N-(4-hydroxyphenyl)retinamide-induced death in human lymphoblastoid cells: 50 kb DNA breakage as a means of distinguishing apoptosis from necrosis

Experimental studies of N-(4-hydroxyphenyl)retinamide, a potential cancer chemopreventive agent, have primarily involved breast cancer and neuroblastoma cell populations together with an investigation of myeloid leukemia cells and have principally been concerned with the induction of apoptosis. This investigation of N-(4-hydroxyphenyl)retinamide-induced apoptosis using T-cell-derived human lymphoblastoid lines extends these studies by indicating distinctive features associated with this drug. The induction of apoptosis is restricted to a limited concentration range, which, if exceeded, results in cell death by necrosis. While morphological changes typical of apoptosis induced by many agents are readily demonstrable after treatment of lymphoblastoid cells with 3 μM N-(4-hydroxyphenyl)retinamide, distinctive features evident using the retinoid include the absence of cell cycle arrest along with the mode and pattern of DNA breakage. Analysis by conventional gel electrophoresis indicated that internucleosomal fragmentation of DNA was an unreliable indicator of apoptosis. On the other hand, higher order DNA breakage was consistently detected during drug-induced apoptosis, but not as a result of treatment causing necrosis.