INCREASED ACTIVITY AND SENSITIVITY OF MITOCHONDRIAL RESPIRATORY ENZYMES TO TUMOR-NECROSIS-FACTOR ALPHA-MEDIATED INHIBITION IS ASSOCIATED WITH INCREASED CYTOTOXICITY IN DRUG-RESISTANT LEUKEMIC-CELL LINES

The drug-resistant leukemic cell lines, CEM/VLB(100) and K/DAU(600), a re more sensitive to tumor necrosis factor alpha (TNF alpha)-mediated cytotoxicity compared with their parental cell lines, CCRF-CEM and K56 2 cl.6. Drug-resistant leukemic cell lines have more active mitochondr ial function, which is associated with a greater susceptibility to TNF alpha-induced respiratory inhibition. TNF alpha blocked electron tran sfer at three sites, NADH dehydrogenase (complex I), succinate dehydro genase (complex II), and cytochrome c oxidase (complex IV). Respirator y rate and electron transport chain enzyme activities were significant ly inhibited in the drug-resistant, TNF-sensitive cell lines. Respirat ory inhibition preceded cell death by at least 5 to 8 hours. The respi ratory failure was not compensated for by appropriate up-regulation of the glycolytic pathway. Increasing mitochondrial respiratory rate and enzyme activities by long-term culture with 2 mmol/L adenosine 5'-dip hosphate (ADP) and Pi sensitized both drug-sensitive and drug-resistan t cells to TNF alpha-induced cytolysis. Intramitochondrial free radica ls generated by paraquat only had a limited and delayed effect on resp iratory inhibition and cytolysis in comparison with the effect of TNF alpha. We conclude that TNF alpha-induced cytotoxicity in leukemic cel ls is, at least in part, mediated by inhibition of mitochondrial respi ration. Free radical generation by TNF alpha may not directly lead to the observed inhibition of the mitochondrial electron transport and ot her mechanisms must be involved. (C) 1996 by The American Society of H ematology.