Combined radiation-protective and radiation-sensitizing agents. IV. Measurement of intracellular protector concentrations

Journal Article · Fri Mar 31 23:00:00 EST 1989 · Int. J. Radiat. Oncol., Biol. Phys.; (United States)

DOI:https://doi.org/10.1016/0360-3016(89)90908-5· OSTI ID:6098039

Koch, C J; Stobbe, C C; Hettiaratchi, P

Radiosensitization of hypoxic V79 Chinese hamster cells by 0.5 mM misonidazole at approximately 0-4 degrees C is substantially enhanced by pretreating the cells overnight with 0.1 mM buthionine sulfoximine, which lowers the cellular glutathione content to 5% of control values (from 4 mM to approximately 0.2 mM). The enhanced sensitization is reversed by concentrations of exogenous cysteine that are much lower (0.02 mM) than the original glutathione content. Reduced Co-enzyme A affords reversal of the enhancing effect at concentrations of about 1 mM. Sodium ascorbate gives no protection at all even at concentrations of 2 mM. The intracellular concentration of the reducing agents was measured using a spin-through oil technique. There was no diffusion of Co-A (MW greater than 750) or ascorbate (excluded by charge) into the cells. In contrast, cysteine was rapidly concentrated by factors of 4-10, even at the low temperatures used. Extracellular ascorbate's inability to radioprotect argues against electron transfer across the cell membrane as a mechanism for radioprotection. This mechanism could have explained the ability of exogenous thiols to radioprotect in former studies using glutathione, and in the present studies using Co-A. The potential of cysteine to be concentrated by cells poses a problem in the interpretation of exogenous protection by non-diffusing thiols, since trace contamination by cysteine could lead to the actual protection observed. Cysteine could also be formed by exchange reactions of exogenous thiols with the disulfide of cysteine, present in all media formulations.

• Research Organization: Univ. of Pennsylvania, Philadelphia (USA)
• OSTI ID: 6098039
• Journal Information: Int. J. Radiat. Oncol., Biol. Phys.; (United States), Journal Name: Int. J. Radiat. Oncol., Biol. Phys.; (United States) Vol. 16:4; ISSN IOBPD
• Country of Publication: United States
• Language: English

Related Subjects

550603 -- Medicine-- External Radiation in Therapy-- (1980-)
560120* -- Radiation Effects on Biochemicals
Cells
& Tissue Culture
62 RADIOLOGY AND NUCLEAR MEDICINE
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINO ACIDS
ANIMAL CELLS
ANIMALS
ANOXIA
ANTINEOPLASTIC DRUGS
ASCORBIC ACID
AZOLES
BODY
CARBOXYLIC ACIDS
COENZYMES
CYSTEINE
DRUGS
EVALUATION
GLUTATHIONE
HAMSTERS
HETEROCYCLIC COMPOUNDS
IMIDAZOLES
LUNGS
MAMMALS
MISONIDAZOLE
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANS
PEPTIDES
POLYPEPTIDES
PROTEINS
RADIOPROTECTIVE SUBSTANCES
RADIOSENSITIZERS
RESPIRATORY SYSTEM
RODENTS
THIOLS
VERTEBRATES
VITAMINS