Radiation sensitization by thiol-binding agents of radio-resistant and radiosensitive Escherichia coli and the oxygen effect.
Dose-survival curves of four strains of E. coli-B/r her- try-, Bs-1, B/r CSH, and 15T-were obtained in the presence and in the absence of non-toxic levels of several thiol-binding agents-N-ethylmaleimide (NEM), iodoacetamide (IA), and hydroxymercuribenzoate (HMB). The degree of radiosensitization by these agents was estimated from the increase in slope of the dose-survival curve, under anoxic and aerobic conditions. Chemical sensitization of both radioresistant and radiosensitive strains of bacteria with the thiol-binding enzyme poisons NEM, IA, and HMB has been observed. NEM sensitized only under anoxic conditions, IA sensitized under both anoxic and aerobic conditions, although to a much greater extent aerobically, and HMB sensitized only under aerobic conditions. The formation of long-lived radiolytic products toxic to bacteria is observed in sensitization by IA. When sensitization occurs, the magnitude of the dose-modifying factor is equal to or greater than the oxygen enhancement ratio. Inhibition of an energy-requiring enzymic repair process does not seem to be involved as a primary mechanism of sensitization. Interference by thiol-binding agents with a "rapid repair" process which is different from the usual "enzymic repair," and which operates in radio-sensitive as well as in radioresistant bacteria, is suggested.
Moroson
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Division of Biophysics, Sloan-Kettering Institute for Cancer Research, New York, New York, USA.
Tenney
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DN
D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology*; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage*; D013438:Sulfhydryl Compounds / Q000378:metabolism*
D011838:Radiation-Sensitizing Agents; D013438:Sulfhydryl Compounds; D010100:Oxygen