Motexafin gadolinium, a tumor-selective drug targeting thioredoxin reductase and ribonucleotide reductase.
Motexafin gadolinium (MGd) is a chemotherapeutic drug that selectively targets tumor cells and mediates redox reactions generating reactive oxygen species. Thioredoxin (Trx), NADPH, and thioredoxin reductase (TrxR) of the cytosol/nucleus or mitochondria are major thiol-dependent reductases with many functions in cell growth, defense against oxidative stress, and apoptosis. Mammalian TrxRs are selenocysteine-containing flavoenzymes; MGd was an NADPH-oxidizing substrate for human or rat TrxR1 with a Km value of 8.65 microM (kcat/Km of 4.86 x 10(4) M(-1) s(-1)). The reaction involved redox cycling of MGd by oxygen producing superoxide and hydrogen peroxide. MGd acted as a non-competitive inhibitor (IC50 of 6 microM) for rat TrxR. In contrast, direct reaction between MGd and reduced human Trx was negligible. The corresponding reaction with reduced Escherichia coli Trx was also negligible, but MGd was a better substrate (kcat/Km of 2.23 x 10(5) M(-1) s(-1)) for TrxR from E. coli and a strong inhibitor of Trx-dependent protein disulfide reduction. Ribonucleotide reductase (RNR), a 1:1 complex of the non-identical R1- and R2-subunits, catalyzes the essential de novo synthesis of deoxyribonucleotides for DNA synthesis using electrons from Trx and TrxR. MGd inhibited recombinant mouse RNR activity with either 3 microM reduced human Trx (IC50 2 microM) or 4 mM dithiothreitol (IC50 6 microM) as electron donors. Our results demonstrate MGd-induced enzymatic generation of reactive oxygen species by TrxR plus a powerful inhibition of RNR. This may explain the effects of the drug on cancer cells, which often overproduce TrxR and have induced RNR for replication and repair.
Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institute, SE-171 77 Stockholm, Sweden.
Seyed Isaac
SI
Hashemy
Johanna S
JS
Ungerstedt
Farnaz
F
Zahedi Avval
Arne
A
Holmgren
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D003600:Cytosol / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000737:chemistry; D004583:Electrons; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D020128:Inhibitory Concentration 50; D007328:Insulin / Q000378:metabolism; D007700:Kinetics; D008665:Metalloporphyrins / Q000494:pharmacology*; D008956:Models, Chemical; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017382:Reactive Oxygen Species; D012264:Ribonucleotide Reductases / Q000737:chemistry / Q000378:metabolism*; D013053:Spectrophotometry; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism*; D013879:Thioredoxins; D013997:Time Factors
D000970:Antineoplastic Agents; D004220:Disulfides; D007328:Insulin; D008665:Metalloporphyrins; D017382:Reactive Oxygen Species; D013879:Thioredoxins; D009249:NADP; C437683:motexafin gadolinium; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D012264:Ribonucleotide Reductases; D013880:Thioredoxin-Disulfide Reductase; D010100:Oxygen