlorodiazepam (4-ClDz), PK11195, ΔNAP, and ΔOH on Ramos cell viability at 24 hours, determined by PI permeability. The ED₅₀ of Bz-423 is 4 μM. (c) Interference contrast micrographs (×400) of cells treated for 24 hours with vehicle, Bz-423 (10 μM), or Bz-423 (10 μM) plus z-VAD (100 μM). (d) After treatment as in c, cells were analyzed by flow cytometry to detect DNA content; percentages indicate fraction of cells with hypodiploid (apoptotic) DNA. Distribution of nonapoptotic cells in G₁, S, and G₂/M phases was altered by Bz-423 (33%, 42%, and 24% for control vs. 53%, 38%, and 8% for Bz-423). Pretreatment with z-VAD blocked formation of hypodiploid DNA and partially restored cell cycle distribution. All panels are representative of more than five separate determinations.