UNEXPECTED CYTOKINETIC EFFECTS INDUCED BY PUROMYCIN INCLUDE A G2-ARREST, A METAPHASE-MITOTIC-ARREST, AND APOPTOSIS

The potent effects of low doses of PM on the cell cycle have to date been obscured by the conventional usage of this drug at high concentrations (5-50 mug/ml) to inhibit protein synthesis. In this in vitro study undertaken in a variety of malignant and non-malignant human and murine cell types, we found that low doses of PM (0.1-0.5 mug/ml) disrupted significant phase-to-phase cell cycle transitions, causing a G2-arrest, a metaphase-mitotic-arrest, and apoptosis. In HL-60 cells these observations were elicited by PM concentrations starting at 0.1 mug/ml, and were more pronounced at slightly higher PM concentrations, including that (0.5 mug/ml) which inhibited [C-14]leucine incorporation by approximately 20% after one hour, and by approximately 50% after 24 h. A concentration of CHX (0.25 mug/ml) which was equivalent to 0.5 mug/ml of PM, both in terms of molarity (0.9 muM) and degree of inhibition of [C-14]leucine incorporation, failed to induce similar changes to those induced by PM. This suggests that at these particular concentrations the PM-induced changes were likely to have been related to the different mechanisms of protein synthesis inhibition exerted by these two 'classical' translation inhibitors. PM but not CHX generates nascent peptidyl-PM complexes (PMPs), and we therefore propose that the subsequent intracellular effects exerted by the PMPs may account, in part, for the differential cytokinetic effects elicited by these drugs. The role of PM is currently being evaluated in vivo as a low-dose component of a multidrug chemotherapeutic regimen in which its cell cycle-specific effects could potentially be synergistic with other agents.