Development of drug resistance to gallium nitrate through modulation of cellular iron uptake.
We have shown that transferrin-gallium (Tf-Ga) blocks DNA synthesis through inhibition of cellular iron incorporation and a diminution in the activity of the iron-dependent M2 subunit of ribonucleotide reductase. To examine the mechanisms of drug resistance to gallium, we developed a subline of HL60 cells (R cells) which is 29-fold more resistant to growth inhibition by gallium nitrate than the parent line (S cells). R cells displayed a 2.5-fold increase in transferrin (Tf) receptor expression, without a change in receptor affinity for Tf. The uptake and release of 67Ga were similar for both S and R cells. The uptake of 59Fe-Tf by S cells was inhibited by gallium nitrate over 24-48 h of incubation. In contrast, 59Fe-Tf uptake by R cells, although initially inhibited by gallium nitrate at 24 h, was no longer inhibited at 48 h of incubation. 59FeCl3 uptake by R cells was significantly greater than that of S cells, regardless of the time in culture. Despite the increase in 59Fe uptake by R cells, the ferritin content of these cells was lower than that of S cells. The ribonucleotide reductase electron spin resonance signal of R cells was comparable to that of S cells. R cells were not cross-resistant to Adriamycin, vincristine, cis-platinum or hydroxyurea. Resistance to gallium nitrate in this subline of HL60 cells results primarily from the ability of cells to overcome the gallium-induced block in iron incorporation. In addition, intracellular iron in R cells appears to traffic preferentially to a non-ferritin compartment.
Chitambar
C R
CR
Department of Medicine, Medical College of Wisconsin, Milwaukee 53226.
Zivkovic-Gilgenbach
Z
Z
Narasimhan
J
J
Antholine
W E
WE
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004351:Drug Resistance; D004578:Electron Spin Resonance Spectroscopy; D005708:Gallium / Q000494:pharmacology*; D006801:Humans; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D015473:Leukemia, Promyelocytic, Acute; D011990:Receptors, Transferrin / Q000187:drug effects / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D000970:Antineoplastic Agents; D011990:Receptors, Transferrin; D014168:Transferrin; D005708:Gallium; D007501:Iron; D012264:Ribonucleotide Reductases; C027235:gallium nitrate