Radiosensitization of hypoxic tumour cells by S-nitroso-N-acetylpenicillamine implicates a bioreductive mechanism of nitric oxide generation.
The radiosensitizing activity of S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO) donor, was assessed in a model of non-metabolic hypoxia achieved in an atmosphere of 95% nitrogen-5% carbon dioxide. A 10 min preincubation of hypoxic EMT-6 cells (10 x 10(6) ml(-1)) with 0.1 and 1 mM SNAP before radiation resulted in an enhancement ratio of 1.6 and 1.7 respectively. The level of spontaneous NO release, measured by a NO specific microsensor, correlated directly with the concentration of SNAP and was enhanced 50 times in the presence of cells. Dilution of the cell suspension from 10 to 0.1 x 10(6) ml(-1) resulted in a 16-fold decline in NO release, but only a twofold decrease in radiosensitization was observed. Preincubation of hypoxic cells with SNAP for 3 min up to 30 min caused an increasing radiosensitizing effect. Extended preincubation of 100 min led to the loss of radiosensitization although the half-life of SNAP is known to be 4-5 h. Taken together, these observations suggest that SNAP generates NO predominantly by a bioreductive mechanism and that its biological half-life is unlikely to exceed 30 min. The lack of correlation between free NO radical and radiosensitizing activity may reflect a role of intracellular NO adducts which could contribute to radiosensitization as well.
Janssens
M Y
MY
Department of Radiotherapy, Oncology Center, Academic Hospital, Free University Brussels, Belgium.
Verovski
V N
VN
Van den Berge
D L
DL
Monsaert
C
C
Storme
G A
GA
D000818:Animals; D002452:Cell Count; D015687:Cell Hypoxia / Q000187:drug effects / Q000528:radiation effects*; D002470:Cell Survival; D004307:Dose-Response Relationship, Radiation; D006207:Half-Life; D051379:Mice; D009569:Nitric Oxide / Q000096:biosynthesis*; D010396:Penicillamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects
D011838:Radiation-Sensitizing Agents; C110881:S-nitro-N-acetylpenicillamine; D009569:Nitric Oxide; D010396:Penicillamine