1,10 Phenanthroline inhibition of lymphoblast cell cycle

The effects of the metal-chelating agent, 1,10-phenanthroline (OP), on the cell cycle progression of CCRF-CEM lymphoblasts has been studied by flow microfluorometry. Lymphoblasts were incubated with 2,3 dihydro-1H-imidazo[1,2-b]pyrazole in order to block them in G₁-early S. The block was then reversed by incubating the cells in fresh media. Within 2 to 4 hr, ∞90% of the cells were in S phase and, by 6 hr, ∞80% were in late S. Aliquots of these latter cells then were incubated with podophyllotoxin to block them in G₂-M. These cells divided within 4 hr of reversal of the podophyllotoxin block. Lymphoblast populations in G₁-early S, mid-S, or G₂-M were then incubated with 4 μM OP. OP blocked entry of G₁ cells into S as well as progression through S but had no effect on progression from G₂-M to G₁. The OP effects were reversed by addition of Zn²⁺, Cu²⁺, or Fe²⁺ or by dilution of the chelating agent in the growth media. Incubation of CCRF-CEM lymphoblasts with 1,7-phenanthroline, a nonchelating analog of OP, did not affect the cell cycle. The data indicate that OP reversibly blocks progression of cells from G₁ to S and through S by chelation of metals involved in processes essential for those cell cycle events.