Redox cycling by motexafin gadolinium enhances cellular response to ionizing radiation by forming reactive oxygen species.
OBJECTIVE
To examine the mechanism of radiation enhancement by motexafin gadolinium (Gd-Tex) in vitro.


METHODS
Oxidation of ascorbate and NADPH by Gd-Tex was evaluated in a neutral buffer. Growth inhibition of human uterine cancer cell line MES-SA was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye. Clonogenic assays were used to measure radiation response in MES-SA, A549 human lung carcinoma, E89, a CHO cell line variant deficient in glucose-6-phosphate dehydrogenase activity, and murine lymphoma cell lines LYAR and LYAS.


RESULTS
Gd-Tex catalyzed the oxidation of NADPH and ascorbate under aerobic conditions, forming hydrogen peroxide. Decreased viability was observed in MES-SA cells incubated with Gd-Tex in media containing NADPH or ascorbate. Gd-Tex and ascorbate increased fluorescence in dichlorofluorescin acetate-treated cultures. Synergistic effects on the aerobic radiation response in MES-SA and A549 were seen using Gd-Tex in combination with L-buthionine-(S,R)-sulfoximine (BSO). Incubation with Gd-Tex in the presence of ascorbate increased the aerobic radiation response of E89 and the apoptosis-sensitive B-cell line (LYAS).


CONCLUSIONS
Gd-Tex sensitizes cells to ionizing radiation by increasing oxidative stress as a consequence of futile redox cycling. Optimization of the concentration of ascorbate (or other reducing species) may be required when evaluating Gd-Tex activity in vitro.
Magda
D
D
Pharmacyclics, Inc., Sunnyvale, CA 94085, USA.
Lepp
C
C
Gerasimchuk
N
N
Lee
I
I
Sessler
J L
JL
Lin
A
A
Biaglow
J E
JE
Miller
R A
RA
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000378:metabolism* / Q000494:pharmacology; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D005260:Female; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008665:Metalloporphyrins / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects; D014594:Uterine Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000532:radiotherapy
D000970:Antineoplastic Agents; D008665:Metalloporphyrins; D017382:Reactive Oxygen Species; D009249:NADP; C437683:motexafin gadolinium; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid