Inhibition of leukemic HL60 cell growth by transferrin-gallium: effects on ribonucleotide reductase and demonstration of drug synergy with hydroxyurea.
Cellular requirements for iron during DNA synthesis are related to the increased activity of the iron-containing M2 subunit of ribonucleotide reductase, the enzyme responsible for the reduction of ribonucleotides to deoxyribonucleotides. We have previously shown that transferrin-gallium (Tf-Ga) inhibits cellular iron incorporation. In the present study, Tf-Ga-induced inhibition of HL60 cell growth and upregulation of Tf receptor density was reversed with hemin. Cells exposed to 2 mumol/L Tf-Ga for six hours or longer displayed a diminution in the electron spin resonance (ESR) spectroscopy signal of the tyrosyl radical of the M2 subunit of ribonucleotide reductase. The effect of Tf-Ga on the ESR signal was reversed by hemin. Tf-Ga decreased the incorporation of 14C-adenosine into DNA and decreased intracellular deoxyribonucleotide pools, with the maximum diminution seen in deoxyadenosine triphosphate (dATP) and deoxycytidine triphosphate (dCTP) pools. Exposure of cells to combinations of Tf-Ga and hydroxyurea (a known inhibitor of ribonucleotide reductase) resulted in a marked inhibition of cell growth that was consistent with drug synergy. Our studies suggest that Tf-Ga inhibits DNA synthesis through action on the M2 subunit of ribonucleotide reductase and that combinations of Ga and hydroxyurea should be further evaluated in in vivo tumor models.
Chitambar
C R
CR
Department of Medicine, Medical College of Wisconsin, Milwaukee 53226.
Matthaeus
W G
WG
Antholine
W E
WE
Graff
K
K
O'Brien
W J
WJ
D002455:Cell Division / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004357:Drug Synergism; D005708:Gallium / Q000494:pharmacology*; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism; D015473:Leukemia, Promyelocytic, Acute; D011990:Receptors, Transferrin / Q000187:drug effects; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors*; D014168:Transferrin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects*
D004273:DNA, Neoplasm; D011990:Receptors, Transferrin; D014168:Transferrin; D006427:Hemin; D005708:Gallium; D007501:Iron; D012264:Ribonucleotide Reductases; D006918:Hydroxyurea