Mitochondrial membrane sensitivity to depolarization in acute myeloblasticleukemia is associated with spontaneous in vitro apoptosis, wild-type TP53, and vicinal thiol/disulfide status

Nonresponse to remission-induction chemotherapy, which remains a major prob lem in acute myeloblastic leukemia (AML), has been linked to cellular resis tance to apoptosis, Because the apoptosis induced by chemotherapeutic drugs is mediated by loss of mitochondrial transmembrane potential (MTP), it was postulated that sensitivity to mitochondrial membrane depolarization might be heterogeneous in AML. Using the uncoupling agent carbonyl cyanide m-chl orophenylhydrazone (mCICCP), the mitochondrial membrane sensitivity to depo larization (mCICCP concentrations that inhibit 50% of the transmembrane pot ential [IC50]) in AML blasts was measured and demonstrated marked interclon al heterogeneity, with the existence of comparatively sensitive (median mCI CCP IC50, 4 muM) and resistant (median mCICCP IC50, 10 muM) clones. Further more, the mCICCP IC50 was inversely associated with spontaneous in vitro ap optosis (P = .001). It was high in cases with mutant TP53 and correlated wi th the total cellular level of the multidrug resistance-associated protein (P = .019) but not of bcl-2, bar, or bcl-x, It was also found that the dith iol oxidant diamide, in contrast to the monovalent thiol oxidant diethyl ma leate, increased the sensitivity of mitochondrial membranes to mCICCP, To c onfirm that TP53 directly affects MTP in leukemic cells and to establish th e role of vicinal thiol oxidation in the TP53-dependent pathway, CEM 4G5 le ukemia cells with forced, temperature-dependent expression of TP53 were stu died. Monobromobimane, which inhibits mitochondrial membrane depolarization by preventing dithiol cross-linking, inhibited depolarization and apoptosi s in 4G5 cells. It was concluded that in leukemia, TP53 and vicinal thiol/d isulfide status are determinants of mitochondrial membrane sensitivity to d epolarization, which is in turn associated with spontaneous apoptosis, (C) 2001 by The American Society of Hematology.