The ribonucleotide reductase-inhibitor trimidox induces c-myc and apoptosis of human ovarian carcinoma cells

Trimidox (3,4,5-trihydroxybenzohydroxamidoxime), a recently synthesized inh ibitor of ribonucleotide reductase (RR), was shown to exert anti-proliferat ive activities in HL-60 and K562 human leukemia cell lines and to prolong t he life span of mice inoculated with L1210 mouse leukemia cells. Here we te st whether trimidox also exhibits anti-neoplastic properties in ovarian car cinoma cells. Since the mode of action of trimidox on cell fate has not bee n investigated so far, we addressed this unresolved item and find that this polyhydroxybenzoic acid derivative induces apoptosis of N.1 human ovarian carcinoma cells when tested in growth factor deprived medium. Utilizing an improved analysis, based on Hoechst 33258 / propidium iodide double stainin g, apoptosis is quantified and discriminated from necrosis. Trimidox induce s c-myc expression, which is indispensible for apoptosis of N.1 cells, and expression of plasminogen activator / urokinase type (upa), which supports the apoptotic process under more physiological conditions. Surprisingly, tr imidox does not block dNTP synthesis in N.1 cells at the concentrations tes ted and, therefore, trimidox induces apoptosis independent of RR-inhibition , Like TNF alpha or benzamide riboside, which are also inducers of apoptosi s of N.1 cells, trimidox also downregulates the G1 cell cycle phosphatase c dc25A, whereas cyclin D1 becomes up-regulated. This report shows that trimi dox destroys human ovarian carcinoma cells by inducing them to undergo apop tosis as well as corroborating previous investigations which demonstrated t hat apoptosis of these cells depends on c-myc over-expression when survival factors are withdrawn. (C) 2000 Elsevier Science Inc. All rights reserved.