SUBJECTS radiosensitizers

In the first application, acoustic intensities of thousands of W/cm2 and tempera-tures in excess of 98°C are often used to coagulate cancerous tissues. This form of hyperthermia is often referred to as thermal therapy because of its extreme temperature and energy.43 Alternatively, lower ultrasound intensities (0.2 to several W/cm2) produce a mild increase in temperature (41 to 45°C), and enhance the cytotoxicity of radiation therapy and chemotherapy. The enhancing effect of ultrasound on radiation therapy has been linked to the radiosensitization effect of hyperthermia, which increases radiation damage and prevents subsequent repair.28 However, the precise mechanism for ultrasound-enhanced chemotoxicity is still the subject of debate. 

NO-donors. In contrast, the effect of aceto-HX on B. subtilis subjected to oxidative stress is similar to that of HNO. SAHA, but not valproic acid lacking the hydroxamate moiety, enhances the radiosensitization of hypoxic tumor cells in vitro. This effect might also involve its abihty to serve as a NO-donor. It is concluded that HXs, which are HNO-donors under oxidizing environment, might be considered as NO-donors if HNO conversion into NO competes with its reaction with potential biological targets such as thiols and metalloproteins. 

There is some controversy in the literature in regard to the sensitivity of DS lymphocytes to the induction of chromosome aberrations by X-rays. Several investigators have reported X-ray induced aberration frequencies more than 50% greater than those induced in normal lymphocytes (12,18). Others have found that the increase is less than 40% (10, 11). These variations could be explained by differences in the mean age of the DS subjects and differences in experimental conditions. Under our experimental conditions (incubation 1-6 hr prior to PHA stimulation), DS lymphocytes were more radiosensitive than normal lymphocytes only in the presence of 3AB. Additional studies are in progress to determine if 3AB causes an accumulation of DNA strand breaks in DS lymphocytes. 

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