Trimidox, an inhibitor of ribonucleotide reductase, induces apoptosis and activates caspases in HL-60 promyelocytic leukemia cells

Objective. Ribonucleotide reductase (RR) is the rate-limiting enzyme for th e de novo synthesis of deoxyribonucleotides. Its activity is significantly increased in tumor cells related to the proliferation rate. Therefore, the enzyme is considered to be an excellent target for cancer chemotherapy. In the present study, we investigated whether the antineoplastic effects of tr imidox (3,4,5-trihydroxybenzamidoxime), a novel inhibitor of RR, were due t o induction of apoptosis, Method. HL-60 cells were incubated with various concentrations of trimidox, Consequently, cell morphology, DNA condensation, annexin binding, DNA frag mentation, and signature type cleavage of poly(ADP-ribose)polymerase and ge lsolin were determined, We also tested the involvement of CD95 and CD95 lig and in apoptosis induction, Furthermore, we examined the c-myc expression o f HL-60 cells after incubation with trimidox in order to elucidate a possib le association between c-myc expression and induction of apoptosis in the c ase of trimidox, Result. Trimidox incubation caused a time-dependent increase of c-myc RNA e xpression and this was accompanied by the induction of apoptosis, Apoptosis was triggered independently of CD95 by the activation of caspases and PARP cleavage. Conclusion. We conclude that trimidox is able to induce programmed cell dea th, The induction of apoptosis was demonstrated by various biochemical and morphological methods and seems to be associated with the induction of c-my c, Apoptosis was induced by the activation of caspases and without change o f the CD95 and CD95 ligand expression. (C) 2000 International Society for E xperimental Hematology. Published by Elsevier Science Inc.