INDUCTION OF APOPTOSIS BY ANTICANCER DRUGS WITH DISPARATE MODES OF ACTION - KINETICS OF CELL-DEATH AND CHANGES IN C-MYC EXPRESSION

Incubation of CCRF CEM C7A human lymphoblastic leukaemia cells with et oposide (VP16) or N-methylformamide (NMF) induced apoptotic cell death . The kinetics of onset of apoptosis was determined and compared with that for dexamethasone-treated cells. The drugs induced 50% apoptosis at different rates: etoposide by approximately 18 h, NMF by 40 h and d examethasone (DEX) by 52 h. In each case, the onset of apoptosis above 10% was preceded by a delay period. This was 8 h for etoposide, betwe en 8 and 12 h for NMF and 36 h for dexamethasone. When cells were incu bated for 36 h with dexamethasone and the drug washed out, addition of NMF induced apoptosis without any delay, suggesting that certain comm on biochemical events are required to prime the cells for apoptosis. H owever, cells treated for 8 h with NMF did not undergo immediate apopt osis on the addition of DEX. Analysis of the cellular content of the c -myc protein showed this to be undetectable by 2, 6 and 12 h after tre atment with etoposide, NMF and DEX respectively. The rapid onset of NM F-induced cell death after a 36 h DEX pretreatment occurred 24 h after the loss of expression of c-Myc protein, suggesting that the expressi on of c-myc is not required for drug-induced cell death. In contrast t o DEX-induced apoptosis, concomitant incubation of cells with NMF or e toposide and 200 nM of the protein synthesis inhibitor cycloheximide d id not inhibit apoptotic cell death. The idea that drugs with differen t modes of action initiate conserved responses which engage a programm ed cell death is discussed.