ODC activity was measured as the release of CO2 from L-[1-C14] ornithine as previously described.56 Briefly, cell lysates were incubated at 37 °C for 60 min after addition of 0.5 µCi L-[1-C14] ornithine hydrochloride (Perkin Elmer, Waltham, MA), 40 mM sodium phosphate buffer (pH 7.8) containing 0.64 mM pyridoxal phosphate, 0.8 µM EDTA and 8 mM dithiothreitol. The reaction was terminated by addition of 10% trichloroacetic acid. The released 14-CO2 was soaked in scintillation solution (Research Products International Corp., Mount Prospect, IL) and radioactivity was measured by scintillation counter (LS6500, Beckman Coulter, Fullerton, CA) and the results are expressed as percentage of the control, which was set at 100%.