The longevity of pimonidazole adducts in tumors was quantified as an estimate of the lifetime of hypoxic cells. Pimonidazole was given before irradiation to 12 dogs bearing spontaneous tumors, and tumors were biopsied 24, 48 and 72 h later. Pimonidazole antigen was quantified in the biopsies using ELISA and immunohistochemistry. Pimonidazole antigen was detectable in the initial biopsy in all dogs. In 5 dogs the amount of detectable antigen decreased to less than 50% of the initial amount, in 5 other dogs the amount of detectable antigen decreased to an amount between 50 and 100% of the initial amount, and in 2 dogs the amount of antigen appeared to increase relative to the initial amount. Tumors with high initial adduct concentration were characterized by greater decreases in adduct concentration than tumors with low initial adduct concentration. Immunohistochemically, labeled cells were present in 11 of 12 tumors. The geographic area in tumor biopsies labeled immunohistochemically with pimonidazole adducts (labeled area fraction) tended to decrease over time in 6 dogs, remain stable in 4 dogs and seemingly increase in 1 dog. There was no relationship in individual tumors between the relative change in antigen concentration and the relative change in labeled area fraction. Hypoxic cells which bind pimonidazole may persist for days during fractionated radiation therapy, and the potential exists for them to exert a negative effect on the host.

The purpose of this study was to evaluate the effect of hyperthermia on the histologic and functional response of the canine kidney, a late-responding normal tissue, to irradiation. Both kidneys were irradiated. Radiation was delivered in single doses of 0, 10, or 15 Gy. Whole-body hyperthermia was used to produce renal kidney temperatures approximating 42.0°C for 60 min. Thirty-six beagles were placed randomly in the following six treatment groups: control, whole-body hyperthermia alone, 10 Gy alone, 10 Gy + whole-body hyperthermia, 15 Gy alone, and 15 Gy + whole-body hyperthermia. Renal histologic and functional changes were assessed at 1 to 9 months after therapy. No changes were seen in glomerular filtration rate or renal tissue volumes in control or hyperthermia alone groups. Renal vascular and glomerular volumes were not affected significantly by any combination of hyperthermia and/or radiation. In all groups receiving radiation, glomercular filtration rate decreased, percentage renal tubular volume decreased, and interstitial volume increased significantly after therapy. The magnitude of these changes in the functional and histologic response of the kidney and the latent period before expression of this damage were dependent on radiation dose. However, hyperthermia did not modify expression of radiation damage in the kidney based on glomerular filtration rate and histologic quantification of renal tissue components.

The radiation response of the skin of the C3H mouse was evaluated in terms of the dose of radiation required to produce moist desquamation completely surrounding the lower aspect of the hind leg by 21 days following irradiation (DD50-21). Irradiation of the leg under various conditions of local tissue oxygenation indicated that when the animals were breathing air (ambient conditions), the cells in the skin were not fully oxygenated. Heat was administered by immersing the leg for 15 min in 44.5°C water either immediately prior to or immediately following irradiation under various conditions of local tissue oxygenation. Heat administered following irradiation reduced the DD50-21 values by 724 rad for hyperbaric O 2 , 1210 rad for ambient, and 1656 rad for hypoxic conditions. Approximately these same rad equivalents were observed when heat was administered prior to irradiation, under hyperbaric O 2 and hypoxic conditions. However, administration of heat prior to irradiation under ambient conditions sensitized the cells to the effects of ionizing radiation. This sensitization was assumed to result from heat causing an increase in local tissue oxygenation prior to and at the time of irradiation. The effect of the heat dose administered under acute hypoxic conditions immediately prior to acute hypoxic irradiation was not significantly different from the protocol where heat was administered under ambient conditions immediately prior to acute hypoxic irradiation. This indicates an independence of the magnitude of the heat effect on the tissue oxygenation status at the time of heating. The response of the C3H mouse mammary adenocarcinoma to combined wet heat (Δ) and X-radiation (X) administered under either hypoxic, ambient or hyperbaric O 2 conditions of local tissue oxygenation was studied. The heat treatment reduced the radiation dose to reach the end point of 50% tumor control (TCD50) by 1050-2808 rad depending on tissue oxygenation and order of application. The high equivalent rad effect of 2808 rad observed when heat was given following irradiation under hyperbaric O 2 conditions was assumed to be due to an extreme heat sensitivity of the chronically hypoxic tumor cells. The most therapeutically beneficial protocol utilizing heat in terms of maximal reduction of TCD50 and minimal reduction of DD50-21 was irradiation under hyperbaric O 2 conditions followed by heat. Heat treatments of 0-, 8-, 15- and 30-min immersion in 44.5°C water were administered to 8 mm tumors immediately before hypoxic irradiation. The resultant TCD50 values fit the linear equation of TCD50 = [-66 (minimum immersion in 44.5°C water) + 6282] rad with a correlation coefficient of 0.99. Repair of heat damage was evaluated by administering radiation under hypoxic conditions 0, 6, 12, 24, 48 and 72 hours after a 15 min immersion in 44.5°C water. The resultant TCD50 values rose rapidly in the first 12 hr after heating to a level indicative of complete repair of the heat damage.