Retention mechanism of hypoxia selective nuclear imaging/radiotherapeutic agent cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) in tumor cells.
The retention mechanism of the novel imaging/radiotherapeutic agent, Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) in tumor cells was clarified in comparison with that in normal tissue in vitro. With Cu-ATSM and reversed phase HPLC analysis, the reductive metabolism of Cu-ATSM in subcellular fractions obtained from Ehrlich ascites tumor cells was examined. As a reference, mouse brain was used. To determine the contribution of enzymes in the retention mechanisms, and specific inhibitor studies were performed. In subcellular fractions of tumor cells, Cu-ATSM was reduced mainly in the microsome/cytosol fraction rather than in the mitochondria. This finding was completely different from that found in normal brain cells. The reduction process in the microsome/cytosol was heat-sensitive and enhanced by adding exogenous NAD(P)H, an indication of enzymatic reduction of Cu-ATSM in tumor cells. Among the known bioreductive enzymes, NADH-cytochrome b5 reductase and NADPH-cytochrome P450 reductase in microsome played a major role in the reductive retention of Cu-ATSM in tumors. This enzymatic reduction was enhanced by the induction of hypoxia. Radiocopper labeled Cu-ATSM provides useful information for the detection of hypoxia as well as the microsomal bioreductive enzyme expression in tumor.
Obata
A
A
Biomedical Imaging Research Center, Fukui Medical University, Matsuoka, Japan.
Yoshimi
E
E
Waki
A
A
Lewis
J S
JS
Oyama
N
N
Welch
M J
MJ
Saji
H
H
Yonekura
Y
Y
Fujibayashi
Y
Y
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D002286:Carcinoma, Ehrlich Tumor / Q000000981:diagnostic imaging / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D056831:Coordination Complexes; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008956:Models, Chemical; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009942:Organometallic Compounds / Q000493:pharmacokinetics* / Q000627:therapeutic use; D010084:Oxidation-Reduction; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics* / Q000627:therapeutic use; D013882:Thiosemicarbazones / Q000493:pharmacokinetics* / Q000627:therapeutic use
D056831:Coordination Complexes; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D013882:Thiosemicarbazones; C089548:copper (II) diacetyl-di(N(4)-methylthiosemicarbazone); D009243:NAD; D009249:NADP